Does a long life come at the cost of fertility?
Genetic research shows a small trade-off in men: higher testosterone is linked to slightly more children and a slightly shorter lifespan. In women this testosterone effect has not been found, although fertility does decline clearly with age.
In men, testosterone appears to involve a clear trade-off: a naturally higher testosterone level is linked to slightly more children, but also to a slightly shorter lifespan. On average, this amounts to roughly three-quarters of a year less per step up in testosterone level. The same hormone that promotes fertility also raises blood pressure and wears the body out sooner.
This pattern has not been found in women. Genetically higher testosterone in women, in the same study, was not linked to a shorter or longer lifespan, nor to more or fewer children. The trade-off between fertility and survival therefore appears to differ between the sexes, at least where testosterone is concerned.
What does apply to women is that the egg supply shrinks with age regardless. The hormone that reflects that supply, AMH (a measure of how many eggs remain), peaks in the early twenties and then declines steadily until menopause. Older women undergoing IVF more often experience a miscarriage and have a lower chance of a live birth. This suggests that the lining of the womb also loses quality with age, on top of the well-known decline in egg quality.
Whether environmental factors speed this up remains an open question. Smaller studies found higher concentrations of certain microplastics in the fluid surrounding eggs in women with a reduced egg supply. And higher exposure to fine particles in the air, particularly the components nitrate and organic matter, was linked to fewer and lower-quality eggs during IVF treatment. Cause and effect have not yet been proven in people, but it is a direction that continues to be investigated.
This answer draws on one genetic analysis in men and women (a strong method for establishing cause and effect), two summaries combining dozens of studies on age and ovarian function during IVF, and several smaller studies in people examining microplastics and air pollution. The trade-off between testosterone, fertility and lifespan in men is the most solidly supported finding. The evidence on environmental factors such as plastics and fine particles is thin: the studies are small, measure associations only, and cannot separate cause from effect. The researchers themselves explicitly acknowledge this limitation.
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