Scientists re-evaluating relative brain size and mammalian intelligence | Hacker News Reader

Scientists re-evaluating relative brain size and mammalian intelligence

phys.org

61 pointsdnetesn76 comments

Why would relative brain size matter? If your brain were 75 percent of your mass but only consists of 1000 neurons, why would that be predictive of high intelligence over a brain that is 1% of mass, but 10 billion neurons? It has always seemed more intuitive to me that absolute brain size would matter far more.

Also...brain size might be a decent proxy, but there is a large amount of variation in nature for distribution of neurons. Your brain is a centralized cluster, but we have neurons all throughout our bodies too. With octopuses, neurons are far more heavily concentrated in the tentacles than mammals, and they certainly show extremely high intelligence.

If your brain were 75 percent of your mass but only contained 1000 neurons, then you would probably be the smartest sort of whatever tiny, simple organism you happen to be.

Maybe. I feel like there are probably a lot of uses for neurons which don't have that much to do with cleverness

That sounds plausible to me. I don't have a definition of "cleverness"/"intelligence", but I could believe that in many species most of the neurons are working on processing sensory data or controlling muscles, which isn't the essence of (human) intelligence: you do call a juggler "clever", but a human who is blind and mostly paralysed isn't less "intelligent".

I think it has been suggested that the "intelligence" of octopuses might be a side-effect of the huge amount of data processing that is required to control a body without a skeleton.

I've assumed it's because a larger body, with more cells, needs more neurons to monitor and model it, but it's not compelling.

The "law" is mere empirical correlation - e.g. you are smarter than a blue whale.

The fantasy that the baby spiders with encephalization quotients (https://wikipedia.org/wiki/Encephalization_quotient) off the charts (because their brains displace their digestive systems and partly fill their legs) are more intelligent than humans, appeals to me. I suspect raw intelligence doesn't require many neurons. But spiders aren't social.

Parrots are.

That's interesting

I've always felt spiders are different from other bugs. The way they move feels more calculated

Always wondered why spiders have their own phobia defined. I have probably a mild form of arachnophobia, they just give me creeps especially when moving.

Your comment makes me wonder if it is indeed related to their relative intelligence to other insects.

They are different. Most “bugs” people see are insects. Spiders are not insects.

Lots of spiders spins webs. This requires very careful stepping, so you are quite correct, their movements are very calculated. They have to step on a high wire, possibly vertically, while avoiding the sticky parts, getting knocked off, hit by prey, etc

Just want to throw a pretty interesting observation I read about a few months ago in an Edge essay, but can't find a source on - probably because no one is willing to publish or speak freely on it. Would like to find more information.

- There is a difference between average brain mass for human males and females

- male brains are about 15% larger by mass than female brains, after correcting for mass difference of the male and female bodies

Can we assume brain mass is equivalent to neuron count? Please find me a source!

It seems as if birds get a lot more intelligence from a given amount of brain than mammals manage.

But it is curiously limited. For example, ravens easily understand stuff hanging on the end of a string, and pulling the string up in stages to get it. But they cannot understand pulling a string on a pulley down to bring the titbit up.

("Mind of the Raven: Investigations and Adventures with Wolf-Birds" by Bernd Heinrich)

If you believe in "connectionist" models it's not how big it's how rich the cross connects are.

My complete non-scientists guess about brain size is that large brains are used for storing detailed visual information. So that animals that have to navigate and remember large territories, possible remembering the smallest details in wide open plains or tundras will have larger brains.

Those of us with aphantasia[0] might disagree with that.

[0] https://en.wikipedia.org/wiki/Aphantasia

Interesting!

moving further tangentially related, I wonder what the condition I have is called? I read the Assessment section of that aphantasia article https://en.wikipedia.org/wiki/Aphantasia#Assessment [1] and recalled that my brain has another condition, the inability to self-assess on a numeric scale. There are lots of interesting tests online, personality assessment, etc. and I can't complete them. I get 1/4 of the way in and suddenly the scales seem completely arbitrary and I have no way of deciding where I fall.

