In this age of digital hyperlinking, it’s more important than ever to understand the links between humans. Human brains are fundamentally wired to interact: we’re a splendidly social species. Although our social drives can sometimes be manipulated, they also sit squarely at the center of the human success story. You might assume that you end at the border of your skin, but there’s a sense in which there’s no way to mark the end of you and the beginning of all those around you. Your neurons and those of everyone on the planet interplay in a giant, shifting super-organism.