Genesis tells us that we were created ‘in God’s image’ and that other animals weren’t – but what does this really mean? What, when you boil it down, is the crucial difference between ‘us’ and ‘them’? In the seventeenth century, Descartes pinned it down with inexorable Gallic logic, at least to his own satisfaction: we have verbal language – speech – and animals don’t. Words, he declared, are the vital components of thought. Since animals don’t have words, they can’t think. Indeed, though we may whimsically care to assume otherwise, animals are really just automata. In a similar vein, David Hume in the eighteenth century suggested that whereas animals can register pain, fear and other such reactions, they cannot experience the infinite subtleties of the human soul – depression, amusement, friendship, and all the rest. It all seemed clear enough. 

But then Darwin suggested in On the Origin of Species in 1859 that all creatures on Earth including ourselves are related one to another – literally, for all share a common ancestor – and that our own closest living relatives are chimps or perhaps gorillas. He also suggested,