Although many other animals care for sick members of their pack, providing treatment such as medication appears to be uniquely human. An attempt to model how this occurred in early communities of Homo Sapiens and our fore-bearers has found evidence that many distinctly human traits may have developed as a result of communal care.

Providing food and protection to sick individuals is a key behavior of social animals. Infectious diseases make this dangerous, however, because the risk of infection rises with time spent treating the sick individual. Particularly before modern quarantine procedures, this was a tricky balance, the navigation of which Dr Sharon Kessler of Durham University argues has caused us to evolve both biologically and socially.

People whose symptoms alerted others of their sickness were more likely to survive. Kessler points out in Scientific Reports that we can read signs of sickness in “changes in facial coloration due to fever or rashes [and] odor changes due to sweating from a fever.” Similarly, Kessler notes, upper respiratory tract infections change our voices in instantly recognizable ways.

The ways in which caring for sickness has changed our society are more subtle, but possibly more profound.

As Kessler points out, the fossil record does not preserve evidence of the sort of care that was provided, although healed bones and other wounds provide evidence it happened.

Consequently, models of pre-agricultural care structures involve a lot of guesswork. Kessler responded by having hers include variables with a wide range of values. She included factors such as varying rates of death and transmission for diseases, the effects of care on the rate at which the virus or bacteria replicated, and the size and connectivity of the communities in which our ancestors lived.

In the most basic social systems Kessler assumed care was restricted to that provided by mothers to their young, as seen today in other primates. This then progressed to adults caring for partners, then to close relatives and finally to more extended families. Kessler assumed children's intelligence was partially inherited from their mothers, so that if more intelligent family members were better at nursing children through sickness, the intelligence genes were more likely to be passed on.

As medicine became more effective, sharing care in larger communities both improved the chances the sick person would survive and reduced the exposure of any individual, Kessler showed.

This combination meant that care-giving created evolutionary pressure, both towards greater intelligence and more complex societies, even prior to the development of agriculture.

The idea that health care should be a private cost, rather than a social responsibility, is not just a proven failure in practice, it apparently goes against who we truly are.