The key to the evolution of altruism is that a. recipients have to be more likely to carry the altruistic allele than nonrecipients. b. actors have to be more likely to carry the altruistic allele than nonactors. c. recipients have to be unrelated to the actors. d. nonrecipients have to be more likely to carry the altruistic allele than recipients.

The correct answer is b. actors have to be more likely to carry the altruistic allele than non actors.

Explanation:

Altruism is the behavior by an organism that benefits other organisms by costing its own fitness. The actor is the individual who is doing altruism and the recipient is the individual who is getting benefited by the actor's altruism.

An example of altruistic behavior can be seen in animal kingdom easily. Vampire bats give blood to those members of the community who were not able to go for search for blood show altruistic behavior.

Actors have altruistic genes that suggest them to behave altruistically. Non-actors may not contain alleles of altruism but the recipient might have altruistic alleles.

Hamilton's rule says that natural selection will favor the altruistic allele when rb > c.

where r = coefficient of relatedness between donor and recipient

b = benefit received by recipient and

c = cost paid by altruist.

Therefore, the correct answer is b.