Dictyostelium is a slime mold which is well known for having a single cell free living phase and other some conditions (e.g. when food is scarce) for forming communal piles of cells called 'slugs' ...
This is related to How does "be altruist to those who are similar to you" evolve? Altruism that is Not reciprocal Not familiar has little explanation. One possible explanation is that ...