They really need to get out more, dissect a frog brain or something, if they’re still clinging to that triune brain nonsense. According to Salon, some psychologists still think that’s valid. The author summarizes an article that…
…addresses (and debunks) one of the most commonly-used metaphors in evolutionary psychology, the idea that the human brain evolved from lower life forms and hence has evolutionary remnants from those animals — akin to an onion with layers.
If you’ve ever heard someone speak of you possessing a “lizard brain” or “fish brain” that operates on some subconscious, primal level, you’ve heard this metaphor in action. This is called the triune-brain theory; as the authors write, the basic crux of it is that “as new vertebrate species arose, evolutionarily newer complex brain structures were laid on top of evolutionarily older simpler structures; that is, that an older core dealing with emotions and instinctive behaviors (the ‘reptilian brain’ consisting of the basal ganglia and limbic system) lies within a newer brain capable of language, action planning, and so on.”
Whoa. That’s silly. Of course, I have an edge: my early career in graduate school was spent studying the neuroanatomy and physiology of fish, and yes, they have a hindbrain, midbrain, and forebrain — all the pieces are there, they develop to different degrees in different lineages, and there aren’t linear ‘steps’ in evolution where, all of a sudden, there are jumps to whole new brain architectures appearing. Even before that, as an undergraduate taking neuroscience from Johnny Palka, I recall how insistent he was that we had to regard the brain of Drosophila as both existing and capable of sophisticated processing. (It’s true, some people think insects don’t have brains. They’re wrong.)
I wonder if this is another consequence of the belief in Haeckel’s erroneous ideas. I’ve skimmed through Dr Spock’s Baby Book, and was surprised to see how much rekapitulationstheorie saturates that book. The creationists love to claim that introductory biology texts teach it as fact, when my experience is that they explain how it’s wrong; they should look into the child psychology texts if they want better examples of a bad idea being promoted today.
So I had to look into the paper described in the Salon article. It’s titled “Your Brain Is Not an Onion With a Tiny Reptile Inside”, which is excellent. It gets right down to addressing the misconception from the very first words. The abstract is also succinct and clear.
A widespread misconception in much of psychology is that (a) as vertebrate animals evolved, “newer” brain structures were added over existing “older” brain structures, and (b) these newer, more complex structures endowed animals with newer and more complex psychological functions, behavioral flexibility, and language. This belief, although widely shared in introductory psychology textbooks, has long been discredited among neurobiologists and stands in contrast to the clear and unanimous agreement on these issues among those studying nervous-system evolution. We bring psychologists up to date on this issue by describing the more accurate model of neural evolution, and we provide examples of how this inaccurate view may have impeded progress in psychology. We urge psychologists to abandon this mistaken view of human brains.
Then Cesario, Johnson, and Eisthen name names. They show that this misbegotten misconception is a real issue by going through the literature and introductory textbooks.
Within psychology, a broad understanding of the mind contrasts emotional, animalistic drives located in older anatomical structures with rational, more complex psychological processes located in newer anatomical structures. The most widely used introductory textbook in psychology states that
in primitive animals, such as sharks, a not-so-complex brain primarily regulates basic survival functions. . . . In lower mammals, such as rodents, a more complex brain enables emotion and greater memory. . . . In advanced mammals, such as humans, a brain that processes more information enables increased foresight as well. . . . The brain’s increasing complexity arises from new brain systems built on top of the old, much as the Earth’s landscape covers the old with the new. Digging down, one discovers the fossil remnants of the past. (Myers & Dewall, 2018, p. 68) [no relation –pzm]
To investigate the scope of the problem, we sampled 20 introductory psychology textbooks published between 2009 and 2017. Of the 14 that mention brain evolution, 86% contained at least one inaccuracy along the lines described above. Said differently, only 2 of the field’s current introductory textbooks describe brain evolution in a way that represents the consensus shared among comparative neurobiologists. (See https://osf.io/r6jw4/ for details.)
Not to blame only psychologists, they also point out that Carl Sagan popularized the idea further in The Dragons of Eden. I hate to puncture the warm happy glow Sagan’s name brings to many of us, me included, but that was a bad book. Don’t ask an astronomer to explain brain evolution and consciousness, ever. I’m looking at you, Neil.
The authors illustrate the misconception well. It’s a combination of errors: the idea that evolution is linear rather than branching, that humans are the pinnacle of a long process of perfecting the brain, and that we possess unique cerebral substrates to produce human capabilities. It isn’t, we aren’t, we don’t.
