Saturday, August 1, 2009
Nelson Mandela, Dr. King also evolutionary biologists? The answer may lie much farther North on the skin of an Inuit fishing off the southern shores of Greenland while absorbing the Northern Lights— skin unusually dark for being so for North. We might learn how we all got our hues and what the "d" is in skin deep.
I recently had one of those "aha" moments, science related moments, but, I'm going to first backtrack to the first of this type of moment I had years ago in a developmental biology class at Brandeis. There we learned of the miracles of biologist Moscona. We learned that when cells are separated in a blender early in embryonic development, then left alone, the organism reassembled, the cells found each other— they "knew" where to go. Leaving all the ensuing science of cadherins aside, initially learning about this had a true rippling effect on me, almost as if stumbling on an overarching, unifying theory that the great physicists sought (and still do), so effortlessly bridging my nascent philosophies, frameworks, and spiritual questions with the moving certainties of science. Like wind to a dormant sail, these cells took on a new kinetic energy, a meaning, a life. Moreover, it was genuinely satisfying.
Just last month, I had the privilege of sitting at a talk by Dr. Bruce Hollis, one of a growing number of strong proponents of Vitamin D (supplementation and understanding). The exciting part was his segment on the evolution of skin color. He was impassioned, and, to clear the air, he even recommended changing the name of Vitamin D to something else because it currently diminishes the true importance of the "vitamin." This is not your mother's Vitamin D that you get from a glass of milk that will keep your bones strong. Burgeoning evidence reveals that Vitamin D is not just good for bones, but is essential to cardiovascular health, cancer development, the immune system, autoimmune diseases, and metabolic diseases; in fact, Vitamin D receptors are found throughout the body and a substantial portion of the human genome may be directly or indirectly controlled by Vitamin D. Moreover, it seats a high throne in our own evolution. I also recently listened to a TED talk "The Illusion of Skin Color" by anthropologist Nina Jablonski, author of Skin: A Natural History and pioneer in the field of skin color, its reasons, nuances, and consequences. While her findings may be pedestrian to those studying to be anthropologists and evolutionary biologists, it was fascinating and I was astounded that such knowledge hadn't reached its deserved "common" status. While understanding the reasons behind skin color is in it of itself intriguing, its social context is equally so.
So why is my skin darker than that of Michael J. Fox, lighter than that of Naomi Campbell? What is behind the rainbow of complexions around us? We all understand that skin color varies by latitude, but why? No need to go through all the details (you can bing or google Jablonski's research), but it all boils down UV-B rays that hit our skin, which, in turn, produces Vitamin D. In a nutshell, our skin colors are directly related to the amount of UV-B rays that reach us and that depends on how far North or South we are (UV-C deflects off of the atmosphere and UV-A, blocked by sunscreen, purely damages DNA having no known physiological benefits).
Ancestors to modern humans actually started light skinned, but covered with hair. Natural selection shed away this hair to make sweating easier, allowing these primates to stay out for longer, hunt longer, and keep body temperatures stable. The naked skin was thus overexposed to the beating UV-B and evolved the pigment melanin. Modern humans all began in Africa, where we all dawned dark skin. More than a pigment, melanin protected against the abundance of UV-B rays near the equator. We might think that we used melanin to protect ourselves from overexposure to UV-B and thus skin cancer. But, cancer is a long-due process, typically emerging later in life after we have already reproduced. In reality, in addition to shielding against UV-B inflicted DNA damage, humans produced high melanin in Africa to protect against UV-B rays destroying folate within their bodies. Folate is essential for DNA and cell production and has been known for many years now to be central in early embryonic development (e.g., neural tube). Those in Africa with more melanin, darker skin had more reproductive success. They were selected for.
UV-B is truly a double edged sword, because on the one hand it destroys folate, but, on the other, it catalyzes Vitamin D production. About two million years ago, we started migrating North out of Africa. That's when we realized our love-hate relationship with UV-B. Moving North away from equatorial Africa, we were greeted with fewer and fewer UV-B rays and the dark skin that was such an asset in Africa was detrimental in Europe. With minimal UV-B, those with highly melanized, dark skin blocked the little UV-B that they received and could not produce adequate Vitamin D, resulting in malformed bone structures, amidst a host of other conditions. Women with poor pelvic bone structures could not reproduce and so the dark skinned died off in the higher latitudes. Those humans with mutations to produce less melanin and lighter skin were selected for, survived, and carried forward.
Thus, we have the push and pull of evolution, the tightrope that our species has walked, making Northern people light skinned and equatorial/Southern people dark skinned. Equally alluring is the light this knowledge sheds on how we have treated one another and how we can fit this into our social psyche. As Europeans leapt ahead in wealth, productivity, technology, and exploration in the 16th and 17th centuries, they also adopted a false sense of dominance, and this perceived superiority often assigned values to our most prominent, conspicuous, and superficial feature— our skin. Instead of marking of natural diversity, skin became a source of apprehension, misunderstanding, and authority. This often played out brutally, as in the African slave trade, in which upwards of 50 million Africans perished. We have to also remember that the capture, trade, and enslavement of Africans was not impulsive, but came after careful "deliberation" and "counsel," often sanctioned by bishops and leaders within the Church. It is not just a black and white issue. Even in India, lighter skinned people took up posts in the higher castes, while their darker counterparts were demoted and marginalized. Dalits, untouchables, with dark skin were imprisoned to a hundred generations of menial labor. It has only been years of economic development, social mobility, and changing attitudes that have chipped away at these walls. The existence of a skin-bleaching industry is questionable enough.
We have all been taught the historical perspective, but including the evolutionary perspective provides a far richer context. I understand that reality is far more complex, with interactions of political, economic, environmental, and cultural structures and I am, by no means, simplifying our race and culture relations. But, the evolutionary standpoint demonstrates how ludicrous and baseless prejudice, differentiation, and dominance based on skin are. In fact, something unseen and arbitrary was unfolding— a wholly random set of mutations to select for more Vitamin D production.
Adding another layer is the fact that the evolution of lighter or darker skin occurred in multiple, separate instances (migrations). Moreover, it is surprising how quickly skin can change tone. For example, look at South Indians who have migrated North, evolved lighter skin, and then migrated back South, and evolved darker skin. In fact, our complexion today could be completely different to our ancestors less than 100 generations ago.
We are generally flat footed when dealing with race and our histories, often jumping into issues before even framing them properly, and resorting to purely a position of victimization. A newer, more evolved, more lateral thinking-based model would help. It is part of the grain. Just as our physical complexions have evolved, it's time our social and emotional complexions keep pace.
So why is the Inuit unusually dark even while he is living so far up North? He gets his Vitamin D from his fish-rich diet.