He cooked up a new theory on evolution

Richard Wrangham theorized that cooking food is what allowed for the rise of Homo erectus. (Yoon S. Byun/Globe Staff)

One day 10 years ago, Richard Wrangham was lying in front of the fire in his home thinking about human evolution. People like to think in front of fires, and Wrangham, a Harvard professor of biological anthropology, likes to think about human evolution, so it wasn't really a special occasion. Then Wrangham put the two together.

Thus began the "cooking obsession" that set him on a path that would lead to a radical new theory about what it means to be human.

Most anthropologists would agree that cooking has played a role in human evolution. But staring at that fire that day, thinking about our early ancestors roasting their food over an open flame, Wrangham came to a much more dramatic conclusion.

Cooking, he thought, is not just a part of human evolution. Cooking is what made us human.

Wrangham's theory, which is the subject of his book to be published next year, is that the ability to harness fire and cook food is what allowed for the rise of Homo erectus 1.8 million years ago. Cooking, he argues, makes eating faster and easier and allows more calories to be harvested from the food. That extra nutrition, he says, explains why Homo erectus evolved with a larger body and brain than its ancestors, even though it had a smaller gut and smaller teeth.

The 59-year-old professor, who is originally from England and could easily play the dashing British anthropologist in a movie, is well aware that his theory flies in the face of conventional anthropological doctrine.

"The standard argument is that meat-eating is what allowed for Homo erectus," he said recently from his office in Harvard's Peabody Museum. While that, he says, may have been true for the first stage of human development - the shift from Australopithecines to Homo habilis about 2.5 million years ago, which produced a species about the size of a chimp with a bigger brain - it was not true for the second.

That second stage came about roughly a million years later, as Homo erectus evolved with a much larger body and brain - but smaller teeth. "How they were meant to be eating raw meat with smaller teeth doesn't make sense to me," Wrangham said.

He was, he said, stuck. He had been taught that fire was a cultural innovation of beings that were already human, yet he could find no way they could have become human without the nutritional advantage of cooking. Cooking, he argued, was the "human" in the human diet, the only explanation for the evolutionary jump in brain and body size.

It is a reasonable argument, but with one major problem, and you need only walk down the hallway from Wrangham's office to find it.

"There is not a shred of evidence to support his dating," said Ofer Bar-Yosef, a Harvard archaeology professor. "There are no burnt bones. There are no remains of fireplaces. There is no evidence in the records to support the use of fire before 800,000 years ago. No one would disagree that cooking played an important role in human evolution. The question on which we differ is when we start. If you say we started using fire 1.8 million years ago, then you have to prove it by finding evidence in the field."

That is no small challenge. Nor is it one that Wrangham intends to take on.

He has no plans to dig for his proof; he is, after all, a primatologist. An avid bird watcher as a young man, he has been doing field work in Africa since he was 17, and, after graduating from college, he wrote to the famed primatologist Jane Goodall and asked her whether he could "please come study chimpanzees" with her. She said yes.

For the past 20 years, he has had his own field station set up in Kibale National Park in western Uganda, where he studies chimpanzees as a way to learn about human behavior (his observations of how they war and defend territories goes against the thinking that all human behavior is cultural).

He and his wife, Elizabeth Ross, have just published a book, "Science and Conservation in African Forests" that argues long-term field stations like theirs are one of the best ways to ensure the protection of habitats.

While the cooking habits of Homo erectus and the territorial disputes of African chimpanzees are very different things, he believes his observations of our closest genetic relatives supports his theory.

"I've gotten to know chimps well enough to know that I couldn't survive on their diet. It's certainly possible to live on a raw food diet. There are many humans who do, but they eat incredibly choice foods," he notes, "and they use a blender."

"Otherwise, we'd have to be like the chimps and spend about half of our day chewing," he added.

Hometown: Born in Yorkshire, England; lives in Harvard's Currier House, where he and his wife recently became masters.

Education: Bachelor's degree in zoology from Oxford University in 1970, and a PhD in animal behavior from Cambridge University in 1975.

Family: Wife, Elizabeth Ross, has a doctorate in immunology and runs a charity for schoolchildren in Uganda. They have three sons: Ross, 26, works at the Formaggio Kitchen gourmet food store in Cambridge; David, 23, is studying Japanese at Middlebury College; Ian, 20, is a student at Colorado College who is currently studying abroad in New Zealand.

Hobbies: "As soon as the term ends, I go off to Uganda with the chimps, so there isn't a lot of time for play."