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Analyzing Hominin Hominin Phylogeny: Cladistic Approach

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An understanding of the phylogenetic relationships among organisms is critical for evaluating the evolutionary history of their adaptations and biogeography as well as forming the basis for systematics. As the numbers of hominin fossils and hominin taxa have increased over the past 40 years, controversies over phylogeny have expanded and have become a hallmark of paleoanthropology. Concordant with the rise in taxonomic diversity, the increased use of phylogenetic systematics, or cladistics, has provided a valuable tool for reconstructing hominin phylogeny. Despite the widespread view that hominin phylogeny is a source of endless debate, there is a broad consensus regarding many aspects of hominin phylogeny.
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Analyzing Hominin Phylogeny: Cladistic
Approach
David Strait, Frederick E. Grine, and John G. Fleagle
Contents
Introduction ..................................................................................... 1990
Phylogenetic Diversity in Hominin Evolution ................................................ 1991
Reconstructing Phylogeny: The Rise of Cladistics ........................................... 1995
Cladistic Analyses of Hominin Phylogeny .. . . . . . . . . . . .. . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . .. . . 1997
Early Studies .. .............................................................................. 1997
Moving Toward a Rough Consensus ...................................................... 1998
Phylogenetic Implications of a “Golden Age” of Discovery (1994–2004) . .............. 1999
Discoveries Since 2004 and Implications for Early Hominin Relationships . . ........... 2005
Phylogenetic Relationships Within the Genus Homo ..................................... 2005
Conclusions ..................................................................................... 2007
Cross-References ..................................... .......................................... 2009
References .................................... ................................................ .. 2009
D. Strait (*)
Department of Anthropology, University at Albany, Albany, NY, USA
e-mail: dstrait@albany.edu
F.E. Grine
Department of Anthropology, State University of New York, Stony Brook, NY, USA
Department of Anatomical Sciences, Stony Brook University, School of Medicine, Stony Brook,
NY, USA
e-mail: fgrine@notes.cc.sunysb.edul
J.G. Fleagle
Department of Anatomical Sciences, Stony Brook University, School of Medicine, Stony Brook,
NY, USA
e-mail: john.fleagle@stonybrook.edu;jfleagle@notes.cc.sunysb.edu
#Springer-Verlag Berlin Heidelberg 2015
W. Henke, I. Tattersall (eds.), Handbook of Paleoanthropology,
DOI 10.1007/978-3-642-39979-4_58
1989
Abstract
An understanding of the phylogenetic relationships among organisms is critical
for evaluating the evolutionary history of their adaptations and biogeography as
well as forming the basis for systematics. As the numbers of hominin fossils and
hominin taxa have increased over the past 40 years, controversies over phylog-
eny have expanded and have become a hallmark of paleoanthropology. Concor-
dant with the rise in taxonomic diversity, the increased use of phylogenetic
systematics, or cladistics, has provided a valuable tool for reconstructing
hominin phylogeny. Despite the widespread view that hominin phylogeny is a
source of endless debate, there is a broad consensus regarding many aspects of
hominin phylogeny.
Introduction
Phylogeny is central to our understanding of virtually any aspect of an organism’s
biology. An appreciation of the phylogenetic relationships of an organism not only
provides a perspectiveon its place in the history of life and a basis for taxonomy but is
also critical for evaluating biogeography as well as ecology and behavior. The
adaptations of all organisms, even those as adaptively flexible as primates, are
inherited, and thus any proper statistical analysis of physiological adaptations requires
a consideration of phylogeny (Harvey and Pagel 1991; Purvis and Webster 1999).
In paleoanthropology at the beginning of the twenty-first century, the study of
phylogeny hardly needs to be justified. The first questions that are asked about any
new fossil discovery are “How is it related to us?” and “What does it tell us about
our evolutionary past?” Paleoanthropology has a reputation in the popular press as a
discipline characterized by disagreements over phylogeny, and this is perhaps not
unfair if one considers the seemingly diverse array of phylogenetic hypotheses
that have been proposed in the last two decades (Delson 1986; Walker et al. 1986;
Chamberlain and Wood 1987; Grine 1988; Kimbel et al. 1988,2004; Wood
1988,1991,1992; Skelton and McHenry 1992,1998; White et al. 1994;
Leakey et al. 1995,2001; Brunet et al. 1996,2002; Lieberman et al. 1996; Strait
et al. 1997; Strait and Grine 1998,1999,2001,2004; Asfaw et al. 1999; Senut
et al. 2001; Martino
´n-Torres et al. 2007; Berger et al. 2010; Organ et al. 2011).
Certainly much of the current interest in hominin phylogeny has been fueled by new
paleontological discoveries. Nine new early hominid species have been described
in the decades between 1994 and 2014 (White et al. 1994; Leakey et al. 1995,2001;
Brunet et al. 1996,2002; Asfaw et al. 1999; Senut et al. 2001; Haile-Selassie
et al. 2004; Berger et al. 2010). Many of these discoveries have been accompanied
by phylogenetic hypotheses, not all of which are compatible with each other.
However, the current importance of phylogeny in paleoanthropology and the
current understanding of hominin phylogeny are not just the result of new fossil
discoveries. They also reflect major theoretical and methodological advances in the
discipline during recent decades (Tattersall 1999). Thus, before discussing current
1990 D. Strait et al.
views on hominin phylogeny, a brief history of this endeavor during the last century
is provided. The term hominin is used to mean taxa that are more closely related to
humans than to any other primate.
Phylogenetic Diversity in Hominin Evolution
As numerous authors have emphasized, theoretical approaches to hominin phylog-
eny changed considerably through the course of the twentieth century (Fleagle and
Jungers 1982; Tattersall 1999; Gundling 2005). In the early decades, discussions of
hominin phylogeny were largely limited to evaluating whether the few fossil taxa
that were known at the time – Pithecanthropus erectus from Java, Cyphanthropus
rhodesiensis, or Rhodesian Man from Africa, Piltdown (Eoanthropus dawsoni)
from England, Neanderthals from Europe, and, after 1925, Australopithecus and
allied forms from Africa – were ancestral to living humans in their various forms.
Two distinct issues dominated the literature. First, were any of the various fossil
forms directly in the lineage leading to modern humans? As noted by Dobzhansky
in 1944, most authorities found that all fossils had features which precluded placing
them directly in human ancestry so that phylogenetic trees generally show a main
trunk leading from somewhere in the primate past to modern humans, with each
fossil taxon occupying a side branch leading to extinction (Fig. 1; Dobzhansky
1944; Tattersall 1999). Despite the lack of reliable estimates of the geological age
of any extinct taxa, they were generally suggested to have branched from the (main)
human lineage at different times, such that each documented some aspect of human
ancestry. However, all discussion concerned the relationship of the extinct taxa to
the main human lineage, with little discussion of the relationships among the extinct
taxa themselves. The notable exception to this was Weidenreich’s trellis model of
hominin evolution in which all living and extinct taxa were interconnected but with
temporal and geographic differentiation (Weidenreich 1946; Smith 1997). To a
large degree, these trees showing humans at the crown just reflect the fact that in the
early part of the twentieth century, as today, paleoanthropology was different from
other aspects of zoology in being by definition focused primarily on tracing the
history of a single organism, humans, rather than on the interrelationships of a large
group of more or less equally important taxa. After all, it is the human species that
writes the books.
