Re: Modern Neanderthals?
David \ (dsierra@lonestar.jpl.utsa.edu)
Tue, 22 Oct 1996 15:30:47 -0500
On Mon, 21 Oct 1996, Larry Devich wrote:
> On 20 Oct 1996 17:39:32 GMT, "Rohinton Collins"
> <rohinton@collins.prestel.co.uk> wrote:
>
>
> >Again, splitter or lumper? I would describe a distinct species as one which
> >is reproductively isolated. But this is, of course, very difficult to
> >determine in extinct species.
>
> It seems to me that this definition of a species is very slippery.
> How do you determine if a population is reproductively isolated? For
Okay, I'll be gentle.
Reproductively isolated means that representative individuals from the
two populations cannot successfuly mate and produce firtile offspring
capable of successful mating with both parents' populations.
> what period of time does this isolation have to persist to qualify?
Now that IS a good question and one that needs some really good
examination. Factors involved would be reproductive rate, enviornmental
pressures and baseline mutation rate for starters. I would hypothosize that
for organisms with a "standard" rate of mutation one would be looking at a
_minimum_ of several tens of thousands of generations. Even then, there
would have to be evolutionary pressures on one or both groups that would
cause significant adaptation to local enviornments and diversification.
> If two groups of organisms are isolated but not really noticeably
> different, can interbreed and produce fertile offspring you call them
> two species?? Using this definition Inuit would be a different
> species from Bushmen, correct?
No. If two groups can successfully interbreed, dispite their
physilogical differences then they are, by defintion, part of the same
species.
> If not, why not? :-) I'm really curious, I had always considered any
> populations that "could" interbreed successfully to be of the same
> species. In extinct animals there would have to be significant
> differences before I'd call them separate.
Ahh, and there in lies the delema! The question is: Are the observed
physilogical differences between H.s.n. and H.s.s. indicative of
speciation processes, or merely minor fluctuations in the species genome,
on the order of minor genetic differences between populations such as the
Inuit and Bushmen (which are clearly members of the same species)? I
would tend to that the differences are great enough to consider the two
groups seperate species, especially in light of recent data on the
subject, but there are those who disagree with valid points to raise.
The key to answering the question (in my humble opinion) is first
answering just how great the selective pressures were on H.s.n. and
H.s.s., how long they were geographically isolated (first step in
reproductive isolation, remember) and of course the aforementioned how
long would they have to have been isolated.
> I'm no expert on any of this so please be gentle :-)
Hope I wasn't to nasty!
Later,
David Sierra
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