Paul MacLean's triune brain model — reptilian core, mammalian middle, rational cortex on top — is one of the most successful wrong ideas in neuroscience. Hannah Critchlow's piece in The Guardian traces the model's arc from respected hypothesis in 1959 to thoroughly discredited framework that nonetheless refuses to leave psychology textbooks, TED talks, and corporate training decks. The question she's really asking isn't anatomical. It's about why bad stories survive. The factual debunking is brisk and well-sourced. Reptiles possess limbic structures once deemed exclusively mammalian. All mammals exhibit neocortical features once reserved for 'higher' species. Behavioural evidence shows 'lower' animals solving problems, learning via emotion, and communicating in complex ways. Guy Leschziner of Guy's and St Thomas' hospital notes that while different brain regions do serve different functions, the layered-onion metaphor doesn't map onto evolutionary or physiological reality. Lisa Feldman Barrett, whose work on constructed emotion has done more than anyone's to dismantle the model, frames the brain as a dynamic, integrated prediction-and-energy-budgeting system — not a battleground between warring layers. Critchlow identifies a 2020 paper cheekily titled 'Your Brain Is Not an Onion With a Tiny Reptile Inside' (published in Current Directions in Psychological Science) as a key document in the campaign to dislodge the myth from education. That paper flagged two specific harms: it gives students a false understanding of how evolution works (additive layers, not branching trees), and it reinforces the idea that only humans can defer gratification or act rationally — a claim the animal behaviour literature demolished decades ago. The strongest move in the piece is Critchlow's diagnosis of why the model persists. It's not just that people love threes (though she opens with that charming observation about Goldilocks, the Musketeers, and Freud's trio). The triune brain tells us we're the pinnacle — rational minds sitting atop a stack of inferior predecessors. It reaffirms human sovereignty over nature and flatters our self-image as computational, orderly beings. The model survives because it's ego infrastructure, not because it's science. What the piece doesn't do is dig into the replacement frameworks with equal depth. Barrett's predictive-processing model gets a sentence; the broader embodied-cognition and active-inference literatures go unmentioned. This is a debunking essay, not a construction essay, and it knows its lane. For a Guardian column by a working neuroscientist promoting her book, that's a reasonable scope — but a reader looking for the positive vision of what the brain actually does will need to go further. The writing is clean, the sourcing is specific (named researchers, named institutions, named papers), and the concluding insight — that we need to update our story from one about human supremacy to one about shared animal cognition — lands without moralising. It's science communication doing what science communication should: not just correcting a fact, but explaining why the wrong fact felt so right.
