Evolution may have capped human brain size to balance energy costs and survival

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u/sailingtroy 17h ago

I mean, it was either that or bigger pelvises.

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u/Vio_ 16h ago

Bigger and rounder. We also made our skulls squishier and stalled full maturation for a almost 20 years. We can't even walk for almost a year.

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u/leanderr 16h ago

I want to emphasize your point of how energy investment after birth is a really underrated factor.

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u/ShyguyFlyguy 11h ago

Yeah most mammals pop out ready to walk and run. We're completely helpless for another year or two

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u/BwenGun 10h ago

Which is fascinating in of itself, and I do wonder if it's potentially another explanation for bipedalism and the switch to a less arboreal lifestyle our ancestors made. Most other great apes also give birth to young that take time to mature enough to safely get about on their own, but they're usually strong and coordinated enough to instinctively cling onto an adults fur/skin from an early age so that their carer can move through the trees utilising both arms. Bipedalism means the adults can hold smaller infants without the infants assistance, which means less developed infants who can't hang on on their own are more likely to survive to the point where they can start moving on their own.

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u/TheBlackCat13 7h ago

Bipedalism appears to be the ancestral condition of apes. Chimpanzees and gorillas independently evolved knuckle walking.

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u/Ferretanyone 7h ago

So they walked upright first?

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u/Darkhoof 9h ago

To make it clearer, most prey mammals are like that. Predator mammals cubs are more vulnerable.

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u/Lost-Basil5797 9h ago

That would make sense, from an energy conservation point of view. Why invest energy in the infant's ability to flee from the get go if the parents can naturally provide protection already, which predators can, almost by definition.

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u/meatflavored 7h ago

This almost seems like an unnecessary distinction, but I wonder how much the safety of the predator cub would be a result of parent’s ability to defend it versus the lack of predators for the predator. I’m assuming that predator species generally have few natural predators themselves.

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u/MarqFJA87 4h ago

Predators generally avoid other predators because the nutrition vs. injury risk ratio is not worth it. They mostly clash over kills and territory.

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u/Mithrandir2k16 8h ago

A year or two? In this society? Make it 25!

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u/MarqFJA87 4h ago

And the ones that don't pop out so ready manage to finish developing the physical and mental capacity for locomotion within a handful of months at most. Twice as fast as is at minimum.

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u/Masterpiece-Haunting 59m ago

We really really missed out by not ending up with the chloroplast upgrade the plants and protists can get. It’s literally nigh unlimited energy from a nuclear reactor in the sky.

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u/Omni_Entendre 15h ago

There are some theories out there that our unusually slow development also leverages human psychology, such that the parents are more likely to invest resources into the infant if they have already invested a lot.

The sunken cost fallacy, in other words. By infants developing slower, those slow genes ended up having a higher survival (fitness) over other genes because they co-opted human psychology.

Just a theory though.

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u/littlest_dragon 13h ago

I once read that one reason marsupials got outcompeted and went extinct pretty much everywhere placental mammals showed up on the map had to do with their skull structure.

Basically marsupials give birth to embryos who then continue gestating in their mother’s pouch, so their skulls can be solid, since they are still tiny when the mother gives birth. This restricts the size their brains can grow later in life.

When placental mammals give birth their offspring are a lot bigger than those of marsupials, so their skulls had to evolve to be more flexible during birth. That same adaption also means that their braincase can grow larger over the course of their lives, allowing for larger brains, ultimately leading to more complex and adaptable behaviours compared to marsupials competing for the same ecological niche.

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u/nikolai_470000 11h ago

The main thing I gleaned from this is that we were basically a handful of evolutionary accidents away from Kangaroo being the dominant life form on Earth rather than humans.

Darn and we were so close, too.

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u/KaerMorhen 1h ago

I wanna see that alternate reality.

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u/nevergoodisit 9h ago

Thing is that a few marsupials (specifically the fossorial species like marsupial moles and wombats) have brains that are in line with placental mammals of similar size and lifestyle. That constraint is clearly removable.

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u/Elrond_Cupboard_ 15h ago

Not with that attitude.

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u/R3v3r4nD 13h ago

Why rounder? Why not consider that coneheads is an evolutionary possibility?

