Human evolution theory changes with study

WASHINGTON — Research based on two African fossils suggests human’s family tree is more like a wayward bush with stubby branches, challenging what had been common thinking on how early humans evolved.

The discovery by famed paleontologist Meave Leakey shows that two species of early human ancestors lived at the same time in Kenya. That pokes holes in the chief theory of man’s early evolution — that one of those species evolved from the other.

And it further discredits that iconic illustration of human evolution that begins with a knuckle-dragging ape and ends with a briefcase-carrying man.

The old theory is that the first and oldest species in our family tree, Homo habilis, evolved into Homo erectus, which then became human, Homo sapiens.

But Leakey’s find suggests those two earlier species lived side-by-side about 1.5 million years ago in parts of Kenya — for at least half a million years. She and her research colleagues report the discovery in a paper published in today’s journal Nature.

The paper is based on fossilized bones found in 2000. The complete skull of Homo erectus was found within walking distance of an upper jaw of Homo habilis, and both dated from the same general time period. That makes it unlikely that Homo erectus evolved from Homo habilis, researchers said.

The two species lived near each other, but probably didn’t interact, each having its own “ecological niche,” said study co-author Fred Spoor, a professor of evolutionary anatomy at the University College in London. Like chimps and apes, “they’d just avoid each other, they don’t feel comfortable in each other’s company,” he said.

Susan Anton, a New York University anthropologist and co-author of the Leakey work, said she expects anti-evolution proponents to seize on the new research, but said it would be a mistake to try to use the new work to show flaws in evolution theory.

“This is not questioning the idea at all of evolution; it is refining some of the specific points,” Anton said.