All of the great apes are incredibly intelligent in comparison to most other animals. The basic roots of our intelligence are probably a common feature to the whole family, but there's no consensus on why it's so advanced in humans. Any paleoanthropologist can rattle off about half a dozen possible explanations, but we honestly don't have enough evidence to really distinguish if, when, and how these were factors at different points in human evolution. Here's a quick attempt at some broad categories, which each have multiple hypotheses within them:
* Because intelligence had advantages for individual selection (e.g. mimetic recall hypothesis)
* Because intelligence had advantages for group selection
* Because intelligence had advantages for sexual selection (spandrel hypotheses often start here)
* Because adapting to rapidly varying ecological conditions required so many adaptations that we crossed some kind of barrier and "fell into" intelligence
* Because intelligence helped with foraging/hunting (exclusive of sociality)
This highlights just how little we really know, even with decades of fossil, genetic, and behavioral data. What's always struck me is how intelligence might not have been a linear "goal," but more like a byproduct of other traits that just happened to snowball...
The jury is still out on exactly how intelligent other hominins were (and the extent of our involvement in their extinction). Regardless, the term human can apply to all of genus Homo and that's the sense that discussions of "human intelligence" typically use.
I think it might be just competition. Human brains are expensive in terms of energy expenditure. So at certain population scales having less energy to expend might be comparative advantage.
And same really goes for other niches we do not even occupy. You need to get something out of those expensive to keep brains.
Since the invention of contraception, intelligence seems maladaptive, although we may have already reached technological escape velocity so it's not clear to me that it'll matter.
I like that theory although it is depressingly grim ... the top dog species will inherently see any alternative intelligence as a threat and eradicate it. Would definitely make one pause for thought about the wisdom of creating an AGI ...
Considering human intelligence is very social, I wonder if bias to focus on individual humans leads us to a wrong way of understanding why it arose…
One of my pet theories is that it may be related to vocal cord development[0], where losing certain physiology that allows apes to be louder allowed humans to be more specific, if quieter, with enhanced pitch control and stability offering higher information density communication. This unlocks more complex societal interactions and detailed shared maps. (In Iain McGilchrist’s terms, it let the Emissary—the part of the brain shown to specialize in classification and pattern recognition, the requisite building blocks for efficient communication—to take priority.)
This is an example highlighting how it is not about individual humans “becoming smarter”, evolving larger brains, etc., but rather about humans becoming capable of working together in more sophisticated ways. In fact, human brain shrunk in the last few thousands of years, in concert with growing size of our societies and labour specialization[1], which in turn in no small part is helped by communication density offered by our vocal cords. Really, humans in this way are closer ants[2], where being part of human community is the defining part of our nature.
I've read, from a few separate sources that were not research papers, something similar that claimed the development was a result of existing in semi-aquatic environments such as home on land but swimming for food/safety. I neither agree or disagree (not my field, I don't possess appropriate background/information), but I do think of it when evolution of vocal cords is mentioned.
I don't recall the sources ATM, possibly something out of CoEvolution Quarterly or Bucky Fuller. Again, not research papers.
Depending on which factors you weigh most heavily, sociality theories usually fit into either individual or group selection categories. They're sort of the default consensus, but not one that's firm.
Your idea would be what's called a spandrel hypothesis, basically that language (or culture etc) is a side effect of other adaptive traits.
It is not my idea per se, of course… I only gathered (well, it seems sort of obvious) that, given the overwhelmingly social nature of human intelligence, communication with high information throughput is likely the key differentiator between HS and other apes; the rest was ~1 minute of googling.
As to “side effect”, given better communication and consequently cooperation and potential for more complex collectives lead to persistent survival of the species in the environment, they seem like a pretty straightforward evolutionary advantage that would be expected to be naturally selected for in the first place. If anything, chances are in long term the great larynx update is the real side effect, it just happened to be a trait enabling all the above evolutionary advantages.
Stone tools predate even the oldest suggestions of intentional fire use by at least a million years, so the cooking hypothesis isn't particularly compelling. Elsewhere in this thread I've also discussed how it's not really an explanation either.
