Biological Consequences of Declining Human Fertility.

Area of Science:

• Reproductive biology
• Evolutionary genetics
• Demography

Background:

• Human fertility has declined globally for over a century, particularly in developed nations, linked to socioeconomic changes and the demographic transition.
• Reduced infant and child mortality, alongside evolving economic expectations and female independence, have contributed to lower birth rates.
• The rapid pace of fertility decline and its socioeconomic drivers may have outpaced evolutionary adaptation of biological reproductive determinants.

Purpose of the Study:

• To investigate the hypothesis that rapid socioeconomic changes have altered the mutation/selection balance, impacting human fecundity.
• To explore the potential long-term consequences of these genetic alterations on human reproductive potential.
• To assess the implications for the future reliance on assisted reproductive technologies.

Main Methods:

• This study presents a theoretical argument based on existing demographic and evolutionary principles.
• It analyzes the interplay between socioeconomic factors, mutation rates, and natural selection on human reproductive traits.
• The argument synthesizes findings related to the demographic transition and genetic load.

Main Results:

• The rapid socioeconomic shifts driving the demographic transition are hypothesized to have altered the mutation/selection balance affecting human fecundity.
• This alteration may have already initiated a decline in the species' future reproductive capacity, entering a 'post-transition trap'.
• The genetic changes are suggested to be significant enough to impact biological determinants of fertility within a few generations.

Conclusions:

• The observed decline in human fertility may be partly attributable to evolutionary genetic changes impacting fecundity.
• Continued reliance on artificial reproductive technologies may become necessary if methods to mitigate deleterious mutations affecting fertility are not developed.
• Urgent consideration of genetic factors influencing human reproduction is warranted to address potential long-term declines in fecundity.