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u/ZorroCheese 11h ago

Simply because brains need to be protected and the curves of our brain allow impacts to slide off. If you had a conehead it would be easier to damage your skull and your brain.

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u/farfromelite 12h ago

That's the mums as well as the babies.

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u/darkwoodframe 3h ago

This is why I told my wife if our daughter isn't walking by 9 months, it gets fed to the dogs and we try again. I will not be party to the deevolution of our species!

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u/aVarangian 10h ago

you may not like it, but this is what peak brain bigness looks like

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u/Perunov 15h ago

Besides, brain became large enough to give all the needed advantage, there's no point in selecting even larger one at that point.

If we suddenly got mega-smart predators I'm sure a new spiral of evolution would have happened if we were delicious enough.

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u/blolfighter 13h ago

Also, brains are resource hogs. A large brain requires a lot of energy and oxygen, so unless it pays for itself it doesn't increase the organism's overall fitness. Our combination of complex social structures and excellent manual dexterity lets us get the most out of our oversized brains.

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u/IsthianOS 9h ago

Isn't it something like 20% of your calorie burn is for your brain

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u/alexq136 8h ago

bigger brains did not help other mammalian species escape unscathed from the expansion of people over the world (e.g. elephants, extinct apex predators, orcas, whales and their relatives)

and stuff made possible by our brains do not necessarily stem from the size or neuron count_only) in isolation - having all these "perfected" adaptations (e.g. sapience, civilization [as the consequence of innate socialness and the other things in this list; it does not exist at the individual level but rather only ecologically], language, very fine motor control) only rising to their peak in one single extant species is rather unpleasant statistically (non-modern human species we've "dealt with" would have served as important benchmarks for these functions, but ... they're gone)

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u/blolfighter 4h ago

"Large brain" was shorthand for "large relative to body size" as I was on my phone at the time. As you point out, elephants have about three times as many neurons as we do, but this still puts us well ahead of them compared to body size as elephants are huge. An elephant's brain apparently weighs around 5kg (four times the weight of a human brain), which also means their brain takes up a far smaller portion of their total weight (and presumably total resource consumption) than ours.

It is of course patently obvious that brain size or neuron count in isolation doesn't decide intelligence. Parrots and corvids have fairly small brains (in many cases, their entire body weighs less than a human brain) but are famously intelligent.

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u/alexq136 3h ago

as in humans most of the energy consumed by a "working" or "resting" brain is spent on maintenance rather than thinking (or other kinds of functions)

there was a fMRI study00319-X) (full PDF available from a link on google scholar whose title links to this article's page) published around a few months ago in which the PIs found that the oxygen consumption is shuffled across the brain to let the most active regions ingest most of it - so overall the human brain is literally hardwired (even if through its blood supply and gross anatomy and vascular/cellular signaling) to consume a fixed quantity of energy in all "states"

(this article splits their estimates of ATP consumption into "82% for nonsignalling purposes" and "18% dedicated to signaling" so net brain power use is closer to 3-5 W for actively working as a brain at rest (it changes a bit (+5 %, so from 20 W to 21 W or in any case proportional to these values for a different baseline) when "intense thinking" happens - but it still barely causes a rise over the whole brain), as opposed to organs with less spatially differentiated activity (e.g. the liver); they also provide a quirky ordering of various processes in terms of how much they activate various brain regions, with reading at the higher end (e.g. salient artificial patterns are expensive to recognize and to interpret) but general visual processing at the lower end (e.g. shape/color vision is inhibitory; faces are easier to process with dedicated brain anatomy (that feeds from the visual regions) than less specialized sensory processes etc.))

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u/aVarangian 10h ago

The average redditor is also proof of brain size and intellect being unlrelated

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u/inspectoroverthemine 8h ago

Eventually the brain got large enough it could bypass natural selection!

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u/kigurumibiblestudies 16h ago

Can't help but feel like we could have chosen better

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u/clubby37 15h ago

The "bigger pelvises" option is neutral for men, but highly detrimental to women. It would make running nearly impossible, which would be unpleasant but manageable today, but would quickly prove fatal to our ancestors who were not yet at the top of the food chain. The benefit of a bigger brain would have to outweigh the cost of more baby-makers getting eaten, and it didn't, so nature founds its equilibrium at our current morphology.

