Hypothesis of ape evolution, Miocene to present


Allan Krill
 

On Mon, Dec 14, 2020 at 04:25 AM, Marc Verhaegen wrote:
No, Allan: all hylobatids/pongids/hominids lived along the Ind.Ocean.
All hominoids incl.hominids split & dispersed along the Ind.Ocean->Rift (Gorilla) or ->S.Africa (Pan) or ->S.Asia (Homo).
Do you really believe chimp & gorilla ancestors separately flew from E.Africa to your Bioko, and then separately flew back to the Afr.continent??
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Hi Marc
Thanks for asking. Here is my hypothesis.
I think that there were lots of ape species in the Miocene. They were not very mobile, and each had its limited range, like apes and monkeys do today. (Homo became the only mobile primate, and that was after it evolved its big brain on Bioko.) 

The timing of each Last Common Ancestor (LCA) of the living apes is uncertain. But if we use the numbers from http://timetree.org:
LCA Hylobate-Pongo 19.8
LCA Pongo-Gorilla 15.2
LCA Gorilla-Pan 8.6
LCA Pan-Homo 6.4

Here are possible paleogeographic ranges for each of those LCA. No species needed to wander any great distance or have a large range. The species evolved slightly within their range, sometimes splitting into subspecies. But a few individuals would occasionally get outside of the range. They were reproductively isolated from the original group, and evolved into a new species in the nearby area.  

All these ape habitats were rather similar. The selection pressures were similar. So the apes maintained their physical and anatomical similarities (phenotypes). Those apes were all more-or-less arboreal, none were aqua-arboreal. There were too many crocodiles for that. Some were more upright, more orthograde, more bipedal than others. None had bald bodies and sc fat. None had hooded nostrils. None had multi pyramidal kidneys. None had permanently descended larynxes. Etc. Jack has a long list of features that none of those pre-human primate species had. (If they had them, but lost them by convergent evolution, we should be finding "scars of evolution" to show that.)

Then a few chimps were forced to leave the trees. Just a few. They began to evolve in a completely different environment, with completely different selection pressures. That new habitat was not the African savannah (east of the chimps' forest) but was Bioko (west of the chimps' forest.) 

It is a very simple and logical hypothesis.

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