Thursday, March 26, 2009

Placing race

I write about place, and place shapes race. Where you live influences your identity. This is true even in what might be called its “original” sense.

Let me preface what follows with the reminder that race, the idea of human races, is a socio-historical reality, not a biological fact. Indeed, what makes race such an insidious idea is that race seems biological (because we often take our cues about it from people’s bodies) and thus essential.

In most minds – albeit loosely and inconsistently – race is based on skin color. I say loosely and inconsistently because, with white slave owners raping black women or taking them as mistresses, slaves were born with lighter and lighter skin, to the point where in the 19th century it was sometimes difficult to tell by sight who was white (free) and who was black (slave) – which distinctions at this point indicate just how much social status rather than skin color is a determinant of race: slaves were black, no matter how light their skin. Hence the “one-drop” rule.

Back to skin: place really does seem to color our skin, as the map above suggests. The map, based on one used by Nina Jablonski and George Chaplin in “Skin Deep” in Scientific American (2000 [287:74-82]), actually predicts the relative darkness of human skin given variations in sun exposure around the globe. If your ancestors came from certain parts of the planet, you have darker skin, if from other parts, you have lighter skin.

It turns out that skin color is highly mutable. The original humans, coming from northeast Africa, were relatively dark, but their descendants who went north (or farther south to the tip of Africa) grew lighter over time and those who traveled elsewhere remained dark or lightened and then darkened as their movements took them north and south. The genes that govern skin color are remarkably plastic. But they are not suddenly so, which is probably why the relatively recent arrivals in South America are not in fact as dark as people in similar ranges in Africa whose ancestors lived there all along.

Compare the map above to the map below, which indicates the relative intensity of ultraviolet light around the globe. Unsurprisingly, the map below matches the map above.

What changes skin color? Melanin, the pigment that darkens skin, of course. But what causes variation in skin color? I used to think it was skin cancer: melanin protected hairless humans from melanoma-causing solar rays. People in sunnier places had more of it because they were at higher risk for cancer. But cancer is now thought a weak candidate. The onset of cancer from exposure to sun is so late in life that it would have exerted weak selective pressure.

The more likely cause, according to Jablonski (in "The evolution of human skin color," Annual Review of Anthropology, 2004 [33]:585-623) among others, is our body’s attempt to capture critical vitamins: the need for sun-generated vitamin D in northern climes selects for lighter skin; the risk of sun-generated deficiencies of vitamin B folate selects, in sunnier climes, for darker skin. Too little D leads to weak bones, while too little B, to birth defects.

What the two maps suggest is that where people live influences skin color, but where they or their ancestors have been also has an effect. We don’t turn skin tones on and off simply be changing places. Even in the old old days, human beings moved around the planet quite a bit. Our bodies changed over generations, not suddenly. And slow change coupled with extensive migration accounts for the considerable variation in our skin colors today.

We are products of place, but not necessarily or completely of the place we inhabit today. Our evolutionary past in other places lingers as an effect in the present. The combined effect of places-plural (places past and present) suggests some of the complexity involved in the relationship between place and identity.

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