The so-called Levallois technique — which early humans used to make knives and other instruments by flaking off bits of stone — was long thought to have originated in Africa 500,000 to 600,000 years ago, then taken to Eurasia as part of an exodus from Africa.

Now a study in the journal Science throws the second part of that assumption into doubt, suggesting that the technique evolved independently on each landmass — and, more broadly, challenging the notion that the movement of ancient humans can be tracked by the tools they used.

Levallois tools and less advanced ones, like hand axes, are almost never found together, so scientists thought that one type of tool replaced the other as the migrants moved north. But archaeologists working in Armenia have now unearthed Levallois tools in the same layer of soil as hand axes. The most likely conclusion, the researchers say, is that the Levallois method was not taken to Eurasia by African migrants, but evolved there gradually and independently.

Either that, or “you have two different groups of hominins with two totally different toolmaking traditions occupying the same landscape at the same time yet never intermixing,” said the study’s lead author, Daniel Adler, an anthropologist at the University of Connecticut. “We don’t find evidence for that sort of thing anywhere in prehistory.”