The behavioural ecology of modern families: a longitudinal study of parental investment and child development

Abstract

In recent decades, behavioural ecologists have contributed to our understanding of the family \nthrough extensive studies of animal and traditional human populations. This research \nemphasises the importance of sibling competition for parental resources and adaptive \npatterns of biased parental care. In contrast, modern human families are rarely considered by \nbehavioural ecologists, with increases in wealth generally considered to decrease the \nimportance of resource dilution within families and modern cultural rules discouraging of \nunequal treatment of children. In this thesis, I question the validity of these assumptions and \nuse rich longitudinal data to consider family structure effects on parental investment and child \ndevelopment in contemporary Britain. I consider time-based and financial investment in \noffspring and measures of physical, cognitive and behavioural development over a 10 year \nperiod. The following specific hypotheses are tested. First, parents will face a trade-off \nbetween fertility, investment per child and ultimately child well-being. This hypothesis is \nsupported for all measures, except for behavioural well-being. Second, parents will bias \ninvestment towards early-born offspring. This hypothesis is largely supported. Later-born \nchildren receive lower investment and have reduced physical and cognitive well-being. \nHowever, mental health is improved in the presence of older siblings. Third, parents will bias \ninvestment towards male offspring. Support for this hypothesis is mixed. Measures of \ninvestment indicate a male-bias driven by fathers, while number of brothers relative to sisters \nis associated with reduced cognitive, but not physical or behavioural well-being. Fourth, \nchildren with unrelated father figures will receive less investment. This hypothesis is \nsupported. Unrelated father figures are associated with lower investment from both parents \nand reduced physical and behavioural well-being. Finally, I test the hypothesis that higher \nsocio-economic status will alleviate family size trade-offs. This hypothesis is rejected, with \nsome evidence that resource competition is of increased importance in relatively wealthy and \nwell-educated families.

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