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u/kigurumibiblestudies 15h ago

That's just your big brain talking, of course it would say that

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u/clubby37 15h ago

Guess it's big enough already, then -- no need to adjust pelvis size!

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u/shitarse 9h ago

Another win win

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u/cloudncali 15h ago

I won't forgive what they took from us.

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u/R3v3r4nD 13h ago

Mmm… bigger pelvises…

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u/OpenRole 13h ago

Except that assumes that the grown size of our brain is solely dependant on the birth size. Our brains mow take longer to reach maturity and brain size is still increasing. Our adolescence phase could be extended to allow more time for brain development. This also makes sense as humans are getting married and starting families at 30, as opposed to the 20 of our ancestral history

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u/Ashamed-Status-9668 1h ago

I suppose the non coding DNA that tells the brain / skull to keep growing could be left on a bit longer to compensate. We might need a couple years to even talk.

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u/prsnep 17h ago

Surely, this is true in all organisms. If it wasn't for energy consumption and weight, larger and smarter brain would always be selected for. Unless if a high enough intelligence has a negative impact on fertility.

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u/stockinheritance 17h ago

It's obviously true. Domesticated animals have less brain mass than their wild relatives because they don't need to be assessing threats and navigating their survival as much, so there's no advantage to having bigger brains.

Brains are calorically very expensive, so just having what you need is best for survival.

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u/[deleted] 16h ago edited 16h ago

[deleted]

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u/LEPNova 16h ago

Well put, I appreciate your insight

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u/Corsair4 15h ago

yet use a completely novel, and more efficient brain structure called the nidopallium caudolaterale, counter to our pre-frontal cortex... achieving similar cognitive abilities with more energy efficiency.

Do you have any peer reviewed sources that define efficiency in this case, and compare it across species?

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u/BaronOfTieve 15h ago

Not a scientist in the field, but I have a keen interest in neuroscience and attended an open lecture after graduating highschool to sus it out. The professor specifically explored reaction time and intelligence across species, specifically looking at fruit flies, spiders, ants. At the end I asked “what determines intelligence in a species’ brain”, to which he replied “it all comes down to the conectome. Obviously gray matter matters to an extent, for instance a pea sized brain can’t perform executive functions, but once you pass a certain point, it all comes down to how efficiently information in the form of electrical signals can get from point A to point B”. So my suggestion would be to look at studies of connectomes across species.

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u/Corsair4 15h ago edited 14h ago

I have a bachelor's degree in neuroscience, and spent 4 years in an electrophysiology lab studying plasticity mechanisms in mice cerebellum. I have 2 first author publications, and some middle author credits from my time there.

I'm not going to say I'm a subject matter expert - certainly not compared to the PhDs and professors that are likely around here somewhere - but I'm absolutely confident in my ability to read primary research.

There's 3 problems I have.

1) I have never seen a study indicating that X animal performs broadly as well as a human past childhood or early adolescence in cognitive tasks. Hyper specific things? maybe. But in a general sense? no.

This ends up being an inherently skewed comparison because - people don't stop learning after childhood. We're in a community where people are actively learning for literal decades in their fields. So saying that X animal is as smart as a human because they can match children and maybe highschoolers in specific tasks isn't terribly convincing, given that children aren't the pinnacle of human intelligence.

So the idea of "similar cognitive abilities" is problematic, because the tasks that people refer to are almost certainly on the low end of human cognitive abilities.

2) "efficiency" as a word, is exceptionally broad. To the point of being useless without further clarification.

Are we talking about how much metabolic support a single neuron needs? How much metabolic support the entire CNS of a crow needs? Are their channel proteins and firing mechanisms less energy intensive? Do they accomplish tasks of similar difficulty with less neuronal activation? Are the conduction speeds faster? These are all things that need to be measured, which means someone needs to have done research on it to claim anything about efficiency.

3) "efficiency" is not the best predictor of capability. My laptop is extremely energy efficient, compared to the compute cluster on campus I used to remote into. But being energy efficient doesn't help if I just need more computational power for the task at hand. It's entirely possible that a crow is more "efficient", as measured by one of the metrics I outlined in point 2, but if the crow's capability for problem solving has a much lower ceiling, then being more efficient doesn't help.