The only logical pathway is that some genetic mutation or plant-based hallucination allowed for lack of animalistic fear/true context generation within the brain. Understanding that bear/tiger/snake/etc won’t kill you in certain circumstances, means you can expend exponentially less calories and focus on building tools etc. It allows for rapid growth across the species in many areas.
chimpanzees, gorillas, orangutans evolved intelligence too. They are smarter than most other critters in the jungle. Just all not as much as the lineage that leads to humans.
It's actually quite difficult to define human intelligence. Every time we think we find something unique by humans eventually some animal turns up that can do it too. It may be all just a question of degree and how it's used.
From what I've heard, language is unambiguously unique to humans, if you consider grammar an integral part of languages. You can teach chimpanzees hand signs, but they could never make the leap to stringing them together under a coherent rule: something like the difference between "Mom give me cookies" vs "I give mom cookies."
(I'm no expert, so take that with a grain of salt.)
proto-grammers are fairly common. https://en.wikipedia.org/wiki/Alex_(parrot) for example shows that parrots are capable of understanding English word order to some extent.
"Why humans evolved intelligence but orangutans did not".
There's a different way to think about this that is closer to how evolution actually works and will make the answer clear.
Our common ancestor (common to orangutans and humans) did evolve intelligence (concurrently with harnessing fire, clothing etc.). Not all of them, but some of them. And they broke off from the group. We now call them humans.
Intelligence was evolved millions of years after the most recent common ancestor. Harnessing fire, clothing, etc. came later still. The lineage that would ultimately give rise to humans split from the chimp/bonobo lineage as the human ancestors adapted to savanna life, likely due to aridification brought on by the formation of the Himalayas.
It's possible that selective pressure towards intelligence was greater for the human lineage than for the others. It's also possible that the evolution of intelligence was equally likely across the different lineages and humans just happened to be the one where the mutation happened. Regardless, once human ancestors filled the niche, it would have been difficult for another lineage to get in on the game.
I always believed that it was the group that had first mastered fire. Cooking food fundamentally changed human energy budgets. And keeping a fire meant that the group would congregate and form a larger social group, which would then lead to greater communication.
This of course changes the question as to why only/mainly homo erectus developed the capability.
Intelligence must surely be a cluster of evolved changes, let's say A-Z. Each of those letters must have appeared, and been advantageous on their own (or they wouldn't have persisted).
So why didn't chimps get some of them?
For example, chimps have hands, but do not exhibit anywhere near the dexterity and agility of human hands.
There were no chimps back then. We had a shared common ancestor, and subgroups gradually emerged and gradually became different enough that they stopped interbreeding (or were physically separated).
Think less in terms of "this must be inherently better than that" and more in terms of the thermodynamics at play. Dexterous hands probably have some cost. Maybe they aren't as durable as a chimps hands. Maybe they take more calories to run. Maybe they need more brain power dedicated toward the hands and respective energy requirements. I'm not really sure what they may be, but there are usually tradeoffs between any A vs B in an organism.
Now if these costs are indeed less than the fitness advantage of a chimp having more dexterous hands, and that is in biological fitness as in reproductive success not the colloquial 'fitness' as in going to the gym, and that mutation for dexterous hands is present among the breeding population, you will expect to see offspring with that mutation, having higher fitness, to increase in frequency in the population.
There are a lot of potential edge cases to consider as well. Maybe the dexterous hands allele is very close to a very bad allele in chimps, such that through recombination it is likely that these two alleles are inherited together (called linkage). You'd see both these alleles purged from the population over time through purifying selection.
There is the population history aspect to consider. Maybe you don't need dexterous hands if your population is still living in the jungle among plentiful calories like the chimpanzee. Maybe it is more relevant to comparatively more feeble humans that were pushed out of that jungle by physically stronger ape populations into more nutrient poor environments, where suddenly the increased fitness from the advantages dexterous hands might bring now pay for their energy costs.