[1] just a meta footnote to say, aren't HN footnotes dumb, and isn't pasting the link right into the prose a less fussy way to make references?

> I get 1/4 of the way in and suddenly the scales seem completely arbitrary and I have no way of deciding where I fall.

That sounds a bit like Semantic Satiation, where words (usually when repeated) suddenly stop making sense. I have no actual information about that; your description simply reminded me of it.

Discovering I had aphantasia so late in life -- I'm 56 -- just reinforced the knowledge that everyone is wired differently and therefore approaches Life from different directions. I knew that, intellectually, but it was still kind of a slap in the face. [2]

[2] No reason for the footnote. I'm just trying to fit in around here. Maybe if I had multiple footnotes it would make more sense....

Let me guess at the conclusion: Brains that are better at finding patterns that increase survival success are the actual driving force for brain sizes and therefore we should not say that big brain animals are also intelligent animals.

Surprisingly, that was pretty much it.

Given that our higher cognitive powers come from a millimeters thick section the size of an unwrapped golf ball, brain volume doesn't mean much, and brain volume vs body size means even less.

Human assumptions about intelligence are debunked by facts.

I would argue its rather that the facts are too hard for society to handle. A neural network that predicts IQ from physiology/outwardly visible characteristics is certainly possible. Phenotypes exist and display specific behavioral and thought process traits. But to recognize it would be like staring into the sun

I've read some of your other comments and have the strong impression you're trying to make a comment tying IQ to race without actually saying the word outright.

I'm not going to say that you're morally reprehensible, but I do recommend reading about the Flynn effect. The variance in IQ between modern whites and whites 100 years ago is significantly higher than any measurable difference between whites and blacks today. In addition to this, the IQ of blacks is rising at a faster rate than the IQ of whites, and seems to be approaching convergence. Looking at changes over time, it seems that average IQ in large population groups is mostly a function of culture rather than genetics.

It's more so that I am in awe of the widespread brainwashing that I see in society.

Head into a college library, maybe into the biology or genetics section, crack a book from twenty years ago thats not well known. Read dissertations, there are bodies of knowledge inside universities and medical professions that aren't exposed to the public.

Bodies of knowledge about what? I agree with your respondant: your answers obscurity tends to imply you're avoiding saying what you think.

I'm under the opinion that there is widespread brainwashing, and more than trying to prove my point, I just cant help but comment on it.

Brainwashing about what? Be specific.

It's the same story in many fields, including non-controversial fields such as Biomedical Engineering (I only use this as an example because I studied it).

It's less about uncomfortable topics being actively covered up by nefarious actors, and more about bad ideas dying out naturally. The main reason we don't study correlation between race and IQ is because it isn't useful and doesn't explain anything particularly interesting.

I will just leave it at this:

For evolution to work, IQ has to be heritable, otherwise how did humans evolve intelligence? People who believe in evolution, but not in heritability of personality traits are living in a warped reality. I'm not that interested in proving my point, I'm just more shocked at how many people hold obviously false beliefs.

It's not an "obviously false" belief, it's one backed by good data and science.

Intelligence and other personality traits are of course heritable, but controlled by thousands of genes that are unlikely to shift significantly over the course of around 50,000 years.

Intelligence and personality are also a result of culture, and we've seen a 30 point increase in IQ scores in a single century, and a similarly spectacular drop in violent crime rates.

If you honestly believe racial genetics are a significant factor, you are either willfully ignorant or unable to engage in complex thought processes yourself.

  >  thousands of genes that are unlikely to shift significantly over the course of around 50,000 years.

Large evolutionary changes can happen rather rapidly with the right sustained pressures, certainly within a 50,000 year window.

Check out this plot of brain size over time[1]

If we can have such a dramatic increase in brain volume over a 500k year window, then we can absolutely have nontrivial changes to intelligence in a 50k year window.

  > Intelligence ... are also a result of culture

IQ differences between races may be a result of prenatal nutrition, but I struggle to believe that they're a result of culture.

