Re: Fwd: Gliders to Fliers? (Was Re: Ruben Strikes Back)

[Stanley Friesen <sarima@ix.netcom.com>]

At 05:20 PM 9/25/99 -0700, dbensen wrote:
>NOOOOO!  Well, I don't know about tree kangaroos and the climbing hypothesis
>makes sense, but humans did not become bipedal as an adaptation to arborality.
>Humans became bipedal AFTER they descended from the trees. 

Pardon, but all apes are either bipedal or knuckle-walkers when on the
ground.  NONE are normal quadrupeds.  Gibbons are *incapable* of anything
except bipedal locomotion on the ground.  The split between knuckle-walking
and bipedality seems to be size based, with the smaller forms (female
bonobos, gibbons, female orangutans) using bipedality, and the larger forms
(all the rest) using knuckle-walking.  Knuckle-walking is essentially
bipedality with the hands used as an extra support - certainly the basic
posture of the torso is the same as in bipedal apes.

And the brachiating monkeys - the spider monkeys - also use bipedal
locomotion when on the ground.

> According to Steven
>Jay Gould ( I don't remember which article).  The mutation that lead to many
>human characteristics (large head, straitened spine, etc.) were a mutation
on a
>gene that controlled ageing and also happened to alter leg development.
>Serendipitously, the new bipedal stance of humans left the hands free to
>manipulate things, and let humans rear up to gaze of the grassland (as Ray
>Stanford would say, 'like scared bunnies').  ...

Dr. Gould is not sufficiently versed on this matter to give a conclusive
opinion.
[His specialty is snails].

The bipedality as an adaption to keeping a lookout on the savannas is one
of the *weakest* of the scenarios for human bipedality.

Since all smaller apes are bipedal on the ground, there is no need for a
mutation to achieve crude bipedality in our ancestors.  The main changes in
humans from basal apes are in the shortening of the arms so we can no
longer brachiate, and in a substantially improved hip joint, allowing a
more efficient sustained bipedal stance.
[In brachiating apes bipedality is a somewhat tiring posture].

It is really instructive to watch a film of a *wild* gibbon moving through
large trees.  The amount of time they spend moving bipedally, even in
trees, puts a very different perspective on the origin of bipedality.

--------------
May the peace of God be with you.         sarima@ix.netcom.com