The Global Decline in Human Fertility: The Post-Transition Trap Hypothesis

Area of Science:

• Demography
• Human Reproduction
• Genetics

Background:

• Many developed nations exhibit total fertility rates below the replacement level of 2.1.
• These countries have undergone both the first and second demographic transitions.
• Sub-replacement fertility shows no signs of recovery.

Purpose of the Study:

• To examine factors driving demographic transitions.
• To assess the impact of these transitions on fertility and fecundity.
• To investigate potential long-term genetic consequences for human reproduction.

Main Methods:

• Review of demographic trends and socioeconomic factors.
• Analysis of the impact of the first and second demographic transitions.
• Evaluation of genetic and epigenetic influences on fecundity.

Main Results:

• The first demographic transition, driven by socioeconomic factors, had no lasting impact on human fecundity.
• The second demographic transition presents novel risks.
• Factors include relaxed selection for high-fertility genotypes, assisted reproductive technologies, and environmental toxicants.

Conclusions:

• The second demographic transition may compromise future human fecundity.
• Fundamental genetic changes in reproduction are difficult to reverse.
• Monitoring human fecundity is crucial as sub-replacement fertility becomes widespread.