To understand what Kolodny's getting at, I ask Bovaird to walk me through the history of Stone Age technologies. He starts by smashing an irregular, grapefruit-size stone between two larger rocks. He picks through the resulting fragments, looking for a shard with an excellent cutting edge. This is simple Oldowan technology, he tells me—the first stone tools, used by our hominin ancestors as far back as 2.5 million years ago.

Next, he flashes forward a million years to the technological revolutions of Homo ergaster. No longer did toolmakers simply knock stones together to see what they got; now they aimed for symmetry. Bovaird holds up his work in progress, a late Acheulean hand ax—the multi-tool of the middle-to-lower Paleolithic, good for cutting meat, digging dirt, smashing bone. The blade of this ax has a zigzag edge, with tiny, alternating flakes removed from each side of the cutting surface. To achieve this level of serration, Bovaird explains, he needs a precise understanding of how the stone works, as well as the ability to plan his work many steps in advance.

Somewhere on the timeline between the long run of the Oldowan and the more rapid rise of Acheulean technologies, language (or what's often called protolanguage) likely made its first appearance. Oren Kolodny and his co-author, Shimon Edelman, a professor of psychology at Cornell University, say the overlap is not a coincidence. Rather, they theorize, the emergence of language was predicated on our ancestors' ability to perform sequence-dependent processes, including the production of complex tools.

Kolodny's arguments build off the groundbreaking experiments of Dietrich Stout, an anthropologist at Emory University. A flintknapper himself, Stout has taught hundreds of students how to make Acheulean-era tools, and he's tracked their brain activity during the learning process. Stout found that his students' white matter—or the neural connectivity in their brains—increased as they gained competence in flintknapping. His research suggests that producing complex tools spurred an increase in brain size and other aspects of hominin evolution, including—perhaps—the emergence of language.

But language couldn't just pop out fully formed, like Athena from the head of Zeus. "Every evolutionary process, including the evolution of language, has to be incremental and composed of small steps, each of which independently needs to be beneficial," Kolodny explains. Teaching, he says, was a crucial part of the process. When hominins like Homo ergaster and Homo erectus taught their close relatives how to make complex tools, they worked their way into an ever more specialized cultural niche, with evolutionary advantage going to those individuals who were not only adept at making and using complex tools, but who were also able—at the same time—to communicate in more and more sophisticated ways.