The reason I doubt this is transracial adoption studies where the child is adopted out at birth to well-off white parents and tested at a very young age. So I can plausibly see how bad prenatal nutrition could have reduced this kids' IQ but attributing it to culture stretches credulity a bit, in my opinion.

(I could be wrong about that though, as the kids weren't that young, so it's plausible that there's some cultural influence from early school friends, but I still think that it strains credulity).

[1] http://aquatic-human-ancestor.org/anatomy/images/brain-size-...

> Intelligence and other personality traits are of course heritable, but controlled by thousands of genes that are unlikely to shift significantly over the course of around 50,000 years.

This sounds pretty convincing, but it seems to prove too much. Doesn't this also refute the idea of individual gentic differences in intelligence? Which we know exist due to the incredibly high heritability of intelligence?

Couldn't whatever allows these differences to exist not vary in strength depending on the emvironmental pressures sustained over thousands of years?

I don’t think many people doubt that there is a substantial hereditary component to the variation in intelligence between people.

So, presumably, you are talking about something else.

There are ways of categorizing people into different groups which do not cleave reality at the joints.

The further some such categorization is from cleaving reality at the joints, the more foolish one would have to be in order to be preoccupied with an alleged connection between the categories in such a mistaken categorization, and intelligence.

It may be necessary to acknowledge the possibility that heritable intelligence varies between demographic groups to counter accusations that society is engaging in systemic discrimination against [insert group] on the basis that disparities in achievement exist between that group and the general population.

But as it happens, rapid improvement in socioeconomic indicators were seen in the black population, which is the demographic group most commonly alleged to be a victim of systemic discrimination, BEFORE the rise of social welfare spending, and before the post-civil-rights-era racial victimhood culture (e.g. homicide rates among black Americans declined in the 40s and 50s), so the facts are actually quite supportive of the nurture side of the nurture vs nature debate on the causes of racial disparities.

> I don’t think many people doubt that there is a substantial hereditary component to the variation in intelligence between people.

I highly doubt it. Why exactly do you think this? Because some traits have been associated with intelligence?

Adoption and twin studies mostly. I believe the wikipedia article on heritability of intelligence is still decent enough to be a good starting point.

https://en.wikipedia.org/wiki/Heritability_of_IQ

This one? It does not indicate nearly the certainty that other commenters here do. Read it yourself, it's a good argument for what I'm saying. The GP characterized this scientific debate as settled, yet there is actually very slim evidence in that article for what is being claimed.

Why would it be surprising if among 1000s of the highest IQ individuals in some particular place, that there would be genetic similarities between them? It's completely possible that large groups among these people share a closer familial lineage far back into history that has influenced their present-day social and economic status, which are the factors that are actually responsible for developmental health and correspondingly intelligence, and so the genetic similarity is just a byproduct of the conferral of wealth and status between generations over a long period of time.

Why would the “what if inter-generational wealth” point impact what twin studies and such show? If the correlation between the measured IQ of monozygotic twins is substantially more than between other siblings, how would wealthy/poor ancestors impact that? Even if wealth had an impact on the probability of having twins, I still don’t see how that would result in the correlation between twins being more, even when raised apart.

I had other studies in mind (done in China) regarding that specific point, it's what I had assumed a lot of posters here were referring to because it's normally a favorite of people who are eager to jump to certain conclusions about genetics.

There are other problems with twin studies, most importantly that developmental health starts at conception which means that genetics are not the only thing that twins are sharing. Once again I'll refer you to Wikipedia for further criticisms of twin studies:

https://en.wikipedia.org/wiki/Twin_study#Criticism

The heritability estimates have also been done between biological parents, adoptive parents and their children and using comparisons between siblings and half siblings.

There have been many many papers from many angles on this over the years. The high heritability seems to be a well established fact.

The second paragraph in the article says heritability in our modern environment is very high, over 50%. What claim did you think was being made?

Your third paragraph makes me suspect you don't know how twin studies often work. The idea is that you measure the IQs of genetically identical twins and compare how similar they are to how similar non-identical twins are. This lets you isolate what is purely personally genetic.