As a side note, I've got enormous problems with the idea of dividing intelligence into grey vs white matter like that, because that's just not how neurotransmission works. White matter is myelinated axons - axons need to synapse onto something to actually do anything. They synapse onto soma and dendrites, which are considered grey matter. No neuroscientist worth a damn will tell you that soma and dendrites aren't important for learning and memory. Plenty of modifications for learning and memory occur in the grey matter side of things, rather than the presynaptic side of things. Trying to generalize a split like that is incredibly inaccurate.

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u/BaronOfTieve 14h ago

I agree with all those points I also think I’m obliged to reiterate that I’m not a scientist in the field and was just giving a suggestion based off what one professor told me. Also at what point did I compare measures of child intellect with animals? I have an almost if not completely identical standing to you on every one of those points you mentioned.

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u/Corsair4 14h ago

Also at what point did I compare measures of child intellect with animals?

I never said you did.

I was expanding on my issues with OPengiun's comment, where they specifically say

achieving similar cognitive abilities with more energy efficiency.

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u/BaronOfTieve 14h ago

Then here’s a thought, maybe reply to the guy you’re actually responding to?? Did you seriously expect to have a discussion with me about someone else’s statement without even knowing if I agree with that person or not?

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u/Corsair4 14h ago edited 14h ago

Then here’s a thought, maybe reply to the guy you’re actually responding to??

If you're going to bite my head off about it, fine:

My initial comment was asking for a peer reviewed source about efficiency between species.

You responded with a random professor's 2 sentence opinions on intelligence.

Here's a thought - maybe consider if you actually have something on topic to contribute before responding?

You came into this conversation with something - frankly - irrelevant to the comment you replied to, AND you seem to take issue with me expanding on those ideas anyway. What sort of conversation were you looking for anyway?

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u/[deleted] 13h ago

[deleted]

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u/Corsair4 13h ago edited 12h ago

No one is implying that here.

You literally said "our pre-frontal cortex" and "similar cognitive abilities" in your top level comment.

Given that the only organisms in that comment are birds and humans, was I not supposed to take that as a clear comparison to humans?

I'm guessing you actually meant mammals in general, or some category of apes, but I still don't know. Because neither this comment, nor your other sourced one clarify that.

And if you were worth your salt, you'd know that fallacy of ethos is... not quite tasteful.

It's not a fallacy of ethos. I never said anything against the guy who commented or their qualifications. What I did do, is specifically argue the professor's 2 sentence summary, which I think is fundamentally wrong, and I clearly explained why.

I'm not the one who brought up qualifications first, the other guy did by bringing up a professor as an authority figure in the field. And I specifically argued against the content of the comment rather than just relying on my qualifications. That's not a fallacy.

Your initial comment was an anecdotal evidence that applies to basically any vertebrate - you can gain the trust of most things by feeding them. Anecdotes are also not tasteful.

I linked to you the DOI's of a few studies you'd quite enjoy on this topic.

Yeah, about those. It'll take me a bit longer to read them properly, but I'm sure you know that none of them actually address energy efficiency, which is what you very specifically claimed.

Your first source is about neuronal density. Neuronal density is not energy efficiency. Most of the energy in a mammalian neuron goes to maintaining ionic balances necessary for neurotransmission, for instance. That function is independent of neuronal density. It's certainly possible that birds are making efficiency gains somewhere, but that source is not talking about that.

Your second source is talking about a distinct structure that performs some similar functions to mammalian PFCs. This is also not energy efficiency, and nothing in that source gets at energy efficiency, so far as I can tell.

And your last source is talking about parallel evolution between avian mammalian CNS. This is also not energy efficiency.

You linked me 3 very interesting sources that establish similarities between avian and mammalian CNS.

What none of those sources establish is anything even hinting at energy efficiency differences.

You specified energy efficiency, not me. You're trying to reframe it into neuronal density and connectivity, which were never part of my initial question. Who are you arguing against here?

