How could natural selection account for skin colour?

Question

My husband is studying anthropology, and I am currently editing his assignment regarding the evolution of the human brain and it's relationship to the development of culture.

He wrote: "Queensland has the highest skin caner rate in the world. This is due to those currently living in Queensland not having evolved here. If natural selection was left to select those that had darker skin then over time the people of Queensland would progressively get darker."

It just occurred to me that this can't be true. Why?

At what age do white people get skin cancer as a result of sun damage? Usually after the age of 30. Since we reach puberty at around age 12, and many cultures in the past have begun reproducing at this age, most adults over thirty would have already had many children by the time they came down with skin cancer.

Those adults who died from skin cancer would have reproduced long before this malady killed them. Hence, how could natural selection account for skin colour?

afterwkholic... Good point. I forgot about Lemarkian evolution... which is now beginning to be favored again in scientific circles.

fluke... yes, I was thinking there could be some kind of cultural link... ie skin colour may have been culturally selected, rather than for survival.

thanks Imasis2. I can't imagine why everyone gave you thumbs down for being nice! :-)

kendrickflorida... your comments make me think... you seem to know a lot about how it all works.

thanks hyperhealer... I was thinking along those lines, too. :-)

Answer 1

You wrote: "If natural selection was left to select those that had darker skin then over time the people of Queensland would progressively get darker."

This is not necessarily true. However, if a population with darker skin were to move towards the poles, they would over generations become lighter, because a chronic vitamin D deficiency would lend a reproductive advantage to anyone with lighter skin, regardless of age.

Remember that dark hair, dark skin and brown eyes is the default setting for humanity.

Most other physical attribute are just a matter of what different populations find, or found, physically attractive.

Answer 2

Quote
"He wrote: "Queensland has the highest skin caner rate in the world. This is due to those currently living in Queensland not having evolved here. If natural selection was left to select those that had darker skin then over time the people of Queensland would progressively get darker." "

Reply
I agree with his statement given enough time and assuming there weren't any factors working against this direction of evolution.

Quote
At what age do white people get skin cancer as a result of sun damage? Usually after the age of 30. Since we reach puberty at around age 12, and many cultures in the past have begun reproducing at this age, most adults over thirty would have already had many children by the time they came down with skin cancer.

Reply
A miniscule advantage will be incorporated over a large number of generations.

"Natural" selection would imply a more primitive existence. We would have a very hard time competing with the Aboriginies since we would obviously have higher cancer rates. The thinning in the ozone in the south, the winter summer, and the Sun worshipping Australians all account for higher skin cancer rates. Skin cancer can manifest itself in younger people as well. There is an advantage to having older people around to help teach younger ones so I wouldn't necessarily dismiss that benefit to society for people beyond the age of giving birth.

Answer 3

Queensland has a high skin cancer rate because of Australian culture. The white Australians think it's a great idea to lie in the sun on the beach all day and go around with your shirt off in the sun. Most Europeans would disagree, and those of them that do like to sunbathe can only experience a Queensland-style climate by going abroad, which lasts for a few weeks at most. Aussies on the other hand can sunbathe all year round - and also suffer equivalent damage all year round.

I think your husband will ultimately be proved right as the paler Aussies will either suffer visible skin damage before their reproduction age (usually their 20s) or simply move to a more sheltered country. The darker ones would breed amongst themselves, or even with Aborigines - the darkest people of all.

Answer 4

First, I would suggest studying the National Geographics Genography Project.
When I was in school those many years ago, I was taught that the fair skinned people were from the northern climes and that only the northern Eurpeans had red or blond hair. Well, since starting to search for my ancestors on the web, I have found that blondes and red-haired people also lived in the Middle East. I have found that blacks have migrated to cold climes 10,000 years ago, and they are still black; that white people migrated to Africa's coast and 10,000 years later, they are still white.
This "natural selection" business is all part of Darwinism, which is, at most, a theory. There is no proof anywhere that one species evolved into another; there is no proof of natural selection. Consider: if "survival of the fittest" is a scientific fact, then people who are fat, lazy, weak, and prone to be on welfare are the fittest, because they reproduce the fastest!
You mentioned the evolution of the human brain and its relationship to the development of culture. Find a copy of "The Neanderthal's Necklace" and read it. The Neanderthals were huge, standing more than 6 feet tall, very well adapted to the cold of the last ice age, had huge cranial capacities, were stong...but are now extinct.
Of everything I have ever read, the two greatest factors in culture have been the female of the species (wanting protection, comfort, companionship, etc.) and agressiveness (the cultures support war-like postures).
As to cancer rates, I would tend to believe it has more to do with diet; again, a real-life observation: the Orientals used to have such difference in the appearance of the fold of the inner eye. Darwinists claimed it was to protect them from the extreme cold of the Orient. (They obviously never wintered in Nebraska or Montana.) Anyhew, nowadays this feature is fading. Why? Diet.
Perhaps Queensland people spend more time in the sun; perhaps there is something in their diet. They have recently reported on CBS-TV that diet is a major factor in skin cancer, as life observations have already pointed out.
Again, as to "natural selection", look at the people you know, and find out why they picked the mates they have!

