Biological .journal of the Linnean Socieb (1991), 44: 121-139. With 2 figures
Characters: the central mystery of taxonomy
and systematics
W. GRANT INGLIS
South Australian Museum, Adelaide, Australia 5000
Accepted for publication
XI April I990
Taxonomic and systematic theory is hopelessly confused because the term character has nine
different, previously confused, meanings. After a historical analysis, it is shown that some form pairs,
one used in taxonomy ( = operational identification of phenetic patterns of character x individual
spread) and the other in systematics ( = theoretical analysis of patterns of taxonomy). O n the basis
of a stratigramy model, names are given to each usage and are defined for taxonomy, then
systematics, as necessary: component: (tax.) a defined bit-or-piece of one individual (no syst.
meaning); homology: (tax.) conceptual identity of components of several individuals, attributable
(syst.) to common ancestry; homology avatar: (tax.) case of recognized homology which (syst.) shows
broad phylogenetic continuity (e.g. eye) ( = character sensu Sokal and Sneath); homolostratum/
homology state: (tax.) specified condition of a homology avatar whose distribution (syst.) enables
cladogenetic happenings to be identified (e.g. colour : red/green/blue/etc.) ( = character state of
Sokal and Sneath); character sensu stricto: (tax.) homolostratum limited to a taxon which (syst.), with
hierarchy, identifies chronological sequences of most cladogenetic happenings; taxonomoids: (tax.)
mixed group of homolostrata, including yet unknown characters, that identifies a taxon and so
(syst.) has same role as characters ( = roughly symplesiomorphies); Ante- ( A h ) and Post-(Ph)
happening characters: (tax.) the hierarchy levels immediately above and below an empty level which
(syst.) reveal a cladistic happening ( = roughly one usage of synapomorphies and apomorphies).
KEY WORDS:-Characters
- cladistics
-
classification
-
homology - stratigramy
-
systematics -
taxonomy.
CONTENTS
Introduction . . . . . . . . . . .
Single character downwards taxonomy . . . . .
Multi-character upwards taxonomy
. . . . .
Taxonomic terminology . . . . . . . .
A confusion and clarification of characters . . . .
Systematics: interpreting the patterns of taxonomy . .
Systematic analysis
. . . . . . . . .
Confusion and clarification.
. . . . . . .
Concluding comments . . . . . . . . .
References
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INTRODUCTION
Biological taxonomy is notorious for confusion and disagreement about its
aims, procedures and terminology. All attempts to give logical explanations of
what it involves have been unsatisfactory, partly because its aims are unclear,
partly because its procedures are misunderstood, and largely because its
121
0024-4066/91/100121+ 19 $03.00/0
0 1991 The Linnean
Society of London
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W. G . INGLIS
terminology is inadequate. The difficulties come from a complex of interlinked
causes. Firstly, the procedures actually used in practical taxonomy have been
misunderstood because the steps inevitably involved have not been isolated and
identified. Secondly, as a result, the terms used to explain taxonomy are
ambiguous, confusing, ill-defined and incomplete. Thirdly, even when difficulties
have been recognized the solutions proposed have too often added to the
confusion. Fourthly, many attempts to eliminate problems rely on techniques
supposed to reflect evolutionary and/or speciation theories which give fudges
which seem intellectually satisfying to some but make practical taxonomy
impossible to explain. Fifthly, most discussions of taxonomy actually deal with
post-taxonomic systematics, so that end results are rewritten as initial definitions,
even axioms, usually couched in evolutionary terms.
In an effort to identify and then remove such weaknesses I developed a
simplified model, stratigramy, which establishes the steps actually involved in
practical taxonomy (Inglis, 1986); and then considered some of the problems
that arise when the patterns of taxonomy are analysed historically (Inglis, 1988).
A reconsideration of these analyses, while looking at another problem, has
shown they are flawed, because they continue the virtually universal ambiguities
in the meaning of the term ‘character’ that have bedevilled taxonomic and
systematic theory and writing for centuries.
Character is used with an amazing range of conflicting meanings in all
writings on theoretical and applied taxonomy and systematics. While
longstanding, this ambiguity has caused little confusion in the past, probably
because of the limited analyses of evolutionary writers. The difficulties have now
been increased by what are claimed to be more rigorously defined terms, such as
the character: character state duo of Sokal & Sneath (1963) and the many
‘morphies’ of Hennig (1966). These have made the position worse because, in the
first case, character equates to the consequences of recognizing homology and
character state to homolostratum (sensu Inglis, 1986); while, in the second,
synapomorphy in particular has been equated to virtually every distinguishable
unit of taxonomic data in its short history (Inglis, 1988).
T o prevent more confusion, I treat taxonomy and systematics as distinct
activities. Taxonomy is the theory and practice of determining the groups or
taxa, with their hierarchization, into which organisms fall to form a
classification; and systematics is the theory and practice of interpreting and
explaining the patterns so produced. Taxonomy is, thus, largely (nonmathematically) phenetic, and systematics is largely interpretative. The failure
to stress the distinction has not been important for previous analysts, because
they have taken taxonomy virtually for granted and spent most of their time
writing about systematics. If they should wish to treat these terms as synonymous
a new one will be required, because two processes are certainly involved.
Further, when I use the term classification it always means the product of
taxonomy; never the process by which a classification is produced, so eliminating
another common ambiguity.
The processes of taxonomy can be applied to non-animate as well as animate
things, but it always means biological taxonomy when used here, unless qualified
otherwise. The determination of character is, thus, a n aspect of taxonomy.
Further, because taxonomy is a practical activity its guidelines can only be
developed and judged against what is known of reality. However, what is known
THE CHARACTER MYSTERY
I23
has varied through time, because it depends upon the organisms and associated
data available for study. As a result, the methods of taxonomy have also varied
through time. It follows that, no matter how flawed they now seem to be, the
mediaeval single or limited character techniques were inevitable when
developed, and were not errors of inferior judgement as later authors have
suggested. T o justify this and other conclusions I use a model of taxonomy which
is a simplified version of that originally used to develop stratigramy (Inglis,
1986). In so doing unexpected problems concealed by the earlier model will be
revealed.
SINGLE CHARACTER DOWNWARDS TAXONOMY
The earliest procedural stages in taxonomy can be established by considering
a diverse group of hypothetical organisms of whose structure nothing is known.
O n examination it is discovered that each consists of various distinguishable bitsand-pieces of a variety of shapes and sizes, and relationships one to another.
