Fertility in animals reflects access to scarce resources, such as food and territory. In humans the situation is more complex. Patterns of breast feeding, contraception and ideas about age at marriage and desired family size all affect fertility. The relation between these and access to scarce resources such as housing and employment, via income, education and other factors that affect status, is explored. In this book, the gap between socio-ecology and population demography is bridged, by showing how animals and humans adjust their fertility to environmental conditions.