I have trouble with the argument that altruism can be completely explained on evolutionary grounds. Evolutionists now universally agree -- I think Dawkins and Wilson and Dennett would all agree -- that evolution does not operate on the species. It operates on the individual. If that's the case, then it does seem that in any given circumstance, the individual's evolutionary drive should be to preserve their ability to reproduce at all costs.
Okay, that's.... irritating. Because it's not like there aren't one or two theories explaining altruistic behavior. If he doesn't find any of them convincing, and can't bother saying why, whatever. It seems like the actual answer to the question of how he responds to sociobiology is, "I put my fingers in my ears and go LA LA LA."
Well, I don't think the interview was meant to go into all of that. That said, In Mere Christianity, which Collins sites as key to his conversion, Lewis comes near to some of this, and it may be something that Collins has just internalized over all these years since his conversion. I can't guarantee Collins has this in mind when he gives his answer, but since reading the "Moral Law" point in Lewis's book seems to be what grabbed Collins', it's right where my head went, as I was reading the paragraph you quoted, Strega.
Lewis (who I think pre-dates much/most sociobiological theory) differentiates between what he calls the herd instinct (which he doesn't deny) and what he calls Moral Law. He lists several instincts that prompt us (love, sex, hunger). He continues on, saying sometimes, we do feel an instinct—that is, a desire—to help someone else. But then he goes on to say that feeling a desire to help someone is quite a different matter from feeling you "ought" to help them, whether or not you want to help.
He gives the example of hearing a cry for help from someone in danger, and suggests most people will feel two desires in response to that cry: to give help (he chalks this up to the herd instinct), and a desire to keep out of danger (due to the instinct for self-preservation). He's not calling either of these the Moral Law. In Lewis's framework, the Moral Law is that within a person which judges between the two instincts.
One of the Lewis's arguments in this vein, centers on what can happen when two instincts are in conflict, as they are above.
If two instincts are in conflict, and there is nothing in a creature's mind except those two instincts, obviously the stronger of the two must win. But at those moments when we are most conscious of the Moral Law, it usually seems to be telling us to side with the weaker of the two impulses. You probably want to be safe much more than you want to help the man who is drowning: but the Moral Law tells you to help him all the same. And surely it often tells us to try to make the right impulse stronger than it naturally is? I mean, we often feel it our duty to stimulate the herd instinct, by waking up our imaginations and arousing our pity and so on, so as to get up enough steam for doing the right thing. But clearly we are not acting from instinct when we set about making an instinct stronger than it is. The thing that says to you, 'Your herd instinct is asleep. Wake it up,' cannot itself be the herd instinct. The thing that tells you which note on the piano needs to be played louder cannot itself be that note.
There's much more to this section of the book, but found that excerpt, here: [link]