MacLean's Theory, developed by neuroscientist Paul D. MacLean, proposes that the human brain is structured in three distinct layers, each representing different evolutionary stages. These layers are the reptilian brain, responsible for basic survival functions; the limbic system, which governs emotions and social behaviors; and the neocortex, associated with higher cognitive functions like reasoning and language. According to MacLean, these three components interact to shape human behavior and experience. The theory suggests that our actions are influenced by the interplay between primal instincts, emotional responses, and rational thought, highlighting the complexity of human psychology and evolution.