Irreconcilable Differences
JUDITH RICH HARRIS calls "No Two Alike" a "scientific detective story." The mystery is why people — even identical twins who grow up in the same home with the same genes — end up with different personalities. The detective is Harris herself, a crotchety amateur, housebound because of an illness, who takes on the academic establishment armed only with a sharp mind and an Internet connection. Harris the author scrupulously follows clues; Harris the protagonist drives the story forward through force of character, arriving at a theory of personality that could be said to describe herself.
Eight years ago, Harris's book "The Nurture Assumption" set academic psychology on fire by attacking the notion that parenting styles shape children. Scholars, irked by this upstart former textbook writer and grad-school reject, scorned her argument. In her new book, Harris tries to embarrass her critics while synthesizing her work into a theory of personality. "No Two Alike" is two books: a display of human weakness, and a display of scientific courage and imagination.
Every detective has a favorite method. Harris's is behavioral genetics, which attempts to tease out the genetic bases of behavior. To sort genetic from environmental factors, you study people with the same genes but different environments: identical twins raised apart. Or you study people with different genes but the same environment: adoptive siblings raised together.
Using this method like scissors — holding one variable steady while slicing against it with the other — Harris shreds popular theories of personality formation. Does home environment — parenting style, marital harmony, the use or rejection of day care — shape a child's personality, making her more agreeable, less aggressive or more extroverted? Nope. Research shows that twins don't turn out more alike if they're raised together than if they're raised apart. Nor do adoptive siblings. And when you compare apples to apples — making sure that each parent-child unit in a study is as genetically related as any other — being raised in one home rather than another, on average, makes no difference.
Maybe a certain type of home environment affects children with some genes one way and children with other genes the opposite way? Sorry, says Harris, the data show no such patterns. Furthermore, she writes, since twins raised together have the same genes and environments, gene-environment interactions can't explain why they turn out differently. Do kids turn out differently because parents treat them differently — based on birth order, for example? If so, you'd expect siblings raised together, in manifest birth order, to differ more than siblings raised apart. But they don't.
If parents don't shape children, what does? Harris realigns her scissors and cuts again. She looks for studies that pit the influence of parents against the influence of the larger environment. Children raised in Canada by parents born in Hong Kong become Canadian. When parents have an accent but most of the neighborhood doesn't, their children lose the accent. The village, not the family, prevails.
Why? Because that's what makes evolutionary sense. If your parents raise you poorly, Harris argues, you're better off diluting the damage. If they dote on you, you're better off adjusting to the tougher social world in which you'll have to find your way. Throughout most of human evolution, parents had little time for children old enough to run around. They learned from one another and from watching adults.
From this evolutionary logic, Harris builds a theory of personality based on three systems in our brains. The socialization system absorbs language, customs and skills, making us more alike. Mommy and Grandma wear dresses; you're a girl, so you want a dress too. The relationship system distinguishes people so we can deal with each one appropriately. Crying gets milk from Mommy but not Grandma; Billy is gentle, but Bobby hits people. Even random differences are important: Anne helped you with your homework, but her twin sister owes you a dollar. You find ways to tell people apart because you have to.
Harris offers a variety of interesting evidence for these systems: brain scans, animal studies and neurological diseases that knock out one system but not the other. She sprinkles her book with humor, but spends much of it savoring acrimonious relationships. No grudge is forgotten; no enemy spared. They key to understanding this behavior, and the mystery, is her third system: status.
Harris portrays herself as a hard-nosed lay scientist hunting and slaying academic frauds. And slay them she does. Years ago, at an academic conference held shortly after the publication of "The Nurture Assumption," a researcher named Stephen Suomi chided her, in what she calls a "scornful voice," for ignoring gene-environment interactions. Suomi "wasn't afraid of a little woman from New Jersey," she writes. "Maybe he should have been." Harris spends the next dozen pages hunting down and eviscerating Suomi's research, calling it "vaporware" — a term used in the software industry to describe a product that's announced in order to scare off competitors but then never materializes. Later, she sinks her teeth into the researcher Frank Sulloway, who has argued that personality is shaped by birth order. When his work was questioned by another researcher, Harris writes, Sulloway refused to show his data to skeptics he called "unqualified." Her persuasive scientific critiques of both men are overshadowed by her seeming determination to humiliate them. Hell hath no fury like this little woman scorned.
Hence the status system. Your socialization system figures out how to conform to your group. Your relationship system figures out how to get along with each person. Your status system figures out how to compete. It monitors people's reactions, gathering information about how smart, pretty, weak or talented they think you are. It looks for virtues, activities and occupations at which you're most likely to best your peers. It notices tiny differences between the way people regard you and the way they regard others in your peer group, or even your twin. By choosing pursuits based on these differences, it magnifies them. It drives you to be different.
This is the paradox behind the book's subtitle. Human nature causes human individuality; the mental systems that we share are also the ones that distinguish us. But if these three systems are, as Harris concludes, the "perpetrators" of individuality as we know it, the mystery of how we got here gives way to the mystery of where we're going. The perpetrators remain at large. The evolutionary forces that gave us distinctive personalities don't end here. Human nature isn't finished with human individuality, or with itself.
Harris attributes half of our traits to genes, noting the roughly 50 percent personality correlation between identical twins. She figures that "evolution provided humans with a certain amount of plasticity in behavior so they can profit from their experiences." When hominids developed "subtle and multidimensional" abilities to read minds and adjust behavior, it became "advantageous to be able to modify patterns of social behavior on a long-term basis."
Ultimately, however, long-term behavior modification is at odds with itself. As our minds become subtler and our occupations less stable, short-term modifications suited to the situation at hand become more advantageous than permanent modifications. This is already happening, according to her theory. The reason parental influence doesn't control children's behavior outside the home is that they adjust to context. "Children are capable of generalizing — of learning something in one context and applying it in another — but they do not do it blindly," Harris observes. At home, where you're the younger sibling, you yield. At school, where you're one of the bigger kids, you don't. And unlike other animals, you can shuffle your self-classifications. In seconds, you can go from acting like a girl to acting like a child to acting like a New Yorker.
In short, the evolutionary logic that makes us different from one another will gradually make us different from ourselves, context by context. Personality — behavior that is "consistent across time and place," as one textbook puts it — will fade. We'll miss characters like Harris, the little woman from New Jersey who boasted of giving psychologists a "wedgie" and tried to solve the puzzle of human nature. There won't be another one like her.
No comments:
Post a Comment