Imagine a scene where a troop of ape-like human ancestors a little more than four feet tall, with brains roughly equal in size to those of their evolutionary cousins chimpanzees, come upon a pack of large carnivores—say, lions or hyenas—feeding on a fresh carcass. Rather than run in fear from these predators, the hominins approach them screeching, waving their arms, and trying to be as frightening as possible. The carnivores, perhaps baffled or intimidated by this display, run away, leaving the hominins to feast on the fresh meat.
According to research by a team of European biologists, this type of scene may have been common enough to cause the extinction of large carnivores across East Africa. These extinctions became more frequent as early hominin brain size began to increase, perhaps about three million years ago. Using previously published data, the researchers were able to rule out climate change as the cause of these extinctions. The data also shows a correlation between large carnivore extinctions and increased hominin brain size. “The surprise was actually how clear the results are,” says Søren Faurby, a biologist at the University of Gothenburg. Next, the researchers hope to document how widespread the impact of early hominin evolution was on other, perhaps less vicious, animals.