1
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
MANUSCRIPT:
Title: The Fossil Records of Early African Homo
Byline: Kes Schroer and Chrisandra Kufeldt
Introduction:
Molecular and paleontological evidence suggests that modern humans first originated in
Africa as early as 250,000 years ago. However, fossil remains in Eurasia dating to at least 1.8
mya (million years ago) suggest that some of our ancient relatives had already migrated out of
Africa by the time modern humans emerged. Thus, the peopling of the world does not begin with
modern humans. Rather, the fossil record suggests a long history of previous occupations in
Africa and Eurasia.
In this review, we discuss the nearest fossil relatives of modern humans. The fossil
species we review include the early members of the genus Homo, a group within the broader
category of “hominins” (all primate species more closely related to modern humans than to any
other living taxon). Early Homo likely shared its environment with non-Homo hominins such as
Paranthropus, a taxon with a suite of morphological features distinct from the derived
characteristics of the genus Homo. When we speak of derived traits in Homo, we mean traits
shared with modern humans. In contrast, primitive traits are morphological features shared by all
hominins and therefore not unique to Homo. Both primitive and derived traits are combined to
define the morphology of a fossil taxon. “Taxon” (pl. taxa) refers to a hierarchical category and
although taxon is often equated with species, this is not necessarily correct. “Homo” is a genuslevel taxon while our species, Homo sapiens, is a species-level taxon. Because it is difficult to
establish speciation events for certain in the fossil record, we prefer to use the term taxon and
begin by reviewing the definition of the taxon Homo.
Definition: What is Homo?
In 1940, Franz Weidenreich proposed the inclusion of several hominin fossils in the
genus Homo on the basis of their morphological similarities with two well-established taxa of
Homo known at the time, H. sapiens and Homo neanderthalensis (Neanderthals). These
additional specimens were classified as Homo erectus. The addition of a new taxon to the genus
Homo necessitated an improved definition of the genus Homo. In 1950, Ernst Mayr proposed
that Homo was a genus of modern human-like creatures whose members showed morphological
evidence of increased brain size and bipedal locomotion. However, this definition was
unsatisfactory, for it would have included specimens belonging to, Australopithecus, a different
hominin genus established in 1925. Wilfrid Le Gros Clark expanded upon Mayr’s definition and
provided four critera for inclusion into the genus Homo: a minimum endocranial volume of 750
cc (cubic centimeters), evidence of tool use, evidence of a precision grip, and evidence of spoken
language. Additionally, he suggested that derived morphological traits of Homo included a
cranium with less robust muscular markings, a flatter (more orthognathic) face, a rounded dental
arcade with no evidence of a premolar-canine honing complex, smaller teeth, and adaptations for
bipedalism.
2
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
This description of Homo has undergone many revisions and interpretations, especially in
light of the discoveries of many more hominin fossils since the 1950s. Some of the modifications
to this definition are discussed in the text that follows, but it is important to note that researchers
today have the benefit of more fossils and more rigorous phylogenetic methods to assess the
evolutionary relationships of modern humans and fossil hominins. One prominent cladisticsbased definition describes the crania of members of Homo as possessing, relative to
Australopithecus, a thicker cranial vault, greater cranial vault height, reduced postorbital
constriction, increased contribution of the occipital bone to the cranial sagittal arc length; an
anteriorly-situated foramen magnum, reduced prognathism, narrow tooth crowns especially in
the premolars, and reduction in the length of the molar row (Chamberlain and Wood, 1987).
Another phylogenetic study found only four derived features common to all members of the
genus Homo – a larger brain, the absence of a nasal sill, reduced temporal lines, and fewer air
cells in the temporal squama (Strait et al., 1997). Though there are discrepancies between
analyses, definitions of Homo are becoming more specific and quantifiable.
In both historic and modern approaches to defining the genus Homo, there is a wellrecognized distinction between the earliest forms of Homo that still share many traits with
Australopithecus and intermediate forms of Homo that appear more like H. sapiens but have not
yet reached complete anatomic modernity. We refer to these groups as transitional Homo and
pre-modern Homo, respectively, and discuss the significance, morphology, and key fossils of the
taxa within these groups below.
Historical Background:
Transitional Homo – Homo habilis
Significance
From 1960-1963, a series of fragmentary fossils were found in Olduvai Gorge, Tanzania
that seemed to belong to a new Homo taxon. Despite some morphological similarity to younger
Homo remains, these fragments (OH 4, a mandibular fragment, and OH 6, cranial fragments and
an upper molar), were considered too incomplete to determine a new species. Instead, the
announcement was made after the discovery of OH 7, an associated find of fragmentary parietal
bones, a badly damaged juvenile mandible but with the tooth crowns in good condition, an
isolated upper molar, and hand bones. The discoverers of OH 7 noted derived traits shared
between this specimen and members of the genus Homo, but the endocranial volume of OH 7
was unusually small for Homo. The discoverers of OH 7 combined its announcement with a
revision to the criteria for membership in Homo that reduced the requisite endocranial volume to
only 600 cc and thus within the upper range of Australopithecus. This decision was met with
objection by other researchers.
