gender

Wondering what makes a girl "girly" or tom boy. I know it has a lot to do with society and parenting but I have 3 daughters that I think I have raised exactly the same. I have one uber girly girl, one muddy scrapped knee'd little t-ball player, and one that is some where in between. I have been told my son is "all boy" by some and that he is "so sensitive and sweet" by others. What gives? Is it DNA? Is it birth order? hmm...