They did get some of them. Functionally, chimps are pretty smart compared to almost anything but a human. Only if you define intelligence specifically as the gap between humans and chimps (or whatever other reference) can you say chimps didn't get any of the pieces. We can ask why humans have more of the pieces, but that's basically the same question as why any species diverges. So, some inscrutable combination of chance, path dependence, etc
I have no expertise in the field whatsoever but can't help but wonder if it is at all related to our consumption of cooked foods. At the very least it reduces the incidence of parasites but I am sure there are myriad benefits beyond treating foods for longevity through methods like smoking.
I have zero expertise either, but I find this field fascinating. Cooking makes it easier to chew so we can devote less of our skulls to chewing muscles. At birth our skulls are barely small enough to fit through the birth canal in one orientation, and one of the prerequisites for a baby to be born is that it’s facing head down and shoulders rotated into that orientation. Maybe cooking is beneficial because it allowed us to have a bigger braincase but also it gave us access to more nutrients from the same food.
I think this is actually an easy question to answer because you’ve accidentally preselected your demographics.
Imagine this: among primates, there is an even distribution of species of differing levels of intelligence. All the primates who became intelligent have similar evolution paths because intelligence defines their evolution path (opposable thumbs, large heads, standing upright, etc.) Then because they all have similar evolution paths we put all those into the genus “Homo.” Each of species of the genus Homo eventually either breeds with each other or genocides one another until there are only the Homo Sapiens left.
So with an even distribution of intelligence among all primates, it’s logical that, given enough time, all that is left are primates of sufficient intelligence enough to breed with each other or be genocided until there is only one species, or many species of primates who weren’t intelligent enough.
This is my guess (I’m not a biologist or ancient historian or anything)
Because we are farther way on the evolutionary tree then is commonly thought, there is a tree of common ancestors going much further back (5 million or more years) that links humans with monkeys
All apes are intelligent. Studies have shown that their causal reasoning is almost on par with humans. What they seem to lack is language for communicating sophisticated concepts and persisting them across generations.
That question is analogous to asking why did some fish grow legs and become mammals.
The answer is mutations sometimes specific members of a group will gain a mutation that will overtime cause that group to split off away from the ancestor group. It’s all a matter of chance evolution doesn’t have a direction.
Multiple lines of mammals have independently evolved back into being marine life. Whales, seals and manatees do not have a common ancestor, for example.
Given that the future human is different than you are today, they could ask you the same questions. How does it FEEL for you to communicate worldwide with an HN post, but not yet have the ability to (insert advanced capability here).
Every one of our evolutionary ancestors was the best human yet, just like we are.
I can extrapolate based on my toddler that a modern human dumped in the wild would invent language. He has made several phonemes that aren’t in the language we speak at home. And he’s clever enough that even though he’s never seen us stand on furniture, he still climbs drawers and chairs if there’s something he wants that’s out of reach. I think that tool use and language are borne of some innate drive that’s accelerated by culture.
Evolution doesn't have end goals like building the most powerful computer possible. If caloric excesses are a factor, it's because there was some other selective pressure that made use of the energy to support more neurons. But even then, more hardware isn't the same thing as more intelligence. Elephants and whales have bigger brains than we do. Shrews and birds have a higher brain/body mass ratio. None of them are intelligent to the degree humans are. An explanation for human intelligence has to explain us, not just our brain mass.
Sperm whales may have more massive brains, but they have fewer cortical neurons total, and of course a much smaller brain to body mass ratio.
But more importantly for this conversation, our brains use up a staggering 20-25% of our resting metabolic needs. A whale brain uses something like 3%.
For us to be able to devote 20% of our calories to our brains, we simply needed to have a huge excess in the number of calories we had available. This is why the cooking hypothesis makes sense. Once we were smart enough to get lots of excess calories, that opened the door to this new fitness landscape of organisms that could devote a ridiculous proportion of their food to their brains. It wasn't that we gave up something else, it's that this wasn't even a possibility before.
All the evidence we have points to the vast, vast majority (>90%) of non-african human ancestry originating from hominin populations that were in Africa around 60-80k years ago, and were anatomically modern about 300k years ago. This article is about an ancestral clade of archaic hominins that contributed around 2% of modern non-african ancestry globally, that we've known about for years.
