"When I was a student at Cambridge I remember an anthropology professor holding up a picture of a bone with 28 incisions carved in it. 'This is often considered to be man's first attempt at a calendar', she explained. She paused as we dutifully wrote this down. 'My question to you is this: what man needs to mark 28 days? I would suggest that this is a woman's first attempt at a calendar.' It was a moment that changed my life. ...How often had I overlooked women's contribution