Since OH 7 was found in the same stratigraphic level as primitive (i.e., Oldowan) stone
tools, it was dubbed Homo habilis, the Handy Man. In addition to proposing a new species of
Homo, the announcement of H. habilis changed our understanding of the depth of the
evolutionary history of the genus Homo. The stratigraphic level of OH 7 dates to 1.8 mya, a
million years earlier than the previously known emergence date of Homo.
Morphology
3
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
Some researchers argue that H. habilis marks the first evidence for derived features such
as encephalization (Tobias, 1966; 1971), a more modern human-like cranium and face
(Bromage, 1989), and reduction in the size of the tooth and jaw size (Vandebroek, 1969).
H. habilis appears especially distinct from Australopithecus in the shape of its cranial base
(Wood, 1996).
Until the discovery of potential tools at Dikika dating to 3.39 mya, H. habilis was also
considered the oldest tool-making hominin. H. habilis has some modern human-like features of
its hand bones that suggest the ability to craft tools. The trapezium, the wrist bone that articulates
with the thumb, has a broad articular surface that would have allowed for a wide range of medial
rotation, and H. habilis has broad apical tufts on the distal phalanges that suggest robust finger
tips (Napier, 1962; Tocheri et al., 2008).
However, some researchers consider the morphology of H. habilis too primitive for
inclusion in the genus Homo. With an average of 680 cc among specimens, the cranium of H.
habilis is only slightly larger than Australopithecus, and the crown areas of the cheek teeth are
not notably reduced. Even the bones of the hand appear less modern human-like than originally
believed. The phalanges are curved and robust, with fibrotendinous marks suggesting frequent
climbing. Some aspects of the wrist, including broad lunate and scaphoid articular surfaces, also
appear primitive. Whether or not H. habilis possessed the precision grip that defines modern
human hands cannot be reliably determined from the current evidence.
Whether or not emerging Homo possessed the striding gait of modern humans is also a
matter of debate. Although the foot of H. habilis (OH 8) possesses some adaptations for
supporting the body during bipedal walking, its morphology does not suggest a propulsive role
for the big toe. The foot overall retains ape-like morphology consistent with climbing, and the
femur has a knee-joint not well adapted for modern bipedalism. It is possible that H. habilis
shared a form of bipedalism with Australopithecus that was unlike the gait of H. erectus and later
H. sapiens. Recently, some researchers have re-opened the proposal that the OH 8 foot may not
belong to early Homo, but to Paranthropus boisei (Gebo and Schwartz, 2006).
Notable fossils
In addition to the type specimen OH 7, Olduvai has yielded many fragmentary remains of
H. habilis. Notable specimens include OH 8, dating to 1.76 mya. The fossils comprising OH 8
are a well preserved left foot (see above), some dental fragments, and the adult hand bones
originally grouped with OH 7. The foot is likely adult and therefore not part of the juvenile OH
7. However, some researchers argue that the foot is juvenile, in which case it could belong to the
same individual as OH 7, and the remains of a tibia and fibula (OH 35) may also belong to the
same individual (Susman and Stern, 1982). However, this unlikely as the discrepancies in joint
surfaces and the respective stratigraphic and spatial locations of OH 7, OH 8, and OH 35 are not
consistent with them belonging to the same individual.
Other discoveries of H. habilis at Olduvai include two fragmentary juvenile skulls (OH
13 and OH 16) a fragmented and distorted cranium (OH 24), and a partial skeleton (OH 62). The
skulls of OH 13 and OH 16 date to 1.7 mya, and the OH 24 and OH 62 date to at least 100,000
years earlier. The OH 24 cranium includes derived cranial traits distinct from Australopithecus
such as reduced postorbital constriction, an inverted V-shape formed by the lamboidal suture,
4
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
and a more modern human-like mandible. The cranial capacity, however, is small even compared
to the juvenile OH 7.
The OH 62 partial skeleton allows for a poor estimate of body proportions in H. habilis,
and the forelimb to hindlimb proportions are suggested to be more ape-like than those of
Australopithecus. Although these differences in limb proportions may be the result of
intraspecific variation, they may also be evidence that H. habilis did not share the locomotor
style of later hominins.
