Evidence for evolution in response to natural selection in a contemporary human population

Abstract

It is often claimed that modern humans have stopped evolving because cultural and technological advancements have annihilated natural selection. In contrast, recent studies show that selection can be strong in contemporary populations. However, detecting a response to selection is particularly challenging; previous evidence from wild animals has been criticized for both applying anticonservative statistical tests and failing to consider random genetic drift. Here we study life-history variation in an insular preindustrial French-Canadian population and apply a recently proposed conservative approach to testing microevolutionary responses to selection. As reported for other such societies, natural selection favored an earlier age at first reproduction (AFR) among women. AFR was also highly heritable and genetically correlated to fitness, predicting a microevolutionary change toward earlier reproduction. In agreement with this prediction, AFR declined from about 26-22 y over a 140-y period. Crucially, we uncovered a substantial change in the breeding values for this trait, indicating that the change in AFR largely occurred at the genetic level. Moreover, the genetic trend was higher than expected under the effect of random genetic drift alone. Our results show that microevolution can be detectable over relatively few generations in humans and underscore the need for studies of human demography and reproductive ecology to consider the role of evolutionary processes.reproductive timing | heritability | Homo sapiens | life-history traits | lifetime reproductive success

Does natural selection favour taller stature among the tallest people on earth?

“…Genetic variation in common single nucleotide polymorphisms measured in unrelated individuals also supports this interpretation [34]. Studies by both biologists and demographers also show a moderate genetic component to fertility traits, such as number of children ever born and the age at first birth, which explains up to 40-50% of the variance in these traits [11,[35][36][37][38]. Such findings were also observed for a historical Dutch population [39].…”

Evaluating reproductive decisions as discrete choices under social influence

“…Evolutionary theory is becoming more prominent in studies of changing fertility [1], especially those that examine changes in fertility norms over historical timescales [2]. Central to most theories of the demographic transition-a decline in human fertility and mortality in a society [3]-is individual choice, often structured with the assumptions of rational choice theory [4], including the trade-off between quality and quantity of children [5].…”

Natural and sexual selection in a monogamous historical human population

“…For example, Byars et al (12) found some traits of medical significance in the United States to be currently influenced by selection (see also ref. 13). By using summary statistics for birth and death rates in a population, it is also possible to estimate opportunity for total selection (i.e., variance in relative fitness) and its two components-opportunity for selection because of survival to reproductive age and opportunity for selection because of fertility-at the scale of the entire organism (10).…”