The New York Times reports that Paul D. MacLean, a neuroscientist who developed the theory that the brain is divided into three broad areas that developed during different phylogentic phases of evolution, died on December 26 at the age of 94. According to Jeremy Pearce, who wrote the Times‘ obituary:

In the 1960s, Dr. MacLean enlarged his theory to address the human brain’s overall structure and divided its evolution into three parts, an idea that he termed the triune brain. In addition to identifying the [mamalian] limbic system, he pointed to a more primitive brain called the R-complex, related to reptiles, which controls basic functions like muscle movement and breathing. The third part, the neocortex, controls speech and reasoning and is the most recent evolutionary arrival.

Although the “triune” theory of the brain was never fully accepted in the scientific community, it became a standard scheme in neuroscience and psychology textbooks in the last quarter of the 20th century.