Is it not worth considering "cuteness" to be defined in terms of threat levels. It seems to me that in most cases there is a direct correlation between cuteness and perceived threat.

By threat I am referring not just to physical (claws versus soft paws, large vs small, dominant versus meek, hard versus soft) but even biological (messy / unhygenic looking creatures versus fluffy / cuddly looking ones) or social (flawed versus flawless).

This may explain why some people perceive cuteness differently. One person may look at a human baby and see no possible threat, others may be more inclined to be considering health implications or even the threat of embaressment / fear it is associated with.

With this association in mind it would seem that selection towards lower threat is prevalent - babies looking cute leads to lower abandonment or attack by other parties, animals allowed to come close to humans without fear and benefiting from shelter / food / care etc.