Babies

Interesting, is it not, that the human urge to protect extends not only to our own young but to the babies of many other creatures. I say 'many' because you don't see a lot of us cooing over baby jellyfish, for example. I've been trying to work out what it is then that determines that paternal response. Mammals? (But baby birds are so cute.) Warm-blooded? (Ever gone gooey over a little crocodile?) Land-dwelling? (Ditto and dolphin-ettes.) There's obviously a point where we draw the line, as with the jellyfish, but I couldn't put it in the sand for you. Is this only a human thing? I wonder too if other animals can feel protective towards the young of other species - you read about baby animals that have been 'raised' by parents not of their own kind. Does it represent a leap forward in compassion, or is it an all-pervading instinct that we might actually have managed to smother a bit over the millennia?