A) illustrate the adaptive value of cooperation between two individuals.
B) show that under most circumstances, reciprocity would probably be selected against.
C) predict that altruism rather than reciprocity explains why animals cooperate.
D) show why reciprocity is so common and widespread in the animal kingdom.

A) cooperative hunting by the members of a lion pride.
B) reciprocity that occurs by hunting in groups of lions.
C) altruism exhibited by some hunting lions in a group.
D) the exploitation of some helpful lions by others in their pride.

A) the decision faced by aphids taken captive by slave-making ants over whether to escape or to cooperate with the ants.
B) a model of decisions regarding defection or cooperation with another individual.
C) reproductive decisions faced by animals at the edge of their species' range regarding whether to hybridize with another species or continue searching for a member of their own.
D) "buyer's remorse" by a member of a mated pair, wishing to choose a different mate but facing the high costs of searching.