Experience has shown that each such bit-or-piece has to be delimited and
defined before it can be used in further analysis. A large number of names have
been used for such bits-and-pieces in general, including structure, feature,
attribute, organ, and very often, character, all of which are ambiguous and
potentially confusing because they have also been used with several other
meanings. To overcome this I call each bi t-and-piece a component, mainly because
this is the only suitable term not previously used in this sense. It follows that a
component is a recognized, delimited and defined bit-or-piece of one organism.
Study and comparison of further individuals will then establish that a
component in one individual is mentally conceived as being exactly the same as
a component in another. That is, an in-mind conceptual identity is recognized to
exist between tyo or more corresponding components of two or more
individuals, even when the components are not identical in appearance. This
condition of absolute identity is termed homology in biology, and always indicates
a relationship involving two or more organisms (Inglis, 1966, 1986).
The recognition of homology is an essential stage of taxonomy, biological or
otherwise, usually acknowledged by a phrase such as ‘like must be compared
with like’. This leads to a paradox which causes great confusion for those who
meet it for the first time, because the production of a classification depends upon
the in-mind absolute identities showing an actual variety of form (Inglis, 1986).
As a result, the next step is to delimit states of the variety of form shown by the
homologically identical components. Such defined homology states of different
appearances are homolostrata (Inglis, 1986). While it is convenient when each of
these corresponds to a component, this is neither necessary nor essential, because
a homolostratum may be defined to cover a range of form initially treated as
several components, or as part of a single component. Obviously it is most useful
when homolostrata correspond to already defined components.
The pattern of a classification can now be determined or revealed, during
which the defined limits of all homolostrata must remain constant. That is,
defined homolostrata are unchanging secondary absolutes which can cover a
range of form (Inglis, 1986).
The use of ‘determined’ and ‘revealed’ is intentional, because it reflects the
two ways in which taxonomy can be undertaken; both of which have been and
I24
W. G . INGLIS
still are used in practice. In historically early taxonomy a classification was
determined by the selection of contrasting pairs of homolostrata to form
characters. Only later, about the middle of the 18th century, was the pattern
revealed by using all, or most, available homolostrata. That is, concomitant
single-character downwards taxonomy was replaced by spontaneous multicharacter upwards taxonomy. This is best demonstrated by continuing our
consideration of the hypothetical collection.
When a range of defined homolostrata has been determined, individuals can
be matched and formed into taxa of identical (including considered identical)
individuals which have all their homolostrata in common. Such taxa are termed
(Linnaean or morpho-) species. The next questions are: How are such taxa to be
further ordered? How are the homolostrata restricted to, and so diagnostic of,
each taxon to be recognized? How are the taxa to be ordered in a hierarchy?
With the earlier technique a number of matching homolostrata, usually in
pairs, were selected and sequenced from the top down as diagnostic characters.
This procedure is still used to produce the classifications we call keys. A ready
example is that of books: large vs small, fiction vs non-fiction, scientific vs arts,
then subject matter and finally initial letter of surname. Here two design
decisions are needed. Firstly, the diagnostic characters are selected by the
designer which automatically and concomitantly determine the groups/taxa;
and secondly, the sequence in which the dichotomies/polychotomies are to be
ordered is selected, so that the form of the classification is determined
extrinsically by choices of its constructor, and is independent of the correlation of
the characters. This means that some characters have been chosen in preference
to others, a process commonly called weighting. Therefore, single-character
taxonomy depends upon concomitant weighting (Inglis, 1970), where character
selection automatically produces taxa. Characters, it follows, in this system are
known before taxa.
As knowledge increased, it was found by observation *that many single
character taxa corresponded to a suite of characters whose members always
occurred together in the same organisms. That is, correlation of structure was
recognized by observing nature, and multi-character taxonomy became
increasingly common, by default if not intent. But taxonomists could not escape
their pasts and now began a search for that ideal single character which would,
as before, diagnose a taxon. In a n effort to attain that end they continued the
distortion of weighting, although their diagnoses became increasingly more
elaborate.
Adanson ( 1763) first recognized unequivocally that multi-character taxonomy
had become possible (I think inevitable), with the loss of the need to weight.
Although now given credit for this insight, his great claim to fame has continued
to be overlooked. That is, he also tried to show how such classifications could be
produced. This was the crucial step, because the formation of multi-character
classifications is totally different from single-character.
The significance of this aspect of Adanson’s work has been concealed by the
arguments about the advantages of non-weighting techniques over singlecharacter weighted methods; often by authors who continue to talk about the
former in terms derived from and only appropriate to the latter. The conflict is
particularly marked in discussions on the preferential selection of characters, that
is weighting, as a necessity in forming any classification. Most such argument is
T H E CHARACTER MYSTERY
I25
vacuous because, although weighting is essential in single-character taxonomy, it
is almost certain to be a source of distortion in multi-character, even when a
posteriori.
MULTI-CHARACTER UPWARDS T A X O N O M Y
To demonstrate the procedures involved in producing a multi-character
classification, we return to the collection of hypothetical organisms. So far we
have species taxa within each of which all individuals have all homolostrata in
common. This is the crucial point: not that they all look the same, because that
fact is a result, not a prerequisite. How is this condition reached? One specimen
is selected and progressively compared with all others, and two groups formed:
those with all homolostrata in common with the initial individual, and those
without. In normal practice the former group is a Linnaean or morpho-species,
species- 1 (variation is ignored for convenience). And this conclusion can be
reached although the diagnostic characters of species-1 are as yet unknown.
The organisms of species-1 are now put aside and the procedure repeated,
beginning with any member of the group of non-species-1 organisms. Again a
number have all homolostrata in common, and so form species-2, whose
members all differ from those of species-1 and all the now reduced remainder. As
before, although species-2 is known to exist, its diagnostic characters are
unknown. Such matching by commonality continues until all the organisms
have been sorted into species.
In this way, all species in the collection can be isolated, while their diagnostic
characters remain unknown. I was, therefore, wrong in claiming that the
formation of taxa identified their diagnostic characters (Inglis, 1986), because
such characters can only be isolated when the members of an ‘initial’ taxon are
compared with those of another of equivalent level. Thus, as a simplified
example, assume (as is likely) two of the revealed species have some homolostrata
in common. Therefore, when matched some homolostrata will spread over, or
occur in, both and the remainder will be limited to one or the other of the
species. In this way the homolostrata limited to, and so diagnostic of, each
species are isolated as specific diagnostic characters. Meanwhile the presence of
another, higher, taxon has been established, provisionally a genus with two
species. However, its diagnostic characters are unknown and will not be isolated
until the spread of its homolostrata across another appropriate taxon is known.