Beginning in the 1970s, transitional Homo remains were also recovered from the site of
Koobi Fora, Kenya (Figure 1). KNM-ER 1813 is a nearly complete cranium with a cranial
capacity of only 510 cc. It dates to 1.88-1.90 mya, although earlier dates have been proposed
(Gathogo and Brown, 2006). The incomplete skull KNM-ER 1805, which is possibly older than
1.87 mya, is similar to KNM-ER 1813 and both specimens are often designated as examples of
H. habilis. However, some researchers argue that some unusual features of the cranium and teeth
of KNM-ER 1805 preclude it from belonging to early Homo. A recent discovery at Koobi Fora,
the KNM-ER 42703 maxilla, dates to 1.44 mya, and expands the temporal range of H. habilis to
much later than previously thought.
Also found at Koobi Fora is KNM-ER 3735, a partial skeleton with evidence of the
cranium, the upper limb and its girdle, the sacrum, and the lower limb dating to 1.88-1.9 mya.
The postcranial evidence of KNM-ER 3735 is more similar to Australopithecus than OH 62; the
scapula and radius are especially ape-like.
The geographical range of H. habilis expands beyond the boundaries of the principal sites
of Olduvai and Koobi Fora. A fragmentary cranium, L 894-1, dating to 1.8 mya, that comes from
the Shungura Formation, Omo, Ethiopia is comparable to OH 13 and OH 24. A maxilla from
Hadar, Ethiopia (AL 666-1) extends the earliest known date of appearance for H. habilis to 2.3
mya. A temporal bone KNM-BC 1 from the Tugen Hills, Kenya dates to 2.4 mya and has also
been referred to transitional Homo.
One African specimen outside of eastern Africa has been likened to H. habilis though
never formally included in its hypodigm. STW 53 is a well-preserved cranium from Sterkfontein,
South Africa that dates to at least 2.0-1.5 mya. Examination of the bony labyrinth of STW 53
suggests that it is not similar to later Homo and may have relied on less bipedal locomotion than
Australopithecus (Spoor et al., 1994). Cladistics analyses that treat this specimen as its own
taxonomic unit suggest it is a sister-taxon to a H. habilis/H. erectus/H. sapiens clade (Smith and
Grine, 2008).
Transitional Homo – Homo rudolfensis
Significance
Several of the transitional Homo fossils found at Koobi Fora, Kenya in the 1970s were
referred to transitional Homo and later subsumed within the H. habilis hypodigm (i.e., KNM-ER
1813). Others, however, exhibited more robust features than the Olduvai sample of transitional
Homo (i.e., KNM-ER 1470). Aleexev (1986) argued that KNM-ER 1470, a cranium dating to
1.88-1.95 mya, was distinct enough to constitute a new species and recommended the name
Pithecanthropus rudolfensis. Groves (1989) later transferred this taxon to Homo since the genus
name Pithecanthropus was no longer used.
5
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
There remains considerable debate over the Koobi Fora sample of H. rudolfensis and
whether it represents a taxon distinct from H. habilis. Some authors argue that the variation
within a combined H. habilis/H. rudolfensis sample reflects a high degree of sexual dimorphism
or anagenetic change rather than evidence of speciation. However, if the specimens belonging to
H. rudolfensis are incorporated in the H. habilis hypodigm, the resulting interspecific variation is
greater than seen in several extant ape species and the pattern of variation is different from that
seen in any great ape or in modern humans. Additionally, KNM-ER 1813 shares with H. habilis
buccolingually narrow premolars and molars while KNM-ER 1470 does not. It is likely that two
transitional Homo taxa are sampled at Koobi Fora.
Morphology
The suite of derived and primitive traits in the crania of H. habilis and H. rudolfensis are
distinct. H. rudolfensis retains several primitive traits, including a thin-walled cranium with
marked postorbital constriction and an inflated mastoid region, deep zygomatics, and larger
postcanine teeth with more complex premolar and molar crowns and roots. The face of H.
rudolfensis is also wider at the midface rather than the upper face as in H. habilis. However, H.
rudolfensis also has more some features more derived than H. habilis, including a more
orthognathic face. At 800 cc, its endocranial volume is larger than H. habilis and larger than its
contemporary KNM-ER 1813, which has a cranial capacity of only 510 cc. However, when the
effects of body size are taken in account, the endocranial volume of KNM-ER 1470 and H.
habilis are not significantly different.
Notable fossils
There are several craniodental discoveries at Koobi Fora referred to H. rudolfensis but
none as complete as the lectotype, KNM-ER 1470. There are no postcranial remains
unequivocally referred to H. rudolfensis; the site at which potential H. rudolfensis postcrania
have been found is also where cranial evidence of P. boisei, H. habilis, and H. ergaster has been
found. Two femora, KNM-ER 1472 and KNM-ER 1481, may belong to H. rudolfensis.
A mandible found in 2.5-2.3 mya sediments of Uraha, Malawi (HCRP-UR 501) has also
been referred to H. rudolfensis. If this designation holds true, it greatly expands the geographic
and temporal range of this taxon.
