From cats to caterpillars, hedgehogs to humans, we divide the world of living things into distinct and separate organisms. But while central to our perception of the world and evolution, these distinctions now look dangerously simplistic. Studies show that the boundaries between one creature and the next are not clear. Forests of 'distinct' trees are often connected by networks of fungi which, like a great nervous system, are essential to their survival. And almost all large creatures co-exist with great swarms of bacteria that are essential to their very life function.

Should we move away from an organism-centred biology, and recognise the interconnected character of life? Should we reject the idea that a living thing constitutes a distinct and stable entity? Or are discrete units of life essential to our understanding of the world?