The 'bushy' hominid tree

Andrew Gyles syzygium at alphalink.com.au
Thu Aug 23 21:38:59 EST 2001


Thank you for your questions. May I preface my reply by saying that my
hypothesis is not without experimental support. As I understand it, there is
little sequence variation in human nuclear (and mitochondrial) genes
compared with apes. I have
answered your questions in the order you wrote them, below:

"Laurence Martin Cook" <LCOOK at fs1.scg.man.ac.uk> wrote in message
news:9ltujf$28u$1 at mercury.hgmp.mrc.ac.uk...
>
>
>
> Andrew Gyles wrote
> >
> > The 'bushy' hominid tree, hominid extinction and human linkage
> > disequilibrium (hypothesis)
> >
> > I propose that the common ancestor of the hominids adapted to a changing
> > climate and environment by rapid genetic change.
> [which was] ..... the rapid loss of alleles in the germ line
> > through unusually vigorous repairing of mispaired bases in
> > heteroduplex segments during crossing over in meiosis.
>
> What would cause that to occur and how was it adaptive

I said that one cause of unusually vigorous repairing in heteroduplexes
might have been a few random mutations in the ancestor of the hominids (by
which I meant random mutations in the genes controlling the rate of
repairing).

I also remarked that an alternative possibility was that this mechanism lay
latent in many species, waiting to be called into action whenever a species
faced extinction (by which I meant starvation or loss of territory to
competitors). If that were so, perhaps the acceleration of repairing in
heteroduplexes is effected by a stress hormone.

I said that the loss of different alleles in isolated groups would produce
different average phenotypes, comparing group with group. Whether a new
phenotype enabled each new branch of hominid to adapt to the changing
environment would be a matter of luck. I suggested that all but one hominid
branch or line became extinct because their new phenotypes were not
adaptive. They were not lucky.

The proposed mechanism of rapid genetic change enables a species faced with
starvation or excessive competition to do something rather than nothing to
meet the challenge. It does not guarantee success.
>
>
> > I propose that in the ape lines of descent the repairing of mispaired
bases
> > in heteroduplexes was not as vigorous as it was in the hominids.
>
> same question.

I meant that the apes did not do what the hominids did. They did not
accelerate their rate of repairing mismatched bases in heteroduplexes. Some
repairing of mispaired bases is normal in all species that form
heteroduplexes, including viruses and yeast.

Therefore the apes evolved by the known (non-hypothetical) mechanism of
natural selection acting on randomly occurring mutations, most of which are
deleterious. The disadvantage of this mechanism for an organism in a rapidly
changing environment is that it is slow. The end result in the ape line
leading from the common ancestor of humans and chimpanzees was another ape.
>
>
>
> Laurence M. Cook
> The Manchester Museum
> University of Manchester
> Manchester M13 9PL U.K.
> and:_lcook2 at excite.com
>

Andrew Gyles










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