Lecture 19: Evidence on Hominine Evolution
Study of the pelvis and the base of the skull proved that she was bipedal.
In quadrupedal species, the spine enters the skull from behind, not from
below. Yet her brain (at about 450 cc) was only slightly larger than that of
a chimp (chimp brains average 350 cc). Clearly, bipedalism evolved before
large brains. In 1978, Mary Leakey discovered fossilized footprints left by
three australopithecines who had walked through still-warm lava, in Laetoli,
Tanzania (also in the rift valley), about 3.6 million years ago. They con¿ rmed
that australopithecines were bipedal. Skeletons can tell us much more. For
example, paleo-dentists can tell whether a tooth was used to eat plants or
meat, and knowledge of diets can tell us a lot about lifestyles.Louis Leakey (1903–1972) and his family made Olduvai gorge, also on the
rift valley, one of the most famous of all sites for human paleoanthropology.
Like the South Dakota badlands, this is an area where geological processes
break open the Earth’s crust for us, revealing large numbers of fossil remains.
In 1964, Leakey’s son Jonathon found a 2.3-million-year-old skull that was
about half the size of a human skull (about 600 cc). Despite the smallness of
the skull, Louis Leakey announced that a new species had been found, and
he classi¿ ed it as Homo habilis, placing it within the same genus as us.Leakey insisted on classifying these remains within the genus Homo because
habilis made tools. Their tools are known as “Oldowan,” after the Olduvai
Gorge. Oldowan stone tools were made from pebbles of quartz, À int, or even
obsidian that were struck together to remove À akes that could be used as
cutting edges. The leftover cores may have been used as crude hammers.
Leakey was impressed because these tools, though unsophisticated by
later standards, suggested the sort of technological creativity he expected
from humans. Modern attempts to manufacture Oldowan tools suggest
considerable skill was needed for their manufacture. Microscopic study of
stone tools can suggest what materials they were used on, and this can tell
us something about diets and lifeways. For example, Homo habilis seem to
have had an omnivorous diet dominated by plant foods such as leaves and
fruits. Microscopic studies of cut marks and scratches on animal bones at
hominine sites can determine whether hominines hunted for themselves or
scavenged animals killed by others. The cut marks inÀ icted by the stone tools
of habilis often lie over the teeth marks of carnivores, which suggests that
they generally scavenged from animals already killed by other carnivores.