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u/Rich-Anxiety5105 15h ago

This is why i read reddit. Thank you good sirs

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u/BaronOfTieve 14h ago

My pleasure

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u/[deleted] 15h ago edited 15h ago

[deleted]

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u/-LsDmThC- 15h ago

Bunch of Lamarckism in this thread

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u/grahampositive 15h ago

Y'all need to go read origin of the species

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u/abu_nawas 15h ago

No? It would likely result in genetic drift. I don't think domestication actively breeds boredom tolerance.

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u/monsantobreath 13h ago

Unless if a high enough intelligence has a negative impact on fertility.

Going back to your home town kinda observational science.

People who aren't very smart reproduce a lot. I wonder how much that'd a modern phenomenon vs a durable one found across time in humans.

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u/Hour_Baby_3428 12h ago

This. Once something is good enough, evolution stops being a driving factor.

Idk if our current observations translate well to prehistoric levels of intelligence, but at some point you are smart enough to feed yourself and survive and that’s all it takes.

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u/monsantobreath 12h ago

And intelligence is also shaped by class ie access to resources and encouragement to increase intelligence so if some ancient humans were more egalitarian in small enclaves were people collectively more intelligent (more nutrients, better development, more sharing privileges that give higher status people intellectual advantages) and so perhaps less driven to reproduce to maximize benefit to the family?

People have lots of kids when they're insecure because of higher death rates for kids. Better resources equals healthier kids and less reliance on labour of the family to secure resources.

I'd read about thag stuff for a couple hours.

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u/prsnep 4h ago

I wouldn't be so sure that egalitarian societies lead to higher IQs. All selection pressure on intelligence is removed, and the void is taken up by expansionist ideas and cultures.

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u/Mickmack12345 7h ago

The thing most people neglect is how overpowered our ability to record information is, which stems from the ability to create language rather than random sounds to indicate a variety of things we can make extremely precise sounds to not only mean things we see but concepts and ideas we can’t. Then the ability to write those sounds down and physically record them gives our future generations even higher chance of utilising knowledge we already have and become even more intelligent and capable of survival, without really needing any of the original survival instincts we evolved to have

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u/HarmoniousJ 14h ago

Unless if a high enough intelligence has a negative impact on fertility.

Yeah, about that...

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

https://pubmed.ncbi.nlm.nih.gov/25131282/

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u/genshiryoku 10h ago

This is now outdated as fertility is dropping among every single demographic in the world now. It was seen as the "idiocracy effect".

It's just that those effects were first visible in demographics with higher IQ like East Asian countries and White countries, causing a correlation that wasn't causative.

We now see a similar drop globally regardless of intelligence.

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u/prsnep 6h ago

I think it's more correlated with religion rather than race or IQ now.

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u/genshiryoku 1h ago

It used to a couple of years ago, but that correlation now has broken down as well as Latin American and Muslim countries experience rapid fertility rate decline over the last 5 years.

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u/prsnep 1h ago

If you look at the west, Islam is growing and pretty much all others are shrinking. I would think the association persists.

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u/joshTheGoods 8h ago

It's just that those effects were first visible in demographics with higher IQ like East Asian countries and White countries, causing a correlation that wasn't causative.

Huh? Demographics with higher IQ? This is pretty clearly about socioeconomics, education, and decline in mortality rates (or things like 1-child policy in China) not "higher IQ" east asian and "white countries." What does that even mean? Are eastern european countries that lagged behind in fertility drops included? How about Ireland?

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u/genshiryoku 1h ago

I think you missed the point of my post. The fact that it isn't correlated with IQ or intelligence as every demographic under the sun now experiences rapid fertility drop. It was just a pattern first observed in high IQ countries like my nation of Japan which contaminated studies into linking IQ to fertility which was a false causative link.

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u/Fuzzy974 16h ago

That was my though exactly. Most species would gain by being more intelligent as long as that doesn't come up with a cost higher than what's to gain from intelligence.

But again we see here a study that state the obvious, which is something we see more and more in Science nowadays.

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u/llmercll 15h ago

Lambda lambda lambda

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u/Maleficent_Twist3060 15h ago

Might be stupid thing to say, but in most parts of the world today, wouldnt the abundance of food and therefore energy bypass this, allowing brain sizes to continue increasing?

