" We do not inhabit a perfected world where natural selection ruthlessly scrutinizes all organic structures and then molds them for optimal utility. Organisms inherit a body form and a style of embryonic development; these impose constraints upon future change and adaptation. In many cases, evolutionary pathways reflect inherited patterns more than current environmental demands. These inheritances constrain, but they also provide opportunity. A potentially minor genetic change […] entails a host of complex, nonadaptive consequences. The primary flexibility of evolution may arise from nonadaptive by-products that occasionally permit organisms to strike out in new and unpredictable directions. What “play” would evolution have if each structure were built for a restricted purpose and could be used for nothing else? How could humans learn to write if our brain had not evolved for hunting, social cohesion, or whatever, and could not transcend the adaptive boundaries of its original purpose? "

― Stephen Jay Gould , Hen's Teeth and Horse's Toes: Further Reflections in Natural History