The Reptilian Brain and Thinking Critically

How many of us learned at some point in our education about the triune brain - the theory that the brain consists of three parts, reptilian, mammalian and human?

According to this theory, the most evolutionarily primitive part of the brain, the reptilian brain, i.e. the brain stem, which controls basic body functions like movement and breathing. It's called the reptilian brain because reptiles' brains are similar.

Somewhat more advanced is the mammalian brain, i.e. the limbic system, which controls emotion. Sitting at the apex of evolutionary development is the human brain, the cerebral cortex, which controls language, reasoning, etc.

Denyse O'Leary at Mind Matters News notes that this theory, published in the 1960s by Yale University physiologist and psychiatrist Paul D. MacLean, was made popular by astronomer Carl Sagan in his best-selling 1977 book Dragons of Eden.

The theory was popular because it fit the evolutionary paradigm that holds that the brain was constructed gradually by building more advanced parts on top of more primitive parts. Thus, our reptilian brain is a holdover from an earlier stage of our evolution.

O'Leary, however, is skeptical. She asks, "Do we have a three-part brain - reptilian, mammalian and human? Curiously, psychology textbooks teach us that we do and neuroscience studies teach us that we don’t. Who to believe? And how did that happen anyway?"

Neuroscientists scoff at the idea that the human brain is organized the way the triune brain theory suggests. O'Leary writes:

As University of Oslo psychology professor Christian Krog Tamnes puts the matter in an interview at Science Norway, “Those of us who research brain development and brain evolution have known for quite some time that this isn’t true.”

Tamnes points, to a paper on the topic last year: Despite 320 million years of separate evolution, lizards and mice share a core set of neuron types that are found all over the brain, “including in the cerebral cortex, challenging the notion that certain brain regions are more ancient than others.”

Eldrid Borgan, in an article titled “No, you don’t have a reptilian brain inside your brain,” states that,

Emotions, such as fear and sadness, are not made in one specific place in the brain. In fact, several parts of the brain are always involved. Which parts of the brain are active vary from time to time, and from person to person.

Northeastern University neuroscientist Lisa Feldman Barrett offers, “So if we absolutely need to have a metaphor, it’s much better to think of the brain as an orchestra. Even playing a simple song requires a lot of pieces to talk together effectively and in a coordinated way.”

So we can still have lots of problems but our Inner Lizard is not one of them.

Despite the findings of neuroscientists, psychology students are apparently still being taught that we do indeed have an "Inner Lizard."

Psychology lecture rooms and textbooks have been curiously slow to let go of the reptilian brain myth however....In 2020, Joseph Cesario and colleagues reported on a study of what psychology students are told about such matters:

This belief [the triune brain theory], although widely shared and stated as fact in psychology textbooks, lacks any foundation in evolutionary biology.

Our experience suggests that it may surprise many readers to learn that these ideas have long been discredited among people studying nervous-system evolution. Indeed, some variant of the above story is seen throughout introductory discussions of psychology and some subareas within the discipline…

There's more on this at the link, but one lesson we might take from the above is that we should mix any pronouncement from scientists, and a forteriori the media, with a healthy dose of skepticism until were shown compelling evidence. Scientific ideas and political ideologies which were yesterday's fashion are often today's rubbish.

Regarding any claim made by anyone which we're urged to accept we should ask, does it offend common-sense, what's the evidence for it and to what consequences does it appear to lead? Until we're shown persuasive evidence for a scientific claim presented to us by others, particularly any claim that has political implications, violates common sense or conflicts with other beliefs we hold, we're intellectually justified in withholding acceptance.

If more people were to remain skeptical, not just about scientific theories which sound far-fetched, but also about some of the dogmas advanced by contemporary social movements, such as those involving climate, race, religion and sexuality, our culture might be a lot less confused and adrift today.