We are independent & ad-supported. We may earn a commission for purchases made through our links.
Advertiser Disclosure
Our website is an independent, advertising-supported platform. We provide our content free of charge to our readers, and to keep it that way, we rely on revenue generated through advertisements and affiliate partnerships. This means that when you click on certain links on our site and make a purchase, we may earn a commission. Learn more.
How We Make Money
We sustain our operations through affiliate commissions and advertising. If you click on an affiliate link and make a purchase, we may receive a commission from the merchant at no additional cost to you. We also display advertisements on our website, which help generate revenue to support our work and keep our content free for readers. Our editorial team operates independently of our advertising and affiliate partnerships to ensure that our content remains unbiased and focused on providing you with the best information and recommendations based on thorough research and honest evaluations. To remain transparent, we’ve provided a list of our current affiliate partners here.

What is the Triune Brain?

By John Markley
Updated Feb 26, 2024
Our promise to you
WiseGeek is dedicated to creating trustworthy, high-quality content that always prioritizes transparency, integrity, and inclusivity above all else. Our ensure that our content creation and review process includes rigorous fact-checking, evidence-based, and continual updates to ensure accuracy and reliability.

Our Promise to you

Founded in 2002, our company has been a trusted resource for readers seeking informative and engaging content. Our dedication to quality remains unwavering—and will never change. We follow a strict editorial policy, ensuring that our content is authored by highly qualified professionals and edited by subject matter experts. This guarantees that everything we publish is objective, accurate, and trustworthy.

Over the years, we've refined our approach to cover a wide range of topics, providing readers with reliable and practical advice to enhance their knowledge and skills. That's why millions of readers turn to us each year. Join us in celebrating the joy of learning, guided by standards you can trust.

Editorial Standards

At WiseGeek, we are committed to creating content that you can trust. Our editorial process is designed to ensure that every piece of content we publish is accurate, reliable, and informative.

Our team of experienced writers and editors follows a strict set of guidelines to ensure the highest quality content. We conduct thorough research, fact-check all information, and rely on credible sources to back up our claims. Our content is reviewed by subject-matter experts to ensure accuracy and clarity.

We believe in transparency and maintain editorial independence from our advertisers. Our team does not receive direct compensation from advertisers, allowing us to create unbiased content that prioritizes your interests.

The triune brain refers to a hypothesis about how the human brain evolved and functions that was first proposed by neuroscientist Paul D. MacLean in the 1960s. It posits that the brain can be divided into three parts, called the reptilian complex, the paleomammalian complex, and the neomammalian complex, which originated sequentially in the course of evolution and are tied to progressively more advanced forms of thought. It is now considered disproved due to subsequent research in neurology, paleontology, and related fields, though it retains a presence in popular culture.

According to the triune brain hypothesis, the oldest and most basic part of the human brain is a group of nerve clusters called the basal ganglia, located below the cerebrum. This is called the reptilian complex, so named because this part of the triune brain was posited to have evolved in humanity's distant pre-mammal evolutionary ancestors. In the triune brain model, the reptilian complex governs primitive instincts such as aggression, dominance, and the fight-or-flight response.

The second part, the paleomammalian complex, encompasses the structures in the brain now referred to as the limbic system. This includes the amygdala, hippocampus, and hypothalamus, along with the cingulate cortex and parts of the cerebral cortex. MacLean argued that these structures governed the emotions and behaviors such as reproduction, parenting, and feeding. According to the hypothesis, this part of the brain first evolved among early mammals. MacLean was the first neuroscientist to identify the limbic system and its importance, and the concept is still widely used in modern neuroscience despite the subsequent discrediting of the triune brain hypothesis as a whole.

The third part, called the neomammalian complex, is the neocortex. The neocortex is a part of the cerebral cortex found exclusively in mammals. In the triune brain model, the neomammalian complex is the newest part of the brain to evolve and is responsible for higher mental functions such as language and abstract thought.

The basal ganglia are present in all vertebrates, and so their evolution probably substantially predates the emergence of reptiles. Similarly, brain structures included in the paleomammalian complex are not unique to mammals, and many non-mammalian vertebrates display the nurturing and child-rearing behaviors attributed to it. Sauropsids, a classification encompassing birds, reptiles, and dinosaurs, were all subsequently discovered to have brain structures similar in function to what MacLean called the neomammalian complex, which indicates that the evolution of these structures also predates the evolution of mammals. Sophisticated mental abilities once thought to be exclusive to mammals, such as toolmaking, are also present in some species of birds.

The idea of the triune brain also lost credibility due to greater understanding of the human brain. For example, brain damage in some areas classified as part of the paleomammalian complex can impair cognitive functions that are supposedly the sole domain of the neomammalian complex. This is difficult to account for in a model of the nervous system that attributes all higher mental functions to a single, specific part of the brain.

WiseGeek is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Discussion Comments
WiseGeek, in your inbox

Our latest articles, guides, and more, delivered daily.

WiseGeek, in your inbox

Our latest articles, guides, and more, delivered daily.