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While significant, the emergence of powerful social/educational factors that impact human TFR might not overly concern us because, in principle, such trends should be readily addressed with appropriate policies and increased levels of Governmental and societal support. However, in parallel, a variety of lifestyle and environmental factors are also conspiring to suppress human fecundity and, as a result, the impact may be more permanent. Nowhere is this more evident than in the male. Human semen quality is notoriously poor and male infertility is known to be a highly prevalent condition (Agarwal et al., 2015; Aitken, 2020a). Moreover, sperm counts have halved in the past 50 years in both the industrialized West and the East, including China (Levine et al., 2017; Las Vegas et al., 2021; Swan and Colino, 2021). This change is occurring so universally and so rapidly that it cannot have a genetic basis but must be environmentally induced. This phenomenon raises important questions about the nature of the environmental factors involved and whether such changes in sperm number are materially affecting human fertility.

To address the causative mechanisms first, it may be significant that several studies have also recorded a parallel secular decline in circulating testosterone levels. Thus, in Nordic countries (Perheentupa et al., 2013), the USA (Travison et al., 2007) and Israel (Chodick et al., 2020) evidence has been presented indicating that testosterone levels have been declining since the 1970s, in concert with the decline in sperm counts. The situation is complex because serum testosterone levels decline with age and advanced industrialized societies are becoming ‘super-aged’. Nevertheless, even when we take age into account, a decline in testosterone levels is still evident, as clearly illustrated by the Israeli data (Chodick et al., 2020).