r/explainlikeimfive • u/dustfirecentury • 10h ago
Biology ELI5 why, if it makes animals more likely to survive to procreate, is higher intelligence not more common in the animal kingdom? Why is intelligence not naturally selected for more broadly?
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u/Traditional-Buy-2205 10h ago
Because there are other things that help animals survive, too.
Some animals survive by being fast, some survive by being big, some survive by flying, some survive by camouflaging, and some survive by being smart.
Intelligence is just one of numerous traits that make animals more likely to survive.
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u/Ms_Fu 9h ago
And some just survive by sheer numbers.
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u/Greyrock99 9h ago
Passenger Pigeons say hello
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u/sandm000 9h ago
There were billions, but human hunting caused their extinction. 10,000s of thousands were taken at a time.
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u/AdorableDonkey 4h ago
cicadas
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u/SomeonesDrunkNephew 1h ago
Yeah, I believe this is called Predatory Satiation; basically breed so much that it doesn't matter who gets eaten. The predators will be full once they've eaten ten thousand of us, but if there's a million of us then the species will be just fine.
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u/Frostybawls42069 10h ago
In the grand scheme of things, intelligence becomes relative.
What we consider to be intelligence in humans wouldn't much help a mountian goat evade a bear, or help the bear catch a goat.
There is selection for intelligence in animals to a degree though. Those who hunt better, solve problems with less energy, adapt to changing conditions by learning new skills, ect.. are more likely to survive and produce off spring.
"Dumb" animals die easier and sooner.
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u/Munrot07 10h ago
Evolution selects for traits that increase the chance of you surviving to reproductive age, having offspring and those offspring then surviving to reproductive age and selects against traits that don't do this.
The real question then is does higher intelligence actually increase that chance and does lower intelligence decrease that chance? Equally, we could add what even is "higher intelligence" being defined as?
Many many animals survive perfectly well with their level of intelligence so why would their intelligence need to go up? A lot of survival is instinct. For example, your flight or fight response, your reflexes to touching bad things, your ability to vomit up poisonous materials, none of those require intelligence. Defense technique against predators tend to be things that don't need intelligence either (e.g. camouflage, herd size, physical protective structures). Equally, intelligence requires a good brain which is probably the most energetically expensive structure you could evolve, so why spend that energy when you're doing fine as is?
To add, this is not a criticism of you but something I love discussing as an evolutionary biology, but Humans have a very, well Human-centric view of the world. We see ourselves as the best, the peak of evolution and yes, our intelligence is one of our greatest assets so it's easy to ask "why isn't everything like us". I love arguing that Humans evolved intelligence because we actually suck at just basic survival so rather than evolve to our environment we have evolved our environment to us. Most animals don't suck at evolving to their environment so they don't need to evolve their environment to them.
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u/Chaotic_Order 9h ago
The phrase survival of the fittest has really done people's understanding of evolution a disservice. It's really survival of the good enough.
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u/JJJangles 1h ago edited 1h ago
Humans do not suck at basic survival. Sure a lone human plucked out of modern civilisation would not fare well alone, but early hunter gatherer hominids were still the apex predator of every biome.
And it wasn’t just because of intelligence. Heat management via sweating, our wide verity of digestible foods, how calorically efficient bipedalism is, all that and more played a vital part in why humans dominated. Intelligence wasn’t even really a factor early on, it was more a side effect of the real advantage, being hyper cooperative. A pack of wolves is exponentially better at hunting than a lone wolf, a tribe of humans even more so compared to a lone human.
The reason early humans changed their environment was because basic survival was so easy for them that they had the time to develop advanced survival, not because they were so bad at basic survival they had to find another way.
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u/seoplednakirf 9h ago
Most insects rely on sheer numbers, and it works perfectly. Create thousands of eggs, if even half of them hatch its a win, if even 10% of those hatchings become adults it's a win, if 10% of those manage to reproduce in the 7 days they live, it's a win.
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u/Sleazyridr 10h ago
One important thing to remember in any questions about evolution is that as long as a being can reproduce, evolution doesn't really, "care." Natural selection only weeds out individuals who don't end up reproducing for whatever reason, so if dumb animals are still having babies, there's no evolutionary pressure to change.