However, as Gundling (2005) has argued, a related but distinct and in many cases
more important issue in the first half of the twentieth century was the taxonomic issue
of whether the various extinct species were hominins or apes. That is, where should
the ape-human boundary be drawn? In most cases, these two approaches yielded
concordant views. Fossils that were placed on the ape lineage were clearly not
hominins. However, in some cases fossil taxa might be considered offshoots of the
main human stem but still considered apes because they lacked the critical hominin
character. This was at the heart of much of the debate regarding the place of Piltdown
and Australopithecus in hominin phylogeny during the early part of the twentieth
century. In general, most researchers limited the human family to modern people.
Analyzing Hominin Phylogeny: Cladistic Approach 1991
Fig. 1 A phylogeny of Primates from Hooton (1931) showing a tree with human races at the crown and the few known fossil taxa as long side branches from
the main stem
1992 D. Strait et al.
As Tattersall (1999) has so eloquently discussed, all of this changed in
mid-century as paleoanthropologists began, however slowly, to adopt the tenets
of the New Darwinian Synthesis. Despite a growing record of new fossils, human
evolution was increasingly seen as a unilinear progression through time, with all
morphological diversity consigned to intraspecific variation due to geography or
sexual dimorphism (Buettner-Janusch 1966; Brace 1967). All of the divergent
branches from earlier in the century were incorporated into the main stem, and
human evolution was seen as one continuous chain of forms separated mainly by
time. The most extreme expression of this approach was Mayr’s (1950) inclusion of
all fossil hominins (including “robust” and “gracile australopithecines”) into a
single genus, Homo, with three species. Certainly there were other views, for
example, Robinson, following Broom, repeatedly argued that Paranthropus was a
separate lineage of hominin from Australopithecus and Homo, and Louis Leakey
argued from time to time that the ancestry of the human lineage was not to be found
among known fossils of the time. However, for much of the discipline, there was
little appreciation of phyletic diversity in human evolution (Fig. 2). This view of
limited phyletic diversity was very compelling. It was supported by the leading
authorities on evolutionary biology at the time, such as Mayr and Dobzhansky; it
brought paleoanthropology in line with the rest of evolutionary biology; and it
conformed well with what is seen in the world today: a single species of humans
with considerable intraspecific variation. Moreover, there were theoretical reasons
offered to justify a lack of phyletic diversity in a culture-bearing creature (Mayr
1950; Wolpoff 1971). And while extrapolating human behavior backward into the
fossil record may not be totally justified, especially for the Pliocene, it is not totally
unreasonable.
However, by the 1970s the unilinear view of human evolution was being
seriously challenged on several fronts and had become increasingly difficult or
even impossible to support. There were clearly two distinct hominin lineages
present in the Late Pliocene and Early Pleistocene at Olduvai Gorge and Koobi
Fora (Leakey and Walker 1976), and there was increasing evidence that in other
parts of the world modern humans had preceded or were contemporary with
European Neanderthals (Leakey 1969; Stringer 1974,1978; Howells 1975;Bra
¨uer
1982). Likewise, “new” analytical approaches emphasized the view that morpho-
logical changes over the past 3 Myr or so did not follow a simple temporal pattern of
increasingly modern features through time (Eldredge and Tattersall 1975). With an
increasing number of contemporaneous taxa, the potential phylogenetic complexity
of the hominin fossil record continued to grow and came to a head with the
description of Australopithecus afarensis (hereafter called Praeanthropus
afarensis) in 1978 and the ensuing debate over taxonomic diversity and phyloge-
netic relationships in early hominin evolution (Johanson et al. 1978; Johanson and
White 1979; Tobias 1980; Olson 1981,1985; White et al. 1981; Rak 1983; Kimbel
et al. 1984; Skelton et al. 1986). The level of debate over early hominin diversity
and phylogeny was heightened even further with the discovery in Kenya of the
Black Skull (KNM-WT 17000) several years later (Delson 1986; Walker
et al. 1986; Grine 1988; Kimbel et al. 1988; Wood 1988). Similarly, the debate
Analyzing Hominin Phylogeny: Cladistic Approach 1993
over the timing and geography of modern human origins and the relationship
between Homo sapiens, Neanderthals, and Homo erectus expanded in the 1980s
and has yet to abate (Smith and Spencer 1982; Mellars and Stringer 1989; Trinkaus
1989; Stringer 2002,2012a).
Fig. 2 A chart of hominin evolution from a major textbook from 1966 (Buettner-Janusch 1966)
showing the conservative lumper’s view on the left and the extreme splitter’s view on the right
1994 D. Strait et al.
Reconstructing Phylogeny: The Rise of Cladistics
The increasing evidence of taxonomic and phyletic diversity in hominin evolution
during the 1970s and 1980s coincided with the increasing prominence of phylogenetic
systematics or cladistics in paleoanthropology (Eldredge and Tattersall 1975; Luckett
and Szalay 1975;Delsonetal.1977; Tattersall and Eldredge 1977;Delson1985;
Skelton et al. 1986;Woodetal.1986; Grine et al. 1987; Grine 1988). The methods of
phylogenetic systematics, or cladistics, were developed by the German entomologist
Willi Hennig in 1950, but it was only with their publication in an English translation
(Hennig 1966) that his methods became widely known and applied in morphological
studies to understanding the phylogeny of all sorts of organisms.
Cladistics is a method of phylogenetic reconstruction premised on the notion that
not all morphological similarities are indicative of phylogeny. Rather, only those
similarities that are derived (i.e., novel) and inherited from a recent common
ancestor should be indicative of patterns of relatedness. In practice, it is difficult
(if not impossible) to discern, a priori, such features (called synapomorphies) from
other types of similarities such as primitive retentions (symplesiomorphies) or traits
that have evolved convergently or in parallel (homoplasies). Thus, cladistics relies
on the principle of parsimony to identify synapomorphies and, hence, to reconstruct
phylogeny. In a general sense, parsimony is the idea that the simplest explanation is
the best one because it makes the fewest assumptions. As applied to cladistics,
parsimony dictates that the best cladogram is the one that requires the fewest
number of homoplasies or independent appearances of the same feature. Parsimony
analysis is conventional in evolutionary biology (Kitching et al. 1998) but is viewed
with skepticism by some paleoanthropologists (Trinkaus 1990; Asfaw et al. 1999;
Hawks 2005). This skepticism is misplaced because, at its core, the logic of
parsimony is intuitive and not too dissimilar from that of “traditional” evolutionary
systematics (e.g., Olson 1981). More significantly, it provides a replicable criterion
for evaluating alternative hypotheses beyond preconceived notions of how things
should be (Tattersall 1996).
Consider an example in which a phylogenetic analysis is being performed on the
living hominoids (Hylobates,Pongo,Gorilla,Pan, and Homo) and a fossil hominin
(Australopithecus). Now consider a character with two states (knee joint valgus or
varus). The nonhuman apes and various outgroup taxa (other Old World higher
primates) have a varus knee, while Homo and Australopithecus have a valgus knee.
