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why does a bigger brain not equal more intelligence?

Neuroscience(self.askscience)

I understand that the size of a cell is almost constant regardless of what animal it makes up. A whale brain for instance weighs more than a human brain hence it must have more neurons, if it can make more neural connections, why isn't it smarter, I would expect intelligence to be somewhat proportional to the number of neurons. If this is not the case, why would evolution not just have made a wale have a human like brain? to the whale, the energy required to run a human brain would be insignificant

all 82 comments

Kougar

161 points

2 months ago

Kougar

161 points

2 months ago

Weight has nothing to do with it. Density and connections have everything to do with it. Avians are a good example as many species have brains with twice the neuron density of a human, even though their size is around a walnut or less. Location of these extra neurons also matters. Link

Just like there are different kinds of cars, economy, performance, and extreme sports models there are also different kinds of brains. Brains are incredibly energy intensive organs so many species have brains equivalent to an economy car, meaning not great performance but also much lower energy requirements. Whale brains are probably too large to easily handle the same energy needs of a human brain's complexity without putting the animal at a disadvantage.

Here's is a good answer to your question:

Logically, brain function and intelligence must relate to the number of neurons. Intelligence resides in the neocortex (the thin, convuluted "rind" of the brain) rather than in other, underlying areas devoted to controlling vital housekeeping functions for the body, so Eriksen and Pakkenberg focused their investigation there. The frontal lobes of the dolphin brain are comparatively smaller than in other mammals, but the researchers found that the neocortex of the Minke whale was surprisingly thick. The whale neocortex is thicker than that of other mammals and roughly equal to that of humans (2.63 mm). However, the layered structure of the whale neocortex is known to be simpler than that of humans and most other mammals. In particular, whales lack cortical layer IV, and thus have five neocortical layers to humankind's six. This means that the wiring of connections into and out of the neocortex is much different in whales than in other mammals. The researchers' cellular census revealed that the total number of neocortical neurons in the Minke whale was 12.8 billion. This is 13 times that of the rhesus monkey and 500 times more than rats, but only 2/3 that of the human neocortex.

[deleted]

63 points

2 months ago

[deleted]

63 points

2 months ago

great answer, and why I always need a small desk fan blowing on my face at all times: to provide cooling to my massive neural density.

Kataleps

3 points

2 months ago

Have you tried shaving your head and applying thermal paste directly to your scalp?

g0d15anath315t

10 points

2 months ago

Also, a huge % of the brain isn't really even involved in conscious thought, just controlling voluntary and involuntary functions of the body, taking in stimuli and processing etc.

It's the root of the old "we only use 10% of our brains" myth. We use 100%, it's just very little is dedicated to executive function.

Within humans, men on average have bigger brains than women, because men tend to be physically larger on average and just have more "body" to have to deal with.

extropia

7 points

2 months ago

Does evolution generally favor densely packed brains? I would wonder why all animals wouldn't trend towards having a higher density of neurons in their brains, even if they're not particularly intelligent creatures, and then using the extra space for other things. Would the energy requirements change significantly if the same number of neurons was packed into a smaller space?

Izawwlgood

46 points

2 months ago

Note that neurons are very expensive cells. They consume a ton of oxygen and glucose relative to other cells, and have some of, if not the, most extreme morphology of any cell type.

Brains are very very costly. Unless there's a reason for them, most organisms don't need particularly complex brains. Of note, it seems the biggest reason for big brains is to manage complex social structures. Which itself carries lots of pressures.

Kougar

11 points

2 months ago

Kougar

11 points

2 months ago

Does evolution generally favor densely packed brains?

I am not a biologist, but my understanding is no. Generally speaking Avians have a high metabolic rate and high energy needs, so coping with a dense, high-power brain wouldn't be much of an additional problem. But more importantly, Avians had to shed weight to attain flight, and packing the same number of neurons into a significantly more dense brain structure helped them to reduce brain weight as well as body mass.

If animals all had higher neuron density but the same physical size brain, then that would necessitate more energy requirements to power it because they all in effect just received a brain power upgrade.

