The traditional ideas about human evolution are being forced to change with new genetic and physical evidence that may prove that humans didn’t diverge from chimpanzees until about 4 million years ago.

Four million years may not seem like a lot of time but, when compared to the original idea that human ancestors, known as hominids, originally diverged about 17 million years ago, this is an enormous change.

Part of the reason for the mystery around the exact time of divergence is that there was still integration between the genes of chimpanzees and humans until about 4 million years ago.

“Maybe after chimps and humans diverged they were still having sex. We could call this integration,” said Milford Wolpoff, a professor of anthropology and research scientist at the University of Michigan,who presented his research in the Sun Room of the Memorial Union Wednesday night.

His research stemmed largely from a hypothesis that one of his former students developed. The student, Leonard Greenfield, undergraduate chair and faculty adviser in the department of anthropology at Temple University, wrote about the idea of divergence of humans from chimpanzees.

Wolpoff said that, in Africa during the Miocene Age, there were an “awful lot of fossil apes.” Most of these apes were labeled as part of the genus Proconsul, and they were considered to be the ancestors to later apes.

Greenfield had just graduated and, when he looked at fossils of Proconsuls, he found that some looked like gorillas.

The accepted mode of teaching was that, from seven to nine million years ago, there was already divergence between apes, chimpanzees and hominids, Wolpoff said.

Greenfield questioned the accepted thinking about human and ape divergence that was taught in the late ’70s because it didn’t fit into the theory of Darwinian Evolution.

According to the Darwinian evolution model, hominids arose due to a series of very specific changes.

“They became terrestrial, which means they began to live on the ground,” Wolpoff said.

Once this happened, Wolpoff said, the hominids realized that they could eat the animals if they could kill them.

“They had to use tools to kill animals,” Wolpoff said. “This changed their diet, which was a fruit-eating diet, into a meat-eating diet.”

Wolpoff said the product of this diet change was that hominids didn’t need large canines, like those of chimpanzees, because the tools developed could cut meat. This led to a reduction in the size of canine incisors, which is the next step in the Darwinian model.

“Then, finally, they had to develop big brains to transmit the cultural information of tool use from generation to generation,” Wolpoff said.

So, Wolpoff said, Greenfield looked at all of this information and decided the old hypothesis did not fit very well.

Up until this point, bipedalism, or walking upright, was the one of the largest indicators of hominid evolution and scientists had been using bipedalism to classify the various primate species, Wolpoff said.

He then said that this was misleading because there were different kinds of bipedalism.

At this point, Wolpoff climbed down off of the stage and began to demonstrate, in slow motion, the way people walk.

“I move forward,” he said lifting his right leg into the air, “and my other foot swings forward freely.”

He said there aren’t any major muscles that are used, and the entire process works because humans have big toes.

“Bipedalism, to do it really well, requires a toe-off, and that requires a toe that doesn’t look like that of chimpanzees and apes,” Wolpoff said.

He said humans use something called obligate bipedalism that is different from just having the ability to walk upright because it is their only option.

Greenfield concluded in the late 1970s that humans had not diverged until about 6 million years ago. This was not a popular theory at the time, but it has gained credence, though Wolpoff said that he now thinks humans didn’t actually diverge until about 4 million years ago.

He cited evidence that said the previous modes of thought about primate evolution were wrong, and that humans were not as far removed from chimps and apes as previously believed.