Given a cladogram in which Australopithecus and Homo are sister taxa (Fig. 3a),
what can be concluded about the evolution of the knee joint? There are actually
many ways in which the knee joint might have evolved. It is possible that a valgus
knee joint was present in all of the ancestors represented by the internal nodes of the
cladogram (Fig. 3b). Such a reconstruction requires that a varus knee joint evolved
in parallel in each nonhuman ape lineage. Alternatively, it is possible that a varus
knee joint was present at all of the nodes of the cladogram, including the one
representing the last common ancestor of hominins (Fig. 3c). This reconstruction
requires that a valgus knee joint would have evolved in parallel in Homo and
Australopithecus. Neither of these reconstructions is satisfying because both are
Analyzing Hominin Phylogeny: Cladistic Approach 1995
needlessly complex. There is instead a much simpler (i.e., more parsimonious)
explanation for the evolution of the knee joint, namely, that a valgus knee joint
evolved once in the last common ancestor of the hominins Australopithecus and
Homo, who subsequently passed that trait onto its descendants (Fig. 3d). Such a
reconstruction does not require any homoplasy.
Now consider an alternative cladogram in which Australopithecus is the sister
taxon of all of the living hominoids (Fig. 3e). In this tree, the most parsimonious
Fig. 3 Principles of cladistics. (a) Cladogram depicting possible phylogenetic relationships
among hominoids. (b) Pattern of character evolution in which a varus knee evolves many times
in parallel in each of the nonhuman hominoids. (c) Valgus knee evolves in parallel in Homo and
Australopithecus.(d) Most parsimonious pattern of character evolution in which a valgus knee
evolves once in the last common ancestor of Australopithecus and Homo.(e) Cladogram depicting
an alternative phylogeny. (f) Most parsimonious pattern of character evolution in the alternative
cladogram. a(¼d) is preferred over (e) because it involves fewer changes, and it is therefore the
most parsimonious
1996 D. Strait et al.
reconstruction of the evolution of the knee joint is one in which a valgus knee
evolved in parallel in Australopithecus and Homo (Fig. 3f). No other possible
reconstruction of character evolution in the knee joint requires fewer character
state changes or steps. Now consider that the two cladograms presented here
(Fig. 3a and e) represent alternative interpretations of hominoid phylogeny. How
can these cladograms be compared so as to select one of them as the better
hypothesis of phylogeny? Parsimony states that the preferred cladogram is the
one that is simplest, namely, the one that minimizes the number of homoplasies
required. Fewer homoplasies are required in Fig. 3d than in Fig. 3f, so the preferred
cladogram is the one in which Australopithecus and H. sapiens are sister taxa
(Fig. 3a). There is nothing controversial about this example, and both cladists and
noncladists would agree with the result. The only difference between this example
and an actual cladistic analysis is that most analyses would examine many charac-
ters at once. This is a great advantage of numerical cladistic analysis over “tradi-
tional” evolutionary systematics in which only a handful of characters tends to
strongly influence the shape of phylogenetic trees. Even more significant is the fact
that cladistic studies make explicit assumptions and predictions so that analyses are
replicable, and the results are testable.
Cladistic Analyses of Hominin Phylogeny
Early Studies
The first cladistic analysis of hominin evolution was by Eldredge and Tattersall
(1975) who also coauthored a series of papers delineating various levels of phy-
logeny reconstruction from producing a cladogram, to creating a phylogenetic tree,
and finally an evolutionary scenario (Delson et al. 1977; Tattersall and Eldredge
1977). In the late 1970s and early 1980s, cladistic analyses in paleoanthropology
were relatively simple and often consisted of little more than producing a clado-
gram and identifying a few shared derived characters at each node (Olson 1978;
Andrews 1984; papers in Luckett and Szalay 1975; Delson 1985; Wood et al. 1986;
Grine et al. 1987). Nevertheless, this was major advance from much previous work
in primate phylogeny in that there was a clear effort to distinguish shared derived
features from shared primitive ones, and authors provided explicit morphological
justification for phylogenetic grouping at every level. Falsifying a set of relation-
ships based on a cladistic analysis generally requires identification of additional
morphological features that produce a different cladogram when analyzed. As
Tattersall (1999) has pointed out, the rise of cladistics has led to a tremendous
increase in the detailed documentation and analysis of hominin morphology.
The mid-1980s saw the first use of quantitative cladistic analyses in hominin
evolution. By using computer algorithms researchers were able to evaluate dozens
of characters and compare thousands of trees (or more), tasks that were
simply unfeasible otherwise. The first efforts to evaluate hominin phylogeny
using numerical methods were in an analysis of early hominin phylogeny by
Analyzing Hominin Phylogeny: Cladistic Approach 1997
Chamberlain and Wood (1987) and a study of the genus Homo by Stringer (1987).
Numerous subsequent analyses of the phylogeny of hominins and many other
groups of primates have used essentially the same methods (Fleagle and Kay
1987; Kay et al. 1997; Strait et al. 1997; Ross et al. 1998).
Moving Toward a Rough Consensus
The 1987 study of early hominin phylogeny by Chamberlain and Wood did not
include Paranthropus aethiopicus, which subsequently became the linchpin of
early hominin phylogeny. The first study to include this species was that of Wood
(1988), who examined the trait list provided by Walker et al. (1986) in their
description of KNM-WT 17000. Wood (1988) found that Paranthropus robustus
and Paranthropus boisei are sister taxa, that Homo is the sister taxon of this clade,
and that Pr. afarensis,P. aethiopicus, and Australopithecus africanus branch off in
sequence from the base of the hominin tree (Fig. 4a). Notably, the three “robust”
species are paraphyletic. A subsequent study by Skelton and McHenry (1992),
Fig. 4 Cladistic analyses of early hominins from various studies. (a) Cladogram of Wood (1988)
and Skelton and McHenry (1992). (b) Cladogram of Wood (1991,1992). (c) Cladogram of
Lieberman et al. (1996). (d) Cladogram of Strait et al. (1997) and Kimbel et al. (2004)
1998 D. Strait et al.
using a more extensive trait list, found an identical cladogram. Wood (1991,1992),
using a data set composed entirely of craniometric measurements, found a most
parsimonious cladogram in which A. africanus is the sister taxon of Homo,
H. habilis sensu stricto and H. rudolfensis are sister taxa, and P. boisei and
P. robustus are monophyletic (Fig. 4b). Technically, Wood’s (1991,1992) clado-
gram does not include P. aethiopicus, but it is reported in the text of his analysis that
this species is the sister taxon of P. boisei. Lieberman et al. (1996) found a most
parsimonious tree (Fig. 4c) in which Paranthropus is paraphyletic, P. robustus and
P. boisei are sister taxa, and A. africanus is nested within the Homo clade.
Subsequently, Strait et al. (1997) found a cladogram in which Paranthropus is
monophyletic and the sister taxon of Homo (Fig. 4d). Recently, an independent
analysis by Kimbel et al. (2004) has largely corroborated Strait et al.’s (1997)
results. Kimbel et al. (2004) found two equally parsimonious trees: one is equiva-
lent to those of Strait et al. (1997) and the other differs only in placing A. africanus
as the sister taxon of the Paranthropus clade.
