“But to Holland, the concept of prediction and models actually ran far deeper than conscious thought-or for that matter, far deeper than the existence of a brain. "All complex, adaptive systems- economies, minds, organisms-build models that allow them to anticipate the world," he declares. Yes, even bacteria. As it turns out, says Holland, many bacteria havve special enzyme systems that cause them to swim toward stronger concentrations of glucose. Implicitly, those enzyme model a crucial aspect of the bacterium's world: that chemicals diffuse outward from their source, growing less and less concentrated with distance. And the enzymes simultaneously encode an implicit prediction: If you swim toward higher concentrations, then you're likely to find something nutritious. "It's not a conscious model or anything of that sort," says Holland. "But it gives that organism an advantage over one that doesn't follow the gradient.”