Hamilton’s law (1964)
Social behavior evolves under specific combinations of relatedness, benefit and cost.
Evolution can support altruism so long as its cost is at least met by the sum of the benefit times the relatedness of the beneficiaries to the altruist
Cost = (Sum of time X indirect benefits)
Altruism occurs even when sociality is facultative
In most cases, altruism is under positive selection via indirect benefits.
It exceeds direct fitness costs and social behavior.
It commonly generates indirect benefits by enhancing the productivity or survivorship of kin.
Usurped female guards shared nest versus leaving to nest alone
Providing protection against usurpation that increases nest survivorship and providing benefits of division of labor that increase nest productivity
These study suggest that environmental variability creates temporally fluctuating selection for sociality so accounting for the coexistence of social and solitary behaviors within populations.
"Joining behavior is positively selected at low but not at high group sizes"
Source: Johanna Bryson