Australopithecus afarensis (3.6 to 2.9 million years ago)
Australopithecus afarensis had a very low forehead,
a face that projected far forward (as viewed in profile), and a very prominent
brow ridge. A. afarensis is the earliest species for which we have
reliable brain and body size estimates, thanks to a rich fossil record for
The brain of A. afarensis was about one-third the size of
the average modern human brain, or about the same size as a modern ape's brain.
Males and females varied significantly in body size, with males standing
approximately 4 feet 11 inches tall and weighing 100 pounds and females standing
about 3 feet 5 inches tall and weighing about 62 pounds. Males also typically
had large crests on top of their skulls; females did not.
The knee and pelvic
bone structure of A. afarensis were very humanlike, leaving no doubt that
A. afarensis walked upright. A. afarensis probably inhabited the
savannas and open woodlands where they likely found fruits, seeds, and roots.
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