Definition of altruist
: one that adheres to or practices altruism: such as
a : an unselfish person whose actions show concern for the welfare of others Kim signed up with Compass, a District-based group that serves the growing number of altruists who donate not only time and money to charity and the arts but also their professional expertise.— Robert McCartney
b : an animal that behaves in a way which is not beneficial to or may be harmful to itself but which benefits the survival of others of its species Reciprocal altruism refers to the exchange of beneficial acts between individuals, in which the benefits to the recipient exceed the cost to the altruist. … Although the potential for reciprocal altruism exists in many animal societies, most interactions occur between closely related individuals …— Robert M. Seyfarth et al.
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