IT’S UNDENIABLE
There is no such thing as race. We are all the same race. We all come from a common ancestor. We are homo sapiens with different skin colors and skin color is a tiny, recent, and transient feature of human genetics brought about for the most part by geographic location and the prevailing climate. Race, as it is commonly understood, is an illusion. Racism has no foundation in science and is the product of humankind’s ignorance and fear of the strange and unknown, down through the millennia. It is kept alive today by bigotry and that same fear of the unknown. Isn’t it about time the enlightened enlightened the un-enlightened. Then it would only leave religion to cause the world’s conflicts. Oh… and money,
As an elementary-school kid in the 1960s, I was very aware of race and racism. Back then, Washington, D.C., was in many ways a racist Southern town. That awful sentiment was just part of the scene. I could hear it without listening very hard. It was right there in background conversations in busy restaurants, along with the sound of clinking glassware. I could also see what was happening. Newspaper headlines described famous people who were assassinated for clearly racial reasons.
At the same time, the civil rights movement achieved sweeping changes in laws and perceptions. It all had a deep effect on me. Today, it’s easy for me to see that racism starts on the surface. Nowhere are the forces of evolution that have shaped our societies more apparent than in the color of our skin. The surprising thing is that skin color does not mean what a great many of us think it does.
I’ve traveled around the world a little bit (largely because I often attend the International Astronautical Congress, which is held in a different city every year). If nothing else, I’ve learned that people are a great deal more alike than they are different. In evolutionary terms or fact, we are all almost identical. We each share 99.9 percent of the same DNA. I can prove it to you. Better yet, you can prove it to yourself. What do you think would happen if a man from Scandinavia married and enjoyed sexual encounters with a woman from East Africa? They might easily have a child. That kid would be a human. This union is not going to produce anything else but a human.
There is only one species of Homo sapiens. We all share common ancestors. This may be where myths like Adam and Eve living together in a garden come from. If you just sit and think about it, and realize that we are all extraordinarily alike, you might just conclude that there must have been an original pair of humans that led to you, me, and everybody we’ll ever see. The author or authors of the Book of Genesis may have reached the same conclusion logically, i.e. by just thinking about it. Humans, all of us, must have had a common ancestor. Otherwise, how could we all be of one species, able to reproduce so effectively? There are more than 7 billion of us strutting, sexing, and texting in the world today.
Despite that line of reasoning, people of different tribes or geographic regions have been warring with each other, distrusting each other, and forbidding marriages with each other for millennia. In many instances, skin color has been a trigger for these conflicts. It raises a fascinating evolutionary question: If we are all one species, why do our colors differ so dramatically? Is skin color connected with deeper differences between various groups of humans? Or you could turn it around and ask, are races real?
Here’s the short answer: No. Skin color is a tiny, recent, and transient feature of human genetics. One of The Eyes of Nye television shows was about this issue. I stood in a field with a few dozen cattle. I pointed out that the colors of those particular animals varied widely. There were black, white, and brown cows of various shades, and they exhibited no discrimination. They roamed and grazed showing no preference for any one variation. Racism did not seem to be an issue with them; they were all of one species. So are we. Race, as it is commonly understood, is an illusion. But don’t take my word on it. Let’s see what two centuries of evolutionary research have to say.
The first place to look for answers is on the skin of our closest primate relatives. As our understanding of DNA has increased, we have come to understand that we share around 98.8 percent of our gene sequence with chimpanzees. This is striking evidence for chimps and chumps to have a common ancestor. Chimpanzees have very light-colored skin; you can see for yourself where the skin is exposed on their cute cheeks and jowls. So, we might expect humans to have about the same color of skin as our very close genetic cousins. But with few exceptions, we don’t.
Anthropologists have been all over the world looking for fossils of our ancestors. And they’ve found them: dozens of closely related human skulls and nearly-human skulls (my old boss?) and other bones, which all indicate that humankind started out in East Africa. That’s where we find the greatest genetic diversity of humans to this day, and that’s where we find the oldest fossils and oldest evidence of human activity. If we started out related to an ancestor of chimpanzees, did we start out with skin about the same color? Fossil bones can’t tell us. At least, if there is a way to extract information about the color of the skin that once protected those bones we haven’t figured it out yet.
Since fossils don’t provide the answer, scientists have turned around and tried to understand the adaptive function of skin color from an evolutionary point of view. Most obviously, our skin protects our insides from what comes at us from the outside—wind, rain, and the wipping tree branches. Less obviously, skin is an organ that produces a chemical we cannot live without, vitamin D. This vitamin got its D designation by being the fourth one to be identified. Themain form is cholecalciferol; that’s C27H44O. Researchers studied our beloved dogs to find it. The ability to synthesize vitamin D goes way back in evolution. Plankton at sea have been manufacturing it for 500 million years. Sea creatures use it to capture and make use of calcium in their environment. So do we.
