Why do we grow up to look, act, and feel as we do? Through most of the twentieth century, scientists and laypeople answered this question by referring to two factors alone: our experiences and our genes. But recent discoveries about how genes work have revealed a new way to understand the developmental origins of our characteristics. These discoveries have emerged from the new science of behavioral epigenetics--and just as the whole world has now heard of DNA, ""epigenetics"" will be a household word in the near future. Behavioral epigenetics is important because it explains how our experience