> This lets you isolate what is purely personally genetic.

No it doesn't. Not at all actually.

https://en.wikipedia.org/wiki/Twin_study#Criticism

Maybe an actual geneticist can jump in here, but it's my non-expert opinion that you all are jumping to conclusions about a topic that you're not experts in either.

I am indeed not an expert in this topic. But "Not at all actually" is drastically overstating the case.

The very first critique is basically a nitpick. Yes, figures will be overestimated, but not taking into account air resistance when dropping your bowling ball off the tower of Piza isn't going to invalidate a conclusion that gravity is an accelerational force of at least 9m/s^2.

In fact, with the exception of the statistical critique by the guy with a giant axe to grind it seems mostly nitpicking. Dr Axe Grinder seems to mostly be critiquing the additive model, claiming it gives wrong results, but more recent papers (such as Polderman et al (2015)) seem to say that the additive model is mostly correct. And given the latter paper is a many-author meta-analysis rather than an emotionally charged rant by a single professor and is much more recent, I'm inclined to go with the latter paper.

Is it not well known that smart people tend to have smart children (though there is also regression to the mean).

I’m not talking about it being correlated with other traits, just intelligence itself being heritable. Well, I say “itself”, I imagine the same genes also have other impacts on other unknown things that are not noticed, because the interactions between genes is super complicated (I think?), but that’s practically the same as “itself”.

Why else would intelligence be attractive, if it weren’t heritable?

You've done all this supposed work and don't know the difference between heritability and genetic? Someone's favorite soda is hereitable too.

Anatomically modern humans have been around for 2.5 million years. Behaviorally modern humans only about 200k. Initially this was assumed to be evidence of a simple gene that created a breakthrough to language, culture, etc. Continuing archeological evidence is now strongly slanted against that, particularly evidence from microlithic industries. It now appears far more likely that behavioral modernity emerged organically as a primitive social complex. Different locations independently discovered different pieces of the "toolkit" but it wasn't until the full kit of critical tools came together that we have the breakthrough to complex societies.

Basically, your perspective on IQ and heritability is very cartoonish. I'd suggest spending some time on wikipedia. I'd also familiarize yourself with the classic rebuttal of The Bell Curve, which clarifies the difference between heritability and genetic determinism. Culture and social complexes are heritable.

This is a lazy and unverifiable response. Point at a specific book or search term if you want to convince people.

I'm not here to convince you of anything, more so to understand, maybe just a little, how people are being convinced of things that arent true. And how is it happening on such a wide scale. How did knowledge that was common 100 years ago, and then reaching back thousands of years, completely disappear or become so shunned.

Man, I’m doing a thesis on regulatory genomics. Just tell how exactly do you think I’m brainwashed and we can discuss that.

What things? You mention 100 years ago, so I found a quote from the debate of the Dyer bill, a piece of anti-lynching legislation, in 1921 - would you say you agree with it?

"Representative Percy Quin of Mississippi, spoke of lynch law, "Whenever an infamous outrage is committed upon a [Southern] White woman the law is enforced by the neighbors of the woman who has been outraged? The colored people of [the South] realize the manner of that enforcement, and that is the one method by which the horrible crime of rape has been held down where the Negro element is in a large majority. The man who believes that the Negro race is all bad is mistaken. But you must recollect that there is an element of barbarism in the black man, and the people around where he lives recognize that fact." (Holden-Smith, 1996, p. 15) "

I can only assume you are talking about the widely debunked 'race science' component of biology. Most of that was not only wrong, but explicitly constructed just to provide a scientific sounding excuse for slavery and associated practices, like widely cited 'studies' comapring IQs of black and white children in apartheid South Africa.

This is all not to mention that 'race' is not a biological construct, and virtually none of these studies actually check the genetics of the individual. They simply assume that black skin correlates with a particular genotype, without any reason to believe that thr genes for skin color are in any way correlated with any genes which could predict IQ.