Pre-modern Homo: Homo ergaster/Homo erectus
Significance
In the early 1890s, a hominin fossil found on the island of Java was classified as a new
hominin called originally Anthropopithecus erectus and later Pithcanthropus erectus. This
discovery, the Trinil calotte, demonstrated a smaller brain size and more primitive features than
the two species of Homo (H. sapiens and H. neanderthalensis) known at the time of its
discovery. The calotte was also much older than these taxa, dated originally to 500,000 years old
and later closer to between 700,000 and 1 mya. Similar finds were subsequently discovered at
the site of Sangiran, also on Java and at what is now called Zhoukoudian, in China. The overall
6
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
similarity of the cranial morphology of these Asian specimens to modern Homo eventually led to
their inclusion within the genus as Homo erectus.
Fossils of similar morphology were later found in Koobi Fora and dated to around 1.5
mya, 0.5 mya older than the Trinil calotte. Although the Koobi Fora specimens shared some of
the derived features of H. erectus, they were less well-defined. For example, H. ergaster
generally had thinner cranial vaults, less sagittal keeling, and larger and more complex
premolars. Groves and Mazak (1975) argued that these early African specimens do not share the
morphology of Asian H. erectus and they provided a new species name, Homo ergaster, for the
East African sample. However, some researchers argue that the East African sample is an early
form of H. erectus that does not require a separate name and they refer to this taxon as “early
African Homo erectus” (Kramer, 1993).
Morphology
Homo ergaster is, in general, more modern-human like than transitional Homo. The
mandible of H. ergaster is reduced in size compared to transitional Homo as is the dentition of
H. ergaster. However, the endocranial volume of H. ergaster is still relatively small, and when
body size is taken into account, the endocranial volume is not significantly larger than
Australopithecus.
Homo ergaster is the earliest hominin to demonstrate a modern body form. H. ergaster is
also larger than hominins of the past, with an especially significant increase in the height of
females. The lower limbs of H. ergaster and its modern thoracic shape suggest bipedal
locomotion, with no evidence of climbing adaptations. Cross-sectional measures of the femoral
and humeral shafts demonstrate a modern human-like strength in the forelimbs and hindlimbs,
and the pelvis is similar to modern humans. Additionally, the semicircular canal structure of the
inner ear is similar to modern humans and suggests upright posture (Spoor et al., 1994). It is
probable that H. ergaster was capable of long-distance walking and transport, and possibly
adapted to endurance running. Archaeological evidence from H. ergaster localities suggests that
raw materials for stone tools were being carried over long distances (Anton, 2003).
Notable fossils
The KNM-ER 992 mandible that dates to 1.5 mya is the type specimen of H. ergaster.
The first well-preserved cranium of H. ergaster to be recovered is KNM-ER 3733, which dates
to 1.78-1.65 mya; it has an endocranial volume of about 848 cc. This is similar to the endocranial
volume estimates for KNM-ER 3883, an H. ergaster calvaria that dates to 100,000 years later.
The 1.55 mya cranium without a face, KNM-ER 42700, is referred to H. ergaster but it has an
estimated adult body size more similar to transitional Homo. This relatively large range of body
size suggests that H. ergaster may have retained a high degree of sexual dimorphism.
Among the postcranial remains known for H. ergaster, two notable discoveries are
KNM-ER 803, a partial skeleton dating to 1.5 mya, and KNM-ER 3228, a 1.9 million year old
pelvic bone. These fossils provide evidence that H. ergaster shared a similar walking pattern
with modern humans.
Perhaps the most significant fossil remains of H. ergaster are those of KNM-WT 15000
(Turkana Boy), a well-preserved skeleton of an 8-12 year-old boy dating to 1.55 mya. Found in
1984, KNM-WT 15000 took four seasons to excavate and is one of the most complete skeletons
7
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
in the early human fossil record. The discovery demonstrates conclusively that H. ergaster
possessed modern limb proportions and a modern body shape. The teeth of KNM-WT 15000
provide for some life history reconstruction, and it has been determined that H. ergaster shares a
similar dental development pattern with transitional Homo (Dean and Smith, 2009). This
suggests that modern life history patterns originated late in human evolution. Turkana Boy also
has a cranial capacity of 909 cc, which is still small relative to later Homo.
All specimens formally referred to H. ergaster come from Kenya, but other H.
ergaster/H. erectus-like remains have been found in Ethiopia, Tanzania, and South Africa. At
Konso, Ethiopia, the left side of mandibular corpus with preserved postcanines was found in
association with Acheulean tools. This specimen, KGA 10-1, dates to 1.4 mya and has strong
similarities to KNM-ER 992.
