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Comment by tchaffee | Hacker News Reader

> A change like the loss of melanin requires selective pressure

It does? What about genetic drift, random mutations, and artificial selection, where humans select based on qualities not necessarily conducive to survival?

There is also some evidence that this change in skin color was only widespread as recently as 8,000 years ago [1].

> which in this case was likely furnished by less vitamin D

How likely?

> The pressure must have been significant since being white carries a big downside: : higher vulnerability to sunburn and skin cancer.

Unless you are trying to hide from predators or your prey in snow? As far as skin cancer, as long as it doesn't kill you before you breed, it's not going to have a big impact on natural selection, right?

[1] https://www.smithsonianmag.com/smart-news/heres-how-european...

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One aspect of sexual selection is that a disadvantageous trait needn't kill to cause differential outcomes in reproduction. If a deficiency results lower hunting success, diminished fighting prowess, loss of mental acuity etc. the individual will be disfavored in mate selection. Iterated over generations, this eventually extinguishes some genes.

There's also the aesthetic aspect, where some traits seem to be favored simply because they are attractive to the opposite sex, which can be justified because offspring will have more favorable opportunities for reproduction, but only because the trait is well liked. A strange attractor in the genetic code, if you will. This happens across species, so I wouldn't call it artificial selection - artificial selection applied to humans is also known as eugenics.

> One aspect of sexual selection is that a disadvantageous trait needn't kill to cause differential outcomes in reproduction. If a deficiency results lower hunting success, diminished fighting prowess, loss of mental acuity etc. the individual will be disfavored in mate selection.

That makes sense, and it also supports my claim that skin cancer would likely not be a trait selected against, right? It's something that usually happens later in life and that would not be involved during mate selection.

> so I wouldn't call it artificial selection - artificial selection applied to humans is also known as eugenics.

Thanks for that distinction. If this attraction is happening naturally and unspoken, it's fair to include it as a part of natural selection. However, I do think some of it is cultural, is spoken, and goes beyond natural attraction. A common example might be the preference for lighter skin in mates that we unfortunately find in several cultures. Maybe we should start calling it eugenics instead of softening it to artificial selection.

For skin cancer narrowly, sure. I don't know what it's like to live with white skin near the equator with primitive or no clothing and no access to sunscreen, though. Losing melanin every winter, getting scorched every summer... It seems like you'd have an individual who is pretty useless for persistence hunting across the savannah. On the other side, a darker skinned individual may experience lethargy and malaise in winter at higher latitude. So we should broaden the considerations to include chronic, nonlethal conditions, and competitive sexual selection amplifies their effects. This was my only point.

> A common example might be the preference for lighter skin in mates that we unfortunately find in several cultures. Maybe we should start calling it eugenics instead of softening it to artificial selection.

You can do that if you want. People really like their mate preferences and this seems more likely to soften their perception of eugenics as a concept than the other way around.

> It does? What about genetic drift, random mutations, and artificial selection, where humans select based on qualities not necessarily conducive to survival?

It seems unlikely to be due to these factors since there's a gradient from black to white as you move away from the equator.

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