What would happen if an artificial community of rats was manipulated to give a changing pattern of 'role distribution' over time such that it mimicked the human race's changing patterns?
For the sake of simplicity, let us say that one human generation = 100 rat generations.
Initially, at T-10,000 years (~500 human generations, about 50 years in rat timescales) we have 100% wild type rats.
As the generations pass, some rats will begin to take the role of 'farmers' and the rest will remain wild. The farmer rats will have an electronic tag fitted which will allow their environment to be controlled in respect of that particular rat.
All rats will be able to 'forage' for a slightly inadequate amount of food, but the bulk of their food will only appear when the 'farmer' rats have done enough 'work'.
Farmer rats will release food upon having delivered a certain amount of work. These rats will be able to eat only the food released by their own work, in addition to the small amount available for foraging. Wild type rats will still be able to forage, they will also have access to food released by all the 'farmers'!
The proportion of 'farmers' will increase from 0 to 90% until we get to T-200 years when we will introduce a third role, the 'worker rat'. The worker rat will not be able to work for food or forage for food. Worker rats will enjoy a life of leisure but will be dependent on 'farmer' rats for food. Wild rats will still be able to forage and take food from both other kinds of rat.
Throughout the experiment, rat populations will be allowed to follow the same rate of increase as human populations did over the relative timescales. Whenever populations get 5% bigger than they should be, food supplies are constricted for one generation and excess rats are removed at random, sacrificed, and examined at the molecular level.
That's the basic outline anyway. The purpose of the experiment is to look for neurological changes that might give us clues as to whether or not the changing role structure of the human race could be responsible for the development of psychiatric disorders such as autism, adhd, sociopathy and related.