Caring for individuals with diseases may have enabled prehistoric humans to prevent disease transmission as social networks became more complex and the threat from socially transmitted diseases increased, according to a study in Scientific Reports.
Sharon Kessler and colleagues used computer modelling to simulate the evolution of care-giving in four different social systems, using community sizes of 50-200 individuals reconstructed for early Homo habilis, H. erectus, H. heidelbergensis, H. neandertalensis, and H. sapiens. The authors show that before effective care-giving strategies were established, a kin-based system in which parents, siblings, cousins and other family members provided care, was the most likely to facilitate the evolution of care-giving in the human lineage. They suggest this is because individuals within the family would have shared the cost of care-giving and associated disease exposure, limiting individual risk of infection. At the same time, the risk of transmission remained limited to individuals within the family, preventing the spread of disease outside of it. Once effective care was established, care-giving networks became more flexible, contributing to the complexity and diversity of human social systems.
The authors suggest that as hominins evolved, care-giving also produced selection pressures that may have led to the evolution of certain typically human traits. These included psychological, social and cognitive attributes that supported disease recognition and cooperative care-giving, physical features that made symptoms easier to spot, and an immune system adapted for pathogens that spread among care-giving hosts.
Care-giving may therefore, have been a key element of the psychological and behavioural traits that are associated with the success of the human lineage, and the ability to suppress disease spread may have been fundamental to the evolution of complexity in human societies, the authors conclude.