CALIFORNIA STATE UNIVERSITY, NORTHRIDGE
LATE AUSTRALOPITHECINE TAXONOMY
'
'
AND HOMINID PHYLOGENY
A thesis submitted in partial satisfaction of the
requirements for the degree of Master of Arts in
Anthropology
by
William Cromwell ../"
Hcintosh, Jr •
..
January, 1976
The thesis,-"1>f Wi lliarn C. Mcintosh, Jr. is approved:
California State University, Northridge
December, 1975
ii
TABLE OF CONTENTS
Page
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . v
LIST OF FIGURES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . vi
ABSTRACT ••.••••• . . . . . . .. . . . . . . . . .. .. . . . . . . . . . . . . ....•.•. vii
LIST OF TABLES ••
Chapter
1.
INTRODUCTION • •••••••••••••••••••••••••••••••••••
1
2.
REVIEW OF LITERATURE .•••••
. . . . . . . . . .. . . . . . .. . . . .
5
INTERPRETATIONS
OF HOMINID PHYLOGENY ••••
GENEP~
RECENT
. . . . . . . . . . . . . . . . . .. . . . 6
ODONTOMETRIC ANALYSES. . . . . . . . . . . . .. . . . . 17
SUMMA.RY • ••••••••••••
3
8
MATERIALS AND
~.ETHODS.
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. . . . . . . . . . .. . . . . . . . .
Sample. . . . . . .. . . . . . . . . . . . . .
MATERIALS •••••••••••••••••
A. Early Hominid
20
B. Comparative Samples.
22
23
28
C. Measurement Data ••••••••••••••••••••••••• 30
METHODS • •••••••••••••••••
.. . .. . .. . ... . . . . .... . .
A. Univariate Analysis.
B. Multivariate Analysis.
4.
33
. . . . .. . . . . .. .. . . . . .
. . . . . . . . .. . . . . . .. . . . . . . .. .
ANALYSIS . ... . . . . . . . . .. . . .. . . . .. . . . . .
RESULTS OF ANALYSES •••
UNIVARIATE
32
35
45
45
A. Variance Ratios: The F-statistic.
45
B. Histograms: Early Hominid
Sample Variation •••••••••••••
51
iii
. . . .. . . . . . . . . . .
Page
C. Summary of Univariate Results •••••••••••• 53
MULTIVARIATE
ili~ALYSIS
••••••••••••••
. . . . .. . . . . .
A. Early Hominids: Within-group
Relationships............................
54
54
B. Within-group Variance Relative
to Between-group Variance ••••••••••••••••••• 63
.. . . . . . . . . . . . . . . 73
DISCUSSION •••••••••• . . . . .. . . . . . . . . . . . . . . . . . . . . . . 75
LINEAGES, SPECIES, AND GENERA. . . .. . . . . . . . . .. . . 76
A. Size .........-; .. .. . . . . . . .. . . . .. . . .. . .. . .. 79
SUHMARY OF RESULTS ••••••••••••
s.
B. Shape . . . . . . . . . . • . . . . . . . . . . . . . . . . . . . • • . . . . 81
THE EVIDENCE FOR MORE
THAN ONE LINEAGE ••••••
.. .... . .. .. .. .. ... . .. . . . 83
THE TAXONOMIC DISTINCTION
BETWEEN THE LINEAGES ••••••••
6.
CONCLUSIONS.
. . . . . . . . . . . .. . . . . .
86
. . ....... . .. . . ..... .. . .. . . ... . . . . . ..
91
LITERATURE CITED. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •
93
APPENDICES
A
Early Hominid Sample Data ••••••••••••••••••••••• lOO
B
Descriptive Statistics for
Hominid and Pongid Samples •••••••••••••••••••••• lOl
iv
..
LIST OF TABLES
Table
Page
1.
Provenience of Early Hominid Cases ••••••••••••••• 24
2.
Early Hominid Cases used in Multivariate
Analyses • . . . . . . . . . . . . . . . . . . . . . . • . . . . . . • . . . • . . . . 41
3.
Coefficient of Variation Values for
Mesio~distal and Bucco-lingual
Measurements of Hominid and Pongid
Teeth by Sample •••..•••••.•••••.•••••.•.•.•••.• 46
3.
Results of F-tests of Significance of
Differences in the Magnitude of the
Coefficient of Variation bet"t.o~een Early
Hominid Sample Measurements and
Comparative Sample Measurements •••••••••••••••• 49
5.
Rotated Principal Component Matrices
and Dendrograms for Early Hominid
Subsarnples (a) and (b) .••••••••••••••••••••••••• 56
v
LIST OF FIGURES
Figure
Page
1.
Histograms of Dimensions of
C through M3 for Early Hominids •••••••••••••••• 52
2.
Comparisons of Size and Shaperelated Dendrograms for Early
Hominid Subsamples (a) and (b) ••••••••••••••••• 61
3.
Last Ten Grouping Events (of 96) for a
Dendrogram Depicting Size Relationships
among Specimens of H. sapiens, Gorilla,
Pan, and Early Hominid Subsample (a) ••••••••••• 65
vi
ABSTRACT
LATE AUSTRALOPITHECINE TAXONOMY
AND HOMINID PHYLOGENY
by
William Cromwell Mcintosh, Jr.
Master of Arts in Anthropology
January, 19 76
This thesis was an attempt to determine if contemporary populations of lower Pleistocene fossil hominids may be
classified as representatives of. a single species or of
more than one lineage. This problem is of interest to anthropologists because the presence or absence of speciation
within the hominid phylogeny bears directly upon early
hominid adaptive characteristics and the interaction between
taxa during the Pleistocene. In order to test for evidence
of speciation, samples of fossil hominid dentition dated
with reasonable accuracy to between 1.0 and 2.0 million
years BP were compared with the dentition in samples of
extant hominoid species. Univariate and multivariate statistical methods were utilized to analyze the size and shape
variability of the fossil hominids with respect to that of
vii
the extant species samples. The results of the analyses
suggested that speciation did occur and that two lineages
of fossil hominids were sampled. The implications for a
multi-linear model of hominid phylogeny were discussed.
viii
Chapter 1
INTRODUCTION
The remains of fossil hominids are widespread, show
considerable morphological diversity, and have been found
in deposits ranging in age from the late Pliocene to the
middle Pleistocene. The temporal and morphological extent
of this variability suggests to some paleoanthropologists
that the hominid phylogeny includes more than one evolving
lineage; i.e., more than one species at a given point in
time. This thesis is an attempt to determine if the fossil
remains of contemporary populations of lower Pleistocene
hominids may be classified as a single species or a representatives of two or more lineages.
Hominid remains which have been suggested as representatives of separate lineages have been recovered from the
same sites in East Africa, notably in Bed I, Olduvai Gorge
(Leak~y,
1966) and Lake Rudolf (Leakey, 1974). Proposed
multiple lineaqes would appear to have been sympatric for a
considerable length of time. Sympatric hominid taxa, and
speciation itself, have considerable implications for
models of early hominid development and adaptation, particularly in reference to the role of bipedalism and interspecific (hominid) competition. Consequently, the lineage
issue and the interpretation of the fossil material has
1
2
generated much controversy.
Pilbeam and Zwell (1972) have suggested that the maximum extent of hominid variability can be seen among specimens of late lower Pleistocene age. For this study, a
sample of fossil hominids was chosen to include specimens
from deposits dated between 1.0 and 2.0 my BP. This time
"band" includes, among other sites, those from Olduvai
Gorge Beds I and II and the upper levels at East Rudolf and
the Omo Basin, from which both "robust" and "gracile"
australopithecines have been recovered. The specimens in
this sample were taken to represent a single species, so
that a null hypothesis that only a single evolving lineage
is indicated in the fossil record could be tested by a comparison of apparent fossil hominid variability with that of
extant populations of similar animals. In order to minimize
the effects of evolutionary changes on apparent phenetic
variability, the time band was made as narrow as was possible without excluding important specimens or critically
reducing sample size.
Teeth are the most frequent of hominid remains; moreover, variation in dental morphology is generally accepted
as having an exclusively genetic basis, so that odontometrics suffer little in the way of ontological variability
other than from wear. The dentition has therefore been the
basis for many of the analyses of fossil hominid variability, as the works of Robinson (1972), Brace (1972), and
' others cited in Chapter 2 indicate.
3
The fossil hominids analyzed in this study are represented by dimensions of the mandibular permanent dentition;
this is because the frequency of individual specimens with
in situ maxillary dentition is low compared to that of specimens with mandibular teeth. This is a result of the relatively greater density of mandibular bone. Dimensions
represented in the sample are for the canine through the
third molar, since the incisors are infrequently preserved.
Both univariate and multivariate statistical methods
were used to compare patterns of metric variation of fossil
hominid teeth with those of extant hominoid species teeth.
Univariate statistical analysis involved primarily the use
of the coefficient of variation as a measure of species
diversity. This method has been successfully applied by
Pilbeam and Zwell (1972), Greene (1973), and Gingerich
(1974}. Multivariate cluster analysis was used to determine
if consistent groups of specimens could be distinguished
within the fossil hominid sample. Linear functions of the
measurement variables which did allow such discrimination
were then used to compare fossil hominid variability with
that observed in extant populations of hominoid species.
It was anticipated that if more than one lineage was
found to be represented in the fossil hominid sample, it
would be necessary to consider the relative taxonomic
status of the contemporary species in each lineage. They
might represent the same or different genera; both alter-
natives have advocates. While the phenetic perspective of
~--
-
4
dental variability on which the present analysis was based
is not an entirely satisfactory means of assessing fossil
genera, it was possible to suggest a tentative conclusion
and review the phylogenetic problems inherent in such an
interpretation.
Chapter
2
REVIEW OF LITERATURE
The purpose of the chapter is to introduce what has
become a complex and often conflicting accumulation of
.opinion bearing on Plio-Pleistocene hominid phylogeny.
Until recently research was limited by the paucity of hominid remains and the underdeveloped state of radiometric
dating technology. The widespread use of taxonomically invalid nomenclature further limited progress and remains a
pervasive problem. During the past decade, however, the
volume of fossil hominid material and both absolute and
relative age determinations of sites involved have increased dramatically.
Two basic and contrasting positions of hominid.phylogeny have emerged.
(1} Single species proponents (Wolpoff,
197lb,l973; Brace, 1972) maintain that available evidence
does not support a phylogenetic scheme more complex than
that of a single evolving lineage, in spite of the considerable morphological variability seen among contemporary
:fossil hominid forms.
(2) Multiple lineage proponents main-
'tain that this observed variability suggests a phylogeny
:involving two or more contemporary taxa, either as cognate
l
!
'species, separate genera, or both. Robinson's (1953,1963,
i 1972)
"dietary hypothesis" has influenced many multilinear
;
L---·-·~·- ---·--
5
models and pervades the popular concepts of hominid evolution. Further proposals can be viewed as either elaborations or modifications of the single or multiple lineage
models. For instance, L.S.B. Leakey (1966) and R.E.F.
Leakey (1974) have both suggested that three or even four
contemporary lineages or forms may be represented in the
Pleistocene deposits of East Africa. Robinson (1953) has
maintained that "gracile" and "robust" australopithecines
are in evidence both in South Africa and in Java.
Most investigators eventually turn to the underlying
crucial problem of the presence or absence of speciation
within the hominid phylogeny, since it reflects directly
upon the nature of the basal hominid adaptive pattern. That
pattern was either generalized enough to allow radiation
and subsequent divergence of adaptation or it was initially
!somewhat specialized so that a single adaptive pattern
characterized a ulilinear succession of taxa in the absence
of speciation. Since the initial hominid adaptation is of
primary interest to anthropologists, the lineage issue is
continually being re-evaluated.
GENERAL INTERPRETATIONS OF
HOMINID PHYLOGENY
Robinson's (1953,1963) multilinear model remains well
supported. He proposed that two genera could be clearly
·. distinguished in the South African cave deposits; Paranthi
ropus is represented at Kromdraai and Swartkrans while
7
Australopithecus is represented at Sterkfontein, Makapansgaat, and Taungs. According to Robinson the difference between these "robust" and "gracile" forms are best seen in
the dentition and cranial morphology: when compared with
Australopithecus, Paranthropus exhibits larger postcanine
dentition, smaller canines and incisors, heavier masticatory muscle attachments, and a larger body size. His dietary hypothesis attempts to explain these differences as the
result of an adaptive specialization of Paranthropus to a
largely vegetarian diet within a
so~ewhat
moist and restri-
cted ecological setting, and the genus is regarded as an
aberrant hominid. Australopithecus was a more generalized,
omnivorous form which occupied drier savanna habitats, and
was probably a tool user and occasionally a meat eater.
More recently Robinson (1972) sunk the genus Australopithecus into Homo on the basis of:
(1) similarity between
A. africanus and "H. habilis" in East Africa, and (2) the
classification of several specimens at Swartkrans as Homo
("Telanthropus") • He considered Paranthropus to be a late
representative of the basal hominid lineage, a conservative
form which remained extant for some time after giving rise
. to the Homo lineage but which did not exhibit the cultural
. adaptation characteristic of the latter genus. Robinson and
:Steudel (1973) and Frayer {1973) have also suggested that
:Gigantopithecus bilaspurensis, a very robust and probably
. vegetarian specimen from the Asian Pliocene, could be an, cestral to Paranthropus and the hominid family as a whole.
8
While reception of Robinson's interpretation of hominid
phylogeny has varied, especially regarding Gigantopithecus,
his dietary explanation of hominid dental variation remains
a useful concept.
Objections to both the dietary hypothesis of Robinson
and to any form of
multilinea~
hominid phylogeny have been
raised principally by Wolpoff (197lb, 1973}, Brace (1972),
and Brace, Mahler, and Rosen {1972). Their position is that
sexual dimorphism in a single species provides an hypothesis
sufficient to explain the observed variability among lower
Pleistocene hominids which Robinson has attributed to differences in dietary adaptation. For instance Brace (1972) ,
using means and standard deviations of mandibular tooth
crown areas, has compared fossil hominid samples from
Sterkfontein and Swartkrans with samples of male and female
chimpanzees, gorillas, and baboons, and with samples of
Homo. He suggested that the ranges of variation seen in the
two South African "taxa" overlap and that, when combined,
the overall variability of the fossil hominids is not
greater than that observed in the extant taxa. He also
pointed out that depositional and sampling error factors
may have skewed the distributions in the Transvaal sites so
that the more robust Swartkrans specimens and the more
;gracile Sterkfontein specimens have been taken as represen: tati ve of the two forms.
Wolpoff (1973) has questioned the distinguishing char; acteristics used by Robinson ( 1967) to supp<?rt his dietary
L-··-·~·-··-·
9
hypothesis, particularly with reference to the differences
in anterior-posterior tooth proportionality and size and in
cranial morphology between the two forms. Wolpoff concluded
that differences between the proposed taxa remaining after
careful analysis could be related to differential body size
and that there is little indication of two distinct adaptive patterns among the South African samples.
