According to Hamilton's rule, altruistic behaviour can evolve when rb > c, where b is the extra benefit gained by the recipient as a result of the altruistic act, c is the cost to the actor arising from performing the altruistic act and r is the relatedness between the:
1
Individual performing the altruistic act and the offspring of the recipient
2
Individual performing the altruistic act and the recipient
3
recipient and the offspring of the individual performing the altruistic act
4
Individual performing the altruistic act and the members of its population