During the past month, I've been phoned several times by several different journalists keen to write a feature on mother/daughter envy. "Why are mothers envious of their daughters?" I am asked.

Female friendships are well-known for their passionate nature. A female friend is a "soulmate", or, if the relationship turns sour, she is a "betrayer" who dashes one's faith in all friendships. But for some reason, there is a general cynicism about passionate closeness between a male and female friend.

At the turn of this century I studied the transition from adolescence into adulthood.

I have a particular fondness for the story of Hansel and Gretel. First, there is that soul-warming image of sibling love and protection. Second, there's that feisty young girl, who scouts out every plot against her, solves every problem, and saves her brother. Third, there's that underlying justification of dislike for the step-mother which, for reasons I won't go into, strikes a chord in me.

It may be that 17-year-old Bristol Palin made a decision not to use birth control when she had sex with her boyfriend. It may be that she thought using birth control was a greater sin than having sex. But as a mother of two daughters and a psychologist interested in how we can talk straightforwardly and effectively to our children about sex and sexuality, my best guess is that Bristol did not really make a decision, and that she would agree with her mother that her pregnancy is the result of a simple "mistake" that anyone can make. But most parents I speak to want to reduce the risk that their teenager will make such a mistake.