Re: chimps on the savanna? Nooooo.....
Gerrit Hanenburg (ghanenbu@inter.nl.net)
Sun, 22 Oct 1995 22:42:37 GMT
Paul Crowley <Paul@crowleyp.demon.co.uk> wrote:
>> There's no particular reason of which I am aware that the species we
>> call "chimps" has been around any longer than homo sapiens, let alone
>> as long as genus homo or australopithecus.
>This is an important topic because it affects the way we think about
>the CA. We have a fair amount of evidence about chimps: we know a
>lot about the existing species and can make some firm conclusions
>from DNA analysis, even if the fossil record is almost non-existent.
>It's agreed that they split off from the CA about 6mya.
The DNA analyses are still controversial.There are estimates of 8-10 mya
for gorilla divergence and 6.3-7.7 mya for the chimpanzee-hominid split
based on DNA hybridisation techniques,and a possible trifurcation at
6.3-8.1 mya based on nuclear DNA sequencing.
>The question is "have they changed much since?".I believe that, in the absence
>of evidence to the contrary, the most parsimonious conclusion is that
>they have not.There has been no significant change in their habitat.
>The predators, competitors, food sources, and all other factors appear
>to be almost identical.
The late Miocene and the Pliocene in Africa are characterized by increased
seasonality leading to more open-country habitats and associated
faunas.There is no reason to believe that environment of the ancestors of
the modern chimp was unaffected by these changes.
>Two important adaptions were the development
>of their avoidance of night predation by building nests in trees and
>knuckle-walking.However they share these with gorillas, which split
>from their CA at around 7mya.
>Their most distinctive differences from gorillas are their group behaviour
>and their more generalised diet.Since these are what make the species viable,
>surely it is parsimonious to conclude that they were present in a similar form at the time of
>speciation and that there have been no significant changes in behaviour
>or morphology since that time?
There are also significant differences in morphology between gorillas and
chimps.
If we assume that the chimp changed little then this means most of the
change in morphology and behaviour is on the part of the gorilla.From an
evolutionary point of view it seems highly unlikely that the chimp remained
stationary for several million years.
Since the other apes subsist mainly on a vegetarian diet and the chimps add
a considerable amount of meat to theirs,it may be the chimps who have done
the changing in the direction of an increased predatory lifestyle in a more
open environment.
As to the evolution of their social behaviour,there is little to say about
that since the other apes all have a different group behaviour.
The assumption that chimps have changed little during the past 5-6 myr is
at best the nul-hypothesis.
Gerrit.
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