As with species, the homolostrata restricted to the genus will then be isolated as
(diagnostic) characters, and the remainder will establish the existence and extent
(i.e. contained individuals and species or other lower taxa) of the next higher
taxon. As before, the characters of that taxon continue to be unknown until
another is available into which further homolostrata spread can be established.
And so on upwards ad intnitum, or until we run out of specimens/taxa.
Of course this is a simplification, because supposed homologies may be wrong,
homolostrata need not fit neatly together, structural correlation is often
incomplete, variation can blur the boundaries of taxa, and the possibility of
convergence/parallelism can weaken confidence in results. However, such
uncertainties arise with all analyses of taxonomic procedures, so that this model
still demonstrates accurately the principles of stratigramy, or character spread
analysis, that underlie all taxonomy, while also establishing that taxa can be
known before their diagnostic characters have been revealed.
I26
W. G. INGLIS
In summary, the procedures of multi-character upwards taxonomy which
reveal diagnostic characters at their appropriate level in a hierarchy, while also
forming that hierarchy and its member taxa, involve six stages: (1) components
are recognized in individuals and defined; (2) conceptually identical components
in different individuals are recognized as homologous, or homologues of each
other; (3) different forms or states of homology are recognized, delimited and
defined as homolostrata; (4)taxa are revealed by grouping individuals with all,
or all remaining, homolostrata in common and (5) diagnostic characters, that is
homolostrata restricted to a taxon, are isolated by removing those that spread
across other already recognized taxa; thus (6) establishing the existence and
extent of the next higher taxon, but not its diagnostic characters.
TAXONOMIC TERMINOLOGY
Distinct names exist for homolostrata at some of these stages, but not all. And
most of them, including what I call components, have been widely and
consistently called characters. This has caused, and continues to cause, confusion
which can be removed by using a distinct term a t each of the identified stages.
First, as already explained, defined bits-and-pieces of individuals are delimited
as components. Then equivalent components in more than one individual are
recognized to be conceptually absolutely identical, and so homologous or
homologues of each other. The range of form shown by such an absolute is then
divided into defined segments, or homology states, of different appearance,
called homolostrata which can occur in more than one individual.
Taxa are now established as groups of individuals, or already known taxa,
with all available homolostrata in common, some of which will later be found to
be restricted to the given taxon, while others are not. The members of this
mixture of potentially diagnostic (limited spread) and non-diagnostic (universal
spread) homolostrata have not been previously recognized and are, therefore,
unnamed. I call them taxonomoids. It follows that the taxonomoids that enable a
species to be recognized in the first instance are all the homolostrata of its
individual members, and these are increasingly sorted out as the process of
taxonomy proceeds. Finally, the taxonomoids which reveal the last, highest,
taxon of a group of organisms must include a mixture of homolostrata, some of
which will spread across as yet unstudied organisms. Because these, and the
putatively diagnostic characters cannot yet be distinguished, the unsorted group
consists of universal taxonomoids.
This may seem empty theorizing, giving a complex terminology and little else.
I t is not: it is very useful, because it establishes and labels the steps in practical
taxonomy, and clarifies the meanings of many widely used terms, particularly
those to which the word character has so often, and so ambiguously, been
applied.
A CONFUSION AND CLARIFICATION OF CHARACTERS
The classical definition of a character is that it is diagnostic. That is, a
homolostratum found in only one taxon. I have used it with this meaning above,
by implication, and use it consistently hereafter. A case might be made for the
character :character state terms of Sokal & Sneath (1963), but these seem to be a
T H E CHARACTER MYSTERY
I27
minority usage. Because of this, and other problems with these terms, I reject
them. In any case, the diagnostic meaning is supported by priority and history.
After all, as Mayr (1969) points out, the diagnostic definition (although not its
unambiguous usage) was universal until the confusion of character :character
state; and, as Colless ( 1985) stresses, the diagnostic meaning is etymologically
correct; and most convincingly, a character can only be diagnostic in the earliest,
single-character taxonomy.
In spite of giving the diagnostic definition specifically for taxonomic character,
Mayr (1969) uses character with at least five meanings and uses characteristics
and properties as absolute or virtual synonyms of it. Similarly, Hennig (1966)
defines character as a distinguishing peculiarity, but also uses it to mean
component and homolostratum, and almost certainly taxonomoid. While I
(Inglis, 1986) consistently confuse the same four meanings : character,
homolostratum, component and taxonomoid. Most interestingly, Stace ( 1989)
employs character with a comparable range of meanings, and recognizes the
inherent ambiguity with a definition which covers every possible usage of the
term. This makes his presentation thereafter ambiguous and confusing, to say the
least, but no more so than those of the rest of us.
Sokal & Sneath (1963) introduce a new term, character state, as a dependent
derivative of character which they employ with a non-diagnostic meaning,
which they do not define. They developed this approach after rightly
recognizing that diagnostic characters cannot be known until taxa have been
formed. In response they discarded the diagnostic definition as illogical, rather
than recognizing that usages are ambiguous, and replaced it with their
character : character state terminology. This has been widely used since then,
particularly in mathematical studies; but in most cases character has also been
used with its original diagnostic meaning.
This pair of terms raises two interesting points. Firstly, its wide use, even by
Ax (1987: discussed below), demonstrates that it is very useful and so must fill a
previously unrecognized need, because there is no prior equivalent for character
state. However, replacement terms for this pair are now needed if character is to
be used with its original diagnostic meaning. Secondly, there are no definitions of
either character or character state in Sokal & Sneath’s sense, because they found
the problem of producing them so severe that they admitted defeat and
demonstrated their ideas by examples. And no definitions have been produced
since then. The reason is plain and goes back to homology as absolute identity,
an origin inevitably overlooked by those who view homology as resemblance or
similarity.
In practical analysis, however, when homology is recognized between a range
of components, differences in appearance are submerged within a conceptual
identity, so that a unit of absolute homology identity comes into being. However,
while its existence has inevitably been used unknowingly by all taxonomists and
comparative anatomists etc. in the past, there is no distinctive name to cover the
identity unit so formed. It is only since Sokal & Sneath took the first
unrecognized step that its status has been acknowledged by implication,
although its real origin and definition has, paradoxically, continued to be
formally overlooked.
