This article showed up today, nicely confirming one of the suggestions I made in my post two days ago.

“Scientists have found compelling evidence for the co-evolution of early Stone Age slaughtering tools and our ability to communicate and teach, shedding new light on the power of human culture to shape evolution. . . .

“In testing five different ways to convey Oldowan stone-knapping skills to more than 180 college students, the researchers found that the demonstration that used spoken communication – versus imitation, non-verbal presentations or gestures – yielded the highest volume and quality of flakes in the least amount of time and with the least waste. . . .

“‘If someone is trying to learn a skill that has lots of subtlety to it, it helps to engage with a teacher and have them correct you,” Morgan said. “You learn so much faster when someone is telling you what to do.’ . . .

“‘At some point they reached a threshold level of communication that allowed Acheulean hand axes to start being taught and spread around successfully and that almost certainly involved some sort of teaching and proto-type language,’ Morgan said.”