A new study supports the idea that Neanderthals likely went extinct because of how they lived — in isolation.

The early human species were antisocial, which could be what led to their demise, according to the study by researchers at the University of Copenhagen’s Globe Institute. It was published in the science journal Cell Genomics on Sept. 11.

Neanderthals went extinct roughly 40,000 years ago and many scientists have tried to pinpoint why. A widely accepted theory is that they remained isolated; however, evidence was lacking to confirm the theory for Western European Neanderthals until now.