These conclusions are best illustrated by examples, which are widespread in
biology. Thus, when talking of eyes of various appearance, red, blue, round,
128
W. G . INGLIS
prominent and so on, eye is a Sokal & Sneath character and shape or colour are
character states. Similarly, leaf is a character and lobed, serrated, lanceolate, etc.
are character states. Perhaps the extreme example is character :gill cleft and
character state: human ear.
This usage is now common, and has caused problems in the past, because it
can lead to a regress in which a character state can also be a character (in this
sense) relative to something else (see, for example. Colless, 1985). I n spite of
these problems, which are due to using a variable reference point or sliding
cursor, the terms must be of value as they are so widely used. However, they
need new names, because they cannot continue to be called characters now that
their true status has been determined. I , therefore, propose the following terms:
A homology avatar is an actual identity established when homology is recognized
(avatar = a visible manifestation of an abstract concept); and a homolostratum or
homology state is a defined unit of form distinguished within the range covered by
a homology avatar. These definitions are readily applied: for character sensu
Sokal & Sneath write homology avatar, and for character state write
homolostratum or homology state, with the advantage that they can now be
defined, because we know how they are obtained in practice.
Character has also often been used for a component, and Davis & Heywood
(1963) even define it in this way as: “any attribute or descriptive phrase referring
to form, structure or behaviour which the taxonomist separates from the whole
organism for a particular purpose”. I do not understand the reference to
“descriptive phrase”, but the definition is otherwise that of component in my
sense. This they then contradict by referring to characters as abstract entities
with whose “expressions or states taxonomists deal”, because “For purposes of
comparison a character must be divisible into two or more expressions or states”.
Here, like Sokal & Sneath, character means a homology avatar, and expression
and state mean homolostratum.
More recently, Ax (1987: English translation) has fallen into the same trap in
a less immediately obvious way, when he uses ‘feature’ (Merkmal in the 1984
German edition) with a range of meanings for which most authors would use the
term character. However, feature is defined as a delimitable peculiarity or
characteristic which can be distinguished from other corresponding units of one
and the same organism. Thus, ‘feature’ by initial definition corresponds exactly
to component in my sense. I had intended to use Ax’s terms in this way until I
recognized that his usage is subsequently ambiguous.
Ax confirms his intended meaning of feature when he says that ‘the totality of
all the mutually delimitable elements of a n organism’ is its ‘pattern of features’.
However then he defines a number of ‘feature patterns’, such as ‘species-specific
feature patterns of closed descent communities’ and ‘feature patterns of
supraspecific taxa’, in such a way that they cover homolostrata, taxonomoids
and characters. This is all due to the usual failure to recognize that homology
must be recognized before any further ‘patterns’ can be identified. Then feature
becomes even more ambiguous when the apparently synonymous terms ‘feature
state’ and ‘feature expression’ are introduced (Ax, 1986: 108). Here feature is a n
implied synonym of homology avatar, because feature state/expression are
synonyms of homolostratum and homology state. This example again shows how
attractive this terminology is and how easily it can be used, even when in conflict
with other terms.
THE CHARACTER MYSTERY
129
These few authors have been used as examples because they have written
major works, in which, in spite of the thought involved, they have all fallen into
recognizably the same traps. The extent of that confusion suggests that we have
all been able to determine the intended meanings fairly readily. O u r ability to
overlook such obvious ambiguities is understandable. After all, most taxonomy is
subconscious, and most finally identified characters begin as components
recognized as homologous with those of other individuals. Then these
components are, generally, used as homolostrata and so, finally, as taxonomoids
and characters. It is, therefore, understandable how the term used at the end of
the process can be applied ambiguously, with little apparent confusion, to the
beginning, particularly as the only difference between homolostrata,
taxonomoids and characters is theoretical: the former becoming the latter when
spread is determined. Thus, defining a homolostratum also defines the
taxonomoid and character it later becomes.
Although understanding how the confusion has arisen offers some excuse for
its existence, it is of obvious importance that it be eliminated from taxonomic
theory. I can understand, but not accept, that this may seem to be of little
immediate practical significance, because, after all, we have lived in ignorance
and confusion with no obvious ill-effects, so far. However, clarification is even
more important to the systematic analysis of the patterns of taxonomy that tell us
so much about evolutionary history, particularly that part which identifies
cladistic branchings in their relative chronological sequences.
SYSTEMATICS: INTERPRETING THE PATTERNS OF TAXONOMY
The completed taxonomic process has revealed the correlation pattern of
characters and individuals, which can be summarized as a stratigram. This is a
diagram with lines at right angles; the verticals representing individuals or taxa,
and the horizontals homolostrata, taxonomoids and characters occurring in
some or all individuals. Like the stratigramy from which it derives, a stratigram
is a phenetic (non-mathematical) representation of what is known, formed
without a hypothetical time dimension of evolutionary history. The next step is
to interpret and explain the patterns. This is the role of systematics, which is made
even more difficult than it intrinsically is by the confusion in terminology. Let us
consider what systematics involves.
Systematic analysis only makes sense on the basis of evolution, which I accept
as given and do not consider further. This does not, however, imply that I agree
with those, such as Mayr (1969), Wiley (1981) and Ax (1984, 1987), who argue
that such analysis also depends directly upon speciation. It does not, as I will
show. The crucial consequence of evolution, and the basis of systematics, is that
homology can be attributed to evolution. It follows that the patterns of
homolostrata spread give information about phylogeny. T o establish such
patterns is, therefore, crucial but is not as easy as the outline given above may
have implied, because of the possibility of convergence/parallelism, discordant
rates of evolutionary change and apparent cases of homology that are actually
analogies; all in addition to inadequate or biased data. None of this is made any
easier to overcome by the confusion about how it is supposed to be done.
Returning to the model, the spread of characters across individuals has been
established, and the revealed pattern expressed as a stratigram (Fig. 1). For
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W. G . INGLIS
Figure 1. Stratigram showing phenetic patterns of homolostrata spread across individuals:
horizontal blocks represent characters and vertical lines individuals.
simplicity the example consists of four individuals, each represented by a
vertical. These are linked in pairs by homolostrata, strictly characters, found in
both; represented by the horizontal lines at ‘5’ and ‘6’.Then all four, and both
pairs, are also bound by homolostrata, strictly taxonomoids, common to them all
at ‘7’.
