WHAT is it about humans that makes us such late developers? Chimps are ready to reproduce by the age of eight. Gorillas are all grown up at six. Yet human childhood lasts twice as long as it should do for an ape of our size and rate of growth. We spend more time as children than any other animal on Earth. And we alone continue to feed our offspring well into adolescence. It takes an estimated 13 million calories to bring up a child – a huge investment on the part of parents. And that’s not to mention all the GameBoys and tickets to Disneyland. Why do we do it?
The puzzle of childhood has intrigued researchers for decades. Some believe that a long childhood is simply a by-product of our long lifespan and requires no special explanation. But many anthropologists are convinced there must be some evolutionary advantage to prolonged immaturity. Humans live complicated lives: we have culture, language and technical skills enabling us to migrate across the globe and prosper. We can build cities and civilisations, and survive on our wits and intellect. Perhaps our childhood is so different because we have so much more to learn than other animals? Or perhaps, as one anthropologist now claims, long childhoods evolved to benefit parents, not kids. He believes it’s only now, in the developed world at least, that childrearing has become so costly.
One possible clue to the extended childhood enigma is found by looking at when it evolved. The first human-like creatures, the australopithecines, which lived about 4 million years ago, seem to have had no real childhood – fossil evidence suggests that, like apes, they moved swiftly from infancy to adolescence. But about 1.5 millions years ago, with the appearance of our genus Homo, childhood began to lengthen. The size and proportions of young skeletons from this time, and the timing of their tooth eruptions, suggest that these ancestors were staying young for years. By the time Homo sapiens appeared, about 100,000 years ago, childhood was the extended affair it is today.
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Interestingly, the appearance of a long childhood coincides with a rapid increase in human brain size. Could the two be connected? It can’t simply be about giving our big brains longer to grow because they stop growing way before adulthood. But perhaps it provides the time required for rewiring the hardware to help us cope in the adult world?
Hillard Kaplan from the University of New Mexico, Albuquerque, argues that we need a prolonged childhood to learn how to survive our complex adulthood. During this time of fewer responsibilities, he says, children have the space and freedom to acquire the skills and technical knowledge that will serve them as adults when no one is watching or helping. Those skills could mean the difference between life and death. Quite simply, childhood is an investment in the future.
Kaplan points out that our ancient ancestors were hunters and gatherers, occupations that require physical and mental agility that would tax the mind of today’s average sedentary office worker. John Bock from California State University at Fullerton, who studies children in Botswana, agrees. Hunters, he points out, must be able to make their own weapons, track down animals, kill and butcher them, and bring home the bacon. And that’s on top of all the other abilities they need just to stay alive out in the bush. Gathering plants also takes skill. Other primates, including chimps, tend to rely on vegetation they pluck from the abundant forest, but human gatherers search out roots and nuts that must be processed before they can be eaten. Gatherers also use digging sticks and baskets and many other tools to make foods more digestible. Hence, Kaplan and Bock argue, children need a long apprenticeship to cram in the critical learning they need to support themselves.
It’s an appealing idea because it fits with modern notions of childhood, where kids spend time in school, studying and acquiring skills to help them function effectively as adults. But there is little direct evidence to support it and other anthropologists protest that learning is not the point of childhood, and never was. New findings support their view that kids are actually quite proficient in survival skills, at least as hunters and gatherers. If childhood has become a time of learning today, these researchers argue, that’s simply modern culture taking advantage of an extended life cycle stage that is already in place for other reasons.
Earlier this year, Nicholas Blurton-Jones from UCLA and Frank Marlowe from Harvard University published results from their studies of Hadza people from northern Tanzania (Human Nature, vol 13, p 199). The Hadza are primarily hunters and gatherers, but some children also attend boarding school where they sit at desks all day. Would time spent away at school affect the children’s bush skills? Blurton-Jones and Marlowe devised a series of contests to discover. They found that young men who had been practising all their lives were no better at using a bow and arrow or climbing baobab trees to collect honey than those who had been away at school. Although hunting skills, in particular, varied among individuals, childhood experience had almost no effect on who became the best hunters. In fact, hunting efficiency peaks at around 40, so adult experience is probably more significant. Blurton-Jones and Marlowe also found that women who spend all day and every day digging tubers are no better at it than men who have little training in this subsistence activity.
If childhood for modern hunter-gatherers is not about learning or refining adult skills, then our ancestors probably didn’t need childhood for extensive learning either. “There is a lot for foragers to learn,” comment Blurton-Jones and Marlowe in their paper. “But does it really take so much time to learn it? Perhaps it would if we learned mostly by trial and error, like a rat or a pigeon in the laboratory. But from an early age, humans imitate and get instruction, and hear people talking about work. Human learning is very rapid. Even small children are rapid and capable learners.”
