Re: [MLUG - DISCUSSION] [MLUG][POLITICS] So, white people are Mutants?

[Jonathan King <EMAIL:PROTECTED>]

On 12/18/05, Mike Miller <EMAIL:PROTECTED> wrote

On Sun, 18 Dec 2005, Rick Buford wrote:

> "Researchers believe the gene, in one of the fastest-evolving regions of
> the human genome, has been under considerable selection pressure. One
> potential reason is that lighter skin improves the body's ability to
> synthesize vitamin D, offering an advantage in light-limited Northern
> Europe but not in more sun-abundant tropical locales. Sunlight-assisted
> vitamin D production is crucial for preventing rickets, a disease that
> weakens bones."
>
> Isn't this a really prime example of evolution. i.e.,
> 1. Darker skin protects from heavier sun exposure, and is adequate for
> producing enough vitamin D while in said sunny environment
> 2. Lighter skin is less protective of heavy sun exposure, but is adequate
> protection in lighter sun while being more efficient at producing vitamin D
> in said environment

That's the classic theory.  There may be other factors at work in addition
to this melanoma-vitamin-D tradeoff.  For example, it has been suggested
that darker skin is protective against some kind of fungal infections.

I don't think we'll really understand what's going on here, though, until we figure out the mystery of relative human hairlessness.  Interestingly, skin color per se can vary a lot even in primates (chimps are relatively light skinned, while gorillas are not; both are way hairier than people).  Humans are extreme outliers on the hairiness continuum, though.  For whatever reason, the pressure on genes that had a main effect (or a side effect) of hairlessness  were really strong and pretty much universal, while skin color can be all over the place.
 

> p.s. I am not attempting to make the argument that light people are more
> evolved than dark people.

Of course not.  There's no such thing as "more evolved" anyway.

Certainly not in the sense of "having made more progress" (which doesn't make much sense, when you think about it).  There are genes that have diverged more between species and individuals, and some species that have made more substitutions in their (coding) genomes than others, when you project back to the presumed ancestral state of a group.  Humans are (last I knew) pretty remarkable in our relative lack of genetic diversity, although that doesn't mean the differences are trivial.  If I had been born in sub-Sahara until very recently, my skin color would quite likely have been lethal.  My ability to withstand the cold, however, is pretty impressive.  That's probably not because my skin is light in color, though; I actually have no idea why that is although I could tell a pretty (but completely post hoc) story that this came about because I had dozens of generations of ancestors who grew up on the shores of the Baltic Sea.

But speaking of interesting mutations and oddities...I have notable epicanthal folds around my eyes, and what some describe as a "single lid"  (weird fact, if I put my thumb on my eyebrow and hold it there, I can't shut my eye completely because of this configuration).   If that's the only thing you knew about me, it would tend to suggest that either I am of Asian ancestry or that I have one of a number of exotic developmental disorders.  As it turns out, I'm just a slightly unusual Lithuanian;  weird eyes, really tall, and (tragically) no basketball skills whatsoever. :-)

Of course, lots of people try to come up with a strong selection story for epicanthal folds, but last I knew this wasn't really going anywhere.

jking

 
 

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