Rapid evolution of reproductive age contributed significantly to the growth of a contemporary Canadian human population, finds a study published in Nature Communications this week. The authors estimated that genetic changes in the age at which women began to have children led to a 12% increase in population size over a 100-year period.

Evolution has traditionally been considered to be a slow process. However, recognition is growing that evolution can be fast enough to make a measurable difference in the ecological dynamics of species, including by speeding up the rates of population growth and geographic spread. Nevertheless, the relevance of such ‘rapid evolution’ to human populations has been discounted.

Fanie Pelletier and colleagues analysed the genealogical records of the ile aux Coudres community in Quebec, Canada, focusing on women born between 1772 and 1880. They found that how much a woman contributed to the growth of the population depended on how early she began having children, variation of which partially depends on genes associated with this trait. Without the evolution of earlier reproduction, the growth of the population would have been approximately 6% slower, leading to a 12% smaller population.

Although some of the variation in age of first reproduction may reflect cultural influences, the pattern of this trait in families corresponds to a significant genetic contribution. Therefore, the potential for human evolution to drive contemporary population processes may be greater than has been previously appreciated.