Is it farther or further?
mid-15c., variant of human (cf. german/germane, urban/urbane), used interchangeably with it until early 18c., by which time it had become a distinct word with sense of "having qualities befitting human beings." But inhuman still can be the opposite of humane. The Royal Humane Society (founded 1774) was originally to rescue drowning persons. Such societies had turned to animal care by late 19c.