OOA (with minor admixture) is the consensus position for a lot of excellent reasons.
It is also the consensus position for a lot of bad reasons though.
There is an assumption that belief in, or even reasonable agnosticism towards, any other theory can only be motivated by racism.
There are many people that believe OOA because they want to believe it, because they want to believe we are all more similar than we are different, etc.
Multiregional hypotheses are perfectly plausible. We have very limited information one way or another. Out of Africa may be more likely but it is far from certain.
Just to be clear about what the term multiregionalism means, it's an argument that there's anatomical continuity between archaic hominin populations around afroeurasia and modern human populations. That is, anatomical modernity didn't evolve once in Africa, but multiple times all over the world in populations that are still extant today. A multiregional hypothesis might say that modern Chinese people evolved from archaic populations in Asia.
This is completely and unequivocally rejected by the genetic evidence. The evidence is so absolutely overwhelming that even fucking Wolpoff came around and now says:
It is broadly agreed that all recent/living human populations ultimately descend from Africans.
Now, if you mean something completely different to the commonly understood definition of multiregionalism, I'm willing to hear it.
There are many people that believe OOA because they want to believe it
But, also, There are many people that [do not] believe OOA because they [do not] want to believe it.
That's why we look at genetic evidence, to eliminate nonsense. That evidence strongly points to chimps, gorillas, humans etc all coming from the same place.
If it makes you feels better, think of it this way:
we don't believe OOA because the evidence says we're related to blacks. We believe it because the evidence says we're pretty much hairless apes. (And a lot of us aren't even hairless!)
theres actually almost zero clarity around the common ancestor between apes and humans, and a lot of speculation that the common ancestor lived 6-8 million years ago.
> That evidence strongly points to chimps, gorillas, humans etc all coming from the same place.
No. Non-African humans have genetic lineages that do not occur anywhere in Africa.
This doesn't mean OOA is necessarily false, but does makes it much less likely.
Also, lumping in primates is a red herring. The resolution of our gene clade knowledge doesn't go that far back. Dreaming about some hypothetical ape ancestor is a vibe, not a science.
You're going to have to explain this one. The only thing I can figure is that you're making a distinction about "traditional" RAO vs modern hybridization models, but my comment already mentions those (albeit indirectly, given that I'm writing to an audience).
But if you're genuinely trying to say that the broad strokes out of africa model isn't consensus, I have no idea what you're talking about. Just to make sure I haven't missed some momentous event since the last time I was doing fieldwork, I even checked some unpublished books, review papers, and actual research. They all talk about OOA as completely settled or instead simply assume it.
We know there were indigenous folks here in Australia ~50K years ago, and we know that we didn't evolve in Australia, so any origination must be further back than that.
You are completely wrong. Out of Africa is correct. Out of Asia is incorrect, and is outdated sino propaganda. Even the modern Chinese state admits that DNA evidence pretty conclusively points to out of Africa.
All of the great apes are incredibly intelligent in comparison to most other animals. The basic roots of our intelligence are probably a common feature to the whole family, but there's no consensus on why it's so advanced in humans. Any paleoanthropologist can rattle off about half a dozen possible explanations, but we honestly don't have enough evidence to really distinguish if, when, and how these were factors at different points in human evolution. Here's a quick attempt at some broad categories, which each have multiple hypotheses within them:
* Because intelligence had advantages for individual selection (e.g. mimetic recall hypothesis)
* Because intelligence had advantages for group selection
* Because intelligence had advantages for sexual selection (spandrel hypotheses often start here)
* Because adapting to rapidly varying ecological conditions required so many adaptations that we crossed some kind of barrier and "fell into" intelligence
* Because intelligence helped with foraging/hunting (exclusive of sociality)
Less extinction, and more evolution.
And same really goes for other niches we do not even occupy. You need to get something out of those expensive to keep brains.
I dunno ... 10 bits/second ain't so lavish...
