Species boundaries are pretty hard boundaries to the transfer of useful genetic information. So once proto-humans stumbled on key brain innovations there really wasn’t much of a way to transfer that to chimps. The innovation could only spread via the spread of humans. But within the human world innovations have spread not just by displacement, but also by imitation and communication. Yes conflicting cultures, languages, and other standards often limit the spread of innovations between humans, but even so this info leakage has limited the relative gains to those first with an innovation. The key question is then what barriers to the spread of innovation would prevent this situation from continuing with future innovations.
Species boundaries are pretty hard boundaries to the transfer of useful genetic information. So once proto-humans stumbled on key brain innovations there really wasn’t much of a way to transfer that to chimps. The innovation could only spread via the spread of humans. But within the human world innovations have spread not just by displacement, but also by imitation and communication. Yes conflicting cultures, languages, and other standards often limit the spread of innovations between humans, but even so this info leakage has limited the relative gains to those first with an innovation. The key question is then what barriers to the spread of innovation would prevent this situation from continuing with future innovations.