Encyclopedia of Evolution.pdf - Online Reading Center

0 Homo ergaster
Stone tools. Like earlier humans, H. ergaster made
stone tools. The earliest tools of H. ergaster were Oldowan,
like those made by H. habilis. Later, H. ergaster made
Acheulean tools, which were more structurally complex (see
technology). Stones were worked into complex teardropshaped
hand axes by the removal of numerous flakes from
stone cores. Both the flakes and the cores were apparently
useful as tools, for cutting meat and skin. The most likely
use was for cutting pieces of flesh and cracking open bones
from animals that had been killed by large predators. H.
ergaster may have been a scavenger. This interpretation is
reinforced by the microscopic analysis of cut marks upon
the bones of prey animals from about two million years ago.
Cut marks made by stone tools cross over tooth marks from
hyenas, indicating that H. ergaster cut meat from prey animals
after the hyenas had finished with them. A few of the
teardrop-shaped axes were quite large, and anthropologists
have not figured to what practical use, if any, these cores
Ian Tattersall, of the American Museum of Natural History in New York,
holds a cast of a stone tool found at Isimila, Tanzania, which resembled
the Acheulean tools made by later populations of Homo ergaster. Only a
few of the tools were this large; too large and heavy to use, these tools
served an unknown function. (Photograph by Stanley A. Rice)
might have been put. One (see photo below) was almost
20 inches (nearly a half meter) in length and almost a foot
(15 cm) wide at its widest point, and weighed 25 pounds
(11 kg). These structures may have represented the earliest
example of human art.
Larger brains and complex cultures. The brain of H.
ergaster, at about 50 cubic inches (800 cc), was smaller than
that of modern humans (which is more than 75 cubic inches
or 1,200 cc), but still large enough that a very human type
of birth was necessary. If H. ergaster fetuses developed along
the same timeline as those of modern apes such as chimpanzees,
the head at the time of birth would have been too large
to have passed through the birth canal of an upright walking
woman. In H. ergaster, as in modern humans, the solution
was for the infant to be born prematurely and in a condition
much more helpless than that of chimpanzee infants.
Once born, the infant could continue its brain development.
Enhanced brain growth is just one of many juvenile characteristics
that modern humans possess even into adulthood, a
process known as neoteny. This process had already begun
with the evolution of H. ergaster. The helpless infant would
need exceptionally active parental care, and this may have
been the starting point of family life and human culture, in at
least a rudimentary form in H. ergaster.
Another indicator of complex culture is that individuals
of this species apparently took care of one another. A skeleton
of a woman (specimen KNM-ER 1808) who died of
hypervitaminosis A, caused perhaps by eating the liver of a
carnivore, has been found in the Turkana region of Africa.
She lived for several weeks with her affliction, during which
time other humans apparently took care of her.
Use of fire. H. ergaster was apparently also the first
human species to make controlled use of fire. It is very difficult
to demonstrate evidence for hearths that are more than
a million years old.
Language. Although human culture may have begun
with H. ergaster, modern language apparently did not. The
canal inside of the spinal cord of modern humans remains
wide until near the coccyx. This allows a great abundance of
nerves to receive sensory information from, and control the
movements of, all the body parts. The canal inside the spinal
cord of H. ergaster was restricted even by the time it reached
the neck, implying that it not only had restricted manual
coordination but also may not have been able to have articulate
speech. Uncertainty remains, however, as to whether the
brains of H. ergaster possessed structures that allow modern
humans to produce and understand language (see language,
evolution of).
Homo ergaster coexisted, at least during its early period,
both with the robust australopithecines (genus Paranthropus)
and with populations of more primitive hominins usually
assigned to H. habilis. Numerous hominin lineages existed at
the same time and very nearly in the same place as H. ergaster,
but it was the only one that was the ancestor of modern
humans.
The larger brains and more complex tools of H. ergaster
evolved quickly, at a time when cooler and drier condi-