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u/wassuupp 11h ago

Yes but food surplus from civilization existing hasn’t existed long enough to have this impact. We would need another 100k years to even start seeing a noticeable difference in brain size most likely

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u/MonkeManWPG 8h ago

We've also kind-of solved selection pressure. There's nothing that stops less intelligent people from reproducing, so there's nothing to push future generations to be more intelligent.

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u/linkdude212 3h ago

Disagree. Society itself forces everyone, on average, to be more intelligent, and as society becomes more advanced, those pressures will increase and continue to drive the development of intelligence. Civilization is the modern human's environment.

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u/MonkeManWPG 3h ago

Have you met a member of the public? I'm somewhat serious here, there are some people with kids who have definitely not been prevented from reproducing by their lack of intelligence.

Our society even does somewhat of the opposite - particularly intelligent people are often in more demanding careers and therefore less likely have (as many) children.

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u/linkdude212 2h ago

I hear you. I personally believe that many, many humans do way too much cognitive offloading to an authority because thinking take a lot of calories. To the point where they are essentially highly trained animals with the training to survive their environment => Go to work, get paid, use pay to provide food and shelter for self and offspring. When the authority tells them things, they do it —to the wider world's detriment— in order to maintain the relationship of cognitive offloading.

That said, society is more advanced in every way and demands more ability from its members on average: in part, thanks to the work of the highly intelligent and capable. Thence, over time, I hypothesize that members of society will become more intelligent on average.

I think the lack of intelligence you are seeing is a clarifying of where the lowest common denominator is —and it is much lower than expected, at least for me— because their society (environment) is both giving them more opportunities to make better choices —and they don't— as well as demanding more from them.

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u/FrighteningWorld 10h ago

Is that true though? Most dog breeds came to be in less than a thousand years. I suppose it will come down to how beneficial increased brain size becomes to your ability to reproduce. If people with bigger brains thrive then chances are you will see a blooming of them. The opposite could also be the case, that modernity makes it so brainlessly easy to survive that we have no use for extra neurons.

An interesting mutation may be brains that burn more energy and consequently reduce the chance of obesity. The lack of obesity could lead to sexual selection of people with that mutation and make it bloom.

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u/Uberzwerg 9h ago

dog breeds

We controlled evolution here.
Could do the same with humans in 10 generations or so.
...if you don't care about ethics or so.

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u/Jaded-Currency-5680 8h ago

we are doing the same with humans, just in the opposite direction

our modern society is making it easier for stupid people to survive and breed, while sidelining smart people

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u/HayatoKongo 3h ago

Yeah, it seems as though our policies are providing downwards pressure to IQs. Intelligent people continuously seem to be punished for having offspring and rewarded for remaining childless.

Whereas, if you are of mediocre intelligence with little ability to provide for yourself, you stand to gain from popping out as many babies as possible.

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u/wassuupp 3h ago

Dog generations are 8 times faster and we artificially select them

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u/LordDeathScum 8h ago

Probably that’s what is fascinating about evolution, thousands of possibility’s and a lot of elimination by the environment.

I heard the first crops were a lot smaller in size and did not give enough calories agriculture barley made it.in the book guns, germs and steel. Explained that the crop sizes we see are huge compared to the first ones. Hunter gathers were consume more calories than those who did agriculture for a few hundred years.

Yet look at us now, we reap crops that would be considered phenomenons 12000 thousand years ago in the Neolithic era.

Several time in our history we barely made it.

Another interesting thing is our brain is only 2% of our body mass yet consumes 25% of our energy. It is a crazy organ!

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u/Hot-Significance7699 17h ago

Thats literally the case for every organ, isn't it.

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u/SketchesFromReddit 16h ago edited 16h ago

No.

A simple example is skin. Excessive skin is detrimental. Even if skin cells cost half as much energy to maintain, we would not expect to evolve to have twice as much of it.

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u/greenskinmarch 15h ago

Twice as much area or twice as thick?

If your skin was thicker it would be harder for mosquitoes to bite you, for example.

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u/Merry-Lane 14h ago

Yeah but we evolved to sweat so that we can outrun thicker skinned animals ;)

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u/FartingBob 8h ago

You'd also overheat quicker which would be bad.

