Anthropological Review • Vol. 61, pp. 75-8 3 , Poznaii 1998
Facial growth and remodeling in the australopithecines
- a review
K atarzyna A. Kaszycka
Abstract
The purpose o f this paper is to review the previous investigations o f the facial grow th and rem odeling patterns o f
early hom inids (the australopithecines), and to present som e o f the problem s that arise from these kinds o f analysis. :
Katarzyna A. Kaszycka 1998; Anthropological Review, vol. 61, Poznan 1998, pp. 7 5 -8 3 , figs 4, ISBN 83-8696935-0, ISSN 0033-2003
Introduction
Growth o f the face is influenced by a
variety o f factors which play different
roles in different stages o f development.
It appears that during the late prenatal
and early postnatal stages, the dominant
factor contributing to facial growth is the
growth o f the cranial base, including the
nasal capsule, and the nasal septum.
Later, growth is known to occur by re­
modeling processes (apposition and re­
sorption), sutural growth, neural and
synchondroseal growth, dental develop­
ment, and the development o f the maxil­
lary alveolar process. By age seven, once
the anterior cranial base has become
stable, the growth o f the midface is in­
fluenced mainly by the process o f down­
ward and forward displacement and pe­
riosteal remodeling [CARLSON 1985],
The basic concept o f the growth and
Institute o f Anthropology
. Adam Mickiewicz University
61-701 Poznan, Poland
remodeling of the craniofacial skeleton
originated more than 200 years ago with
the pioneer works o f J. Hunter [HUNTER
1771]. In the 1920s and 1930s Brash
revised and developed Hunter’s “remo­
deling” theory claiming that cranial
growth was due to ectocranial apposition
and endocranial resorption [BRASH
1934]. During the 1940s-1960s three
hypotheses were put forward to explain
the mechanisms influencing midfacial
growth. These were: the sutural hy­
pothesis (see e.g. PRITCHARD ET AL.
[1956]), the nasal septum hypothesis
[SCOTT 1953], and the functional matrix
hypothesis [M O SS 1976].
Other major contributions to the study
o f facial growth were made in the 1960s
and 1970s by Enlow and Bjork. Enlow’s
contribution consisted in making major
generalizations about the facial growth of
both humans and rhesus monkeys. In
1966 the author wrote: D etailed studies
o f remodeling patterns in the facial
skeleton o f extinct members o f the genus
Homo as well as other related genera
76
Katarzyna A. Kaszycka
and species, both living and fossil, are
now needed. It should be determined if
t e distinctive resorptive nature o f the
forw ard p a rt o f the maxillary and mandibular arch is a specific characteristic
o f H. sapiens. [E n lo w 1966a, p. 302].
Follow ing this directive, T. Brom age
performed studies to answer the question
o f how bones o f the face grew and
rem odeled in extinct australopithecine
species.
The purpose o f this paper is to review
tlie previous investigations o f the facial
bone growth processes o f early hominids,
and to present some o f the problems that
arise from these kinds o f analysis.
1
Facial growth of Homo
and Macaca
A ccording to Enlow [EN LO W 1968;
& H a r r i s 1964; ENLOW &
1965; D UTERLOO & ENLOW
1965], three principles apply to bone
ENLOW
BANG
growth and remodeling: (1) The concept
o f “area relocation” (the changing rela­
tive positions o f all areas within a bone);
(2) The principle o f the “V” (the enlarging V involves deposition on its inner
surface and resorption on its outer surface); and (3) The principle o f “cortical
drift” (surfaces that face the actual direction o f growth are depository, while
surfaces that face away from the direction o f growth are resorptive; the result is
a drift movement o f the bone in the direction o f the depository surface),
One o f the major points made in Enlow’s generalization is that the maxilla
grows downward and forward by a
process o f bone deposition on the posterior and superior surfaces. There are two
major areas o f maxillary growth: the
maxillary tuberosity, and the roof o f the
oral cavity, both o f which receive new
bone deposits. In contrast, the anterior
surface o f the maxillary complex is resorptive in character. The mandible, like
Fig. 1. T he distribution o f depository (light) and resorptive (dark) surfaces in (A) the rhesus m onkey, and (B) human
faces. A fte r E n l o w [ 1966a]
Facial growth and rem odeling in the australopithecines.
the maxilla, is continuously repositioned
in a forward and downward direction as
actual new growth proceeds posteriorly;
the mandibular ; condyle represents an
important growth site.
