A tomato looks innocent, but it is not. It tastes like a vegetable, it is excellent in soups, its flavour is enhanced by olive oil and salt, and yet the tomato is – the experts tell us – a fruit, a cousin of the apple. Political realism looks innocent too. One wonders whether it is a fruit or a vegetable. Political theorists, like botanists, need to classify their crops. And like botanists, they look to genetics and evolution to provide answers to their questions of classification.