Because the four initial individuals are the result of evolution through time,
the taxonomoids in common indicated by the transverse bar ‘7’, in conjunction
show that something happened in
with the two blocks of characters a t ‘5’ and ‘6’,
the history of all four individuals. Put another way, all four individuals have part
of their phylogeny in common and are the result of a happening which altered
their structure at the same time in their shared history. The altered, i.e. posthappening, conditions are now indicated by the characters ‘5’ and ‘6’,and the
ante-happening by the taxonomoids ‘7’.
Similarly, the double spread of the ‘5’ and ‘6’characters, in conjunction with
the four blocks at ‘1-4’’ indicates two further happenings, each of which led to a
pair ofindividuals: 1 & 2 and 3 & 4. It can also be deduced that the happening
that separated taxa ‘5’ and ‘6’ occurred before those that separated ‘1’ from ‘2’
and ‘3’ from ‘4’;but we cannot tell on the data available whether the split ‘1-2’
occurred before, after, or at the same time as ‘3-4’. Finally, we know that the
taxonomoids ‘7’ contain some characters that will only be revealed when a
further group or taxon is available at the appropriate level of spread.
In this way, the pattern of hierarchized character and taxonomoid spread
which establishes four individual taxa and three higher taxa in a hierarchical
array gives information about their phylogeny. It tells us that three things
happened during that evolutionary history, and something of the chronological
sequence in which these took place. The vertical lines of the individuals in the
stratigram, therefore, correspond to lines of phylogeny, such that characters of
greater spread across individuals indicate a condition that existed earlier than
that, or those, indicated by sets of contained (subsidiary) characters of lesser
spread. All these results can be derived directly from a wholly phenetic
taxonomic procedure which only reorders the original data, on the basis that
evolution has occurred and that homology reflects evolutionary relationships.
It is important to note that a stratigram has turned out to be as useful in
practice as in theory, because it shows completely and without distortion the
distribution of the homolostrata and characters across the individuals to which
they belong. Further, a stratigram contains no prior assumptions about
THE CHARACTER MYSTERY
131
A
0
b
Figure 2. Cladistic equivalence of a stratigram. a, Stratigram of two species with six individuals
each, seven specific characters (P) and seven (A) in common; b, equivalent cladogram with
individuals replaced by phylogeny lines. A, Ante-happening characters; P, post-happening
characters; H, empty cursor level of stratigram and corresponding position of cladistic happening.
evolution or speciation and, because none of the vertical lines meet, gives no
misleading impression that it represents cladistic branching or evolutionaryphylogenetic change.
SYSTEMATIC ANALYSIS
The systematic analysis of a stratigram can be simplified to a three-taxon
model in which two terminal taxa have homolostrata in common which form the
third taxon at the next higher level (Fig. 2a). Because there must have been a
cladistic happening between the level of greater spread and that of lesser, the
stratigram can be redrawn as a Y-shaped cladogram (Fig. 2b). Here the
occurrence of characters is represented by bars across the arms, and the
bifurcation indicates the happening. What can we deduce about the history of
the terminal taxa? Before considering this question, however, note that although
I refer to characters in what follows, the same conclusions can be reached when
the higher taxon reflects taxonomoids.
Five conclusions can be drawn: ( 1 ) a phylogenetic happening is identified by a
pair of taxa being members of the same higher taxon: that is, having characters
in common; (2) of the characters bracketing the happening, those of greater
spread (i.e. in the lower arm) reflect ante-happening conditions and those of
lesser spread (i.e. in the upper arms) reflect post-happening conditions; (3) the
vertical dimension of the cladogram only indicates a relative temporal sequence,
and so chronology of evolutionary history, or phylogeny; (4) the deduced time
scale is relative and gives no indication of how long a happening lasted, or when
it occurred in time; (5) the number of events of change represented by a
happening cannot be deduced from a cladogram (or a stratigram), because more
than one event may have been involved, rather than the single event (speciation)
implied by most cladistic theory and analysis.
Many of these conclusions will be readily accepted. The problems lie in the
terms used to describe them, because of the theoretical assumptions built into
other existing definitions. That confusion can, however, be largely overcome by
presenting the situation in simple language with no theoretical content or bias,
I32
W. G. INGLIS
using terms that have not been used by any of the polemical schools of systematic
theory.
Because a cladistic happening is located between two levels of a hierarchy
corresponding to two (terminal) taxa with one taxon, preferably the next higher,
common to both, it follows that the characters of the lower pair of taxa must be
post-happening (Ph) and those shared by both must be ante-happening (Ah).
Applying this logic progressively up or down a known hierarchy, each level in
turn can represent Ah and Ph characters, and vice versa (Fig. 2). From this it can
be further deduced that the intervening ‘empty’ or ‘happening level’ between each
category level corresponds to a cladistic happening; and that the higher
happening levels correspond to happenings that occurred earlier and the lower
later in the chronological sequence of phylogeny branching, using the
terminology for cladistic chronology established elsewhere (Inglis, 1988).
Because definitions of systematic terms usually, in my opinion unnecessarily,
rely on some model of evolutionary change or speciation theory, before those
implied by this model can be finalized three problems remain: (1) Do both
characters and taxonomoids establish the existence of a taxon and so reveal a
cladogenetic happening?; (2) What does such a happening represent?; and (3)
What terminology best reflects the identification of cladogenetic sequences by
character spread and their subsequent systematic interpretation?
Firstly, while the difference between characters and taxonomoids was not
recognized until this analysis, the distinction is of long implied standing,
indicated by insisting that only characters that distinguish a taxon from all
others should be used in its diagnosis. This precept is certainly useful on grounds
of economy, simplicity and aesthetics. But it can only be applied because any
strict diagnosis also includes all its taxonomoids, by implication, because these
are represented by the higher taxa of which that under consideration is a lower
member. Put briefly, a diagnosis always begins with the name of the next higher
taxon or taxa. Examples from Ax (1987) demonstrate this argument.
