Re: East Side Story
J. Moore (j#d#.moore@canrem.com)
Wed, 1 Nov 95 18:24:00 -0500
Cl> SCIENTIFIC AMERICAN May 1994, East Side Story by Yves Coppens.
Cl> It actually attempts to answer some of the questions about Pan/Hominidae
Cl> speciation I have been asking.
Cl> For those who have not read it, briefly it asserts that the formation of
Cl> the African Rift valley some 8 MYA split the population of Miocene apes
Cl> into a group to the west in the humid forest, and a group to the east in
Cl> the drier savannah/forest environment. The group to the west became
Cl> chimps, the group to the east became Australopiths. The time of Rift
Cl> formation matches nicely the last common ancestor time given by DNA
Cl> evidence.
Cl> I have to admit that this makes me officially neutral about the AAT/H/S.
Cl> The East Side Story (Scenario?) or ESS meets my objections to a direct
Cl> arboreal to terrrestrial transition because it provides the population
Cl> isolation needed for speciation, and it is at least plausible that the
Cl> selection pressure for bipedalism could have been provided without need
Cl> to invoke a water phase.
You may also be overestimating the difficulty of effective
isolation occurring. Even a medium- to large-sized river could
provide such isolation: Even for pygmy chimpanzees (bonobos),
which are much more accustomed to water than common chimps, such
rivers form the geographical barriers at the limits at the
northern and southern limits of their range. Their eastern limit
seems to be determined by a change in vegetation. Takayoshi Kano
(1992 *The Last Ape*) points this out, along with the observation
that even smaller rivers form such barriers, and says that
"Although the pygmy chimpanzees of the Wamba region seem to be
continuously distributed, the whole population is actually cut up
into several isolated populations" (Kano 1992:59).
This (a seemingly continuous population actually being composed
of groups which are isolated to varying degrees) is also found
among common chimpanzees, and for these chimps there has been a
lot of study about differences in behavior, and especially tool
use, seen in different areas. William McGrew's *Chimpanzee
Material Culture* (sorry, I don't have the date here; it's late
1980s or 90-something) is a book-length treatment of these
"pre-cultural" or "cultural" differences. One example is in the
use of tools to crack open nuts: groups in some areas use tools
for this purpose while groups in other areas do not. Reports of
this differential tool use go back well over 100 years, which means
it's a long-term difference between groups in different areas.
This sort of relatively small difference, given the fact that there
is effective isolation (even without a major rift system opening),
could, in time, lead to speciation.
Cl> On the other hand I do not reject out of hand, the possible
Cl> role of water in Hominid evolution. There is still several
Cl> million years from the formation of the Rift to the first know (bipedal)
Cl> fossils and selection on even smaller isolated groups could have played
Cl> a role. Not enough evidence either way.
Cl> Tom Clarke
I don't reject the AAT out of hand, either, but the fact is it
doesn't deal with the problems that arise when one considers it
seriously. As only a few examples there are hominids' lack of
numerous characteristics that are ubiquitous among aquatic and
marine mammals; or that the observed and measured excretions in
human tears far more closely resemble the excretions from the
"salt" glands of terrestrial birds and reptiles than those of
marine birds and reptiles.)
As Harry Erwin said toward the end of September:
He> My take on the AAT is that it is a beautiful theory, murdered by ugly
He> facts. There are a lot of people out there who have come up with similar
He> theories, and the test of their intellectual honesty is how they deal
He> with inconvenient facts.
He> --
He> Harry Erwin
If the AAT's proponents continue to refuse to address the
"inconvenient facts" that leave gaping holes in the theory,
it's sunk.
Jim Moore (j#d#.moore@canrem.com)
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