It showed that the frog’s visual system is sensitive to small moving dark spots on the retina, tiny shadows cast in almost all natural circumstances by flies flying in the vicinity. This “fly-detector” mechanism is appropriately wired to the hair trigger in the frog’s tongue, which handily explains how frogs feed themselves in a cruel world and thereby help propagate their kind. Now what does the frog’s eye tell the frog’s brain? Unless there were “meaningless” or “indeterminate” variation in the triggering conditions of the various frogs’ eyes, there could be no raw material (blind variation) for selection for a new purpose to act upon. The indeterminacy that Fodor (and others) see as a flaw in Darwinian accounts of the evolution of meaning is actually a precondition for any such evolution. The idea that there must be something determinate that the frog’s eye really means—some possibly unknowable proposition in froggish that expresses exactly what the frog’s eye is telling the frog’s brain—is just essentialism applied to meaning (or function). Meaning, like function, on which it so directly depends, is not something determinate at its birth. It arises not by saltation—huge leaps in Design Space—or special creation, but by a (typically gradual) shift of circumstances.
Philosopher Daniel Dennett's Book Intuition Pumps