Evolution and the Teenaged Brain

From The New Yorker, August 31st, a review/essay by Elizabeth Kolbert on two books about the teenaged brain, The Terrible Teens. Many interesting points.

Every adult has gone through adolescence, and studies have shown that if you ask people to look back on their lives they will disproportionately recall experiences they had between the ages of ten and twenty-five. (This phenomenon is called the “reminiscence bump.”)

Why do teens engage in dangerous behavior like drinking games?

And what goes for drinking games also goes for hooking up with strangers, jumping from high places into shallow pools, and steering a car with your knees. At moments of extreme exasperation, parents may think that there’s something wrong with their teen-agers’ brains. Which, according to recent books on adolescence, there is.

Proximate cause:

According to Steinberg, adults spend their lives with wads of cotton in their metaphorical noses. Adolescents, by contrast, are designed to sniff out treats at a hundred paces. During childhood, the nucleus accumbens, which is sometimes called the “pleasure center,” grows. It reaches its maximum extent in the teen-age brain; then it starts to shrink. This enlargement of the pleasure center occurs in concert with other sensation-enhancing changes. As kids enter puberty, their brains sprout more dopamine receptors. Dopamine, a neurotransmitter, plays many roles in the human nervous system, the sexiest of which is signalling enjoyment.

“Nothing—whether it’s being with your friends, having sex, licking an ice-cream cone, zipping along in a convertible on a warm summer evening, hearing your favorite music—will ever feel as good as it did when you were a teenager,” Steinberg observes. And this, in turn, explains why adolescents do so many stupid things. It’s not that they are any worse than their elders at assessing danger. It’s just that the potential rewards seem—and, from a neurological standpoint, genuinely are—way, way greater. “The notion that adolescents take risks because they don’t know any better is ludicrous,” Steinberg writes.

Ultimate cause:

Steinberg explains the situation as the product of an evolutionary mismatch. To find mates, our primate ancestors had to venture outside their natal groups. The reward for taking chances in dangerous terrain was sex followed by reproduction, while the cost of sensibly staying at home was genetic oblivion. Adolescents in 2015 can find partners by swiping right on Tinder; nevertheless, they retain the neurophysiology of apes (and, to a certain extent, mice). Teen-agers are, in this sense, still swinging through the rain forest, even when they’re speeding along in a Tundra. They’re programmed to take crazy risks, so that’s what they do.

And then the impact of what this means for contemporary society, in which, as in so many things, our evolutionary honed behavior is at a mismatch with our current environment.

“If we were genuinely concerned about improving adolescents’ health, raising the driving age would be the single most important policy change we could make,” Steinberg writes. He favors a minimum age of eighteen.

Much the same logic applies to drinking, smoking, and doing drugs. Each year, the U.S. spends hundreds of millions of dollars on public-service campaigns designed to alert adolescents to the perils of such dissipations. Hundreds of millions—perhaps billions—more are spent reiterating this message in high-school health classes. The results have been, to put it kindly, underwhelming.


Many recent innovations—cars, Ecstasy, iPhones, S.U.V.s, thirty racks, semi-automatic weapons—exacerbate the mismatch between teen-agers’ brains and their environment. Adolescents today face temptations that teens of earlier eras, not to mention primates or rodents, couldn’t have dreamed of. In a sense, they live in a world in which all the water bottles are spiked. And so, as Jensen and Steinberg observe, they run into trouble time and time again.

But perhaps, it occurred to me the other day after one of my twins nearly plowed into a mailbox, to look at the problem this way is to peer through the wrong end of the MRI machine. Yes, adolescents in the twenty-first century pose a great risk to others and, statistically speaking, an even greater risk to themselves. But this is largely because other terrifying risks—scarlet fever, diphtheria, starvation, smallpox, plague—have receded. Adolescence evolved over a vast expanse of time when survival at any age was a crapshoot. If the hazards are new, so, too, is the safety. Which is why I will keep telling my kids scary stories and why they will continue to ignore them.

One of many examples about how modern human behavior seems irrational or counter-productive, but which can be understood by contrasting the environment in which human brains evolved to the modern world. (The other big one is why so many people are obese: sweets were rare in our evolutionary past, but valuable, and so humans evolved to crave them; now that sweets are plentiful, the craving has not diminished…)

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