At Olduvai, several specimens have been formally referred to early African H. erectus.
The OH 9 partial calvaria has a well-preserved supraorbital region and dates to 1.5-1.2 mya. The
OH 12 skull, which comprises a fragmentary calvaria plus part of the mandible, is more recent
(c. 0.78 mya) yet its endocranial volume of 727 cc is substantially smaller than that of OH 9.
Among the hominin remains at Swartkrans, SK 15, SK 45, and SK 847 have been
referred to early H. erectus. SK 15 is a distorted mandibular corpus dating to 1.5-1.0 mya, and
SK 45 is a fragment of the right mandible dating to 2.0-1.5 mya. SK 847 is known as the
“Composite Cranium” and also dates to 2.0-1.5 mya. In 1969, 20 years after their discovery, Ron
Clarke realized that the fossils SK 80, SK 846, and SK 847 belonged to the same individual.
Today, SK 847 is composed of the left side of the face and cranial base. Some authors argue its
affiliation is with H. erectus, but others refer all three of these specimens to transitional Homo
(Strait et al., 1997).
Key Issues:
Phylogenetic relationships
Phylogenetic analyses demonstrate that H. habilis is not consistently grouped more
frequently with Homo than with Australopithecus, and some argue for its removal from the
hypodigm of Homo. Still other researchers maintain that there exists phylogenetic support for a
clade of Homo that includes H. habilis, with H. habilis as the possible sister-taxon of H.
ergaster. Regardless of whether or not H. habilis belongs in the genus Homo, it is unlikely to
prove an ancestor of later hominins such as H. ergaster because some remains of H. ergaster are
found in the same fossil localities and date to the same era as H. habilis.
Homo habilis and H. rudolfensis overlap significantly both temporally and
geographically, and their potential sister-taxa relationship is often debated. Like H. habilis, H.
rudolfensis does not group consistently with Homo, and it is possible this taxon represents a
member of Australopithecus. However, Homo rudolfensis may also represent a better candidate
for the ancestor of H. ergaster/H. erectus than H. habilis based on its cranial shape (GonzalezJose et al., 2008). This ancestral relationship, however, is unlikely since H. rudolfensis and H.
ergaster also overlap considerably in time and place.
H. ergaster’s inclusion in the genus Homo is well established, but its relationships to
other Homo taxa are debatable (Figure 2). Homo ergaster overlapped significantly in time and
place with members of transitional Homo, suggesting they do not have an ancestor-descendant
relationship. Similarly, the earliest known emergence dates of H. ergaster in Africa and
8
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
H. erectus in Asia are close, and it is hard to reconstruct an ancestor-descendant relationship
between these two taxa if these earliest known dates of emergence are correct. Although
traditionally described as “early African Homo erectus,” H. ergaster may be a sister-taxon of H.
erectus or both taxa may be descendants of an earlier taxon.
Dispersal from Africa
Paleoenvironment
Transitional Homo and H. ergaster are known from 1.9 mya and older geological
sediments in east and southern Africa. Around 2 mya, Africa experienced great climate change,
especially increasing aridity. Olduvai fossil plants from the same stratigraphic level as OH 7
imply the emergence of more grasslands during this time, and high C4 isotopic signals suggest
the same (Cerling, 1991). High C4 signals have also been found in the lacustrine sediments
around Koobi Fora (Cerling et al., 1988) and in southern Africa (Hopley et al., 2007). Grazing
bovids appear to become more prevalent in East Africa around 2.4 mya, also suggesting the
emergence of more grassland. Current environmental reconstructions suggest that transitional
Homo and H. ergaster evolved during a time of increasing complexity and heterogeneity in the
landscape, which was likely composed of a mixture of closed forests and open grasslands. While
the fossil and archeological records of transitional Homo do not yet support long-distance travel,
it is reasonably certain that H. ergaster made use of a wider range of landscapes than previous
hominins. Certainly the presence of H. erectus in east Asia implies that hominins must have left
Africa sometime before 1.3 mya ago.
Out-of-Africa and the Multiregional Hypothesis
Historically, there are two theories concerning the dispersal of hominins beyond Africa.
The “Out of Africa” hypothesis argues that the genetic changes giving rise to modern humans
evolved only once in an African population, then dispersed to Asia and Europe and subsequently
the rest of the world. This theory has since been divided into Out of Africa I (the dispersal of H.
ergaster/H. erectus) and Out of Africa II (the dispersal of H. sapiens). Genetic evidence
demonstrates that the most parsimonious origin for modern DNA variation is Africa, lending
support for this theory. The alternative hypothesis, the “Multiregional Hypothesis,” argues that
gene flow between hominin populations gave rise to modern humans. Neanderthal DNA is more
similar to non-African populations of modern Homo, suggesting some interbreeding between
Homo populations. The debate between Out-of-Africa and the Multiregional Hypothesis is
ongoing; new morphological and molecular data promise to provide some resolution in the
coming years (Figure 3).