The analyses noted above appear to differ from each other, but in fact they are
similar to a much greater degree than is generally acknowledged. The results of
Strait et al. (1997) and Kimbel et al. (2004) differ from those of Wood (1988) and
Skelton and McHenry (1992) only with respect to the relationships of
P. aethiopicus. They differ from those of Wood (1991,1992) principally with
respect to the relationships of A. africanus. The most parsimonious tree of
Lieberman et al. (1996) differs from that of Wood (1988) and Skelton and McHenry
(1992) only with respect to A. africanus. Thus, these cladograms disagree primarily
with respect to only two taxa, A. africanus and P. aethiopicus. There are also
disagreements concerning the exact relationships of H. habilis and H. rudolfensis,
but all analyses that include these taxa place them at the base of the Homo clade. In
short, it appears as if cladistic analyses of early hominins are converging on a
common set of relationships. It would be an overstatement to claim that the pattern
of early hominin phylogeny is known, but insofar as repeatability is a key compo-
nent of any scientific result, it would appear that the broad strokes of early hominin
phylogeny are perhaps better understood than commonly acknowledged.
Phylogenetic Implications of a “Golden Age” of Discovery
(1994–2004)
There were many discoveries of new fossil hominin species in the decade between
1994 and 2004 (White et al. 1994; Leakey et al. 1995,2001; Brunet et al. 1996,
2002; Asfaw et al. 1999; Senut et al. 2001; Ward et al. 2001; Haile-Selassie
et al. 2004). Despite the common refrain that phylogenetic debates can be resolved
by the discovery of new fossils, many of these new finds raised rather than resolved
phylogenetic questions. Although most of the new discoveries were accompanied
by a phylogenetic hypothesis, those hypotheses often only addressed the relation-
ships among a few hominin taxa. Moreover, these hypotheses were potentially
difficult to test using cladistic analysis because they specified ancestor-descendant
Analyzing Hominin Phylogeny: Cladistic Approach 1999
relationships without specifying sister-group relationships. At the time, the remains
of many of these new hominin taxa were not yet thoroughly published, and further
documentation of their morphology will doubtless permit more complete analyses.
However, on the basis of information available so far, one can use cladistic analysis
to test many of the initial hypotheses that have been proposed because
phyletic relationships imply sister-group relationships. In particular, it is an
accepted principle that a species can only be an ancestor of another taxon if it is
the sister species of that taxon and if its character states resemble those
reconstructed as being present in the relevant internal node of a cladogram
(Szalay 1977; Smith 1994; Wagner and Erwin 1995; O’Keefe and Sander 1999).
Accordingly, the phyletic hypotheses that have been proposed for many recent
fossil discoveries in hominin evolution can be evaluated through reconstruction of
sister-group relationships (Fig. 5).
Strait and Grine (2004) tested many of the hypotheses generated by these new
taxa. They found that the pattern of hominin phylogeny is unbalanced such that
many species branch off by themselves from the base of the tree, while the top of
the tree is dominated by two multispecies clades, Homo and Paranthropus (Fig. 6).
Sahelanthropus and Ardipithecus are, respectively, the first two branches of the
tree, with subsequent branches successively represented by Australopithecus
anamensis,Pr. afarensis,Australopithecus garhi, and A. africanus.If
Kenyanthropus platyops is a valid species, then its position within the Homo +
Paranthropus clade is unresolved; it is either the sister taxon of the rest of the clade
or of Paranthropus. Relationships within Paranthropus are also unresolved, with
P. boisei being the sister taxon of either P. aethiopicus or P. robustus. The position
of H. habilis relative to H. rudolfensis is unresolved, but it is clear that one or the
other is the basal branch of the Homo clade. Homo ergaster and H. sapiens are sister
taxa. These results are consistent with certain of the hypotheses offered in the
original descriptions and inconsistent with others.
Ardipithecus ramidus
At the time of its description (White et al. 1994), Ardipithecus ramidus was
the oldest and most morphologically primitive hominin species then known.
White et al. (1994) suggested that Ar. ramidus lies near the ancestry of all other
hominins and that it may be the actual ancestor of those species. A cladogram
consistent with this hypothesis would place Ar. ramidus as the sister taxon of a
clade that includes all other hominin species (Fig. 5a). Strait and Grine (2004)
found that Ar. ramidus is the sister taxon of all hominins except Sahelanthropus
(Fig. 6). These results support the hypothesis of White et al. in a general sense
insofar as Ar. ramidus branches off near the base of the hominin tree, if not
necessarily at the basal node.
Australopithecus anamensis
The following year, Leakey et al. (1995)describedAustralopithecus anamensis as a
species intermediate both chronologically and morphologically between Ar. ramidus
and Pr. afarensis. Leakey et al. (1995) and Ward et al. (2001) have suggested that
2000 D. Strait et al.
A. anamensis is more closely related to later hominins than is Ar. ramidus and may be
directly ancestral to Pr. afarensis (Kimbel et al., 2006). A cladogram consistent with
this hypothesis would depict A. anamensis as diverging from a higher node on the
hominin tree than Ar. ramidus and as the sister taxon of all later hominins (Fig. 5b).
An alternative topology that might also be consistent with the phyletic hypothesis
Fig. 5 Phylogenetic hypotheses associated with recently discovered hominins
Analyzing Hominin Phylogeny: Cladistic Approach 2001
would make A. anamensis the sister taxon of Pr. afarensis. Strait and Grine’s (2004)
results (Fig. 6) are consistent with the hypothesis that A. anamensis is the sister taxon
of all hominins except Ardipithecus (and, presumably, Sahelanthropus).
Australopithecus bahrelghazali
The discovery of Australopithecus bahrelghazali was notable primarily because it
represented the first early hominin species found in central Africa. Brunet
et al. (1996) did not offer a detailed phylogenetic hypothesis for A. bahrelghazali
but rather noted merely that the species is more derived than the contemporaneous
Pr. afarensis. Not all workers accept that A. bahrelghazali and Pr. afarensis are
distinct species (Kimbel et al. 2004). This species was not included in the analysis
by Strait and Grine because it is known from only a few remains.
Australopithecus garhi
As described by Asfaw et al. (1999), Australopithecus garhi preserves an unex-
pected combination of cranial and dental characteristics. In particular, it has
megadont molars and premolars but a relatively primitive-appearing face and
neurocranium. Asfaw et al. (1999) implied that A. garhi could be a suitable ancestor
for Homo, although they noted that the exact phylogenetic relationships of this
species remained unresolved. They presented a cladogram in which A. garhi,
A. africanus,P. robustus,P. boisei,P. aethiopicus, and Homo form a clade but in
which relationships within that clade were left unresolved. However, they presented
four phyletic trees, and in three of those, A. garhi was posited to be an ancestor of at
least some members of the genus Homo. Moreover, they (Asfaw et al. 1999, p. 632)
state that “If A. garhi proves to be the exclusive ancestor of the Homo clade, a
cladistic classification would assign it to genus Homo.” Such a classification would
only be valid if A. garhi and at least some of the Homo species form a monophyletic
group, as in Fig. 5c. Furthermore, in reference to the morphology of A. garhi, Asfaw
et al. (1999, p. 634) state that “its lack of derived robust characters leaves it as a
sister taxon to Homo but absent many derived Homo characters.”