Ax (1987: 153), in agreement with Hennig (1966), claims to be able to
distinguish the diagnostic features (i.e. characters) of a taxon from its
‘constitutive features’ (i.e. evolutionary novelties or autapomorphies), and tries
to demonstrate the difference with three examples, of which I will consider his
first two: Mammalia and Crustacea. Ax contends that diagnostic and
constitutive features in mammals are the same, and demonstrates this by listing
the strictly diagnostic features of the taxon. He then concludes from this that
phylogenetic (cladistic) systematics interprets these as “evolutionary novelties
acquired only once in the stem lineage (presumably the evolutionary history) of
the Mammalia”. That is, in Ax’s terminology, the diagnostic characters are
autapomorphies (or Ph-characters mihi), relative to therapsids and amniotes. I
agree. Ax then argues that the Crustacea demonstrate the opposite, but to do so
has to treat them in a different way. This he does by claiming that the
traditional diagnosis of crustaceans contains eight characters which “provide in
every case an unmistakable combination of diugnosticfeutures” (my italics), not all
of which are limited to crustaceans. That is, they are not all autapomorphies.
Obviously. And by his mammalian standards they are not strictly diagnostic of
Crustacea either. Then, after arguing that only two of the items he listed are
restricted to crustaceans, Ax concludes that only these two ‘relatively
inconspicuous characteristics’ establish (i.e. diagnose) the Crustacea and show it
T H E CHARACTER MYSTERY
133
to be a ‘monophyletic taxon’; so that his initially diagnostic features are not also
autapomorphies. Absolutely correct, because the initial list is not strictly
diagnostic, but the two items that are, are also autapomorphies.
O n first reading I took this to be a strawman to illustrate some point that
eludes me, because the data do not support the conclusions. The Mammalia case
shows that characters do establish a happening, with the taxonomoids referred to
the Amniota, while the Crustacea example shows that taxonomoids, which is
what Ax lists, also do so when they include the diagnostic characters. This is
obviously so because, as Ax stresses, his mixture can only occur in crustaceans,
and so must establish one side of a happening. The major weakness of such an
extended diagnosis is that of complexity and aesthetics, because the Arthropoda
taxonomoids have not been removed from the Crustacea mixture, compounded
by Ax’s apparent annoyance that the diagnostic characters of Crustacea are, he
thinks, inconspicuous.
Secondly, it has been accepted by all practising systematists that appropriate
patterns of groups of characters indicate a historical branching happening of
some kind. However, the evolutionary school has tended to take such happenings
for granted, because they are obvious, and has paid most attention to the
associated and or subsequent changes. In contrast, many cladists insist that only
such happenings are of analytical significance, and that they typically represent
single speciation events. In this they are incorrect, as mammals and birds, among
many other groups of organisms, demonstrate; and some of their colleagues
agree. Thus, Mammalia are diagnosed by at least nine, and probably more,
characters, including hair, a single left aortic arch, and enucleate erythrocytes. It
is as certain as anything can be that, although now always together, these did
not all arise at the same time, in spite of the macro-mutationists and
punctuationists. Reliable fossil evidence shows the hard body changes between
mammals and therapsids occurred in stages, while logic argues that this must
also apply to the soft parts. If there be any doubt, Archaeopteryx makes the case
irrefutably for birds (De Beer, 1956), and my analysis of the Paracoelomata
shows the same conditions among invertebrates (Inglis, 1985).
Consequently, while stratigramy can establish a happening, it does not
establish in all (?any) cases how many lesser cladogenetic and other processes of
change are represented, or were involved. Two terms are, therefore, needed: a
happening is the cladogenetic step established by stratigramy; and an event is a
smaller step, several of which may be concealed within a happening. The
interesting questions, which cladists seem to deny themselves, are to establish
how many events are represented by a happening, the order in which these
appeared and the form they took.
Whether or not the distinction between happenings and events can be made in
practice is not important here. However, the possibility, I believe certainty, of its
existence makes the repeated reference to species and speciation events confusing
and misleading. As a result, like Wiley (1981) and others, I do not accept, even
as a working tool, the Axiom of the Matricidal Twins, whereby the mother
species dies in giving birth to her daughter and herself becomes her daughter’s
sister.
Thirdly, in considering the best terms to use when establishing and explaining
cladogenetic relationships, a major but generally ignored source of confusion
exists, because the appropriate character qualifying adjectives are determined by
I34
W.G . INCLIS
a level relative to the happening level under consideration. Thus, the
Ah-characters lie above that level and the Ph-characters lie below it. So, when
the level in which one is interested changes, it acts as a hierarchy cursor such that,
when moved up one level the originally Ah-characters become Ph, while on
moving it down one level the originally Ph-characters become Ah and the
previously Ah-characters disappear.
This complication and inconvenience lends weight to those who argue that
only synapomorphies are important. We can then refer to unqualified
(diagnostic) characters whose level in the hierarchy identifies the antehappening side of cladogenetic happenings, without the complication of all the
other ‘morphies’ and ‘features’. This is simple but unsatisfactory, because two
hierarchical levels are needed to reveal a happening. So I prefer to qualify
characters as ante- and post-happening, which also reminds us that one level lies
above and one below the level of hierarchy cursor under consideration.
There is, however, a further complication in that characters are also qualified
as primitive and advanced relative to the polarity of a sequence of anagenetic
changes. This is particularly so with evolutionary theorists who are primarily,
almost exclusively, interested in the anagenetic consequences of the cladogenesis,
which they take largely for granted, along with the results of other sources of
change. Many cladists seem also to be interested in such polarity, but it is not
always possible to be sure because of their terminology. In any case, further
complication is introduced, because the determination of anagenetic sequences
and their polarity is largely independent of cladogenesis, and so can be
established for homolostrata as well as characters. That is, anagenetic sequences
and their polarization do not depend upon prior pattern recognition
taxonomoids, characters or hierarchization. They can be, and frequently are,
recognized and polarized by morphologists and other analysts of comparative
data who have no interest in taxonomy or classifications. It is not even necessary
that homolostrata be recognized, it is only necessary that the components be
homologous.
So what does this tell us? I t clarifies the steps implicit in, and so the
terminology of, biological taxonomy. It confirms that multi-character taxonomy
is inevitably, at least in theory, from the bottom up, and that characters are
generated by stratigramy, but not automatically by taxa. I t establishes that in
one aspect of systematics a cladistic happening is represented by the ‘empty level’
between different taxon levels of the hierarchy of a stratigram, and that the
chronological sequence in which cladogenetic happenings occurred is
represented by the sequence of levels in the hierarchy.