ENLOW [1966a, 1970, 1982] com ­
pared and contrasted the remodeling
changes that occur during the growth o f
the human and rhesus monkey faces. The
detailed distributions o f resorptive and
depositionary surfaces were determined
and mapped in the diagram (Fig. 1). His
findings are as follows:
(1) The general plan o f facial growth
is similar in both species.
(2) The m ajor differences exist in
the muzzle area. In the monkey the
whole anterior surface o f the m axilla is
depositionary, w hile in the human the
forward part o f the m axillary arch is
resorptive. These differences, accord­
ing to Enlow, provide the basis for
the reduced degree o f prognathism
which is characteristic o f the human
skull.
(3) The anterior part o f the mandible
also demonstrates differences. In the
rhesus monkey, the entire labial side o f
the mandible is depositionary, while in
the human mandible the alveolar portion
located between the mental foramina is
resorptive. This could be one o f the rea­
sons for chin formation in the human
mandible. The opposite (lingual) side o f
the human mandible is entirely deposi­
tory, while in the rhesus monkey it is a
combination o f resorption and deposi­
tion. This combined process produces the
“simian sh e lf’.
(4) Rem odeling differences in the
zygomatic area also exist, although the
general pattern, i.e., resorption at the
anterior surfaces, rem ains the same for
both species.
77
Facial growth in the
australopithecines
Brom age’s . study [BROM AGE 1985,
1989, 1992] is an “Enlowian” type o f
study; his interpretations are based on
concepts and principles o f craniofacial
growth and remodeling taken from Enlow’s studies o f modern humans [ENLOW
1966b, E n l o w & B a n g 1965, E n l o w &
HARRIS 1964], and from a comparative
study o f Homo sapiens and Macaca
mulatto [E n l o w 1966a, E n l o w 1982,
D u t e r l o o & E n l o w 1970].
,
Bromage used bone surface replicas
to study bone formation and resorption
with the scanning electron microscope.
The periosteal surfaces o f immature early
hominid specimens were analyzed. The
australopithecine specimens were di­
vided into two groups [BROMAGE 1989]:
(1) Australopithecus, including^, africanus and A. afarensis (10 specimens), and
(2 ) Paranthropus, including P. robustus
and P. boisei (15 specimens). The age
range for the first group o f the early
hominids (“gracile” australopithecines)
was from 3.3 to 11.3 years, according to
Bromage’s estimation based on pongid
dental development [BROM AGE 1987,
B r o m a g e & D e a n 1985], or from 5.0 to
15.6 years based on human-like dental
ages at death taken by Bromage from
M a n n [1975] and S k in n e r & S p e r b e r
[1 9 8 2 ], The youngest specimen o f this
group is one numbered LH 2 (mandible)
with complete deciduous dentition and
first perm anent m olars. The oldest
specimen, STS 52 (maxilla and mandi­
ble), has all its permanent dentition with
M 3 ju st erupting. The age range for the
second group o f early hominids (“robust”
australopithecines) is from 1.0 to 11.3
, based on pongid dental ages
78
Katarzyna A. Kaszycka
[BROMAGE 1987], or from 2.0 to 15.4
years using the more conventional method
o f M a n n [1975]. The specim en num ­
bered SK 438 (m andibular fragm ent)
w ith dm2 was the youngest specim en,
w hile SK 52 (m axilla) was the oldest
specim en - w ith com plete perm anent
dentition —considered.
