Re: First Family and AAT

Thomas Clarke (
25 Sep 1995 18:52:49 GMT

In article <445388$> (Gerrell
Drawhorn) writes:

> I have three points to make regarding the AAT.
> 1) The AL-333 Locality suggests that A. afarensis was poorly adapted
> to dealing with even moderate levels of water. The lithostratigraphy and
> taphonomy of this "First Family" site indicates the group was incapable of
> escaping from a slowly rising water level while they were trapped on a
> spit of land along an embayment or slow moving river.

Can you elaborate on this, provide references? I find it difficult
to imagine a trapped group being slowly drowned by rising water and yet
remaining together in a group. I would think the water would be rather
deep before they drowned and as a result the bodies would float/wash away
into dispersed locations. I would think it more likely that after they
died, the "family" bodies were washed downstream to an area where
the flow stagnated and the bodies settled. The depostion of the
bodies could have happened all at once or seperately over a period of time.

At any rate, I would like to hear more detail.

> Clearly these hominids
> were utilizing littoral environments-
> but why would they have so quickly
> lost the "Aquatic" adaptations that would have profoundly benefitted them?
> I reason that A. afarensis probably did not have Aquatic ancestors
> ("wading" ancestors perhaps, but many primates do this, including lowland
> gorillas and's a pervasive catarrhine character).

That is interesting. If most old world primates wade, then the
situation postulated by the AAT might not be so unique.
What is that monkey in SE Asia that is rather semi-aquatic?
Ah, the swamp monkey, you mention it below.

> 2) Bipedal adaptations in early hominids appear to be mechanically
> designed to deal with increasing gravitational forces applied to the hip,
> hindlimbs and foot. Swimming would seem to completely release the
> hindlimbs from these verticle forces - selection would take the climbing
> foot, ankle and leg of an ancestral hominoid on an opposite trajectory
> than ultimately attained in hominids. Even wading by a quadruped would
> reduce these forces to some degree.

I always envisioned it as wading in a bipedal posture while gathering
and carrying food.
That's how I wade :-)

> 3)
>The fact that
>Japanese macaques, Nasalis, and swamp monkeys (C. mitis) are capable of
>swimming suggests a broader capability not restricted to humans.

Personally, I think the swamp monkeys are almost a perfect model for
the hypothesized aquatic phase in the develoment of hominids.
Do you have details of how the swamp monkey's bone structure and
musculature differs from close relatives that do not swim? I would
be most curious.

> there may be many traits attributed as derived from a human AA phase
> that are clearly "pre-adaptations" from an earlier set of features.

Yes indeed. Evolution hardly ever starts with a clean slate.
These preadaptions could well have been emphasized during an aquatic or
littoral interlude leading to the current distrution of traits found in

> Until
> we know what the distribution of these characters are in hominoids (ie.
> can it clearly be stated that no other hominoid except humans has a
> "diving reflex"), these characters should be given very low weight in any
> argument.

That would be an intersting research project for some youg primatologist.

Tom Clarke