The Nature of Nurture

New science reveals that your DNA isn’t your destiny


| July - August 2008



Nature or Nurture?

image by Christiane Grauert

Darlene Francis is talking about the frontal cortex, decision making, and high-stress profiles in rats when she suddenly shifts the focus to poor, single, inner-city moms—that is to say, stressed-out humans. Working with rodents, the behavioral neuroscientist points out, makes it easier to study and talk about social problems without stirring up a political battle. But if you want to understand the effects of maternal stress on childhood development, Francis says, just look at her rats.

As a graduate student, Francis conducted an experiment in which she swapped pups between a litter of rats bred for calmness and another that was predisposed to anxiety. The genetically calm mothers tended to be better nurturers, licking and grooming their pups more than the anxious mothers did. But when a calm, nurturing mother raised the genetically anxious pup added to her brood, the adoptee switched tendencies. The anxious rat behaved calmly throughout life, performed better in cognitive tests, and was more willing to explore new environments. The calm mother’s behavior, Francis discovered, had caused permanent changes in the operations of the anxious rat’s genes. Even more stunning: The acquired traits—calmness and nurturing habits—were passed on to the anxious rat’s next generation.

In the question of nature versus nurture, we’ve embraced the view that our fates are written in genetic code. The news in recent years has been filled with reports about the isolation of genes said to “cause” everything from diabetes to voter turnout. Increasingly, though, researchers are finding that genes don’t tell the whole story.

In a rapidly developing field called epigenetics, scientists are discovering that nutrition, exposure to toxics, even a mother’s touch (or lack thereof) can cause heritable changes in gene expression without any corresponding change in DNA sequence.

Francis’ work has been among the first to show that epigenetic influences go far beyond the common conception of “environment” to include things such as social interactions. With that in mind, her lab at the University of California, Berkeley, collaborates with scientists across the spectrum: in molecular biology, public health, psychology, and even moral reasoning. The links may strike some hard-core geneticists as alien territory, but with findings like Francis’, doubters may soon find themselves arm in arm with the “soft” sciences. Francis considers herself a member of both camps. “I’m a Ph.D. in neuroscience, but at heart a social worker,” she says.

In the 1990s Francis took a break from her graduate studies at McGill University to work with troubled young children in Montreal. She knew all about their early life experience—many of her charges were the children of friends she had grown up with. How, she couldn’t help but wonder, had she ended up in a Ph.D. program while her friends were visiting their kids in jail?