Fig. 6 Early hominin
cladistic relationships found
by Strait and Grine (2004)
2002 D. Strait et al.
Strait and Grine’s (2004) results are consistent with the hypothesis that A. garhi
belongs to a clade that also includes A. africanus,Paranthropus, and Homo, insofar
as A. garhi is reconstructed as the sister taxon of a clade comprising those taxa
(Fig. 4). In addition, the relationships of Ardipithecus ramidus,A. anamensis, and
Pr. afarensis are equivalent to those proposed by Asfaw et al. (1999). However,
Asfaw et al. (1999) also suggested that A. garhi may be ancestral to all or part of the
genus Homo. Cladistic analysis fails to find a sister-group relationship between
Homo and A. garhi (Fig. 6). Moreover, A. garhi is excluded from a clade that
includes only Homo,Paranthropus,A. africanus, and K. platyops. Thus, there is no
support for the hypothesis that A. garhi and Homo are sister taxa, so A. garhi is
unlikely to be the direct ancestor of Homo.
Orrorin tugenensis
Found in Late Miocene deposits (Senut et al. 2001), Orrorin tugenensis supplanted
Ar. ramidus as the oldest known fossil hominin. Senut et al. (2001) claim that on the
basis of dental and postcranial characters, O. tugenensis is the basal member of the
Homo clade, to the exclusion of australopiths. Moreover, they suggest that Ar.
ramidus is not a hominin but an ancestor of Pan. A cladogram consistent with these
hypotheses (Fig. 5d) would have Orrorin and Homo as sister taxa, a clade of all
australopithecines except Ardipithecus being the sister taxon of the Orrorin +
Praeanthropus +Homo clade, and Ardipithecus as the sister taxon of Pan.
Strait and Grine’s (2004) analysis did not include Orrorin because too few
characters are preserved in that species. However, their data set can be used to
examine the effect of making Ardipithecus the sister of Pan and the other
australopiths monophyletic (Senut et al. 2001). The most parsimonious tree
found by Strait and Grine’s data set for the hypothesis that Ardipithecus in the
sister taxon of Pan is 30 steps longer than that shown in Fig. 6. Considering
that Senut et al.’s (2001) hypothesis is based on only a few characters (e.g., molar
size, enamel thickness, details of the proximal femur), which cannot account
for so many steps, it is fair to conclude that this hypothesis is not favored by
cladistic analysis.
Kenyanthropus platyops
The discovery of Kenyanthropus platyops was notable because it demonstrated the
existence of multiple hominin lineages in the Middle Pliocene. Leakey et al. (2001)
noted that Kenyanthropus platyops appeared to share several derived character
states exclusively with H. rudolfensis. They posited (Lieberman 2001) that this
might imply that these two species had a particularly close relationship. A clado-
gram consistent with this hypothesis (Fig. 5e) would have K. platyops and
H. rudolfensis as sister taxa. Although the validity of the species diagnosis of
Kenyanthropus platyops has been questioned by White (2003), who has implied
that many of the defining features of the type specimen are artifacts of postdepo-
sitional distortion, others have found no reason to doubt its validity.
The results of the analysis by Strait and Grine (2004) are inconsistent with the
hypothesis that K. platyops shares especially close affinities with H. rudolfensis
Analyzing Hominin Phylogeny: Cladistic Approach 2003
even to the point of removing the latter from the Homo clade. Rather,
Kenyanthropus is the sister taxon of either Paranthropus or the Homo +
Paranthropus clade (Fig. 6). There is no strong evidence supporting the hypothesis
that H. rudolfensis and K. platyops are sister taxa, and thus the transfer
of H. rudolfensis to the genus Kenyanthropus is at present unwarranted. One
implication of these results is that some of the facial features shared between
H. rudolfensis and K. platyops may be primitive for the Homo +Paranthropus
clade, while others may be convergent. Another implication concerns the timing of
early hominin cladogenic events. If K. platyops is a valid species, then its age
(3.3–3.5 Ma) and cladistic relationships suggest that Homo and Paranthropus may
have diverged from other hominin taxa up to 700 kyr prior to the earliest known
specimens currently attributed to those genera (Suwa et al. 1996). It follows,
therefore, that this divergence would not be explained by the Turnover
Pulse Hypothesis (Vrba 1988) because the divergence would have predated the
desiccations event that she postulates to have occurred in Africa between 2.7 and
2.3 Ma. These two clades may have each diversified during this period, but their
origins are likely to have been earlier in the fossil record.
Sahelanthropus tchadensis
The title of “oldest hominin” now belongs to Sahelanthropus tchadensis (Brunet
et al. 2002). Brunet et al. (2002, p. 151) note that S. tchadensis appears to be “the
oldest and most primitive member of the hominin clade, close to the divergence of
hominins and chimpanzees.” The authors are cautious about the precise phyloge-
netic relationships of the species, but note the possibility that Sahelanthropus is the
sister taxon of all other hominins, including Ardipithecus. A cladogram consistent
with this hypothesis would have Sahelanthropus as the basal branch of the hominin
clade (Fig. 5f).
Brunet et al. (2002) discuss the possibility that Sahelanthropus is the sister taxon
of all known hominin species, including Ardipithecus. The Strait and Grine study is
consistent with this hypothesis insofar as Sahelanthropus was found to be the basal
branch of the hominin clade (Fig. 6). It also does not group with African apes as
suggested by Wolpoff et al. (2002).
Ardipithecus kadabba
Fossils attributed to Ardipithecus kadabba were first assigned to a subspecies of
Ardipithecus ramidus (Haile-Selassie 2001), but subsequent discoveries led to the
elevation of this assemblage to species status (Haile-Selassie et al. 2004). The
species is notable for its extremely primitive canine-premolar honing complex. Its
describers imply that it is the best candidate to be the sister taxon or ancestor of all
other hominins and that fossils of the other two known Miocene species,
O. tugenensis and S. tchadensis, are in fact representatives of Ar. kadabba.This
species was not included in the analysis of Strait and Grine (2004) because it is
currently known from only a few body parts.
2004 D. Strait et al.
Discoveries Since 2004 and Implications for Early Hominin
Relationships
The phylogenetic relationships described above collectively represent a reasonable
working hypothesis of early hominin phylogeny, but more recent discoveries and
descriptions of hominin fossils may necessitate important revisions in the near
future. In 2009, a relatively complete skeleton of Ar. ramidus and other fossils
from this species were comprehensively described (e.g., White et al. 2009). These
descriptions confirm that Ar. ramidus possesses a small number of derived cranial
traits that seem to place it within and near the base of the hominin clade. However,
as described, the species also seems to lack nearly all of the postcranial traits
traditionally associated with bipedal locomotion, as well as most of the traits seen
in living apes that are functional related to suspensory locomotion. The describers
of Ar. ramidus interpret this suite of characters to mean that the earliest hominins
were not descended from an ancestor possessing suspensory traits. While possible,
this hypothesis appears to be wildly unparsimonious, because it also implies that
many suspensory traits must have evolved in parallel in multiple ape lineages. It is
difficult to imagine cladistic analysis supporting this hypothesis but formal study
is needed. Indeed, in light of the new postcranial evidence, the possibility that
Ar. ramidus is not a hominin warrants further investigation, even if its hominin
status is ultimately upheld.