One of my pet theories is that it may be related to vocal cord development[0], where losing certain physiology that allows apes to be louder allowed humans to be more specific, if quieter, with enhanced pitch control and stability offering higher information density communication. This unlocks more complex societal interactions and detailed shared maps. (In Iain McGilchrist’s terms, it let the Emissary—the part of the brain shown to specialize in classification and pattern recognition, the requisite building blocks for efficient communication—to take priority.)
This is an example highlighting how it is not about individual humans “becoming smarter”, evolving larger brains, etc., but rather about humans becoming capable of working together in more sophisticated ways. In fact, human brain shrunk in the last few thousands of years, in concert with growing size of our societies and labour specialization[1], which in turn in no small part is helped by communication density offered by our vocal cords. Really, humans in this way are closer ants[2], where being part of human community is the defining part of our nature.
[0] https://www.theguardian.com/science/2022/aug/11/how-quirk-of...
[1] https://www.bbc.com/future/article/20240517-the-human-brain-...
[2] Ants that farm and have stronger division of labour have smaller brains: https://www.smithsonianmag.com/science-nature/how-ants-becam...
I've read, from a few separate sources that were not research papers, something similar that claimed the development was a result of existing in semi-aquatic environments such as home on land but swimming for food/safety. I neither agree or disagree (not my field, I don't possess appropriate background/information), but I do think of it when evolution of vocal cords is mentioned.
I don't recall the sources ATM, possibly something out of CoEvolution Quarterly or Bucky Fuller. Again, not research papers.
Your idea would be what's called a spandrel hypothesis, basically that language (or culture etc) is a side effect of other adaptive traits.
As to “side effect”, given better communication and consequently cooperation and potential for more complex collectives lead to persistent survival of the species in the environment, they seem like a pretty straightforward evolutionary advantage that would be expected to be naturally selected for in the first place. If anything, chances are in long term the great larynx update is the real side effect, it just happened to be a trait enabling all the above evolutionary advantages.
It's actually quite difficult to define human intelligence. Every time we think we find something unique by humans eventually some animal turns up that can do it too. It may be all just a question of degree and how it's used.
(I'm no expert, so take that with a grain of salt.)
As does house finches: https://royalsocietypublishing.org/doi/full/10.1098/rspb.202...
Sperm whale codas exhibit contextual and combinatorial structure: https://www.nature.com/articles/s41467-024-47221-8
Ants have developed symbolic language: https://pmc.ncbi.nlm.nih.gov/articles/PMC10093743/
Everywhere we look close enough, we find life doing smart things.
Some great apes can learn to use symbols for communication. Bees can use specific dances to indicate direction and distance.
There's a different way to think about this that is closer to how evolution actually works and will make the answer clear.
Our common ancestor (common to orangutans and humans) did evolve intelligence (concurrently with harnessing fire, clothing etc.). Not all of them, but some of them. And they broke off from the group. We now call them humans.
It's possible that selective pressure towards intelligence was greater for the human lineage than for the others. It's also possible that the evolution of intelligence was equally likely across the different lineages and humans just happened to be the one where the mutation happened. Regardless, once human ancestors filled the niche, it would have been difficult for another lineage to get in on the game.
This of course changes the question as to why only/mainly homo erectus developed the capability.
So why didn't chimps get some of them?
For example, chimps have hands, but do not exhibit anywhere near the dexterity and agility of human hands.
The chimps that did get them we now call humans.
There were no chimps back then. We had a shared common ancestor, and subgroups gradually emerged and gradually became different enough that they stopped interbreeding (or were physically separated).
Now if these costs are indeed less than the fitness advantage of a chimp having more dexterous hands, and that is in biological fitness as in reproductive success not the colloquial 'fitness' as in going to the gym, and that mutation for dexterous hands is present among the breeding population, you will expect to see offspring with that mutation, having higher fitness, to increase in frequency in the population.
There are a lot of potential edge cases to consider as well. Maybe the dexterous hands allele is very close to a very bad allele in chimps, such that through recombination it is likely that these two alleles are inherited together (called linkage). You'd see both these alleles purged from the population over time through purifying selection.
