Global meta-analyses have documented a decline in sperm concentration of approximately 50% since the 1970s, with rates accelerating from 1.16% to 2.64% annually. A parallel decline in serum testosterone (approximately 1.2%/year) has been documented. Integrating evolutionary, epigenetic and epidemiological perspectives may clarify the vulnerability of human spermatogenesis to contemporary environmental conditions.
This narrative review synthesizes epidemiological evidence with evolutionary biology (sperm competition, life-history trade-offs) and molecular epigenetics (DNA methylation, histone–protamine remodelling, sperm-borne small RNA), and trajectory modelling employed four-parameter logistic decline models.
The evolutionary history of humans – moderate sperm competition and relaxed modern selection – creates baseline fertility vulnerability. Extensive epigenetic reprogramming during spermatogenesis opens pathways for environmental exposures to impair sperm production. Trajectory modelling suggests that, under baseline assumptions, the mean sperm concentration could approach the World Health Organization’s reference limit within the coming decades, and testosterone may reach the hypogonadism-relevant threshold earlier, although projections carry substantial uncertainty and are conditional on continued current trends.
Evolutionary vulnerability and epigenetic susceptibility may contribute to the decline in male reproductive health. Priorities include coordinated semen surveillance, preconception risk reduction, strengthened chemical regulation, and longitudinal exposure–outcome studies.
https://www.rbmojournal.com/article/S1472-6483(26)00338-X/fulltext
Hey! If you found this post interesting or useful, you can help us get even better by subscribing to our newsletter. Just write your email and you’ll have the latest fertility news.
Thank you once more for your help.
