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http://www.nytimes.com/2002/07/02/science/social/02CHIL.html

Why Childhood Lasts, and Lasts and Lasts

By NATALIE ANGIER

n the isle of Mer, a rugged landspit in the Torres Straits near Australia that could fit easily inside Central Park, some 430 traditional foragers called the Meriam subsist by grace of the sea.

At low tide, young and old alike rush out to the reef. Women hurriedly gather up shellfish like conchs, clams and cowries, breaking open the shells to extract the meat and so keep their burdens bearable. Men aim bamboo spears tipped with iron to lance up snappers, sea perch, cod and squid; or they toss out baited hand lines to yank in needlefish, perch, tuna and mackerel. Boys and girls — some of them barely old enough to walk — gather, spear and fish by hand with equal zeal.

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Shellfish collecting is a physically demanding but relatively simple task, and the surest way to guarantee a meal. Spearfishing and hand-line casting, by contrast, are high-skill enterprises, which require detailed knowledge of the nature and behavior of each type of prey, robust powers of concentration and great dexterity in casting and jabbing. The best and most admired spearfisher on the island, the Meriam concur, is a 48-year-old man named Walter Cowley, who impales his quarry maybe half the time.

Yet as Dr. Douglas Bird and Dr. Rebecca Bliege Bird, anthropologists at the University of Maine in Orono, discovered in their studies of Meriam life, the proudest spearmen on the island are just barely better than . . . the children.

In a detailed analysis of the productivity and fishing success rates of the people of Mer, the anthropologists were startled to find that children of crayon age were already dazzling with their spears and lines, and fully cognizant of the nuances of their marine ecosystem, bringing to mind an old Groucho Marx line: "A child of 5 could understand this. Fetch me a child of 5."

Where the children proved less successful than adults was in the straightforward "woman's work" of collecting shellfish. The children were avid gatherers of any mollusk they could find, but they were simply too small and weak to compete with the adult women, who loped and scooped and cracked their way across the reef.

The new analysis of life on Mer, where people stubbornly adhere to the ways of their ancestors, suggests to Dr. Bird and Dr. Bliege Bird that human childhood may not be what it so often is assumed to be: a built-in Little Red Schoolhouse, and a time when the young can master the many skills they will need to thrive as autonomous adults.

Instead, the anthropologists propose that a long childhood exists on one end of the human life span mainly because a comparatively long old age exists on the other end, and that in a long-lived species there are benefits to slow growth that have little to do with learning — benefits like not threatening the older competition before said elders are safely stooped and toothless.

The Mer work appears, along with studies of the Maya of Mexico, the Hadza of Tanzania, and a multiethnic community in the Okavango Delta of Botswana, in the newest issue of the journal Human Nature, which is devoted to the deceptively innocent question: Why childhood — or, more precisely, why such a supersized childhood?

As any parent can attest, human childhood is absurdly protracted. Children are dependent on adults for food, shelter and protection for about 18 years (give or give a couple of decades), which is a good 5 to 7 years longer than are the offspring of our nearest relatives, the chimpanzees; and the age of sexual maturity among humans is likewise delayed.

The existence of a prolonged childhood virtually defines our species, shaping our social lives and forging the all-powerful family fetters that nurture and nudge, buoy and stifle us. How in the name of Seuss did we evolve to the point where we spend almost a third of our lives being small, vulnerable, subject to the whims of others, and not yet able to do what evolution supposedly wants us to do most of all: reproduce?

"It's a fantastic problem," said Dr. Douglas Bird. "It goes to the heart of who we are, our sociality, our willingness to cooperate and provision and care for each other as no other species does."

The orthodox explanation for childhood has been a variation on the "brain growth" model. By this theory, the big, hungry human brain is a very useful tool, which has allowed humans to colonize nearly every habitat on earth, and to extract resources from the most forbidding of landscapes.

A big brain presumably needs a long time to grow, and to be programmed, and to learn in gradual, cumulative style what it must know to survive. Such an explanation seems sensible to those living in a technologically advanced and ruthlessly competitive culture like our own, where anybody who fails to get at least a college degree, if not an M.D./Ph.D./J.D., risks spending a life busing tables or telemarketing.

Yet as the anthropologists make clear in the new issue of Human Nature, "sensible" does not mean proved, or even true, and they no more concur on the reasons for the evolution of childhood than siblings would on who deserves the biggest piece of cake.

Some insist that the need to learn is likely to be at the core of our dilated childhood. Dr. Hillard S. Kaplan of the University of New Mexico, whose work has been broadly influential in evolutionary anthropology, argues that human styles of hunting and gathering are often quite complex compared with the foraging strategies of other creatures, and thus require long periods of learning, practice and apprenticeship.

In his studies of the Ache people of Peru and Paraguay, for example, he has found that on average, a man's hunting prowess quadruples between the ages of 22 and 35.

"My own view is that while there is tremendous amount of ecological variability, humans have as a rule been oriented toward the most difficult, highest quality foods in an environment," Dr. Kaplan said in a telephone interview. "We've specialized in knowledge-oriented environments, where it took a long time to become an effective hunter or forager, and there are still a lot of reasons to believe the learning-intensive nature of such strategies are responsible for the long childhood period."

As an example of how sophisticated and well-schooled in the hunting craft a person must be to succeed, Dr. John Bock, an anthropologist at California State University in Fullerton and an author on one of the new reports, relayed in an interview a story from his research in Botswana.

