The Song of the Cell: An Exploration of Medicine and the New Human

by Siddhartha Mukherjee

But for more primitive multicellular organisms—sponges, say—for which competitive existence is an everyday battle, every morsel of food precious, constancy a looming threat, and territory a limited resource, the potential invasion by another self isn’t a trifling matter. Such an organism must query: Where do I end and you begin? Its self can exist only if its borders are strictly enforced. Such an organism must constantly ask each of its cells, “Who are you?”