But one kind of innovation that never fails to have far-reaching consequences is change in a society's basic subsistence technology...changes in subsistence technology have ramifications that are felt in almost every other area of life (1991, p. 54).

Many changes in human societies arise in response to changes in either their biophysical or social environments (1991, p. 54).

Finally, one of the most neglected causes of change has been human fecundity...Human societies, however, are able to respond to population pressures with cultural innovations.  Ideological changes to customs or in laws, for example, may cause people to delay the age at which they marry, or legitimate such practices as abortion.  Alternatively, technological changes may provide the population with better methods of contraception, or enable them to produce more food to keep a growing number of children alive and well (1991, p. 54).