Daniel Dennett has advanced the opinion that the evolutionary purpose of the cuteness response in humans is to make us respond positively to babies. This does seem plausible. Babies are pretty cute, after all. It's a tempting explanation.
Here is one of the cutest baby pictures I found on a Google search.
And this is a bunny.
Correct me if I'm wrong, but the bunny is about 75,119 times cuter than the baby.
Now, bunnies are not evolutionarily important for humans to like and want to nurture. In fact, bunnies are edible. By rights, my evolutionary response to the bunny should be "mmm, needs a sprig of rosemary and thirty minutes on a spit". But instead, that bunny - and not the baby or any other baby I've seen - strikes the epicenter of my cuteness response, and being more baby-like along any dimension would not improve the bunny. It would not look better bald. It would not be improved with little round humanlike ears. It would not be more precious with thumbs, easier to love if it had no tail, more adorable if it were enlarged to weigh about seven pounds.
If "awwww" is a response designed to make me love human babies and everything else that makes me go "awwww" is a mere side effect of that engineered reaction, it is drastically misaimed. Other responses for which we have similar evolutionary psychology explanations don't seem badly targeted in this way. If they miss their supposed objects at all, at least it's not in most people. (Furries, for instance, exist, but they're not a common variation on human sexual interest - the most generally applicable superstimuli for sexiness look like at-least-superficially healthy, mature humans with prominent human sexual characteristics.) We've invested enough energy into transforming our food landscape that we can happily eat virtual poison, but that's a departure from the ancestral environment - bunnies? All natural, every whisker.1
It is embarrassingly easy to come up with evolutionary psychology stories to explain little segments of data and have it sound good to a surface understanding of how evolution works. Why are babies cute? They have to be, so we'll take care of them. And then someone with a slightly better cause and effect understanding turns it right-side-up, as Dennett has, and then it sounds really clever. You can have this entire conversation without mentioning bunnies (or kittens or jerboas or any other adorable thing). But by excluding those items from a discussion that is, ostensibly, about cuteness, you do not have a hypothesis that actually fits all of the data - only the data that seems relevant to the answer that presents itself immediately.
Evo-psych explanations are tempting even when they're cheaply wrong, because the knowledge you need to construct ones that sound good to the educated is itself not cheap at all. You have to know lots of stuff about what "motivates" evolutionary changes, reject group selection, understand that the brain is just an organ, dispel the illusion of little XML tags attached to objects in the world calling them "cute" or "pretty" or anything else - but you also have to account for a decent proportion of the facts to not be steering completely left of reality.
Humans are frickin' complicated beasties. It's a hard, hard job to model us in a way that says anything useful without contradicting information we have about ourselves. But that's no excuse for abandoning the task. What causes the cuteness response? Why is that bunny so outrageously adorable? Why are babies, well, pretty cute? I don't know - but I'm pretty sure it's not the cheap reason, because evolution doesn't want me to nurture bunnies. Inasmuch as it wants me to react to bunnies, it wants me to eat them, or at least be motivated to keep them away from my salad fixings.
1It is possible that the bunny depicted is a domestic specimen, but it doesn't look like it to me. In any event, I chose it for being a really great example; there are many decidedly wild animals that are also cuter than cute human babies.
About me.
In person, I'm fairly obviously girl-shaped. No one has ever made this mistake when interacting with me in person, and I don't have to do Obvious Girl Things™ to get that accuracy - don't have to swish around in crinoline, don't have to conveniently quote third parties who refer to me as "she", don't have to carry my purse everywhere I go, or even say my name (which is a girls' name). People don't assume based on where I am or what I'm doing or how surprising it would be for me to be a girl before they figure out that I am one anyway and pronoun me accordingly.
And - in person, when people can't tell what gender someone is, they don't guess, unless they feel able to rely on visual cues or maybe being married to someone of a known gender (and when they are wrong they are mortified). People will bend over backwards to avoid using the wrong pronoun for someone who's in the room with them. They'll ask third parties or construct their sentences to avoid making the assumption or learn the person's name to get a clue. It's just not socially acceptable to get it wrong.
Online, people feel free to guess, and on the geeky parts of the Internet I frequent this is most likely to affect women negatively. (I also frequent various anti-prejudice parts of the Internet, but there a) I generally lurk and b) under the circumstances they take the trouble to be careful about that sort of thing!)
Now, I recognize this disparity is because it's considered insulting to say that someone looks like the opposite gender, and not so with writing like the opposite gender... except that when people talk about third parties one of them knows in person and the other doesn't, the one who doesn't know doesn't casually hurl pronoun caution to the wind even though someone is right there to correct them should they be wrong without any implications about anyone's looks having been made. When there is a mechanism to find out a real person's gender, it gets taken advantage of. With real people, you don't guess, you find out, and if you're wrong, that's not okay.
Getting my gender wrong when it would have been pretty easy to get it right (for crying out loud, ask me! Or someone else! Or do the most cursory of searches for "alicorn gender" on this very site - it's in the second result!) signifies that I am not a "real person" in the above sense. It's okay to guess. It doesn't matter if you get it wrong. He won't care, and if she does, it's about eir politics or something dismissible like that, not about whether you took four seconds to fact-check. Not about identity, or consideration, or the fact that this happens about once a week and the blogger, unlike most people who make the mistake, doesn't even have a way for me to correct em.
I'm pretty sure that's a function of where you hang out.
My impression is that transgendered people have a hard time getting their choices taken seriously in most social circles.