In 1990, when computers were still merely in the process of taking over the world, John Daugman, a computer scientist and researcher at Harvard University, published an article titled “Brain Metaphor and Brain Theory,” noting a habit he had observed among his peers. “Invariably,” he wrote, “the explanatory metaphors of a given era incorporate the devices and the spectacles of the day.” In other words: We describe everything as if it were technology. The metaphors we use to talk about brains and minds struck Daugman as especially susceptible. The technology that Greeks and Romans developed for pumping water, for instance, underpinned their theories of the four humors and the pneumatic soul. Later, during the Enlightenment, clockwork mechanisms left their imprint on materialist arguments that man was only a sophisticated machine. And as of 1990, it was concepts from computing that explained us to ourselves: “Today’s embrace of the computational metaphor in the cognitive and neural sciences is so widespread and automatic that it begins to appear less like an innovative leap than like a bandwagon phenomenon,” he wrote. “There is a tendency to rephrase every assertion about mind or brains in computational terms.”

Nearly three decades later, now that computing has become truly ubiquitous, its metaphors are deployed without a moment’s thought. We don’t just talk intuitively about the ways in which people are “programmed” — we talk about our emotional “bandwidth” and look for clever ways to “hack” our daily routines. These metaphors have developed right alongside the technology from which they’re derived, starting with hardware and then moving to software, apps and networks. Now we’ve arrived at a tempting concept that promises to contain all of this: the stack. These days, corporate managers talk about their solution stacks and idealize “full stack” companies; athletes share their recovery stacks and muscle-building stacks; devotees of so-called smart drugs obsessively modify their brain-enhancement stacks to address a seemingly infinite range of flaws and desires.