Early Representatives of the Genus Homo 169whether a collection of ancient bones and teeth repre-
sents a distinct species, these paleoanthropologists tend
to be “lumpers,” placing similar-looking fossil specimens
together in more inclusive groups. For example, gorillas
show a degree of sexual dimorphism that lumpers attribute
to H. habilis. “Splitters,” by contrast, focus on the variation
in the fossil record, interpreting minor differences in the
shape of skeletons or skulls as evidence of distinct biologi-
cal species with corresponding cultural capacities. Refer-
ring to the variable shape of the bony ridge above ancient
eyes, South African paleoanthropologist Philip Tobias has
quipped, “Splitters will create a new species at the drop of
a brow ridge.”^22 Splitting has the advantage of specificity
while lumping has the advantage of simplicity. We will
use a lumping approach throughout our discussion of the
genus Homo.Differences Between Early Homo
and Australopithecus
By 2.4 mya, the evolution of the genus Homo was proceed-
ing in a different direction from that of Australopithecus.
In terms of body size, early Homo differs little from
Australopithecus. Although early Homo had teeth that are
large by modern standards—or even by those of a half-
million years ago—they are smaller in relation to the size
of the skull than those of any australopithecine. Early
Homo also had undergone enlargement of the brain indi-
cating that early Homo’s mental abilities probably exceeded
those of Australopithecus. Early Homo likely possessed a
marked increase in ability to learn and to process informa-
tion compared with australopithecines.
The later robust australopithecines from East and
South Africa that coexisted with early Homo evolved into
more specialized “grinding machines” with massive jaws
and back teeth for processing plant foods. Robust aus-
tralopithecine brain size did not change, nor is there firm
evidence that they made stone tools. Thus in the period
between 1 and 2.5 mya, two kinds of bipeds were headed
in very different evolutionary directions: the robust aus-
tralopithecines, specializing in plant foods and ultimately
becoming extinct, and the genus Homo, with expanding
cranial capacity, a varied diet that included meat, and the
earliest evidence for stone tool making.
Without stone tools early Homo could eat few
animals (only those that could be skinned by tooth or
nail); therefore, their diet was limited in terms of animal
protein. On the arid savannah, it is hard for a primate
with a humanlike digestive system to satisfy its protein
requirements from available plant resources. Moreover,rudolphensis. Whether one chooses to call these or any
other contemporary fossils Homo rudolphensis or Homo
habilis is more than a name game. Fossil names indicate
researchers’ perspectives about evolutionary relationships
among groups. When specimens are given separate spe-
cies names, it signifies that they form part of a reproduc-
tively isolated group.
Some paleoanthropologists approach the fossil record
with the perspective that making such detailed biologi-
cal determinations is arbitrary and that variability exists
within any group.^21 Arguing that it is impossible to prove
Supraorbital
torusKNM ER 1470 KNM ER 181305 cmSupraorbital
sulcusFigure 7.18 The KNM ER 1470 skull—one of the most
complete skulls of Homo habilis—is close to 2 million years
old and is probably a male; it contrasts with the considerably
smaller KNM ER 1813 skull, probably a female. Some
paleoanthropologists feel this variation is too great to place
these specimens in the same species.
(^21) Miller, J. M. A. (2000). Craniofacial variation in Homo habilis: An analy-
sis of the evidence for multiple species. American Journal of Physical An-
thropology 112, 122.^22 Personal communication.