Evolutionary Game Theory – Eusocial
We talked about evolutionary game theory in class about a week ago. Evolutionary game theory is essentially the application of the principles of game theory to evolving populations that make decisions that can ultimately decide whether individuals are able to survive and reproduce. At a higher level, those decisions decide whether species endure or become extinct. It is one of the only theories that explains why an individuals in a species might act altruistically toward another individual in the species rather than in pure self-interest.
One particularly notable example of this is the concept of eusociality. Eusocial behavior of a species is characterized by division of labor, cooperation of adults in caring for young ones, and only a small fraction of females reproducing. This is seen most commonly in ants, but also happens for other species of insects. But, from a Darwinian perspective, this makes no sense at all! If many of the female ants in the colony are fertile, why do only a few females reproduce while the rest do not? Shouldn’t it be as it is for most other species – that the main goal of life is to pass down your genes to future generations? This is where evolutionary game theory comes in. It turns out that for a eusocial insect, an insect’s total fitness is the sum of the fitness of their direct offspring (if they have any) and the product of the fitness of other offspring and the extent to which they are related to that offspring. An individual get fitness indirectly from offspring of other insects due to the fact that the social colonies work together to a common goal. As it turns out for the genes of these types of insects, which are haplo-diploid, a female has ¾ of her genes in common with her full sister but only ½ of her genes in common with either a daughter or son. So the payoff in fitness is higher for having many sisters rather than having many children. As a result, it makes sense that not all female insects would see it in their best interest to reproduce. Only a few females need to reproduce (only enough to create new ants at a fast enough rate so that ants don’t run out), while the rest gain a good amount of fitness indirectly from sisters rather than progeny. In terms of maximizing payoff, which is fitness of an individual insect in this case, most females will choose to not reproduce. The behavior of eusocial insects was entirely unintuitive from the classical perspective of the purpose of reproduction, but with evolutionary game theory, the process makes a lot of sense. This illustrates why evolutionary game theory can provide some good insight into biology.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3279739/