In 2010, partial skeletons of a new hominin species, Australopithecus sediba,
were discovered in southern Africa that similarly possess an unexpected mosaic of
primitive and derived traits. The species exhibits craniodental traits that may align
it with early Homo, but has postcranial characters (especially in the foot) that
appear to be more primitive than those in Pr. afarensis (Berger et al. 2010; Zipfel
et al. 2011). It has been hypothesized that it lies near the ancestry of Homo, but such
a position might imply extensive homoplasy in hominin postcranial traits.
A difficulty in assessing the phylogenetic significance of these new data is that
cladistic analyses of early hominins have traditional been based on cranial
rather than postcranial characters because several early hominin species lack
well-associated postcranial remains. Thus, it is difficult to quantitatively evaluate
how the new postcranial data will affect parsimony-based assessments of early
hominin phylogeny. Clearly, a research priority of the next decade will be to
formally incorporate postcranial data into cladistic analyses of early hominins.
Phylogenetic Relationships Within the Genus Homo
Compared with studies of early hominin evolution in the Late Miocene and
Pliocene, research on the phylogeny of Pleistocene hominins (Fig. 7) is complicated
by ongoing debates on the number of species involved. The extremes range
from those who, like Mayr in 1950, have argued for a single species in the genus
Analyzing Hominin Phylogeny: Cladistic Approach 2005
Homo (Wolpoff et al. 1994) – thus precluding any phylogeny within the genus – to
others who suggest the presence of more than 15 species (Tattersall 1999). How-
ever, the majority of researchers recognize, at least for the purposes of discussion,
between seven and nine species. Homo habilis,Homo rudolfensis,Homo ergaster,
Homo erectus,Homo heidelbergensis,Homo neanderthalensis, and Homo sapiens
are widely recognized, with Homo antecessor and Homo floresiensis more poorly
known and/or less widely accepted.
As noted above, the relationships of H. habilis and H. rudolfensis are poorly
resolved. On the basis of an assessment of adaptive differences between Homo and
Australopithecus, Wood and Collard (1999a,b) have argued that these taxa should
be removed from the genus Homo, although their suggestion has yet to be widely
adopted. Among other early Pleistocene species, there are ongoing debates over
whether Homo ergaster from Africa is more closely related to later species of Homo
than is the mostly Asian Homo erectus (e.g., Fig. 4b) or whether any of the early
species of the genus Homo can be distinguished at all (e.g., Wood 1994; Bra
¨uer
1994; Rightmire 1992; Lordkipanidze et al., 2013).
Fig. 7 Hypothetical
cladogram (a) and
phylogenetic tree (b)of
evolution within the genus
Homo (Modified from
Tattersall 1999)
2006 D. Strait et al.
Like studies of early Homo, studies of phylogenetic relationships among later
species of the genus Homo are bedeviled by problems of proper taxonomic alloca-
tion of fossils to be included in any analysis. Many researchers agree that the
descendant of the Early Pleistocene H. erectus (or H. ergaster?) is a Middle
Pleistocene taxon usually referred to as H. heidelbergensis (Rightmire 1998),
which in turn may have given rise to both Neanderthals and modern humans
(Fig. 7b). However, it has also been suggested that the immediate ancestor of
H. heidelbergensis is not H. erectus, but the poorly known H. antecessor from
the latest Early Pleistocene of Atapuerca, Spain (Bermudez de Castro et al. 2004),
and possibly Italy as well (Manzi 2004). The relationships between
H. heidelbergensis,H. neanderthalensis, and H. sapiens are also uncertain.
Although Neanderthals have traditionally been viewed as either a subspecies or
sister taxon of H. sapiens, many authorities now argue that H. heidelbergensis and
H. neanderthalensis are sister taxa or even a single anagenetic lineage with no clear
break (Arsuaga et al. 1997; Hublin 1998). From this perspective, H. sapiens is the
sister taxon of a H. heidelbergensis and H. neanderthalensis clade (Fig. 7a). In this
scheme H. sapiens is the descendant of a distinct early Middle Pleistocene taxon
from Africa, usually given the name Homo rhodesiensis. Stringer (2012b) has
recently argued that reconstructions of the population history of Middle Pleistocene
humans might be clarified by removing the hominins from Sima de los Huesos out
of H. heidelbergensis and instead grouping them with Neanderthals.
An interesting recent debate concerns the phylogenetic relationships of
H. floresiensis. Although once considered to be a dwarf descendant of Homo
erectus, there is tantalizing evidence from both cranial and postcranial anatomy
suggesting that it may, in fact, represent a H. habilis-like hominin whose lineage
pre-dates the appearance of H. erectus (Argue et al. 2009; Jungers et al. 2009).
More study is needed, however, and this, again, speaks of the need to incorporate
postcranial characters into cladistic analyses of hominins.
Conclusions
It is too soon to say whether a consensus will emerge concerning the phylogenetic
relationships of the hominin species described over the last two decades, not to
mention those likely to be discovered in the coming years. Strait and Grine’s
(2004) results on early hominin phylogeny need to be tested by other, independent
cladistic analyses, and a comprehensive phylogenetic analysis of the genus Homo is
long overdue. Postcranial characters need to be incorporated into future studies. New
fossils of almost all of these species are badly needed in order to provide a better
representation of characters and a better understanding of intraspecific variation.
Improvements in techniques to assess character independence, morphological inte-
gration, and developmental modularity (McCollum 1999; Ackermann and Cheverud
2000;Strait2001) will also greatly improve the accuracy of cladistic analysis. At the
heart of all attempts to understand hominin phylogeny are unresolved issues regarding
the identification of species in the fossil record (Tattersall 1986,1992,1996;
Analyzing Hominin Phylogeny: Cladistic Approach 2007
Kimbel and Rak 1993; Plavcan and Cope 2001). This is especially critical within the
genus Homo, in which genetic evidence has demonstrated that population history is
perhaps more complicated than might have been expected based on a consideration of
the fossil record alone (Green et al. 2010; Reich et al. 2010).
Despite these caveats, a broad consensus regarding the phylogenetic relation-
ships of many hominin taxa has emerged (Fig. 8). It is likely that disagreement will
persist as to the exact relationships among S. tchadensis,Ar. kadabba, and
O. tugenensis until they are known by more body parts that can be directly
compared, but most workers accept that these species all lie somewhere near the
base of the hominin tree. The greatest disagreement will probably focus on A. garhi
and K. platyops and the relationships of these species to the genus Homo, as well as
whether or not Ar. ramidus is a hominin. While there is broad general agreement
about overall phylogenetic relationships in later hominin evolution, there is less
consensus about the number of taxa that should be identified. The number and
relationships of the early species of the genus Homo remain a source of ongoing
debate (Wood and Collard 1999a,b; Wood and Lonergan 2008; Henke and Hardt
2011; Stringer 2012a), and there are various alternative interpretations concerning
the few fossils from the Early and Middle Pleistocene (Tattersall 1986; Rightmire
1998; Bermudez de Castro et al. 2004; Manzi 2004).
