Re: Early diets and bipedalism

Krister Olsson (
Wed, 04 May 1994 11:00:59 -0500

As far a bipedialism is cvoncerned, I'm not really sure our "this
environment happaned, so this animal must have evolved to meet it" linear
ideas of evolution really hold. Animals use what structures they already
have to adapt to a new environment rather than evolving new structures to
deal with the new environment. For instance, the primate progenitor
probably already had grasping paw like structure before becoming a lemur,
but the lemur's evolutionary tract lend to a further development and
differentiation of that grasping paw into a hand. Likewise, the human
progenitor probably already used a more bipedal like posture in the trees,
rather than a chimp-like posture. This is the idea that a gibbon-like
primate, already preadapted to a bipedal gate, found that preadaption
useful when it had to leave the lifestyle of the trees. The evidence for
this idea is the biomechanical analysis of human knuckles and shoulders,
chimp and gorilla knuckles and shoulders, and homo and australo knuckles
and shoulders. Who ever did that analysis supposedly decided that humans
did not have the bone structure evolutionary remnants of a knuckle walking
The idea humans descend from a gibbon-like tree dwelling primate rather
than from a savana dwelling chimp-like primate is very attrachtive. It
emphasises the limits of evolution. It also explains why chimps aren't
becoming more bepedal when they spend so much time on the ground: the
chimps have evolved a knuckle walking gate rather than a bipedal gate and
there is no return.
Whether or not the Bipedal Tree Dwelling Ancestor is the correct
hypothesis is realatively unimportant. What is important is the idea that
evolution can only work with what it already has. Population pressures
cannot indiscriminately push structure A to structure B unless both are
already pretty darn similar.