It has just occured to me - in a blinding flash of the obvious, dawn breaks over Marblehead - that in crime fiction, the MEN write about MEN and the WOMEN write about WOMEN. And they almost never ever cross that bright line. Furthermore, there are a lot fewer books with female protagonists, at least in the collections that I've read.
Now, there are some exceptions. Magdalen Nabb's man in Florence was Guarnaccia, and there are Louise Penny, Ann Cleeves, Grace Brophy, and Donna Leon writing about men. (Many about Italian men. Is it the men, or Italy, or the food?) But other than Michael Genelin (Jana Matinova), have I come across many male writers have female protagonists? (Charles Todd is sui generis, being a mother and son who write together under a pseudonym about a man.) There are some men who write excellent supporting female characters: Christopher Fowler's Janice Longbright and Phoebe and Sarah and really all the messed-up gals in Benjamin's Black's works are compelling characters in their own right, essential participants if not the driver of the plot. Maybe I'm not looking hard enough.
Women write about women. Rebecca Cantrell gave us the interesting Hannah Vogel, negotiating Nazi Berlin, and Cara Black's Aimee Leduc charges around Paris. And Charles Todd has that nurse, Bess whatshername Crawford doing good in WW1 England. (They are equal opportunity that way.)
It has also just occured to me that generally speaking, I don't find the female protagonists that appealing. Do I judge them more harshly? Do they not meet my preconceived notions of what a crime-solver should be? Do I just not want to deal with girl problems? I liked Hannah Vogel, am on the fence about Jana Matinova, and couldn't stand Aimee Leduc. Have I just been conditioned in some nefarious social manner to prefer male protagonists?
I don't actually think there is much sexism happening here, but I like phrase, from Caitlin Moran's How To Be a Woman, "is some sexism happening to you?" Her litmus test for sexism is, is this polite or not? I believe I am being perfectly polite in my interpretations of these characters. But am I viewing them all through some social goggles that I didn't realize I was wearing? Am I aiding and abbeting some sexism without knowing it?