Neuroscientists challenge the evolutionary “lizard brain” myth

Researchers have challenged the long-standing “lizard brain” myth, which posits that humans possess an ancient, primitive reptilian brain layered beneath a newer, rational center. A study published in Science Advances, involving anatomical measurements from 182 mammalian species and artificial neural network experiments, suggests that brain evolution is not a matter of stacking new layers onto old ones.

Instead, the research indicates an evolutionary trade-off between the neocortex and the limbic system. Lead author Dr. Nabil Imam of the Georgia Institute of Technology explains that these regions represent two different computational systems rather than “old” and “new” brains. The neocortex is wired to preserve spatial relationships, such as analyzing neighboring points in the visual world, while the limbic system uses more diffuse connections to support holistic associations across various pieces of information.

This distinction suggests that different species allocate brain space to either the neocortex or the limbic system based on practical needs. For example, the nine-banded armadillo possesses a large limbic system due to its reliance on smell, whereas the squirrel monkey has a brain dominated by the neocortex due to its reliance on vision.