One of the wonderful things about vitamin D is that you don’t need to eat it; your body can make it. You and I just need a little exposure to ultraviolet light to give a form of cholesterol in the skin a jolt and convert it to vitamin D. But there is a catch: Too much ultraviolet light means trouble. It carries more energy than visible light and is able to break down or dissociate delicate biological molecules, especially your folic acid, your folates. Ultraviolet can burn your skin, for example. So to be successful, animals like us need a way to block a large fraction of the ultraviolet light that hits us while letting just enough through to maintain a proper level of vitamin D.
If you’re a chimpanzee, you have solved this problem with one of the oldest tricks in the evolutionary book. You grow hair. Hair is made of keratin proteins that are not too different from those of distant relatives on the Tree of Life who use keratin to produce feathers and scales. As you no doubt realize, hair blocks light. Chimpanzee bodies are covered almost everywhere with thick, dark hair. Even if you make jokes about hairy guys, the hairiest among us don’t come close. Chimps are protected from excessive UV rays by their hair. But if hair offers such good protection, why did we humans lose most of ours?
A likely answer emerges from the following thought experiment, which I hope none of us ever has to actually conduct. You may have heard about people who kept a chimpanzee as a pet. Everything is just fine while the chimp is young, but as he or she grows older, a chimpanzee proves to be surprisingly strong compared to a human. A chimpanzee can easily outwrestle you and pull your arm right out of its socket. But if push comes to shove and you get into a violent disagreement with a chimpanzee, there’s one thing to do. You can outrun him or her.
Humans are champion long-distance runners. As soon as a person and a chimp start running they both get hot. Chimps quickly overheat; humans do not, because they are much better at shedding body heat. You see where I’m going. According to one leading theory, ancestral humans lost their hair over successive generations of hunter, gatherer, scavenger offspring because less hair meant cooler, more effective long-distance running. That ability let our ancestors outmaneuver and outrun prey. Try wearing a couple of extra jackets—or better yet, fur coats—on a hot humid day and run a mile. Now, take those jackets off and try it again. You’ll see what a difference a lack of fur makes. Overheating slows us endothermic animals down.
With the loss of hair our ancestors faced a new challenge, though, because it exposed them to more ultraviolet light. Ultraviolet helps make vitamin D, yes, but it also breaks down similarly crucial folic acid along with other ultraviolet sensitive compounds. You get your folates (like folic acid) from leafy green vegetables. Unlike the case with vitamin D, the human body cannot manufacture its own folates. Folates play a role in the growth of fetuses. Babies born to women who have been exposed to too much ultraviolet have defects in their spines and central nervous systems. They cannot survive. So those early humans who had a little extra sun blocking melanin in their skin did better in strong ultraviolet light environments than those with paler skin.
In general, the closer people live to the equator, the more ultraviolet exposure they receive and the darker their average skin color. Strong local weather conditions can also attenuate the ultraviolet levels. Take a look at the map of skin color of people native to different regions of Earth. Near the equator, people have darker skin. Where it’s cloudy a lot, as it is in Britain, people have lighter skin. Where people live closer to outer space, as they do in Tibet, they are exposed to more ultraviolet and have darker skin. Skin color is basically a measure of the local ultraviolet levels, and it is controlled by relatively minor adaptive changes in the genome.
This fascinating line of reasoning was explained to me by Nina Jablonski, the scientist who did the fundamental research. (She was at the California Academy of Sciences at the time; now she’s at Penn State.) She points out that between two people—any two people— the genetic differences are minuscule. Jablonski is a studious observer of those subtle differences. For her, the most stable physical distinctions are not in the color of our skin, but in the configuration of our bones, especially the shape of our heads. During our interview, she paused and leaned toward me with her hands open as though she were going to reach for a melon on a shelf. As she did she remarked, “Bill, you have a perfect European skull.” I had to stop her and explain that she couldn’t have my skull right then, as I was still using it (I’m still very attached to it). But she got my attention for the rest of what she had to say about human migrations around the world.
With their success in Africa, our human ancestors went looking for new pastures and presumably new adventures to the north in what is now Iran and Iraq. Here, farther from the equator than East Africa is, any individuals who happened to be born with slightly lighter skin did a little better. They got just the right amount of vitamin D without breaking down their folic acid and other essential, ultraviolet-sensitive compounds. They survived a little longer than those who were born in this region but retained African, or very dark skin. Sure enough, modern Northern Africans have lighter skin than equatorial East Africans.