It would make more sense to compare IQ across geographical locations, since geographical separation is a strong predictor of genetic separation as well. However, there you end up with huge confounding factors stemming from culture when trying to measure IQ.

The Flynn effect appears to be over. I agree with you on culture and genetics. Thomas Sowell is worth reading on this. We should stop categorizing on the basis of 'race' and think about cultural groups and the dynamics of their characteristics.

https://www.sciencealert.com/iq-scores-falling-in-worrying-r...

I tried to look up graphs of the iq gap over time but such data is harder to find than it was five years ago. I did find that the convergence of math scores seems to have slowed down or stopped though: https://upload.wikimedia.org/wikipedia/commons/5/57/NAEP-lon...

For the American "black"-"white" IQ gap itself (and I think it's very important to specify American, as conclusions about "blacks" in the USA are likely to be very misleading if applied to Botswanans for example) the I found a few seemingly contradictory studies, but it looks like the childhood gap is closing quickly (3+ IQ points per decade) while the adult gap is closing much more slowly (<1 IQ point per decade).

Do you have any good sources on this?

>it seems that average IQ in large population groups is mostly a function of culture rather than genetics.

Probably environment more than culture (unless you are counting environment in that). Just look at the effects nutrition during pregnancy has or the effects lead has on IQ.

Further, as I understand it, nurture are huge factors, if not the biggest. Poverty, abuse, pollution, zip code, etc.

Noob me: Sure, some fraction of IQ is hereditary for individuals. But there's no correlation between hereditary (genetic) IQ and group sizes larger than families, and mosdef none at population levels.

PS- Reprehensible is the nicest adjective I can think of for those retrograde beliefs.

IQ is verifiably a tool to exclude people based on race. It used inane things like vocabulary to deign intelligence. It has no merit and is not worth discussing.

This is a completely unscientific claim. IQ is extremely well studied by credible scientists and found to be a very reliable indicator of general intellectual ability, as reflected in competence in a wide variety of intellectual tasks.

You should read more about IQ and it’s failure to predict success. Like Nassim Taleb has said - IQ just shows you’re not dumb, not that you’re smart.

Which you are a perfect example of, I’m sure.

IQ is, by definition, how well you perform at solving a particular kind of puzzle. "Success" means fulfilling whichever criteria you have defined for a particular goal/objective.

IQ results are of some use in predicting how well children will do at school, i.e. what exam results they will get after being taught. That's usually a "success criterion" for the school, though not necessarily for the children, who may have other goals in life, e.g. becoming a footballer.

Players that want to play football in the NFL have to take an IQ test[1] and score decently well. Using a rough conversion[2], NFL teams require a minimum IQ in the low 90s to play, because players below that threshold are incapable of learning the plays[3]. So even for persons who want to play competitive football, a certain level of intelligence is extremely important.

I don't know much about soccer beyond pickup games, is it roughly as cognitively demanding as football at the highest levels?

[1] https://jobdescriptionandresumeexamples.com/10-important-fac...

[2] https://wonderlictestpractice.com/how-does-the-wonderlic-cor...

[3] https://clutchpoints.com/patriots-news-new-england-requires-...

Who knows? Maybe intelligence can be tied to handedness, gingerness (heaven forbid!), or body symmetry. A tricky thing to measure given difficulties in testing, lack of twin studies, and the like.

Admittedly it would be interesting to take a million people, give them various sorts of cognitive tests, do a DNA sample, feed in biographical details, and let 'er rip on a big ol' computer. There might be outrage and a need to twiddle knobs on the AI or there might be nothing noteworthy. Some Chinese researcher will let us know soon enough.

If you keep using HN for ideological flamewar we are going to have to ban you. We've asked you before to stop, and you've continued to do it. Please stop.

https://news.ycombinator.com/newsguidelines.html

Brain matter is metabolically very expensive to build, and I assume maintain, so it has to provide a significant evolutionary advantage per mm^3 to make it evolutionarily worth having larger brains.

If brain volume doesn't mean much then why is it so big it causes death in childbirth in humans?

