Grit(25)

It’s unlikely that the gene pool has changed all that dramatically in just a few generations. Instead, the most powerful height boosters have been nutrition, clean air and water, and modern medicine. (Incidentally, generational gains in weight have been even more dramatic, and again, that seems to be the consequence of eating more and moving around less rather than changes in our DNA.) Even within a generation, you can see the influence of environment on height. Children who are provided healthy food in abundance will grow up taller, whereas malnourishment stunts growth.

Likewise, traits like honesty and generosity and, yes, grit, are genetically influenced and, in addition, influenced by experience. Ditto for IQ, extroversion, enjoying the great outdoors, having a sweet tooth, the likelihood that you’ll end up a chain-smoker, your risk of getting skin cancer, and really any other trait you can think of. Nature matters, and so does nurture.



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Talents, in all their varieties, are also genetically influenced. Some of us are born with genes that make it easier to learn to carry a tune, or dunk a basketball, or solve a quadratic equation. But against intuition, talents are not entirely genetic: the rate at which we develop any skill is also, crucially, a function of experience.

For instance, sociologist Dan Chambliss swam competitively in high school but stopped when it seemed clear he wasn’t going to make it as a nationally ranked swimmer.

“I’m small,” he explained, “and my ankles won’t plantar flex.” Come again? “I can’t point my toes. I can only flex them. It’s an anatomical limitation. Which means, basically, at the elite level, I could only swim breaststroke.” After our exchange, I did a little research on plantar flexion. Stretching exercises can improve your range of motion, but the length of certain bones does make a difference in how flexible your feet and ankles are.

Still, the biggest impediment to improving wasn’t anatomy; it was how he was coached: “In retrospect, I look back now and can see I had horribly bad coaches in a couple of crucial places. One of my high school coaches—I had him for four years—literally taught me zero. Nothing. He taught me how to do a breaststroke turn, and he taught me incorrectly.”

What happened when Dan did, finally, experience good coaching, in part from hanging around the national and Olympic coaches he was studying?

“Years later, I got back into the pool, got in shape again, and swam a two-hundred-yard individual medley as fast as I did in high school.”

Again, same story. Not just nature, and not just nurture. Both.



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How do scientists know, with unwavering conviction, that both nature and nurture play a role in determining things like talent and grit? Over the past few decades, researchers have been studying identical and fraternal twins, raised in the same family or raised in different families. Identical twins have all the same DNA, while fraternal twins, on average, only share about half. That fact, and a whole lot of fancy statistics (well, not that fancy—more mundane, really, once a good teacher explains them to you), allows researchers to infer, from how similar the twins grow up to be, the heritability of a trait.

Very recently, researchers in London let me know they’d administered the Grit Scale to more than two thousand pairs of teenage twins living in the United Kingdom. This study estimated the heritability of the perseverance subscale to be 37 percent and the passion subscale to be 20 percent. These estimates are on par for heritability estimates for other personality traits, and in the simplest terms, this means that some of the variation in grit in the population can be attributed to genetic factors, and the rest can be attributed to experience.

I hasten to add that there isn’t just one gene that explains the heritability of grit. On the contrary, dozens of research studies have shown that almost all human traits are polygenic, meaning that traits are influenced by more than one gene. Many more, in fact. Height, for example, is influenced by, at last count, at least 697 different genes. And some of the genes that influence height influence other traits as well. In total, the human genome contains as many as twenty-five thousand different genes, and they tend to interact with one another and with environmental influences in complicated, still poorly understood, ways.

In sum, what have we learned? First: grit, talent, and all other psychological traits relevant to success in life are influenced by genes and also by experience. Second: there’s no single gene for grit, or indeed any other psychological trait.



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I’d like to make a third, important point: heritability estimates explain why people differ from the average, but they say nothing about the average itself.

While the heritability of height says something about variability—why in a given population some people are taller and some shorter—it says nothing about how average height has changed. This is important because it provides evidence that the environment we grow up in really does matter, and it matters a lot.

Here’s another striking example, and one more relevant to the science of success: the Flynn effect. Named after Jim Flynn, the New Zealand social scientist who discovered it, the Flynn effect refers to startling gains in IQ scores over the past century. How big are the gains? On the most widely used IQ tests today—the Wechsler Intelligence Scale for Children and the Wechsler Adult Intelligence Scale—gains have averaged more than fifteen points in the last fifty years in the more than thirty countries that have been studied. Put another way, if you scored people a century ago against modern norms, they would have an average IQ score of 70—borderline for mentally retarded. If you scored people today against the norms of a century ago, we would have an average IQ score of 130—the typical cut score for mentally gifted programs.