As can be seen in Enlow’s work, and
also according to Bromage, the bones of
the face grow and change shape through
a combination o f two processes: deposi­
tion and resorption. These are said to be
the key mechanisms accounting for the
different craniofacial forms in each
species. Australopithecus africanus (the
Taung child) was shown by BROMAGE
[1985, 1989, 1992] to have an ape-like
pattern o f facial growth and remodeling,
while the facial growth o f the “robust”
australopithecines (in Bromage’s papers
Paranthropus) resembles that o f humans.
The different degrees o f prognathism
between these early hominids can be
explained on the basis o f different re­
modeling patterns. Maps o f distribution
o f bone deposits and locations o f bone
resorption are presented in Fig. 2.
B
Fig. 2. Frontal and lateral views o f (A) A. africanus, and (B) A. robustus facial rem odeling. Light represents areas o f
deposition, and dark represents areas o f resorption. A fter BROMAGE [1989]
Facial growth and rem odeling in the australopithecines.
As can be seen from Figure 2, Austra­
lopithecus africanus’ facial growth is. char­
acterized by bone deposition on the whole
of the anteriorly-facing aspect o f the face.
The “robust” australopithecines differ from
the former by having resorptive areas on
the anterior wall o f the temporal fossa, the
“nasoalveolar clivus”, and the anterolateral
comers o f the mandibular corpus. The two
latter features are said to correspond to
remodeling patterns that are characteristic
o f modem humans [BROMAGE 1989],
Downward facial growth in the “robust”
australopithecines is opposed to downward
and forward facial growth in A. africanus.
Remodeling fields have four main at­
tributes, according to BROMAGE [1985]:
size, shape, placement, and rate o f activity.
Bromage suggests that the first three are the
same for the Taung baby and the chimpan­
zee. Differences in the last one, i.e., the rate
of activity o f remodeling fields, show that
the Taung baby is not an ape.
Discussion
As was mentioned before, Enlow’s
contribution to the study o f facial growth
and remodeling was making generaliza­
tions about these processes. His studies
were based on looking at the surface of
the bone to establish whether it was re­
sorptive or depository. According to
Enlow [e.g. ENLOW & BANG 1965], not
much growth occurred in the sutures, and
therefore practically all the growth was
the result o f remodeling (deposition and
resorption). After SCOTT [1953] put for­
ward the hypothesis that the maxilla
grew in length by apposition o f its ante­
rior^, surface, Enlow [e.g. ENLOW 1966b]
was"the first to report that the surface of
the human maxilla was not depository
but resorptive.
79
Another series o f major contributions to
our understanding o f facial growth and
remodeling was made by BJORK and
SKIELLER [1972, 1976], Their longitudinal
studies o f a group o f children, using metal­
lic implants as reference points, focused on
individuals, and not on averages. Their
findings were that while remodeling played
a role in craniofacial growth, sutures were
important too. The midface increases in
height (vertically), depth (anteriorly) and
width. An increase in maxillaiy height
takes place by sutural growth and by ap­
position. Growth in width is not only a
result o f remodeling processes but occurs
by growth o f the median suture as well. In
addition, growth in length o f the maxilla
occurs suturally (toward the palatine bone)
as well as appositionally in the maxillary
tuberosities.
B jo rk ’s n ext fin d in g [BJORK &
SKIELLER 1976] w as that the anterior sur­
face o f the maxilla w as neither depository
nor resorptive, but sagittally stable (from
the age o f about 4 to 21). A lso, the anterior
surface (contour) o f zygom atic process
appears to be stable, in contrast to ENLOW
and BANG’S [1965] classical v iew that the
anterior surface o f that process is resorptive
and the posterior surface is depository.
Enlow also postulated that deposition took
place on the posterior maxillary surface,
Bjork argues, however, that this is not the
case because sutures are able to grow.
There are other problems with the point
o f view of Enlow and Bromage. Firstly,
these authors establish which portion o f a
bone is depository and which is resorptive
at the point o f death o f an individual. This
does not allow a knowledge o f what hap­
pened during the lifetime of the individual.
