Re: Aquatic Ape Theory

28 Apr 1994 15:29:12 GMT

: > rh@ishmael.UUCP (Richard Harter) writes:

: >Let me see if I can put this simply. Arboreal mammals will indeed have a
: >certain amount of pelvis rotation and "pre-adaptation to bipedalism".
: >Selection for this is a natural consequence of the mechanics of living
: >in trees. There are many instances of arboreal mammals walking more or
: >less upright when they are on the ground.

: Not arboreal mammals in general. Arboreal apes which are hind-limb
: dominant to begin with.

There are a number of primate species that can be described as "vertical
clingers and leapers." They tend to be preadapted for bipedalism. Note
also that gibbons are bipedal on the ground.

: >This means less than it might seem. Walking upright is an expensive
: >proposition for animals which are not fully adapted to it for at least
: >two reasons...

: How do you know it is cheaper? Is this based on data or is it an
: assumption on your part?

If bipedalism were not the primary evolutionary innovation, it could
have become fixated via premature convergence. Then, all our argument is
empty. I suspect it was the primary innovation, but even in that case if
the selective advantage in becoming ground-dwelling was sufficiently
high, it could still have become fixated in preference to alternatives,
since apes still capable of evolving a more energy-efficient ground-
dwelling mode would have become extinct in a time much less than the
time needed for evolution. Most workers in this field have no idea how
advantageous it is to be ->first<- to adapt to a new environment.
Even a crappy adaptation can exclude alternatives from evolving. Once
one adaptation has evolved, the only way for alternatives to appear is
if the alternative does not compete against the original adaptation.

: Australopithecus afarensis, the females at least, retained some tree
: climbing ability. As I have pointed out, the forests didn't disappear
: and there is no evidence that early hominids slept in caves. It is
: much more likely that they slept in trees.

The specimens from caves show evidence of Panthera pardis predation. A.
afarensis probably avoided caves.

Harry Erwin
Working on Katchalsky nets....