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Re: First Family and AAT
Phil Nicholls (pnich@globalone.net)
Wed, 27 Sep 1995 18:19:24 GMT
szpltdwn@dale.ucdavis.edu (Gerrell Drawhorn) graced us with the
following words:
> 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. 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 bonobos...it's a pervasive catarrhine character).
> 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 find it difficult to envisage a situation where the lateral
> system in the pelvic musculature, the increased surface areas and
>angulation of the knees, the development of the longitudinal and
>transverse arches of the foot, etc. could arise if animals were in an
>environment where they were buoyant. Either a lightly-built knuckle-walking
>or (more generalized) brachiator (not as specialized as hylobatines)
>would seem to provide a better progenitor than an aquatic form.
> 3) Many of the soft-anatomical features cited by the AAT proponents
>of an aquatic past are found in related hominoids and cercopithecoids.
> Digital webbing is found in siamangs (hence the name Symphalangus
>syndactylus), gorillas and bonobos.These are probably adaptations to the
>brachiatory hand of hominoids. I suspect the diving reflex, and many
>other AAT traits would also be found in our near relatives. The fact that
> Japanese macaques, Nasalis, and swamp monkeys (C. mitis) are capable of
>swimming suggests a broader capability not restricted to humans. If so,
>there may be many traits attributed as derived from a human AA phase
>that are clearly "pre-adaptations" from an earlier set of features. 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.
> Jerry Drawhorn
> Dept. of Anthropology
> University of California
> Davis, CA 95616
Excellent post! I was hoping that someone would come in on the
biomechanics end.
The so-called "diving reflex" is now known to occur in all mammals
that can be trained to dive, most noticably dogs. If they can
control the panic, they get a diver's reflex.
Phil Nicholls pnich@globalone.net
"To ask a question you must first know most of the answer"
-Robert Sheckley
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