Re: First Family and AAT

Gerrit Hanenburg (
Mon, 2 Oct 1995 10:06:38 GMT (Clara N. Fitzgerald) wrote:

> [I'm having some trouble following your terms (what changed in the
>angulation of the knee, and what effect did it have?)

It concerns the bicondylar angle.The bicondylar angle in humans is higher
than in apes.In humans the angle is about 9 dgs.,in chimpanzees it's about
1 dgs.while in an A.afarensis specimen such as AL 333-4 it's 9 dgs.
The relatively high angle positions the knee,lower leg and foot close to
the midline of the body.As a result,the centre of gravity of the body need
move only a short distance laterally to lie above the stance leg during
walking.It makes bipedal locomotion more efficient.
(L.Aiello & C.Dean,1990.p.457,458 and 475)

> Wading would involve an environment that requires balancing against
>a shifting current - shifting the knees relative to center of gravity,
>and developing arches in the foot, could assist in maintaining balance.

In order to maintain balance against a shifting current you don't bring
your legs closer to the midline of the body but you do the opposite,you
move them away from the midline to create a broader,more stable base.

Humans have a shorter total foot length in relation to trunk length
compared with apes.The arche of the foot is a specialization that deals
with the mechanical forces generated during bipedal walking and not so much
an adaptation for dealing with balancing problems.(L.Aiello &

> Bouyancy doesn't overcome weight until you're at least chest deep -
>this would then involve swimming rather than wading.

I assumed that wading as well as swimming in at least chest deep water made
up a considerable part of the life of the aquatic ape and that most of its
"adaptations" were due to water of such depth.

> I seem to remember a summary of the 10 my evolution of whales; the
>early 'whales' kept the four legs for foraging on land, then developed
>webbed foot, presumably until the webbing became awkward on land, then
>went through a phase where the hindlimbs developed into grasping arms
>before they atrophied entirely. They also started with tails - a hominid
>with reduced legs would be tending toward a blob with arms, and would
>have a very hard time moving with any speed - there was to be something
>powerful to move water around.

The point of that comparison was not that the aquatic ape should develop
the same kind of anatomical features as the Cetaceans but to illustrate
that an animal that spends a considerable time of its evolutionary history
in an aquatic environment shows certain osteological changes that deal with
locomotion in such a medium.

> What kinds of adaptions are you referring to? I thought otters were
>basically weasel-shaped.

To take the seaotter as an example.It has short,sturdy legs with webbed
Reference:Aiello,L & Dean,C._An introduction to human evolutionary anatomy_
Academic Press,1990.