User-13227694684444020075 is right. The right comparison is with babies, not adult humans, and the comparison is deeper than you think. It's a phenomenon called "paedomorphic cuteness" (yes, that's a really biology term!) that is a consequence of a broader phenomenon called neoteny (which itself is about extending the learning/development phase beyond the womb, not cuteness).

http://en.wikipedia.org/wiki/Neo...

Basically, all mammals have the same "cuteness" characteristics when young, which have co-evolved with corresponding nurturing instincts in adult mammals. This includes big eyes in proportion to the head, big head in proportion to body etc. That's why Disney can make all characters look cute.

In our common pet animals, like cats and dogs, the domesticated versions retain into adulthood the characteristics that make their wild counterparts cute in kitten/puppyhood. This was the main mechanism by which these pets self-domesticated around prehistoric humans, and were then further bred by humans:

http://en.wikipedia.org/wiki/Ped...

If that sounds complicated, think of it this way. Adult domestic dogs look like baby wolves. Adult domestic cats look like baby lions or tigers. We respond to that by nurturing them, and that's why they evolved (with some help) that way -- to take advantage of our nurturing.

In fact, getting back to human babies... human adults look more like monkey/ape babies than monkey/ape adults (take a look next time you're in the zoo).

Not only does this work on both men and women, it is in fact cross-species. I've heard of (and once seen) dogs taking care of kittens and cats taking care of puppies. There was even a Tolstoi story about a lion in the Moscow zoo taking care of a puppy. I don't know if that was based on a true story.

Update: http://news.discovery.com/animal...

"Food is often used as a token of affection, and the ways that cats
and humans relate to food are similar in nature to the interactions seen
between the human caregiver and the pre-verbal infant," co-author Jon
Day, a Waltham Centre for Pet Nutrition researcher, told Discovery News.
"Both cat and human infant are, at least in part, in control of when
and what they are fed!"

For the study, led by Kurt Kotrschal of the Konrad Lorenz Research
Station and the University of Vienna, the researchers videotaped and
later analyzed interactions between 41 cats and their owners over
lengthy four-part periods. Each and every behavior of both the cat and
owner was noted. Owner and cat personalities were also assessed in a
separate test. For the cat assessment, the authors placed a stuffed owl
toy with large glass eyes on a floor so the feline would encounter it by
surprise.