Some have argued that hominin phylogeny will never be resolved in a timely
fashion because of the many gaps in the fossil record (White 2002). That view is
unduly pessimistic. Of course there are gaps in the fossil record! Despite the fact that
knowledge of that record is constantly expanding, it will never be complete. That is
Fig. 8 A summary of the temporal span and phylogenetic relationships among fossil hominins
2008 D. Strait et al.
not an excuse for failing to do the best one can with the material that is available in
order to evaluate phylogenetic hypotheses. There is no doubt that the fossil record
samples only a portion of the organisms, including hominins, that have ever lived and
that new discoveries always document new, unanticipated aspects of evolutionary
diversity. This is why paleontology is such an exciting and rewarding field of study.
Despite this serendipitous sampling of the history of life, and ongoing uncertainties
regarding some taxa, cladistic analysis has led researchers toward a general consensus
of the phylogenetic relationship of many of the hominin taxa that can be documented
and remains the best hope for resolving future questions about hominin phylogeny.
Cross-References
General Principles of Evolutionary Morphology
Historical Overview of Paleoanthropological Research
Homo ergaster and Its Contemporaries
Homo floresiensis
Homology: A Philosophical and Biological Perspective
Later Middle Pleistocene Homo
Neanderthals and Their Contemporaries
Paleoecology: An Adequate Window on the Past?
Quantitative Approaches to Phylogenetics
Quaternary Geology and Paleoenvironments
The Earliest Putative Homo Fossils
The Miocene Hominoids and the Earliest Putative Hominids
The Paleoclimatic Record and Plio-Pleistocene Paleoenvironments
The Species and Diversity of Australopiths
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Reference
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... Cladistic analyses of hominin phylogeny based on craniodental characters consistently position A. africanus as more closely related to Homo than is A. afarensis (Dembo et al., 2016;Strait et al., 2015). Therefore, either (1) A. afarensis and H. sapiens independently evolved relatively larger lower limb joints (i.e., their similarities are homoplastic), (2) A. africanus and H. habilis evolved more apelike joint proportions from an ancestor with more human-like limb proportions (i.e., the similarities between A. africanus, H. habilis, and apes are homoplastic), or (3) A. afarensis is more closely related to Homo than are A. africanus and H. habilis (Figure 1). ...
... Our study provides a fresh perspective on alternative hypotheses for the evolution of limb joint proportions introduced by previous workers (McHenry and Berger, 1998;Green et al., 2007;Haeusler and McHenry, 2007). The reconstruction of patterns of hominin evolution relies on phylogeny, and, since the early adoption of cladistics, no quantitative analysis of hominin phylogeny has recovered a sister taxon relationship between A. afarensis and Homo (Dembo et al., 2016;Strait et al., 2015). The recovery of purported Homo fossils significantly predating the appearance of A. africanus and A. sediba may falsify hypotheses of exclusive ancestry and descent (Du and Alemseged, 2019). ...
... To visualize evolutionary scenarios, we conducted ancestral states using parsimony on a variety of phylogenetic hypotheses. These hypotheses included both formal cladistic analyses (Dembo et al., 2016;Strait et al., 2015;Mongle et al., 2019) and published hypotheses that have not been recovered in phylogenetic analyses (Asfaw et al., 1999;Wood and Schroer, 2017;Villmoare, 2018). ...
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The evolution of bipedalism and reduced reliance on arboreality in hominins resulted in larger lower limb joints relative to the joints of the upper limb. The pattern and timing of this transition, however, remains unresolved. Here, we find the limb joint proportions of Australopithecus afarensis , Homo erectus , and Homo naledi to resemble those of modern humans, whereas those of A. africanus , Australopithecus sediba , Paranthropus robustus , Paranthropus boisei , Homo habilis , and Homo floresiensis are more ape-like. The homology of limb joint proportions in A. afarensis and modern humans can only be explained by a series of evolutionary reversals irrespective of differing phylogenetic hypotheses. Thus, the independent evolution of modern human-like limb joint proportions in A. afarensis is a more parsimonious explanation. Overall, these results support an emerging perspective in hominin paleobiology that A. afarensis was the most terrestrially adapted australopith despite the importance of arboreality throughout much of early hominin evolution.
... (2) the earliest hominin foot fossils (Ardipithecus, Gona Ardipithecus, Burtele, StW 573) do not cluster together and instead represent distinct branches reflecting mosaic foot evolution and perhaps bipedal experimentation early in the hominin lineage; (3) a mixed assemblage at Sterkfontein member 4 is supported here, with some fossils (Sterk M4a) aligned with StW 573; (4) OH 8 is positioned within the Paranthropus clade, indicating that this foot probably belongs to P. boisei; (5) the A. afarensis foot is quite derived and clusters with Homo, which may indicate homoplasy in the evolution of the foot of A. afarensis and Homo We find Homo and Paranthropus to be sister clades, a result also supported using craniodental characters (Dembo et al., 2016;Strait, Grine, & Fleagle, 2015;Villmoare, 2018). The australopiths branch in a pectinate manner at the base of the Homo-Paranthropus clade, ...
... Ardipithecus is the sister group of all other hominins. The basal branching of Ardipithecus and the derived position of A. sediba have been supported in other phylogenetic analyses using cranial and dental characters (e.g., Berger et al., 2010;Dembo et al., 2016;Dembo, Matzke, Mooers, & Collard, 2015;Strait et al., 2015). A noticeable result that does not conform to the current phylogenetic consensus is the gathering of Pan, Gorilla and ...
... The first is that the shared derived foot anatomies in A. afarensis and Homo descend from a common ancestor with a similarly derived foot. Given recent craniodental cladistics work arguing against an A. afarensis-Homo clade (e.g., Dembo et al., 2016;Strait et al., 2015), an alternative interpretation is homoplasy in the foot bones of A. afarensis and fossil Homo, including the independent evolution of a large calcaneal tuber and mediolaterally flat talar trochlea (e.g., Prang, 2015a). We note in this context that the large calcaneal tuber is obtained in developmentally different ways in A. afarensis and in modern humans (DeSilva, Gill, et al., 2018). ...
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Bipedalism is a hallmark of being human and the human foot is modified to reflect this unique form of locomotion. Leonardo da Vinci is credited with calling the human foot “a masterpiece of engineering and a work of art.” However, a scientific approach to human origins has revealed that our feet are products of a long, evolutionary history in which a mobile, grasping organ has been converted into a propulsive structure adapted for the rigors of bipedal locomotion. Reconstructing the evolutionary history of foot anatomy benefits from a fossil record; yet, prior to 1960, the only hominin foot bones recovered were from Neandertals. Even into the 1990s, the human foot fossil record consisted mostly of fragmentary remains. However, in the last two decades, the human foot fossil record has quadrupled, and these new discoveries have fostered fresh new perspectives on how our feet evolved. In this review, we document anatomical differences between extant ape and human foot bones, and comprehensively examine the hominin foot fossil record. Additionally, we take a novel approach and conduct a cladistics analysis on foot fossils (n = 19 taxa; n = 80 characters), and find strong evidence for mosaic evolution of the foot, and a variety of anatomically and functionally distinct foot forms as bipedal locomotion evolved.
