The egregious William Saletan is at it again on heredity. Last time we paid attention to him, he was trying to sell us on the genetic character of racial differences on IQ tests. His credibility got shredded on that issue, so this time he is back on the subject of obesity, and for good measure, is taking the side of nurture rather than nature. The logic works like this: obesity develops in childhood, obesity is overwhelmingly genetic, but, obesity is increasing and genes can't have changed, so it must be the parents fault. An editorial on the study, published in the same journal, explains: [T]he shared-environment effect is the result of the degree of variability of environments that were observed in the sample, and, therefore, it cannot be used to infer the possible effects of altering the environment in which we all live and that may vary only modestly among families. If all homes, for example, had the same poor dietary and exercise practices, the shared-environment effect woul