An important but not frequently stated characteristic
of the single species position is that the basic hominid
adaptation, involving an interaction of culture, tool use,
and bipedalism as advocated by Washburn (1951,1963), precludes the development of dietary specialization and
speciation. This position was clearly developed by Wolpoff
(197lb) and reviewed by Jolly (1972). Wolpoff takes Washburn's feedback model as the best explanation of early
'hominid radiation and finds speciation theoretically unacceptable as well as poorly supported by comparative.morphology.
Until recently, the South African australopithecines
have been central to most controversies over the recognition of sexual dimorphism but the poor stratigraphic
control among the Transvaal sites, their lack of absolute
dates, and the ambiguous distinctiveness of the populations
·represented make the region a poor testing ground for the
:single species hypothesis. This is unfortunate as they are
. among our largest samples. Often, futile arguments have
, developed as to the proper composition of comparative
10
samples. Robinson (1972) has argued that dental statistics
clearly show two distributions when populations represented
at specific sites are compared, \V'hile his opponent Wolpoff
, (1968) argued that the appropriate samples for comparison
should include all specimens attributed to the two taxa.
Frequency distributions of tooth crown areas, while they
often show clear bimodality, also frequently overlap and
the addition or deletion of a few specimens can alter conelusions which are already somewhat subjective. It may be
that the lineage issue is irreconcilable
with regard to
the S6uth African material.
~
may also be present in South Africa at Swart-
krans. Robinson (1953) first proposed a new taxon "Telanthropus capensis" for two specimens of uncertain provenience
.which exhibited distinctively "hominine" (similar to that
seen in Homo sapiens) dentition relative to Paranthropus
(SK 15 and SK 45). He later sunk the genus into Homo erectus (Robinson, 1961) and Clarke et al (1970) have supported
this interpretation, allocating a third specimen, SK 847,
to Homo. In his review of the current status of the material, Brain (1975) states that the provenience of SK 15 is
younger and distinct from the Paranthropus-bearing breccia
but that the other two specimens referred to Homo are
indeed contemporary with the australopithecine material.
Thus, the two specimens SK 45 and SK 847 could be inter. Preted as representative of either an extension of the
' range of variation of Paranthropus or another indication
..
11
of a second taxon.
East Africa has recently become a source of considerable fossil material. At Olduvai Gorge, Leakey (1966) assigned fossil hominids from Beds I and II to two new taxa,
11
"Zinjanthropus boisei" and Homo habilis", and to Homo
erectus. His opinion was that the dental and occipital
morphology seen in specimens of "H. habilis" {OH 7 and OH
13) contrasted sufficiently with that seen in H. erectus
(OH 16 and OH 24) to warrant their identification as separate species. It was Leakey's (1966) opinion that the
three taxa were "broadly contemporaneous and developing
along distinct and separate lines"(Leakey, 1966:1281). He
also proposed that the low maximum cranial breadth in H.
erectus, as compared to that of"H. habilis"y made the
latter a more likely ancestor to H. sapiens. This
amounted
to the relegation of H. erectus to extinction and was not
universally accepted. But the distinctiveness of "H. habilis" remains an issue. r1ost researchers either find the "H.
habilis" material indistinct from similar forms, as does
Robinson (1965), or they give it an intermediate status in
a lineage including A. africanus and H. erectus (Tobias,
1965,1975). "Zinjanthropus" is usually sunk into one of the
previously proposed "robust" taxa.
Brace (1972} has also argued that "H. habilis" cannot
be distinguished from the South African "gracile" australopithecines. He parts company with Robinson (1972} by in: sisting that there is no justification for an extension of
12
the genus Homo to include either lower Pleistocene form. In
his opinion, dental cross-sectional area profiles align the
Olduvai specimens of "H.
- habilis" with -A. africanus and the
/
'observable cranial variation can best be explained by sexual dimorphism.
Therefore, the taxonomic status of the major mandibular material from Olduvai, OH 7, OH
13~
and OH 16, which
were used in this study, remains indefinite. Tobias (1965)
and Leakey (1966) maintain that OH 7 and OH 13 are distinct from Homo erectus and A.
afric~nus
in crmvn size and
morphology and in mandibular robusticity. Robinson (1965)
and Brace (1972)
find them indistinct from A.(or
~.)
afri-
canus. On the other hand, the Bed II specimen OH 16 is
sometimes referred to "proto erectus" and sometimes to "H.
habilis: Thus, the Olduvai "H. habilis" remains are by
concensus a mixed or intermediate group which may represent
either:
(1) Australopithecus africanus (Brace, 1972), {2)
Homo
-
africanus (Robinson, 1965), or (3} the proposed new
taxon "H. habilis" (Tobias, 1965; Leakey, 1966), which is
essentially an argument over the antiquity of the genus
Homo. Von Koenigswald (1965) has taken the extreme position
that the "grade" represented by "H. habilis" could "be
accorded separate generic or subgeneric status,; (von Koenig.swald, 1965:401).
From the area east of Lake Rudolf, Kenya, Leakey
(1971,1972,1973a,b,l974) has provided a steady supply of
.new discoveries of.hominid fossil material ranging in age
13
from about one to three million years BP. Detailed anatomical descriptions of much of this material have been published (Leakey, Mungai, and Walker, 1971, 1972; Leakey and
Walker, 1973; Day and Leakey, 1973; Leakey and Wood, 1973)
and much work has been done on local stratigraphy (Brock
and Isaac, 1974), but thorough comparative morphometric
analyses of any of the material have yet to be published.
Leakey tentatively placed the material from East Rudolf into two broadly conceived genera: Homo and Australopithecus, with the gracile specimens in the Homo lineage
and the robust specimens in Australopithecus, postponing
in both instances species assignments. His allocation of
the mandibular material to these two genera seems to follow
Robinson's (1963,1972) observations that they are distinguished by differences in-tooth size proportions, premolar
"molarization", and robusticity of the mandible.
Recently, however, Leakey (1974) made the claim that
perhaps as many as foUr lineages are indicated and that
"all these forms may be traced back well beyond the PlioPleistocene boundary"(Leakey, 1974:656). This proposal
includes:
A. boisei,
(1} one genus with the species A. robustus and
(2) another genus with the gracile specimens
. from East Rudolf, Sterkfontein, and Olduvai (OH 24),
(3)
the genus Homo withER 1470, OH 7, and OH 16, and (4) a
; fourth "form" of "unusual .. specimens including ER 1482 and
"Paraustralopithecus" from Orne. Leakey's hypothesis of separate generic status for these four "forms" was not
14
accompanied by any explicit supporting argument.
In a recent colloquium at California State University,
Nothridge, Day (1975) discussed some of the more recently
discovered specimens from East Rudolf and compared them
with other material from East and South Africa. In his
opinion, three broad divisions of apparently contemporary
forms could be made:
Homo erectus,
(1) a lineage clearly aligned with
(2) a clearly robust lineage, and (3) an
intermediate form including "H. habilis". However, he
pointed out that many of the new specimens did not fit
neatly into these three categories because distinctions
drawn on the basis of one set of characters often were not
reflected in similar partitioning of specimens on the basis
of other characters. For instance, the ER 1470 cranium has
a broad, shallow palate with thick dental roots similar to
robust australopithecines, yet the specimen is usually aligned with the Homo lineage because of its large cranial
capacity. On the other hand, the ER 1805 cranium, which has
"gracile" teeth, also has a crested occiput, a feature seen
in some robust australopithecines such as SK 48 from Swartkrans. This mixing of characters apparently makes the identification of More than two lineages or forms difficult.
French and American expeditions have recovered hominid
:material from north of Lake Rudolf in the Orno River Basin
:of southern Ethiopia. The deposits are well. dated and span
much of the lower Pleistocene. Like the material from East
, Rudolf, the Omo specimens show considerable morphological
15
variability. According to Howell (1969), the specimens bear
close resemblances to both robust and gracile australopithecines as they are known elsewhere in Africa and indicate
" ••• the coexistence of (at least) two australopithecine
taxa through much of the range of Plio/Pleistocene time"
(Howell, 1969:1239). He has tentatively referred the material to the taxa "A. cf boisei" and "A. cf africanus" while
observing that one very robust individual, L7a-125, may be
sufficiently different from other specimens to be separated
as a third Australopithecus form because of the extreme
"m.olarization" of the mandibular premolars. Howell prefers
not to extend the genus Homo to include material from early
stratigraphic levels, a position also advocated by Brace
(1972), but he does support the existence of two evolving
lineages.
The remaining early hominid sites of major significance are in the Sangiran Dome area in Java. Lower and
middle Pleistocene deposits in this area are divided into
two broad stratigraphic divisions defined on the basis of
faunal elements: the upper Kabuh Formation (Trinil Fauna)
and the underlying Pucangan Formation (Djetis Fauna). Precise stratigraphic and radiometric controls are only recently being developed (Jacob, 1973). An absolute date of 1.9
· x 10 6 ± 0. 4 BP from a lower Pucangan Formation site and an
:average, from several determinations, of 0.83 x 10 6 BP for
the middle Kabuh Formation place the Pucangan hominids in
; rough contemporaneity with the Olduvai Beds.I and II
16
hominids. The main source of controversy over the taxonomic
relationships between Asian and African homir: ,·Js are the
two robust mandibular fragments labeled "Meganthropus paleojavanicus"(Weidenreich, 1945), from the Pucangan Formation,
and a third manibular fragment recovered in 1953 at the
base of the Kabuh Formation
w~ich
has also been assigned to
"Meganthropus"(Marks, 1953). Thus, these three specimens
are contemporary with H. erectus in Java and much of the
African material between one and two my BP.
Advocates of multiple hominid lineages have been interested in the posibili ty that "Meganthropus" may be ev.idence
of sympatric hominid lineages outside of Africa. Robinson
,(1953) proposed that "Meganthropus., was a robust australopithecine; the 1941 "type" mandible is very deep and thick,
as are many robust South African specimens. Tobias and von
Koenigswald (1964) proposed a close dental similarity
between the Asian H. erectus specimens and the 01duvai Bed
II hominid OH 13 and between "Meganthropus" and the Bed I
hominid OH 7; these observations were used to support separate species status for "Homo habilis". Von Koenigswald
(1973) agreed with Robinson (1953,1972) that Homo and
Paranthropus in Africa and H. erectus and "Meganthropus" in
Java are evidence of two syrnpatric genera during Bed I
·times. Lovejoy (1970) rejected separate status for "Megan'thropus". He pointed out that the dentition. is not outside
, the H. erectus range of variation in size or occlusal mor:phology and that all that remains notable is the very
17
thick mandibular corpus. In view of the generally robust
Asian H. erectus cranial material, Lovejoy found this an
insufficient basis for defining a separate lineage.
RECENT ODONTOMETRIC ANALYSES
Several important attempts have recently been made to
develop a specific perspective of the hominid phylogeny by
means of quantitative analyses of fossil hominid material
based upon data derived from the dentition.
Pilbeam and Zwell (1972) argued that if lineages are
to be distinguished, only samples of specimens known to be
contemporary should be compared. For each of several groups
of contemporary fossil hominids of decreasing absolute age,
they found that the coefficient of variation, used as a
measure of within-group variability based on tooth crown
diameters, increased with more recent samples until about
1.5 my BP, and thereafter decreased sharply. The maximum
extent of this variability, seen in the sample dated at 1.5
to 2.0 my BP, was found to be significantly in excess of
variability seen in samples of single extant hominoid
species. Statistical significance was determined using Ftests of variance ratios at the 0.05 level of probability.
Their interpretation of these results was that the increase
,in variability with more recent fossil hominid samples, and
, the magnitude of that variability as compared with extant
single species, did not present the sort of pattern to be
expected if sexual dimorphism was the primary factor
18
influencing early hominid variability.
Pilbeam and Gould (1974) suggested that allometric
relationships among tooth area, body size, and cranial capacity for fossil hominids reveal two distinct patterns: one
"hominine" and the other australopithecine. They interpret
A. africanus, A. robustus, and A. boisei as allometric
variants of one australopithecine form, which ,.,as probably
herbivorous. This interpre~tion lends some support to Robinson's (1963) dietary hypothesis, although Robinson does
not associate A. africanus with the.robust lineage. The
authors view Homo, characterized by "H. habilis" and H.
erectus, as quite distinct from the australopithecine
pattern. The antecedent lineage may have arisen from a form
similar to A. africanus; however, they give "H. habilis"
the status of the first clearly "hominine" species. This
view is based upon an age estimate for the South African
sites of between two and three my BP in order to remove the
possibility of contemporaneity between
11
H. habilis" and A.
africanus.
Read (1974), beginning with the assumption that indexderived allometric relationships between bucco-lingual and
mesio-distal crown diameters should be lineage or speciesspecific, tested the fossil hominid dental material for
· divergence from the modern allometric relationship for each
·tooth. Only the "super robust" East African specimens OH 5,
Omo L7a-125, and ER 729 showed a consistent difference in
1
size from the other specimens: little shape difference
19
among specimens was seen. The large East African A. boisei
specimens were placed in one lineage and all the other
australopithecine and H. erectus specimens, which formed a
reasonably homogeneous group on the basis of indices, were
placed in a second lineage. A. robustus from South Africa
was the only taxon which showed an intermediate position
between the robust and gracile lineages as represented by
A. boisei and A. africanus, respectively. Read pointed out
that while A. robustus could be placed in a third lineage,
its inclusion in the robust lineage with
~-
boisei was most
consistent with the morphometric evidence.
Greene (1973) tested Brace's (1971) contention that
the variation between Paranthropus and Australopithecus is
no greater than that due to sexual dimorphism among the
pongids or Homo sapiens. Using a Student's univariate ttest of the means of two populations, Greene compared mean
differences for maxillary and mandibular tooth crown diameters between "H. transvaalensis"
(the Australopithecus
specimens from Sterkfontein) and Paranthropus (the Swartkrans hominids)
~.-~ith
differences within each of thre·e
extant single species samples: H. sapiens, Pan troglodytes,
and Gorilla gorilla. Dimorphism between the two fossil
hominid taxa was found to be significantly greater than
due to sexual dimorphism in the comparative samples, especially for the maxillary dentition, supportipg the conclusion that a specific distinction between the two fossil
· taxa is appropriate.
20
S Utft..MARY
The primary controversy regarding the hominid phylogeny centers on the presence or absence of multiple lineages. Single species advocates, for instance Brace (1972)
and Wolpoff (197lb, 1973) prefer a unilinear model in which
all fossil hominid remains represent a single lineage leading to Homo sapiens. The other researchers reviewed here
prefer one of several multilinear schemes in which contemporary hominid species are suggested to have been in existence during the lower Pleistocene. The first objective
in this study is to assess the probability associated with
these two basic positions.
