'humanely' ultimately derives from the adjective 'humane', which comes from Latin 'humanus' meaning 'of man' or 'humane'; the adverb is formed by adding the English suffix '-ly' to 'humane'.

'humanus' passed into Old French as 'humain' and into Middle English as 'humane' (adjective); English then formed the adverb 'humanely' by adding the suffix '-ly' to the adjective 'humane'.

Originally related to 'humanus' meaning 'of or belonging to man' (and later 'cultured, civilized'), the word 'humane' shifted toward the sense 'kind, compassionate', and 'humanely' now means 'in a compassionate manner'.