Other new research by Rebecca Biege Bird and Douglas Bird from the University of Maine also suggested that childhood is more about growing into complex tasks than learning them (Human Nature, vol 13, p 239). Observing Meriam children and adults of the Torres Strait, Australia, as they gathered shellfish or fished with lines and spears, the Birds discovered that children were just as good as adults at both line fishing and spear fishing, tasks that are technically difficult and require a lot of know-how about fish, tides and bait. But strangely, kids were not as good as adults at gathering shellfish, a job that anyone can do by simply bending over and grabbing. “Shellfish collecting on Mer involves lots of walking to search for tridacnid clams and conch that are thinly dispersed across the mid-littoral of the reef,” says Bird. “So if you walk faster, your encounter rate for highly profitable prey types will increase.” But once the kids were older and larger, more efficient walkers and less often distracted, they made competent gatherers.
The point is that kids grow into the task simply through physical development, not through learning or practice. The children were great at fishing although fishing takes almost adult cleverness to figure out, and they were held back at gathering only because they were smaller and less able than adults. “It doesn’t take the whole length of the human childhood to learn even complex foraging tasks,” says Biege Bird. “Size and strength often trump experience.”
If childhood isn’t about learning to feed yourself, is it about acquiring the social skills humans are so good at? “Understanding the complexities of social interactions takes many years with many opportunities for social engagement, social interaction and social reasoning about experiences,” says developmental psychologist Melanie Killen of the University of Maryland. But recent research suggests that children know more about social relations than we give them credit for, and they learn the ropes early. Even babies will start to cry when they hear other babies in distress, which suggests a degree of empathy, fundamental for all positive human social behaviour. Children as young as four have a sense of fairness, according to studies done by William Damon of Stanford University. And Killen’s own work with preschool children indicates that they use this, as well as remarkably well-developed negotiation skills, in their everyday dealings with one another.
Killen’s findings, based on videos of children playing with no adults around, confirms what Peter Verbeek of Miyazaki International College in Japan has discovered. By age three or four kids manage their interpersonal conflicts differently with family than with peers. What’s more, they are often much more capable without adult intervention. Children of this age change their style of interaction depending on how intense they feel a friendship is, Verbeek found, and they use adult social tools like negotiation, conciliation and making up after a conflict. And other studies confirm what any parent knows: kids don’t learn how to make and break friendships through parental instruction, they learn by interacting with others. All this flies in the face of the traditional view of children as primarily egocentric and unconcerned with building and maintaining relationships.
“The degree to which young children understand relationships is still an open question,” admits Verbeek. But there’s no doubt that by age eight children’s social skills are quite sophisticated. What’s more, research by Clark Barrett from UCLA suggests their understanding of the way other individuals think extends beyond the boundary of our own species. Preschool kids readily attribute intentions to predators, demonstrating the sort of mind-reading skills that would have been vital for their survival in the ancestral environment (91av, 13 April, p 34). All in all you get the picture of kids operating pretty much as miniature adults. Which has left a growing number of experts in human evolution questioning the notion that learning is the raison d’être for our extended childhood. “Hard evidence that what we learn in childhood contributes to our fitness is conspicuous by its absence,” comments anthropologist Ruth Mace of University College London, who studies the evolution of human life cycle stages.
If a long childhood isn’t designed to give kids time to learn, then what is it for? Anthropologist Barry Bogin of the University of Michigan-Dearborn has proposed a radical alternative. He believes it evolved for the benefit of parents. Bogin argues that early childhood – between about age three to seven in modern humans – is a new phase inserted into the life cycle of our ancestors to increase reproductive success. He points out that all other mammals continue suckling their young until their permanent molars have erupted and they can fend for themselves. This limits the number of offspring each mother can produce. Bogin’s idea is that our prolonged childhood is the result of evolution favouring this new life cycle phase where infants are no longer totally dependent on their mothers, but can rely on other family members for food and help. This means mothers can become pregnant again even though they still have small children.
The simple fact that humans are a highly successful species supports Bogin’s idea. Despite our size, our long generation lengths and our long lives, we breed at the rate and with the success of small mammals with short lives. The typical interval between children is two and a half years, compared with five years for chimps, for example. More significantly, about twice as many human babies reach the age of 15 than do chimp babies.
What’s more, the idea of kids as “dependent” is a modern concept that clouds our understanding of what it really means to be a child. In many parts of the world children contribute significantly to the household and are not really burdens. Across the globe, children typically look after their younger siblings and do household chores such as gathering firewood, weeding fields and tending livestock. And they do all this while still small and not competing much for resources such as food and household space. For parents in these cultures, childhood may be too short rather than too long.
Of course, for many families these days the tables have turned. Children may have evolved as “little helpers” but in the developed world, at least, they have become a drain on household energy and income. If parents originally benefited from an extended childhood, kids have the upper hand now. We feel compelled to keep providing for our offspring even well after they reach sexual maturity. Paying for a good education makes perfect sense as an investment for our kids’ future – even if it means they don’t become independent until well into their twenties. And so what if they demand cash for new computer games, the movies or a holiday. Childhood, we tell ourselves, is special. Even if, occasionally, we wonder why it has to be so damn long.
