June 21, 2014

Claim of 13 Ma Pan-Homo split

[Update (Jun 29): new entry on this issue available].

[Update: the origin of this news is Venn 2014 but I could not find the mention of the 13 Ma split initially, as it was not something they underlined at all. I will write something as soon as possible. Thanks to all the people who helped my confused mind].

Live Science reports this week that the divergence of the human and chimpanzee lines may be as old as 13 million years. This is the oldest range of what Langergraber 2012 suggested (8-13 Ma in Fig.1, although in text they wrote "6.8-11.6 Ma") and older than the Wilkinson 2010 estimates (8-10 Ma), and would totally break all the usual "molecular clocks" so extremely abused in human genetics because it is double of the usual scholastic mindless parroting (5-7 Ma, which are necessarily too recent because they do not allow for Sahelanthropus' evolution and not even for bonobo evolution under the protection of the mighty Congo river).

Sadly the article includes no reference to the source, not even the name of the scientists involved, and I could not find it any reference online. For a moment I thought it could be another new study on gender bias in chimpanzee mutation rate (Venn et al. 2014 (ppv)) but after getting a copy it does not seem to have any direct relation.

So I would appreciate if someone can give me a lead on where this claim may come from.

6 comments:

  1. Indeed, this is a comment on the publication signed, among others, by Venn and McVean.

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    1. Thanks. Some other readers have told me the same and I was today finally able to find the relevant quote, which eluded me in the first reads.

      I will write something if not today, tomorrow.

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  2. So, naively, about 11/13th of the mutations that distinguish the genus Homo from the genus Pan should already be present in Homo Erectus, which is a pretty safe bet as ancestral to all species of Homo that have left any discernable genetic trace in modern humans, Neanderthals, Denisovans, etc.

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    1. Assuming neutrality, yes. It should not surprise us: chimps do not walk, we do and so did Sahelanthropus 7 Ma ago, which also had already some of our modern brain configuration, as opposed to chimps and bonobos. But maybe some of those mutations, at least the functional ones, accumulated in bouts under selective pressure of some sort (positive selection probably, as negative selection tends to be conservative).

      Anyhow, please remember that chimps have also evolved a lot, maybe even more than our line, as suggested by a chromosomal study from last year. Also chimpanzee chromosome 12 (human ref. count) seems more directly linked to the gorilla branch, so there may be the product of admixture with the proto-gorilla branch.

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  3. Just reading this paleo-ecological study of Neogene Africa: http://horizon.documentation.ird.fr/exl-doc/pleins_textes/pleins_textes_6/b_fdi_47-48/010013166.pdf (in English)

    For East Africa, studies on the Neogene fauna indicate that rain forest environments were widespread at the end of the Oligocene and in the lower Miocene (Denys et al. 1985). Various palaeobotanical data then make it possible to conclude that it is from the middle Miocene that the vegetation cover became more open, with mosaic type patterns of forest and savanna...

    If we consider loss of forest cover as an evolutionary pressure to bipedalism, this is in agreement with a c. 13 Ma date for the Pan-Homo split, right in the middle of the Miocene. Chimpanzees fare badly in open lands (I watched a documentary on a clan isolated in a forest patch and they did not dare to go out almost ever) but our ape-like bipedal ancestors like Toumaï were surely much better adapted to those environments instead.

    I think that some of the data in this study also suggests a tropical forest in the early Miocene much more to the north than today, and expanding into Asia. This would explain the Africa-Indonesia span for the great ape family, which at that time would need to be almost always in forest areas.

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  4. New entry on this study: http://forwhattheywereweare.blogspot.com/2014/06/pan-homo-split-11-17-million-years-ago.html (sorry for the delay).

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