McGill Refutes Pop-Psych Claim that Humans Have a “Lizard Brain”

July 8, 2026 - 06:01

A popular pop-psychology concept that humans are driven by a primitive "lizard brain" has been firmly rejected by researchers at McGill University. The idea, which suggests that a reptilian core within our skulls controls basic instincts like aggression and territoriality, has no basis in modern neuroscience, according to a new analysis from the Montreal-based institution.

The false belief traces back to the fact that Carl Sagan was one of its strongest proponents. In his 1977 book "The Dragons of Eden," the famed astronomer and science communicator popularized the triune brain model, which divided the human brain into three layers: the reptilian complex, the limbic system, and the neocortex. While Sagan intended it as a metaphor for evolutionary development, the concept took on a life of its own in self-help books and corporate training seminars.

McGill scientists point out that the triune brain model was originally proposed by neuroscientist Paul MacLean in the 1960s and has since been thoroughly debunked. Modern imaging and genetic studies show that the human brain did not evolve by simply stacking new layers on top of old ones. Instead, the entire structure was remodeled over millions of years. Structures once thought to be "reptilian," such as the basal ganglia, are now understood to be highly interconnected with the cortex and involved in complex functions like decision-making and motor learning.

The university's statement emphasizes that clinging to the lizard brain myth can lead to harmful oversimplifications. It excuses aggressive behavior as hardwired and unchangeable, when in fact human actions are shaped by learning, culture, and conscious choice. By refuting this outdated idea, McGill hopes to encourage a more accurate and nuanced understanding of the brain's true complexity.