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"To these scientists, and to biomedical researchers all over the world, twins offer a precious opportunity to untangle the influence of genes and the environment-of nature and nurture. Because identical twins come from a single fertilized egg that splits in two, they share virtually the same genetic code. Any differences between them-one twin having younger looking skin, for example-must be due to environmental factors such as less time spent in the sun. Alternatively, by comparing the experiences of identical twins with those of fraternal twins, who come from separate eggs and share on average half their DNA, researchers can quantify the extent to which our genes affect our lives. If identical twins are more similar to each other with respect to an ailment than fraternal twins are, then vulnerability to the disease must be rooted at least in part in heredity. These two lines of research-studying the differences between identical twins to pinpoint the influence of environment, and comparing identical twins with fraternal ones to measure the role of inheritance-have been crucial to understanding the interplay of nature and nurture in determining our personalities, behavior, and vulnerability to disease. Lately, however, twin studies have helped lead scientists to a radical, almost heretical new conclusion: that nature and nurture are not the only elemental forces at work. According to a recent field called epigenetics, there is a third factor also in play, one that in some cases serves as a bridge between the environment and our genes, and in others operates on its own to shape who we are."

"Almost 150 years ago, English scientist Francis Galton coined the phrase "nature versus nurture" - and proposed that research on twins could resolve the debate. Genetics have long seemed to weigh heavily in favor of the role of nature in shaping the people we become. But even identical twins are different to varying degrees, and some researchers believe those differences suggest a third influence at work, called epigenetics. Peter Miller of National Geographic Magazine wrote the magazine's January cover story, "A Thing or Two About Twins." Miller explains how scientists are expanding the field of epigenetics with research on twins."

"Daniel Kahneman spent part of his childhood in Nazi-occupied Paris. Like the other Jews, he had to wear a Star of David on the outside of his clothing. One evening, when he was about 7 years old, he stayed late at a friend's house, past the 6 p.m. curfew. The intellectual, cultural and scientific findings that land on the columnist's desk nearly every day. He turned his sweater inside out to hide the star and tried to sneak home. A German SS trooper approached him on the street, picked him up and gave him a long, emotional hug. The soldier displayed a photo of his own son, spoke passionately about how much he missed him and gave Kahneman some money as a sentimental present. The whole time Kahneman was terrified that the SS trooper might notice the yellow star peeking out from inside his sweater. Kahneman finally made it home, convinced that people are complicated and bizarre. He went on to become one of the world's most influential psychologists and to win the Nobel in economic science. Kahneman doesn't actually tell that childhood story in his forthcoming book. "Thinking, Fast and Slow" is an intellectual memoir, not a personal one. The book is, nonetheless, sure to be a major intellectual event (look for an excerpt in The Times Magazine this Sunday) because it superbly encapsulates Kahneman's research, and the vast tide of work that has been sparked by it. I'd like to use this column not to summarize the book but to describe why I think Kahneman and his research partner, the late Amos Tversky, will be remembered hundreds of years from now, and how their work helped instigate a cultural shift that is already producing astounding results. Before Kahneman and Tversky, people who thought about social problems and human behavior tended to assume that we are mostly rational agents. They assumed that people have control over the most important parts of their own thinking. They assumed that people are basically sensible utility-maximizers and that w