He and his wife, an animal behaviorist, were trying to figure out the whereabouts of some lions that had recently been lying in a patch of grass. They asked a couple of men who had lived in a local village their entire lives. The men examined the grass and surrounding footprints, and then fell into a lively debate over where to look next.

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"They were talking at such a high level that we couldn't possibly participate," Dr. Bock said. "After an hour, one said, O.K., you sold me, that's where they must be. We jumped in a truck, drove there, and, sure enough, that's where the lions were. This had to do with 30 years' experience. The guy knew how a lion thought."

Yet for the anthropologists, like Dr. Douglas Bird, who are skeptical of the childhood-is-for-learning hypothesis, stories about the difficulty of hunting are not persuasive. They observe that many of the studies cited by Dr. Kaplan and others, of the differences in hunting success between younger and older men, show not that learning must occur in the context of being a dependent and pre-fertile juvenile, but rather that a hunter or forager gets better throughout life, often while already on the job, and long past the age of first reproduction.

Dr. Nicholas Blurton Jones of the University of California at Los Angeles is an author of one new report, which presents data from the Hadza foragers in Africa that cast doubt on the learning model of childhood. Comparing hunting success rates among men and the acquisition of difficult plant foods like tubers among women, he and his colleague Dr. Frank Marlowe of Harvard found that older adults did outshine children and young adults.

But are those adults better than children at bringing home the bushbuck because they know more, or because they are bigger and stronger? And when an older man outhunts a younger man, is that necessarily because the senior has learned more over time — i.e., is it proof that the brain learns things slowly, rather than quickly?

"It's true that young adult Hadza improve their skills over time," Dr. Blurton Jones said. "But are they learning more, or are they more motivated and less distracted? We don't know."

For Dr. Blurton Jones, the remarkable thing about the human brain is how quickly it learns, particularly when incentives are high. "Certainly there's a lot that hunters must learn," he said. "My argument is that they can learn it all rather fast. The brain seems designed to absorb things very rapidly."

Dr. Blurton Jones and Dr. Marlowe sought to determine experimentally if some of the more complex foraging and hunting skills among the Hadza really did require lengthy tutelage in childhood.

They had Hadza of both sexes and varying ages compete for prizes to see who could dig up the most tubers, or who was most adept at the quite difficult task of climbing baobab trees to obtain honey, or who among the males was best at shooting arrows at a bull's-eye target — this last type of competition finding such favor among the Hadza that they did it without the need for prizes, and asked the researchers to test them apart from the formal studies.

Among other parameters, the researchers compared the success rates in these tests of people who had spent some time away from the bush at boarding school with people who had not, to see whether a loss of practice affected one's skillfulness; and they contrasted the capacity to find an all-important food source, underground tubers, between women, who spend all their time doing it, and men, who rarely tuber hunt.

In each test, practice had far less to do with making perfect than did size and strength. Hadza who had attended boarding school could shimmy up trees and shoot arrows as well as those who had stayed at home, and men, when given the incentive of a prize, were every bit as good at tuber-collecting as were the women. The findings, said Dr. Marlowe, "do not support the practice theory."

Neither do the results from Dr. Bird and Dr. Bliege Bird of the Meriam and fishing skills. If children were constrained by skillfulness rather than by size, they said, then the differences between adults and children should show up in measures of success in fishing tasks requiring keen cognitive powers, and they did not.

Instead, the children lagged when it came to their capacity to walk quickly and crack open large cowrie shells. More recently, the researchers have studied the Mardu people of the Western Desert of Australia, and again found that children were adept hunters by the age of 5 or 6, and thereafter success was measured not by age, but by size.

Why, then, do children grow slowly and stay small?

The researchers suggest that it is related to our so-called life history. By this premise, the longer an animal lives, the more sense it makes to grow slowly and postpone reproduction, because the more one invests in physical development early on, the higher one's reproductive success and quality of offspring in adulthood.

Studies comparing the life histories of many mammalian species have shown that age of first reproduction tracks closely with average age of mortality. As these researchers see it, the augmented longevity of humans, brought about by people learning to forage for nutritious foods like tubers and to hunt with weapons, allowed childhood to be extended.

With early mortality reduced, there was a good chance that the investment in an extended phase of juvenile growth would pay off in higher reproductive fitness later.

"The length of human childhood is exactly what you would expect from adult mortality," said Dr. Blurton Jones. "There's nothing weird about it."
Dr. Douglas Bird and others have proposed that there can be advantages to staying physically small and immature. Children not only look cute and therefore elicit caretaking behaviors from adults, but they are less threatening as well.

Dr. Bird observes that male orangutans that grow up in stressful or highly competitive environments sometimes remain juvenile in features and behavior well into adulthood, the better to stick it out safely until the opportunity to mate improves.

Such behavior finds a corollary among humans, when, in large families, the youngest children, who have no chance of competing with their big siblings, are the most apt to play Peter Pan.

Dr. Bock proposes something of a middle ground between the two theoretical camps. As he sees it, learning is an important aspect of childhood, but it occurs in punctuated bursts rather than slowly and cumulatively, the timing driven, perhaps, by the dynamic architecture of the developing nervous system.

He is particularly interested in mapping out the so-called sensitive periods of childhood development, those windows of opportunity when certain tasks must be learned, or else.

The most highly motivated and driven adult can never learn to speak a second language as fluently and as accent-free as a child can, for example, and those who take up piano at the age of, say, 28, can practice, practice, practice until their fingers bleed, and they will still not make it to Carnegie Hall.

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