Written and first recorded (as a demo) by Steve Porcaro (1983).
Hit version by Michael Jackson (1984).
From the wiki: “‘Human Nature’ was written by Toto band member Steve Porcaro about a playground incident his daughter had at school earlier in the day. (A boy had hit her after she fell off the slide – Porcaro said ‘she asked [me] why?’ and he replied ‘it was human nature.’) Procaro wrote the song that night in a studio while the band was mixing their single, ‘Africa’, in another studio.
“Soon after, bandmate David Paich called Procaro one day to make a cassette tape of 2 songs David had written for Michael Jackson’s new Thriller album project, for someone to pick up for delivery. Procaro happened to use the cassette he recorded ‘Human Nature’ on, putting Paich’s songs on the opposite side and switching the labels to read Side-A. It was a happy accident that auto-playback kicked in while Jackson producer Quincy Jones was in his car listening to Porcaro’s cassette demo. Jones got to hear ‘Human Nature’ on Side B, and loved it.”
Michael Jackson, “Human Nature” (1984):