Abstract
One of the striking features of human social complexity is that we provide care to sick and contagious individuals, rather than avoiding them. Care-giving is a powerful strategy of disease control in human populations today; however, we are not the only species which provides care for the sick. Widespread reports occurring in distantly related species like cetaceans and insects suggest that the building blocks of care for the sick are older than the human lineage itself. This raises the question of what evolutionary processes drive the evolution of such care in animals, including humans. I synthesize data from the literature to evaluate the diversity of care-giving behaviors and conclude that across the animal kingdom there appear to be two distinct types of care-behaviors, both with separate evolutionary histories: (1) social care behaviors benefitting a sick individual by promoting healing and recovery and (2) community health behaviors that control pathogens in the environment and reduce transmission within the population. By synthesizing literature from psychology, anthropology, and biology, I develop a novel hypothesis (Hominin Pathogen Control Hypothesis) to explain how these two distinct sets of behaviors evolved independently then merged in the human lineage. The hypothesis suggests that social care evolved in association with offspring care systems whereas community health behaviors evolved as a type of niche construction. These two types of behaviors merged in humans to produce complex, multi-level healthcare networks in humans. Moreover, each type of care increases selection for the other, generating feedback loops that selected for increasing healthcare behaviors over time. Interestingly, domestication processes may have contributed to both social care and community health aspects of this process.
Highlights
This paper provided a novel synthesis of animal care-giving in sickness contexts
I reviewed both social care behaviors which are directed at the sick individual and community health behaviors which benefit the community by controlling pathogens in the environment
In examining the mosaic of behaviors present across species, it appears that social care may have evolved in association with offspring care systems while community health behaviors may have evolved convergently in several taxa that engage in striking niche construction behaviors, like nest building
Summary
Human healthcare, including biomedical care, has enabled our species to exert an unprecedented amount of control over the pathogens which affect our species (Ferguson et al, 2003; Kessler et al, 2017, 2018). I include responses to dead individuals because (1) care behaviors may start before death and continue afterward (Anderson et al, 2010; Bearzi et al, 2018) and (2) corpses are potential sources of pathogens (Octavio Lopez-Riquelme and Luisa Fanjul-Moles, 2013; Cremer et al, 2018; Porter et al, 2019) To my knowledge, this is the first review which integrates the biological literature (animal behavior, citations below) with the psychological and anthropological literature [e.g., compassion (Gilbert, 2017; Seppälä et al, 2017) and attachment theory (Fogel and Melson, 1986; Preston, 2013; Cassidy and Shaver, 2016), fossil evidence of social care during human evolution (Dettwyler, 1991; Lebel et al, 2001; DeGusta, 2003; Hublin, 2009; Spikins, 2015; Spikins et al, 2018, 2019)] to produce a new hypothesis explaining the integration of social care and community health behaviors. Because grooming often occurs along established social (often kinship) networks, it is possible that because these individuals are already likely to be in close proximity that grooming does not significantly elevate the risk that already exists (Griffin and Nunn, 2012)
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