Incorrect views (a, b) and correct views (c, d) of human evolution. Incorrect views are based on the belief that earlier species lacked outer, more recent brain structures. Just as species did not evolve linearly (a), neither did neural structures (b). Although psychologists understand that the view shown in (a) is incorrect, the corresponding neural view (b) is still widely endorsed. The evolutionary tree (c) illustrates the correct view that animals do not linearly increase in complexity but evolve from common ancestors. The corresponding view of brain evolution (d) illustrates that all vertebrates possess the same basic brain regions, here divided into the forebrain, midbrain, and hindbrain. Coloring is arbitrary but illustrates that the same brain regions evolve in form; large divisions have not been added over the course of vertebrate evolution.
I’m kind of disappointed that this obvious flawed thinking has to be pointed out, but I’m glad someone is explaining it clearly to psychologists. Can we get this garbage removed from the textbooks soon? Or at least relegated to a historical note in a sidebar, where the error is explained?
I guess that’s why reptiles are so well-known for being emotional
/s
I thought, broadly speaking, this was the simplified way to explain some phenomena like blindsight — is that not accurate?
An onion with a tiny dinosaur inside? If you could work out how to make the onion half-red with a black band separating the two halves, and made the dinosaur out of food, you could make a fortune offering it as a dish to Pokémon enthusiasts.
Well yes, but it is true that our cerebral cortex is uniquely large. It’s a matter of degree, not of kind, but it’s still a difference,
But, as everyone knows, it’s the olfactory lobe that is the seat of the soul, and it’s pathetically underdeveloped in humans.
You know, every species has a “difference”. It’s arbitrary which one is labeled as unique and special.
I recall Joseph LeDoux deconstructing the “limbic system” itself as not being a thing. I think Pinker effectively covered the dismantling of Paul MacLean’s triune concept in How the Mind Works. Old news.
every species has a “difference”. It’s arbitrary which one is labeled as unique and special.
Indeed. For example, observes the mildly deranged penguin, Lego bricks are unique in having being almost indestructible with a very nasty bite when one steps on them in the dark with bare feet. This is, she says, the real reason elephants avoid mice, from their great height, there’s not much difference between a plastic pest and a furry brick.
Well yes PZ, every species is unique, by definition. Species is a nominal category. But if you’re studying human psychology then you are interested in humans, including both the properties they share with other species, and the ways in which they are unique. That’s the whole point of psychology. Obviously we’re the only species that can talk, invent higher mathematics, and manufacture firearms, among other unique qualities. And it’s because of our uniquely large cerebral cortex. There’s no error in pointing that out. I’ll retract this when a shark gets a blog.
PZ, Haven’t you noticed that many of the people you mention on this blog act like mammals, e.g., xenophobic, as in us vs them, white woman vs dangerous black man? Or like reptiles e.g. Republicans. The actual anatomy and physiology of the brain is intellectually interesting to some people, but not nearly as important as how that biology is expresses outside the skull.
Just did a quick skim. Have it bookmarked for later. They suggest a paper I have buried somewhere at home: Reiner, A. (1990). Review: An explanation of behavior. Science, 250, 303–305.
But couldn’t pass up: “ Of course, asking about a specific species’ cognitive or behavioral repertoire can yield important insights about both evolutionary history and the nature of a species’ current phenotype (e.g., Tomasello, 2009; Tooby & Cosmides, 2005).”
Being:
Tooby, J., Cosmides, L. (2005). Conceptual foundations of evolutionary psychology. In Buss, D. M. (Ed.), Handbook of evolutionary psychology (pp. 5–67). Hoboken, NJ: Wiley
… only 2 of the field’s current introductory textbooks describe brain evolution in a way that represents the consensus shared among comparative neurobiologists.
Anybody want to set up a betting pool as to when the next such survey will be taken, and if/when the updated explanations will pass, say, the 30% level?
Human exceptionalism rides again – including in this comments thread. It as if each of the other animal species is incomplete, and only Homo sapiens, at the top of the pyramid just below angels, is capable of the full range of sensing, feeling, reacting, thinking.