There is the population history aspect to consider. Maybe you don't need dexterous hands if your population is still living in the jungle among plentiful calories like the chimpanzee. Maybe it is more relevant to comparatively more feeble humans that were pushed out of that jungle by physically stronger ape populations into more nutrient poor environments, where suddenly the increased fitness from the advantages dexterous hands might bring now pay for their energy costs.
We destroyed the many other humanoid/intelligent species, who did compete with us.
Imagine this: among primates, there is an even distribution of species of differing levels of intelligence. All the primates who became intelligent have similar evolution paths because intelligence defines their evolution path (opposable thumbs, large heads, standing upright, etc.) Then because they all have similar evolution paths we put all those into the genus “Homo.” Each of species of the genus Homo eventually either breeds with each other or genocides one another until there are only the Homo Sapiens left.
So with an even distribution of intelligence among all primates, it’s logical that, given enough time, all that is left are primates of sufficient intelligence enough to breed with each other or be genocided until there is only one species, or many species of primates who weren’t intelligent enough.
This is my guess (I’m not a biologist or ancient historian or anything)
The answer is mutations sometimes specific members of a group will gain a mutation that will overtime cause that group to split off away from the ancestor group. It’s all a matter of chance evolution doesn’t have a direction.
What would "intelligence" look like WHILE it was evolving?
A slightly more unsettling thought: How would newly-emerging intelligence FEEL like, internally?
Also, how would humans fare if born and raised in the wild, without any language or tools taught to them?
Every one of our evolutionary ancestors was the best human yet, just like we are.
But more importantly for this conversation, our brains use up a staggering 20-25% of our resting metabolic needs. A whale brain uses something like 3%.
For us to be able to devote 20% of our calories to our brains, we simply needed to have a huge excess in the number of calories we had available. This is why the cooking hypothesis makes sense. Once we were smart enough to get lots of excess calories, that opened the door to this new fitness landscape of organisms that could devote a ridiculous proportion of their food to their brains. It wasn't that we gave up something else, it's that this wasn't even a possibility before.
Is GPU already the metaphor du jour? I thought we were still aboard the steam engine ;)
Survival of the fittest never includes the gene impacts plants and fungi can force onto creatures.
Also cyclical 12kyr catastrophic events leading to small condensation of species under stress.
OOA (with minor admixture) is the consensus position for a lot of excellent reasons.
There is an assumption that belief in, or even reasonable agnosticism towards, any other theory can only be motivated by racism.
There are many people that believe OOA because they want to believe it, because they want to believe we are all more similar than we are different, etc.
Multiregional hypotheses are perfectly plausible. We have very limited information one way or another. Out of Africa may be more likely but it is far from certain.
This is completely and unequivocally rejected by the genetic evidence. The evidence is so absolutely overwhelming that even fucking Wolpoff came around and now says:
Now, if you mean something completely different to the commonly understood definition of multiregionalism, I'm willing to hear it.But, also, There are many people that [do not] believe OOA because they [do not] want to believe it.
That's why we look at genetic evidence, to eliminate nonsense. That evidence strongly points to chimps, gorillas, humans etc all coming from the same place.
If it makes you feels better, think of it this way:
we don't believe OOA because the evidence says we're related to blacks. We believe it because the evidence says we're pretty much hairless apes. (And a lot of us aren't even hairless!)
There, feel better about it now?
No. Non-African humans have genetic lineages that do not occur anywhere in Africa.
This doesn't mean OOA is necessarily false, but does makes it much less likely.
Also, lumping in primates is a red herring. The resolution of our gene clade knowledge doesn't go that far back. Dreaming about some hypothetical ape ancestor is a vibe, not a science.
It isn't really. Serious historians and geneticists take great issue with it.
It's only really the pop-anthropologists (the non-rigorous social science ones) who think OOA is a settled issue.
But if you're genuinely trying to say that the broad strokes out of africa model isn't consensus, I have no idea what you're talking about. Just to make sure I haven't missed some momentous event since the last time I was doing fieldwork, I even checked some unpublished books, review papers, and actual research. They all talk about OOA as completely settled or instead simply assume it.
Is this like a CAS thing? Truly baffled.