There are people doing fine with half of it removed - https://www.inquirer.com/philly/news/local/20160214_20_years...

There’s a huge difference between “doing fine” in a modern society and in nature where she wouldn’t have survived. The article mentions her case is also rather atypical.

I believe the facts support a different conclusion:

(1) There's been a dramatic increase in our brain size over the last million years, is just a coincidence that we've also gotten way smarter?

(2) What about the high correlation between brain volume and IQ within humans?

(3) What would the evolutionary purpose be of supporting such an expensive organ if its size is irrelevant?

A possible answer would be that greater volume also implies greater surface area (modulo shape).

An OS only takes a small part of the computer's overall storage.

Imagine you bought one of those high-capacity SSDs off AliExpress, and unbeknownst to you, what you got is a small flash drive in an SSD enclosure, cleverly preformatted to report it's 10x as big as it is.

You install your OS on this drive, and happily do your work, but then you start realizing that some files are going missing, even though you're sure you've saved them...

Something similar may be happening with the brain - perhaps the core compute runs on the surface layers, but that doesn't mean non-critical functionality isn't occupying the deeper parts, and a person with less of those parts may not realize they have decreased capacity.

> Something similar may be happening with the brain - perhaps the core compute runs on the surface layers, but that doesn't mean non-critical functionality isn't occupying the deeper parts, and a person with less of those parts may not realize they have decreased capacity.

That's at once fascinating and existentially horrifying to me.

I need to know more...

It definitely happens at some point — I saw it in my mother when her Alzheimer’s progressed to later stages. She only seemed to be aware of her condition in the initial stages.

I have wondered if Alzheimer’s preferentially damages certain parts of the brain? And also if eventual death is unpredictable because it depends on when the damage interferes with autonomous bodily functions such as heartbeat, breathing, or gut peristalsis?

I wonder if instead of looking at relative size, relative energy expenditure of the brain relative to the rest of the body might be more useful.

That might assume brains all have roughly the same energy efficiency... Personally, I don't mind these heuristics too much, but we should remain focused on a teleological approach to intelligence. Size absolute or relative, energy expenditure, etc... I think the best brain is the one capable of producing the best solutions to complex problems, with the least possible disadvantages.

We should also consider a carbon tax on the less efficient ones

I find the 'expensive tissue hypothesis' (based on brain/gut ratio) quite persuasive.

See https://en.wikipedia.org/wiki/Expensive_tissue_hypothesis

From my layperson POV, I always assumed body/brain size ratio was simply a way of normalising the volumes to make comparisons between different species, and not an absolute proxy metric for "intelligence".

> The authors say that these complex patterns urge a re-evaluation of the deeply rooted paradigm that comparing brain size to body size for any species provides a measure of the species' intelligence.

The "deeply rooted paradigm" is not what it seems.

People aren't saying bigger brain size means X. They'd say something different next year, if that's what was necessary to fit their narrative. What they are really saying is that humans are more entitled to resources than other animals.

It's always been that way, whether the metric is brain size, skin colour, religion, ethnicity, nationality, or football team allegiance. Humans find whatever facts are convenient to support their own team.

When humans talk about "intelligence", what they really mean is entitlement to resources.

Brain/body ratio is not a measure of intelligence but a sign of evolutionary process probably favoring intelligence.

Not sure how to compare intelligence across species (one idea is length of focus time?), but it would be interesting to make a chart with crows, hornbills, people, and dolphins.

The hornbill is the most aware animal that I've seen in zoos - they actively watch the visitors, even beyond their enclosures.

This is the first time I've seen somebody domesticate them:

https://www.quora.com/What-are-your-thoughts-on-the-hornbill

How about this: beyond a few structures and functions, "brain mass" is mostly unimportant. The brain is like a tumor, the encysted symbiotic parasite fungal infection that made plants walk and then made them vote. The only meaning "brain to body mass" has, is how "fat" the critters lives were while they stabilized into new shapes.

I could probably wiff some more about domesticated animals and how placidity, or the ability to tolerate boredom, might be the biggest effect brains have... or most useful.

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