Sounds to me a lot like a physicalised version of the Aristotelian model of the human soul – which consists of the uniquely human Rational Soul as well as the Motive Soul that is shared with animals and the Vegetative Soul shared with plants.
cartomancer@13, And — at least according to the mildly deranged penguin, who only just thought the idea up(? sideways?) and is now writing the definitive textbook — the all-overriding Cheese Soul. In cheese, this is a consuming passion to be ate. In penguins, this is the consuming passion to eat (such cheeses, albeit her current model seems to leave out that important qualifier). In others, it’s not possible, albeit the learned behaviour, eat cheese or be ate (as, or perhaps by, a cheese) is possible.
Ok I’m home and found the musty old Reiner article from Science that was recommended in the article Salon referenced. I’m seeing multiple problems across the board so hopefully I don’t lose the plot and remember them all as I type. I had read MacLean in original works so long ago. I had gotten then via ILL. I transcribed notes but screw trying to find those. I will rely on wikipedia to baseline MacLean:
https://en.m.wikipedia.org/wiki/Triune_brain
“The reptilian complex, also known as the R-complex or “reptilian brain” was the name MacLean gave to the basal ganglia, structures derived from the floor of the forebrain during development… The paleomammalian brain consists of the septum, amygdalae, hypothalamus, hippocampal complex, and cingulate cortex. MacLean first introduced the term “limbic system” to refer to this set of interconnected brain structures in a paper in 1952… MacLean maintained that the structures of the limbic system arose early in mammalian evolution (hence “paleomammalian”)… The neomammalian complex consists of the cerebral neocortex, a structure found uniquely in higher mammals, and especially humans.”
Anton Reiner in the 1990 article cited by ur-article (and likewise does Pinker in How the Mind Works) corroborates baseline: “…MacLean says three areas of the cerebral hemispheres evolved in succession- the R-complex (that is, the basal ganglia) in reptiles, the paleomammalian complex (that is, the limbic system) in early mammals, and the neomammalian complex (that is, the neocortex) in modern mammals, with each being retained in the evolutionary progression.”
And more here: https://blogs.scientificamerican.com/guest-blog/revenge-of-the-lizard-brain/
Which adds brainstem to R-complex and other nuance.
Well right away the ur-article gets confusing: https://journals.sagepub.com/eprint/TWK8BX6W2M4FFRTYXBZD/full
They say: “Many psychologists believe that as new vertebrate species arose, evolutionarily newer complex brain structures were laid on top of evolutionarily older simpler structures; that is, that an older core dealing with emotions and instinctive behaviors (the “reptilian brain” consisting of the basal ganglia and limbic system) lies within a newer brain capable of language, action planning, and so on.” They seem to be rolling the “paleomammalian“ limbic system into the R-complex here. Poorly worded at best. Later they improve with: “ MacLean later proposed that humans possess a triune brain consisting of three large divisions that evolved sequentially: The oldest, the “reptilian complex,” controls basic functions such as movement and breathing; next, the limbic system controls emotional responses; and finally, the cerebral cortex controls language and reasoning (MacLean, 1973).”
And the Salon article crows about nemesis evolutionary psychology (an easy target):
https://www.salon.com/2020/05/17/no-you-dont-have-a-lizard-brain-why-the-psychology-101-model-of-the-brain-is-all-wrong/
“No, this isn’t an article debunking fringe conspiracy theories about how the world’s leaders are a bunch of literal lizard people. Rather, it addresses (and debunks) one of the most commonly-used metaphors in evolutionary psychology, the idea that the human brain evolved from lower life forms and hence has evolutionary remnants from those animals — akin to an onion with layers.”
Yeah well the way the ur-article authors address evolutionary psychology comes across as positive to me. They for instance say: “In evolutionary biology and psychology, life-history theory describes broad principles concerning how all organisms make decisions about trade-offs that are consistent with reproductive success as the sole driver of evolutionary change (Daly & Wilson, 2005; Draper & Harpending, 1982)…” They also reference Tooby and Cosmides in a noncritical way.
And evolutionary psychologist Pinker was well aware of Anton Reiner’s 1990 article when he wrote How the Mind Works in 1997. I leave it to the reader to decide if Pinker was one of those naive evolutionary psychologists who would latch onto the triune brain idea and run with it uncritically.
Here’s an interesting take: http://people.wku.edu/richard.miller/triune.pdf
With these gems:
“ The fact of the matter is that all vertebrates undergo a tripartite division of the nervous system early in embryonic development. Three swellings occur in the developing vertebrate brain; the prosencephalon, the mesencephalon, and the rhombencephalon (Romer, 1970). Thus, in a sense, a triune division of the brain is not a set of stages but a common vertebrate trait.”