Early fossil evidence of Homo outside of Africa
While this review has focused on the fossil records of transitional Homo and H.
ergaster/H. erectus, there are several sites outside of Africa that show evidence of these
hominins or very similar taxa. Morphological analyses of these fossils provide an especially rich
source of information for assessing the migration patterns of pre-modern hominins and the
9
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
evolutionary origin of H. sapiens. These fossils deserve their own review, and we include here
only a few highlights found in the Republic of Georgia and China.
At the site of Dmanisi in the Republic of Georgia, a Homo mandible dating from 1.851.78 mya has been referred to the H. ergaster/H. erectus hypodigm. This mandible shares with
Homo its small size, relative gracility, and symphyseal shape, but the mandible is also smaller
than the earliest Homo currently known and includes a diminutive P4, M2, and M3. The premolars
are especially narrow, similar to OH 13, a representative of H. habilis. The discovery of several
skulls at Dmanisi sharing a unique combination of transitional Homo and pre-modern Homo
traits has led some researchers to propose a new taxon, Homo georgicus, for this population, and
at least one phylogenetic analysis suggests the cranial shape is similar to H. ergaster samples
(Rosas et al., 1998). The postcrania of the Dmanisi fossils are a mosaic of primitive and derived
traits, combining a small estimated body size and an encephalization coefficient within the range
of H. habilis. There is no evidence of the humeral torsion seen in later Homo and the glenoid
cavity is cranially oriented as in apes, suggesting the retention of adaptations for climbing. The
clavicle, however, is modern like H. ergaster/H. erectus. The Dmanisi hominins also appear to
have modern body proportions, including relatively long lower limbs.
Longgupo Cave, a 1.96-1.78 million year old site in the Sichuan Province of China, is the
site of another mosaic hominin referred to both H. ergaster and H. habilis. The Longgupo Cave
remains include a fragmentary left mandible and right upper later incisor, originally referred to
H. erectus. The same authors, however, note affinities with H. habilis and H. ergaster. The
mandibular corpus of Longgupo Cave hominin is small for this taxon and the cusp morphology
more primitive, leading some authors to identify it as an ancient ape (Etler et al., 2001). The P4 is
especially distinct from the hypodigm of Asian H. erectus, having different talonid and root
morphologies. Like other transitional Homo remains, the Longgupo Cave hominin was found in
association with two items that may represent Oldowan tools.
A second fossil site from China dating to the same era as Longgupo Cave is Yuanmou
Cave in southwest China. The incisors of a hominin found in this cave strongly resemble the
incisors of H. ergaster and have similarities to H. habilis. The Yuanmou Cave hominin was also
found in association with stone tools.
Conclusion:
We are the last surviving species of a diverse hominin lineage. Previous members of our
genus, Homo, were likely the earliest hominins to spread beyond Africa, having expanded
beyond that continent by at least 1.8 mya. The diversity of transitional and pre-modern Homo
forms is a testimony to the adaptive radiation of hominins to occupy new landscapes and
ecological niches in a changing world 2 million years ago. The evolutionary and cognitive
abilities that have enabled modern humans to occupy many different environments have their
origins millions of years prior to the emergence of H. sapiens. Ongoing analysis of our fossil
relatives H. habilis, H. rudolfensis, and H. ergaster will improve our understanding of these
abilities and help us reconstruct the phylogenetic history of our lineage. Like the many modern
human populations we observe today, these fossils of early Homo provide us with a view of the
great antiquity of human migration, adaptation, and diversity.
10
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
References:
ANTON, S. 2003. Natural history of Homo erectus. Yrbk. Phys. Anthropol. 46:126-70.
BROMAGE, T. 1989. Ontogeny of the early hominid face. J. Hum. Evol. 18:751-73.
CERLING, T.E., J. BOWMAN & J. O’NEIL. 1988. An isotopic study of a fluvial-lacustrine
sequence: The Plio-Pleistocene Koobi Fora sequence, East Africa. Palaeogeogr. Palaeocl.
63:335-56.
CERLING, T.E. 1991. Carbon dioxide in the atmosphere: evidence from Cenozoic and Mesozoic
paleosols. Am. J. Sci. 291:377-400.
CHAMBERLAIN, A.T. & B.A. WOOD. 1987. Early hominid phylogeny. J. Hum. Evol. 16:119133.
DEAN, C. & B.H. SMITH. 2009. Growth and development of the Nariokotome youth, KNMWT 15000, in F. Grine, J. Fleagle & R. Leakey (ed.) The first humans – origin and early
evolution of the genus Homo. New York: Springer.