However, among advocates of multiple-lineage models
are those who favor a phylogeny {1) with lineages distinct
at the generic level (Leakey, 1974: Robinson, 1972;-von
Koenigswald, 1973) and (2) with lineages representing the
same genus (Read, 1974; Pilbeam and Gould, 1974; Howell,
1969). While there are individual variations in interpretations of multilinear phylogenetic models, generally with
respect to the antiquity of the genus Homo, the central
issue regards the presence or absence of differences at the
generic level among contemporary hominid species within a
multilinear phylogeny.
Therefore, if analyses of fossil hominid dentition in
this study suggest that the observed variability is too
21
great to be incorporated in a single species and that two
contemporary species are· represented, it will be necessary
to consider the generic status of the taxa.
Chapter
MATERIALS
&~D
3
METHODS
The sample of fossil hominids chosen for analysis includes all specimens for which mandibular dentition is represented and chronometric age estimates are available. The
taxonomic variability represented by the fossil hominid
sample was evaluated using comparative samples of extant
species and specimens of Homo dated to the middle Pleistocene or later. These comparative samples include two pongid
taxa, Pan troglodytes and Gorilla gorilla, and three hominid taxa, Homo sapiens, H. sapiens neanderthalensis, and
H. erectus, and were selected in order to provide:
(1)
samples of single species and (2) pooled samples of more
than one species for each genus (or family in the case of
the pongids) • In this chapter the provenience of the specimens, the data representing specimens, and the statistical
methods used are described.
MATERIALS
Including the fossil hominids from the time "band"
between 1.0 and 2.0 my BP, six comparative samples were
·used in the analyses. The names of these samples and the
·number of specimens in each are as follows:
Sapiens ••••••••••• 81
22
23
Neanderthal ••••••••• lO
Erectus •••••••••••••• 7
Pan . ••.•..•..•••.... 2 3
Gorilla •••.••••••••• 38
Early Hominid ••••••• 35
These names are used in reference to individual samples and
are not underlined like the taxonomic names of the individuals included in
samples~
In order to maintain the distinc-
tion between the sample of H. erectus specimens and the
sample of fossil hominids which are the subject of this
study, the latter sample is called "Early Hominid", and no
further use is made of the term "fossil" in reference to
samples. Individual early hominid and extant sample specimens will be referred to as "cases" in order to maintain
the distinction between cases and variables in multivariate
analyses.
In this section the provenience of cases in each sample and the measurement data representing cases are described under the headings:
(A) Early Hominid Sample, (B) Com-
parative Samples, and (C) Measurement Data.
A. Early Hominid Sample
Table 1 lists the provenience of Early Hominid cases.
Each case is identified by its museum accession number
wherever possible. For each of the six geographical areas
represented, data on the local stratigraphy and current
radiometric or chronometric age estimates are presented
following the identification of each case. There are ten
cases from East Lake Rudolf, Kenya, from sites in the
..
24
Table 1
Provenience of Early Hominid Cases
Local Stratigraphy
Age(my)
ER992
Ileret, below Chari tuff
1.4-1.6
ER818
ER729
ER806
Ileret, below middle tuff
tease
East Rudolf
ER801
ER802
ER820
ER1171 .
1.6
Ileret, below lower tuff
1.6-1.8
ER730
Koobi Fora, below KF tuff
1.6
ER810
Koobi Fora, above KBS tuff
1.6-1.8
Omo Basin
OM/L7a-125
. OM/29-43
.. OM/L74a-21
OM/75-14a,b
OM/75i.:..l255
OM/75s-15
OM/136-1
OM/136-2
r1ember G (Shungura Formation)
between tuffs G and I2
1.84-1.93
OM/74-18
Member H, between tuffs I 2 and I 4
1.8
OM/F-203-1
OM/K-7-19·
Member L, assoc. with tuff L
1.34
MK; lower Bed I
FLK,NN; middle Bed I
FLK; Bed I (inferred)
1.75
FLK; base Bed II
Maiko Gulley N, lower Bed II
MNK; lower middle Bed II
1.0+
· Olduvai Gorge
OH4
, OH7
OH6
OH16
OH30
OH13
25
Table 1 (cont.)
Provenience of Early Hominid Cases
Case
Local Stratigraphy
Age(my}
Lake Natron
NAT RON
Peninj lacustrine facies
1.5
Taungs
Buxton Lime Quarry
1.0-1.5
SANGl
SA.L'JG5
SANG6a
SANG6b
SANG9
Pucangan Forrnation{Djetis Fauna)
1.4-1.8
SANG8
Kabuh Forrnation(Trinil Fauna); base
TAUNG
Java
1.3
26
Ileret and Koobi Fora areas. These sites are all above the
KBS tuff (Koobi Fora) and below the Chari tuff (Ileret).
Brock and Isaac (1974) gave these sites temporal limits
ranging between 1. 4 and L 8 x 10
6
BP. Eleven cases are from
the Omo Basin in Southern Ethiopia, from sites in the Shungura Formation Members G,H, and L. Temporal limits for the
6
sites are 1.34 to 1.93 x 10 BP (Howell and Coppens,. 1974;
Merrick et al, 1973). Six cases come from Olduvai Gorge,
Tanzania, Beds I and II. An average of several radiometric
6
dates places sites in lower Bed I at near 1.75 x 10 BP
(Evernden and Curtis, 1965). Dating for the top of Bed II
has been a problem for some time but similarities with the
Peninj lacustrine facies and other factors have led to a
recent estimate of about 1.0 x 10 6 BP (Day, 1975). The
Lake Natron (Peninj) specimen has been dated at approximately 1. 5 x 10 6 BP (Isaac, 19 6 7) • The 'I'aung specimen from
South Africa is included in the analysis because it is our
most well known fossil and because recent work at the Buxton Lime Quarry where it was found suggests that it is one
of the most recent, rather than the oldest, of the South
African sites (Butzer, 1974; Partridge, 1973). In spite of
Partridge's estimate of 0.8 million for the site, it is
likely to be closer to between 1.0 and 1.5 million (Butzer,
1974). The last six cases are from the Sangiran Dome area
in Java. These are identified here following Jacob {1973)
as Sangiran numbers 1,5,6a,6b,8, and 9. The relationships
between these numbers and specific names which have been
27
assigned to the specimens by different authors since 1889
are as follows:
Sangiran no.
l •••• Pithecanthropus mandible B(4) 1936
P. robustus (Weidenreich, 1945)
P. mojokertensis (von Koenigs\'la1d,
1"950)
5 •••• Pithecanthropus dubius 1939; fragment
found with Meganthropus type specimen
6a ••• Meganthropus pa1eojavanicus 1941
11
type 11 spec~men
6b ••• "unpublished fragment" (Meg. II: Tobias
and von Koenigswald,-r964)
8 •••• "Meganthropus III" mandible (Marks, 1953)
9 •••• Pithecanthropus C mandible 1960
As described in Chapter 2, age estimates for the middle
Kabuh Formation and the lower Pucangan Formation are 0.5 to
'0.9 x 10 6 BP and 1.9 x 10 6 BP, respectively (Jacob, 1973;
Stress, 1971). Each of the cases listed in Table 1 is from
the Pucangan Formation with the exception of Sangiran 8
which is from the base of the Kabuh Formation. Stratigraphic relationships described by Sartono (1961) and Jacob
{1973) support upper and lower limits of approximately 1.3
and 1.8
x
10
6
BP for the six cases.
The distribution of the thirty-five cases in the Early
,Hominid sample within the time period between 1.0 and 2.0
my BP is skewed such that the relatively older cases are
better represented. While the absolute dates are subject to
error, the stratigraphic evidence favors the assumption
I___ ·------ - .. -· -- ... ---
2R
that the relatively younger cases are well within the time
limits imposed, so that the actual time span represented by
the sample is probably on the order of 0.75 million years.
OH 13 and Sangiran 8 are two such relatively younger specimens; a 0.5 million-year time band of 1.5 to 2.0 my BP,
used by Pilbeam and Zwell
(1972) , would have been a better
check on evolutionary sources of variation, but would have
excluded these two important specimens and reduced the
sample by several other cases as well.
B. Comparative Samples
The samples of extant hominoid species and upper Pleistocene taxa of the genus Homo were composed as follows:
Sapiens. Data on eighty-one cases of H. sapiens were selected from Wolpoff (197la). All specimens, subfossil and contemporary, with data on the canine through the third molar
were included. The incisors have been excluded from consideration because of their scarcity in the Early Hominid
sample. Cases are from several geographical areas and
racial groups; they are not, however, equally representative of the various populations. All cases are of late
Wisconsin glacial age or later and are not sexed.
Pan and Gorilla. Data for the two pongid samples were
taken from Pilbeam (1969) and represent forty Gorilla gorilla (20 males; 20 females) and twenty-six Pan troglodytes
(14 males; 12 females) mandibles. Because of unrepresented
29
teeth in four cases, these sample sizes were reduced to
thirty-eight for Gorilla and twenty-four for Pan where
multivariate methods were used, in order to maintain complete variable representation.
Erectus and Neanderthal. Data for the two samples of fossil
taxa of the genus Homo were also taken from Wolpoff (197la);
seven cases of H. erectus and eleven cases of H. sapiens
neanderthalensis were selected. These samples were used
both (1) individualy as comparative species or subspecies
samples and (2) pooled as a multispecific sample of one
genus.
The lower time boundary for inclusion of specimens of
H. erectus in the Erectus sample is crucial since some
fossils included in the Early Hominid sample have also been
assigned to that species, for instance Sangiran 1 and 9.
However, the objective here is not to assign species labels
to individual cases but rather to assess the relative variability in the Early Hominid sample. Therefore, the two
samples, Early Hominid and Erectus, need only be distinct
stratigraphically and separated by a reasonable time period, which in this case is about 0.75 million years,
roughly the effective range of the Early Hominid sample
dates. The Erectus sample includes the three Ternifine
specimens, two individuals from Choukoutien lower cave, and
the specimens from Mauer and Rabat, all of which are dated
· to well within the middle Pleistocene.
30
c.
Measurement Data
Data for each case are measurements for the mesio-
:distal and bucca-lingual crown diameters of the lower dentition, C through M3 • Appendix A lists the data for Early
Homin~d
sample cases and a key to sources of data.
Original fossil specimens are not readily available
for measurement and the data were taken from primary sources when possible. Considerable inter-observer variation
has been observed for measurements taken on the same
specimen (Robinson, 1965). Ideally, an investigator would
use a complete data set recorded by one individual (preferably himself). However, this is unattainable and variation
in interstitial wear, preservation, and cases of aberrant
development probably introduce more error than that contributed by inter-observer differences in measurements.
Measurements for each tooth were recorded in tenths of
a millimeter. For specimens in the Early Hominid sample,
the left side was recorded unless a missing tooth is preserved on the right. For other hominid cases, the average
of measurements for the two sides was recorded when both
sides were present.
Descriptions of fossil hominid mandibles often include
features other than crown diameters. Crown morphology and
corpus dimensions and morphology have been the subject of
'research as well (Weidenreich, 1939; Tobias, 1971).
Hm-Y'-
ever, with consideration of these characters, the familiar
..
31
problem of sample size versus number of variables arises.
With the original specimens unavailable, the use of nonmetric characters in this study is dependent upon the observation and publication of such data by those researchers
who had access to the material. Also, these characters must
be observed in the first place; often they are not. Both
the tooth crowns and the body of the mandible are subject
to wear and poor preservation. Thus, the reported presence
or absence of a character is dependent upon several factors
of preservation, wear, and observation.
There is little systematic description of morphological characters of the mandibular corpus. Using Weidenreich
(1939} as a basic source, the "simian shelf" may be identified with the lower transverse torus of the posterior
aspect of the mandibular symphysis while the sloping plane
posterior to the incisors is the planum alveolus. Both of
these features have been referred to as a
11
simian shelf" by
various investigators. Weidenreich showed that the crosssection of the symphysis is one of the most variable and
inconsistent aspects of the mandible. In spite of this evidence, Tobias (1971} recently gave this feature considerable attention in an analysis of mandibular robusticity in
South African hominids.
Another problem in interpreting non-metric features is
that accurate frequency distribution values for H. erectus
and H. sapiens are needed but not systematically reported.
Thus, non-metric observations were not used in this study.
32
This is not to suggest that such characters have no utility;
in fact, crown
~orphology
can be a primary feature of mam-
malian fossil systematics, especially among herbivores, but
:the current state of fossil hominid evidence precludes
reliable systematic treatment of such data.
METHODS
The main purpose of analyzing the variability within
and between the samples described was to determine if the
variability within the Early Hominiq sample exceeds that
expected for a single species. The samples of other known
species provided the basis for evaluation of this expected
variability and testing of appropriate hypotheses.
The analyses of Early Hominid sample variability carried out are grouped into two broad categories: (1) those
based upon univariate methods and (2) those based upon
multivariate methods. Univariate analysis was used in two
treatment formats, one designed to describe within-group
variability of the Early Hominid sample and the other to
compare within-group variability for all samples. The multivariate analyses also followed this pattern, dealing first
with within-group variability of early hominids and second
with within-groups variability relative to between-groups
variability. For each of these two multivariate categories,
methods based upon measures of size and shape were treated
separately.
The grouping of analysis formats thus used three
33
characteristics--multivariate vs. univariate, within-group
vs. between groups, and size vs. shape--to divide the results into six categories. The methods applied to each were
designed to test the working hypothesis that the Early
Hominid sample represents more than one species. In some
analysis formats it was possible to test null hypotheses
equating Early Hominid sample variability and that of known
species samples. In others it was only possible to compare
variability by a less explicit means.
A. Univariate Analysis
Utilizing univariate analysis formats,
(1) histograms
were used to reveal within-group variability of the Early
Hominid sample and {2) the F-test of variance ratios was
used to compare Early Hominid sample variance with that of
known species samples.
Histograms. Histograms were constructed as follows. Measurement data for the full sample of early hominids (n=34)
were standardized (Zx = x - x/ sx> for each of the twelve
measurements representing the diameters of C through M3 •
Twelve histograms were then constructed to show the distribution of cases within the sample for each variable. The
distributions served as a preliminary indication of the
presence or absence of bimodality and overlap. Pilbeam and
· Zwell (1972) suggested that among the extant primates,
sexual dimorphism is_ expressed in bimodal distributions
;only for the canine, and not for postcanine dimensions.
34
The distributions also served as a simple illustration of
the data set which was the basis of all further analyses.
Variance ratios. F-tests of variance ratios were used to
compare Early Hominid sample variance estimates (s 2 ) for
each measurement variable with values obtained for the
comparative samples of known taxonomic rank. Early hominids
were compared with the comparative samples labeled (1)
Sapiens,
(2) Pan,
(3) Gorilla, and with two pooled samples:
(4)Pan plus Gorilla, labeled Pongid, and (5) Sapiens plus
Erectus plus Neanderthal, labeled Homo {multispecific). In
each comparison, the F-statistic was used to test null hypotheses that variance within the Early Hominid sample is
less than or equal to that within each of the other samples;
slight variations in the five resulting null hypotheses are
explained in the following chapter. This method is useful
and frequently used, and it is used here to (1) compare the
results of this study with those of other studies (Pilbeam
and Zwell, 1972; Gingerich, 1974: Greene, 1973) and (2}
provide a simple description of the relative magnitude and
patterning of the variance within the Early Hominid sample.