... Methods of phylogeny reconstruction can be divided into statistical methods requiring an explicit model of evolution, such as for example Bayesian phylogenetic methods based on Monte Carlo Markov chains (BMCMC) used by Dembo et al. (2016), and non-statistical methods such as cladistic Maximum Parsimony (MP) used by Caparros and Prat (2021) that do not require a model of evolution. MP is the most commonly used method of phylogenetic reconstruction in Paleoanthropology (Strait et al., 2015), and is an integral part of the Phylogenetic Systematics school of thoughts in taxonomy, commonly known as cladistics (Hennig, 1966). In essence, cladistics is the analysis of individual characters (anatomical or genetic) free to evolve independently with the application of the principle of maximization of the number of evolutionary novelties on the Initial Data S1 The initial complete data set will be called Data S1. ...
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Our protocol combines Maximum Parsimony and Phylogenetic Networks approaches to understand the phylogenetic relationships and evolutionary processes of hominin species that might have shared inheritance from multiple ancestors. By addressing the questions of pattern and process in human phylogeny, the protocol can be used to clarify the taxonomic definition(s) of diverse hominin groups and ascertain whether or not the mode of evolution of genus Homo is reticulate. Using high quality and informative phenotypic data sets is necessary to yield meaningful results. For complete details on the use and execution of this protocol, please refer to Caparros and Prat (2021).
... The arrows denote that one species serves as food for another. (b) A phylogenetic tree (dendogram), showing inter-specific relationships (after [72]). ...
Preprint
Measurement theory is the cornerstone of science, but no equivalent theory underpins the huge volumes of non-numerical data now being generated. In this study, we show that replacing numbers with alternative mathematical models, such as strings and graphs, generalises traditional measurement to provide rigorous, formal systems (`observement') for recording and interpreting non-numerical data. Moreover, we show that these representations are already widely used and identify general classes of interpretive methodologies implicit in representations based on character strings and graphs (networks). This implies that a generalised concept of measurement has the potential to reveal new insights as well as deep connections between different fields of research.
... The resulting selective pressures apparently led to increased survival of megadont varieties capable of feeding on tougher fruit and open woodland/open savannah food items. This is true for early hominins as well as numerous large eastern and southern terrestrial African vertebrate lineages at ~2.5 Ma (Turner & Wood 1993), and resulted in the phyletic splitting of Australopithecus afarensis into Paranthropus and Homo lineages after ~2.8 Ma (Bromage & Schrenk 1999;Strait et al. 2015). It appears likely that our ancestors had a eurybiomic lifestyle. ...
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We present a methodological phylogenetic reconstruction approach combining Maximum Parsimony and Phylogenetic Networks methods for the study of human evolution applied to phenotypic craniodental characters of 22 hominin species. The approach consists in selecting and validating a tree-like most parsimonious scenario out of several parsimony runs based on various numerical constraints. An intermediate step from tree to network methods is implemented by running an analysis with a reduced apomorphous character dataset that generates multiple parsimonious trees. These most parsimonious trees are then used as input for a Phylogenetic Networks analysis that results in consensus and reticulate networks. We show here that the phylogenetic tree-like definition of the genus Homo is a relative concept linked to craniodental characters that come in support of hypothetical Last Common Ancestors of the most parsimonious scenario, and infer that the Homo reticulate network concords with recent findings in paleogenomic research regarding its mode of evolution.
Chapter
Adaptation to the savanna and transition to bipedality probably triggered the divergence of the hominins from other apes in Central-Eastern or Southern Africa between 5 and 7 MYA. The human lineage (here identified with the genus Homo) appeared between 3 and 2 MYA, its earliest distinctive traits being increased brain size, the loss of fur, improved thermoregulation, and arm/torso anatomy adapted to high-energy throwing. Coercive suppression of conflict of interest probably favoured kinship-independent aggregation into cooperative groups. Cooperative hunting and social rearing improved the diet, thus providing the extra resources necessary for the development of larger and metabolically more active brains under selection pressure for higher cognition. In a complex network of mutual interactions, kinship-independent cooperation paved the way to the evolution of language and the emergence of culture, a body of shared knowledge and beliefs transmitted across generations. Culture accumulation and donated culture triggered cultural niche construction, the development of a continuously expanding environment, partly physical and partly cognitive and social, which was the main driver in the evolution of modern humans (Homo sapiens). Sapiens appeared in Eastern Africa around 200 KYA, migrated to the Middle East twice, around 100 and 70 KYA, and from there started a worldwide expansion about 60 KYA. Fire became embedded very early in human behaviour and was involved in almost all technological advances. The transition to food production, from about 11.5 KYA, was pivotal to the emergence of modern societies. Most genomic changes that distinguish humans from their primate relatives are in non-coding sequences with regulatory functions.
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The origin of Neanderthal and modern human lineages is a matter of intense debate. DNA analyses have generally indicated that both lineages diverged during the middle period of the Middle Pleistocene, an inferred time that has strongly influenced interpretations of the hominin fossil record. This divergence time, however, is not compatible with the anatomical and genetic Neanderthal affinities observed in Middle Pleistocene hominins from Sima de los Huesos (Spain), which are dated to 430 thousand years (ka) ago. Drawing on quantitative analyses of dental evolutionary rates and Bayesian analyses of hominin phylogenetic relationships, I show that any divergence time between Neanderthals and modern humans younger than 800 ka ago would have entailed unexpectedly rapid dental evolution in early Neanderthals from Sima de los Huesos. These results support a pre–800 ka last common ancestor for Neanderthals and modern humans unless hitherto unexplained mechanisms sped up dental evolution in early Neanderthals.
Article
Studying extant apes is of central importance to paleoanthropology. This approach is informative in inferring how hominin skeletal morphology reflects phylogeny, behavior, development, and ecological context. Traditionally, great apes have dominated the paleoanthropological literature as extant analogs for extinct hominins, to the exclusion of their phylogenetic sister group, the hylobatids. Phylogenetic proximity, large body size, and high encephalization quotients may have contributed to decisions to use great apes as models for hominins. However, if we reexamine hylobatids as extant models for extinct hominins—using modern phylogenetic, behavioral, and ecological data—this clade is uniquely poised to inform future frameworks in paleoanthropology. The following features make hylobatids strong analogs for extinct hominins: taxonomic diversity, the timing of diversification, hybridization between species, small body size, and reduced sexual dimorphism. Based on these shared features, hylobatids offer future opportunities to paleoanthropology, and provide a much richer extant analog than is currently recognized.
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A mandible and first upper premolar discovered in North Chad by the Franco-Chadian Paleoanthropological Project demonstrate for the first time the presence of an australopithecine west of the Rift Valley. The Chad hominid presents a combination of primitive and derived characters which distinguishes it from all other early hominid taxa and which suggests that this new species represents a clade independent since 4 Ma or more.
Chapter
Paleoanthropology attempts to describe the diversity of extinct primate forms, to interpret this diversity in a phylogenetic framework based on the distribution of shared evolutionary novelties, and to explain the emergence and transformation of novelties in terms of a positive causal relationship between changes in structure/function and enhanced organismal fitness (i.e., adaptation). These components may be viewed as a sequence of steps toward a “complete” explanation of evolutionary change, each step logically contingent on those preceding it. Thus, hypotheses seeking to explain the adaptive basis of evolutionary morphological change necessarily depend on the prior acceptance of a hypothesis of vectored phylogenetic change. In turn, a phylogenetic hypothesis must be grounded in some theoretical concept of the units of diversity, among which the pattern of phylogenetic relationships is sought.