I don't see where the problem is with evolving context-specific altruism. We have numerous strategies that we evolved and use in specific contexts. Screaming, or crying or laughing for instance. Altruism could be another.
ok and that answers my question. Altruism as one item in our evolutionary library toolkit vs more deeply ingrained in our behaviors or even genes. My hope is that it is selfishness which is more an item in our library... that we evolved more towards being cooperators while still being able to defect (free-riders) some times...