On Trade-offs and Communal Breeding The Behavioural Ecology of Agta Foragers

<p>Time is finite and no organism can avoid the allocation dilemma that this necessarily entails. A quintessential trade-off is that between parental investment and reproduction, otherwise known as the quality-quantity trade-off. However, humans may be exceptional among apes given our high quantity production of high quality offspring. This success has been argued only to be possible by breeding communally. In this thesis I explore questions surrounding trade-offs, communal breeding and their fitness consequences in a small-scale foraging society, the Agta. The first analysis examines the composition of Agta childcare using an innovative form of data collection to maximise sample sizes, previously a major limitation in hunter-gatherer research. The Agta, like many small-scale societies are prolific communal breeders. However, contra previous conclusions, juveniles and non-kin appeared to provide more allocare than grandmothers. Interactions with non-kin were associated with significant decreases in maternal workload, while interactions with siblings and grandmothers were not. The next analysis explores why both kin and non-kin behave cooperatively, finding support for kin selection among close kin and reciprocity for distant kin and non-kin allocare. Communal breeding appears to be an important mechanism to ensure enough childcare was received in the absence of other strategies to counter shortfalls in household energy budgets. The next analysis asks, what are the fitness consequences of maternal social networks and allocare? Mothers’ network centrality positively correlated with non-kin allocare as well as reproductive success, revealing the adaptive value of communal breeding. These results highlight the optimising nature of hunter-gatherer cooperation and life history strategies.</p>