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A Fishy Take On Human Skin Tones

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A Fishy Take On Human Skin Tones

A Fishy Take On Human Skin Tones

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MICHELE NORRIS, Host:

From NPR News, this is ALL THINGS CONSIDERED. I'm Michele Norris.

Humans are the only species on Earth that do radio shows - you probably knew that already. But why is that the case? Why, of all creatures, did humans evolve with such a wide array of skills?

To try to answer that question, NPR is launching a new series called The Human Edge. We'll explore the anatomic, intellectual and cultural steps that led us to where we are today.

And to start off, NPR's Joe Palca looks at the genetics that resulted in us, homo sapiens.

JOE PALCA: There's a lot of ways to describe human beings.

DAVID KINGSLEY: Humans are primates. Humans are mammals. Humans are vertebrates.

PALCA: David Kingsley is a geneticist at Stanford University. He's interested in how genes changed as evolution took us from vertebrates to mammals to humans. Kingsley says it's important to think of humans as part of a bigger picture.

KINGSLEY: As you go further and further back in the history of life on Earth, you do include humans in the large branching set of relationships that is what's produced all the organisms we see around us.

PALCA: To get a better idea of how humans emerged out of these branching relationships, Kingsley has turned to fish.

KINGSLEY: I think of this as biology in your backyard.

PALCA: Kingsley is standing by the bank of a stream, not far from the Stanford campus.

KINGSLEY: Let's see if there's any fish.

PALCA: He pulls up a trap he placed in the stream...

(SOUNDBITE OF MOVIE THEME SONG, "JAWS")

PALCA: ...and looks to see if he's caught anything.

(SOUNDBITE OF MOVIE THEME SONG, "JAWS")

PALCA: He's got three sticklebacks. Stickleback is about as unscary as fish get - little guys about an inch or two long.

KINGSLEY: We didn't choose them because we want to understand sticklebacks themselves. We chose them because they're a model that makes the process of evolution something that can be dissected and taken apart in the lab.

PALCA: Until about 15,000 years ago, sticklebacks lived in the ocean, and they all pretty much looked the same. But 15,000 years ago, an Ice Age was ending, and glaciers were receding, creating a variety of new environments for the fish. The sticklebacks evolved new colors and shapes as they adapted to their new homes.

Kingsley figured if he could find the genes that caused these changes to take place, that might - just might - tell him how human color and shape evolved.

KINGSLEY: Pick a room. So these are the large tanks where we raise the genetic crosses between different forms.

PALCA: To find the genes, he breeds the small fish in 30-gallon tanks in the basement of the Stanford Medical School. Kingsley has collected sticklebacks from around the world: big ones, small ones, brown ones, white ones. By breeding big ones with small ones, and white ones with brown ones, he can follow genes for color and size through successive generations, and zero in on the ones he's interested in.

For strictly practical reasons, Kingsley has become quite an expert in stickleback sex habits. And he says on this day, quite a few males appear to be ready to get with the program, as it were.

KINGSLEY: Now we're getting very red throats and blue eyes. That's classic mating coloration in the male fish. And I actually think...

PALCA: Oh, wow. there is a blue eye. That was a really blue eye. I just got the full blast. He looked right at me.

KINGSLEY: You're ready to mate with a stickleback?

(SOUNDBITE OF LAUGHTER)

PALCA: Let me at him. Uh, maybe not.

Recently, Kingsley has found the genes responsible for stickleback color. And that's an important step because when humans left Africa about 100,000 years ago, they, too, started evolving new colors. And humans, as it turns out, have very similar versions of each of these genes.

KINGSLEY: Fish are not humans, but humans came from fish. And that relationship is probably the reason that the mechanisms discovered in one organism are often predictive of what happens in other organisms.

PALCA: So Kingsley looked to see if the same genes played the same role in human coloration. Early results suggest they do. Like fish, humans have evolved a variety of skin colors that are striking and easy to recognize.

KINGSLEY: And turn out to involve exactly the same genes, and exactly the same mechanisms, that we've also found in the stickleback.

PALCA: This is a theme in Kingsley's work, and in evolution in general. If something works in one organism - say, the genes for controlling skin color - it tends to get passed on to that organism's evolutionary descendants. So it's not surprising the same genes play the same role in humans and fish. We all share a genetic tool bag that gets used over and over, just in slightly different ways - not just for skin color, but for all sorts of crucial traits, from opposable thumbs to big brains.

When we started this series on human origins, my colleague Christopher Joyce suggested we ask everyone we interviewed the same question. So I wrote the question down and had it with me when I interviewed Kingsley in his Stanford lab.

So it's time for the question.

(SOUNDBITE OF RUSTLING PAPER)

KINGSLEY: You pull out a piece of paper with a question.

PALCA: Yeah, it's carefully worded.

If there's one thing that makes humans different from their ancestors, what would it be?

KINGSLEY: That's a great question.

PALCA: Actually, his pause was much longer than that. I shortened it through the magic of radio.

KINGSLEY: I think my pause is related to the fact that humans really are so closely related to other groups that their distinctiveness is not at the genomic level or the genetic level or the anatomical level.

PALCA: What Kingsley is saying is it's very hard to point to the gene or bone that allowed humans to flourish the way we have. We're just not that different from fish, let alone being all that different from apes.

But somehow, these small changes in our genes, and the way they switch on and off, can result in big effects. For us, it meant language and big brains, and that's let us do things other species can't.

KINGSLEY: We build the cities. We do radio shows. We have the technology and the ability to communicate and interact, and study ourselves and where we came from. That's unique to humans. We're studying the sticklebacks. The sticklebacks aren't studying us.

PALCA: At least, we don't think they are.

Joe Palca, NPR News.

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