Abstract
Maternal care decision rules should evolve responsiveness to factors impinging on the fitness pay-offs of care. Because the caretaking environments common in industrialized and small-scale societies vary in predictable ways, we hypothesize that heuristics guiding maternal behaviour will also differ between these two types of populations. We used a factorial vignette experiment to elicit third-party judgements about likely caretaking decisions of a hypothetical mother and her child when various fitness-relevant factors (maternal age and access to resources, and offspring age, sex and quality) were varied systematically in seven populations—three industrialized and four small-scale. Despite considerable variation in responses, we found that three of five main effects, and the two severity effects, exhibited statistically significant industrialized/ small-scale population differences. All differences could be explained as adaptive solutions to industrialized versus small-scale caretaking environments. Further, we found gradients in the relationship between the population-specific estimates and national-level socio-economic indicators, further implicating important aspects of the variation in industrialized and small-scale caretaking environments in shaping heuristics. Although there is mounting evidence for a genetic component to human maternal behaviour, there is no current evidence for interpopulation variation in candidate genes. We nonetheless suggest that heuristics guiding maternal behaviour in diverse societies emerge via convergent evolution in response to similar selective pressures.
Highlights
Maternal care behaviour should be modulated in response to factors impinging on the fitness pay-offs of that care, which include maternal, offspring and environmental factors [1,2,3]
We conceptualize the benefits of care as increases in the direct fitness of current offspring, and the costs as lost ability to invest in future offspring or other components of maternal fitness [4,5]
Theoretical and empirical work suggests that mothers may use these sorts of ‘simple heuristics’ for maternal care decision-making [3,5,10]
Summary
Maternal care behaviour should be modulated in response to factors impinging on the fitness pay-offs of that care, which include maternal, offspring and environmental factors [1,2,3]. We conceptualize the benefits of care as increases in the direct fitness of current offspring, and the costs as lost ability to invest in future offspring or other components of maternal fitness [4,5]. This sort of responsiveness to fitness-relevant factors may increase maternal fitness but evolves only when the fitness benefits outweigh the costs of plasticity [6,7]. We predict that societies facing similar selective pressures will develop similar maternal caretaking heuristics via convergent evolution [11]
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