Abstract

My research focuses on maternal investment, in the broad human behavioural ecology sense, where parental investment is viewed as any investment in an offspring which incurs a cost to a parent’s ability to invest in other current or future offspring. Thus I take maternal investment to encompass not only investment in individual offspring once they are born, but also first the decision as to whether to reproduce, when to reproduce, and which sex to produce. Here I will present results from three different strands of my research dealing with these decisions: first I will consider the factors influencing the decision to continue reproducing, presenting results from the first studies to look at the impact of postnatal depression on parity progression and interbirth intervals in both women from WEIRD populations and the forager-horticulturalist Tsimane of Bolivia. Next, I will discuss the impact of extrinsic mortality risk on sex ratios at birth, presenting evidence for skewed male sex ratios at birth in the Agta hunter-gatherers of the Philippines. Finally, I will consider factors influencing postnatal maternal investment with a specific focus on what might cause variations in mother-infant bonding and long-term mother-offspring relationship quality in women in contemporary, industrialised, low fertility contexts.