Kin selection is the theory that we behave more altruistic towards people who share our genes—-given we believe in the darwinian paradigm that the overarching aim for an organism is to further its genes, of course.
Or as John Haldane humorously concluded while working on the mathematics of kin selection:
“I would lay down my life for two brothers or eight cousins.”
The idea being that brothers and sisters share genes by 50% and cousins 12,5%. The math being something like this:
1 person = 8 cousins (12.5×8=100)
1 person = 4 nephews (4×25=100)
1 person = 2 siblings (2×50=100)
The Green Beard Effect started as a thought experiment that would explain why we exhibit altruistic behaviors towards people who share a genetic trait with us, i.e a green bearded person favors another green bearded person over someone else. It’s is a poor mans version of kin selection.
The behavior has been confirmed studies on fire ants in 1998.
… and a Review of Behave by Robert Sapolsky is coming soon!