Migration toward and away from the equator led very quickly to changes in our skin color. The remarkable thing is that all people, in all places, evolved similar skin color as they moved to places with similar levels of ultraviolet light. As our ancestors developed agriculture, they moved from Africa to Mesopotamia and then east across Eurasia. If they wandered southward into what is now India, the offspring who had slightly darker skin fared better than those with lighter skin. People native to southern India often have skin so dark it seems almost blue.
Here’s the punch line: Just like their ancestors back in Africa, southern Indians’ dark skin color comes from melanin, but in southern India the pigment is turned on by a different combination of genes. They seem to have retained some of their ancestral pigmentation from their African ancestors, but have some additional gene combinations that help produce melanin polymers. These people migrated to southern India from an area that receives slightly less ultraviolet exposure, and they chanced on a melanin-activating gene that helped their offspring survive under a bit more ultraviolet. The changes in skin color happened because of completely indewpendent mutations in skin color genes.
A similar pattern emerged when people moved from northeast Asia (low ultraviolet) across the ice-age land bridge that is now the Bering Strait into North America and south into Central and South America (higher ultraviolet). Their skin color is produced by melanin in lockstep with the intensity of ultraviolet light in the land where they live. The same process produced lighter skin color in the groups of people who moved into relatively sunless Western Europe and eastern Asia. They lost pigmentation in order to maximize their ability to make vitamin D. Where it’s sunny year round, native people have dark skin. Where it’s only seasonally sunny, natives have much lighter skin. It’s true everywhere.
This convergent evolution of melanin provides further evidence that skin color cannot be taken as a mark of racial identity. It also provides yet another way to trace human evolution. The existence of two distinct skin-pigment genes indicates that humans migrated out of Africa separately to areas to the north and east, probably at two different times. Then, through convergent evolution, the Indian populations ended up with melanin-triggering genes that gave their babies the same kind of advantage in a high-ultraviolet environment as the other melanin-triggering gene present in the people of East Africa.
When we compare the skin color of people native to Tibet, who live at high altitudes, with those in surrounding countries, we find that the Tibetan people have slightly darker skin than those neighbors at lower altitudes. By the way, they can get a tan easily. That makes sense. When you’re at a high altitude, there is less atmosphere between you and the Sun, so you and your neighbors are illuminated with more ultraviolet rays than those living down below. Your offspring who had the slightly darker skin have a better chance of surviving and giving you grandchildren than those who had skin a tad too light for producing a good extended family.
Skin color is so sensitive to environment that scientists can study the skin colors of indigenous peoples to map human migrations out of Africa and across the world. Modern humans, Homo sapiens, first left Africa about 80,000 years ago. We moved through Mesopotamia and started across Eurasia starting around 60,000 years ago. Just 15,000 years ago, people crossed the Bering Strait from Siberia to North America. Now take a look at the two maps. As Africans explored to the east and north, native tribes developed lighter and lighter skin in successive generations. As they migrated south, their skin got dark again. Moving farther east and farther north, their skin color changes back to a somewhat lighter shade.
By the time humankind had made its way to South America, the
tribes doing well there had developed skin almost as dark as those ancestral tribes back in Africa. But there’s a bit more going on here than meets the eye, as Jablonski found when she compiled data from several studies and documented the relationship between ultraviolet, vitamin D, and folic acid.
American tribes living in tropical latitudes do indeed have dark skin, as do those back in Africa. But, the American tribes have skin that is not quite as dark; it’s ever-so slightly lighter than Africans. Why might that be? For one thing, people haven’t been in the Americas as long as they have been in Asia and Africa, so the evolutionary changes have not had as much time to accumulate. Scientists also note that, by the time humans made it south along the American coasts, people had developed straightforward ultraviolet protection technology: I’m talking about hats and jackets. Their tribes had formed the habit of dressing, and that stayed the progression of darker and darker skin as they headed south, where sunshine is strongest. It is just amazing.
The takeaway message here, as Jablonski points out, is that there is no such thing as different races of humans. Any differences we traditionally associate with race are a product of our need for vitamin
D and our relationship to the Sun. Just a few clusters of genes control skin color; the changes in skin color are recent; they’ve gone back and forth with migrations; they are not the same even among two groups with similarly dark skin; and they are tiny compared to the total human genome. So skin color and “race” are neither significant nor consistent defining traits. We all descended from the same African ancestors, with little genetic separation from each other. The different colors or tones of skin are the result of an evolutionary response to ultraviolet light in local environments. Everybody has brown skintinted by the pigment melanin. Some people have light brown skin. Some people have dark brown skin. But we all are brown, brown, brown.
Our reactions to other groups are real enough, but evolutionary biology shows that those reactions have nothing to do with race, because race is not real. Scientifically speaking, there is tribalism and group bias, but there cannot be any such thing as racism. We are all one.
from Undeniable by Bill Nye 2014
