December 26, 2011
The Hormone Surge of Middle Childhood
By NATALIE ANGIER
VIEWED superficially, the part of youth that the psychologist Jean Piaget called middle childhood looks tame and uneventful, a quiet patch of road on the otherwise hairpin highway to adulthood.
Said to begin around 5 or 6, when toddlerhood has ended and even the most protractedly breast-fed children have been weaned, and to end when the teen years commence, middle childhood certainly lacks the physical flamboyance of the epochs fore and aft: no gotcha cuteness of babydom, no secondary sexual billboards of pubescence.
Yet as new findings from neuroscience, evolutionary biology, paleontology and anthropology make clear, middle childhood is anything but a bland placeholder. To the contrary, it is a time of great cognitive creativity and ambition, when the brain has pretty much reached its adult size and can focus on threading together its private intranet service — on forging, organizing, amplifying and annotating the tens of billions of synaptic connections that allow brain cells and brain domains to communicate.
Subsidizing the deft frenzy of brain maturation is a distinctive endocrinological event called adrenarche (a-DREN-ar-kee), when the adrenal glands that sit like tricornered hats atop the kidneys begin pumping out powerful hormones known to affect the brain, most notably the androgen dihydroepiandrosterone, or DHEA. Researchers have only begun to understand adrenarche in any detail, but they see it as a signature feature of middle childhood every bit as important as the more familiar gonadal reveille that follows a few years later.
Middle childhood is when the parts of the brain most closely associated with being human finally come online: our ability to control our impulses, to reason, to focus, to plan for the future.
Young children may know something about death and see monsters lurking under every bed, but only in middle childhood is the brain capable of practicing so-called terror management, of accepting one’s inevitable mortality or at least pushing thoughts of it aside.
Other researchers studying the fossil record suggest that a prolonged middle childhood is a fairly recent development in human evolution, a luxury of unfolding that our cousins the Neanderthals did not seem to share. Still others have analyzed attitudes toward middle childhood historically and cross-culturally. The researchers have found that virtually every group examined recognizes middle childhood as a developmental watershed, when children emerge from the shadows of dependency and start taking their place in the wider world.
Much of the new work on middle childhood was described in a recent special issue of the journal Human Nature. As a research topic, “middle childhood has been very much overlooked until recently,” said David Lancy, an anthropologist at Utah State University and a contributor to the special issue. “Which makes it all the more exciting to participate in the field today.”
The anatomy of middle childhood can be subtle. Adult teeth start growing in, allowing children to diversify their diet beyond the mashed potatoes and parentally dissected Salisbury steak stage. The growth of the skeleton, by contrast, slows from the vertiginous pace of early childhood, and though there is a mild growth spurt at age 6 or 7, as well as a bit of chubbying up during the so-called adiposity rebound of middle childhood, much of the remaining skeletal growth awaits the superspurt of puberty.
“Adulthood is defined by being skeletally as well as sexually mature,” said Jennifer Thompson of the University of Nevada, Las Vegas. “A girl may have her first period at 11 or 12, but her pelvis doesn’t finish growing until about the age of 18.”
The 18-year time frame of human juvenility far exceeds that seen in any other great ape, Dr. Thompson said. Chimpanzees, for example, are fully formed by age 12. With her colleague Andrew J. Nelson of the University of Western Ontario, Dr. Thompson analyzed fossil specimens from Neanderthals, Homo erectus and other early hominids, and concluded that their growth pattern was more like that of a chimpanzee than a modern human: By age 12 or 14, they had reached adult size.
Life for Neanderthals was nasty and short, Dr. Thompson said, and Neanderthal children had to get big fast, which is why they hurtled through adolescence at the equivalent of today’s chapter-book age. Our extreme form of dilated childhood didn’t appear until the advent of modern Homo sapiens roughly 150,000 years ago, Dr. Thompson said, when adults began living long enough to ease pressure on the young to hurry up and breed.
And what an essential luxury item middle childhood has proved to be. “It’s consistent across societies,” Benjamin Campbell, an anthropologist at the University of Wisconsin in Milwaukee said. “In middle childhood, kids start making sense.”
Parental expectations rise accordingly. “Kids can do something now,” said Dr. Campbell, who edited the special issue. “They can do tasks. They have economic value.”
Boys are given goats to herd and messages to deliver. They hunt and fish. Girls weave, haul water, grind corn, chop firewood, serve as part-time mothers to their younger siblings; a serious share of baby care in the world is performed by girls not yet in their teens.
Workloads and expectations vary substantially from one culture to the next. Karen Kramer and Russell Greaves of Harvard compared the average number of hours that girls in 16 different traditional cultures devoted each day to “subsistence” tasks apart from child care. Girls of the Ariaal pastoralists in northern Kenya worked the hardest, putting in 9.6 hours daily. Agriculturalist girls in Nepal worked 7.5 hours a day.
Then you come to the more laid-back lives of the foragers. The researchers focused on the Pumé, a foraging group in west-central Venezuela, where preadolescent girls do almost nothing. They forage less than an hour a day, significantly less than their brothers, and are very inefficient in what little they do. They prefer hanging out at the campsite. “Pumé girls spend their time socializing, talking and laughing with their friends, beading and resting,” Dr. Kramer said.
But most cultures mark the beginning of middle childhood with some new responsibility. Kwoma children of Papua New Guinea are given their own garden plots to cultivate. Berber girls of northern Africa vie to prove their worth by preparing entire family meals unassisted.
In the Ituri forest of Central Africa, Mbuti boys strive to kill their first “real animal,” for which they will be honored through ritualized facial scarring. And in the United States, children enter elementary school, for which they will be honored through ritualized gold starring.
In middle childhood, the brain is at its peak for learning, organized enough to attempt mastery yet still fluid, elastic, neuronally gymnastic. Children have lost the clumsiness of toddlerhood and can become physically gymnastic, too, and start practicing their fine motor skills. And because they are still smaller than adults, they can grow adept at a skill like, say, spear-tossing, without fear of threatening the resident men.
Middle childhood is the time to make sense and make friends. “This is the period when kids move out of the family context and into the neighborhood context,” Dr. Campbell said.
The all-important theory of mind arises: the awareness that other people have minds, plans and desires of their own. Children become obsessed with social groups and divide along gender lines, girls playing with girls, boys with boys. They have an avid appetite for learning the local social rules, whether of games, slang, style or behavior. They are keenly attuned to questions of fairness and justice and instantly notice those grabbing more than their share.
The mental and kinesthetic pliancy of middle childhood can be traced at least in part to adrenarche, researchers said, when signals from the pea-size pituitary at the base of the brain prod the adrenal glands to unleash their hormonal largess. Adrenal hormones like DHEA are potent antioxidants and neuroprotectants, Dr. Campbell said, and may well be critical to keeping neurons and their dendritic connections youthfully spry.
Evidence also suggests that the adrenal hormones divert glucose in the brain to foster the maturation of the insula and anterior cingulate cortex, brain regions vital to interpreting social and emotional cues.
In middle childhood, the brain is open for suggestions. What do I need to know? What do I want to know? Well, you could take up piano, chess or juggling, learn another language or how to ski. Or you could go outside and play with your friends. If you learn to play fair, friends will always be there.
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