My priors before I started paying attention at all (i.e. before the first time it came up in a conversation I was part of, on the internet, that someone was uncomfortable / sad / whatever that they were being referred to as the wrong gender - which, for record, was a post-op man genetically female who still had a few culturally-programmed female-expected behaviors) were around about .4 female to .6 male for any random person I meet and discuss with on the Internet.
Even that .4 seems rather high compared to the base stats I've seen since then for some populations, but there's apparently some factor which makes me more likely to engage and enjoy discussions and interactions over the web with women, for some reason I don't yet understand.
However, since then, I've had to update downwards. Even with my abnormal encounter rates (e.g. meeting 30% women in communities that are 3% women overall), on average I still only expect and observe that I "befriend" (or otherwise engage and interact with more actively with) women only one in five times of such people, i.e. the other four are men. This if I only include so-called "normal" men and women, because I also end up meeting abnormally high numbers of transgenders, asexuals, queers, and other nonstandard genders.
On top of that, out of the women that I do tend to interact with (which are already at less than 0.2 expected rate), only one in two cases I'll end up having to refer to them before their gender becomes "revealed" in some manner (sometimes because of an obvious nickname). Of the half where I do, nowadays I use gender-neutral format, but before I started doing so, only one in four (well, three out of thirteen to the best of my memory, in total) got slighted/offended/whatever that I used male pronouns.
Which basically ends up with there being an approximately 2% expected probability that for any person I start interacting with I might use a male pronoun for a woman that will be affected by it, unless there is a high amount of women who get hurt from wrong pronoun usage but never reveal this. This is including my current rate of female:male encounter ratio, which I've already confirmed is abnormal from other stats (e.g. I've eliminated cases like women just befriending more people than men or similar situations).
I would expect that most people have their expectations somewhere around this or even rarer, so I can't fault them for using male pronouns on the Internet by default without first having to fault them for thousands of other, much worse things.
For bias evaluation purposes: I have been identified and referred to with female pronouns at least twice on the Internet, and wasn't offended (in one case, I was actually flattered, for various contextual reasons). In the past week, excluding work colleagues and LessWrong, I've maintained more meaningful Internet-based interactions with three regular men, two women, and one genetically-male unclear-someone who hasn't quite yet resolved his own personal gender-identity yet and would probably fall in some gray area between "queer" and "pre-op transgender".
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.