Which term describes behavior that benefits another at the expense of the altruist?

The term that describes behavior benefiting another individual at the cost of the altruist is altruism. Altruism refers to actions that provide a benefit to someone else while potentially incurring a cost to the individual performing the behavior. This concept is significant in biology and social sciences as it addresses how certain behaviors can evolve despite seeming disadvantageous to the individual.

In contrast, the other options illustrate different social interactions. Cooperation describes a mutually beneficial interaction where both parties gain from the behavior. Selfishness refers to actions that primarily benefit oneself without regard for the impact on others. Mutualism involves interactions where both individuals involved benefit simultaneously, making it different from altruism, where the benefit is lopsided.