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Re: Date for Last Common Ancestor?
Stephen Barnard (steve@megafauna.com)
Sun, 11 Aug 1996 21:13:58 -0800
Susan S. Chin wrote:
>
> Stephen Barnard (steve@megafauna.com) wrote:
> : T&B Schmal wrote:
> : >
> : > I am interested in bracketing the dates for the last common ancestor of
> : > humankind. Would a good guess be somewhere between "Eve" and the
> : > appearance of modern man - say, between 200 and 50 Kya? It seems to me
> : > that dates outside this range would be impossible.
> : >
> : > Is this on track and can this range be narrowed? Suggestions welcomed.
> : >
> : > Tom Schmal
> :
> : The attribute of being "the last common ancestor of humankind" has a
> : very peculiar property. That person can only be identified long after
> : the fact, and the identity and date of that person is liable to be
> : changed radically at any time. For example, if a new disease were to
> : decimate the world's human population, with only say 10% of the people
> : surviving because of an inherited resistance, then the date of the last
> : common ancestor would probably be moved forward in time considerably.
>
> : Steve Barnard
>
> Whether or not we will ever determine who and when this last common
> ancestor occurred, I don't see how it can arbitrarily be moved forward in
> time due to a scenario of catastrophic decimation of 90% of humankind. The
> assumption is that by that time, the LCA had already split off to form
> these various populations.
>
> Even if you subscribe to the theory of multiple and separate evolutionary
> roots of mankind per geographic regions, at one point, there was
> a species of organism from which Homo sapiens sapiens arose.
>
> The "Eve" that we hear about as the "mother of us all" is really a
> population which contained the genes which ultimately resulted in all of
> humakind as we see it today. It was not meant to imply (though of course
> it does anyway) that we all arose from one female individual, but from a
> population of individuals with those genes.
>
> The question should be how reliable is the molecular data, and to what
> extent should paleoanthropologists rely on it in developing their
> theories of evolution and the LCA?
>
> Susan
> --
> susansf@netcom.com
It's really very simple. The mutation that gave rise to the immunity to the
disease could easily, and probably would have, occured much later than the
erstwhile LCA. Therefore, the new LCA would be that person who first exhibited
the mutation.
Meanwhile, all the other gross phenotypical characteristics that we commonly
attribute to "humanity" would be more-or-less unchanged.
This has nothing to do with the "theory of multiple and separate evolutionary
roots of mankind per geographic regions", which I consider to be highly
unlikely. I also don't quarrel with the concept that there *is* an LCA, which
is clearly the case from purely logical arguments. The point is that the
attribute of being the LCA has some very peculiar semantic properties.
Steve Barnard
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