The·F-statistic is usually obtained from sample variance ratios in the form F = sy
I s~ • An assumption basic
to the use of variance ratios is that the means of the respective samples are of equal magnitude, but this assumption is not met by the samples used in this study. When
samples possess unequal means it is appropriate to trans-
35
form the data to logarithmic form and test logarithmic
variance ratios. An approximation of the logarithmic
variance can be easily provided by the squared coefficient
of variation:
cv2 =
(s 2; Y) 2 (Sokal and Rohlf, 1973; Lewon-
tin, 1966). Accordingly, the values for Fused in this
study were calculated as F =
.,
cv12 ;cv2.
B. Multivariate Analysis
Several separate analyses of the samples described
above were performed using factor analysis. Factor analysis
is a general term applied to a family of mathematical
models which are designed to describe, in various ways, the
variance within a sample or the variance within and between
several samples on the basis of a given set of several
variableso One purpose of factor analysis can be to reduce
the dimensionality of the data matrix (i.e., the matrix of
cases each of which is represented by several variables} so
that patterns of variance may be more easily interpreted.
Often three or four uncorrelated factors "replace" the many
original variables and yet still explain a large percentage
of the overall variance. Another purpose of factor analysis
can be to generate new variables for cases which better
represent those aspects of sample variance which are of
specific interest; for instance, size or shape.
Two factor models were used in this study: principal
components analysis and canonical discriminant function
analysis. Description of the objectives and results of
36
multivariate analyses requires the use of concepts specific
to these t\<10 factor models. Therefore, the following sections introduce
(1) principal components analysis,
(2) can-
onical discriminant function analysis, {3) cases and
variables included in the Early Hominid sample for multivariate analysis formats, and. {4) the individual multivariate analysis formats used.
Princioal components analysis. The variety of principal
components analysis used here is based upon the standardized.variance-covariance matrix {i.e., the correlation
matrix). The analyses were performed using Veldman's (1967)
program FACTOR. A factor, or principal component, can be
interpreted as a function of unknown independent variables
which explains a certain proportion of the variance expressed by the correlation matrix. A program will compute as
many principal components as are required to explain all
of this variance, and they are collected in a principal
component matrix, the columns of which are the principal
components {technically eigenvectors) • The degree to which
original variables can be used to predict the value assumed
by a principal component are indicated by the individual
values {loadings) within the principal component matrix.
Each component is associated \·lith an eigenvalue which
measures the percentage of total variance explained by the
component. Principal axis scores are values which represent
the original cases with respect to the principal components
37
(Rummel, 1967; Van de Geer, 1971).
A geometric model of principal components analysis
identifies principal components with the principal axes of
a hyper-ellipse of points in multi-dimensional data space.
The first principal component is the primary (longest)
axis; other succesively smaller axes are identified with
the "residual" components. Principal component loadings
represent the relationship between these original and new
axes. The new axes are orthogonal (at right angles) to each
other and as the cosine of the angle between such axes is
equivalent to the correlation coefficient, normal principal
components are uncorrelated. Principal axis scores are
therefore also uncorrelated: it is for this reason that
principal components analysis can be used to circumvent the
redundancy among original variables and provide new, uncorrelated "variable" scores for cases.
One further aspect of principal components analysis is
of particular importance to the present study. The correlation matrix upon which the factoring process depends can
be either for variables--R-mode--or for
cases~-Q-mode.
In
R-mode analysis principal component loadings and scores are
computed as introduced above. In Q-mode analysis, however,
cases, rather than variables, assume principal component
loadings and scores are not normally computed.
In R-mode analysis the first principal component is
often interpreted as. a function of size variation among
cases and, where highly correlated variables such as teeth
38
are used, it can account for a large percentage of variance.
This situation was common in this study and it can cloud
the contributions of residual components which may contain
other information, for instance shape variation (Rummel,
1967; Corruccini, 1973).
In Q-mode analysis, the standardization process required to compute a case-wise correlation matrix {a twoway standardization) has the effect of producing coefficients ltThich reflect the similarity between cases in their
profile across the standardized variables. This is frequently interpreted as a measure of shape relationships.
For taxonomic purposes it is useful to distinguish
size and shape, since the latter is often interpreted as a
better representation of differences between genera (Corruccini, 1973). There are other measures of shape differences: the R-mode residual components have been mentioned,
but these are frequently associated with relatively low
eigenvalues, so that inferences about shape depend upon a
small percentage of overall variance as it is represented.
Consequently, in this study R-mode and Q-mode analysis have
been interpreted as size and shape-related methods, respectively. R-mode principal axis scores and Q-mode principal
component loadings were used to represent size and shape
relationships.
Principal components analysis was (1) used in all
multivariate analysis formats in order to provide new,
, uncorrelated, scaled, size or shape-related variable sets
39
and (2) used to identify certain original measurements with
similarities or differences among cases in the Early Hominid sample.
Canonical discriminant function analysis. The algorithm
used to perform the computations for canonical discriminant
function analysis was BMD 07M" (Dixon, 1974). The input for
this program is a set of groups, rather than a single
sample, and the "factors" in this case, canonical discriminant functions, identify not the major axes of variation
in a single group but the set of axes which best discriminate among several groups. In other words, functions are
identified which maximize between-group variance relative
to within-groups variance. Canonical discriminant function
analysis is directly analogous to multivariate analysis of
variance
(~illNOVA).
The important portion of the output of
BMD 07M for this study is (1) the matrix of F-raties of
within and between-group variance \vhich can be tested for
significance using a table of critical values for F in the
same way univariate ratios are tested and (2) the measures
of within-group distances between cases based upon Mahalanobis' D2 statistic, which can also be measures of withingroup variation (Van de Geer, 1971).
In this study, canonical discriminant function analysis was used to analyze the shape variation of the Early
Hominid sample relative to that within comparative samples
' included in the input-groups-set. Data representing cases
40
in the input-groups-set were first transformed to shaperelated variables by Q-mode principal components analysis.
:Early Hominid sample. Of the original thirty-five cases
selected for the Early Hominid sample, few take values for
all twelve measurements and some take values for only two
measurements (one tooth). Since most multivariate analyses
require complete data matrices and a large variable set is
desirable, minimum cri.teria for inclusion of a case in
multivariate analysis were established. The presence of at
least three teeth (six dimensions) representing more than
one dental field or tooth type was required. Fourteen· cases
were accepted. Then the distribution of missing values
among the fourteen cases were studied and eleven cases were
selected such that two subsamples could be delineated (see
Table 2) • Subsample (a) was compiled in order to maximize
variable representation (six cases; ten variables) and subsample (b) was compiled to maximize case representation
(ten cases, six variables).
Subsamples (a) and {b) were used together for analyses
of variance among the early hominid cases. Subsample (a)
alone was used in comparative analyses with extant taxa.
Individual analysis formats. Multivariate analysis formats
;were grouped according to whether the objective was (1) to
identify patterns of variance within the Early Hominid
sample(s) or (2) to compare Early Hominid sample variation
'with that of comparative samples. For both of these
L·--:--------------------~-·-------------------- ·-------------------- ·----- -------------- -- -- ---------- . . :__________ -----------~-----'
41
Table 2
Early Hominid Cases used in Multivariate Analyses
Dimension (rom x 10)
c
Case
(1)
p3
(b)
( 1)
(b)
p4
(1)
(b)
M2
Ml
( 1)
(b)
(1)
(b)
174
162.
120
153
158
138
162
180
123
147
138
122
174
162
120
153
138
195
175
135
135
197
162
180
123
147
122
180
154
125
134
180
M3
( 1)
(b)
188
182
128
158
152
200
151
135
146
220
163
148
123
144
110
190
141
127
125
180
Subsamp1e (a)
NAT RON
OM/L7a-125
ER992
OH16
OH7
OH13
73 81 92 135 145 152 164 153
78 96 112 175 117 189 168 187
90 81 95 111 84 111 120 109
99 101 103 115 101 110 143 128
89 98 95 102 103 106 l41 125
76 79 90 92 92 87 127 116
Subs ample (b)
NAT RON
OM/L7a-125
ER992
OH16
OH13
ER729
OM/75-la,b
SANG9
S.Ai~G1
ER818
145
117
84
101
92
140
114
90
90
145
152
189
111
110
87
150
127
107
109
160
42
divisions, measures of size and shape were considered. The
follm.,ring four sections introduce analysis formats under
the headings (1) Early Hominid sample size variation,
Early Hominid sample shape variation,
(2)
(3) Early Hominid
sample size relative to comparative samplesp and (4) Early
Hominid sample shape relative to comparative samples.
1. Size variance within the two Early Hominid subsamples (a) and (b) was analyzed using principal components
and cluster analysis. R-mode principal components analysis
was used to transform raw data into scaled, uncorrelated
scores for cases and dendrograms depicting inter-case similarity were constructed on the basis of these scores, using
a mean-distance method (Everitt, 1974).
Principal component matrices and associated dendrograms for each subsample were analyzed in order to reveal
(1) the distinctiveness of "robust" and "gracile" varieties
among the hominids represented and (2) the variables associated with the. differences and similarities between and
within these two varieties. Comparison of dendrograms for
subsamples (a) and (b) were made in order to reveal changes
in clustering resulting from changes in variable represent. ation.
2. Shape variance, as approximated by Q-mode transfermation of raw data, within the two Early Hominid subsarnples
was analyzed using the same methods applied to investigate
size variation, except that reference to original measure-
43
ments was not possible because of the Q-mode transformation
used.
Dendrograms of inter-case shape similarities were compared:
(1) for subsamples (a) and (b) in order to reveal
changes in clustering with changes in measurement representation and (2) with the two size-related dendrograms for
the same subsamples in order to test the possibility that
·the robust and gracile size-varieties also exhibit shape
differences.
3. Early Hominid sample size variation was compared
with that within comparative samples of extant taxa. A
sample of ninety-six specimens including H. sapiens, Pan,
Gorilla, and Early Hominid subsample (a) was compiled. Rmode principal axis scores were computed in order to provide scaled, uncorrelated new variables. The rotated principal axis scores were then used to (1) construct a dendrogram depicting inter-case similarity, using Veldman's (1967)
program HGROUP,_and {2) compute inter-case squared distances (D 2 ), which are analogous to Mahalanobis'
o 2 statistic.
The clustering sequence obtained in the dendrogram was
inspected in order to compare the integrity of groupings of
Early Hominid sample cases with respect to those of other
·taxonomic groups. The
o 2 values between cases were reduced
to Euclidean distances (D) and used to compare withingroup variation among the samples.
4. Early Hominid sample shape variation was compared
44
with shape variation in other taxa using a pooled sample of
fifty-five cases partitioned into six groups including H.
sapiens, H. sapiens neanderthalensis, H. erectus, Pan, Gorr
filla, and Early Hominid subsample {a). Data for this sample'
were transformed using Q-mode principal components analysis
and principal component loadings were used as data to (1)
perform canonical discriminant function analysis and (2)
compute inter-case squared distances (D 2 ).
Discriminant function analysis was used to test the
null hypothesis that Early Hominid sample shape variance
does not differ from that of H. erectus, its nearest phylogenetic neighbor, using the F-value matrix. Shape variation
within groups was compared using both the distance values
computed by the discriminant analysis and those computed by
the separate squared-distance program.
'--·-----~ ---~~--~~-----------------------------------------------------------------------------~·
..
Chapter
4
RESULTS OF ANALYSES
The results of analyses of variability among and within the samples described in Chapter 3 are presented in this
chapter under the headings:
(1) univariate analysis,
(2)
multivariate analysis, and (3) summary of results.
UNIVARIATE
&~ALYSIS
A. Variance Ratios: the F-statistic
Coefficients of variation for measurement variables
were computed for each sample in order to provide a means
of comparison of the variance within the Early Hominid sample with that within comparative samples. The five comparative samples utilized in this portion of the analysis, introduced in Chapter 3, are those labeled Sapiens, Gorilla,
Pan, Homo(multispecific}, and Pongid.
Coefficient of variation values CV
=
(s/ Y) x 100 for
each of the twelve measurement variables are presented in
Table 3. A complete listing of descriptive statistics for
the samples is to be found in Appendix B. Inspection of
Table 3 reveals several patterns. By scaning the values for
P 3 through M3 in each of the tt,oTelve rows it can be seen that
M1 takes the smallest value six times and P 3 twice. Thus,
M1 appears to be the· least variable postcanlne tooth, as
45
46
Table 3
Coefficient of Variation Values for Mesio-distal and Buccolingual Measurements of Hominid and Pongid Teeth by Sample
Sample
Tooth
c
p3
p4
Ml
M2
M3
Mesio-distal
10.8
9.2
20.0
11.8
15.6
14.9
Sapiens
7.7
8.1
8.1
6.5
7.0
7.9
Gorilla
18.1
9.9
6.7
4.8
6.4
17.3
Pan
11.7
4.6
6.8
5.4
5.4
6.0
Homo
8.2
(multispecific)
Pongid
20.7
(Pan+ Gorilla)
10.5
11.3
8.7
8.2
8.1
19.9
19.1
17.7
20.5
16.7
11.4
18.7
21.1
14.2
14.5
15.3
Sapiens
8.4
7.6
9.0
6.2
6.1
7.2
Gorilla
15.9
12.0
7.5
5.5
7.0
7.5
Pan
11.6
8.4
5.2
5.5
6.1
5.5
10.5
9.0
7.6
8.4
8.6
20.5
17.6
15.1
17.7
19.0
14
81
40
26
27
66
17
81
40
26
27
66
19
81
40
26
27
66
19
81
40
26
27
66
19
81
40
25
27
65
Early Hominid
Bucco-lingual
Early Hominid
Homo
(multispecific) 10.4
Pongid
(Pan+ Gorilla)
14.8
Sample Sizes
i
Early Hominid
Sapiens
Gorilla
Pan
Homo
Pongid
8
81
38
24
27
62
-
...
-
---~---.----
·-·-·----·----- -----
''
---------~
47
suggested by Gingerich {1974). Mesio-distal and buccolingual dimensions of M1 are about twice the magnitude of
those for the other samples except for the Pongid sample.
This suggests that variability among postcanine measurements for the Early Hominid sample might be significantly
greater than for the samples of single species. Postcanine
values for the Early Hominid sample are smaller but closer
in magnitude to those for the Pongid sample than those for
the other single species samples or the rnultispecific
sample of Homo. Values for the canine and the mesio-distal
diameter of P 3 in the Early Hominid sample are not nearly
as large in magnitude compared with corresponding values in
other samples. This was anticipated where pongids were cornpared with horninids because of the pattern of sexual dimorphisrn seen in pongids; but even compared with other heminids, the Early Hominid sample variability for these dimensions is only slightly increased, if at all.