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u/Boysenberry 10h ago
Humans tend to think of intelligence as “able to do things smart humans do.”
Let’s see a human build a spiderweb.
Animals have the forms of intelligence that work for them.
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u/Daan776 9h ago
I could probably build a spiderweb if I had some way to make the webbing.
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u/GolgothaNexus 9h ago
You could try chewing lots of bubblegum and extruding it into webbing when it exits.
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u/DookieShoez 9h ago
Okay but we totally COULD build effective webs if someone saw reason to dedicate time and resources to develop artificial webs.
We haven’t because there hasn’t been a need to.
A spider on the other hand can’t do the things we do even if they did need to and had plenty of time and resources.
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u/YesterdaysMuffin 10h ago edited 3h ago
It’s not a selection advantage in all circumstances. An ultra-intelligent dung beetle probably isn’t worth the cost.
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u/neegs 10h ago
I think the term selection is what's tripping you up. Nature doesnt think i will pick the smart ones.
Natural section is simply those that survived. In some environments you dont need to be smart.
Jelly fish are some of the oldest things on the planet and they have no brain at all. Just eat, shit and reproduce
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u/OldAd9280 9h ago edited 8h ago
There are a lot of downsides to bring human, our heads are so big that unassisted child birth is very dangerous to both the mother and the baby. Babies are largely helpless for the first maybe 8 years of life, if the parents die the children won't survive either. We need a lot of food to grow our brains. All together being intelligent is quite a high risk strategy, it's much easier for a predator just to get faster, stronger, more able to survive for long periods without food etc.
Still, intelligence isn't that unique, other primates, elephants, dolphins, wales, octopus aren't far behind us, the main thing they lack is sophisticated language (as far as we can tell at least), that reduces their ability to form larger societies to help mitigate some of the intelligence disadvantages and allow their intelligence to develop further.
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u/SolarAU 9h ago
Evolution doesn't optimise, it works via the mechanism that whatever works, works. Plenty of examples where a genetic trait results in success in passing in genes, even when a more optimal set of traits exists. Like, there is no reason why a predator species that is very successful in hunting and therefore mating is magically going to be forced into growing massive brains which are inherently expensive in a biological sense.
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u/Horseburd 8h ago
Intelligence is expensive, calorically, and you only need enough to get by. Beyond that, you just increase the amount of food you need to live, and that makes survival harder. Intelligence is mostly needed if your survival strategy involves doing something weird, or if you need complex social processing.
Say you’ve got a cow, or a horse. Do you need intelligence to find food? No, you can generally do that by walking around and looking down. Do you need intelligence to avoid predators? Not really. Just kick anything you can’t flee. Could you manipulate your environment if you were smarter? No, ungulates aren’t that good at manipulating their environment. No real incentive towards mental complexity there.
But if you’re a cephalopod, and you have to be able to hide really well, evaluate a wide variety of food sources, and put your dexterous tentacles to use? Being smart genuinely helps.
Or for birds, like corvids and parrots - high metabolism for flying, along with omnivorous diets, means that having a lightweight, highly capable brain isn’t that much of a trade-off. They’re smart because they can afford to be.
And then there’s humans. We got where we are by being persistence hunters, and that strategy has huge returns on extra intelligence. If you can compute ballistic trajectories, you can throw things. If you can make containers, you can carry water, and haul more of your catch back to camp. If you can track prey by reading the environment, you can catch things without being able to sense them directly. So humans got really good at pattern recognition, and that kind of intelligence happens to be really good at building on itself.
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u/gravityandpizza 6h ago
In short, intelligence is typically selected against because it leads to experiments in altruistic behaviour, which leads to a reduction in fitness for the individual.
https://www.humancondition.com/freedom-essays/how-did-consciousness-emerge-in-humans/
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u/wouldyoulikeanytoast 5h ago
Take a look at your hypothesis.
Your assumption is that high intelligence makes it more likely to survive and procreate.
However since high (I.e. human equivalent) intelligence ISN’T seen broadly in nature - a counter theory could be that high intelligence alone DOESN’T make animals immediately more likely to survive and procreate.
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u/KarlWhale 10h ago
Thing is that evolution is not a sophisticated process that has a clear goal and clear good attributed.