Answer 5

Overall, it sounds acceptable, although I do have a few critiques for both you and your husband, which follow:

First, he's assuming a negative correlation between skin cancer and increased skin pigment concentration. I'm not sure that such a relationship is that well defined. I could be wrong on this point; he had just better be able to back it up with a study or two.

Second, one needs to consider the length of time that humans have inhabited Queensland. Evolution seldom acts quickly, and according to the movers and shakers of evolutionary theory, evolution does not happen quickly by our standards. This takes hundreds generations, at the absolute minimum, and that is referring to something that is always lethal in the homozygote. Something like pigmentation would take even longer.

The third problem that I have with it is that his verbiage and tone implies that evolution has stopped. Natural selection has yet to take a break. I'd also apply my first critique with your argument as well. While it is logically sound, you must establish that most skin cancers do not strike until after reproductive age, and even more importantly, that skin cancer susceptibility is heritable. As far as I know, skin cancer has truly limited heritability. It occurs as a result of mutations caused by exposure to the sun, and may or may not be passed on to offspring. You are also assuming that the mutation that produced the cancer occurred early and did not express until late in life. I fear that this is a flawed assumption.

I'm no expert on skin cancer, it's timeline for action or its heredity, but you need to address the questions that I have outlined in order to make the claims that you both do. As an aside, what you describe is a perfect example of the evolution of senescence, a truly fascinating topic in my opinion, and one that you seem to be versed in. Whatever the case may be, kudos for thinking critically! Those conclusions would have escaped most people, so rock on for catching what most wouldn't!

Answer 6

I have no idea if people can evolve from light to dark
Early humans were dark skinned, and as some moved into temperate regions, their skin got lighter. This was probably because with more pigment we could not absorb enough vitamin D.
There was no need for people in regions with more sun to evolve this way, because they got more sun hence more D.

There is no mechanism I know to pass down pigment from parent to child. Just because you got tanned every year of your life and ended up far darker than you were born, does not mean you are going to magically have darker skinned children. You pass on your genes and whatever habits you can while the child is in the womb. Tans fade, while pigmentation is genetic.

One thing you might want to look into would be the earliest onset on skin cancer - if only a small percentage die before they are done with children, it would have a cumulative effect.
Also, consider when skin cancer might occur if people used no sun screen - he could alter his argument to include that if it helped.

Answer 7

Hi! I think you just got a li´l confused. Skin cancer is due mainly to the hole in the ozone layer caused by human beings in the last 40 years, let´s say. That´s like a fraction of a second to the cosmic time. Evolution takes hundreds and hundreds of years to happen. Probably 70 years from now, our grandchildren´s kids will be born only if their parents´ skins will be able to afford UV at least until they can give birth to a new breed. And that probably means that they´re are gonna have a different skin color than you do now.....

Answer 8

From NewScientist
10 March 2007
NewScientist.com news service
Jessica Marshall

"So why did different populations evolve different skin tones? The leading theory, proposed by Nina Jablonski, also at Penn State, is that our colour reflects a balance between conflicting needs. Not only can sunlight damage our skin, it also breaks down folic acid (also known as folate), an essential B vitamin. On the other hand, we need ultraviolet light to make vitamin D.

Jablonski and colleagues have shown that skin colour around the planet correlates more closely with winter UV levels than with summer levels (New Scientist, 12 October 2002, p 34). This suggests that our skin colour has evolved to optimise folic acid and vitamin D levels during winter, with tanning allowing us to adapt to higher UV levels in summer."

Answer 9

Melanin would build up in successive generations if they were continuously exposed to high levels of UV radiation. The argument not put forth here is in simple sexual selection. Not all traits are inherited or continued because of natural selection. Humans pick disadvantageous traits a good deal of the time because we find them appealing. Tall, thin women are not prime candidates for child birthing. The birth canal is narrowed and the child has to have its still soft skull forced between constricted pubic bones. Today they are often C-sectioned to prevent complications, not exactly natural. So as for skin cancer, tough I disagree with the age of death from skin cancer (I would put it closer to 50) by age 30 many people will show spots from cancerous cells around age 30 and these are not exactly attractive. You are less likely to pick up a lover if they have discolored spots covering their bodies. Throughout all societies symmetry is always considered attractive and random blotches covering your exposed skin is not exactly symetrical.

Answer 10

Those are good questions you raise, but I can think of three problems with your thinking.

Female puberty occurs at 12, these days, but even 100 years ago, it didn't occur until at least 16 or 17. A lot of nutritional factors probably play into that.

You also say that TODAY, skin cancer usually starts at 30. I don't know if that is true, but consider that today, we spend most of our time indoors and often wear clothing over most of our skin. When humans were first evolving, we wore no cloths and lived outdoors so our exposure to sun was much greater. It is possible that light skinned people living a few hundred thousand years ago would have gotten skin cancer at a much younger age.

A third factor is that even if people die at age 30-40, that gives them less opportunity to raise all of their children to the age when they themselves can have children nor can they help in raising their grandchildren. We must have grandchildren or our genes die out in our children.

All three of these factors would contribute to people with light skin having a smaller window of time to reproduce and pass on their genes. Inevitably, people with darker skin would predominate in the population.