The statistical significance of each of the differences in the magnitude of CV as a measure of within-sample
variance was tested using the F-statistic. If the Early
Hominid sample is hypothesized as sampling a single biological species, then both its sample variance s 2 and that of
other samples of single species should approximate a parametric value ~ 2 appropriate for a single biological species.
Comparisons between Early Hominid sample variance and samples of more than one species (samples labeled Homo and
Pongid) provided a further estimate of the taxonomic
48
significance of the former samples' variance.
Table 4 lists the null hypotheses associated with comparisons of sample variances and the results of F-tests of
significance. The null hypotheses Ho,l through H0 , 3 state
that Early Hominid sample variance is less than or equal to
that for one of the single species samples; i.e., both
values of CV estimate a parameter of "single species" magnitude. Critical values of F at the 0.05 level of probability with the appropriate degrees of freedom provided tests
of the null hypotheses. If the F-value obtained exceeded
the critical value then the null hypothesis was rejected
and the alternative was not rejected. For each of the first
three null hypotheses, the alternative is that Early Hominid sample variance exceeds that .expected for a single
. species.
The fourth and fifth null hypotheses compare Early
Hominid sample variance with that of samples which include
more than one species; the directionality is modified aceording to the actual values of CV listed in Table 3. All
tests are one-tailed, i.e., directionality is anticipated.
The significance of the comparisons made in Table 4
follow the pattern anticipated by Table 3. Where Early
Hominid sample variance is compared with that for the sam;ples labeled Sapiens, Pan, Gorilla, and Homo(multispecific)
i
there is a clear break between anterior and posterior
·dimensions at P 3 ; for dimensions posterior to P 3 length,
i.e., P 3 breadth and all dimensions of P 4 through M3 , Early
49
Table 4
Results of F-tests of Significance of Differences in the
Magnitude of the Coefficient of Variation between
Early Hominid Sample Measurements and
Comparative Sample Measurements
Comparative
Sample
Mesio-distal
Sapiens(Ho, 1 >
ns
ns
0.001
0.001
0.001
Gorilla(H 0 , 2 >
ns
ns
0.001
0.001
0.001
Pan (H 0 , 3 >
ns
0.001
0.001
0.001
0.001
Homo (H 0 1 4 >
ns
0.001
0.001
0.001
ns
0.01
ns
ns
ns
0.001
ns
0.05
0.025
Sapiens (H 0 , 1 )
ns
0.001
0.001
0.001
0.001
0.001
Gorilla(H 0 2 )
I
ns
0.025
0.001
0.001
0~001
0~001
Pan(H
)
013
Homo (H 0 , 4 )
ns
0.001
0.001
0.001
0.001
0.001
ns
0.01
0.001
0.001
0.01
0.01
Pongid (Ho 15 )
ns
ns
ns
ns
Pongid (H 0 5 >
1
ns
ns
Bucca-lingual
ns
ns
(ns =not statistically significant)
Null Hypotheses
Ho,1=
Ho,2=
Early Hominid s 2 less than or equal to Sapiens s2
(Hl,l:
>s~)
Early Homin~d s~ less than or equal to Gorilla s 2
sy
(Hl,2:
SJ.
>s2)
Ho,3=
Early Homin~d s~ less than or equal to Pan s 2
(Hl,3: Sl >S2)
Ho,4=
Early Homin~d s~ less than or equal to Homo s 2
(Hl,4: 5 1> 5 2)
Ho,s=
Early Hominid
greater than or equal to Pongid s 2
(Hl,5: si <s2)
s;
so
Hominid sample variance is very significantly in excess of
that of the other samples. For the canine and P 3 length,
Early Hominid sample variance is not significantly in
·excess of that for the other samples. The three exceptions
to this pattern
(of 48 ratios) involve P3 length for H , 3
0
:(Pan), M3 length for H0 , 2 (Gorilla), and M1 length for
Ho,4 (Homo). The anterior-posterior break is clearer for
the bucco-lingual dimensions and the obtained significance
levels are slightly higher on the average.
Not only was Early Hominid sample variance found to be
significantly greater than that of the Homo(multispecific)
sample for postcanine dimensions, but it was also found to
be not significantly less than that of the Pongid sample
for the same dimensions. The results of these tests and
those for the other three null hypotheses indicate that
'when postcanine dimensions alone are considered, (1) Early
Hominid sample variability is significantly in excess of
expected values for a single species and (2) that it approaches the magnitude seen in samples of pooled genera.
This high postcanine variability also implies that in multivariate techniques sensitive to anterior-posterior size
, ratios, as well as general size, the postcanine variables
may account for most of the differences.
The taxonomic significance of the high variability of
the Early Hominid sample is not, however, proportional to
:the significance of the F-tests. To illustrate this, the
i samples
~-·--·-·----
labeled Pan and Sapiens were pooled, and values for
- - -~-- ---·--·--·------·--
51
CV re-computed. The values obtained for P 3 through M3
breadth for this pooled sample, compared with corresponding
values for the Sapiens sample alone, are as follows:
Sapiens
Sapiens plus Pan
p3
p4
Ml
M2
M3
7.6
8.0
9.0
7.9
6.2
8.2
6.1
6.1
7.2
7.1
Only minimal differences exist for these dimensions between
the single species sample of Homo and a sample combining
Homo and Pan, two taxa of demonstrably different dietary
adaptations. The fact that the Early Hominid sample was
found to approach the variability expressed in the Pongid
sample (Pan plus Gorilla) does not then support any interpretation as to adaptive differences among Early Hominid
sample cases. These observations do, however, support the
assumption maintained in analyses of shape differences that
·species differences are generally size-related and generic
or adaptive differences shape-related.
B. Histograms: Early Hominid Sample Variation
Histograms were constructed to illustrate the actual
within-group variability for the Early Hominid sample.
Figure 1 illustrates the histograms obtained for the standardized measurement variables representing the canine thr.ough M3 , at a class interval of one-half of one standard
. deviation. Each of the histograms shows some departure from
:normality. and a suggestion of bimodality is seen for the
i
canine, P 4 , and M3.
l__________________________ -... ---- ... .. --
52
Figure .1
Histograms of Dimensions of C through M3 for Early Hominids
(class interval= 0.5 standard deviation}
Tooth
Dimension
Mesio-distal
Bucca-lingual
Canine (n=8)
I
-1.0
1.0
P 3 (n=l4)"
P
4
(n=l7}
M1 (n=l9)
2
(n=l9)
M3
(n=19)
M
-:z.o
2.0
-z.o
-/.0
0
0
0
0
0
0
0
0
1.0
3.0
53
It has, however, been suggested by Pilbeam and Zwell
(1972) that sexual dimorphism among the primates is not
often expressed in bimodal distibutions for postcanine
dimensions. The distributions in Figure 1 might therefore
lend some support to the results of the tests of variance
ratios which indicated that sexual dimorphism is not a sufficient explanation of Early Hominid sample variance.
C. Summary of Univariate Results
The differences between Early Hominid sample variance
and variance values for samples of single extant species
was found to be highly statistically significant for most
postcanine dimensions. The significance level was often
found to exceed 0.001. High variability with respect to
single species for about seventy-five percent of the measurements used likely indicates the presence of representatives of more than one biological species in the Early
Hominid sample. Each of the comparative samples for Homo
sapiens, Pan, arid Gorilla includes variation due to sexual
dimorphism while the Homo sapiens sample also represents
polytypic variation. Therefore the effects of sexual dimorphism and polytypicality alone are unlikely explanations
of Early Hominid sample variation.
The indications of bimodal distributions among the
histograms may result from either sexual dimorphism or from
the presence of different populations of unknown taxonomic
status. It is probable that both sources of variability are
54
involved here. The results of univariate analysis further
suggest that the bucca-lingual dimensions of the postcanine
teeth may be found to be particularly important in multivariate analyses of Early Hominid sample variability.
MULTIVARIATE ANALYSIS
The results of multivariate analyses are presented in
two parts within this section:
(A) analysis of the segrega-
tion of individual cases within the Early Hominid sample
and (B) analysis of within-groups variance relative to
between-group-means variance. For each of these divisions
measures of size and shape variation were treated separately using R and Q-mode principal components analysis to
define new variable scores for cases as explained in Chap.ter 3.
A. Early Horninids: Within-group Relationships
Early Hominid subsamples (a) and (b), introduced in
Table 2, Chapter 3, were analyzed using R and Q-rnode principal components techniques. In each instance, varimax
rotation of the principal component matrix was performed;
for R-mode analyses principal axis scores were computed. Rmode principal axis scores and Q-mode principal component
loadings were standardized for each case. From these standardized "scores" four case-wise correlation matrices were
computed which were used to construct dendrograms depic·ting
·inter-case similarities for each of the four treatment
55
formats. Each of the two subsamples was in this process
translated into two dendrograms of
inter~case
similarities:
0ne depicting size similarity and the other shape similar-
1
ity.
The principal components matrices and dendrograms were
used to investigate (1) the distinctiveness of groupings of
"robust" and "gracile" specimens suggested by univariate
analysis and by other researchers,
(2) changes in inter-
case relationships as case and variable representation were
altered, (3) variables associated with similarities among
cases, and ( 4) the correspondence bet\'leen dendrograms
depicting size and shape.
R-mode results: size. Table 5 lists the rotated principal
component matrices obtained for the two subsamples. Associated with each matrix is the dendrogram of inter-case
relationships constructed from the rotated principal axis
scores. Included above each principal component matrix are
the original eigenvalues for unrotated components and the
percent variance associated with rotated components.
The unrotated principal component matrices for both
subsamples, represented in Table 5 only by the eigenvalues,
showed the first component to be size-dominated, accounting
for seventy-three and eighty-eight percent of trace in subsamples {a) and (b) respectively. All variables in subsample {b) exhibited high positive loadings for the first component, indicating that most of the variance is size-
56
Table 5
Rotated Principal Component Matrices and Dendrograms
for Early Hominid Subsamples (a) and (b)
Subs ample (a) C-M2
original
eigenvalue ••
%variance
(rotated) •••
c
c
1
b
P31
P 3b
P4l
P 4b
M1 1
M1 b
M2l
M2 b
I
7.33
II
III
1.58 (0.49)
44
27
16
-.03
.21
.59
.91
.53
• 91
.70
.88
.45
.76
-. 09
-.16
-.37
-.34
-. 83
-.37
-.67
-.39
-.83
-.57
.96
.42
.42
.18
.11
.07
.07
-.11
.16
• 22
ER992
OH13
OH7
OH16
OM/L7a
NAT RON
/I
1.0
!f
r
-.3
.7
I
I
-.s
Subs ample (b) p4~2~3
original
eigenvalue ••
%variance
(rotated) •••
P4l
P 4b
M2 1
M2 b
M3 1
M3 b
I
III
II
5.32 (0.41) (0.11)
39
32
15
-.70
-.30
-.85
-.58
-.57
-. 6 2
.42
.91
.35
.69
.43
.40
-.40
-.22
-.30
-.30
-.64
-.31
ER992
SANGl
OH13
OH16
SANG9
ER729
OM/75
NAT RON
OM/L7a
ER818
!O
.<t
I
.7
r
I
.0
I
I I f
-:3
f I
-.6
t
57
related, as expected. Subsample (a) departed slightly from
this pattern, as a second component with an eigenvalue of
greater than 1.0 (15 percent of trace) was obtained, with a
high loading on the canine. The variance in size within
subsample (a) is dominant but restricted to the postcanine
'variables, as was anticipated by univariate analysis.
The rotation of the principal component matrices maximizes the association between components and correlated
groups of variables which reflect some particular "dimension". The rotated principal component matrices in Table 5
appear to be quite different from each other, as expected,
but there are underlying similarities which were investigated via the associated dendrograms.
The dendrogram for subsample (b) replicates the patterns in that of subsample (a) quite well; both dendrograms
suggest two size-groups among the cases represented with
the same individuals included in each. The groupings are
consistent with the usual division of australopithecines
into "robust" and "gracile" varieties. The similarities
between the "pithecanthropine" cases SANGl and SANG9 and
the Olduvai hominid cases, as suggested by Tobias and von
Koenigswald (1964), are demonstrated, as are similarities
among.the East African "robust" specimens. Overlap between
· the groups in subsample (b) is demonstrated by the pairing
• of ER729 and OM/75-14a,b, which were placed in
11
robust" and
"gracile" groups, re.spectively, by Frayer (1973). This mix: ing could be due to the reduced variable set in subsample
..
58
(b) ; it is possible that if the two specimens each had
canines they would have been separated if included in subsample (a). Obviously, variable representation is quite
important in discrimination among Early Hominid sample
cases, and a dependence upon postcanine variables alone can
alter results. On the other hand, the groupings suggested
by Frayer are by no means unquestionable.
The first few pairing events in each dendrogram were
most consistent with the large vs. small dichotomy. It was
possible to relate these pairing events with particular
variables. As a result of the factoring process, high. positive correlations were obtained between the pairs of cases
involved in the initial pairing events in each sample, and
in each instance it was clear which component was most associated with the high value of the correlation coefficient.
For example, in subsample (b) OH16 and SANG9 are paired
(r=.983). The coefficient is computed as the scalar product
of the two standardized principal axis score vectors for
the two cases. These were:
OH16
SANG9
Principal Component
I
II
III
0.7708 -1.4121
0.6416
0.5383 -1.4017
0.8634
The correlation coefficient r
=
((0.7708 x 0.5383)+
(-1.4121 X -1.4017)+
(0.6416 X 0.8634))/3
{0.4149+ 1-.9793+ 0.5540)/3
=
(2.9482)/3
= 0.983
59
The high negative score for each case on component II contributes sixty-seven percent of the value of the coefficient
(1.9793/2.9482 = 0.67). The highest variable loading on component II for subsample (b) is 0.91, for P 4 breadth (Table
5), and the square of this loading, 0.83, is the degree to
which the
11
Value 11 of the component can be "predicted" by
the variable P 4b. The product of the component/variable
association and the component/pairing-event association
(0.83 x 0.67= 0.56) suggests that the pairing of SANG9 and
OH16 is
related to the measurement P 4 b at a "level" of
fifty-six percent.
These associations between dendrogram pairs and specific measurement variables were traced for all primary
pairing events with coefficients .of over 0.90. In each instance one component was founc to be responsible for from
sixty-one to sixty-nine percent of the coefficient value.
The measurements identified with pairing events at levels
of over fifty percent were C length, for the pairing of
ER992 with OH13 and of OH7 with OH16 in subsample (a), and
P 4 breadth, for the pairings of NATRON with OM/L7a-125 and
SANG9 with OH16 in subsample (b). M2 length was also implicated at.just under fifty percent for the pairing of SANGl
with OH13 in subsample (b).
These observations suggest that the canine and forth
;premolar are of particular importance to the inter-case
relationships indicated by the dendrograms. The same meas; urement~ \>Jere also implicated for case pairs with high
60
negative correlation coefficients. It is particularly interesting that the canine was not seen to be significantly
variable with respect to comparative samples in univariate
analysis, yet it is clearly important in discrimination
among Early Hominid sample cases, as suggested by Robinson
(1972).
