Jan. 14, 2003 -- Man brought home the meat, well-fed children flourished, the human brain developed and humankind evolved. … Or so the story goes.
Now anthropologists are reconsidering traditional theories about the importance of male hunting, of meat and of the so-called nuclear family in human evolution.
Instead, a renewed look at archaeological records and observations of a contemporary hunting and gathering tribe in East Africa suggest the key roles in nourishing the evolution of people's ancestors may have been played by females — mothers and grandmothers.
Meanwhile, male hunting was likely more about elevating one's social status than providing for the family, researchers say.
"The return rate of hunting and scavenging large animals just doesn't pay off," explained James O'Connell, director of the Archaeological Center at the University of Utah in Salt Lake City and lead author of a recent paper about the subject in Journal of Human Evolution. "You just can't make enough out of it to feed your kid."
Scavengers, Not Hunters
The idea that hunting and meat-eating helped trigger the evolution of modern man has been based largely on archaeological remains of Homo erectus, a species that lived in Africa and Asia approximately 2 million to 400,000 years ago.
These upright, long-armed hominids developed brains that were 50 percent larger than their predecessor's, Homo habilis. The question is how.
Based on sites containing jumbled collections of large animal bones and primitive tools, scientists developed a theory that Homo erectus males learned how to hunt large animals. This allowed them to bring their kill back to "home bases" where they shared the meat with women and children. The protein-rich meat helped the brain develop and evolution favored larger brains since hunting required the development of tools and strategy.
But O'Connell, his colleagues and authors of other recent studies have begun to cast doubt on that assumption.
"I think the brain change associated with meat-eating is overrated," he said.
Instead, they say the collections of animal bones represent where early men had dragged scavenged prey that had been killed by other animals, such as lions. O'Connell's team observed that many of the bones have cut marks from both stone tools and animal predators. When they compared these marks with ones made by modern scavengers, they found the remains were very similar.
And, they add, it's unlikely the ancient people were able to acquire large kill — either by hunting or scavenging — very often.
Hunting: High Risk, Low Return
One reason is that most sites containing piles of animal bones and tools were found in what would have been predator-filled areas near rivers — not the kind of place to serve a family dinner.
And studies in the late 1980s of the Hadza people of East Africa show that male members of this contemporary hunting and gathering culture rarely make successful large kills, even with their advanced bows and arrows. The men managed to kill or scavenge large animals only once every month — hardly enough to support a family.
"With erectus, bows and arrows hadn't even entered the picture. They may have thrown stones to harass predators off the kill," he said. "So they were probably even less successful."
If true, this would have left a huge gap in child upbringing.
Leaning on Grandma
It's known that among the Hadza people, senior women in the tribe play a big part in helping overburdened mothers. These no longer fertile women help rear the young and gather foods — mainly tubers such as yuccas and other plants. Hadza women also hunt smaller prey, such as rodents and turtles, which, together with plants, make up the main part of their diet.
Homo erectus may also have leaned on grandmothers, O'Connell suggests. This, in turn, would have favored longer life spans (long enough to have grandmothers around as her daughters give birth). And longer life spans would have required delayed maturity and ultimately larger body and brain size — all crucial developments toward modern man. All thanks to Grandma.
"There's a longstanding theory that nuclear families where the man brings home the food and the woman takes care of the young are the basic deal. That may or may not always have been true," said O'Connell. "We're skeptical it was true in the past."
O'Connell is hardly the only researcher to break out of traditional thinking on human development and recognize the significance of grandmothers. Studies of historical human populations have suggested that survival rate of children hinges on whether or not grandmother is present.
Cheryl Jamison, an anthropologist at Indiana University in Bloomington, examined unusually complete records from a Japanese village from 1671 to 1871. She and her colleagues found that boys were 52 percent less likely to die in childhood when a maternal grandmother lived in the house.
And Ruth Mace and Rebecca Sear of University College in London found that in rural Gambia from 1950 to 1974, a grandmother's presence decreased child mortality by half.
Cooperation: Secret to Success
Others point out that body size changes in Homo erectus further hint that females were playing more significant roles.
"Before Homo erectus, females were much smaller than males," said Richard Klein, an anthropologist at Stanford University. "But for the first time, females became larger. It suggests they were doing something they weren't doing before — they may have been on the food quest."
If mothers and grandmothers were doing most of the feeding, then why did males bother with the dangerous business of hunting and scavenging large prey?
"Look what everyone was doing last weekend," said O'Conner. "Watching football. Investment in impressing the girls — whether by football or killing an antelope — is a mammalian trait."
Klein, however, is not so quick to dismiss early man's role as a provider. At least, he points out, early man (and woman) knew how to share.
"Going back to prehistory, individuals have always shared food resources," he said. "That's what has distinguished us from apes and it has clearly been good for the species."