Over 1.9 million years ago, human beings were still having dinner dates, according to a recently published article by Professor of Anthropology Richard W. Wrangham.

The article, published in the December issue of Current Anthropologist, hypothesizes that at this time humans first harnessed fire for cooking.

The first use of fire brought great changes to the human social structure, Wrangham said.

With the advent of cooking, the article argues, human beings moved from a " hunter/gatherer" existence to a "producer/scrounger" social structure.

"Before, people lived like apes--everybody fed himself," Wrangham said. "[With] cooking, it became worthwhile to bring food in large quantities to a central location, and the concepts of ownership and theft came into existence."

Females often found themselves victims of theft from the larger males. As a result, it was advantageous for a female to align herself with a male interested in protecting their mutual food stores--hence the modern-day couples.

"The male fought off thieves in exchange for sex and hot food. It's a protection racket, really," he said.

Females selected stronger males. In return, males selected more sexually attractive females. It is possible this resulted in hidden ovulation--women, unlike other mammals, do not show external signs of ovulating.

Wrangham plans to use this material in the Core's Science B-29: "Human Behavioral Biology," popularly known as "Sex." He was one of the course's three professors last fall and will take on greater teaching duties next fall after Professor of Biological Anthropology Irven DeVore's retirement.

Wrangham said he has experienced a great deal of crossover between his research and his teaching.

In fact, it is this link between his classes and his research work that led to his new discovery.

"The idea came to me while I was thinking about human evolution in preparation for my class, and I just happened to be at home staring at the fire," he said. He was planning for Anthropology 115: "Primate Evolutionary Ecology" in February last year.

Many of the key ideas came quickly, he said.

"In a few minutes, I had sketched out the importance fire could play in human evolution," Wrangham said. "In a few days, I had checked on crucial dates that would make the idea plausible."

Gathering evidence in support of the hypothesis largely involved finding the date man first harnessed fire.

Wrangham said he reasoned that the nutritional effect of cooking should be evident from the fossil record. There was only one period that shows dramatic changes in tooth structure and body size, about 1.9 million years ago.

It is this time period that marks the appearance of the genus Homo. Wrangham said it was very encouraging to find that archaeologists placed the harnessing of fire around the same date.

Before this period, human ancestors inhabited the trees, and size differences between males and females were much more pronounced. Wrangham said that, anytime during the Homo period, after the harnessing of fire, if a human ancestor were to put on modern clothes, a hat, and strut down Manhattan, he would not be noticed.

"We believe that one of Anthropology's major challenges is to develop a hypothesis that explains this critical change," Wrangham said. "And we think our hypothesis might be right."