Q-mode results: shape. Using the same methods applied to Rmode principal axis scores, dendrograms which presumably
depict shape relationships among cases were constructed
'
.
.
.
from Q-mode princ:lpa:i . component loadings. The R-mode dendrograms suggested that two size-groups of cases exist; in
Figure 2, Q-mode and R-mode dendrograms are compared for
the two subsamples in order to indicate the correspondence
between size and shape-related groupings of cases.
Size and shape among cases in subgroup (a) show some
correspondence, best seen in the pairing of the two "robust"
cases NATRON and OM/L7a-125 and the two "gracile" cases OH7
and OH16. OH13, however, is dissimilar in shape relative to
either set of groupings, and it pairs with the robust group
at a low level of correlation in spite of its close similarity in size to ER992. In such a small sample with the
:best possible measurement representation, the variable
position of OH13 for size and shape suggests only a partial
correspondence exists between the two measures of relation. ship.
Size and shape for subsample (b) show very little cor-
61
Figure 2
Comparisons of Size and Shape-related Dendrograms
for Early Hominid Subsamples (a) and (b)
Size
(R-mode)
Shape
(Q-mode)
Subsample. {a)
OH7
OH16
ER992
OH13
r:ZATRON----------~
~--~
OM/L7a
I
-:6
-.<J
-:z.
.3
.7
.'I
1.0
/,0
,'f
.7
Subs ample (b)
ER992
SANGl
OH13
NAT RON
OH16
SANG9 :J
[ER818
OH/L7a
OH13
SANGl
I
I
-;'t
'
-:1.
'
~'I
'
-:6
-:7.
-:'1
-:6
p4~2~3
ER992
SANG9
OM/75
OH16
ER729
I
r
r
r
-:6 -.y
.3
I
OM/L7a
NAT RON
ER818
I
ER729
OM/75
I
.3
.1
.7
r
},O
1.0
.<t
,7
r
.3
62
respondence. In fact, cases which were consistently seen in
different groups based on size differences were often closely associated based on shape similarities. This is best
.seen in the pairing of OM/L7a-125 with OH13. Apparently
some correspondence of size and shape differences exists,
but i t is dependent upon the measurement set used for subsample (a) and is probably related to the inclusion of the
canine.
Summary: within-group size and shape. Two size-groups within the Early Hominid sample were suggested by the results
of R-mode cluster analysis but some overlap was indicated
where groups were defined on the basis of postcanine dimensions
.alone. The relationships between primary pairing
events and specific measurements implicated the canine and
the fourth premolar as particularly important.
Shape differences, so far as they exist (and so far as
Q-mode methods describe them) , \-rere expected to correspond
with size differences if they are of allometric or taxonomic origin. This correspondence was not found to exist for
groupings based on postcanine measurements alone. Partial
correspondence was seen when canine dimensions were included as variables. Within-group clustering of cases for the
Early Hominid sample is primarily a function of size rela. ted to both the anterior and posterior measurements, but
some shape variation due to allometry may be present.
63
B. Within-group Variance Relative to Between-group Variance
In this section results of comparisons of variation in
size and shape between the Early Hominid sample and samples
of extant taxa are presented. Each analysis format was preceeded by transformation of raw data by R and Q-mode principal components analysis in 9rder to provide scaled, uncorrelated scores for cases as explained in Chapter 3.
Comparisons of size variance were based upon analysis
of a single pooled sample including H. sapiens, Pan,
Gorilla, and Early Hominid subsample (a). Two methods were
utilized:
(1) analysis of a dendrogram depicting inte~-case
relationships and (2) computation of inter-case distances
D2.
Comparisons of shape variance were based upon analysis
of five comparative samples of H. sapiens, H. sapiens neandethalensis, H. erectus, Pan, and Gorilla, and Early Hominid subsample (a). Again, two methods were utilized:
(1)
canonical discriminant function analysis and (2) inter-case
distances
n2 •
Size. Fifty H. sapiens, twenty Pan, and twenty Gorilla
specimens were selected at random from main comparative
samples. These were combined with Early Hominid subsample
(a) for a pooled sample size of ninety-six cases. Data for
· ten dimensions from C through M2 were utilized.
Raw data for this sample were submitted to principal
components analysis and the principal axis scores obtained
64
were used as data input for two further programs:
(1) Veld-
man's (1967} program HGROUP, to obtain a dendrogram of
inter-case size similarities, and (2) a Euclidean distance
program to compute inter-case dist·ances
n2
and D.
1. Program HGROUP pairs cases or groups of cases on
the basis of profile magnitude until only two groups remain.
Such pairings were noted as "misclassifications" if cases
from different taxa or different pongid sexes were paired.
It was found that until the t\'Tenty-six-group level few misclassifications occurred. These accounted for a seven percent error in clustering of taxa and a sixteen percent
error in clustering of pongid sexes. To this point, then,
the clustering represented taxonomic relationships with
accuracy. Beyond this point misclassifications increased.
The last ten grouping events are depicted in Figure 3,
which begins at the eleven-group level. Misclassifications
still amounted to only a few misplaced individuals; for
instance, in group number eleven, three cases of H. sapiens
are included in a group of eighteen Pan cases. At the
eleven-group level, misclassifications account for an eleven
percent error in clustering of taxa.
The important aspects of the dendrogram in Figure 3
are the degree to which the groupings of Early Hominid
cases remained distinct while mixing of other taxonomic
groups occurred, and the taxa with which th.e Early Hominid
sample case-groups finally paired. The overall pattern until late in the grouping process was one of fairly good
..
65
Figure
3
Last ten Grouping Events (of 96) for a Dendrogram Depicting
Size Relationships among Soecimens of H. sapiens,
Gorilla, Pan, and Early Hominid subsample (a)
Group number and membership
at eleven.-group level
Early Hominids
1)
OM/L?a----------------------~
2)
NATRON ______________________
+ (lHS)
~
------------------
3) ER992+0H7
OH16+0Hl3
+ ( lHS)
+ ( lGF)
Gorilla
4)
4GM+ ( lPM)
5)
3GM+4GF
+(3HS)
6)
6GF+lGM1
H. sapiens
7)
SHS+ ( 2GM)
8)
l?HS
9)
10)
-
t
I
6HS
14HS
+( lPF)
Pan
. 11)
9PM+9PF
+(3HS)
20
30
40
.so
error (% trace)
60
70
GM = Gorilla male; GF = Gorilla female; PF =Pan female;
' PM = Pan male; HS = Homo sapiens. Misclassifications according to taxa in parentheses
66
separation of taxa for a large and variable sample of related species and genera. It is of particular importance
that the "robust" Early Hominid sample cases or-1jL7a-125 and
NATRON did not pair until the six-group level and remained
isolated from the other Early Hominid cases throughout the
remaining grouping levels. Thus, two Early Hominid subgroups, with the same membership as was found in previous
analyses, were maintained throughout the grouping process.
The four "gracile" cases were grouped at the sixteen-group
level and remained fairly distinct until the ten-group
level 'l.vhen they grouped with Gorilla, not Homo sapiens.
The degree to which the integrity of taxa was maintained during the grouping process was taken to be a measure of within-group variation with respect to between-group
overlap on the basis of size. Since at least t't>TO Early Hominid subgroupings were maintained throughout the grouping
process and the "robust" group was not paired with any
other group, it appears that size differences among the
Early Hominid sarrple cases are considerably greater than
those within or between any of the other taxa represented.
This would support at least species distinction between
these two subgroups in the Early Hominid sample.
2. The same principal axis scores used to construct
the dendrogram in Figure 3 were used to compute inter-case
distances D. The resulting matrix (96 x 96) of inter-case
distances was partitioned into groups according to taxa and
the means of distances D within each were computed.in order
67
to illustrate the size variation within each taxonomic
group. For the pongids, separate means were also computed
for each sex. The values obtained are as follows:
Group
D
minimum
---.-
max1.mum
mean
H. saEiens
1.40
8.04
3.62
Gorilla
male
female
1.18
2.50
1.18
7.83
5.87
6.84
4.46
4.29
4.30
Pan
male
female
1.23
2.03
1.23
5.09
5.09
3.85
3.04
3.19
2.58
Early Hominid
2.88
9.11
6.29
The minumum, maximum and mean inter-case Euclidean distances within the Early Hominid sample all exceed corresponding values obtained for the comparative samples of single
species. The mean for Early Horninid sample distances is
nearly twice the magnitude of the value for H. sapiens.
The mean distance between "robust" and "gracile" cases
(n=8) in the Early Hominid sarople is 7.58 with a range of
6.25 to 9.11, while that within H. sapiens is 3.62. The
values obtained between sexes in Gorilla, the most dimorphic of the two pongid taxa, ranged from 2.08 to 7.83 with
a mean of 4.97; each of these values was also exceeded by
those obtained for the early hominids. Hm.,ever, the· distance between the two "robust" specimens OM/L?a-125 and
NATRON is 8.81, greater than the mean distance between the
two early hominid varieties or within any one of the comparative samples as well.
68
The inter-case Euclidean distances and the dendrogram
constructed from the same data indicate that:
(1) size vari-
ation within the Early Hominid sample is greater than that
within or between the comparative samples of single species,
(2) size differences between "robust" and "gracile" varieties of early hominids are greater than those seen between
sexes in Gorilla, and (3) the two "robust" specimens are as
different from each other in size as they are from "gracile"
specimens. These findings suggest that at least two, and
perhaps three, taxa are represented in the Early Hominid
sample.
Shape. A sample of fifty-five cases \vas compiled, including
H. sapiens (n=ll) , H. sapiens neanderthalensis (n=7), H.
erectus (n=7), Pan (n=l2), Gorilla (n=l2), and Early Hominid subsample {a)
(n=6). Data for ten dimensions from C
through M2 were utilized.
The sample was submitted to Q-mode principal component
analysis and the loadings obtained were used as data input
for two further programs:
(1) canonical discriminant funct-
ion analysis and (2) a Euclidean distance program to compute inter-case distances
o 2 and D.
1. Canonical discriminant function analysis computes
functions which best discriminate among group means. The
ratio of between-group variance to within-group variance
provides a basis for an F-test of the null hypothesis that
the samples were obtained from a single population. Since
69
the six 1roups in the sample analyzed were known to come
from different populations, there were two working hypotheses:
(1) is the mean "shape" of the Early Hominid group
distinct from that of the other groups'? and (2) is the
shape variation within the Early Hominid group less or
greater than that within other groups? One null hypothesis,
then, is this: early hominid shape does not differ from
that of H. erectus, its nearest phylogenetic neighbor.
The F-matrix derived was as follows:
NeandSapiens Erect us erthal
Erect us
Neanderthal
Pan
Gorilla
Early Hominid
11.31
5.90
55.77
49.58
10.93
3.90
48.92
35.91
1.95
41.16
35.01
4.34
Pan
Gorilla
6.28
37.16
25.63
(Degrees of freedom: 8,42)
The critical value of F at the 0.05 level of probability
for 8 and 42 degrees of freedom is 2.53 for a two-tailed
test. Since the obtained value of 1.95 for Erectus and
Early Hominid groups is less than this critical value, the
null hypothesis is not rejected. Therefore, the shape profiles for the early hominids and H. erectus are not statistically significantly different.
The distances D of each case from each group mean provide another measure of group integrity and within-group
variation. The robust specimen m1/L7a-125 was the only
early hominid misclassified, and one H. sapiens grouped
with the neanderthals and two gorillas grouped with the
70
chimpanzees, indicating that discrimination of taxa was generally effective. The dlstances of cases from their own
group mean were as follows:
Grou:e_
Sapiens
Erect us
Neanderthal
Pan
Gorilla
Early Hominid
D
--r-minimum max1mum
1.62
4.70
1.45
4.01
1.96
4.11
1.12
2.61
1.82
3.50
1.55
3.50
mean
2.98
2.46
3.20
1.67
2.66
2.51
Thus, within-group variation for case distances from the
mean for the Early Hominid group is less than that for the
other samples with the exception of Pan. Maximum distances
exhibit the same pattern. It is significant that the maximum
value among early hominids is no greater than among specimens of Gorilla, a measure of sexual dimorphism within the
latter taxon. Together with the multivariate F-tests of
variance ratios, these D-values suggest that less "shape"
difference exists among the early hominid specimens than
within any of the single species taxa represented, except
for Pan, which is well known for exhibiting little sexual
dimorphism.
However, the discriminant functions indicated that the
major axis of discrimination was between the pongids and
the hominids, as might be expected. To examine more closely
the differences among the hominids alone and to test the
posibility that the four "gracile" specimens were biasing
the six-case Early Hominid sample in the direction of H.
71
erectus, discriminant function analysis was repeated with
the pongids removed. The Early Hominid sample was partitioned into two groups: two
11
robust" specimens and four
"gracile" specimens. The original Q-mode scores were utilized, however, in order to maintain scaling according to
the original total sample of _pongids and hominids.
The F-value matrix derived was as follows:
Sapiens Erectus
Erect us
Neanderthal
Gracile
Robust
11.48
4.45
12.36
4.31
4.46
2.01
0.73
Neanderthal
6.75
2.45
Gracile
..
0.87
(Degrees of freedom: 8,19)
In this case the critical value of F at the 0.05 level of
probability is
2o98~
No statistically significant differ-
ence is seen between the gracile and robust early hominids
or between either early hominid group and H. erectus. The
F-value between the Robust and Neanderthal groups is not
statistically significant either.
The results of both discriminant function analyses
suggest that:
(1) mean differences in shape beb.,reen the
early hominids and H. erectus are not statistically significant (while shape differences between all groups and modern
H. sapiens are statistically significant) and {2) shape
differences between the gracile and robust subgroups in the
Early Hominid sample are not statistically significant.
2. The Q-mode principal component loadings which were
72
used as data for canonical discriminant function analysis
of the pongid and hominid groups were also used to compute
inter-case distances D. The minimum, maximum, and mean Dvalues obtained were as follows:
Group
minimum
D
--r
max1mum
mean
Sapiens
Erect us
Neanderthal
0.50
0.47
0.47
1.53
1.39
1.35
1.02
0.90
1.03
Pan
male
female
0.20
0.20
0.23
0.85
0.85
0.66
0.49
0.41
0.44
Gorilla
male
female
0.33
0.42
0.33
1.83
0.91
0.92
1.07
0.69
0.56
Early Hominid
0.50
1.39
0.87
These distance values are not directly comparable to those
obtained in the canonical discriminant function analysis
but the proportions among the values in the two analyses
are, in fact, quite similar. The mean of shape distances
within the Early Hominid sample is less than that within
any other single species sample except for Pan. However,
more significant is the. fact that the maximum distance
value for the Early Hominid group, 1.39, is less than that
for H. sapiens, a."ld equal to that for H. erectus.