Everything, which can be observed, would
have happened only recently. The next
problem arises from looking at dead bones
80
Katarzyna A. Kaszycka
to determine how much, for how long and
how long ago growth occurred. These
¡questions simply cannot be answered from
observations o f the bones. Yet another
problem is that there is age variation in
growth patterns. In order to account for
this, growth series were studied, but then
one general •pattern o f facial remodeling
was presented as if there was no variation,
and as if areas o f deposition and resorption
were immutable for the entire life o f an
individual. Finally, there is the problem
o f individual variation. Bjork’s studies
[BJORK & SKIELLER 1972, 1976] clearly
reveal that not all individuals have the same
growth and remodeling patterns.
Bromage has said that the face becomes
more prominent during growth if deposi­
tion o f bone on the front surfaces is com­
bined with resorption o f the back. There­
fore, according to him [B r o m a g e 1992],
the Taung face, for example, is typical o f a
monkey (or ape) because it does not have
resorption areas as seen in modem humans.
However, as BJORK and SKIELLER [1976]
noticed, maxillary projection in the face
(alveolar prognathism) depends not only on
its growth in length, but may also be a re­
sult o f displacement and rotation o f the
maxilla. In addition, there is little evidence
that surface deposition could account for
downward and forward midfacial growth in
humans during the first seven years o f life
[CARLSON : 1985]. It has, however, been
noticed that in prognathic apes after a cer­
tain age, all maxillary growth in length is
by surface deposition. In the phylogenetic
development o f primates, prognathism
decreases as a result of shortening of. the
jaw s [BJORK 1951].
Among the australopithecines there are
differences in the degree o f facial pro­
gnathism . The A. africanus face is pro­
gnathic, w hile the face o f the “robust”
specimens is considered to be more orthognathic,'and therefore more like the Homo
face. However, as RAK [1983] has pointed
out, similar degrees o f prognathism in
Homo and A. boisei reflect two different
configurations (Fig. 3). In modem Homo, it
Fig. 3. A comparison between (A) a prognathic chimpanzee,
and two orthognathic primates - (B) “robust” australopithecine, and (C) modem Homo. After RAK [1983]
Facial growth and rem odeling in the australopithecines.
is not a result o f the retraction o f the palate
as seen in the “robust” australopithecines,
but a result o f reduction in the length o f the
palate. In fact, when the length o f the palate
is expressed as a percentage o f independent
measurements, the index value in A. boisei
does not differ from that of a chimpanzee.
In contrast, A. ajriccmus has strong facial
prognathism - the index o f prognathism
can be as high as 137% [WOLPOFF 1975],
The upper jaw and therefore the palate,
project far anteriorly. The medial part of
the midface is located more anteriorly than
its lateral (peripheral) portion. Although all
the australopithecine faces are prognathic,
this feature in the “robust” forms is not as
pronounced. The most orthognathic face is
that o f A. boisei, where the index o f pro­
gnathism can be as low as 113%.
Fig. 4. Lateral view o f the face o f (A) A. africanus, and
(B) A. boisei. A fter R a k [1983]
81
, Generally, the medial part o f the face
and the dental arcade are located more
posteriorly in the “robust” specimens,
while the lateral part o f the face is lo­
cated more anteriorly. With such a posi­
tion o f the peripheral face, i.e., the zy­
gomatic bones (see Fig. 4), the medial
part becomes concave and the nose, in
lateral view, is hidden behind it. This
configuration is also a reason why the
face o f the “robust” australopithecines
seems to be more orthognathic.
***
To sum up, one can say that although
Bromage is probably right in what he
observes, there are certain problems, as
presented in this paper, with that kind o f
analysis. While bones reflect remodeling
processes, the whole o f the growth his­
tory o f bone is not reflected in the tissue
itself. Detailed sequences o f growth
changes, therefore, cannot all be recon­
structed.
