Does a Small Brain Make You Dumb?

Faith & Science Conversation
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Some of the most devastating causes of intellectual disability involve specific effects on the cortex. There is no point (and no hope of success) in reiterating the plain fact that both size (of the brain/cortex) and the network elements themselves are major influences on cognitive capacity.

If we’re talking about brains in long-gone ancestors, our two best tools are braincases (from fossils) and comparative genomics. Another tool is experimental: we have ever-improving animal models of cortical development in which we can study the genetics of brain development, especially the central questions about cortical development. Here’s a great example from last year:

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It’s a fine comparison (chromatin condensation compared to gyrification) and it’s true that gyrification (wrinkling/folding of cortex presumably to help fit more of it into the skull) seems to be necessary for extreme cortical expansion. (The biggest story of human brain evolution is extreme cortical expansion.) You might be interested to learn that intelligence in humans has been liked to gyrification of particular cortical regions. See article below, which, of course, begins by noting that intelligence is affected by brain size.

https://www.cell.com/current-biology/fulltext/S0960-9822(16)30197-X

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This whole post is of great importance…including the reason for our social structure stemming from big brains and also metabolic needs with gut size. Well put.

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“…wouldn’t necessarily matter…” in terms of achieving a high neuron count, but it is inaccurate to say it doesn’t matter at all. Volume and density are both factors to determine how much matter is in something. Imagine you were helping somebody load a moving truck, and you were looking around their house for items you could carry. You spot a huge unknown box. For all you know it may be full of really “undense” stuff (like styrofoam) and you might be able to pick it up single-handedly. But you probably don’t assume that and you rather expect you may have to get help or get a dolly. Why? Because size matters. Which is not to say that density does not matter. Obviously it does too which is why arranging your friend’s moving truck items in a long row according to their mass would not yield a perfect correlation to their size. But it would not give no correlation. In general the larger items like pianos and appliances will indeed be heavier than books and knickknacks. Why? Because size matters, and you know it (whether we’re talking about simple mass or neuron quantities). It is disingenuous of you to insist otherwise. So … yes. If you spot two boxes, one only slightly larger than the other, then it may be a nearly equal toss-up as to which one will be heavier because density (rather than size) will be the dominant factor in play. But when you stare at an appliance sized box and a tiny little jewelry-sized box, there is no doubt in your mind which is heavier - size alone makes you certain. Just as there will be no doubt between a primate brain or an insect brain which has more cognitive capacity. Density differences can only get you so far after all.

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Thanks for the answers! But the time stamp makes me wonder what your Saturday nights are like. Were you drunk texting us about science? haha.

The article on mutant ferrets has one of the coolest nature images that I’ve ever seen. It’s tempting to make it a wallpaper.

Stem%20cells%20in%20the%20brain
Caption: In a ferret’s developing brain, stem cells (green) send long fibers (green threads) throughout the cortex. These fibers shepherd new neurons to the right place – and ultimately help the cortex form its folded structure.
Credit: Walsh Lab/Howard Hughes Medical Institute/Boston Children’s Hospital

From the article:

Over the last seven million years, human brain size has tripled. Most of this expansion has occurred within the cerebral cortex. Indeed, in the mutant ferrets, researchers traced the cerebral cortex deficits to a type of stem cell called outer radial glial cells (ORGs). ORGs are created by stem cells capable of making all sorts of different cells in the cortex. Walsh’s team found that Aspm regulates the timing of the transition between these stem cells and ORGs. This affects the ratio of ORGs to other types of cells. Thus, tweaking Aspm can actually dial up or down the number of nerve cells in the brain, Walsh says, without having to change many genes all at once.

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Har! Not to worry, it was a unique Saturday night. I’m at the annual Evolution conference right now, sitting in a talk about sex-specific adaptation. Last night was at dinner with a young evolutionary biologist, along with both of his parents. There were 3 of us at dinner… think about it. :slightly_smiling_face:

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Your turn, Jay. Given your presumption here, now I’m curious to hear a rundown of just how your typical Saturday nights go. Should we be expecting any above-average amusement from you here on Saturday mornings? :beer::laughing::beer:

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Mervin, appreciated thoughts, as always.

