If you look at the prehistoric evidence of mankind, you will notice that the original role o male and female was that the males would go hunt for food while the females would stay behind and look after the young. This included feeding them. However, it's been 3 million years since the birth of mankind, so I would say that it was time for a change of pace. Also, another note on how the role of a woman as a mother has affected the female of the human species is that women are more likely to have psychic ability. This was probably a trait that developed to help the women keep track of their kids. My mom has exhibited a great degree of psychic awareness. She can read the "loud" thoughts of people she is close to or if she is touching someone's chakra point (no, not a naruto chakra) where the flow of chi concentrates.