Larger Brains, Longer Lives

URL: http://www.abqjournal.com/scitech/178889science05-23-04.htm

Sunday, May 23, 2004
Larger Brains, Longer Lives
By John Fleck
Albuquerque Journal Staff Writer

By his own admission, anthropologist Hillard Kaplan was "hopeless" when he first tried to live in the jungles of eastern Paraguay with the hunter-gatherers known as the Ache. When the group would head out on a hunting trip, Kaplan could not keep up with the fast-moving men, so he would fall back in a jungle that to him seemed trackless.

"For them, it was a superhighway," he recalled. "To me, it didn't even look like a trail."

The basic skills of living in the jungle were in fact the product of a life of learning that Kaplan didn't have. Understanding the way those lives play out has led Kaplan and a group of colleagues to new ideas about what distinguishes us as humans.

The work has led the University of New Mexico professor to Peru, Paraguay and Bolivia, where he and his colleagues used hunter-gatherer communities as stand-ins for our ancient human ancestors in an effort to understand how we came to be what we are today.

To hunt, humans use vast knowledge of prey rather than speed or brawn. Elaborate preparation allows us to make food out of plants that other animals pass by. These unique characteristics are rooted in basic anatomy.

Basic difference

Consider the fundamental difference between us and our nearest living relative, the chimpanzee. The typical adult human brain weighs 3 pounds. The chimpanzee's brain weighs 1 pound. The difference, according to Kaplan, a UNM anthropologist, is a matter of economics. Think of that big brain as an investment. It takes a while to build, with mom and dad kicking in most of the up-front costs.

Once built, it takes a long time to take advantage of it?- to learn the intricacies of finding one's way along a faint jungle trail, for example.

"Children are net consumers all the way up to age 20," Kaplan said.

In the long run, the payoff is huge. The knowledge gained in the lengthy period of tutelage makes grown humans remarkable economic engines, whether in the jungles of Paraguay or a modern technological society. That payoff requires, however, a long adult life. According to Kaplan and his colleagues, fewer than one in 10 chimpanzees live to age 40, while among hunter-gatherer cultures, one in seven people lives to age 70.

Building a theory

By taking their research from the jungle to mathematics or economics, Kaplan and his colleagues have used that central insight to painstakingly build a theory of why we are the way we are. Why are our brains so big? Why do we live so long? Why do we, more than any other species, spend so much of our time and energy feeding and caring for our children, until an age at which most species have long since cut the youngsters loose?

Kaplan's pursuit of the answers to those questions dates to his years as a graduate student. For two years, he lived with the Ache (pronounced ah-chay), a community in the wilds of eastern Paraguay that did not come into contact with modern technological society until the 1970s.

"We would go out with them in the middle of the jungle and live off of hunting and gathering," Kaplan recalled.

In much the same way an economist looks at the flow of money and goods through modern society, Kaplan and his colleagues measured the flow of goods and services through the hunter-gatherer cultures. Because humans have lived as hunter-gatherers for most of their history, it seemed like the best starting point for understanding how we evolved to be the way we are, Kaplan and his colleagues believe.

The resulting detailed studies?- who does the hunting, who finds and prepares the edible plants, and then who shares what with whom?- can provide a foundation for understanding human evolution, the anthropologists believe. It is a story, Kaplan and his colleagues believe, of what evolutionary biologists call "co-evolution"?- the simultaneous development of two traits, neither beneficial without the other. In the case of the anthropologists' story line, it is the co-evolution of big brains and long lives.

Bigger brains

Kaplan and a team of UNM colleagues?- Kim Hill, Jane Lancaster and Magdalena Hurtado?- laid out the basics of their idea in a paper in the journal Evolutionary Anthropology. Two years later, Kaplan and Simon Fraser University economist Arthur Robson fleshed out the theory's economics in detail in a 2002 paper in the prestigious Proceedings of the National Academy of Sciences.

The central empirical observations underlying the work are the facts that our brains are at least three times larger than those of gorillas and chimpanzees and that we live twice as long. The evidence for why this is so can be found in the field work conducted by Kaplan and his colleagues over the years.

Humans, the anthropologists found, are picky eaters.

Our evolution into modern humans is distinguished, they argue, by a shift to foods with high nutritional value that take a lot of work to get. Kaplan tells the story of the way the Ache processed the heart of a palm tree. They would chop it down and cut a straight vertical line on each side, peeling open the bark. They removed the pulp from inside the trunk, pounding it into a fiber from which they could squeeze out starch. They would then boil it into a porridge that was essentially pure carbohydrates. It's great food, but it requires a series of steps far more complex than the way our animal relatives pick and eat. The steps must be taught, elder to child.

"Humans were really focused on a high-quality diet compared to the other primates," Kaplan said. Combined with learning from elders, our big brains "give humans access to resources other animals don't have access to," Kaplan said.

Like any good scientific theory, the ideas of Kaplan and his colleagues suggest related predictions about human life history, which the scientists are now testing. Their new work is being done with the Tsimane, a hunting-gathering-fishing culture in the jungles of northern Bolivia.

One corollary of all this is the hypothesis that it is better to be smart than to be strong, an issue the researchers are examining among the Tsimane. They are measuring the weight, height, body fat and strength of the residents of some 20 villages, as well as their knowledge of food gathering and production.

The scientists do not believe that the hunter-gatherer cultures they are studying are perfect prototypes of our prehistoric ancestors, but they think the Tsimane and others like them are living under conditions close to those under which modern human characteristics evolved.

Time is of the essence, the scientists believe, because relatively intact and isolated communities like those being studied will soon be gone entirely and, with them, the opportunity to learn how we came to be the way we are.