One additional point can be made
here. Even if certain early hominids ex­
hibit remodeling patterns more consistent
with macaques, and even if Enlow and
Bromage are correct in claiming that this
leads to, or is consistent with, greater
maxillary prognathism, this means noth­
ing as far as human lineage and adapta­
tion/evolution are concerned. It may
simply mean that in order to have pro­
gnathism one must have more bone
deposition at the labial surface o f the
maxillary complex. We already know
that monkeys and apes tend to be more
prognathic than modern humans, so by
definition they must exhibit greater bone
deposition along the surface o f the maxil­
lary complex, if we assume Enlow to be
correct. One test o f this, which would
still not be definitive with respect to
82
Katarzyna A. Kaszycka
questions o f lineage, would be to look at
remodeling patterns in prognathous vs.
ortoganthous primates. Also, it would be
interesting to examine the remodeling
patterns in different humans with age:
prognathous vs. orthognathous.
References
B j ÛRK A ., 1951, The nature o f facial prognathism
and its relation to normal occlusion o f the
teeth, A m . J. O rthod., 37: 106-124
B j Or k A ., V . S k iell er , 1972, Facial development
an d tooth eruption, A m . J. O rthod., 62:
3 39-383
B jô r k A ., V . S k ieller , 1976, Postnatal growth
and development o f the maxillary complex,
[in:] Factors affecting the growth o f the mid­
fa ce, J; M cN am ara Jr. ed., C en ter fo r H um an
G row th and D evelopm ent, U niversity o f
M ichigan, A nn A rbor, pp. 61-99
B rash J.C .. 1934, Some problem s in the growth
and developmental mechanics o f bone, E d in ­
b urgh M ed. J .,n .s . 4th", 41: 305-387
B r o m a g e T .G ., 1985, Taurig fa cia l remodeling: a
growth and development study, [in:] Hominid
evolution: Past, present and future, P .V . T o ­
b ias ed., A . L iss Inc., N e w Y ork, pp. 239-245
B r o m a g e T .G ., 1987, The biological and chroni­
cal maturation o f early hominids, J. H um .
E vol., 16: 2 5 7 -2 7 2
B r o m a g e T .G ., 1989, Ontogeny o f the early
hominid face, J. H um . E vol., 1 8 :7 5 1 -7 7 3
B r o m a g e T .G ., 1992, Faces from the past, N ew
Sci., 11 January, pp. 38-41
B r o m a g e T .G ', M .C . D e a n , 1985 , Re-evaluation
o f the age at death o f immature fo ssil homii : nids. N ature, 317: 525-527
C a r lso n D .S., 1985, Introduction to craniofacial
biology. Growth and adaptation o f the cranio­
facial complex, C enter for Hum an Growth and
Developm ent, University o f M ichigan, A nn A rbor
D u ter l o o H .S., D .H . E n l o w , 1970, À compara­
tive study o f cranial growth in Homo and
M acaca, A m . J. A nat., 127: 357-368
E n l o w D.H., 1966a, A comparative study o f facial
growth in Homo and Macaca, Am. J. Phys.
Anthrop., 24: 293-308
E n l o w D.H., 1966b, /( morphogenetic analysis o f
fa cia l growth, Am. J. Orthod., 52: 283-299
E n l o w D.H.; 1968, The human face. An account
o f the postnatal growth and development o f
the craniofacial skeleton, Hoeber Med. Div.,
Harper & Row Publ., New York
ENLOW D.H., 1982, Facial growth and develop­
ment in the Rhesus monkey, [in:] Handbook o f
fa cia l growth. Second ed., W.B. Saunders,
Philadelphia, pp. 283-293
E n l o w D.H., S. B ang, 1965, G rowth and re­
modeling o f the human maxilla, Am. J.
Orthod., 51: 446-464
E n l o w D.H., D.B. H a r r is , 1964, A study o f the
postnatal growth o f the human mandible, Am.
: J. Orthod., 50: 25-50
H u n t e r J., 1771, The natural history o f the human
teeth, explaining their structure, use, form a­
tion, growth, and disease, J. Johnson, London
M ann A.E., 1975, Paleodemographic aspects o f
the South African australopithecines, Univ.