But of course! That’s why I qualified with the word “necessarily”, of course! :wink:

I’m really not sure if I’m talking past everyone here or not. I have tried to carefully qualify my statements such that this much is of course granted…

I grant of course that there is some lower limit of size, wherein any much smaller and the necessary neurons simply could not be dense enough to have the required number or complexity to achieve said intelligence. As an organism approaches that lower limit, there would presumably be a certain decline in intelligence, and the converse as well, as it grows past that threshold, there would presumably be a corresponding increase.

But all that would apply, and can in theory be examined in modern humans as well. there is a certainly some certain size that would preclude normal human intelligence in those with dwarfism. There is some limit where, if human population approached that small size, the population would decrease in intelligence, cognition, communication, etc., depending on the part(s) of the brain affected.

But conversely, there would come a point where raw size simply wouldn’t add anything more, once the necessary number and arrangement of neurons can exist and function. Hence why it doesn’t seem an issue that our brains seem to be slightly decreasing at present.

And it doesn’t seem difficult to recognize that at certain sizes that we can observe, perhaps around 3-8 ounces, a human brain seems quite able to function normally. Thus it seems that somewhere around that size, the arrangement and required number of neurons can (and do) exist within a brain of that size. Whatever the lower limit of size that would start to affect intelligence, it appears to be smaller than 8 ounces.

Thus my observation is that, given the fact of normal intelligence in very small human brains, then apparently, the needed neuron count and arrangement to achieve said intelligence, indisputably, can and does exist in brains of around 3-8 ounces.

Let me offer one more example… if I can trust National Geographic, the diminutive human species Homo floresiensis had a “chimp-sized brain.”

I simply suggest it would be unwarranted and premature to infer anything about the intelligence or lack thereof of these relatives of ours based on their brain size. According to what I’ve read regarding archaeology, they seem to have exhibited all the other traits of intelligence of other homo species at that time period. If we can observe modern diminutive humans of similar, or even smaller brains, that have normal human intelligence, I simply see no reason why we should use as a starting assumption that Homo floresiensis must have been of lesser intelligence than any other variety of homo due only to the fact they had brains a third the size of ours.

Is this really such an odd position?

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We don’t need that simplistic and poorly documented factoid. We have extensive data from large samples, and we have clear evidence from awful conditions like microcephaly that show how devastating a greatly reduced brain size, and especially cortex size, really is.

We know that you’re wrong to draw that hard line, because we know so much more than this shallow emphasis on brain size can reveal.

For a person who is reasonably well informed, yes. I wouldn’t say “odd.” I would say “uninformed, and apparently forced by virtue of other commitments.”

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Is this the proverbial “Jedi” hand wave? “We don’t need to see his information. This isn’t the evidence we’re looking for. Move along…”

Regardless, if you want well-documented, ought we discuss anatomical hemispherectomy in adults? These are well studied and documented… adult humans who have had half their brain removed. They (now) have a brain quite literally (and documented as) being half the size as normal, and have been carefully studied and shown to have an IQ the same (or higher) than it was with their full brain. Certain functions are lost (sight in one eye, certain motor functions, etc.). But intelligence is well documented as not being one of them.

Thus, whatever it is that causes human cognition and intelligence is extensively documented as being able to function quite well in brains exactly half the size of normal human brains, no?

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Given the brain consists of two hemispheres, I would say this is a case of normal intelligence using just one hemisphere. Nature does appear to love bilateral symmetry and it appears it has given us a redundant hemisphere.

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I’m curious, Mr Fisher–what is the concern with brain size and complexity?
Why would it be concerning that the intelligence is directly correlated with size? Is it concern that we cover up the soul with naturalism?

