I understand that natural selection is not the same thing as evolution.

I understand that individuals do not evolve.

I understand that populations do evolve.

I even understand how - in general - we say that selection operates on the individual.

What I don't understand is how correct it is to say that evolution of altruism occurs via selection on individuals.

It could be that if I cogitate on this for a while, it will come to me. Maybe it will be one of those "aha! why didn't I get that before!" type moments. But right now, I'm just not getting it.