Sunday, July 4, 2010

What Makes Us Human

Nature via Nurture: Genes, Experience, & What Makes Us Human by Matt Ridley. HarperCollins,

The News & Observer

December 14, 2003

Nature or Nurture or Both?

By Phillip Manning

What makes us the way we are? Why does Sally get all A’s while little Susie is lucky to get a C? Why are some people depressed while others see only the sunny side? Why are so many of us deathly frightened of snakes and spiders? Were we born that way or are we products of our environment? Or both?

This is the essence of the nature vs. nurture debate, a 300-year-old argument over questions that go to the heart of human existence. Science has made strides these past three centuries in exploring this question. However, we are still a long way from a final answer, an unsettling fact for modern societies that expect science to unravel the world’s
mysteries. In response to these demands, scientists offer data,
hypotheses, and informed opinion before their findings are mature enough to support solid conclusions. There is nothing wrong with this; it’s how science advances. Hypotheses are tested against new data. Winning hypotheses become theories; winning theories become laws.

It is in this provisional spirit that British science writer Matt Ridley, author of the best seller “Genome,” offers a new way of looking at the nature vs. nurture debate. In “Nature via Nurture,” Ridley asserts that the debate is framed incorrectly because it pits the two against one another. Nature and nurture, he claims, are not independent but symbiotic. “Genes,” he writes, “are not puppet masters pulling the strings of your behavior but puppets at the mercy of your behavior.” His book aims to substantiate that hypothesis, a goal that is only partially realized because the evidence Ridley marshals to support it is slim and occasionally inapposite.

First, a caveat. We do know that some human attributes are determined entirely by genetics (nature) and some entirely by circumstance (nurture). If you inherit a specific mutant gene, you will get Huntington’s disease no matter how well you look after yourself, no matter what medicines you take. However, no one is genetically programmed to learn a certain language, say, Russian rather than Japanese. All humans have the knack for syntax, but you learn your native tongue entirely through nurture, by listening to people use that language. Ridley is less interested in these certainties than in the broad middle ground where genes and the environment interact in complicated feedback mechanisms that play a major role in determining who and what we are.

“Genes,” he writes, “are designed to take their cues from nurture.” This is undeniably true. Consider phobias. Most of us quickly learn to fear snakes and spiders, both of which were threats to our Stone Age ancestors. Experience with creepy crawlies over millions of years has wired our brains in ways that make it easy for us to learn to avoid them. And genes created the wiring. This is eminently sensible; natural selection via snake bites would weed out people who didn’t quickly learn to fear snakes. But given that the appearance of every attribute is governed by the rules of natural selection, one could argue that all genes are ultimately attributable to environment.

More important than asking how we got our genes is how our behavior causes them to be expressed or suppressed. Ridley gets at this issue with an example involving IQ scores. Studies of adopted siblings indicate that the genetic component of IQ scores rises from 20 percent in infancy (when nurture is critically important) to as much as 80 percent for people beyond middle age. Ridley believes that the change comes not because of innate differences in intelligence but because genes steer some people toward intellectual pursuits and others toward, say, athletics. “Genes,” he writes, “are the agents of nurture.”

This conclusion is speculative. Nobody has ever identified genes that incline one toward intellectual pursuits. But sometimes speculation is all science can provide, and Ridley’s interpretation seems sound. Environment clearly plays a part in determining IQ scores as evidenced by its dominant role in infants. Thus, it is reasonable to assume that the environment would continue to affect the IQ scores of adults. This indicates that people who score high on IQ tests do so because they choose an intellectual environment that produces good scores. And since the scores of adults largely depend on a genetic component, it is possible that their genes cause them to prefer that environment. If so, genes would indeed be the agents of nurture.

Ridley peppers his book with other scientific studies in an attempt to show how genes interact with environment to govern human behavior. Some of these are not persuasive. For instance, the discussion of how genes affect personality doesn’t do much to advance his principal argument. A combination of two genes partially accounts for the incidence of depression among adults. But this example only shows how genes can affect human behavior, and it has only a tenuous connection with the concept of nature via nurture.

Dead ends like this one arise because the idea Ridley is pursuing is new, and the science to prove his points is not fully developed. In fact, science cannot account for the behavior of most people most of the time. Genes, the environment, and the interaction of the two are certainly involved, but in most cases, the data is too skimpy to tell us how. Ridley’s writing style —witty, breezy, anecdotal, and entertaining — exacerbates the confusion. This style worked beautifully for his previous book “Genome,” in which Ridley played the well-informed voyeur cruising through the chromosomes searching for interesting genes. However, this book is more ambitious, an attempt to synthesize a new way
of looking at how we humans operate. And though his style makes “Nature via Nurture” an easy read, it often obscures the science that supports his central thesis.

Nonetheless, Ridley may be on to something important, something that will help us understand why we are the way we are. He has thrown out a broad hypothesis that should stimulate scientists, writers, and readers to think long and critically about an important issue.