My intellectual life is motivated by the assumption that we are part of nature, part of life. If we are part of life, then in principle everything about us must ultimately be explainable in terms of evolutionary theory, our only scientific theory of life. But how can we understand such uniquely human traits as rationality, values, morality, aesthetics, and culture itself in terms of evolutionary biology? I approach this problem through the venerable question of how nature (biology) and culture (shared learning) interact during development to produce human behaviour.
I thus use the principles of evolutionary ecology, life history theory, sexual selection theory, and parental investment theory to generate models of the development of human reproductive strategies. In conjunction with data about the behaviour of nonhuman primates and the cultural ecology of existing hunter-gatherer peoples around the world I develop models of the evolution of human behaviour, particularly the origin of male parental investment and the family. I also use these models to generate testable hypotheses about the causes and consequences of individual differences in such life history traits as age at menarche, first sexual intercourse, marriage, and first reproduction; the relationship between number and quality of close emotional ("attachment") relationships throughout life (a major part of the new field of evolutionary psychology); and the trade-offs between quantity and quality of offspring. Understanding these individual differences should help us understand better such modern concerns as teenage pregnancy, AIDs, single parenthood, family dysfunction, etc. Using evolutionary theory in this way is what the emerging fields of evolutionary medicine or evolutionary public health are all about. To the extent that an evolutionary perspective on health and well-being provides a rational basis for social policy my work is also relevant to evolutionary ethics. Most of these ideas are discussed in greater detail in my new book Death, Hope, and Sex: Steps to an Evolutionary Ecology of Mind and Morality (Cambridge University Press, 1999).