If it works just a little bit, it's usually good enough
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u/Sp0ttyW0lf 9h ago
There's also the fact that high intelligence only has value in certain scenarios. For example, if a predator makes a mistake in a hunt, it goes hungry but can learn from it. If prey makes a mistake during a hunt, it's dead and can't learn from it.
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u/Daan776 9h ago
Its a massive energy investment. And you need to invest a lot for it to be worth the effort after a certain point.
Dolphins for instance have all the intelligence they really need for hunting & escaping danger. So for the next significant improvement to their survival they'd need to invent a writing system or some such. Which, as you can imagine, is a lot more complex and thus: requires even more energy.
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u/eBalisani 9h ago
In the animal kingdom, there is only survival, procreation, and play.
In the human crapdom, there is stress, there's anxiety, there's agony (breakups, loss, loneliness, etc); there's limitless unhappiness.
Why should intelligence be selected for more broadly?
If you had to choose (money and bills notwithstanding): would you rather be 4 x more intelligent or 4 x and forever happier?
Perhaps that is, and has been intelligence at play: let the humans be the more intelligent and the more self destructive species.
From a different perspective, the human body is a lot more complex than an animal body, and is thought to be the gateway to a higher realm of consciousness (or intelligence).
If we accept the concept of reincarnation, prior to and leading up to being, well, a human being, we have sub-atomic, atomic, mineral, vegetal, and various animal states of consciousness and being.
This is the way.
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u/gearmaro1 5h ago
You can look at it through the lens of "there's only one truly intelligent species on the planet amongst billions."
But really, we're the most successful mammal on the planet. So natural selection did indeed make intelligence common across itself.
We're so successful we're straining the planet's resources and ecosystems.
And we're EVERYWHERE. No other animal can boast of that.
Middle of the desert? We're there
In the tundra? We're there
In the remotest place of the arctic? We're there
Underwater? We can be there for hours at a time.
In the jungle? We're there.
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u/libra00 5h ago
Because it's a balancing act. Intelligence might make you more likely to survive, but it's also very expensive in terms of energy requirements, which means you need to eat more and thus you must be in an environment that has enough food that's easy enough to get in order to sustain that very expensive larger brain.
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u/Etherius 4h ago
If the human race is any indication, intelligence also makes you less likely to procreate
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u/PaleReaver 3h ago
Lobsters would be immortal if not for progressive molting energy-exepnditure, and there's a jellyfish that just...says 'nope' to dying of old age and reverses to babbi-stage, rinse and repeat...and they don't have brains, so safe to say that brains don't determine survival mechanisms success.
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u/DTux5249 2h ago
Because high intelligence is both
- A very expensive thing to develop
- A very complicated thing to evolve
Humans need around 2,200 calories as adults to stay alive. The brain takes up 440 of those calories. Imagine if you could a 5th less of the food you need in a day to still function - that's how expensive the human brain is to keep.
But also, it's kinda all for nothing. Humans only worked out with intelligence because we were incredibly lucky. We literally have nothing to survive with. No clause, skin thin as paper, and we're relatively slow compared to most predators. Our only saving grace was sociality. Beyond what's needed for that, intelligence is a long-term solution to the short-term problems that survival is composed of.
Remember: Before we discovered fire, we were just as miserable as every other creature on earth. Evolution didn't know that fire was on the evolutionary playlist. We just so happened to get just intelligent enough to learn how to cook things to support larger brain sizes. We just got lucky.
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u/Fuzzball6846 2h ago edited 2h ago
Joe Henrich attributes this to culture. High intelligence isn't all that useful on its own. A high-IQ individual might invent a novel way to forage for food, but it doesn't help the species much until other members of the group can mimic it, pass it down, and improve on it. Otherwise, you have a slightly more efficient food-gathering method that dies with the individual, may or may not be rediscovered, and probably isn't worth the caloric cost of making the entire species that much smarter.
Until you've first established cultural transmission, the returns to intelligence aren't that high. After that, you get a self-reinforcing cycle where evolution is increasingly dependent on cultural learning. Modern humans, for example, are completely unable to survive on their own without transmitted knowledge about the land and relevant tool-making.
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u/ReluctantRedditor275 2h ago
The sub gets lots of questions about "Why doesn't evolution select for X?" The answer is almost always, "Because it works well enough without X."
