Wealth, fertility and adaptive behaviour in industrial populations

Abstract

The lack of association between wealth and fertility in contemporary industrialized populations has often been used to question the value of an evolutionary perspective on human behaviour. Here, we first present the history of this debate, and the evolutionary explanations for why wealth and fertility (the number of children) are decoupled in modern industrial settings. We suggest that the nature of the relationship between wealth and fertility remains an open question because of the multi-faceted nature of wealth, and because existing cross-sectional studies are ambiguous with respect to how material wealth and fertility are linked. A literature review of longitudinal studies on wealth and fertility shows that the majority of these report positive effects of wealth, although levels of fertility seem to fall below those that would maximize fitness. We emphasize that reproductive decision-making reflects a complex interplay between individual and societal factors that resists simple evolutionary interpretation, and highlight the role of economic insecurity in fertility decisions. We conclude by discussing whether the wealth–fertility relationship can inform us about the adaptiveness of modern fertility behaviour, and argue against simplistic claims regarding maladaptive behaviour in humans.

The Reproductive Ecology of Industrial Societies, Part I

“…Such data can therefore provide the empirical grounding for evolutionary psychologists’ claims that shifts in the nature of environmental cues can and will result in maladaptive behavior. After all, if we do not collect measures of fitness, the idea that behavior in industrial settings is maladaptive is simply an unsupported assumption (see also Stulp and Barrett 2016b). Moreover, investigations into psychological mechanisms alone are insufficient (Alexander 1990): if novel cues feed into psychological mechanisms but have no adverse effects on fitness outcomes, then, by definition, the behavior is not maladaptive.…”

“…Fertility norms, for instance, may explain why many couples end up having two children in contemporary populations, whereas individual circumstances (e.g., health, wealth) and previous experiences may affect birth intervals or parity-specific progression (see Stulp and Barrett 2016b for further discussion). These measures also provide a basis for comparison with small-scale societies.…”

“…Similarly, Balbo and Barban (2014) have shown that the fertility decisions of individuals are influenced by the decisions of their friends. Structural changes in society, changing social influences, and the spread of novel ideas through networks, may explain some of the quirks in contemporary industrialized populations, such as an increasing number of individuals who have actively (and happily) decided to be child-free throughout their entire lives, despite having the economic means to raise children (Nazarinia Roy et al 2014)—something that is difficult to reconcile with classic behavioral ecological principles (see also Stulp and Barrett 2016b). The increasing number of ethnographic and mixed-method accounts of reproductive decision-making in industrial societies (e.g., Bernardi et al 2014; Cooper 2014; Edin and Kefalas 2005) can provide the kind of qualitative detail needed to flesh out quantitative patterns derived from large-scale surveys.…”

“…Across industrial populations there is wide variety in cultural background as well as the nature of social institutions, both of which markedly affect behavior. For instance, the extent to which female earnings are associated with the probability of becoming a parent or having further children depends on population-specific policies, such as the availability of childcare, the length of maternity (and paternity) leave, and whether or not it is paid leave (see Stulp and Barrett 2016b for review). We want to make clear, therefore, that although this paper makes broad points about “industrial societies,” we do not consider such societies to form a single homogeneous unit.…”

A New Comprehends about the Process from Non-living to Living Organisms: Based on a Metabolism Perspective

“…The study method used in biology is in the following succession: "observe, question, hypothesize, predict, and test". It may be more appropriate if "observe" is changed to "perceive" as the eye is not the only sensory organ for humans [4]. We named this study method the "five-element method."…”