What You Do is Who You Are

Photo by Martin Schoeller, National GeographicWe’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 been a matter of mystery and controversy for some time.”This is a tough thing to study in people. After all, scientists can’t pluck a pair of newborn identical twins from the arms of their mother, raise them for years in absolutely identical environments, and watch how they diverge.Scientists can do that with mice, though, and now they have. In today’s issue of Science, neuroscientist Gerd Kempermann and colleagues report that genetically identical mice raised in the same environment show striking differences in their brains and exploratory behaviors. What’s more, these individual differences — individual personalities, you might say — become more and more pronounced over time.Read more at...Only Human, May 2013.