What could fingers and sex possibly have in common? What does the shape of a child's fingers reveal about future musical talent? And why should professional footballers have longer fingers than other men? This book is about a simple measurement of the human hand: the 'finger ratio', or the length of the ring finger relative to the index finger. John Manning uses a tiny difference between the sexes - that men tend to have a greater finger ratio than women - to examine a dizzying group of questions about human behaviour and what makes us as we are.