Thanks.

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Agreed, amazing residency to be able to do that. only point remains that whatever the number and arrangement of neurons necessary to accomplish intelligence don’t need a 3 pound brain to organize. and of course were not comparing apples directly to oranges in this case, as evolutionary process had presumably already established this redundency, and a growing brain needed the additional space on both, not just one, side.

Point is only that whatever neurons are needed for intelligence don’t seem to need all that size in some form or fashion.

When I compare that with certain early humans, seemingly just as intelligent on the evolutionary scale as any other species of homo but with chimp-sized brains, and with modern humans that likewise have chimp sized brains but are clearly just as intelligent… all these things make me skeptical of any claims about intelligence across hominids based on brain size.

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People have two lungs and yet get along quite well with one. Does this mean evolution should have reduced the size of the lungs or stopped with they reached half their current size?

And it has been pointed out intelligence is the result of more than just a large brain. I think they call that a necessary but not sufficient condition.

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Of course not. Our current brainnsize does seem to be ideal. I’m a Darwinian skeptic, but I have no issue with the basic idea in itself that evolutionary process honed the biology until it reached an ideal. or that our creator made us this way as it is an ideal.

Again, I fear I’m not communicating well or talking past everyone. I absolutely agree that a brain of some certain size was of course a necessary condition for human (as opposed to chimpanzee-level) intelligence. At some small size it simply could not function as such. Only point is that while our current brains certainly seem ideal, a chimp-sized brain seems clearly sufficient to house fully functional human level intelligence. Can we all agree that far at least?

So when we discover a humanoid creature with a chimp-sized brain, i simply suggest we ought make no assumptions, based on brain size, about its intelligence or lack thereof. The scientists that have studied Homo floresiensis certainly seem to have followed this approach. Analysis of those beings’ intelligence was made based on archeological evidence irrespective of brain size. Everything I’ve read about them speaks of high intelligence in spite of brain size. They had brain size of Australopithecus, but no one seems to think this fact ought have any bearing on our estimate of their intelligence.

And thus to my only real observation: No one seems to suggest that Homo floresiensis needed for their brains to be significantly larger over their primate ancestors in order to “explain” how they could have such sophisticated intelligence.

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I will just interject here that evolution seems to be the master of “just good enough” and never actually achieves “ideal”. See the giraffe RLN.

Not to be disagreeable but a chimp-sized brain without the other changes associated with the modern human brain is not sufficient to result in human intelligence.

I may be wrong but I was under the impression that the other changes, the rewiring so to speak, have been identified as to the time frame they made an appearance. If this is correct then it wouldn’t be out of bounds to say to H floresiensis wouldn’t have modern human levels of intelligence. Do you have any evidence that would show they had the same level of neuron density, interconnections, and folding of the cortex as the modern human brain?

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This paragraph overstates what we know about cognitive function after hemispherectomy and conflates improvement (pre vs. post surgery) with an effect on cognition in general.

Uh, in short, no. It’s not extensively documented, in fact I cannot find a comparison of (for example) IQ in these patients compared to the general population.

But more to the point: you have chosen to focus on adult patients. Why? Is it because we know that in young patients (who are developing), loss of intellectual capacity is a major risk factor for the surgery? Is it because this fact tells us that loss of brain volume (roughly speaking) during development is, in fact, a huge problem for cognition and therefore weakens your argument, evolutionarily speaking, substantially?

Is this the well-documented phenomenon of psychological projection, wherein a person who is engaging in a particular psychological or ethical tactic ignores it in their own life then assumes that others are doing it to them? Yes. It is. The evidence that human brain growth has fueled cognitive capacity, in a runaway fashion, is overwhelming. This fact is damaging to some intellectually ludicrous historical narratives popular among particular (large) religious populations. So there is strong motivation to attempt to get fellow believers to ignore huge tracts of science, urging them to choose between childishly simplistic strawman extremes. The source of this motivation is not hard to understand. The end result portrays Christian belief as a rich source of intellectual dysfunction and badly eroded integrity.