I t follows that, using character in a strictly diagnostic sense, those of the higher
taxon relative to any empty or happening level are ante-happening (Ahcharacters) while those of the lower are post-happening (Ph-characters) . And
when the empty/happening level is used as a hierarchy cursor, happenings
represented by higher taxa occurred earlier in the cladogenetic chronology than
those represented by lower, included taxa. Finally, the anagenetic terms
primitive and advanced should only be used to describe the polarity of
transformation series of homologous components under their many guises,
because they are not necessarily nor solely adjectives qualifying characters.
A vast range of adjectives is given in textbooks, such as chemical structural,
embryological and so on, which also need not qualify characters, and actually
'THE CHARACTER MYSTERY
I35
make no significant contribution to theory or practice that cannot be covered by
saying that taxonomy can utilize any comparative data. There is, therefore, little
left to say about the essential terminology and procedures of taxonomy and
systematics. The steps have been clearly identified and defined and the
terminology is now unambiguous. It only remains to consider how the various
earlier vocabularies correspond, if at all, to that developed here, and how this
mess of ambiguity and confusion arose in the first place.
CONFUSION AND CLARIFICATION
Taxonomy, its spokesmen proudly proclaim, is the rock on which all other
biology is built. The trouble has been that no-one knew how to teach it or
explain what it involved. Taxonomy is an art, they said, to be acquired by
apprenticeship and doing. This situation, we have been told more recently, has
been overcome with the development of a range of insights and associated
techniques not available to earlier generations. These, it has now turned out, are
just as confused as anything that went before, even on the evidence and
arguments of their own practitioners. The trouble is and has always been that
taxonomists, while good at producing classifications, have not understood what
they were doing, and so have been incapable of telling others how to go about it.
Interminable fights about the true method, the true definitions, and the true
results to be aimed for have resulted, as shown most recently by the polemics of
cladists in all their guises. None of this is new. I have yet to read a textbook on
taxonomy (most of which only deal with systematics) which makes complete
sense, or matches what I or anyone else does, or could do, in practice. The
analysis developed here shows why. Our understanding of procedures has been
unclear and our terms ambiguous and confusing, when not contradictory.
A number of questions remain, the answers to which may ensure that
confusion neither continues nor returns. How did the confused mess arise in the
first place? How have taxonomy and systematics been carried on for so long in
spite of it? How useful are existing terms? How do different terms correspond, if
at all? How reliable are existing classifications? O f these the last is most
important, because the work of all biologists depends upon the answer.
The first two questions reflect the ease with which our minds carry out
practical taxonomy, biological and otherwise. Much of what we do is so innate
that we do not consciously know that we are doing it, so that the confused
terminology and the procedures given in textbooks of all ranges of opinion are
not a handicap. They are just ignored. This conclusion may be unexpected, yFt
should not be, because taxonomy is only a formalized extension of the way in
which our minds generalize about and order the data they receive from the
world around us. Basic to all this is our inherent ability to recognize that
condition of identity between things and parts of things that are not identical in
appearance, structure and form. The result biologists term homology,
philosophers universals, and psychologists concepts and schemata. Without this
all taxonomy is impossible.
Scientists do not like to acknowledge that their craft is based on such
intangibles, and biologists try to escape the impasse by defining homology, as
with many other terms, on a theoretical basis, mainly some view of how
I36
W.G . INGLIS
evolution took place. While this approach seems to give intellectual satisfaction
to many of us, it is spurious and misleading particularly when applied to
taxonomy and systematics where homology is crucial, yet can only be established
as a spontaneous in-mind relationship by observation and comparison.
Like all those forced by their discipline to deal with, and so attempt to
understand, concepts of this kind, biologists have difficulty in deciding and
describing what homology is as a real and concrete general relationship. As a
result, when not synonymized with similarity (which it certainly is not),
taxonomic or practical homology is not easily defined in abstract terms and so is
always demonstrated by examples. The difficulty arises, as with all concepts (see
Smith & Medin, 1981), because we recognize and so establish the identity it
covers without conscious thought, and no-one knows how we do it. Yet, in spite
of that, it is not going too far to say that anyone without the ability would be
ineducable, and would certainly be viewed as abnormal, if not subnormal. The
corollary is that taxonomy is innate and simple in practice, and its
hierarchization is spontaneous, so that its practitioners have never needed to
analyse throughly what they do. They just do it. The consolation is that there is
no other way of recognizing concepts by biologists, chemists and everyone
(Inglis, 1989).
I t follows that definitions of taxonomic terms must always describe, because
they can only describe, results obtained in practice. In this way: components are
bits-and-pieces of distinct appearance, distinguished from other bits and-pieces
of the same individual by inspection and subsequent delimiting definition;
homology is a relationship of identity between corresponding components of two
or more individuals spontaneously established by practical examination and
comparison; characters are defined homolostrata, or states of homology, shown
by practical stratigramy to be restricted to a group of individuals or taxa; and
hierarchy is the outcome of the observed fact that some characters have greater
spread than others across members of the same group of individuals.
In systematics the situation is completely different. This is rarely clear from
the literature, because the same taxonomic terms continue to be used for the
same things. The definitions in systematics, however, are given in theoretical
terms based on some view of evolution, in spite of the fact that the things to
which they apply can still only be identified as in taxonomy. It follows, therefore,
that systematics is wholly dependent upon taxonomy for most of its vocabulary
and all of its raw materials, including characters, taxa and hierarchization.
This can only be done because of the linkage through homology, the property
without which neither discipline is possible. So, taxonomy begins with
provisional conceptual homology, which is then judged and verified by the
consistency of the correlation patterns of homolostrata established by the
classifications produced by stratigramy. As a result, while systematics relies upon
the taxonomic patterns of homolostrata spread (i.e. characters) to establish
cladogenetic happenings in their chronological sequences, the homology
identities on which this depends derive their value from the judgement that has
already been made of them by the taxonomic procedures themselves. In this
way, taxonomy gives systematics its raw material in an ordered form, with an
assessment of its reliability.
Systematics, because of evolution, now attributes homology to common
THE CHARACTER MYSTERY
I37
ancestry and uses the spread of homolostrata as evidence for cladogenetic
happenings in the shared phylogeny of all the individuals with characters in
common. Replacement systematic definitions are, therefore, applied to these and
the other terms developed for use in taxonomy. Thus, homology is an absolute
relationship attributable to common phylogeny. Homology avatar is a general
identified example or expression of a condition of homology indicating
phylogeny in common. Homolostratum or homology state is an identified and
defined specified condition within homology absolutes whose distribution across
individuals allows cladistic events to be identified. Characters are homolostrata
of identified spread over individuals, or taxa, which enable groups with common
phylogeny to be established. Hierarchy is the nested (known or implied)
arrangement of taxa which enables cladogenetic events in their appropriate
phylogenetic chronological sequences to be identified. Taxonomoids are of lesser
importance because, as a group, they fulfil all the functions of characters,
although less economically and artistically.
