darkuser Wrote:
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> thx Bernard, but i still don't understand what you
> mean by selected. If i were to live in Africa,
> will my descendents get darker in a few thousand
> years, or will they die off? In other words, are
> you talking about "survival of the fittest"?

"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.

let me give you another example that will make it clearer. Suppose we have a population of locusts on a farm and the farmer sprays DDT. In any population there will be a large variety of traits (or in our previous case a possible range of skin hues depending on the particular genotype). Here most locusts will be killed by the DDT, but there will be some that have the ability to metabolize the insecticide and will survive to reproduce. Their offspring will have that level of resistance to DDT. If the farmer wants to kill the same percentsge of locusts as before, he will have to increase the amount/acre of DDT he uses. Again, most locusts will be killed but there will be some who can still survive and reproduce. Their descendants will inherit that extra resistance to DDT. and so on. There are bees now in Brazil who eat DDT as food. The same thing applies to our skin color example. If parents have some characteristic that gives them a better chance of reproducing and passing on that characteristic (trait = gene) to their descendants, over time that characteristic will become the norm (i.e. fixed) in the population. Here the ability of melanin to protect folate from destruction by sunlight and causing stillbirths is the trait that is selected for "reproductive advantage"
Bernard


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> Edited 1 times. Last edit at 04/16/05 11:16AM by
> darkuser.