Undeniable (32 page)

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 independent 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 skin tinted 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.

 

33

IS THE HUMAN SPECIES STILL EVOLVING?

I still have strong memories of meeting Ivan. He had a great many fans, so I was behind the barricade and could only wave, but I think he noticed me and waved back. I found it all very exciting. This happened a couple of times—once in Tacoma, Washington, and then several years later in Atlanta, Georgia. I got so excited because Ivan was something special. Unlike most readers of this book, Ivan was a mountain gorilla.

Modern gene sequencing informs us that Ivan and I had a lot in common. Inside, we are about 97 percent the same. It's a short evolutionary distance between us, and as I stood there, I could feel it—so close, yet so far. Why did my line diverge from Ivan's over the last few million years? Looking at Ivan, I couldn't help but wonder how we will continue to change. Will we take control of our own evolution, the way we have taken control of our crops and started taking control of our stem cells? If you were in charge of your own genome, what improvement would you specify? And what about Ivan: Will we be leaving his kind, or primate kin, further and further away on the Tree of Life?

I visited Ivan while I was working at Boeing in the Seattle area, making subtle improvements to the 747 airplane. Ivan was well-known. Going to see him was just something you did as a Pacific Northwest sightseer, like going to the Western Washington State Fair in Puyallup [Pew-AL-upp] for scones and strawberries. At that time, Ivan lived in a concrete box in the basement of this odd old department store called “the B&I,” named for its original owners Bradshaw and Irwin. He had a rubber tire swing and a great many bananas. He was brought to the U.S. as a baby around 1964. His sister died young, and Ivan carried on in his box with his swing until he was thirty-two years old.

As I looked through the glass of that weird store basement, it was impossible not to compare the two of us. It's astonishing how closely related we are, yet how different we look and behave. I don't know much about gorillas, but to my human mind, he looked bored with his life, and I could see why. Humans, lots of humans. Same food every day. Rubber tire on chain. By then, the B&I was no longer in its glory days. It was on its way out of business. A deal was made, and Ivan was transferred to the Atlanta Zoo. That's where I saw him last.

By that time, I was working for Disney, frequently passing through Atlanta. I met an old friend and her kids at the Atlanta Zoo. And there was Ivan again. On that visit, Ivan looked great. He now had several girl gorillas clearly smitten with his gorilla-ness. He basked in the sun and interacted with the ladies. I felt deep relief. He seemed a lot happier. By that I mean his posture and the way he moved among his zoo family. In
Julius Caesar
, by William Shakespeare, I remember the dialog, where Cassius says, “'Tis Cinna, I do know him by his gait; He's a friend.” I remember realizing, first of all, you can recognize someone by the way he walks, and furthermore, you can often infer a good deal about that person by his posture and movement. That's how I felt about my buddy Ivan. He was in a bad mood in Tacoma and a very good mood in Atlanta.

For some reason, this kind of meditation about my primate relatives kept following me, though meditation may be an overstatement. I got my start in television on Seattle's local comedy show
Almost Live!
(Bob Nelson, who wrote the Oscar-nominated film
Nebraska
, and the terrific actor Joel McHale started on that show as well.) I impersonated Ivan. Wearing a gorilla suit, and using subtitles, Ivan (well, mock-Ivan) explained that everything was fine for me, really, except I was stuck in Tacoma! In the course of related comedy bits, we had Ivan playing tennis. Anyone watching can tell it's me playing tennis, even though I was dressed in a gorilla suit. You knew me by my gait. I did my best to seem bored and angry, as I presumed Ivan to be. My claim is that a primate's behavior is evident for the same reasons our behavior and posture are evident. It's deep within us. It's in that 97-percent-in-common DNA.

About three years later I was working on my own show,
Bill Nye the Science Guy
. Show number 53 is entitled “Mammals.” As part of the filming I visited another gorilla named Vip at the Woodland Park Zoo in Seattle. He was fine. I mean, he was gnawing away on what looked to me like bok choy, and he was looking at me. I felt like I could sense his resentment and resignation. I paraphrase: “What's the deal, man? You're out there with no hair. You look like a pathetic weakling; I feel like bending you over my knee and snapping you in half—and I'm a vegetarian. Somehow, you and all your kind got us all stuck in here, on this side of that see-through wall [thick glass]. I mean, dude—this sucks. And thanks for the lousy bok choy, you hairless geek…”

I admit, this dialog was entirely in my head, but I challenge anyone to go to a zoo where you can get close to gorillas, look them in the eyes, and not feel that they know what the deal is. You and I have the natural dumb luck to be more clever and dexterous than the gorillas are. They can't quite tell how the humans set this all up, but they can tell that they got the shorter end of the genetic stick. You have to wonder if this is how we would feel if we could gaze upon future humans—or whatever it is that we become.

Since scientists and engineers developed machines and chemical reagents that can determine the exact sequence of chemical bases in strands of DNA, we have discovered that humans and gorillas share 97 percent of their genetic code. We may be just 3 percent different in our DNA but wow, how different we look and behave (my old boss excluded). From time to time, you hear people make reference to the 800-pound gorilla in the room. Although for most gorillas, 800 pounds would be an overestimate; it's usually closer to 500. Gorillas generally walk with the feet and their knuckles. We're feet exclusive. Gorillas don't quite stand upright. We do. Gorillas are covered with hair. We are not. Gorilla brains are bigger than ours, but ours are larger compared with our weight and size. All those distinctions emerge from that little 3 percent.