The identification of cladogenetic happenings by characters depends upon
distinguishing between ante-happening (Ah) characters of greater spread, and
post-happening (Ph) characters of lesser spread within the same group of
individuals, relative to a specified ‘empty’ level of the hierarchy cursor, because
characters of greater spread are historically earlier than those of lesser included
spread. Among existing terms only those of the cladistic school resemble this
vocabulary, and then only in confusing and ambiguous part.
However, with new definitions which approximate to one of the existing
cladogenetic usages, synapomorphous characters can be brought into
correspondence with Ah-characters, autapomorphous with Ph-characters, and
symplesiomorphous with taxonomoids whose multi-level spread may or may not
have been identified. This shows that I was wrong when I equated
synapomorphous, as defined here, to diagnostic characters (Inglis, 1988). They
do correspond, but only in part, because autapomorphous characters are also
diagnostic, although symplesiomorphous characters need not be, since they can
also be taxonomoids.
Redefined in this way, synapomorphous and symplesiomorphous cannot
continue to be used as adjectives describing anagenetic polarity, as most of those
who employ them seem to believe. To prevent confusion, advanced and
primitive must always be used in such cases (Inglis, 1988). Further, if cladistic
terms are to be used, the habit of converting them into nouns (synapomorphy,
symplesiomorphy, etc.) must be avoided to prevent falling into the common trap
of treating them as something independent of the characters they qualify. This is
the cause of some of the confusion in cladistic theory, such as Patterson’s (1982)
argument that synapomorphy and homology (or vice versa) are the same thing.
That conclusion is wrong, because all characters and taxonomoids must be
homologous before they can be identified and interpreted in a cladistic, or any
other sense.
While cladistic adjectives can be made respectable by narrow redefinitions,
their range of confusing meanings is so great that I prefer to ignore them and use
the plain language terms (Ah and Ph, primitive and advanced) developed
above. If, as I suspect, authors continue to use the ‘morphies’ range they should
do so with more care than has usually been shown in the past, and then only
I38
W. G . INGLIS
after nominating which meaning they intend to convey. And those who persist in
using character: character state must recognize that they are referring to the
results of recognizing homology and not to diagnostic data.
CONCLUDING COMMENTS
Fortunately for the users of taxonomy, in spite of the amazing confusion that
has been shown to exist, none of this analysis affects or alters the classification
that is the end product. There are, as we are all too well aware, considerable
disagreements between the forms in which a classification is presented,
particularly in the number of categories used and the ranks given them by
cladists and evolutionists. However, such disagreements are due to systematic
analysis and the theory it is supposed to reflect, so that it is essential that the
bases from which the form of presentation of a classification derives are known
and given. That is, the story underpinning the classification should be given or,
as with cladistics, a well-known series of axioms accepted. This, as I have pointed
out elsewhere (Inglis, 1986), is a great potential strength of cladistics, but it still
remains a matter of choice if this advantage is considered to outweigh the
problems and limitations of the technique.
Be all that as it may, and I do not enter the argument here, it is also essential
that the technique employed is clearly presented and understood; which depends
upon the terms used to describe it being unequivocal and unambiguous.
Although this requirement could not be met in the past, as the examples given
above have shown, this is now possible, because it has been established that the
same steps in the same sequence are always involved in taxonomy. Further, these
have been identified and named, and the distinction between their operational
taxonomic and theoretical systematic meanings laid bare. As a result, taxonomy
can now be understood as a scientific procedure, rather than absorbed as an art,
although all experience suggests that we will continue to do it as before by
looking, conceiving and identifying patterns.
Nevertheless, the sequence of steps involved and the matching pairs of
taxonomic and systematic terms to be applied to each can act as a check on what
is being done, as well as illustrating the distinction between theoretical
systematics and practical taxonomy. All this is summarized in the following
definitions, where the taxonomic meaning is given first, followed by the
systematic and ending with some of the more common misapplications of the
term ‘character’.
Component is an identified and defined, distinct bit-or-piece of an individual
which, therefore, has no direct role in either taxonomy or systematics, until its
status relative to a component in another individual has been assessed as that of
homology: defined as character by Davis & Heywood (1963) and featured by Ax
(1984, 1987).
Homology, the crucial condition upon which all else depends, is (Tax.) absolute
in-mind conceptual identity between corresponding components in more than
one individual and (Syst.) a condition attributable to, and so indicative of,
evolutionary relationships.
Homology Avatar is (Tax.) an actual absolute due to recognizing homology
between components and (Syst.) an indication of broad commonality of
T H E CHARACTER MYSTERY
I39
phylogenetic continuity: equated to character by Sokal & Sneath (1963) and so
used by many others, including Ax indirectly.
Homolostratum or Homology State (Tax.) is a defined part of the range of
variation shown by, or found to occur in, a homology avatar whose spread across
individuals produces taxonomic hierarchization and (Syst.) is a unit of identity
whose distribution across individuals and/or taxa allows cladogenetic
happenings to be identified, generally in their chronological sequences: character
state of Sokal & Sneath (1963), Davis & Heywood (1963), and others: widely
called characters.
Hierarchy (Tax.) is a nested pattern of homolostrata X individuals found to
exist in nature by applied stratigramy which (Syst.) is a pattern due or
attributable to, and so indicative of, the cladogenetic relationships of the
individuals involved.
Character (Tax.) is a homolostratum whose spread is limited to and so is
diagnostic of a group of individuals forming a taxon, and so (Syst.) identifies
lines of common phylogenetic descent and, in conjunction with hierarchy,
enables the sequences in which cladogenetic happenings occurred to be largely
established: this term has been applied to almost everything in taxonomy and
systematics.
Tuxonomoids (Tax.) are a group of homolostrata which includes those
diagnostic of a taxon (Le. characters) and those with potentially greater, but as
yet unidentified, spread which (Syst.) fulfil, as a group, all the functions of
characters because they include the as yet unidentified characters of the taxon: a
new term, usually called characters by everyone.
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