For more than a century, scientists have debated whether the differently shaped brains of Neanderthals implied lower cognitive abilities than those of modern humans. A new study led by Indiana University argues that such assumptions may have been overstated, suggesting that brain differences between Neanderthals and early modern humans fall within the range of variation seen among people today.

The research, published in Proceedings of the National Academy of Sciences, was led by Thomas Schoenemann of IU Bloomington, alongside collaborators from Columbia University, Peking University and the Beijing Institute of Technology.

The team re-examined claims made in a widely discussed 2018 study which suggested Neanderthals possessed smaller cerebellums than early modern humans. Because the cerebellum is associated with functions such as attention, language and working memory, some researchers proposed that these anatomical differences may have contributed to Neanderthal extinction.

To test that idea, the researchers analysed MRI brain scans from two groups of living humans — 200 Americans of European descent and 200 Han Chinese individuals — using the same methods applied in the earlier Neanderthal study. They found that many of the differences between the modern human groups were actually larger than the estimated differences between Neanderthals and early modern humans.

According to the study, the predicted cognitive gap between Neanderthals and modern humans would have been extremely small. Researchers concluded that such minor differences are unlikely to explain the disappearance of Neanderthals tens of thousands of years ago.

Instead, the findings support alternative explanations already gaining traction among archaeologists and paleoanthropologists, including demographic decline, interbreeding with modern humans and competition with expanding human populations.

The study also cautions against interpreting differences in brain anatomy as evidence of intellectual hierarchy. The researchers argue that variation in brain structure among living humans does not determine cognitive ability, and that similar assumptions should not be projected onto Neanderthals.