In hunting large mammals to near extinction, early modern humans may have prompted an explosion in brain size—in a good way. Humans emerged as big-game hunters in Africa 2.6 million years ago but would ultimately see large animals dwindle as a result of hunting practices, according to Miki Ben-Dor and Ran Barkai of Tel Aviv University. Whereas the Neanderthals went extinct, humans rose to the challenge, adapting to hunt fast-moving small game. It was a major transformation, requiring more energy, more sophisticated tools, and increased cognitive ability, per a release. Indeed, Ben-Dor and Barkai, whose study appears in the Quaternary journal, observed an increase in human brain volume from 650cc to 1,500cc in ancient remains from east Africa, southern Europe, and Israel during the Pleistocene Epoch (roughly 2.6 million years ago to 11,700 years ago).
This is linked "with the need to become smarter hunters," Ben-Dor proposes in the release. "As the size of animals continued to decrease, the invention of the bow and arrow and domestication of dogs enabled more efficient hunting of medium-sized and small animals." His research also suggests this period of growth allowed for the development of human language, which would've aided in hunting. Toward the end of the Pleistocene, though, the average size of land mammals would diminish to about 110 pounds—about a tenth of the figure at the dawn of humanity, per the Jerusalem Post. And humans, who were spending more energy hunting than they were getting out of it, turned to agriculture. As "there was no more need for the allocation of outstanding cognitive abilities to the task of hunting," brain size then decreased to its current volume of 1300cc to 1400cc, Ben-Dor notes in the release. (Read more evolution stories.)