Actually, today the concept is brought up "What if you are a man trapped in a woman's body"? If you get pregnant, aren't you a man? According to modern day liberalism, I sure hope your answer is yes, otherwise you're a bigot. ;-)
But what I was really getting at is that there are men out there who are motherly, and nurturing in the way they *behave*.
But yeah, men cannot produce milk or babies, etc. Women also cannot produce semen. So that's something both genders differ on, and have an advantage at. I agree, the motherly attribute seems to be bigger, and more important. That's something feminism puts women down for wanting. Bearing children, raising them, homemaking, etc - women who want these things are usually considered to be sexists themselves by feminists today.