ETLER, D.A., T.L. CRUMMETT & M.H. WOLPOFF. 2001. Longgupo: Early Homo colonizer
or late Pliocene Lufengpithecus survivor in south China? Hum. Evol. 16: 1-12.
GATHOGO, P.N. & F.H. BROWN. 2006. Revised stratigraphy of Area 123, Koobi Fora, Kenya,
and new age estimates of its fossil mammals, including hominins. J. Hum. Evol. 51:471-9.
GEBO, D.L. & G.T. SCHWARTZ. 2006. Foot bones from Omo: implications for hominid
evolution. Am. J. Phys. Anthrop. 129:499-511.
GONZALEZ-JOSE, R., I. ESCAPA, W.A. NEVES, R. CUNEO & H.M. PUCCIARELLI. 2008.
Cladistic analysis of continuous modularized traits provides phylogenetic signals in Homo
evolution. Nature 453:775-9.
GROVES, C.P. 1989. A theory of human and primate evolution. Oxford: Clarendon.
HOPLEY, P.J., J.D. MARSHALL, G.P. WEEDON, A.G. LATHAM, A.I.R. HERRIES & K.L.
KUYKENDALL. 2007. Orbital forcing and the spread of C4 grasses in the late Neogene: stable
isotope evidence from South African speleothems. J. Hum. Evol. 53: 620-34.
JORDE, L.B., W.S. WATKINS, M.J. BAMSHAD, M.E. DIXON, C.E. RICKER, M.T.
SEIELSTAD & M.A. BATZER. 2000. The distribution of human genetic diversity: a
comparison of mitochondrial, autosomal, and y-chromosome data. Am. J. Hum. Genetics 66,
979-88.
KRAMER, A. 1993. Human taxonomic diversity in the Pleistocene: does H. erectus represent
multiple hominid species? Am. J. Phys. Anthropol. 91: 161-71.
11
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
NAPIER, J.R. 1962. Fossil hand bones from Olduvai Gorge. Nature 196: 409-11.
ROSAS, A. & J.M. BERMUDEZ DE CASTRO. 1998. On the taxonomic affinities of the
Dmanisi mandible (Georgia). Am. J. Phys. Anthropol. 107: 145-62.
SMITH, H.F. & F.E. GRINE. 2008. Cladistic analysis of early Homo crania from Swartkrans
and Sterkfontein, South Africa. J. Hum. Evol. 54: 684-704.
SPOOR, F., B.A. WOOD & F. ZONNEVELD. 1994. Implications of early hominid labyrinthine
morphology for the evolution of human bipedal locomotion. Nature 369: 645-8.
STRAIT, D.S., F.E. GRINE & M.A. MONIZ. 1997. A reappraisal of early hominid phylogeny.
J. Hum. Evol. 32: 17-82.
SUSMAN, R. & J. STERN. 1982. Functional morphology of Homo habilis. Science 217: 931-4.
TOBIAS, P. 1966. The distinctiveness of Homo habilis. Nature 209: 953-7.
TOCHERI, M.W., C.M. ORR, M.C. JACOFSKY & M.W. MARZKE. 2008. The evolutionary
history of the hominin hand since the last common ancestor of Pan and Homo. J. Anat. 212: 54462.
VANDEBROEK, G. 1969. Evolution des vertebrates de leur origine a l’homme. Paris: Masson
and Cie.
WOOD, B.A. 1996. Human evolution, in I. Douglas, R. Huggett & M. Robinson (ed.)
Companion encyclopedia of geography. London: Routledge.
Further Readings:
ALEXEEV, V. 1986. The origin of the human race. Moscow: Progress.
BOBE, R. & A.K. BEHRENSMEYER. 2004. The expansion of grassland ecosystems in Africa
in relation to mammalian evolution and the origin of the genus Homo. Palaeo. 207: 399-420.
BOBE, R. 2011. Fossil mammals and paleoenvironments in the Omo-Turkana basin. Evol.
Anthropol. 20: 254-63.
BRAMBLE, D. & D. LIEBERMAN. 2004. Endurance running and the evolution of Homo.
Nature 432: 345-52.
HOWELL, F.C.1978. Hominidae, in J.V. Maglio & H.B.S. Cooke (ed.) Evolution of African
mammals. Cambridge: Harvard University Press.
KIMBEL, W., Y. RAK & D.C. JOHANSON. 2004. The skull of Australopithecus afarensis.
New York: Oxford University Press.
12
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
LEAKEY, L.S.B., P.V. TOBIAS & J.R. NAPIER. 1964. A new species of the genus Homo from
Olduvai Gorge. Nature 202: 7-9.
LE GROS CLARK, W.E. 1955. The fossil evidence for human evolution. Chicago: University of
Chicago Press.
