Genes are the tiny biological programmes that make a person an individual: they determine the colour of the eyes and hair, height, even personality. One of them, DRD4-7R, appears in 20 per cent of the people. It is also called the ‘restless gene’ or the ‘travel gene’. It asserts itself in leaders and urges them to see what lies beyond the horizon, and on the other side of the mountain. When individuals do this, the gene releases a rewarding shot of the ‘feel good’ chemical, dopamine. It is nature’s way of ensuring the continued evolution of the human race. It also explains how humans colonised every environment on earth.