Re: Neanderthals were not stupid, just a bit anti-social


nmp wrote:
floyd wrote:

Deep Burke wrote:
Could Neanderthals cross-breed with homo sapiens?

The currently available "best evidence" suggests that they did not.
Mitochondrial DNA comparissons show that neandertals were well-outside
of the modern human norm.
There are a few possible alternative explanations. Any of the following
would be consistent with the available data:

1) we tried to cross breed, but the hybrids could not form into viable
embryos
2) we successfully cross-bred, but the viable hybrids were sterile, so
they did not reproduce themselves.
3) we were partially interfertile. A male neandertal + female human
mating could produce viable, fertile offspring, but a male human +
female neandertal mating could not.
4) we were fully interfertile, but the female neandertal mitochondrial
lineages were lost to drift in small populations
5) we were partially interfertile, male hybrid zygotes would develop but
female ones could not (I don't know how that would work, but it's
hypothetically possible).
6) we would have been interfertile, but we did not recognise them as
potential mates and/or vice versa, so we never even tried.

Nah, that wouldn't be possible ;)

Unlikely, I admit. There are humans who recognise sheep as potential
mates! ;-)



7) we were fully interfertile and cross-bred with them regularly, and we
just haven't tested enough people to find traces of the fact yet. 8)
humans of the time (roughly 40,000-27,000 years ago) were also very
different than modern humans, so the distinction between us and the
neandertals is illusory.

In what sense were we very different then?


If 7 and/or 8 is the correct interpretation (as Milford Wolpoff, Alan
Thorne and a few others propose) then we are the same species, not
really different at all in any important ways, and the anatomical
differences between us and the neandertals (chins, orbital tori,
occipital buns, long bone curvature, etc) are merely superficial.

Until recently, that was the "majority opinion" among
paleoanthropologists. Now it has drastically fallen from favour.
Chris Stringer's _African Exodus_ is a good "popular" account of why,
and Cameron and Groves' _Bones, Stones and Molecules_ is a more recent
(and much more detailed, but somewhat less accessable) explanation.


That's not an exhaustive list of the possibilities, I'm sure other, more
creative thinkers can come up with other possibilities. Of these eight
options, 1 seems the strongest, based on current evidence. There have
been a few claims for 2 but these are not widely accepted by most
paleoanthropologists and archaeologists. Options 7 and 8 are proposed
by a minority of anthroplogists. The idea that neandertals were
ancestral to humans used to be the numerically dominant idea, but the
evidence collected over the past 20 years or so increasingly makes it
seem like this was not the case.

Yes, but where did I read that the gene for red hair in present day humans
may have originated from Neanderthals?


I'm not certain where you read it, but it's based on Rosalind Harding's
work.

Harding RM, Healy E, Ray AJ, Ellis NS, Flanagan N, Todd C, Dixon C,
Sajantila A, Jackson IJ, Birch-Machin MA and Rees JL (2000) "Evidence
for variable selective pressures at the human pigmentation locus,
MC1R." _Am. J. Hum. Genet._ 66:1351-1361

is probably the reference you're remembering, although there were also
a lot of press reports, so you might have heard it somewhere else.

More recent work, especially by Jonathan Rees at Edinburgh (discoverer
of the M1CR "ginger gene") suggests that the human red hair gene might
be as recent as 20KYA. That's not to say that neandertals didn't
_also_ have red hair, but they may have developed the trait
independently. It's also possible that the gene is older than either
Rees or Harding believe and was present in the shared (_H. ergaster_?)
ancestor of both neandertals and humans. I don't know enough about the
work to be certain one way or the other, or even make an informed
guess. I probably should (I'm a red head myself, so "this time it's
personal!" as they say) but I admit I don't.


If that is true it would indicate
some form of crossbreeding, right?


Not necessarily. _If_ the gene confers a selective advantage in
Europe, which is possible, two seperare lineages could have converged
on the trait because of its adaptive advantages (sort of like sharks
and dolphins are both streamlined in shape, despite their distant
relationship).

Even more likely (IMO, and IANA geneticist so take it with an entire
salt mine), if the gene existed in our shared African ancestor, >600
KYA, but was only rarely expressed in Africa, it could have become
increasingly common in two seperate lineages that both occupied the
same environment where it was favoured.

That's not to say that red hair, itself, confers any selective
advantage, but rather, that it is plieotropic to a gene that is
favoured in Europe, namely, lighter coloration in general. Low UV
exposure tends to favour skin that it easily penetrated by UV, for
photosynthesis of Vitamin D. The M1CR variant does a lot more than
just influence the colour of hair (of course) and is also linked to sun
sensitivity and freckles. In Africa, it is generally a highly
maladaptive trait, so homozygous redheads are selected against (mating
opportunities are, shall we say, "somewhat limited" when you've got an
all-over sunburn!), but heterozygotes have no problem. So the gene may
have been present all along, but "hidden" and only started to become
common when humans (and neandertals) moved into low-sunlight
environments.

That's idle speculation though, don't take my word for it. Ask a
geneticist.



Thanks, by the way, for your thoughtful post :)

Entirely my pleasure.

.

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