I'll set aside much of the rest of the recent posts, on the grounds that we've beaten the "racism" idea into the ground in the Bones of Contention thread. However,
jcrawford wrote:This is exactly the same as saying that we shouldn't study how sunlight affects differently colored skin because to make distinctions between light-skinned and dark-skinned people is racist.
Not really, since melanin does play a role in dertermining human skin shades whereas natural selection does not.[/quote]I guess you'd say that god darkened the skin of some folks because of some imagined reason for doing so. However, the actual story is this:
1. melanin shades skin cells from UV (fact that you can't deny)
2. people with more melanin receive less UV radiation to their skin cells (again, fact, based on #1)
3. people with less melanin receive more UV radiation (fact, the flip-side of #2)
4. UV causes mutations; in skin cells, some of those mutations cause skin cancer (fact; check the medical literature)
5. UV induces the formation of vitamin D (fact; check even old biochemistry texts)
6. UV causes the breakdown of folic acid (fact; recently shown, but I can't remember where. I could look it up if you want to quibble)
7. There's a higher incidence of UV at the equator than near the poles (fact; just measure it) there's also more UV in Australia (fact based on measurement)
8. Too little UV results in too little vitamin D, which results in Ricketts (fact, just look it up)
9. Light-skinned people exposed to high UV get skin cancer at a high rate (look at Australia's rate relative to the rest of the world)
10. Dark-skinned people exposed to too the average UV dose in, say, New York city have a higher rate of Ricketts than light-skinned people in the same environment. Although milk is fortified with vitD to prevent this, many African Americans are (duh) not of European descent, and therefore lack the mutation that causes adult persistence of lactase. Hence, they are lactose-intolerant, and can't drink milk past weaning. Soymilk is not vitD fortified. Hence, the Ricketts.
THEREFORE there is intense selective pressure for skin color. Equatorial Africa has high UV, which selects for lots of melanin--to protect DNA from mutation, and to protect folic acid from degradation. There's enough UV there to produce adequate vitamin D. Europe has low UV, especially in Scandinavia, and therefore selects for light skin--to produce enough vitamin D for bone development; there's not enough UV to cause the other effects often enough to offset selection for vitamin D production. In short, skin color has been, and still is being selected for.
So, here are a bunch of incontrovertible facts. You may, if you like, claim that no conclusion can be drawn from them, and claim that natural selection cannot occur. But you'd be ignoring the science if you did so. Since the facts point inescapably to selection, but since you stated confidently that no such thing could occur, I humbly suggest that you learn some evolution.