Us

The recently announced discovery of a nearly intact skeleton of a juvenile Austrolopithecus afarensis is an appropriate occasion for the final installment in my promised series on evolution. That doesn't mean I won't continue to discuss the subject, but this completes the previously stated agenda.

The human lineage diverged from the lineage of chimpanzees about 6 million years ago. More than 4 million years ago, the genus Australopithecus became fully bipedal. What the new fossil skeleton tells us however, is that 3 million years ago, the species was otherwise much more like an ape than a human -- including having a brain not much larger than a chimp's.

Not long, in geological terms, after the time of the Australopithecus child (or cub) -- a little over 2 million years ago -- the species Homo habilis and Homo erectus emerged. Their brains were bigger, though not as big as ours. And they made stone tools. However, in marked contrast to us, their ways of life were highly static. They continued to make very similar looking tools for more than a million years. We have found no evidence of art, or religion, or cultural development among them, although it could be hard to find given their great antiquity.

Creatures who paleontologists consider to be Homo sapiens appear in the fossil record about 400,000 years ago, and skeletons completely indistinguishable from those of modern humans appear 100,000 years ago.

Something extraordinary and as yet quite unexplained happened only about 50,000 years ago -- a sudden explosion of cultural development. Instead of seeing the same toolkit appearing in ancient sites over hundreds of thousands of years and across great distances, we see continual innovation and dramatic variation in time and space. We begin to see ritual burials, works of art, ornamentation. At almost exactly the same time, people began to spread outward from Africa. Within a mere 5,000 years, they had landed in Australia, having evidently crossed a large stretch of open ocean in boats. Within 30,000 years, people had penetrated to every corner of the earth except Antarctica. They had developed agriculture, adapted to climates ranging from the high arctic to deep forest to barren desert, invented baskets, pottery, sewn garments, spear throwers, musical instruments. Within a few thousand years more, they had founded civilizations, built great cities, forged tools of metal, begun to write down their current histories and mythical pasts.

This event was explosive, unprecedented on earth, astonishingly rapid. In a geological eyeblink, we have radically reshaped the planet's ecosystems, and now we are remodeling its very atmosphere and climate. We have even climbed out of the atmosphere and the gravity well and visited our planet's satellite, and sent our robots to other planets and out of the solar system entirely. And we have radically remade our own lives as well.

But what happened 50,000 years ago? The temptingly obvious answer is the development of a huge vocabulary and fully syntactical communication, that is language. With that came the possibility of elaborate reasoning, preservation and dissemination of knowledge, collective problem solving, transmission of knowledge, ideas and values from generation to generation -- the constructed, modifiable, improvable edifice of human culture and social organization. But that begs the question.

How and why could such a powerful and complex faculty as language emerge with such suddenness? Did it depend on a biological event, a genetic modification invisible in the skeleton but profoundly altering the functioning of the brain? Or was the brain somehow prepared to acquire and use language, only awaiting its discovery? The latter may seem improbable, but recent experiments have shown that apes can learn a vocabulary of a few hundred words and use them in a limited syntax. So presumably our earlier ancestors had at least some limited capability to use language, although whether they did so or not we cannot say.

But somehow, at that magic moment, a group of humans acquired the gift of gab -- the fount of unlimited potential, unbounded wonder, and horrific danger.