National Geographic : 2011 Oct
crucially adaptive human beings around. With- out them, humanity might not have so readily spread across the globe. THIS ADAPTIVE ADOLESCENCE view, however accurate, can be tricky to come to terms with--- the more so for parents dealing with teens in their most trying, contrary, or at-out scary mo- ments. It's reassuring to recast worrisome aspects as signs of an organism learning how to negotiate its surroundings. But natural selection swings a sharp edge, and the teen's sloppier moments can bring unbearable consequences. We may not run the risk of being killed in ritualistic battles or being eaten by leopards, but drugs, drinking, driving, and crime take a mighty toll. My son lives, and thrives, sans car, at college. Some of his high school friends, however, died during their driving experiments. Our children wield their adaptive plasticity amid small but horri c risks. We parents, of course, o en stumble too, as we try to walk the blurry line between helping and hindering our kids as they adapt to adulthood. e United States spends about a billion dollars a year on programs to counsel adolescents on violence, gangs, suicide, sex, substance abuse, and other potential pitfalls. Few of them work. Yet we can and do help. We can ward o some of the world's worst hazards and nudge adoles- cents toward appropriate responses to the rest. Studies show that when parents engage and guide their teens with a light but steady hand, staying connected but allowing independence, their kids generally do much better in life. Ado- lescents want to learn primarily, but not entirely, from their friends. At some level and at some times (and it's the parent's job to spot when), the teen recognizes that the parent can o er cer- tain kernels of wisdom---knowledge valued not because it comes from parental authority but because it comes from the parent's own struggles to learn how the world turns. e teen rightly perceives that she must understand not just her parents' world but also the one she is entering. Yet if allowed to, she can appreciate that her parents once faced the same problems and may remember a few things worth knowing. MEANWHILE, in times of doubt, take inspiration in one last distinction of the teen brain---a nal key to both its clumsiness and its remarkable adaptability. is is the prolonged plasticity of those late-developing frontal areas as they slowly mature. As noted earlier, these areas are the last to lay down the fatty myelin insulation---the brain's white matter---that speeds transmission. And at rst glance this seems like bad news: If we need these areas for the complex task of en- tering the world, why aren't they running at full speed when the challenges are most daunting? e answer is that speed comes at the price of exibility. While a myelin coating greatly ac- celerates an axon's bandwidth, it also inhibits the growth of new branches from the axon. Ac- cording to Douglas Fields, an NIH neuroscien- tist who has spent years studying myelin, " is makes the period when a brain area lays down myelin a sort of crucial period of learning---the wiring is getting upgraded, but once that's done, it's harder to change." e window in which experience can best rewire those connections is highly speci c to each brain area. us the brain's language cen- ters acquire their insulation most heavily in the rst 13 years, when a child is learning language. The completed insulation consolidates those gains---but makes further gains, such as second languages, far harder to come by. So it is with the forebrain's myelination during the late teens and early 20s. is delayed com- pletion---a withholding of readiness---heightens exibility just as we confront and enter the world that we will face as adults. is long, slow, back-to-front developmental wave, completed only in the mid-20s, appears to be a uniquely human adaptation. It may be one of our most consequential. It can seem a bit crazy that we humans don't wise up a bit earlier in life. But if we smartened up sooner, we'd end up dumber. j BRAIN GAMES Delve deep into the workings of the human mind in a three-part special airing this month on National Geographic Channel. Check local listings.