That is the lesson of this thread.

During this discussion, there was never any claim (by me or others besides you) about whether size is the only thing that determines cognitive capacity. There was never any doubt that simplistic focus on EQ (for example) is unsatisfactory. You can see this in my very first response to you, in which I praised the overall theme of your initial comment. You have persisted in advancing a pitiful strawman that is so discordant with actual data that it makes you look hellbent on distracting yourself and others from a fact of the natural world. That, to me, is the last remaining question. Namely: why do you and others need to do this?

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You’re not being disagreeable. this is exactly what I’m saying!

In children there is still development happening, and from what I’ve read there is less danger in losing intellect since there are plenty of opportunities to recover. Adults seem to have more risk involved. Hence Adult brains seemed more relevant.

but I for one would be open to exploring with a completely open mind any counterevidence to my ideas.

As for such a study, I simply did a google search and found

https://www.mdedge.com/neurology/epilepsyresourcecenter/article/81897/epilepsy-seizures/hemispherectomy-may-be

Which specified “Forty-one patients underwent additional formal IQ testing postsurgery, and the investigators observed overall stability or improvement in these patients.”

I’m also potentiall wrong, but to my knowledge the rewiring in all extinct homo species (Erectus, etc.) is simply inferred based on other (archaeological) evidence of their intelligence. I believe all we have are fossilized skulls, from which we can only infer brain size, but we have 0 actual empiric evidence of actual neurological structure, no? The brains themselves are entirely gone, all we have are skulls.

I wouldn’t argue they had identical modern human levels of intelligence, but they clearly seemed to have something closer to us than australopithecines…

Notwithstanding the small brain of H. floresiensis , the discoverers have associated it with advanced behaviors. Their cave shows evidence of the use of fire for cooking, and Stegodon bones associated with the hominins have cut marks,[4][7] but some other sources doubt that H. floresiensis controlled fire and note that a small brain requires less energy.[47] The hominin specimens have also been associated with stone tools of the sophisticated Upper Paleolithic tradition typically associated with modern humans, who have nearly quadruple the brain volume (1,310–1,475 cm3 (79.9–90.0 cu in)) and 2.6 times greater body mass. Some of these tools were apparently used in the necessarily cooperative hunting of Stegodon by these hominids.[4]

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I was asking about a comparison of IQ (or similar measure) between the patients and the general population. You are citing data that shows that the procedure tends to improve function in the same person. Totally different question.

There is substantial risk of reduced intellectual function after the procedure. The risk depends on the pre-surgical situation more than anything else. Here’s one paper on the topic.

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Abstract:

Paleoneurologists analyze internal casts (endocasts) of fossilized braincases, which provide information about the size, shape and, to a limited degree, sulcal patterns reproduced from impressions left by the surface of the brain. When interpreted in light of comparative data from the brains of living apes and humans, sulcal patterns reproduced on hominin endocasts provide important information for studying the evolution of the cerebral cortex and cognition in human ancestors. Here, new evidence is discussed for the evolution of sulcal patterns associated with cortical reorganization in three parts of the hominin brain: (1) the parietotemporo-occipital association cortex, (2) Broca’s speech area, and (3) dorsolateral prefrontal association cortex. Of the three regions, the evidence regarding the last is the clearest. Compared to great apes, Australopithecus endocasts reproduce a clear middle frontal sulcus in the dorsolateral prefrontal cortex that is derived toward the human condition. This finding is consistent with data from comparative cytoarchitectural studies of ape and human brains as well as shape analyses of australopithecine endocasts. The comparative and direct evidence for all three regions suggests that hominin brain reorganization was underway by at least the time of Australopithecus africanus (~2.5 to 3.0 mya), despite the ape-sized brains of these hominins, and that it entailed expansion of both rostral and caudal association cortices.

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