Clint Eastwood might sound like an unlikely candidate to help investigate the evolution of the brain, but he has lent a helping hand to researchers doing just that. It turns out that brain regions that do the same job in monkeys and humans aren’t always found in the same part of the skull.

Previous studies comparing brains across species tended to assume that human brains were just blown-up versions of monkey brains and that functions are carried out by anatomically similar areas.

To test this idea, Wim Vanduffel of Harvard Medical School in Boston and the Catholic University of Leuven (KUL) in Belgium, and colleagues scanned the brains of 24 people and four rhesus monkeys while they watched The Good, The Bad and The Ugly. They compared the brain responses of each individual to the same sensory stimulation, and identified which brain areas had similar functions.

The majority of the human and monkey brain maps lined up, but some areas with a similar function were in completely different places.

The team say the discovery is crucial to building more accurate models of our evolution. “You can’t assume that because A and B are close together in the monkey brain, they need to be close together in the human brain,” Vanduffel says.