Religion has been in the past, and still is in a number of countries, the main cohesive force holding populations, particularly genetically disparate ones, together in one system. Patterns of sexual behaviour (often strongly influenced by religious beliefs and prescriptions) in different societies have determined the organisational character of the society - from the nuclear family (now apparently in decline) in most Western countries and the extended family of earlier periods. Both religion and patterns of sexual behaviour as cohesive forces have been radically challenged by science, both as a mode of thought and as the source of technologies which change the environment in which societies operate. A sociobiology of societies has to be fou...