Re: Bipedalism and other factors
Alex Duncan (aduncan@mail.utexas.edu)
27 Jun 1995 04:03:32 GMT
In article <3snsv4$cvv@newsbf02.news.aol.com> Pat Dooley,
patdooley@aol.com writes:
>
>The pack hunters, such as the wild dog and hyena, fill the "exhaustion
>predation" niche. Lions fill the ambush niche, to an extent. Was there
>room for a 10 mph weaponless bipedal ape to go pack hunting on the
>savannah? Doesn't compute for me.
>
>The problem is that the range depends on the ability to carry water. That
>requires a level of tool building sophistication that was not available
>until
>H. Erectus arrived on the scene; an event post dating the evolution of
>bipedalism.
I may have entered this thread too late to fully understand the
arguments. Please clarify something: The AAT is offered as an
explanation for how hominids BECAME bipedal?
Yes, dogs and hyenas occupy the niche, but they don't necessarily
fill it. Hyenas are primarily nocturnal. That leaves the dogs out in
the day time, but does not mean that early humans couldn't also have
occupied that niche.
I wasn't suggesting that any hominids earlier than H. erectus
occupied this niche.
>
>> Another point -- there really isn't a lot of evidence that early
>>hominids were living strictly in a savannah environment. The faunal
>>remains associated w/ A. ramidus are definitely suggestive of a more
>>closed habitat, and much of the evidence for A. afarensis and A.
>>africanus also point to life in a mosaic habitat in which a number of
>>different microhabitats were available. A. boisei is found in
>>depositional environments that are indicative of wetter habitats than the
>>co-eval H. erectus. In fact, its not until the appearance of H. erectus
>>that we see good evidence for "good" adaptation to open habitats
>>(human-like intermembral index, 1.8 m stature, thin "equatorial" body
>>build).
>
>Which leads back to the $64k question. If bipedalism wasn't a savannah
>adaptation, what was it?
>
>Arboreal? The arms would be more orang like, and the legs much shorter.
How about this: hominids evolved from an ancestor that was so specialized
for an arboreal existence that its only effective mean of terrestrial
locomotion was bipedalism (see modern gibbons). In a fragmenting forest
environment, those pre-hominids that were most adept at moving from tree
to tree ON THE GROUND would have been selected for. An important thing
to note here is that this model doesn't suggest that pre-hominids adapted
bipedalism because living in open country was so wonderful. They did it
because they needed to cross open country from one patch of trees to the
next. As time went on, and aridification increased (e.g. terminal
Miocene climatic event) the patches between trees became progressively
larger and larger, selecting for more and more efficient bipeds.
Eventually the adaptation to crossing open ground became effective enough
that early hominids began other activities in open country (looking for
food, etc.).
>
>Display? No sign of sexual dimorphism.
Are you nuts? Most body weight reconstructions indicate male A.
afarensis were about twice as large as females. The same was probably
true of all other australopithecine species as well, and possibly even
earliest Homo (depending on how we slice up the habiline group).
>
>Temperature Regulation? But bipedalism didn't evolve on the savannah.
No, but it may have turned out to have the added benefit of helping temp.
regulation once hominids began routinely living in open country.
>
>Speed? A new-born Gnu can out-run a mature human. You need a great 800m
>time to survive on the savannah.
Or a complex social organization. A single hominid may have been easy
prey for a variety of savannah carnivores, but a group of cooperating
hominids would not.
>
>Tool carrying? Bipedalism predates tools.
Bipedalism predates tools that fossilize. Both humans and chimps use
tools, suggesting that this trait was present in the common ancestor of
humans and chimps, and thus, early hominids.
>
>Wading & Swimming? Crazy notion, but it fits with some other oddities.
I can think of no oddities that wading and swimming fit in with. Please
enlighten me. I'm not suggesting that early hominids didn't occasionally
enter the water, but to postulate an aquatic existence as the precursor
to all that is "hominid" flies in the face of all of the evidence I'm
aware of.
>
>> And finally, a comment on leopards -- yes, they climb trees, but
>>they don't hunt in trees (their prey are almost exclusively terrestrial
>>animals).
>
>But they often hunt from trees. The Tatung boy was, apparently, an early
>victim.
I assume you mean Taung? The fact that leopards hunt from trees would
certainly encourage a pre-hominid to stay IN a tree.
Alex Duncan
Dept. of Anthropology
University of Texas at Austin
Austin, TX 78712-1086
512-471-4206
aduncan@mail.utexas.edu
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