|
|
Re: Palaeontology (1)
Ralph L Holloway (rlh2@columbia.edu)
Wed, 2 Aug 1995 11:19:30 -0400
On Wed, 2 Aug 1995, Elaine Morgan wrote:
> They seem to be saying: "The chimpanzee became quadrupedal because it
> needed to increase its range. The hominid became bipedal because it
> needed to increase its range."
>
> That is a perfectly tenable position, but only on the premise that the
> animals were aleady very different before either of them set a foot on
> the ground - eg maybe the prehominid ape was smaller-bodied, had a
> different intramembral index, etc. But this is pure speculations,
> isn't it? For all we know, at 4mybp all the African apes were
> small-bodied and resembled one another very closely. It has been
> suggested that the l.c.a. looked like a bonobo. The gorilla could have
> become larger much later - as late as 2mybp or even 1mybp. We have no
> fossils.
>
> If they did resemble one another closely, we would need a very good
> reason why one lot would respond to the advent of savannah mosaic by
> becoming quadrupedal and the other by becoming bipedal.
>
It might be a good idea to pick up a copy of Szalay and Delson's
book on the fossil record for primates and read the chapters on pongids.
There is the sense for most of us paleo types that the fossil record has
a lot of different species, but as most of the finds are bits and pieces,
it is almost impooissible to sort it out nice and neat into any picture
approaching what we know about living species. Just trying to sort out
Proconsul major (a thread present here over the past several days)
regarding its affinities proves almost impossible. The impression I have
is far different from Elaine's. I see a lot of diversity of pongids
throughout the Miocene and probably into the Pliocene. I don't have any
trouble at all believing that two different species of ape, living in
roughly sympatric regions could show different adaptations to roughly
similar environmental changes, i.e., one becoming more proficient at
knuckle-walking, the other becoming more proficient at bipedalism. I
think Elaine expects too much homogeneity both in the fossil record and
in evolutionary responses to chaning environments via mutation,
selection, and drift. Minor differences in habitat distribution, gene
frequencies, etc, within a species can eventually lead to some profound
adaptational differences and thus morphological components.
There is a big difference between asserting that the fossil record
for the pongids is unclear as to asserting that it is relatively
homogeneous and small.
Ralph Holloway
|