The recent and historically unique low level of fertility in industrialised nations poses a number of important medical questions, arising because reproductive physiology did not evolve to function optimally in this modern environment. In some non-industrialised regions, such as sub-Saharan Africa, persistent high fertility and rapid population growth are associated with environmental deterioration. How do fecundity and fertility respond to such degradations? Do improvements of industrial environments or nutrition and health measurably alter fertility or fecundity? These are some of the issues explored in this volume, which contains contributions from anthropologists, demographers, reproductive biologists and epidemiologists.