Could care giving have altered the evolution of human immune strategies?

Absract Life history theory indicates that individuals/species with a slow pace of life invest more in acquired than innate immunity. Factors that decrease pace of life and predict greater investment in acquired immunity include increased nutritional resources, increased pathogen exposure and decreased risk of extrinsic mortality. Common care behaviours given to sick individuals produce exactly these effects: provisioning increases nutritional resources; hygiene assistance increases disease exposure of carers; and protection can reduce the risk of extrinsic mortality to sick individuals. This, study, therefore, investigated under what conditions care giving behaviours might impact immune strategy and pace of life. The study employed an agent-based model approach which simulated populations with varying levels of care giving, disease mortality, disease transmissibility, and extrinsic mortality, enabling measurements of how the immune strategy and age structure of the populations changed over evolutionary time. We used multiple regressions to examine the effects of these variables on immune strategy and the age structure of the population. The findings supported our predictions in that care selected for an acquired immunity. However, pace of life did not slow as expected. Instead, the population shifted to a faster, but also more cost intensive reproductive strategy in which care improved child survival by subsidizing the development of acquired immune responses.