Researchers at Georgia Tech and Cornell University have published findings in Science Advances that question a decades-old theory about how the brain evolved. The “lizard brain” concept, popularized in the 1950s, portrayed brain evolution as a hierarchical process in which basic bodily functions developed first, followed by emotional centers in a so-called reptilian brain, and finally advanced reasoning capabilities in humans. However, the new research suggests this model oversimplifies the actual evolutionary process.
The study examined how different brain systems have changed across species and found evidence that brain evolution may be better understood through the lens of neural wiring organization rather than the addition of newer layers on top of older ones. Researchers compared the limbic system, commonly referred to as the “reptilian brain,” with the neocortex, which is associated with higher-level cognitive functions. They discovered that when components of the limbic system expanded in size across species, other parts of that system also tended to expand, while the neocortex typically became smaller. This pattern suggests the limbic system functions as an integrated network rather than a collection of independent structures.
The team identified two fundamentally different neural wiring strategies. The neocortex uses spatial mapping, with brain regions processing nearby body parts positioned close to one another. The limbic system employs what researchers describe as a distributed “barcode-style” organization, with patterns of activity representing smells or memories spread throughout the system. Using artificial intelligence models, the researchers found that spatial networks excelled at processing vision, sound, and touch, while distributed networks performed better with smell recognition and memory tasks.
According to the research, brain evolution reflects competition for limited neural resources. The brain has finite space and energy, so natural selection may favor whichever wiring system proves most advantageous for an animal’s survival in its particular environment. In testing this hypothesis through simulated networks that competed for resources, the researchers observed that when the environment rewarded smell processing, distributed systems expanded while the neocortex contracted. When vision was valued instead, the pattern reversed. Real animals demonstrate this principle: the nine-banded armadillo, which relies heavily on smell, has an enlarged limbic system, while the squirrel monkey, which depends strongly on vision, has a neocortex-dominated brain.
Beyond evolutionary biology, these findings may have applications for artificial intelligence development. If engineers incorporate pre-wired neural organization similar to biological brains into AI systems, they might create more efficient artificial intelligence that requires significantly less training data and energy than current approaches.
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