[…]
“Cory (2002) has proposed a needed correction: “the reptilian complex could be thought of, and perhaps redesignated, as the ancient amniote complex or even the early vertebrate complex””
Or perhaps coopting Neil Shubin’s metaphor our archetypally triune partition reflects our divergence from our inner fish.
Amazing exchange expanding on something related:
http://www.columbia.edu/~lep1/rry/w3410/LeDoux/NYT.Nov.96.html
“One of the biggest surprises from LeDoux’s work is that there may be no such thing as the limbic system — a brain structure that has been supposed to underlie emotion and motivation. All students are taught about the limbic system, LeDoux said, “but in my opinion, it’s no longer a valid concept.”
Anatomists like LeDoux “are funny people,” said Dr. Paul MacLean, the scientist who coined the term limbic system. “They think only about fear and rage,” said MacLean, a senior researcher at the National Institute of Mental Health’s Neuroscience Center in Washington. “They forget love, which more than anything else accounts for the development of the human race.” The limbic system is still a valid concept, he said, adding that efforts to discard the idea were ill-founded.”
Fast forward many years: https://brainsciencepodcast.com/bsp/2019/161-ledoux
“In his new book The Deep History of Ourselves: The Four-Billion-Year Story of How We Got Conscious Brains respected neuroscientist Joseph Ledoux reaches two controversial conclusions. He say that emotion evolved after consciousness and that emotions are not the product of natural selection. We explore these ideas and much more in this month’s episode of Brain Science (BS 161). This is the second in our four part series about the neuroscience of consciousness.
We also discuss why the term “Limbic System” has become outdated and should be avoided.”
“Human exceptionalism rides again – including in this comments thread. It as if each of the other animal species is incomplete, and only Homo sapiens, at the top of the pyramid just below angels, is capable of the full range of sensing, feeling, reacting, thinking.”
This is not what anyone said. Obviously metazoans in general can sense, feel and react, and think in some way. But only one can use syntactic language (some can be taught rudimentary language by humans but don’t use it in nature), do scientific research, write novels, build electronic machinery, build flying machines, travel too the moon, and write comments on blogs, among other unique capacities. It seems more than perverse to deny this.
@17- cervantes
I think with humans (us), being humans there is a problematic tendency to project our values into the surrounding world and classically (or medievally?) impose a hierarchy or ladder of progress. That said there is a dialectic tension best represented by contrasting the radical views embodied in Gould’s Modal Bacter, where prokaryotes still rule the Earth and the Teilhard/Huxley(Julian) noospheric layer view. Are bacterial mats (or ancient stromatolites) or the internet (thinking layer) more important in natural history? Borrowing a goofy progressively projective labeling scheme: we see here the alpha and omega of the popular collective consciousness. But Teilhard had a theistic goal in mind (Jesus), which might help explain how the pesky notion of special creation still influences popular conceptions that transform a phylogenetic shrub into a ladder with us nearing top rung. Just looking at us as a fortuitously well endowed but insignificant twig contradicts the impulse to constructing a self-serving meaningful narrative that implicitly cheats death (sensu Becker).
Dammit, I was perfectly happy exploring Spencer and the popular attribution of social Darwinism cast on him and Sumner and PZ throws raw meat my way. GRRR! Now I am distracted.
As a consequence of my rabbit hole meanderings I now have Joseph LeDoux’s The deep history of ourselves (a bill will be forthcoming). Anyway (I skipped to the more relevant parts) he lays out the A-P hoxology that connects us to arthropods and gets really smitten with the bauplans of organisms. He has short chapters called “Ludwig’s Ladder” and “The Triune Temptress” that pertain to the OP and works cited. Apparently Paul MacLean was merely putting his own stamp on the ideas of Ludwig Edinger.
https://en.m.wikipedia.org/wiki/Ludwig_Edinger
Fascinating stuff. LeDoux is definitely a partisan given his views on the limbic system. LeDoux says: “MacLean took Edinger to heart and described the mammalian forebrain as consisting of three conserved evolutionary partitions—the reptilian, paleomammalian, and neomammalian complexes.”
And charitably: “Edinger and MacLean were both pioneering thinkers and researchers, and did a remarkable job formulating ideas on the basis of what was known in their day. They stimulated a tremendous amount of research.”
Insects have a brain? I thought their nervious system is composed ofna single ganglion. Maybe what I learned in intro to entomology is outdated. Maybe that sole ganglion is enough.