Relationship among Homo erectus, Homo habilis, and Other Proposed Fossil Groups 183“pinching in” of the skull can be seen just behind the mas-
sive brow ridges. H. erectus also possessed a sloping fore-
head and a receding chin. Powerful jaws with large teeth,
a protruding mouth, and huge neck muscles added to
H. erectus’ generally rugged appearance. Nevertheless, the
face, teeth, and jaws of this species are smaller than those
of H. habilis.
Apart from its skull, the skeleton of H. erectus dif-
fers only subtly from that of modern humans. Although
its bodily proportions are like ours, it was more heavily
muscled. Stature seems to have increased from the smaller
size typical of the australopithecines and the earliest
members of the genus Homo. The best evidence for this
comes from a remarkably well-preserved skeleton of an
adolescent male from Lake Turkana in Kenya. Sexual di-
morphism in body size also appears to have decreased in
H. erectus compared to earlier bipeds. A reduction in sex-
ual dimorphism may be due to the increase in female size
as an adaptation to childbirth.^5 The recent discovery of a
capacious female Homo erectus pelvis in Gona, Ethiopia,
supports this notion.^6
Relationship among Homo
erectus, Homo habilis,
and Other Proposed
Fossil Groups
The smaller teeth and larger brains of Homo erectus seem
to mark the continuation of a trend first seen in Homo
habilis. Increased body size, reduced sexual dimorphism,
and more “human” body form of H. erectus are newly
derived characteristics. Nonetheless, some skeletal resem-
blance to H. habilis exists, for example, in the long neck
and low neck angle of the thighbone, the long low vault
and marked constriction of the skull behind the eyes, and
smaller brain size in the earliest H. erectus fossils.
Indeed, as already noted, it is very difficult to distin-
guish between the earliest H. erectus and the latest H. ha-
bilis fossils. Presumably the one form evolved from the
other, fairly abruptly, around 1.8 to 1.9 mya. While the
bones of Asian H. erectus are thicker and the brow ridges
more pronounced compared to H. erectus from Africa,
(^5) Hager, L. (1989). The evolution of sex differences in the hominid bony
pelvis. PhD dissertation, University of California, Berkeley.
(^6) Simpson, S. W., et al. (2008). A female Homo erectus pelvis from Gona,
Ethiopia. Science 322 (5904), 1089–1092.
detailed anatomical comparisons indicate levels of varia-
tion approximating those seen in H. sapiens.^7 Consistent
with the notion of a single species is the observation that
1.8-million-year-old specimens from Dmanisi, in the
Caucasus—a region that lies along the overland route be-
tween Africa and Eurasia—show a mix of characteristics
seen in African and Asian H. erectus populations.^8
Throughout the globe, the most recent fossils are
more derived in appearance, and the oldest fossils (up
to 1.8 million years old) display features reminiscent of
earlier H. habilis. Indeed, distinguishing early H. erectus
from late H. habilis is problematic—precisely what one
would expect if the one evolved from the other. We will
next explore the H. erectus finds by region.
Homo erectus from Africa
Although our samples of H. erectus fossils from Asia remain
among the best, several important specimens are from Africa.
Fossils now assigned to this species were discovered there
as long ago as 1933, but the better-known finds have been
made since 1960, at Olduvai Gorge and at Lake Turkana,
Kenya. Among them is the most complete H. erectus skel-
eton ever found, that of an adolescent boy who died 1.6 mya.
Paleoanthropologists infer the age of this specimen from his
teeth (the 12-year molars are fully erupted) and the state of
maturity of the bones. With a height of about 5 feet 3 inches
at adolescence, this specimen was expected to attain a stat-
ure of about 6 feet by adulthood.
A trail of H. erectus footprints, like those from Laetoli,
were also recently discovered along Lake Turkana. These
footprints support the estimates of body mass (weight)
and stature made from more fragmentary remains.
Homo erectus Entering Eurasia
Evidence of the spread of H. erectus from Africa into
Eurasia is well preserved at the interesting site of Dmanisi
in the Caucasus Mountains of Georgia. Dmanisi was first
excavated as an archaeological site because of its impor-
tance as a crossroads for the caravan routes of Armenia,
Persia, and Byzantium in medieval times. When Oldo wan
stone tools were found at this site in 1984, the hunt for
fossil specimens began there as well.
(^7) Rightmire, G. P. (1998). Evidence from facial morphology for similarity
of Asian and African representatives of Homo erectus. American Journal of
Physical Anthropology 106, 61.
(^8) Rosas, A., & Bermudez de Castro, J. M. (1998). On the taxonomic af-
finities of the Dmanisi mandible (Georgia). American Journal of Physical
Anthropology 107, 159.