Black or white

[andrewdag]

At school we were taught that black absorbs heat and white reflects heat. If that is so why is it that in Africa where it is hot the population is black and therefore absorbs heat and get too hot and in the Artic the population is white and therefore reflects the heat and get cold. Surely it should, on sciencific grounds at least, be the other way around?

[gen2]

There are two factors you have not considered.

1). A good absorber is also a good radiator. A black body in the arctic would rapidly lose heat by radiation.

2). It is not just heat that is absorbed by a black body, but light as well. Most importantly, it absorbs ultraviolet light and therefore gives protection against sunburn and skin cancer. This is far more important to native African people's survival than heating up - perspiration can generally cool them down enough.

[andrewdag]

I had thought about these. But given that UV level are increased with altitude why aren't Tibetans black? Why do Arabs wear white? Why do scientist say as the ice melts and the ground is exposed the darkness of the ground will absorb more heat. It amazed me in Indonesia that those living on the equator were not black but more Mediteranean

[Clanad]

As a point for discussion, one researcher says "...Twelve years after Darwin wrote his book attributing the origin of species to natural selection, he wrote another book 898 pages long, attributing the origin of human races to our sexual preferences, which I described in the last chapter, and entirely rejecting a role of natural selection. Despite that verbal overkill, many readers were unconvinced. To this day, Darwin's theory of sexual selection (as he called it) remains controversial. Instead, modern biologists generally invoke natural selection to explain the visible differences among human races especially the differences in skin color, whose relation to sun exposure seems obvious. However, biologists can't even agree on why natural selection led to dark skin in the tropics."
This research bioligist (Jared Diamond) makes a good case for your observed results having more to do with sexual selection rather than little, if any, natural selection dependant on location... Full article here: http://www.mc.maricopa.edu/dept/d10/asb/anthro 2003/origins/sexselection.html ...

[b-real]

The sun does not affect Black people as much as it does white people for a simple reason. When you buy sun lotion you look for UV protected, but there is actually a better one. Not sure maybe UVA or something. The Difference is drastic, if you buy the lesser UV the danger rays go threw. Black people have more Melaloma, I 'm not sure if I spelled it right. This is sort of what the uva does , blocks the sun. It's like wearing spf 50 all the time

[dawkins]

Hello Clanad, How are you?

That's a good article. Evidence doesn't support natural selection driving racial differences. That is not to say that skin pigmentation doesn't offer marginal advantages/disadvantages in some instances but it has not been the difference between life and death, or breading and not breading. Differences arising through the founder effect (small populations colonise new areas; and augmented by sexual selection is a simpler explanation because it doesn't require specific survival advantages.
Incidentally, genetically speaking, race is a lousy indicator of difference. 85% of global variation can be found between people within countries and of the remaining 15%, national differences account for 8% and racial differences (asian,african,european, etc) count for just 7%. Migration and globalization with probably keep bringing this figure down.

[Zevon]

The biological effects of more melanin in the skin vastly outweigh the physical effects of color with regard to absorbtion of Uv and the prevention of skin burning and cancer. Not everything follows basic physics there are usually more factors to consider.
And although color does affect heat loss and absorption there is such a samll gap between the Arctic and Africa, less than 50 degrees C (ignoring wind chill) the color will have a very small effect.
Skin tone is depecndent on pigmentation not heat loss.