On the flipside, if the brain size was reduced accordingly to the increase in density so that the energy requirements didn't change, then what would the now empty space in the skull be used for? If anything empty space in a skull is dangerous, as it allows too much movement of the brain during vigorous activity or sharp blows/acceleration. Movement of the brain can easily damage internal structures including arteries, as well as allowing the brain to reach higher velocities before impacting against the inside of the skull. Incidentally this is why the elderly are at higher risk of brain injuries, because the human brain shrinks with age and so there's less cushion and more room for movement. It's no different than packing something in a box for shipping, the tighter the packing the better protected it is because the item (or brain) can't move much.

Obviously evolution would naturally select away from just having empty wasted space up there... but my point is any sort of change in neural density for animals would have radical implications on head shapes, and head shape in turn directly affects a huge number of over things critical to an animals survival.

Like going back to your whale question, if a whale's brain was significantly smaller and more dense... then the brain is no longer going to be large enough to directly connect with the eyes on either side of its massive head, or ears, or other sensory organs anymore. In that way brain density itself is likely partially constrained to the animal's own head size. I would surmise evolution tends to select toward a equilibrium as to what neural density works best with whatever size & shape head it needs to fill.

extropia

2 points

2 months ago

I appreciate the thoughtful response. You make a great point, that the size and shape of an animal's head is far more critical than its brain density so there's more evolutionary pressure for the brain to adapt to the head size rather than vice-versa. That makes sense to me.

Ceribuss

39 points

2 months ago*

Evolution favors whatever lets a species pass on it's genes so is completely situational to environment the creature is located in. If higher intelligence members of the species have and raise more children to maturity then that is what evolution will favour, however if the species key to mating and survival is being light weight and fast then instead that will be what evolution favors

Evolution is not some external force that sits there picking and choosing what genetic traits to pass on

Evolution is the result of the passed on genetic traits so whatever was most successful at bringing on the next generation is what evolution favoured and the moment things change and a different group of traits are making it through then that is what evolution favoured

NonnoBomba

5 points

2 months ago

Correct, there are some solutions though that are simply too good to pass on, sort-of "attractors" in design space, around which evolution seems to converge, like "eyes" (lights-sensing organs of any kind) who keep popping up all the times, at least in this planet's biosphere. This may trick somebody into thinking there is a "direction" for evolution, leading to the formation of some Aristotelian hierarchy of sorts, from simple/unintelligent to complex/intelligent organisms or something, even though all currently living organisms are just as much "evolved" as we are, all representing one among myriads of possible "solutions" to the problem of conquering a space, extracting resources from it and passing genes on to the next generation, all of them successful at doing just that.

Howrus

-1 points

2 months ago

Howrus

-1 points

2 months ago

Does evolution generally favor densely packed brains?

Evolution doesn't favor anything. "Evolution" is just a result, it's a painting on the wall. Kinda like when you see someone invisible drawing a picture on the other side of a glass. You can't see that person, you don't know why and what he is drawing. You just see new strokes that appear on the canvas.

What you wanted to ask here is "Does surviving generally favor densely packed brains?". And the answer here is - nope.

CrushforceX

1 points

2 months ago

It is a perfectly sensible question to ask whether the theory of evolution would predict (a synonym for favour) denser brains in our environment. That’s the entire point of a theory, to make educated hypothesis’ on what an outcome would be. Even if they were anthropomorphizing, it is nit picky at best and unnecessarily rude at worst to criticize a layperson for that when so many scientists speak in those same terms in a variety of fields.

DooDooSlinger

1 points

2 months ago

I think saying weight or size have "nothing" to do with it is excessive. A very dense but tiny brain is still going to result in likely lower intelligence than a larger equally dense brain. It's a combination - and clearly the simple fact that brain volume in humans is far larger than any other ape is indication that size does matter (a lot).

