No consensus exists concerning the mechanisms, distribution, or adaptive significance of consciousness. Agreement on any one of these issues would aid in resolving others. Given a reliable behavioral or neuroanatomical test for consciousness, we could map its distribution and describe its evolution. Conversely, if we knew its distribution, we could assess its adaptive value and look for similarly distributed neuroanatomies to help us get at its mechanisms.

Morgan's Canon—the rule that we should avoid attributing humanlike mental states to other animals whenever possible—impedes the use of the comparative method in unraveling this knot. If interpreted in this context as a parsimony criterion, Morgan's Canon is logically equivalent to epiphenomenalism. It is parsimonious if and only if conscious mental events play no causal role in human behavior and human consciousness has no adaptive significance. Rejecting this conclusion entails rejecting the parsimony interpretation of Morgan's Canon.