Adjective
Destitute of function, or of an appropriate organ. Darwin.
Source: Webster's dictionaryDogs have molar teeth behind the carnassials for crushing bones, but cats have only a greatly reduced, functionless molar behind the carnassial in the upper jaw. Source: Internet
He says that the view that mind is an epiphenomenon of brain activity is not consistent with evolutionary theory, because if mind were functionless, it would have disappeared long ago, as it would not have been favoured by evolution. Source: Internet