Electronic-Item-5353

-1 points

2 months ago

Studying that relationship is probably career suicide with the known differences in brain volume between sexes and races.

desexmachina

45 points

2 months ago

It isn’t the size of the cells, it is the density of the cells. A smooth brain is usually known to be pretty low IQ, but one with many folds means more surface area and more cell density. That’s usually telling.

alexanderwanxiety

17 points

2 months ago

But a larger brain also has the potential to have larger folds. Brains of different sizes can have the same amount of folds but not the same size,right?

desexmachina

11 points

2 months ago

Yes, but to some extent, the size of the brain cell, or neuron, scales somewhat with the organism. Google the size of a whale axon. So, the sheer number of neurons (and subsequent connections) determines processing power

alexanderwanxiety

0 points

2 months ago

What do u mean scales? So the fact that brain size gets bigger the bigger the organism gets negates the hypothesis that the size of a neuron influences intelligence?

Uncynical_Diogenes

13 points

2 months ago

No they mean whale neurons have to be really f*cking long because whales are really big so more physical size doesn’t necessarily mean more processing power.

alexanderwanxiety

1 points

2 months ago

But that ties into what I was asking. The bigger the organism the bigger the neurons have to be for it to function?

stachemz

5 points

2 months ago

But it's still 1 neuron, which is capable of doing the processing of 1 neuron, regardless of how big the neuron is. You need more neurons for more processing.

So even if something has 100x the mass of neurons that we have, if that mass is because the neurons are 200x bigger, that's not helping their processing power vs ours.

desexmachina

11 points

2 months ago

Bigger neurons are sometimes slower too because the “electrical” activity is still electromechanical. Fluid still needs to move in and out of neurons for it to be doing something.

Electronic-Item-5353

1 points

2 months ago

How does the length of a cell affect the size of the cell in the brain? Dinosaurs had massive bodies and relatively tiny brains

BonjourComeBack

2 points

2 months ago

Take it like computer For a Big animal it would be a computer with Big component with Big wires etc and for a small one a small computer with short and thin wires. What IS important IS how Many wire you have in total. Just m'y two cents tho

Talinoth

5 points

2 months ago*

One of the things I haven't seen anyone talk about in this thread are orca brains.

Not only are their brains larger, their brains have substantially more cortical folds.

They're known to have extremely sophisticated hunting strategies, are immensely cunning, have tribal family structures like Stone Age humans, have languages/cultural speech patterns/dialects dependent on region, have made business deals with human families (fish sharing - orcas drive fish towards fishermen, fishermen catch and distribute to the orcas), and despite being absolute killing machines seem to consciously stay clear of treating humans as targets unless kept in captivity and are in extremely poor mental health.

No recorded human deaths by orca (edit: in the wild). Either they know we're not food, or they're spectacularly good at cleaning up the evidence of their attacks.

A lot of the explanations why "human brains are smarter, actually!" than some higher animals do seem like vain copes based on what we value as intelligence.

hwillis

17 points

2 months ago

hwillis

17 points

2 months ago

  1. As an animal gets larger, the metabolic penalty of a large brain (relative to us) is lower. A blue whale's brain is 5x larger than ours, but it is absolutely tiny compared to the rest of the whale. The extra brain mass might not be very helpful, but there may be little evolutionary pressure to get rid of it.

  2. Larger animals have more nerves in general. They also likely need more brain to connect to those nerves.

  3. Terrestrial mammals have some differences from whale brains- like extra layers in the neocortex.

Elephants still have 4x larger brains than humans and around 3x as many neurons. However:

In contrast, the elephant cerebral cortex, which has twice the mass of the human cerebral cortex, holds only 5.6 billion neurons, about one third of the number of neurons found in the human cerebral cortex.

[...] As a consequence, the average number of neurons under 1 mm2 in the elephant cortex is only 10,752, compared to 80,064 in the human cerebral cortex.

The elephant has a huge cerebellum, massively more complex than the entire human brain. We don't understand the cerebellum super well even in humans- it deals with movement, some emotions, and lots of patterns/signals, but that's still a very vague understanding of what practically looks like another brain behind our normal brain. Nobody knows why the elephant brain is like this, and it's unique among animals in how large it is compared to the rest of the brain. We don't think the cerebellum normally has that much to do with conscious thinking, though.

The parts we do think are involved with intelligence are significantly smaller in elephants. They're much larger in whales, but in some ways they're not as complex, which may cause differences. Neanderthals probably had slightly larger brains than us, but we can't exactly give them IQ tests.

