The kin selection advantage can be quantified by measuring 3 values.

The benefit to the recipient (B)

The cost to the altruist (C)

The coefficient of relatedness (r):

• Sibling 1 has inherited the allele from parent A.

• There is a probability of 1/2 that sibling 2 will also inherit this allele from parent A.

• The r between the two siblings is 1/2 (0.5).

Kin selection favors altruism when rB > C.