And you know, women tends to be more pressured to have children by others than men are... i.e., "Don't you feel your biological clock ticking?" or "When will you have a child?" or "Are you trying?", etc.
I wonder if that also fosters maternal instinct... I've heard unwilling mothers suddenly fall in love with their babies upon birth and develop maternal instinct, after not even feeling anything during those 9 months, the extreme example being those mothers who were going to give up their babies for surrogate parents or adoption suddenly changing their minds upon seeing the baby upon birth.
I also remember someone telling me that if the mother is planning on giving her baby away, she should never hold it or make eye contact with it upon giving birth or she instantly feels a bond upon seeing and touching it.