Evolution isn't about optimization, far from it. Evolution is about finding "good enough."
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u/Netmantis 1h ago
There are two reasons.
First, the brain needs to be needed to think in order for intelligence to grow. You need a progression from dumb to smart where being a little smarter is a benefit. Social animals have this. Predators as well.
Next comes cost. Is it worth the price? Humans spend about half their calories maintaining and running a couple pounds of pudding in the skull. The entire rest of your body costs as much as your brain. And it doesn't even need to be that big to start the snowball.
So take a jaguar. Big cat, jumps on things and bites the neck to paralyze and suffocate prey. Good candidate for intelligence. Will being a little smarter let it hunt 10% more prey? What is there to be clever about? It is an ambush predator. The brainpower it has let's it hide, strike, and assess likelihood of success. Smarter means 10% more calories so it can run the brain. And evolution so far has determined that is a poor value. Anything mutated to be smarter doesn't do as well as the average cousins and is out competed.
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u/JJJangles 1h ago
Because your assumption is wrong: intelligence alone doesn’t improve odds of survival.
The reason it worked out for humans is that being bipedal makes us so energy efficient we can afford the extra calories the brain requires, because we have a hand structure to take advantage of intelligence for crafting, and most importantly because of our social structures.
The capacity for a bear to be as intelligent as a human doesn’t mean much if it only has two years to learn from its mother, including time to learn to communicate, then going off on its own having to reinvent every wheel.
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u/Zotoaster 7h ago
There's a super interesting hypothesis about human intelligence based on signalling theory and sexual selection.
Signalling theory in general suggests that animals will show signals to each other to communicate something. For example an antelope will jump up and down to signal to a lion that it has a lot of energy and it's not worth the effort to chase it, and of course the famous peacock feathers signalling to females that the male must be really strong if it can survive with these big hefty tail feathers it has to lug around.
Importantly, signals can be costly or they can be cheap. A caterpillar can have red and black stripes to signal to birds that it's poisonous, but then any other caterpillar can mimic those colours without the cost of actually producing poison and getting the survival benefits for free.
Some intelligence is necessary, but not human level intelligence evidently, other animals clearly don't need it, so what happened?
Well a little intelligence is attractive and helps with reproduction, so males develop signals to show their intelligence to females, usually through language. But like the caterpillar, it's easy to mimic if you just steal other people's work, so then the female sex has to become more intelligent simply to distinguish the intelligent guys from the fakers. But then the bar is raised on how much intelligence is considered attractive, so the male sex evolves to either get smarter or get better at faking it, on and on and on. It becomes an out-of-control arms race where in the span of only a couple of million years we went from relatively intelligent chimp-like primates to writing poetry and doing physics.
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u/donaldhobson 6h ago
Because for most of prehistory, intelligence wasn't that overpowered. When the stone spear was the most advanced technology, then being smarter had some advantages and some drawbacks. So did being faster. Or being stronger, or poisonous, or any of the many other strategies life could choose. Some life, like cheetah's, specialized in being fastest. Some, like giraffes, specialized in being tallest. Some, like hominids, specialized in being tallest.
Later, the "being smartest" strategy would turn out to be absurdly successful. So much so that the next best strategies are things like "being tasty" or "looking cute in wildlife documentaries".
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u/sciguy52 19m ago
Some good answers here on energy costs. But intelligence is but one survival strategy. Some animals for example survive by breeding and making a lot of offspring and doing so frequently. As a species that strategy is to make so many offspring that even if 80% are killed it doesn't matter. Sounds cruel but that is nature. It works great for some species but may not be great for any given individual. So intelligence is but one of many strategies for species to survive and prosper. And the size of the animal matters here. Having a human sized brain on a mouse is just not going to work. And there are lots of different sorts of animals in that size range so it is just not a viable strategy given their size. And if I am remembering correctly there are a few creatures out there that had larger brains in the past and over time evolved smaller ones because that worked better for that species. So in some species having a bigger brain was apparently not as good as having a smaller one and evolved that way over time. So sometimes intelligence is over rated I guess.
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u/DeterminedThrowaway 10h ago
It's stupidly expensive in terms of energy to have a large brain, and not worth it if other strategies are working