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We’re living in an age of genetic explanations. Consider a few headlines from the past week alone: Single Gene May Extend Lifespan by 25 Percent. Genes Show One Big European Family. Genetic Test Helps Identify Aggressive Prostate Cancer.
I certainly do my share of gene’splaining. But for all the buzz given to the studies that uncover telltale genes, rarely mentioned are the most obvious and familiar examples of how genes aren’t destiny: identical twins. They share the same genome and, usually, the same parents, same neighborhood, and same food. And yet, as anybody who’s ever met a pair knows, they are not the same person. Why?
“Ten years ago the prevailing theory was that there must be systematic differences in their environments,” says Eric Turkheimer, a professor of psychology at the University of Virginia. One twin is favored by her mother, say, or is bullied in school, or catches fewer colds. But studies looking for big, non-shared environmental influences have come up short. As Turkheimer wrote in a fascinating commentary in 2011: “Exactly what the nonshared environment consists of has...
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