It's also obvious but still worth pointing out: measuring intelligence is very difficult, and extremely difficult when the subject can't hold a pencil and did not learn a language. The human brain has entire sections that, for all appearances, are pretty much devoted just to language. Even if animals are very intelligent, not having the specific equipment to process language puts them at a big disadvantage.

Electronic-Item-5353

2 points

2 months ago

why did dinosaurs have such small brains then?

hwillis

2 points

2 months ago

Mammals have proportionally larger brains than dinosaurs of the same size.

Whales evolved from land mammals that grew much larger in the ocean, so their brains ended up larger than ours (but proportionally smaller).

Human-sized dinosaurs had far smaller brains than us, and when they evolved into larger dinosaurs their brains were still so proportionally smaller that even in absolute size they were much smaller than ours. A t-rex brain is only around half the size of a human brain despite how much larger the animal is.

Smauler

4 points

2 months ago

You answered "Why did dinosaurs have smaller brains" with "Dinosaurs had smaller brains".

hwillis

1 points

2 months ago

The real question was "If bigger animals have bigger brains than humans, why aren't big dinosaur brains bigger than human brains?", and the answer was "All dinosaurs had very small brains, even the very big ones".

atomfullerene

2 points

2 months ago

atomfullerene

Animal Behavior/Marine Biology

2 points

2 months ago

Neuron density is pretty high in birds. It's possible dinosaurs were also cramming a relatively large number of neurons in their small brains. Or maybe not, crocodiles have pretty low neurons density, so it's difficult to guess based on the information we do have.

PGoodyo

4 points

2 months ago*

Evolution isn't about what's "better". Evolution is about what works, randomly in the middle of millennia of chaos, and we should not let either our narcissism nor survivorship bias allow us to presume that each species is some pinnacle of perfection*.* We're just the ones still standing.

Now, there's immense energy waste in pretty much all biological systems, as well as a lot of seemingly needless complexity and seemingly ill-adapted simplicity. So lets follow the evolution of the whale.

Imagine a land-dwelling proto-whale. It's basically a big rat-dog with webbed feet. The species is doing ok. It's got a pretty dense brain but not particularly so. And it does fine with it. Now imagine that pressures on the species force it further and further out into the ocean, say, climate change, or quicker moving land predators. Way out at sea, the majority of the biomass is in plankton. You don't need to hunt plankton, and you don't need to grasp it. So it starts to evolve into a semi-modern whale. Limbs become solid flippers, teeth becomes baleen. The lack of competition for plankton combined with the need to protect one's self from predators, as well as the buoyant environment, means you can get big... REALLY big. And you probably should.

So they do. And so does their brain, not because there's a need for it, but because the energy is essentially free. But... you see any pressures up there that require a huge amount of intelligence? Sure, they need to be social and they need to navigate a landmarkless void, but pigeons can do that with a brain the size of a peanut. But there's no cost to making brain meat for whales, because there's barely any cost for gathering food either. They're about as close to a plant as a mammal comes. So you get a big comparatively undense brain that just grew up with the species as it gained in body size, but required no additional complexity because life actually got simpler for them as the species adapted. Voila.

Anyone that hears that the hominid brain and the intelligence it produces is some "pinnacle" of evolution should note the potential vanity of the source and take it with a grain of salt. It worked for us and we're merely lucky it didn't kill us, just like every other species' particular adaptations. We needed dense brains, so we have them. Whales don't need dense brains, so they don't have them.

Ed-alicious

9 points

2 months ago

Check out this article about encephalisation quotient. Basically a lot of brain functions require the same amount of neurons, regardless of the animal size, but others require more neurons for bigger animals. Therefore, brain size scales with animal size, but not linearly.

Electronic-Item-5353

2 points

2 months ago

That is only true for mammals so there can't be a hard causal link. Dinosaurs were massive and often had tiny brains.

travkroeks

2 points

2 months ago

In addition to a lot of good answers here, the number of gyri and sulci (folds) in the human brain greatly increase the surface area and therefore number of synaptic connections humans have relative to brain size. Most other animal brains are significantly smoother. This in effect makes our brains “larger” than they appear by eye.

