Study: Brain differences between Paleolithic Humans and Neanderthals (separate species) are found to be smaller than those between contemporary Americans and Chinese (same species).

For seemingly ideological reasons, the authors declare that these differences are "not evolutionarily significant."

Obviously, there are evolutionarily significant cognitive differences between modern human populations, such as those that enabled Europeans to conquer ~85% of the Earth's surface from ~1490 to ~1920 AD, and those that prevented Sub-Saharan Africans from inventing the wheel.

https://www.pnas.org/doi/10.1073/pnas.2426638123