"Studies of cooperative animal societies have advanced understanding of social evolution but have also revealed great individual variation in cooperative behaviour and major life history traits, even among individuals of the same age, sex and social status. Research on laboratory mammals suggests that this variation may be explained by early life influences on development, but little is known about the function and mechanism of these developmental effects in wild mammals, or whether these effects are adaptive. We will address this shortfall in knowledge using both empirical and theoretical approaches. Our empirical work will use large-scale field experiments on a model cooperative mammal system, the banded mongoose Mungos mungo, to measure prenatal developmental impacts on offspring growth, care received, stress physiology, cooperation, health, cognition, aging and lifetime fitness. Our theoretical research will build on the recent economic theory of ‘skill formation’, and will generate new testable predictions about the coevolution of developmental responses and maternal and helper investment. The output of the research will be new insights into the evolutionary and proximate causes of individual variation in health, behaviour and life history in social mammals, and a new conceptual understanding of social development in cooperative organisms from insects to humans."