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u/Hagenaar 16h ago

If I had a lateral web of skin connecting my arms to my legs, I'd glide like a flying squirrel. Perfect for getting down from mountains or ambushing prey from trees.

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u/kigurumibiblestudies 16h ago

Would women have sex with you? Would your children survive to adulthood?

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u/Lentemern 15h ago

Yes and yes. Because flying is badass.

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u/kigurumibiblestudies 15h ago

Ah, my mistake, I shouldn't have taken that seriously

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u/Hagenaar 5h ago

The message beneath my joke was that it's tricky to say categorically something like excess skin is detrimental. Obviously there's creatures who grew more skin and it gave them an evolutionary advantage.

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u/pappapirate 5h ago edited 5h ago

Excessive skin is detrimental

Am I missing something or isn't this exactly the point? Excessive skin would cost more energy but be detrimental and reduce survivability, so it's not selected for. If spending the energy to grow more skin paid off in survivability, then it would be selected for and we'd likely have it. So "evolution capped the size of our skin to balance energy cost and survivability" holds, right?

Why are you disagreeing?

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u/FBogg 7h ago

and every organism

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u/pappapirate 5h ago

Seems to me like it should be axiomatically true for literally every part of every thing that has ever evolved.

If something could spend more energy to improve survivability, selection pressure will push it that way. If something is spending too much energy without getting sufficient survivability for the investment, selection pressure will push it back the other way.

I guess it would just be a question of whether or not the organ/organism has actually reached that local balance point yet, and this article is saying that our brains are at the local max where any extra energy spent improving it would be a bad investment, survivability-wise? (I only read the headline, like any good member of this sub)

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u/Danne660 16h ago

Even with no energy usage, eventually the organ would not become any bigger as it would start to collapse under it's own weight.

But yes, essentially it is the case for every organ.

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u/Zaptruder 10h ago

It seems like in many aspects, human brains ride the line of physical effiacy.

They're basically at the size and energy consumption and developmental cost level where they're bumping up against several hard limits - size relates to the heat that it generates and can dissipiate - larger means more heat, means more requirements for heat dissipiation, meaning processing density decreases as a larger proportion of the brain structure is adapted towards basic energy/heating/cooling requirements.

Additionally the latency from the additional processing and distance creates between different parts of the brain and body means there's a sweet spot between brain/neural connection distance and speed of processing.

It also relates to what can exit the pelvis (large enough that birth mortality is a significant contributor to prehistoric deaths). There's of course the amount of energy required - while larger brains to make acquiring caloric resources more effective, there's also a limit to how much calorically digestable food there is in a given density area - so even if you're smarter, you can't get access to more if you've already stripped everything clean. And you generally don't want to do that anyway if you want to be able to return to an area - otherwise youu fall prey to species that have higher population densities.

The brain size that we've achieved mostly allows for group cooperation - cognitive resources can be networked via communication to allow for better information processing, allowing for better adaptation and manipulation of surrounding environments. It's clear that this has given humans a massive edge as a species... but the physical limits of both our biology and our environment girds our development - even though we've now broken out of the limits that our environments imposed on us... our biological substrate still affects a significant hard limit.

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u/sumumeri 14h ago

It seems that my brain didn't get the memo on this. Can we do a little less think and have a little more energy?

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u/rdmusic16 14h ago

I mean, brain size doesn't mean more intelligent - so not sure 'bigger brain' would be an advantage anyways?

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u/Thelancer112 15h ago

Does that mean brain sizes are going to start growing due to c sections?

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u/The_Roshallock 13h ago

That's rather speculative, but given enough time (hundreds, if not thousands of generations) and provided civilization remains a thing you could see a situation where humans can't "easily" give birth naturally.

This isn't unprecedented. There are a number of domesticated animals, certain breeds of dogs come to mind, where they would probably die out without human medical intervention. Who knows though? Evolution is a continual process and your guess is as good as anyone's what the future will bring.

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u/MonkeManWPG 8h ago

I think it's also going to be near impossible to guess what direction evolution may take because human society and development has practically ended more traditional selection pressures like food and predation.

