Neutral theory and the evolution of human physical form: an introduction to models and applications.

Anthropologists have long been interested in explaining patterns of variation in human physical form, in both present-day and ancient humans. Starting in the 1950s, their explanations became more firmly rooted in evolutionary theory, but they have typically focused on adaptive accounts. Neutral explanations - those grounded in models of evolution by mutation, genetic drift, and gene flow rather than natural selection - provide an alternative to adaptive explanations, and in recent years, neutral models have become an important tool for researchers investigating the evolution of human physical form. Neutral models have implications for many areas of biological anthropology, including using morphology to reconstruct the histories and migrations of recent human populations, using morphology to infer the evolutionary relationships among hominin taxa, and clarifying how natural selection has acted on physical form throughout human evolution. Their application to anthropological questions has stimulated biological anthropologists to more seriously consider the roles of history and chance in human evolution. In light of the growing importance of neutral explanations in biological anthropology, the goal here is to provide an introduction to neutral models of phenotypic evolution and their application to human physical form.