Two other mean values are of interest:
(1) that
between sexes for Gorilla (1.44} and (2} that between
Erectus and Early Hominid (1.00). Both of these values, not
included in the table above, are greater than the mean
distance among early hominids (0.87). While the early
73
hominids are slightly more similar on the average to each
other than to H. erect us, they are less :variable than are
the sexes in Gorilla.
On the basis of these distance values and the results
of canonical discriminant function analysis, shape differences within the Early Hominid sample \'lere not found to be
significant compared with shape variance attributed to sexual dimorphism within comparative samples of single species.
SUM~~RY
OF RESULTS
The results of several analyses have been described,
grouped into six categories on the basis of the variables,
samples, and size or shape transformations utilized. The
results for each category can be·briefly summarized as
follows:
1. Univariate F-tests of variance ratios for single
variables suggested that for postcanine dimensions excluding P 3 length, Early Hominid sample variability was very
significantly greater than expected values for a single
species. The great size variability among these specimens
was not, hmvever, exhibited in the dimensions of the canine
or in P 3 length.
2. Univariate distributions of Early Hominid sample
cases according to size were illustrated in histograms and
exhibited indications of overlapping bimodal distribution
for the canine, P 4 , -and M3 • While the small sample of values for the canine were shown to be bimodal in distribution,
74
the results of tests of variance ratios indicated that the
variance for this tooth as compared with that in other
hominid
speci'"'~s
was not great.
3. Multivariate cluster analysis of size distributions
of cases included in Early Hominid subsamples (a) and (b)
indicated that two size groups exist and that the groupings
were best associated with the canine and P , confirming the
4
bimodal distributions seen in the univariate histograms.
4. Multivariate cluster analyses for Early Hominid
subsamples (a) and (b) based upon size and shape were compared; only partial correspondence between groupings for
size and shape was
indicated, and it was particularly sen-
sitive to the presence of the canine.
5. Multivariate measures of. size variability within
the Early Hominid sample as compared with that in other
taxa were illustrated in a pooled dendrogram in Figure 3.
Gracile and robust groups of early hominid cases were distinct and the two robust cases OM/L7a-125 and NATRON remained unique in size relative to the other ninety-four cases
in the sample. Group means for inter-case distance values
indicated a relatively large size variance within the Early
Hominid sample.
6. Multivariate analyses of shape variability of the
Early Hominid sample relative to that within comparative
samples was performed using discriminant function analysis
and inter-case distance values. In neither instance was the
Early Hominid sample more variable in shape than H. erectus.
Chapter 5
DISCUSSION
The results of analyses of size and shape variation in
the dentition of a sample of fossil hominids representing
contemporary populations within a time period between 1.0
and 2.0 my BP were presented in Chapter 4. Comparative
samples of extant and extinct hominoid species were used to
derive and test indications of taxonomic diversity from the
observed dental measurement diversity in the fossil hominid
sample. These indications of taxonomic diversity are interpreted in this chapter in order to assess the probability
which can be associated with particular single or multiplelineage models of hominid evolution.
Among the various taxonomic interpretations of hominid
fossil material reviewed in Chapter 2, there are three
basic alternative phylogenetic models: one single-lineage
model and two multiple-lineage models. The sample of fossil
hominids, viewed as a horizontal section through the hominid phylogeny, may include .(1) a single species,
(2) two or
more species of one genus, or (3) two or more species including more than one genus. For any one of these three
models, a certain proportion of the variability within the
fossil hominid sample would be expected to be related to
sexual dimorphism, polytypicality, and small evolutionary
75
--76
changes within the time span being sampled. The singlespecies model proposes that these three sources of variability are sufficient to account for all the observed
variability in the fossil sample; i.e., that a single lineage has been sampled and it shows only sexual, polytypic,
and short-term evolutionary variability. The last two
models propose that the observed variability is too great
to be incorporated within a single species. Model 2 suggests that at least two species existed while model 3
suggests that these two or more species are sufficiently
different that two genera may be represented.
LINEAGES, SPECIES, AND GENERA
The attempt to distinguish fossil species requires a
synthesis of the neontologist's Linnaean system of animal
classification and the paleontologist's concept of an evolving lineage. Basic to the modern approach to systematics
is the biological species concept, which defines a species
as a "group of interbreeding natural populations reproductively isolated from other such groups"{Hayr, 1970:12).
Since breeding behavior cannot be observed for extinct
species, comparative morphology is frequently the primary
basis for the recognition of
~ossil
species. In the present
study and in several works cited in Chapter 2, comparative
analysis of the dentition was the basis for recognition of
extinct hominid species.
Evolutionary changes in a fossil species are incorpor-
77
ated in the concept of a lineage. Generally, a lineage may
be defined as a succession of ancestor-descendant populations which traces a line of descent (Simpson, 1944). Lineages may trace individual (ontogenic) descent or the interraction of populations within a species but the general
usage of the term, and that used in this study, identifies
a lineage with an evolutionary sequence of species. Clearly,
a lineage refers to what was a biological continuum and
segregation of species along a lineage is arbitrary. However, the paleontological record is limited and only traces
of ancestor and descendant populations are recovered. Therefore, as Simpson (1944:386) explained:
If a single lineage is being considered, and if
it changes so that the desc~naant and ancestral
populations differ about as much as is usual
between two related contemporaneous species, we
say that one species has given rise to another.
Speciation is the process by which one lineage divides, initiating two descendant lineages. Two contemporaneous fossil species in two lineages might then be recognized by
reference to the same criteria by which ancestor and descendant species are distinguished along one lineage; i.e., by
comparison with differences between extant related species.
Subsequent to speciation, the development of differences between the two lineages represents phyletic evolution, which is generally a function of differential adaptation in the species by means of natural selection (Mayr,
1970). At some point after speciation, species within most
78
related lineages will have changed with respect to one another such that higher-order taxonomic categories are needed
to distinguish them. The only higher-order category of concern to the present study is the genus. Obviously two lineages very recently separated from a common ancestor could
be expected to represent species of the same genus. But if
lineages which have been separated for millions of years
are sampled, morphological differences between contemporary
species in each might be so developed that generic distinction between them is appropriate.
Simpson (1944) has referred to speciation as an adaptive process. The genus is generally interpreted as identifying species adapted to a similar pattern. According to
Mayr, Linsley, and Usinger (1953:49):
••• i t is usually found that all the species of
a genus occupy a more or less \'iell defined ecological niche. The genus is thus a group of
species adapted to a similar pattern.
However, it is particularly difficult to apply the concept
of a genus to fossil species, especially in a phenetic perspective. Referring to higher categories in general, Simpson (1944:168) concluded:
No difference of kind regards characters or their
adaptive status in the sequence of different
levels in the hierarchy, but it seems possible
if not probable that there is a general quantitative difference between high and low levels.
In the present study species variability was analyzed ace-
..
79
ording to size and shape-related measurements. Apparently
the relationship between measures of size and shape and
differences between species and between genera is simply
quantitative, and both measures are important in distinguishing taxa. However, the works of Gingerich (1974), Read
(1974}, and Pilbeam and Zwell (1972) suggest that size
differences can be a sufficient basis for the recognition
of similar species.
Accordingl~
it was assumed in this study
that size alone could be used to assess the probability that
more than one lineage of related species was represented in
the fossil sample analyzed. In this way shape differences,
which are generally interpreted to better represent. actual
taxonomic "distances" than size differences (Corruccini,
1973) , could be considered separately with reference to the
two alternative multilinear models introduced earlier; i.e.,
those involving lineages distinct at the species or generic
levels. In the following two sections, the methods in which
size and shape measures have been used by several researchers are reviewed 'l.vi th respect to these assumptions.
A. Size
Read (1974) based his analysis of hominid phylogeny on
the assumption that shape indices may be lineage-specific
if no selection for change in shape has occurred. Such an
assumption is based upon expected similarities in stress
requirements on the dentition among related species. There
seems to be no
~
priori reason tvhy this assumption should
80
not apply both to successive species in one lineage and to
contemporary species in t'vo closely related lineages. In
both situations speciation has occurred and both species
are assumed to represent the same genus. However, these
closely related species, exhibiting shape similarities,
might be quite variable in size. Read in fact found this to
be indicated in his analysis. Pilbeam and Zwell (1972) and
Greene (1973) compared size variation due to sexual dimorphism in extant species with size variation in a fossil
sample; tests of variance ratios or means suggested the
presence of size-variant species groups in the fossil sample; i.e., contemporary representatives of two lineages.
Considering size dimorphism between related species, Gingerich (1974:902) stated that "very closely related species
are often inseparable on form alone, and differ only in
size".
In this study, analysis of size variation by multivariate and univariate methods has been used to test for
the presence of size-variant species in the fossil sample.
This testing was accomplished by a comparison of size variation in the Early Hominid sample with that in the selected comparative samples
of hominoid species. The purpose of
the size variation analyses was not to establish the taxonomic relationship between the lineages suspected to be
present, but only to determine if speciation has occurred.
Given the null hypothesis that only one lineage is present,
a likely alternative hypothesis is that two closely related
81
lineages are represented. Whether the two lineages are related or are sufficiently different to be classified separately at higher taxonomic categories is a second, separate
issue, and was in fact treated as such by Pilbeam and Zwell
(1972) and Greene (1973). Therefore a secondary assumption
of this portion of the analysis was that lineages, or the
fact of speciation, may be distinguished without reference
to shape variation.
B. Shape
While size variation may be a sufficient basis for the
initial support or rejection of a multilinear model, assessment of the taxonomic distinction between representatives
of multiple lineages may be more reliable if based upon
measures of shape. Using odontometric data for a sample similar to the one utilized in the present study, Corruccini
(1973) has shown clearly in multivariate analyses that correct classification of groups of Homo,
Pa~,
and Gorilla
(both sex and species groups) was best approximated using
measures of shape, particularly those involving Q-mode
standardization. As he pointed out, the original misclassification of Australopithecus as a pongid by Ashton and
Zuckerman (1950) was a function of the similarity in size
between the taxa compared. In this study, the close agreement in coefficients of variation for postcanine tooth
dimensions between a sample of Pan plus H. sapiens and
samples of single species, would also lead to a serious
82
misinterpretation if only size were taken into consideration.
However, an issue with respect to the present study is
not whether shape is a better taxonomic indicator than size,
but rather if this is necessarily always the case. In his
analysis sample, Corruccini included pongids and hominids
and the first canonical variate in bivariate plots invariably reflected shape differences between pongids and hominids where preferred shape measures were used; this would
be expected. But the second axis in at least one case ("Qmode correlation similarity components"} showed very little
shape variation among groups within each taxonomic family
(Corruccini, 1973:751, figure 7}. In Corruccini's sample,
the groups represented differences at the sexual, subspecific, specific, generic, and familial levels. The methods used seem to assume that one measure of shape can be
used to place these groups in appropriate phylogenetic
perspective simultaneously. While it was Corruccini's intent only to compare the efficiency of various size and
shape-related measures, most of the shape variance was
shown to occur for higher taxonomic levels. Since Gingerich (1974), for instance, showed that size can be used
effectively to distinguish related species, it seems unnecessary to insist that shape is generally a better measure of taxonomic relationships than size except at the sub. species level (Corruccini, 1973}. Such a position requires
that shape be used both to distinguish taxa in the first
83
place and to assess the taxonomic
11
distance 11 between them.
Corruccini's analysis suggests to me that shape ,variation
clearly
incr~ases
in importance with taxonomic levels, but
it does not suggest that shape is necessarily a better
measure than size for discrimination of related species in
the context of the present study.
In this analysis size differences are assumed to be a
sufficient basis for assessing the probability associated
with models suggesting the presence or absence of more than
one hominid lineage. Shape differences, based upon Q-mode
standardization, are then used as a basis for
assess~ng
the
taxonomic distinction between lineages.
THE EVIDENCE FOR HORE THAN ONE
LINEAGE
In following with the arguments presented in the pre-.
ceeding section, the first portion of this study attempted
to assess the probability for the null hypothesis that a
single lineage best characterizes hominid evolution.
In univariate analyses of size-influenced coefficients
of variation, variability in the Early Hominid sample was
compared to that in samples of Pan, Gorilla,
~
sapiens,
and a multispecific sample of Homo. These comparative
samples incorporated sexual dimorphism as it exists in the
pongids and hominids represented and polytypicality in the
genus Homo; while an approximation of species variability
in Homo was incorporated in the multispecific sample. It
84
was found that Early Hominid sample variance for postcanine
dimensions (excluding P 3 length) was statistically significantly greater than corresponding values obtained for the
single species samples or for the multispecific sample of
Homo. Therefore the Early Hominid sample is likely to incorporate variability which
~s
a function of some factor in
addition to sexual dimorphism and polytypicality. The small
differences between values obtained for the multispecific
Homo sample and single species samples suggested that evolutionary changes in a single lineage within the time period
sampled are also an insufficient basis for
explainin~
the
observed variability. The additional factor contributing to
Early Hominid sample variance could be due either to:
(1)
a degree of sexual dimorphism or polytypicality not seen in
the hominoid species represented here or (2) the presence
of more than one species. If the first of these two alternatives is considered, i t requires an explanation of the
observation that the high variability in the Early Hominid
sample was restricted to the postcanine dimensions and was
not exhibited for the canine or P 3 length. In the pongids
the reverse is found and in Homo sapiens a fairly uniform
---..::----
distribution of variance among the individual teeth was observed. It is more likely that two species are represented.
This interpretation is in agreement with the conclusions,
based upon similar methods, of Pilbeam and _Zwell (1972) and
Greene (1973) that two lineages are represented among lower
Pleistocene fossil hominids.
..
85
Comparisons of size variation within the Early Hominid
sample and comparative samples using multivariate analyses
were based on size-related R-mode principal axis scores for
a sample including H. sapiens, Pan, Gorilla, and early hominids. These scores were used to produce a dendrogram of
inter-case similarities and measures of inter-case Euclidean distance D. An effect of the computation of principal
axis scores was to scale the differences in size among
cases according to the variance for the whole sample which
included three genera. The cluster ·analysis depicted in the
dendrogram (Figure 3, Chapter 4) indicated that the early
hominids represented separated into tt.vo size-goups:
( 1)
"robust" specimens including OM/L?a-125 and NATRON, and {2)
"gracile" specimens including ER992, OH7, OH13, and OH16.
Both of these groups "'Tere clearly separate from Homo sapiens and the two robust specimens remained as a unique
group throughout the clustering process. The pattern seen
in the dendrogram was not taken to be
a
phylogenetic repre-
sentation but it did suggest that the fossil hominids differ
in size among themselves to a greater degree than was seen
within or between any of the other taxa represented. Means
of within-group Euclidean inter-case distances for the same
sample indicated that within-group size variability for the
fossil hominids was approximately twice that obtained for
either Homo sapiens or Pan and over fifty percent greater
than that obtained for Gorilla, the most sexually dimorphic
of the taxa represented.