LIEBERMAN, D.E, D.R. PILBEAM & B.A. WOOD. 1988. A probabilistic approach to the
problem of sexual dimorphism in H. habilis: a comparison of KNM-ER 1470 and KNM-ER
1813. J. Hum. Evol.17: 503-11.
LIEBERMAN, D.E., B.A. WOOD, & D.R. PILBEAM. 1996. Homoplasy and early Homo: an
analysis of the evolutionary relationships of H. habilis sensu stricto and H. rudolfensis. J. Hum.
Evol. 30: 97-120.
MAYR, E. 1950. Taxonomic categories of fossil hominids. Cold Spring Harbor Symp. Quant.
Biol. 25: 109-18.
RIGHTMIRE, P. 1993. Variation among early Homo crania from Olduvai Gorge and the Koobi
Fora Region. Am. J. Phys. Anthropol. 90: 1-33.
ROBINSON, J.T. 1965. Homo ‘habilis’ and the australopithecines. Nature. 205:121-24.
STRAIT, D.S. & F.E. GRINE. 2004. Inferring hominoid and early hominid phylogeny using
craniodental characters: the role of fossil taxa. J. Hum. Evol. 47: 399-452.
STRINGER, C. 1986. The credibility of Homo habilis, in B.A. Wood, L. Martin & P. Andrews
(ed.) Major topics in primate and human evolution. Cambridge: Cambridge Univ. Press.
STRINGER, C. 2002. Modern human origins: progress and prospects. Philos. Trans. R. Soc.
357: 563-79.
WOLPOFF, M.H., X.Z. WU & A. THORNE. 1984. Modern Homo sapiens origins: A general
theory of hominid evolution involving the fossil evidence from East Asia, in F.H. Smith & F.
Spencer (ed.) The origin of modern humans. New York: Alan R. Liss.
WOLPOFF, M.H., J.D. HAWKS & R. CASPARI. 2000. Multiregional, not multiple origins. Am.
J. Phys. Anthropol. 112:129-36.
WOOD, B.A. 1991. Koobi Fora research project. vol. 4 hominid cranial remains. Oxford:
Clarendon.
WOOD, B.A. 1992. Origin and evolution of the genus Homo. Nature. 355.
WOOD, B.A. 1999. Plio-Pleistocene hominins from the Baringo Region, Kenya, in P. Andrews
& P. Banham (ed.) Late Cenezoic Environments and Human Evolution: A Tribute to Bill Bishop.
13
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
London: Geol. Soc.
WOOD, B.A., & J. BAKER. 2011. Evolution in the genus Homo. Annu. Rev. Evol. Syst. 42: 4769.
FIGURE CAPTIONS:
Figure 1. Fossil localities of transitional and pre-modern Homo in East and South Africa.
Triangles denote discoveries of Homo habilis remains, squares denote discoveries of Homo
rudolfensis remains, and circles denote discoveries of Homo ergaster remains. Question marks
indicate that the affinities of specimens to specific taxa are uncertain. Note that most of the
African continent remains unexplored.
Figure 2. Proposed phylogenies and representative crania of Homo taxa. 2A. Four hypotheses of
the taxonomic and phylogenetic relationships of transitional and pre-modern Homo remains
(there may be others). 1) An anagenetic hypothesis suggesting that Homo ergaster is an early
form of Homo erectus, descended from Homo habilis, and gives rise to modern humans. This
phylogeny also shows Homo habilis and Homo rudolfensis as sister-taxa. 2) A second anagenetic
hypothesis, in which Homo ergaster is instead descended from Homo rudolfensis. 3) A
conservative hypothesis that places specimens referred to Homo rudolfensis within Homo habilis
and specimens referred to Homo ergaster within Homo erectus. This phylogeny also indicates a
direct descendant relationship between transitional Homo, pre-modern Homo, and modern
humans. D) A hypothesis arguing that transitional Homo and Homo erectus are sister taxa,
descended from a currently unknown ancestor. In this hypothesis, transitional Homo has no
direct contribution to the evolutionary history of later Homo and modern humans. 2B: Cranial
comparisons of (left to right) Homo habilis, Homo rudolfensis, Homo ergaster, and Homo
sapiens in portrait (top row) and profile (bottom row) views. Casts represent Koobi Fora
specimens in the collection of the National Museums of Kenya and a modern human.
Figure 3. Possible scenarios of the origin of modern humans from early Homo. A) The Out-ofAfrica Hypothesis, in which modern humans evolve from an Homo ergaster/Homo erectus
population in Africa, disperse throughout the world, and replace existing archaic hominin
populations. B) The Multiregional Hypothesis, in which early Homo populations regularly
encounter and interbreed with each other, eventually giving rise to regional but regularly
interbreeding populations of modern humans.