If Man be separated by no greater structural barrier from the brutes
than they are from one another--then it seems to follow that if any
process of physical causation can be discovered by which the genera
and families of ordinary animals have been produced, that process of
causation is amply sufficient to account for the origin of Man.
* This alludes to a foregoing enumeration of the seven
families of Primates headed by the Anthropini containing man
alone.