andrel <a_l### [at] hotmailcom> wrote:
> * if we have 30000 genes and we have 98% of our genes in common with the
> two species of chimp than there are at least 300 ancestors common to all
> humans since our split of the chimp line, and probably much more.

According to http://www.genetics.org/cgi/content/full/156/1/297, it's 199
differences.

Furthermore, there are two basic fallacies in this argumentation:

* Given that the average number of mutations *per individual* is estimated at
about ~175 (!) in each generation (see aforementioned article - man, I confess
this sounds crazy!), all these 199 differences might have been acquired in just
one or two generations.

* It is not even necessary for all of these mutations to have occurred *after*
the split of the chimp/human line. Some may have been genetic differences that
were introduced earlier in the common ancestors of chimps and humans, but with
each variant prevailing in only one branch.

For instance, such a gene may have affected some aspect of visual appearance
which our common ancestors did not care much about, but which may have had a
beneficial side-effect for the new 46-chromosome group, therefore becoming more
and more frequent among it as the groups evolved apart; another mutation may
then have spread in the 48-chromosome group to consider this visual feature
unpleasant, further reducing the interbreeding rate and at the same time
beginning to extinguishing that feature in the 48-chromosome group.


So all we can really say about it all is that there is at least *one* common
ancestor to all humankind with any relation to the chimp/human separation: The
individual to be the first with 47 instead of 48 chromosomes.

Of course, given how many generations have passed since then, there is reason to
argue that virtually all early "46-chromosomians" that are ancestors to *any*
modern human can be expected to actually be ancestors of *all* modern humans -
even if some may not have left any trace in the modern human's gene pool, and
only very few (at *most* 199 :)) have passed on particular genes to *all*
modern humans.

Given this relationship, there's also reason to argue that the 199 genetic
differences between humans and chimps accumulated over time after all, and that
therefore indeed roughly 199 of our many common ancestors may have passed a part
of their genome on to *all* modern humans after all.

Post a reply to this message