Effects of Accelerated Reproductive Timing in Response to Childhood Adversity on Lifetime Reproductive Success in Modern Environments

Psychosocial acceleration theory postulates that human females have an evolved reaction norm that accelerates reproductive timing in response to childhood adversity, such as low socioeconomic status (SES). While this theory has garnered widespread acceptance in psychology, the extant evidence suggests that such a reaction norm was not adaptive in pre-industrialised human populations (and in a wild baboon population). However, there has been no study examining whether such psychosocial acceleration is adaptive in contemporary societies. Therefore, this study, conducted in Japan and the US, tests the hypothesis that early fertility is associated with higher lifetime reproductive success (LRS) among women from low SES families, while it is associated with lower LRS among women from high SES families. Participants were women aged 45–50 years (480 Japanese women in Study 1 and 780 American women in Study 2). Participants reported their childhood SES, early adulthood SES, and number of children. The results were not supportive of the hypothesis. In both the Japanese and American samples, early fertility was associated with higher LRS regardless of childhood SES. In other words, accelerated reproductive timing did not selectively confer fitness advantages on women from low-SES families. The results of this study are generally in line with previous findings in pre-industrialised societies.