darkuser Wrote:
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> bernard Wrote:
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> -----
>
> > "Survival of the fittest" is not the best
> > formulation. a more insightful one is
> "ability to
> > reproduce, or reproductive advantage" And,
> yes, if
> > your descendants lived near the Equator (and
> > particularly if they lived outside and did
> not
> > wear a lot of clothes (like people did in
> the
> > past) they would get a lot darker. In the
> paper I
> > posted, people who have more melanin are
> protected
> > from destruction by sunlight of their folate
> more
> > than lighter skinned people. Therefore they
> will
> > have more offspring than lighter skinned
> people
> > (because destruction of folate affects the
> ability
> > to give birth. Over time this will produce
> what we
> > see now. Skin color is apparently not a huge
> > reproductive advantage, because it takes a
> long
> > time to produce results.
> >
>
> I understand this process of biological evolution,
> but wouldn't it depend on a few things: the
> assumption that some of my descendents WILL in
> fact develop darker skin, and that those who don't
> will be at a survival disadvantage only if the
> SOCIETY permits.
This is NOT a society permission question. Whiter people will have more stillbirths because of the amount of solar radiation and therefore will have fewer descendants-- exactly what "reproductive advantage" means. Indeed natural selection applies to humans not just to other organisms.
Now-- to avoid being simplistic. Humans have culture and can adapt through culture and not solely by genetic means. This is why in my previous answer I covered my rear by specifiying that the people would have few clothes and live outside to guarantee solar exposure. Australians today are at increasing danger due to the destruction of the ozone layer which is allowing a greater amount of ultraviolet to hit Australia. They are adapting culturally-- children are not allowed to play outside as much, they are all required to wear hats, they are liberally spreading SPF 30 lotion, etc. etc. Similarly there could be
cultural selection mechanisms.
I didn't think that the concepts
> of "Survival of the fittest" or "reproductive
> adantage" significantly applied to humans. Also,
> on the former point that my descendents will
> develop darker skin, i presume you meant that the
> process of natural variance is enough, since you
> said, in a reply to wireless, that mutations are
> not necessarily involved. However, despite the
> examples given by others here, does natural
> variance really cause this much change in skin
> pigmentation?
You can see for yourself how much variation there is in human skin color. Look at the range from Swedish blondes to the darkest Nigerians and all the variations in between. All this range comes from different combinations of possibly 8 genes. Look at how dark even lighter colored people can get if exposed to enough sunlight, i.e. sun tanned.
>
> Back to the question of race, it still requires
> thousands of years for this adaptation to occur.
> Are you saying that the gene pool created in this
> time is insufficient to enable taxonomic
> relationships to be established?
There are no taxonomic relationships-- remember there are no races-- I'm just pointing out in fact how useless skin color is for classifying since it is so subject to adaptation to degrees of sunlight. The reason it takes a while is that it is not a severe challenge (that is why I went to DDT as an example because of its strong selectivity). An example in humans, is malaria. Malaria is such a severe selective factor (causes so much mortality) that any adaptation that provides some relief spreads through the population much faster. For example, sickle-cell gene in Africa reached some 30% of the population of Cameroon in about 1000 years.
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> Edited 1 times. Last edit at 04/16/05 02:14PM by
> darkuser.