Pennsylvania Publ. No. 1, Philadelphia
M oss M.L., 1976, The role o f the nasal septal
cartilage in midfacial growth, [in:] Factors
affecting the growth o f the midface, J.
McNamara Jr. ed., Center for Human Growth
and Development, University o f Michigan,
Ann Arbor
P r it c h a r d J.J., J.H. S c o t t , F.G. G ir g is , 1956,
The structure and development o f cranial and
fa cia l sutures, J. Anat., 90: 73
R a k Y., 1983, The australopithecine face, Acad.
Press, N ew York
SCOTT J.H., 1953, The growth o f the human face,
Proc. Roy. Soc. Med., 47: 91-100
S k in n e r M.S., G.H. S p e r b e r , 1982, Atlas o f
radiographs o f early man, A.R. Liss, New
York
W OLPOFF M.H., 1975, Some aspects o f human
mandibular evolution, [in:] Determinants o f
mandibular form and growth, J. McNamara Jr.
ed., Center for Human Growth and Develop­
ment, University o f Michigan, Ann Arbor,
pp. 1-64
Facial growth and rem odeling in the australopithecines..
83
Streszczenie
N a wzrastanie szkieletu tw arzy wpływa wiele czynników. W fazie okolourodzeniowej głów nym czynnikiem jest
powiększanie się podstaw y czaszki, w tym ścian i przegrody jam y nosow ej. N ieco później, rozrost tw arzy odbyw a się
dzięki procesom rem odelow ania (apozycji i resorpcji), w zrastania śródszwowego i w obrębie chrząstkozrostów , rozwo­
jow i zębów i wyrostka zębodołowego szczęki. Od 7 roku życia na rozrost tw arzy zasadniczo oddziałuje ju ż tylko
proces dyslokacji ku dołowi i ku przodowi oraz rem odelowanie odokostnowe. Podstaw ow a koncepcja wzrostu
i rem odelow ania szkieletu kraniofacjalnego liczy ponad 200 lat, a rozwój badań nad tą problem atyką nastąpił
w naszym stuleciu dzięki pracom m .in. Brasha, Pritcharda, Scotta, M ossa, Enlow a i BjOrka.
Celem przedstaw ianej pracy jest ocena dotychczasowych badań nad zagadnieniem w zrostu i rem odelow ania
szkieletu twarzy u naszych przodków - australopiteków i zaprezentow anie niektórych problem ów, które pow stają przy
tego rodzaju analizach.
W kład Enlow a do badań nad wzrastaniem szkieletu tw arzy (lata 60. i 70.) polegał na stw orzeniu uogólnień doty­
czących zarów no człowieka ja k i małp. Jak wynika z je g o prac, kości twarzy rosną i zm ieniają kształt poprzez kom bi­
nację dwu procesów: apozycji i resorpcji. Jest to m echanizm w arunkujący m iędzygatunkow e zróżnicow anie kształtu
twarzy. E nlo w [1966a, 1970, 1982] porów nał i zestawił przem iany w ynikające z rem odelow ania, które pojaw iają się
podczas wzrostu tw arzy człow ieka i małpy rezusa. O znaczył obszary resorpcyjne i apozycyjne (przedstaw ione na
rys. 1). W nioski Enlow a są następujące. (1) Ogólny plan wzrostu tw arzy u obu gatunków je s t podobny. (2) Podstaw o­
we różnice dotyczą okolicy pyska (szczęk). U m ałp cała przednia pow ierzchnia szczęki je s t m iejscem apozycji, pod­
czas gdy u człowieka w przedniej części łuku zębodołowego szczęki zachodzi resorpcja. (3) U rezusa cała policzkow a
strona żuchw y je s t m iejscem apozycji, podczas gdy w przedniej części ludzkiej żuchw y, pom iędzy otworam i bródkowymi, kość ulega resorpcji. Przeciw na - językow a - strona żuchw y u człow ieka całkow icie podlega apozycji, u małp
natom iast jest częściowo resorpcyjna, a częściowo apozycyjna, co pow oduje utworzenie tzw. „m ałpiej półki” .
