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Despite a lot of bone-headed evidence to the contrary, it's safe to say humans are the smartest creatures on Earth. After all, what other species is going to argue with you? But scientists do puzzle over how we got so smart. One way to figure that out is to look at the closest relative we ever had, that lumbering cousin who died out about 30,000 years ago, the Neanderthal.
As NPR's Christopher Joyce reports, scientists have some new insights into what set humans and Neanderthals apart.
CHRISTOPHER JOYCE: Neanderthals lived in Europe alongside humans, and DNA evidence suggests they even mated with us. Despite our alleged intimacy, we think of them as dull, brutish and poor conversationalists. And they went extinct, another sign of inferiority.
Yet their brains were as big as ours, their tools just as good. So what did we, Homo sapiens, have that made us so clever?
Tanya Smith, an anthropologist at Harvard University, explains one idea about how early humans got smarter.
Professor TANYA SMITH (Human Evolutionary Biology, Harvard University): Some of the earliest fossil Homo sapiens that we've looked at show a really long period of growth and development. They did not, you know, live fast and die young. They seemed to have lived slow and die old.
JOYCE: And Neanderthals did live fast and die young.
Prof. SMITH: Yes, they did. Several of the ones that we studied seemed to have matured several years faster than you would have predicted.
JOYCE: Now, maturing quickly does have advantages in a world with many saber tooth cats and no doctors or pharmacies. If you live fast, you can reproduce sooner and you pass on your genes ASAP. But some scientists believe modern humans developed a better way.
Here's Jean Jacques Hublin, from the Max Planck Institute for Evolutionary Anthropology in Germany.
Professor JEAN-JACQUES HUBLIN (Department of Human Evolution, Max Planck Institute): We take a long time to grow up and become adults. And this has a lot of implications in terms of social organization, time for education, maturation of the brain, even psychology somehow.
JOYCE: Like the slow food movement, slow growth gave complex brains more time to cook, so to speak, and then to learn all those things a fancy brain could learn. That's the idea, anyway.
And now, in two research papers just published, Hublin and Smith have laid out some new evidence that confirms what scientists have suspected. Hublin, a paleoanthropologist, used a medical imaging machine to compare the skulls of Neanderthal and human infants. Both grew big brains fast, but the shape of a Neanderthal brain was more primitive. The human shape was different from anything that came before. Hublin says he thinks that took longer and also resulted in different wiring.
Prof. HUBLIN: To put it very simply, I would say Neanderthals did not see the world as we see it.
JOYCE: And Smith's research backs that up with evidence from what lies underneath the brain, the teeth. Prof. SMITH: Teeth have these tiny recorders locked inside them. Like rings in trees, teeth have lines which reflect every single day of their formation - from before birth until the end of childhood.
JOYCE: Using a high-powered X-ray, Smith counted those lines in the teeth of Neanderthals and early humans and found that Neanderthal kids matured way faster than early humans did.
Prof. SMITH: By age 8, they've got an extra couple of teeth already out in the mouth. You know, they're much closer to being adults than we would be at age 8.
JOYCE: Smith published her work in the latest issue of the Proceedings of the National Academy of Sciences; Hublin in the journal Current Biology. And they say slow growth may not seem like such a big difference between two species that were apparently close enough to mate, but Hublin says it doesn't take much in a social species to create a survival advantage.
Prof. HUBLIN: You know, I used to make this joke that we never know what kind of relationship a Neanderthal had with his brother-in-law. And maybe this is what makes the big difference between the Neanderthal and us.
JOYCE: Consider that when the relatives visit this Thanksgiving.
Christopher Joyce, NPR News.
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