"That shift in viewpoint is very important," says Holland. Indeed, evolutionary biologists consider it so important that they've made up a special word for it: organisms in an ecosystem don't just evolve, they coevolve. Organisms don't change by climbing uphill to the highest peak of some abstract fitness landscape, the way biologists of R. A. Fisher's generation had it. (The fitness-maximizing organisms of classical population genetics actually look a lot like the utility-maximizing
