The critical factor that differentiates humans and
apes is bipedal locomotion. Comparative studies of fossils of humans and
animals show differences in the structure of skulls and pelvis. Bipedalism
freed the hands of our ancestors allowing them to carry loads and make tools.
Apart from bipedalism particular aspects of tooth number, size, shape and
enamel of teeth are of value in tracing human ancestry.
The earliest fossil evidence supporting the evolution
of a creature ancestral to humans was found in Kenya. The fossil a single
jawbone has been dated to be 5.5 million years old. More substantial evidence
was found in mid 1990s in northeastern Ethiopia where the remains of more than
40 individuals who lived about 4.4 million years ago were unearthed.
The earliest hominid fossils of australopithecines
from North Kenya have been dated to be 4.2 to 3.9 million years old. Such
fossils were traced in Tanzania and Ethiopia also. The australopithecine
fossils have been found at Hadar in Ethiopia and named Lucy had 40% of bones
preserved. It helped anthropologists to know how australopithecines looked,
stood and moved.
On the basis of fossil evidence it is considered that
australopithecines were small statured and had relatively smaller brains than
modern humans. The fully bipedal australopithecines lived in arid and semi-arid
environments in eastern and southern Africa. They were omnivores subsisting on fruits,
vegetables, insects and small game. No stone tools associated with
australopithecines.
Global weather cooled down about 2.5 million years ago
and it possibly resulted in the evolution of several hominid species. Of these
one was robust australopithecines also known, as Paranthropus.They were larger
than gracile australopithecines with heavier skulls with bony ridges. Robust
australopithecines lived in Africa till about a million years ago and they do not seem to be ancestral to modern humans.
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