Bald, curly, mullet or mohican, whether we like it or not our hair plays a crucial role in how we look. But there's more to our crowning glory than meets the eye Quentin Coopergoes in pursuit of the hirsute. Why did we evolve to lose most of the furthat would have covered our ancestors' bodies? Why might stem-cell research pave the way for a cure for balding and what are top stylist Nicky Clarke 's secrets of a good hairday? Producer Pamela Rutherford