Like the lines of a secret map made dimly apparent by the chemical potion brushed on a piece of paper from a child's detective kit, the outlines of what may be a substantial behavioral biology of human life seem to be coming clear. From genetic science at its most molecular to demography with its assessment of the vital experience of massive populations, there is a growing understanding of the various ways in which the human species reveals underlying commonalities of experi ence through the life cycle and over the web of interactions that constitutes the basic matter of social life. At the...