How does childhood socioeconomic hardship affect reproductive strategy? Pathways of development

Abstract

ObjectivesIn high‐income populations, evidence suggests that socioeconomic disadvantage early in life is correlated with reproductive strategy. Children growing up in unfavorable rearing environments tend to experience earlier sexual maturity and first births. Earlier first births may be associated with higher fertility, but links between socioeconomic disadvantage and larger family size have rarely been tested. The pathways through which early disadvantage influences reproduction are unknown. We test whether physiological factors link childhood adversity to age at first birth and total children.MethodsUsing data from the Newcastle Thousand Families Study, a 1947 British birth cohort, we developed path models to identify possible physiological traits linking childhood socioeconomic status, and poor housing standards, to two reproductive outcomes: age at first birth and total children. We explored birth weight, weight gain after birth, childhood illnesses, body mass index at age 9, age at menarche, and adult height as possible mediators.ResultsWe found direct, negative effects of socioeconomic status (SES) and housing on age at first birth, and of housing on fertility. Although we found links between childhood disadvantage and menarche and height, neither of these were significantly correlated with either reproductive outcome. Age at first birth completely mediates the relationship between childhood adversity and total fertility, which we believe has not been empirically demonstrated before.ConclusionsWhile there are some links between childhood adversity and child health, we find little evidence that physiological pathways, such as child health and growth, link early childhood adversity to reproductive outcomes in this relatively well‐nourished population. Am. J. Hum. Biol. 28:356–363, 2016. © 2015 The Authors American Journal of Human Biology Published by Wiley Periodicals, Inc.

The evolved psychological mechanisms of fertility motivation: hunting for causation in a sea of correlation

“…the likelihood that children can be raised to an age at which they can reproduce themselves [4,[19][20][21][22].…”

Developmental influences on fertility decisions by women: an evolutionary perspective

“…The early adversity and fertility literature, which predominately comes out of the public health and epidemiology fields, is small, correlational and not yet conclusive. In three longitudinal analyses [37,61,81] and one retrospective study [79], early adversity increased fecundity and fertility. This is consistent with an adaptive allocation of resources to current reproduction in a high risk environment.…”

“…Menarche, of course, does not imply sexual activity, let alone early reproduction, but cross-cultural studies often find that age at menarche, age at first sexual intercourse and age at first birth are correlated (e.g. [60]), although not always [37,61]. However, a missing link between an individual's early stress, reproductive strategy and fitness, is fertility.…”

“…Finally, in a prospective study of women born in Newcastle-upon-Tyne in 1947, low socio-economic status and poor housing conditions at birth were associated with earlier first birth, and poor housing was also associated with higher completed fertility. When both outcomes were tested simultaneously, age at first birth completely mediated the relationship between poor housing and total fertility [37].…”

“…However, in such a long-lived species as humans, these pathways are not set in stone as predictive adaptive responses suggest. Crucially, reproductive strategies can be modified throughout a lifetime as subsequent environments influence physiology, behaviour and psychology [4,[34][35][36][37][38]. We will begin by discussing the adaptive and maladaptive explanations of childhood stress before examining associations between early stress and age at menarche and fecundity and fertility.…”