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The trade-off between reproductive investment in early versus late life is
central to life-history theory. Despite abundant empirical evidence
supporting different versions of this trade-off, the specific trade-off
between age at first reproduction (AFR) and age at last reproduction (ALR)
has received little attention, especially in long-lived species with a
pronounced reproductive senescence such as humans. Using genealogical data
for a 19th-century Swiss village, we (i) quantify natural selection acting
on reproductive timing, (ii) estimate the underlying additive genetic
(co)variances, and (iii) use these to predict evolutionary responses.
Selection gradients were computed using multiple linear regression, and
the additive genetic variance–covariance matrix was estimated using a
restricted maximum-likelihood animal model. We found strong selection for
both an early AFR and a late ALR, which resulted from selection for an
earlier and longer reproductive period (RP, i.e., ALR-AFR). Furthermore,
postponing AFR shortened RP in both sexes, but twice as much in women.
Finally, AFR and ALR were strongly and positively genetically correlated,
which led to a considerable reduction in the predicted responses to
selection, or even rendered them maladaptive. These results provide
evidence for strong genetic constraints underlying reproductive timing in
humans, which may have contributed to the evolution of menopause.
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