Stone tools seem to go back further than we realised. There's a BBC post about it here but personally I think the Nature abstract puts the facts very well.
A South African friend has a good story about a research project he was loosely involved in many years ago. The experiment was to teach a captive gorilla how to knap flint, one of these gorillas that was being used for all sorts of experiments in communication. They spent hours with the gorilla, showing it how to hit two rocks together over and over and over again to eventually produce a sharp edge.
Although the gorilla was watching them with interest, it soon got bored. They tried to get the gorilla to copy them but it just looked at them blankly, holding the rocks in it hands.
They eventually gave up.
When they left, the gorilla was watched by its handlers / keepers as it started playing with the rocks the flint-knapping expert researchers had left. It picked them up, examined them, turned them over and then put one on the floor. It threw another rock at it and the rock on the ground split. It repeated this a few times. In just a couple of minutes, with very little effort, the gorilla produced a better, cleaner, blade than the 'experts' had been doing.
My friend says the amusing part was the subsequent fury of the senior academics. It seemed everything we think we know about flint knapping may be wrong. The punchline was, the experts decided the gorilla's behaviour was invalid because it had already had human exposure and this must have influenced it.
And that was the end of that.
Now that's a very interesting story, thanks Simon!
There's nothing I can find written up - and I wasn't expecting to find anything since it all happened pre-web and I don't think it got written up anyway as it did not prove the professor(s)' expectations.
But more recently bonobo chimpanzees in captivity were shown how to knap flint and then, ten years later, when presented with problems that needed tools to solve them, made problem-specific flint tools they had not been shown how to make. Stone tool production and utilization by bonobo-chimpanzees