Boys vs. Girls
My daughter is seven years old. Yesterday we were driving behind a moving van that had a cartoon picture of a woman who looked kind of like Kim Possible from the TV cartoon. My daughter kept saying "Hot Mama" and asking her brothers if they thought she was "hot". Then she asked me if I thought she was "hot". I said yes, and she thought that was funny, at first. Then, after a moment or so of silence, she said "I'm telling mom!".
I have two sons and one daughter, who is the youngest. When the boys were that age, they knew about families and men and women getting together at some point in their lives to form a family, but they had no concept, as far as I could tell, of the forces that bring a man and woman together, or that could break them apart. To my daughter, this is second nature. We have two dogs, a male and a female, and my daughter often talks about how Diego would get jealous if another boy dog starts sniffing Canella, or vice versa. She is much more in tune with this kind of stuff than the boys are, or even than I am.
I'm not sure if this is a "difference between boys and girls" thing; it could also be a birth order thing. My second son is more in tune with this kind of thing than my first son, who really couldn't care less. I was also a first-born child, which could explain my lack of sensitivity in this area. But the difference between my second son and my daughter is far greater than between the two boys. This isn't conclusive proof that boys are fundamentally different than girls, but it has me convinced.