Co-evolution, conflict and complexity: what have we learned about the evolution of parental care behaviours?

- The origin of care is not the same as its subsequent evolution and diversification.
- Biparental care primarily evolves when males join caring females.
- Male (biparental) care increases the productivity of females not survival of offspring.
- Co-evolution of parent-offspring behaviours may occur with or without conflict.
- Parental care is a co-evolutionary game played by the whole family.

Care is complex but recent advances are helping to unravel this complexity. The factors that promote the evolutionary origins of care and those promoting the subsequent evolution, diversification and maintenance of care are not the same. Theoretical and empirical research suggest that the origin of parental care will depend primarily on offspring survival in the absence of care, as long as there are appropriate behavioural precursors and genetic co-variation between parent and offspring behaviours for care to evolve. In contrast, which sex cares and how much care is provided is shaped by a suite of related factors that affect how the behaviour of family members co-evolves, including adult mortality rates, parentage, sexual selection and mechanisms underlying the resolution of evolutionary conflicts. The general outcome of this is that in most taxa where parents provide care females are the primary carer. When males provide care alone they can be as effective as females in caring and increasing offspring survival. In contrast, comparative analyses show that biparental care mainly arises from males joining females and that the main benefit of male (biparental) care is an increase in the productivity of females, not the survival of offspring. The evolution of parental care is a dynamic, multivariate process that involves the co-evolution of multiple traits in males, females and offspring.