Brain theory
We’ve been brainwashed
When a man named Paul MacLean created a theory about the human brain in 1960, we all believed him. Turns out, Paul’s theory, was just that. Paul was an American physician and neuroscientist, who made the Triune Brain Theory. According to it, our brain is split into 3 neat regions. He said that each one evolved after the other, and they work individually, processing our primitive, emotional and rational mental activities. He even gave them names: The Lizard Brain (alternatively Reptilian or Primal), the Mammal Brain (Emotional or Paleomammalian) and the Human Brain (Neomammalian or Rational). Before we go anywhere, no, they’re not split like this:
Lizard, mammal, human
Each bit, Paul said, processes different things. The Lizard Brain, is the oldest of them all at 250 million years old. Located near the brain stem there’s no doubt about it, this dude’s got primal instinct. Subconsciously working away he’s all about that fight or flight response, breathing, digesting, keeping the heart going, ya know, the essentials.
Next up, the Mammal Brain. Also subconscious but ‘more evolved’ at 250 million years old, this lady ensures we stay safe. Somatosensory, she’s the one keeping a record of all our lessons learned the hard way. She also deals with our emotions, bonding, memory and habits. Bang slap in the middle of our head, she is part of our limbic system. (Remember when I said 95% of human behaviour is subconscious? Ta-da, Lizard and Mammal Brains).
Finally, the Human Brain. A spritely 2-3 million years old and our showstopper sat front, centre and on top. Situated in the neocortex, it is the largest part of your cerebral cortex (the big wrinkly bit). The most complex of our trio, this guy is the gun show. Dealing with everything we associate as inherently human, this macho man is consciously doing it all: Abstract thought, language, imagination, reasoning, rationalising, creativity (if only he could cook).
So, all hunky dory, no complaints there. Until 2020 came along and flipped everything on its’ head. Not just a pandemic, a paper was published called, no joke, “Your Brain Is Not an Onion with a Tiny Reptile Inside“. Actually, 20 years before in 1990 when our man Paul published his book, everyone knew his ideas were way off. But he gave us a simple way to describe an extremely complex thing, and hey people loved it, so it stuck.
Evolutionary biology slam dunk
The Onion Brain paper says that from a biological evolutionary perspective, the Triune Brain Theory doesn’t add up. Paul’s idea suggests that as we evolved from Primal to Paleomammalian to Neomammalian, we grew new bits of brain. Hold up for a second there Paul, the neocortex is not unique to humans, primates or mammals at all. In fact, literally all vertebrates (anything with a spine peeps) from fish to humans, have the same general brain layout. Wuut?! Obviously with varying degrees of each bit relative to individual animal needs.
Source, You Don’t Have a Lizard Brain. Original image, Northcutt, R.G (2002). Colour coding, Arseny Khakhalin.
What happened was, vertebrate brains relentlessly evolved over loads of independent lineages or lines of ancestry. ‘Lines of ancestry’ is a deceptive metaphor. Nothing evolved linearly. Evolution was not a neat and orderly progression of growth. It was through evolution that the same existing structures were modified, time and time again, independently, all over the shop, in all vertebrates. It was this melting pot of our animal ancestry that made way for "complex nervous systems and sophisticated cognitive abilities [to] evolve independently many times.” So many times, that they eventually gave us our brains as we know them today. In terms of their age differences then, Paul, we’ve actually had all three all along, and so have vertebrates too. Cool.
Also, while Pauly’s three separate regions ‘work independently’, IRL there actually is no neat division. In reality, our primal (Lizard), emotional (Mammal) and rational (Human) mental processing is the aftermath of neural activity in more than one of these three regions. It’s a mutual agreement, the team working together, that creates our human experience.
Team both
I stand with evolutionary biology in recognising that rather than a gradual implementation, these brain regions have always been there. It’s knarly that we share our basic brain structure with all other vertebrates too. Respect. Also, you can’t deny that our brains have millions of neural pathways, so to assume there isn’t chat going on would be fucking ignorant.
But, our guy Paul! I mean sure, he was way off with the age gaps and the segregated mental processing. Plus the poor man published his book in 1990, the same year fMRI came out. Embarrassing. We’ve know for decades his theory wasn’t biologically correct, but is the concept not quite a useful model at its core? I mean, we do know he was right in defining what each region does. Has Paul over simplified the brain? Obviously. But isn’t that what we use to understand complex things? Duh. And does it continue to offer insight about what goes on up there? Tick. Well then, I’m batting and cheering for both teams thanks, and no one can stop me.
