From National Magazine Awardwinning journalist Wright (Remembering Satan, 1994, etc.), a survey of twin research that is adding fresh fuel to the old argument over nature versus nurture. In this expanded version of a New Yorker piece, Wright describes the history of twin research as ``one of the most appalling chapters in science.'' From 19th-century twin studies used to rationalize the British class system, to the monstrous experiments of the Nazi doctor Josef Mengele on twins in Auschwitz, to studies seized on by American scientists to justify racial discrimination, genetic research utilizing twins has been used both to challenge and to support strongly held beliefs about the relative contribution of genes and environment to intelligence, to personality, to our very identity as human beings. Because studies of genetically identical twins and raised in different adoptive homes are crucial to separating the influence of heredity and environment, research in these areas has often been marked by controversy. Now Wright reveals how behavioral genetics, largely through twin studies, is making a persuasive case for the power of genes, asserting that after a certain age, the environment itself is a reflection of one's genetic disposition. Wright's account is both informative and entertaining, providing scientific data about the still little understood phenomenon of twinning itself and full of intriguing stories about the remarkable similarities in history between identical twins reared separately. Perhaps even more astonishing are accounts of their differences (would you believe identical twins of the opposite sex?). As the author points out, it may be that the differences in identical twins will turn out to be more informative than the similarities. A provocative subject well considered by a talented journalist.