86
Comparisons of size differences among the fossil hominids with those within and between other taxa provide a
statistical measure of the significance of an observation
that can be made visually: robust and gracile varieties of
fossil hominids differ in tooth size to such a degree that
it is difficult to imagine that they represent the same
species.
The maintenance of the single-lineage model as the
more more likely alternative requires that additional assumptions be proposed in order to explain the great variability which has been shown here to exist. For instance,
why should there be such a great degree of sexual dimorphism among individuals in a single species not far removed
from Homo erectus, or
polytypica~ity
ions, and why would its
exp~ssion
among local" populat-
be restricted to the
postcanine dentition? In view of the fact that paleoanthropologists are frequently "up to their knees" in subjective
supporting assumptions for hypotheses, it seems more reasenable to propose that prior speciation producing two lineages, a not uncommon event, rather than unique patterns of
sexual dimorphism and polytypicality, was the source of the
increase.d variability in fossil hominid sample dentition.
THE TAXONOMIC DISTINCTION BETWEEN THE
LINEAGES
As was pointed out in the first section of this chapter, given the conclusion that speciation has occurred in
87
hominid phylogeny prior to the time represented by the
Early Hominid sample, a second issue is the taxonomic status of contemporary species within a multi-linear model.
Analyses of size variation indicated that the Early Hominid
sample specimens may represent two size-variant species.
The possibility of generic distinction between these two
species was investigated on the basis of analyses of shape
variation. Shape differences, approximated by Q-mode principal component loadings, were interpreted as a more reliable indicator of taxonomic relationship above the level of
closely related species. Multivariate analyses including
discriminant function analysis and Euclidean distance measures, based on Q-mode transformation of sample data, were
used to compare the magnitude and pattern of shape variation within and between the Early Hominid and comparative
samples. Comparison was also made of size and shape-related
clustering of cases within the Early Hominid sample in
order to see if the two size groups differ consistently in
shape. The sample on which these analyses were performed
included six groups representing H. sapiens, H. sapiens
neandethalensis, H. erectus, Pan, Gorilla, and six early
hominids.
Analyses of shape variance, based upon Q-mode scores
scaled according to the differences among the hominid and
pongid groups included in the sample, did not support the
existence of significant non-random shape differences among
the early hominids. In discriminant function analysis, the
88
Early Hominid sample was not well distinguished from Homo
erectus and its within-group variance, as represented by
Euclidean distances from the mean, was seen to be less than
that of single species samples of H. sapiens, H. erectus,
or Gorilla, but greater than Pan. Euclidean distances computed directly from the Q-mode loadings exhibited the same
pattern of little within-group shape variance for the Early
Hominid sample relative to other groups. This does not
suggest that shape differences do not exist among the early
hominids, but only that they exhibit shape variation no
greater in magnitude than that within the other single
hominoid species samples used.
Where within-group discrimination among early hominids
according to size and shape were compared, only a partial
correspondence was seen. This suggests that some non-random
shape variation exists, but such shape differences could
not be used to distinguish the two size-variant groups,
particularly when only postcanine dimensions were used.
These results suggest that the two species are primarily size-variants. When shape differences among them were
analyzed with respect to a sample including several pongid
and hominid taxa, they were not sufficiently distinct in
shape from Homo erectus. Inasmuch as the adaptive pattern
of the two species is reflected in the shape of the
denti~
tion, and so far as shape variance has been approximated
and compared here, the two lineages indicated by size differences are likely to represent the same genus. This
89
conclusion is in agreement with Read (1974) who showed that
the two East African forms "H. habilis" and A. boisei exhibited little difference in shape indices and differ primarily
in size. He suggested that two lineages are indicated: "A.
boisei and A. africanus plus 'H. habilis'"(Read, 1974:117).
Campbell (1973)
also suggested, but without explicit sup-
port, that two lineages distinct at the species level are
indicated, represented in East Africa by "A. africanus habilis" and A. boisei.
However, both Read and Campbell and most other researchers cited in Chapter 2 have pointed out \'lhat is perhaps
the central problem with the interpretation that two lineages distinct at the species level are represented. If the
two lineages represent species of Australopithecus, and if
the gracile lineage continues to H. erectus and H. sapiens,
then there must be an arbitrary generic change in the
gracile lineage somewhere between 1.0 and 1.5 my BP; but
there is almost no basis for such a change. Apart from_the
similarities in dentition between the gracile specimens OH7
OH13, OH16, and ERq92 and middle Pleistocene H. erectus
indictaed in this study and by other investigators (Tobias
and von Koenigswald, 1964), excavations at Lake Rudolf
(Leakey, 1970} have produced evidence of material culture
pre-dating the time period sampled in this study and one
hominid specimen, ER1470, with an exceptionally large
cranial capacity for an australopithecine (Leakey, 1973b).
Thus, evidence from other sources than the dentition
90
indicates that the genus Homo may not be restricted to the
middle Pleistocene.
Therefore, once two lineages are proposed, investigation of their generic status is invariably reduced to the
question of the antiquity and characteristics of the genus
Homo. A consideration of the adaptive pattern of Homo is
clearly beyond the scope of a study based on dental evidence alone. As discussed in Chapter 2, Robinson (1972)
found that the adaptive characteristics inferred for early
Homo, combined with the available evidence, suggests that
the genus Homo must characterize the gracile lineage from
its inception. The results of this study suggest that dental measurements, while they may distinguish pongid and
hominid adaptations and size-variant species among the
hominids, do not permit the identification of the genus
Homo as distinct from the proposed hominid genera Australopithecus and Paranthropus.
Chapter 6
CONCLUSIONS
In order to assess the probability which can be associated with single and multiple-lineage hypotheses of hominid
phylogeny, a sample of contemporary specimens of fossil
hominid dentition dated to the time period between 1.0 and
2.0 my BP was selected. As represented by the dimensions of
the mandibular teeth including the canine through the third
molar, the variability of this sample was compared with
that of extant and extinct hominoid species using several
univariate and multivariate statistical methods in order to
determine if more than one lineage of fossil hominid.s could
be distinguishec.
It was found that sufficient size differences exist
among the fossil hominids represented to support the existence of two species-specific lineages during the time period sampled. However, these size-variant species were not
found to differ siqnificantly in shape to be classified as
separate genera, if shape difference in the dentition among
hominids is taken to be a reasonable basis for the recognition of proposed hominid genera. Artifactual evidence may
indicate that the genus Homo is older than the time period
sampled in this study; this suggests that either the distinction between the lineages is of a generic level or that
91
..
92
two species of Homo were sampled. The former alternative is
clearly the more likely since the latter requires either a
common ancestor Homo sp or parallel evolution into Homo in
both lineages, and because the adaptive characteristics
generally attributed to Homo make the maintenance of sympatric species or even speciation an unlikely event. It
must be concluded then that odontometrics among hominids do
not clearly indicate adaptive differences that can be associated with generic categories.
93
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100
APPENDIX
A
Early Hominid Sample Data
Dimension (mm x 10)
p3
p4
Ml
c
Case
( 1)
(b)
( 1)
(b)
( 1)
(b)
( 1)
(b)
( 1)
M3
M2
(b)
( 1)
(b)
NATRONK
73 81 92 135 145 152 164 153 174 162 188 163
ER992G
90 81 95 111 84 111 120 109 120 123 128 123
OH16F
99 101 103 115 101 110 143 128 153 147 158 144
OH7F
89 98 95 102 103 106 141 125 158 138
OM/L7a-125E 78 96 112 175 117 189 168 187 162 180 182 148
0Hl3K
76 79 90 92 92 87 127 116 138 122 152 110
ER729H
120 130 140 150 155 155 195 180 200 190
OM/75-14a,bB
109 116 114 127 156 141 175 154 151 141
SANG9K
135 125 135 127
90 103 90 107
ER806G
92 108
137 126 143 131 147 121
SANGlK.
90 109 128 130 135 134 146 125
SANG6aK
101 117 98 119 148 136
ER818J
197 180 220 180
145 160
ER802G
187 163
137 145 170 160
ER730I
117 117 120 116 130 115
SANG8K
140 135 145 130 155 130
SANG5M
130 130 141 143
OH16K
93 93
OM/75i-1255D
102 103
Of-1/2 9-4 3B
106 102
OM/74-18B
96 100
TAUNGK
140 135
ER820G
120 108
140 130
OM/75s-15D
151 134
OM/K-7-19A
144 138
SANG6bL
175 156
ER810H
172 159
OM/F-203-lD
167 146
OM/136-2D
179 156
OM/136-lD.
ER801H
189 165
OM/L74a-21E 88 97
130 138
165 145
OH30F
78 77
190 168
ER1171G
155 158
151 130
OH4K
105 114
Data sources (last letter in identification field)
(A) Coppens, 1970: (B) Coppens, 1971; (C) Coppens, 1973a;
(D) Coppens, 1973b~ (E) Howell, 1969; {F) Frayer, 1973;
(G) Leakey and Wood, 1973; (H) Leakey, Mungai, and Walker,
1972; (I) Day and Leakey, 1973; (J) Leakey and Walker,
1973; (K) wolpoff, 197la; (L) Tobias and Von Koenigswald,
1964; (M) Lovejoy, 1970
101
APPENDIX
B
Descriptive Statistics for Hominid
and Pongid Samples
mesio-distal·
s
CV
bucca-lingual
cv
s
y
n
y
8
8.39
0.89
10.8
8.86
1.01
11.4
H. sapiens 81
Homo
(ffiUl tisp.) 27
7.32
0.5T
7.7
7.94
0.66
8.4
7.70
0.40
8.2
8.79
0.92
10.4
Gorilla
male
female
38
20
18
15.66
18.10
13.00
2.84
1.37
0.88
18.1
7.6
6.!3
12.89
14.06
10.33
2.05
0.91
0.66
15.9
6.5
6.4
Pan
male
female
24
13
11
12.18
13.12
11.06
1.43
1.27
0.52
11.7
9.7
4.7
9.84
10.62
8.85
1.14
0.88
0.39
11.6
8.3
4.4
Pongid
62
14.31
2.96
20.7
11.87
1.76
14.8
Pan +H. sap.l05
8.43
2.21
26.2
8.37
1.12
13.4
y
s
cv
y
s
cv
'Canine
Early
Hominids
n
p3
Early
Hominids
14
10.00
0.92
9.2
11.44.
2.14
18.7
H. sapiens 81
Homo
{iliUltisp.) 27
7.23
0.59
8.1
8.14
0.62
7.6
7.79
0.82
10.5
8.96
0.94
10.5
Gorilla
male
female
40
20
20
16.19
17.50
14.87
1.61
1.00
0.85
9.9
5.7
5.7
11.21
12.05
10.36
1.34
1.12
0.94
12.0
9.3
9.1
Pan
male
female
26
14
12
11.10
11.06
11.15
0.51
0.60
0.41
4.f'
5.4
3.7
7.78
8.06
7.46
0.65
0.69
0.43
8.4
8.6
5.8
Pongid
66
14.19
2.82
19.9
9 •.86
2.02
20.5
Pan+ H.sap.l07
8 .. 17
1.76
21.5
8.05
0.64
8.0
"'
~"'
--·--·
-- - -
-----·-··
- -·-
.
--
---~ -------~------~-.
___ ,_ ----·
-~
-------
--·····-- :
102
Appendix B (cont.)
p4
Early
Hominids
n
y
mesio-distal
s
cv
_bucco-lingual
s
cv
y
17
11.42
2.31
20.0
12.84
2.71
21.1
H. saEiens 81
Homo
(multisp.) 27
7.53
0.61
8.1
8.60
0.73
9.0
7.69
0. 87·
11.3
9.24
0.83
9.0
Gorilla
male
female
40
20
20
11.21
11.65
10.76
0.75
0.68
0.54
6.7
5.8
5.0
12.94
13.37
12.52
0.97
0.64
1. 06
7.5
4.8
8.5
Pan
male
female
26
14
12
7.65
7.79
7.50
0.52
0.65
0.27
6.8
8.3
3.6
8.92
8.99
8.83
0.46
0.46
0.47
5.2
5.1
5.3
Pongid
66
9.81
1.87
19.1
11.36
2.00
17.6
Pan+ H.sap.l07
7.56
0.58
7.7
8.68
0.68
7.9
y
s
cv
y
s
cv
Ml
Early
Hominids
n
19
14.26
1.68
11.8
13.51
1.91
14.2
H. sapiens 81
Homo
---rrnu1 ti sp . ) 27
11.59
0.76
6.5
11.12
0.69
6.2
11.93
1.04
8.7
11.47
0.87
7.6
Gorilla
male
female
40
20
20
15.28
15.67
14.88
0.73
0.61
0.63
4.8
3.9
4.2
14.15
13.51
12.80
0.72
0.48
0.75
5.5
3.6
5.9
Pan
male
female
26
14
12
10.63
10.73
10.53
0.57
0.61
0.53
5.4
5.8
5.0
9.72 0.53
9.81 0.59
9.62" 0.46
5.5
6.0
4.8
Pongid
66
13.45
2.38
17.7
11.80
1.78
15.1
Pan+ H.sap.l07
11.35
0.82
7.2
10.78
0.88
8.2
103
Appendix B (cont.)
M2
n
y
mesio-distal
s
cv
y
bucco-lingua1
cv
s
!
Early
Hominids
19
15.61
2.43
15.6
14.58
2.11
14.5
H. sapiens 81
Homo
(mUltisp.) 27
11.33
0.79
7.0
10.74
0.65
6.1
11.87
0.98
8.2
11.45
0.97
8.4
Gorilla
male
female
40
20
20
16.77
17.32
16.22
1.08
1.04
0.81
6.4
6.0
5.0
14.98
15.51
14.41
1.05
0.61
1.18
7.0
3.9
8.2
Pan
male
female
26
14
12
11.02
ll.ll
10.90
0.60
0.68
0.49
5.4
6.1
4.5
10.57
10.73
10.39
0.64
0.68
0.56
6.1
6.3
5.4
Pongid
66
14.51
2.98
20.5
13.23
2.34
17.7
Pan+ H. sap.l07
11.30
0.74
6.6
10.70
0.65
6.1
s
cv
s
cv
M3
Early
Hominids
n
y
y
19
16.44
2.45
14.9
14.35
2.20
15.3
H. sapiens 81
Homo
(multisp.) 26
11.25
0.89
7.9
10.60
0.76
7.2
11.56
0.93
8.1
11.16
0.96
8.6
Gorilla
male
female
40
20
20
16.80
17.60
16.00
2.90
1.00
1.12
17.3
5.7
7.0
14.76
15.33
14.19
1.11
0.82
1.08
7.5
5.3
7.6
Pan
Ina:1e
female
25
13
12
10.25
10.40
10.09
0.61
0.77
0.35
6.0
7.4
3.5
10.10
10.23
9.97
0.56
0.69
0.35
5.5
6.7
3.5
Pongid
65
14.28
2.29
16.7
12.97
2.47
19.0
Pan+H.sap.l06
11.01
0.93
8.5
10.48
0.75
7.1