Human Fertility, Molecular Genetics, and Natural Selection in Modern Societies

Felix Tropf, University of Groningen
Gert Stulp, University of Groningen
Nicola Barban, University of Oxford
Peter Visscher, University of Queensland
Jian Yang, University of Queensland
Harold Snieder, University of Groningen

Exploiting recent advances in molecular genetics, this study demonstrates that the number of children ever born (NEB) and the age at first birth (AFB) of women living in industrialized societies is genetically influenced. Results show additive effects of common genes explaining 10 % of the variance in the NEB and 15 % in the AFB as well as a genetic correlation of -0.62 (SE = 0.27, p-value = 0.02) between both traits in a sample of 6,758 unrelated individuals from the UK and the Netherlands. Amongst others, this contributes to the controversial debate of whether humans still evolve. Our findings indicate that women with a genetic predisposition for an earlier AFB have a reproductive advantage, implying that natural selection acts in contemporary populations. The observed fertility postponement in industrialized societies suggests that the genetic effects are small relative to environmental effects, emphasizing the need for an integrative research design from genetics and the social sciences.