A popular name for the residual component of animal behaviour not explained by a monomaniacally self-regarding model of agents.
In case (2) we can file it next to “individual free will”, “will of the people”, and “selfishness”, as one of those irritating terms with implied air quotes that it is polite to pause to acknowledge doesn’t mean anything before proceeding to argue as if it does. That is, while I find “altruism” a defective framing, it is at least a good juncture to muse about what we do attempt to optimise, and at what scale, and how we talk about that.
In case (1), the usual caveats about model construction apply. Also it is worth making explicit what scale the “altruism” is suspected to occur at. (altruistic genes? individuals? with respect to other alleles? The whole genome? A whole society?), or you wade into a weird rocky landscape of gene-versus-individual-versus-group-selectionism.
Altruism is also a useful term in engineering problems: See “design of collectives” a la Wolpert, for the study of how to design optimal utilities, or mechanism design for the study of how to align individual and collective incentives in market and legal transactions. See “behavioural economics” for the study of what people actually do in practice.
🏗 Discuss real-world use and occurrence of “altruism”, esp. altruistic punishment, and the rhetoric of altruism. Gary Becker-style models of utility. See also cooperation for group selection-ish stuff, cooperation and evolution for the evolutionary connections. Then maybe think about cancer, eusociality, genetic, social, individual and other kinds of learning.