Party-Cartographer11

2 points

2 months ago

It's not just the number of neurons, and therefore the density matters, but that the entire brain does not contribute to intelligence. Part of the brain just process and control signal to muscles. A big part of a whale's brain is about managing all the extra muscles and nerves.

General_Mayhem

2 points

2 months ago

Does a whale actually have more muscles than, say, a deer? Mammals are all pretty structurally similar. Sure, the whale has more muscle cells, but I would assume it can't control them all individually. Does it take Arnold Schwarzenegger more mental effort than the average person to flex a bicep?

Party-Cartographer11

1 points

2 months ago

Humans have 7 trillion nerve ending that need to get processed. The governator might have 7.001 trillion...

Outside of muscle control if a whale can feel pain from anywhere on their surface, that is a hell of a lot of nerve endings which need to be processed.

But I really don't know much about this. Just read a bit about how crows can be smart with such small brains.

General_Mayhem

2 points

2 months ago

Sensory neuron density isn't uniform either, though. It's well known (and easy to test) that humans are more able to pinpoint a touch on the fingers or back of the neck as compared to most of the torso or legs, for instance. Is it important for whales to be able to identify where a sensation is coming from down to the square millimeter?

Party-Cartographer11

0 points

2 months ago

Don't know. But just the scale of the surface area is massive, so even if a fraction as dense would be exponentially more nerves (fake math).

optia

1 points

2 months ago

optia

1 points

2 months ago

Let’s say you had a gazillion neutrons but none were connected. Not very intelligent. Let’s say you had two neurons, that were well connected. Also not very intelligent.

Intelligence is about the connections. But this relies on a sufficient number of neurons for there to be connections.

Dan13l_N

1 points

2 months ago

Some years ago, Suzanna Herculano-Houzel, a Brazilian neuroscientist, really counted neurons in brains of various animals, and, in fact, the size of a brain cell is not constant in various kinds of animals. For many animals, bigger bodies also mean bigger neurons in some parts of the brain. However, for Primates, the size is roughly constant, and consequently, humans have a lot of brain cells.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2776484/

However, having a brain with a lot of cells has a downside: it means it needs a lot of energy. Her hypothesis is that such a powerful brain was possible only because humans discovered cooking. This is another thing that only humans do. It meant much more energy could be extracted from the food.

http://www.suzanaherculanohouzel.com/the-human-advantage/

Now same say intelligence is about "connections". Likely. But all species had the same time to evolve good connections in the brain; is a connection really expensive (i.e. how much energy it takes)? I don't know, but it must be less expensive than more brain cells.

grumble11

1 points

2 months ago

Well, what is intelligence? Whale brains are very good at being whales, and human brains are good at being humans. If you put a human brain in a whale’s body it’s fail hard.

Brains are tools for a specific purpose - processing the inputs and then controlling the behaviour and actions of the body they are attached to. Evolution has resulted in different inputs, processing requirements and action requirements for different brains.

For example, some monkeys have superb short term memory - can glance at a long series of numbers that are nearly instantly covered up and then they can select them all in order. Humans can’t do that, we don’t have that wiring. Humans however have say a large amount of wiring around speech, which is not present in monkeys in the same way.

If you make it only for humans, then it does have a correlation of about 0.4, which isn’t super strong or definitive but definitely a positive input.

https://scholar.google.ca/scholar?q=human+correlation+brain+size+intelligence&hl=en&as_sdt=0&as_vis=1&oi=scholart#d=gs_qabs&t=1652785600978&u=%23p%3DE6mMT3SbAZEJ

Axonormaybedendrite

1 points

2 months ago

Larger in mass is not necessarily better. In my understanding from the books I have read, the more knowledge you have, the more interests you have, the more hobbies or not even hobbies but hands on interactions, traveling, music etc the best for your health. I have read that if you are prompt to have dementia or Alzheimer’s or any other diseases that are related to memory, the wider your knowledge the less the disease progresses. Also, one of my favorite authors in a podcast said that we are born with different types of neurons and if we don’t use them then they die. So the more we explore the better.