It's only a bad idea if there's a decent chance of you getting to eat that bunny or its offspring AND if there would otherwise be a shortage. Otherwise a small bunny in the hand is worth dozens of big ones in the bush. As a tribe, or better still a species, there might be benefits to not eating what you catch, but there's unlikely to be real benefits to the individual, so you'd need group selection here.

Even in modern society we can see this: look at the problem of over-fishing for instance. 'Fishermen' and indeed 'humankind' would benefit from more careful fishing, but you need strong international enforcement to try to make indivduals follow this route. As an individual, the food you get from a sprat is more on average than the miniscule chance of you getting bigger fish later because you release it.