Even with severe climate change we could likely build and invent our way to a point where people who are "unfit" for the new environment can still reproduce as normal.

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u/Christopher-Norris 17h ago

For a better explanation of why intelligence is not always selected for, see Idiocracy

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u/Sellazard 14h ago

I mean it is true. But at the same time evolution is just a competition to leave offspring.

If you're so smart that your intricate societal dance of showing off your high IQ, high EQ, that you have been to the therapist and have assets in THIS economy ends up going nowhere it is just bad reproductive design. It's taking too much time with nothing to show for it.

Sometimes being smart is acting on heuristics. Our ancestors did it successfully for millennia. But somehow gut feeling and butterflies in your stomach are bad now.

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u/pohui 12h ago

Whoever thinks intelligence is the only characteristic selected for must have a very poor understanding of evolution.

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u/SketchesFromReddit 16h ago

Rule 5: No off-topic comments, memes, low-effort comments or jokes.

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u/Christopher-Norris 16h ago

Genuinely wasn't intended to be just a meme or joking comment. Highly Intelligent people are being selected against for the same reason presented in the movie.

3

u/vxtmh 13h ago

Highly Intelligent people are being selected against for the same reason presented in the movie.

do you have any evidence for this, besides the movie

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u/aVarangian 9h ago

I guess he already has one data point to support his theory, though the intelligence claim is dubious

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u/Brodellsky 15h ago

Your comment is a great example of one that breaks that rule. Thanks for the example.

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u/[deleted] 17h ago

[removed] — view removed comment

1

u/LetMePushTheButton 15h ago

And still just big enough to be self aware enough to have existential dread and question the meaning of life.

1

u/ixid 9h ago

This is something that I think about more than I should, our fabulous brains were so limited by the energy available to a hunger-gatherer, yet now we have almost limitless access to calories.

1

u/molasses_disaster 9h ago

Also the head still needs to fit out of the pelvis

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u/TheBr14n 9h ago

Makes sense, a bigger brain would probably need more energy than we could realistically consume.

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u/Arrow156 9h ago

Yes, that's how evolution typically works.

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u/Plaineswalker 8h ago

Would this not be the case for every brain that has ever existed?

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u/TacoTitos 8h ago

Evolution hasn’t capped anything. If the environment starts selecting for larger brains then humans will eventually have larger brains.

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u/Beautiful_Debate_114 8h ago

I think it may have shrunk, actually. Take a good look around.

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u/Bryandan1elsonV2 8h ago

Project Hail Mary has a little hypothesis on this- intelligence evolves only enough to outcompete the native environment and then stops. It’s why a human and something else can think and work in a similar way, despite both of them having different structures for thinking and processing. I know that’s fiction, but it makes sense to me- though I’m not nearly smart enough to know if brain size means more intelligence (more data storage?)

1

u/LoveCareThinkDo 7h ago

"may have"?

Evolution caps everything based on energy cost and survival.

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u/Sprinklypoo 6h ago

Energy costs are certainly part of the equation, but our head sizes are limited by the size of the birth canal. We're pretty much maxed out on that front.

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u/joker0812 6h ago

Or maybe to fit inside our head?

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u/Life_Rate6911 1h ago

So over time, the human brain becomes more independent? Interesting!

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u/ninjaandrew 15h ago

So then one could hypothesize that the hotter the climate gets the more energy it takes to cool down and that energy could be taken away from our physical limit to our brain power. A hotter climate will makes us dumber.

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u/Aeiexgjhyoun_III 11h ago

One would need more energy to survive a colder climate, though.

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u/Teamboii 16h ago

Interesting research wow

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u/potatoaster 8h ago

Insightful comment. Amazing.

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u/MoreCoffee729 9h ago

The current human brain is making the planet increasingly inhospitable for itself through its capacity to experience greed and tell lies.

Evolution will probably conclude that was a mistake and select smaller brain creatures in the future

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u/Ariztokot 17h ago

your evolution, maybe!

•

u/lacunavitae 5m ago

Evolution: we need to build a mega nuclear power-plan for human 2.0

Open-AI: hey... that's for our shareholder investment ~~glitch~~ pitch.

Neuroscience Evolution may have capped human brain size to balance energy costs and survival

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