I've covered the symbiont hypothesis of eusociality before - e.g. see my 2011 book - or:
- Tyler, Tim (2014) Eusociality: the symbiont hypothesis
This is a big and important hypothesis relating to the origin of social organization and eusociality. However, it seems to have become absurdly neglected in modern times - where kin selection has got almost all of the limelight.
The field urgently needs more study. It needs computer simulation. In particular, I am thinking about simple agent-based models, or cellular automata - that illustrate its basic idea - that the introduction of symbionts can promote social behaviour. In a termite-like model - where the symbionts directly benefit the hosts, it is pretty obvious that this will happen. However there are an abundance of open questions in this area - associated with how model parameters affect the resulting evolutionary dynamics. Science needs a lot of models in this general area to resolve these questions. So far, as far as I can tell, very few of these models have been constructed.
A basic model might feature hosts, symbionts and walls - creating an environment with cave-like enclosures. Step 1 would be to find some parameter settings where the introduction of symbionts favoured cave-dwelling hosts that interacted with each other more frequently - more effectively spreading the symbionts to newborns.
If you are a programmer with a scientific bent, you can help to resolve the questions associated with these models. If you do a reasonable job, you will probably go down in history in the process for doing so.
This is work of large social and political significance. Humans have cultural symbionts, which make them cooperate. The cultural symbionts make the large difference between modern humans and primitive cavemen. However, because of low levels of scientific study of the symbiont hypothesis of eusociality, science still has a relatively poor understanding of exactly how and why they do this. The study of cooperation has been an active topic historically - partly as a result of this social and political significance. However the symbiont hypothesis of eusociality has been enormously neglected. I think most workers in the field don't understand it - or its importance.