I have a theory. The fire using, tool making, upright walking hominid with a brain 2/3rds of the size of ours was distinguished partially by ‘planning depth.’ It/they could think some number of ‘moves’ ahead. If I make a ruckus here while you head over there at the narrows and wait, likely you’ll snag one of the rabbits I scare up. That sort of thing. All the planning was aimed at increased fitness, as it were.
At some point that expanding future horizon lead to: “oh shit, no matter what we do, we’re all gonna die!” That’s, imho, is when we became human.