Drunkard's Walk - Leonard Mlodinow [83]
In his 1869 book, Hereditary Genius, Galton wrote that the fraction of the population in any given range of heights must be nearly uniform over time and that the normal distribution governs height and every other physical feature: circumference of the head, size of the brain, weight of the gray matter, number of brain fibers, and so on. But Galton didn’t stop there. He believed that human character, too, is determined by heredity and, like people’s physical features, obeys in some manner the normal distribution. And so, according to Galton, men are not “of equal value, as social units, equally capable of voting, and the rest.”29 Instead, he asserted, about 250 out of every 1 million men inherit exceptional ability in some area and as a result become eminent in their field. (As, in his day, women did not generally work, he did not make a similar analysis of them.) Galton founded a new field of study based on those ideas, calling it eugenics, from the Greek words eu (good) and genos (birth). Over the years, eugenics has meant many different things to many different people. The term and some of his ideas were adopted by the Nazis, but there is no evidence that Galton would have approved of the Germans’ murderous schemes. His hope, rather, was to find a way to improve the condition of humankind through selective breeding.
Much of chapter 9 is devoted to understanding the reasons Galton’s simple cause-and-effect interpretation of success is so seductive. But we’ll see in chapter 10 that because of the myriad of foreseeable and chance obstacles that must be overcome to complete a task of any complexity, the connection between ability and accomplishment is far less direct than anything that can possibly be explained by Galton’s ideas. In fact, in recent years psychologists have found that the ability to persist in the face of obstacles is at least as important a factor in success as talent.30 That’s why experts often speak of the “ten-year rule,” meaning that it takes at least a decade of hard work, practice, and striving to become highly successful in most endeavors. It might seem daunting to think that effort and chance, as much as innate talent, are what counts. But I find it encouraging because, while our genetic makeup is out of our control, our degree of effort is up to us. And the effects of chance, too, can be controlled to the extent that by committing ourselves to repeated attempts, we can increase our odds of success.
Whatever the pros and cons of eugenics, Galton’s studies of inheritance led him to discover two mathematical concepts that are central to modern statistics. One came to him in 1875, after he distributed packets of sweet pea pods to seven friends. Each friend received seeds of uniform size and weight and returned to Galton the seeds of the successive generations. On measuring them, Galton noticed that the median diameter of the offspring of large seeds was less than that of the parents, whereas the median diameter of the offspring of small seeds was greater than that of the parents. Later, employing data he obtained from a laboratory he had set up in London, he noticed the same effect in the height of human parents and children. He dubbed the phenomenon—that in linked measurements, if one measured quantity is far from its mean, the other will be closer to its mean—regression toward the mean.
Galton soon realized that processes that did not exhibit regression toward the mean would eventually go out of control. For example, suppose the sons of tall fathers would on average be as tall as their fathers. Since heights vary, some sons would be taller. Now imagine the next generation, and suppose the sons of the taller sons, grandsons of the original men, were also on average as tall as their fathers. Some of them, too, would have to be taller than their fathers. In this way, as generation followed generation, the tallest humans would be ever taller. Because of regression toward the mean, that does not happen. The same can be said of innate intelligence, artistic talent, or the ability to