Under natural selection as described by Darwin, animals should strive to have as great a reproductive success (‘fitness’) as possible. Widespread instances of individuals deliberately reducing their own fitness are a challenge to Darwin’s theory. The usual explanation for the existence of groups of animals in which only a few reproduce and others help (such as bees) is that helpers benefit from increase fitness of their relatives. The theory is known as inclusive fitness, because in calculating fitness biologists include more than just the helper’s own fitness (‘direct fitness’): the fitness of any recipients of help (‘indirect fitness’). This seems to explain why sociality is common in bees, ants and wasps, because they have an unusual reproductive system that means females are more closely related to their own sisters than they are to their own daughters.
This paper states that there are important limitations to inclusive fitness theory than make is almost useless for understanding how societies evolved. It is becoming more apparent that bees, ants and wasps aren’t so special, and species with more typical reproductive systems could also evolve sociality. There are important mathematical reasons that make the theory useless: ow to make it work biologists have to make unrealistic assumptions about how animals interact. Instead, the paper shows that sociality can evolve through several stages, and relatedness is a consequence, not a cause. For example, animals often form groups when there’s limited places to nest and then together defend the place, just as honeybees do.
Hypotheses based on population structure rather than inclusive fitness theory should be the ones that are tested. This new approach would dramatically change how we understand the evolution of animal (including human) societies. Rather than evolving because of shared relatedness, such societies probably evolved where there are limited places to live and a need to collective defence.