Fun Science Fact #31: Young Men are Idiots for a Reason.

A week before my twenty-second birthday, at one o’clock in the morning, I found myself handcuffed in the back of a police cruiser in West Palm Beach.

Also, I was naked.

Twenty minutes earlier, I’d been standing at the end of a fishing pier, maybe three hundred yards from the shore and twenty feet off the water. I was with a boy who I really didn’t like much, and a girl who I liked a lot.

“So,” the girl said. “Think you could make it back to the beach from here?”

The boy shook his head.

“Sharks. They hang around the piers, you know.”

I looked at him. I looked at her.

“Yeah,” I said. “I could do it.”

Strictly speaking, this was true. I was a varsity swimmer. I’d already done almost ten thousand yards in the pool that day.

The pool, of course, was sharkless.

I looked at the girl. She raised one eyebrow. I shucked off my clothes, climbed up onto the railing, and dove.

Here are some ways that evening could have ended up for me:

Dead in the water, broken neck.
Dead in the water, eaten by sharks.
Dead in the water, sucked out to sea.
Dead on the beach, murdered by homeless guys.

Given those possibilities, the way it actually turned out was probably something close to a best-case scenario. The woman working the booth at the entrance to the pier called the cops. They were waiting for me when I waded up onto the beach.

“Boy,” the one who cuffed me said. “You’re lucky you didn’t just get your balls bit off.”

The interesting question here is this:  what was I thinking? The answer, of course, is that I wasn’t. It has been known since our distant ancestors first climbed down from the trees that young men are idiots. They do things like raiding neighboring villages and challenging people to duels and diving off of fishing piers to impress random girls.

Recently, neuroscience has caught up with conventional wisdom, and we know why this is. The region of the brain that’s responsible for impulse control, anticipating consequences, and regulating behavior isn’t fully functional in late adolescents. In most people, those functions don’t come fully on-line until the twenty-fifth year or later. That, however, is what we refer to as a proximal cause. The question of root causes is much more interesting:  why would millions of years of evolution gift us with a brain that doesn’t really work properly until we’re well into our breeding years?

The scene at the end of that fishing pier gives us an important clue here.  I was a foot taller than the girl I was trying to impress. That was an extreme example of our species’ gender differences, but the average man is about six inches taller than the average woman, and roughly fifty pounds heavier. These differences are referred to as sexual dimorphism, and the degree that a particular population displays them is driven largely by that population’s mating patterns.

In particular, if only a limited number of one gender or the other are permitted to breed, the individuals of that gender tend to be larger and stronger. This is a result of the fact that only the largest and strongest members of that gender in each generation are permitted to reproduce. Our cousins the gorillas provide an extreme example of this sort of pattern. In gorilla society, one silverback dominates a band of females, preventing any other males from breeding with them. As a result, male gorillas are roughly twice the size of females. Orangutans, on the other hand, who are solitary and do not need to fight for mating privileges, have no difference at all in size or strength between genders. Humans fall somewhere in between these two extremes. This likely reflects the fact that we’ve spent some but not all of our evolutionary history practicing gorilla-like polygamy.

So, what does this have to do with young men’s brains? Well, consider this: every one of us is descended from some skinny nineteen-year-old who looked at the guy who was running the tribe and said, “yeah, I could take him.”

Most of those idiots probably didn’t get to reproduce. They wound up with broken necks, just like I very well could have that night in Florida. What about the sensible ones, though? What happened to the young men whose brains worked perfectly well, who looked at the silverback and decided that discretion was the better part of valor?

None of them got to breed. As far as human evolution is concerned, they might as well never have been.

So, the next time you see some dimwit kid rock-climbing without a safety harness, or juggling machetes, or drinking something that someone at a frat party mixed up in a garbage can, don’t look down on him. Try to remember that there’s a perfectly good evolutionary reason that he’s doing what he’s doing. He’s not acting like an idiot. He’s just doing what his genetic heritage has primed him to do.