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.
When I first learned about the Flynn effect, I didn’t believe it. How could it be that we’re all getting that much smarter so quickly?
I called Jim to share my incredulity—and my desire to learn more—and, globe-trotter that he is, he actually flew all the way to Philadelphia to meet with me and give a talk on his work. At our first encounter, I remember thinking that Jim looked like a caricature of an academic: tall, a little bony, wire-rimmed glasses, and a rather unruly head of curly steel-gray hair.
Flynn began his talk with the basic facts on IQ change. Digging through the raw scores of IQ tests taken over the years, he found that the improvements on some tests were much bigger than others. He went to the chalkboard and sketched out a steep line indicating that scores had climbed most sharply for IQ tests assessing abstract reasoning. For instance, many young children today can answer the question “Dogs and rabbits: How are they alike?” They might tell you that both dogs and rabbits are alive, or that they’re both animals. In the scoring manual, these answers only earn a half credit. Some children might go so far as to say that they’re both mammals, and for that insight, they’d earn a full credit. In contrast, young children a century ago might look at you quizzically and say, “Dogs chase rabbits.” Zero points.
As a species, we’re getting better and better at abstract reasoning.
By way of explaining massive gains in certain IQ subtests but not in others, Flynn told a story about basketball and television. Basketball, at all levels of competition, has gotten more competitive over the last century. Flynn played a little ball himself as a student and remembers the game changing even within a few years. What happened?
According to Flynn, what happened was television. Basketball was a great game to watch on the small screen and the exposure fueled the game’s popularity. Once television became a household fixture, more kids started playing the game, trying left-handed layups, crossover dribbles, graceful hook shots, and other skills that seemed routine among star players. And by getting better, each kid inadvertently enriched the learning environment for the kids he or she was playing against. Because one thing that makes you better at basketball is playing with kids who are just a little more skilled.
Flynn called this virtuous cycle of skill improvement the social multiplier effect, and he used the same logic to explain generational changes in abstract reasoning. More and more, over the past century, our jobs and daily lives ask us to think analytically, logically. We go to school for longer, and in school, we’re asked, more and more, to reason rather than rely on rote memorization.
Either small environmental differences, or genetic ones, can trigger a virtuous cycle. Either way, the effects are multiplied socially, through culture, because each of us enriches the environment of all of us.
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Here is a graph showing how Grit Scale scores vary by age. These are data from a large sample of American adults, and you can see from the horizontal axis that the grittiest adults in my sample were in their late sixties or older; the least gritty were in their twenties.
One explanation for this data is that there’s a sort of “reverse Flynn effect” for grit. For instance, it’s possible that adults in their seventh decade of life are grittier because they grew up in a very different cultural era, perhaps one whose values and norms emphasized sustained passion and perseverance more than has been the case recently. In other words, it could be that the Greatest Generation is grittier than the millennials because cultural forces are different today than yesterday.
This explanation for why grit and age go hand in hand was suggested to me by an older colleague who, looking over my shoulder at the same graph, shook his head and said, “I knew it! I’ve been teaching the same undergraduates the same course at the same university for decades. And I’ll tell you, they just don’t work as hard these days as they used to!” My dad, who gave his entire professional life as a chemist to DuPont and quite literally retired with the gold watch, might say the same of the Wharton entrepreneur who approached me after my lecture. Even while pulling all-nighters for his present venture, the young man half expected to be on to something entirely new within a few years.
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Alternatively, it’s possible these age trends have nothing to do with generational changes in grit. Instead, what the data may be showing is how people mature over time. My own experience, and the stories of grit paragons like Jeff Gettleman and Bob Mankoff suggest that, indeed, grit grows as we figure out our life philosophy, learn to dust ourselves off after rejection and disappointment, and learn to tell the difference between low-level goals that should be abandoned quickly and higher-level goals that demand more tenacity. The maturation story is that we develop the capacity for long-term passion and perseverance as we get older.
To distinguish between these rival explanations, we need a different kind of study. To generate the data I just showed you, I asked people of different ages about their current level of grit. What I got was a snapshot of grit in younger and older adults. Ideally, I’d follow these people for the rest of their lives, the way psychologist George Vaillant followed the Harvard men. Since the Grit Scale hasn’t been around very long, I can’t play you a time-lapse movie of grit over the life course. What I want is that movie. What I have is a snapshot.
Fortunately, many other aspects of personality have been examined longitudinally. In dozens of studies that have followed people over years and decades, the trends are clear. Most of us become more conscientious, confident, caring, and calm with life experience. A lot of that change happens between the ages of twenty and forty, but, in fact, there’s no epoch in the human life span where personality stops evolving. Collectively, these data demonstrate what personality psychologists now call “the maturity principle.”
We grow up. Or at least, most of us do.
To some extent, these changes are preprogrammed and biological. Puberty and menopause are things that change our personalities, for example. But on the whole, personality change is more a function of life experience.