W latach 80. T. Brom age, w zorując się na pracach Enlowa, przeprow adził badania nad w zrostem i remodelowaniem kości tw arzy u w czesnych hom inidów. Brom age użył odcisków pow ierzchni kości tw arzoczaszek do badań
form acji i resorpcji kości, korzystając z elektronowego m ikroskopu skaningowego. W ydzielił dw ie grupy wczesnych
hom inidów - „m asywne” i „gracylne” australopiteki. U A. africanus B r o m a g e [1985, 1989, 1992] stw ierdził małpi
typ rozrostu i rem odelow ania kości twarzy, podczas gdy u „m asywnych” australopiteków - ludzki. Z różnych wzorów
rem odelowania w ynika zróżnicow any stopień prognatyzm u u w spom nianych grup hom inidów . M apy rozkładu apo­
zycji i resorpcji na kościach twarzy u australopiteków prezentuje rys. 2.
Prace i uogólnienia Enlowa nie w yjaśniły jed n ak wszystkiego. B j Ork i S k ieller [1972, 1976], w wyniku badań
longitudinalnych grupy dzieci, zwrócili uwagę na dodatkowy aspekt wzrostu i rem odelow ania kości tw arzy - znacze­
nie wzrostu śródszwowego. Stwierdzili także, że przednia pow ierzchnia szczęki nie je s t ani apozycyjna, ani resorpcyj­
na, ale strzałkowo stabilna (w w ieku od 4 do 21 lat). Są też inne problem y w ynikające z przyjęcia punktu w idzenia
Enlowa i Brom age’a. Po pierwsze, autorzy ci posługiwali się kośćmi zm arłych osobników , z których m ożna odczytać
procesy zachodzące krótko przed śm iercią. N a podstawie kości nie m ożna ustalić w jakiej fazie życia i ja k długo
trwały procesy rem odelacyjne. Następnym problem em je s t fakt, że istnieje ontogenetyczna zm ienność w zorca w zra­
stania twarzy - nie m ożna w zw iązku z tym przedstaw iać jednego ogólnego w zorca rem odelow ania kości tw arzy oraz
obszarów apozycji i resorpcji. Jest też problem indywidualnej zm ienności - prace B j Orka i S k ieller a [1972, 1976]
dobitnie dowodzą, że nie w szyscy osobnicy m ają ten sam wzór wzrostu i rem odelow ania.
Australopiteki m ają zróżnicow any stopień prognatyzm u twarzowego. Tw arz A. africanus je s t prognatyczna, pod­
czas gdy twarze „m asyw nych” australopiteków są bardziej ortognatyczne i w zw iązku z tym bardziej przypom inają
twarze rodzaju Homo. Tym czasem , na co wskazuje R a k [1983], podobny stopień prognatyzm u Homo i A. boisei
wynika z dwu różnych konfiguracji (rys. 3) - u w spółczesnego człow ieka je s t w ynikiem redukcji długości podniebie­
nia, a u „m asywnych” australopiteków, rezultatem cofnięcia podniebienia. Rów nież bardziej przednie położenie
bocznych części tw arzy (kości jarzm ow ych) u A. boisei potęguje wrażenie ortognatyczności (rys. 4).
C hociaż Brom age m a praw dopodobnie rację w tym, co pisze o rem odelow aniu, pozostają pew ne problem y. Kość
odzw ierciedla procesy rem odelow ania, jed n ak nie cała historia wzrostu kości je s t utrw alona w tkance. W związku
z tym, nie wszystkie sekw encje zm ian w zrastania m ożna szczegółowo zrekonstruow ać. Poza tym , naw et jeśli niektóre
wczesne hom inidy m ają wzorce rem odelow ania zgodne z m ałpam i (co zdaniem Enlow a prowadzi do większego
prognatyzm u), nie m a to znaczenia dla rekonstrukcji zm ian ewolucyjnych w ludzkiej linii.