By CARL ZIMMER - THE LOOM
Added: Sat, 06 Aug 2011 22:15:12 UTC

To understand how we evolved, we have to understand where we evolved. Natural selection exists because the environment is kinder to some individuals than others. Depending on the species, that environment may be a lake miles underneath Antarctic ice, an alpine meadow near the top of a mountain, or an oxygen-free swamp in the sweltering tropics. Each habitat creates its own set of conditions in which individuals thrive or die. We humans are no different. We are the product of where we have lived.

A century ago, paleontologists thought humans evolved in Central Asia. At the time the only known fossils of an ancient human relative (what we now call a hominin) came from Indonesia. The idea of humans evolving in dank rain forests did not appeal to Western scientists who lived in temperate climes. They looked to Central Asia’s windswept plains. In 1926, the American paleontologist Henry Fairfield Osborn laid out this line of thinking in an essay called “Why Central Asia?”

“In that environment, the struggle for existence was severe and evoked all the inventive and resourceful faculties of man,” he wrote. “While the anthropoid apes were luxuriating in the forested lowlands of Asia and Europe, the Dawn Men were evolving in the invigorating atmosphere of the relatively dry uplands.”

It’s hard to imagine worse timing for such a declaration. In 1925, the year before, Raymond Dart discovered the skull of a another hominin in South Africa. It was much older than the one in Indonesia, and it was a lot more ape-like. And since then, paleoanthropologists have found many more fossils of very old hominins in Africa, from South Africa to Kenya and up to Ethiopia and Chad. Hominins first split off from the ancestors of chimpanzees and bonobos (both found only in Africa) about seven million years ago. The oldest hominin fossils date back to about that age, and from seven million to 1.8 million years ago, the fossil record was exclusively African. Only then did hominins start popping up in places like Indonesia and the Caucasus Mountains. Hominins also continued to inhabit Africa, and evolve into new species. The first fossils of Homo sapiens, dating back about 200,000 years ago, are from Ethiopia.
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TAGGED: EARTH SCIENCES, EVOLUTION