Scientists Say the “Lizard Brain” Is a Myth, But the Truth About How Our Brains Evolved May Be Even Stranger

Scientists have debunked the "lizard brain" myth, but new research suggests evolution may be trading one kind of brainpower for another. The study found that mammalian brains are organized around two different computational systems, not an ancient reptilian brain layered on top of a newer one. The divide appears to reflect how different neural systems are wired to process information. The researchers used anatomical measurements and artificial neural networks to show that animals with an unusually large olfactory system tended to have a smaller neocortex, while those with a larger neocortex had a smaller olfactory system. The nine-banded armadillo is a particularly dramatic example, with an unusually large olfactory system and a reduced neocortex. The study also found that the hippocampus and olfactory system changed together, suggesting the important difference might not be what these regions process, but how they are wired to process it.

• The neocortex is wired to preserve spatial relationships, such as neighboring points in the visual world being analyzed by neighboring parts of the cortex.
• The limbic system is more diffusely connected and supports holistic associations across different pieces of information.
• Artificial neural networks trained to handle vision, touch, and hearing produced smooth, highly ordered maps, while the smell network scored just 0.11 on a scale of spatial order.
• The hippocampal network grew along with the olfactory network even though memory was not directly selected for, suggesting evolution may not be selecting individual brain regions one at a time but the functional architecture.

This distinction offers a very different picture from the triune brain theory, which portrayed the human brain as having evolved in distinct layers. The new study suggests that the mammalian brain may be divided very differently—not by evolutionary age, but by how different neural systems are wired to process information. The research indicates that evolution may be trading one kind of brainpower for another, with the brain's organization depending on the type of information it processes.

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