"I think when people say to female writers, 'Your male characters are not realistic,' they mean, 'They don't adhere to the current society's standards of masculinity.'"
And what would those same readers think of the characters if they didn't know the author's gender? Would they still think the male characters were unrealistic if the author was male?
My friend Grace used to conduct this experiment on writing forums: She'd write a short story and post it twice (with time between postings, and a different title so as not to be obvious), once under her own name and once under a male pen name. The responses, she told me, were... enlightening.
As herself, she'd be told that her male characters were unrealistic, that 'girls don't write sci-fi anyway, they should only be allowed to write romances and girl stuff' (NEVER a good idea to be around Grace after she'd read some comment like that - she yells a lot when she's angry), and that she should stick to writing things that female readers like.
BUT... As her alter ego Thomas Flint... Suddenly the same people who had, a few months before, hated that same story, were giving it glowing reviews, talking about how skilled the writing was, how detailed and imaginative the setting, how complex the plot... But they thought the female characters were totally unbelievable.
The only difference? The name used by the author.
My sister-in-law Kate says that men can't write female characters, which is why she refuses to read anything by a male author. "They can't write anything that a woman would want to read," she says. (Is it just me, or is it unkind for her to say that in front of her husband, also a writer?)
I don't think about it much, but I probably have about an even mix of male and female major characters in my fiction. Of course, I don't believe that there is such thing as a distinctly male or distinctly female personality, beyond what a particular culture tells people is acceptable. The first story I ever wrote in first person has a female protagonist, and I think it turned out just fine. (Read it and judge for yourself:
Finder's Fee )
Which leads to something I've noticed myself - readers often assume that, with a first-person story, the protagonist's gender is the same as the author's. They confuse which "I" is telling the story.