Social immunity can be a consequence and cause of social evolution

What is it about?

Living in a group brings many benefits, but it also creates a problem: disease can spread more easily when individuals are in close contact. Many social insects have evolved ways to deal with this risk collectively. Ants, termites, bees, and other group-living insects may groom one another, manage waste, use antimicrobial substances, and even remove infected individuals to protect the group. Our research looks at how this kind of collective disease defence — known as social immunity — evolves. The bigger question is whether disease is just a cost of social life, or whether it can also help shape the evolution of social life itself. Our models suggest that social immunity can be both a result of cooperation and a force that promotes larger, more complex societies.

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Photo by Barnabas Hertelendy on Unsplash

Photo by Barnabas Hertelendy on Unsplash

Why is it important?

The surprising finding was that disease defence may do more than help social groups survive infection. It may also change the kind of societies that evolve. Our models suggest that social immunity can first evolve even in relatively simple social systems, as long as the benefits of protecting others from disease are high enough. Once it is in place, collective disease defence can reduce the risk that a colony dies from infection. This can make it worthwhile for colonies to spend longer growing before they reproduce, leading to larger colonies. Larger colonies may then gain even more from collective disease defence, because there are more individuals to protect and potentially more opportunities for disease to spread. This creates a possible feedback loop between social immunity and colony size, which may then favour more specialised roles among group members. In short, disease may not just be a cost of social life, it may also help shape the evolution of social complexity.

Perspectives