ε is associated with higher fecundity in a natural fertility population.

In many populations, the aε (ε) allele increases the risk for several chronic diseases of aging, including dementia and cardiovascular disease; despite these harmful effects at later ages, the ε allele remains prevalent. We assess the impact of ε on fertility and its proximate determinants (age at first reproduction, interbirth interval) among the Tsimane, a natural fertility population of forager-horticulturalists. Among 795 women aged 13 to 90 (20% ε carriers), those with at least one ε allele had 0.3 to 0.5 more children than (ε3/ε3) homozygotes, while those with two ε alleles gave birth to 1.4 to 2.1 more children. ε carriers achieve higher fertility by beginning reproduction 0.8 years earlier and having a 0.23-year shorter interbirth interval. Our findings add to a growing body of literature suggesting a need for studies of populations living in ancestrally relevant environments to assess how alleles that are deleterious in sedentary urban environments may have been maintained by selection throughout human evolutionary history.