  In complex environments, there are costs to both ignorance and perception. An
organism needs to track fitness-relevant information about its world, but the
more information it tracks, the more resources it must devote to memory and
processing. Rate-distortion theory shows that, when errors are allowed,
remarkably efficient internal representations can be found by
biologically-plausible hill-climbing mechanisms. We identify two regimes: a
high-fidelity regime where perceptual costs scale logarithmically with
environmental complexity, and a low-fidelity regime where perceptual costs are,
remarkably, independent of the environment. When environmental complexity is
rising, Darwinian evolution should drive organisms to the threshold between the
high- and low-fidelity regimes. Organisms that code efficiently will find
themselves able to make, just barely, the most subtle distinctions in their
environment.
