Epidemiology of falling fertility: the contribution of social, environmental, and genetic forces.

The past half century has witnessed a dramatic decline in human fertility as reflected in the total fertility rate. This decline in total fertility rate is thought to have been triggered by an increase in resources and knowledge that precipitated a significant decline in infant mortality. This, in turn, led to a reduction in the desire of couples to have large families, supported in recent times by a series of factors including a delay in childbearing as women acquired the education and autonomy to enter the paid workforce, the progressive urbanization of advanced societies, and, for many, a seismic shift in life's purpose away from procreation and toward self-fulfillment. Notwithstanding the power of such short-acting socioeconomic drivers, they are all potentially reversible given appropriate revisions in governmental policies and societal aspirations. However, we argue that if human societies experience subreplacement levels of fertility for a prolonged period, then there is a danger that our fundamental fecundity (ability to reproduce) will become compromised. A lack of evolutionary selection pressure on fertility, the excessive use of assisted reproductive technology, and the pervasive presence of environmental pollutants in the environment, are all relevant in this context. Addressing the causes of human fertility decline is critical if we are to manage our population rather than become its hapless victim.