A social interaction in which both the donor's fitness and the recipient's fitness are increased is called

a. altruism.

b. selfishness.

c. spitefulness.

d. cooperation.

The answer would be: d. cooperation.

Social interaction can be classified into 4 groups based on the fitness outcome of the donor and recipient. Altruism is when the donor fitness decrease but the recipient fitness increase. Selfishness is when the donor fitness increase but the recipient fitness decrease. Spitefulness is when both donor and recipient fitness decreased.

Cooperation or mutualistic is both donor and recipient fitness increases.