1530s, "action," especially "evil deed," from Latin factum "event, occurrence," literally "thing done," neuter past participle of facere "to do" (see factitious). Usual modern sense of "thing known to be true" appeared 1630s, from notion of "something that has actually occurred." Facts of life "harsh realities" is from 1854; specific sense of "human sexual functions" first recorded 1913.