Online Altruism Lab

Introduction

The extensive hairlessness is a distinctive feature of humans that we only share with a few other mammals. But how did this come about? The most common hypothesis assumes that our bare skin supports thermoregulation in hot areas and is thus an adaptation of early humans to life in the hot savanna (Jablonski, 2010). Another hypothesis suggests the avoidance of ectoparasites combined with sexual selection as cause of our hair loss (Pagel & Bodmer, 2003). The two concepts are not mutually exclusive.

I bring a new hypothesis into play here (that does not exclude the other two either):

Not least, the Covid-19 pandemic demonstrated the efficiency of "social distancing" in preventing the exponential spread of an infection. “Keep distance!” is such a simple and effective method, that it should also play a role in the evolution of social species.

Social immunology is the study of how groups of organisms collectively defend themselves against pathogens, complementing or extending the immune defenses of individuals. Instead of focusing only on the physiological immune system within a single body, social immunology examines how behaviors and social organization contribute to disease resistance at the group level, for example in social insects and how they recognize and remove diseased brood (Meunier, 2015; Cremer et. al., 2018).

But let's think of the most social primates, humans and their ancestors. Like all living species, humans were and are constantly threatened by pathogens. Because of our strong social ties, viruses, bacteria, fungi and other pathogens can be transmitted to other hosts particularly easily. The individual physiological immune defense could soon be overwhelmed here. "Social distancing" would be an effective preventive immune defense. Did early man have such a mechanism and how could it have evolved?

An important protective mechanism to avoid illness and poisoning is disgust (Curtis et. Al., 2004; Curtis & Barra, 2018). Disgust makes individuals keep their distance from potential sources of danger, from spoiled food, feces, vomit, blood, wounds, but also from sick-looking individuals of their own kind. Thus, with this emotional revulsion to something potentially contagious, there is already an adequate protective reaction on the receiver side.

If an infection is to be efficiently avoided, an infection must also be detected as early as possible. Disease symptoms as easily recognizable signals (Lopes, 2014; Tiokhin, 2016) would be a decisive advantage for quickly identifying infected people.

A clear signal for the human eye could be to present the disease clearly visible on bare skin, in conspicuous colors, as bright red rashes or frighteningly pale faces, and with all kinds of decorations such as purulent pustules or large bumps. In fact, our immune system reacts to many pathogens with remarkably visible symptoms. Plague, smallpox, measles, typhus and countless other scourges of humanity are almost "written on our skin".

But why should sick people reveal themselves in order to be avoided by their fellows? As paradoxical as it may seem: Such an evolutionary adaptation could happen almost by itself through stochastic processes if the population is divided into groups. This is demonstrated with the simulation model presented here.