I'm curious why humans evolved intelligence and chimpanzees, gorillas, orangutans did not.
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)
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...
Less extinction, and more evolution.
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...
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.
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.
The stone tools that predate this by a few million years reinforce the cooked food hypothesis in this 'chicken or egg' situation.
That means, if a trait is unaffected by the environment, then there's no attribution of why it developed; this is the default state.
I feel often in biology, there's a mindset of figuring out why features developed and that's great for pushing the field but it runs into a limit. Not every trait developed from a environmental pressure.
I don't agree and that's totally fine-- we have millions of gene edits from parent to child and not every change is environment-selected. Certain features can be dominant by the mechanics of genes, not due to selective pressure.
Blood types are an example of this-- they aren't major environmental pressures for why one blood type is more common than others, it mostly comes down to population mechanics.
My belief is that "spandrel" features are less selected for studies because they have a harder burden to prove; there exists no external reason they exist and this must be verified through proof by contradiction. Its a high bar to prove.
But also, I guess by "feature" I tend to mean "noticeable feature". You might be more right about that, at least as far as terminology goes. At the bottom end you have a point mutation to a codon for the same amino acid, and then eventually you get something like a slightly different color pattern. Those are probably free.
But as soon as you have to, say, add or increase the size of a physical feature, there's a metabolic cost. And when those features aren't used, that (small!) cost drives them to disappear in relatively short order (for instance, all the convergently legless lizards). That strongly implies that for those, there needs to be a persistent reason for them to keep existing.
Entirely aside, I wonder how long we need to have blood transfusions as part of society before blood type compatibility starts exerting selective pressure.
1. Survival is easier in groups
2. In order to survive in groups, we need to communicate
3. We communicate using language
4. Language is directly linked with intelligence
See how computers started displaying intelligence when we taught them our language
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.
Some great apes can learn to use symbols for communication. Bees can use specific dances to indicate direction and distance.
Starting from what should be considered "writing" to how to identify specific artifacts as abstract words.
Some researchers spend years in the forest studying one animal to isolate one single word they're speaking. Understanding other kind of intelligences is a crazy complex task.
(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.
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.
“Humans have visited the Moon and sent human-made spacecraft to other celestial bodies, becoming the first known species to do so.”
How would we know if we’re the first known anything? You don’t know what you don’t know, as they say.
Well, that's false. But we killed off/interbred with all of the peer/near-peer species.
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.
By any useful definition, the intelligence of human ancestors very closely resembled that of chimps for about 4 million years after the human and chimp lineages diverged. While it's impossible to say for certain, that's around the time that endocranial volumes started growing consistently beyond the range seen in chimps. That is also around the time of the first evidence of stone tool making.
As far as we can tell, no branch developed significantly increased intelligence after splitting off from our own lineage. That's not to say it definitely didn't happen or that our lineage was always the smartest, just that there isn't any evidence demonstrating a qualitative difference which has survived to the present. But it's weird that no such evidence exists.
Conversely different primate groups did independently evolve similar levels of intelligence, like Capuchin monkeys (which are new world primates) developed their intelligence after splitting off from the old world primates some 40 million years ago. Baboons and Macaques likewise each evolved intelligence independent of the great apes. Likewise similar levels (if different specializations) of intelligence have evolved independently outside the primates, such as cetaceans, elephants, and corvids. For cephalopods, which likewise are highly intelligent, their common ancestor with us didn't even have a brain.
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.
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.
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).
So it's not just brainpower, it's likely a combination of potential brainpower - which many species have/had - and fine motor control, which set up feedback loop that translated a mind/body synergy into practical evolutionary benefits.
This of course changes the question as to why only/mainly homo erectus developed the capability.
If you had a bunch of human children together and provided them sustenance and all that without adult interaction they might still develop normally and form their own language and means of communication with each other.
We don’t know for sure because such an experiment would be horrible and extremely immoral. However I do remember reading a while back that a similar situation happened where a bunch of deaf children in a an environment without much adult interaction did manage to create their own sign language to communicate with each other.
So it seems the feral child phenomena might be due to the fact that the child is alone rather than simply due to the child not having adult interaction.
You probably had Nicaraguan Sign Language [1] in mind. I think it’s a good example of the human brain’s ability to invent something and acquire knowledge easily. What I tried to show with my comment is that when human intelligence is discussed, it’s easy to refer to all instances of human achievements around us, but they are essentially accumulated cultural knowledge. Because of this, we tend to overestimate our intelligence, at least when comparing an individual human with an individual primate of another kind.
So, it’s also interesting why humans are probably unique in this ability to pass on and accumulate information, while other apes (and crows) limit this to skills like retrieving ants with sticks and breaking shells with stones.
Humans are a protected species, carefully raised and nurtured by higher organisms that are hundred thousand times larger than us (in terms of space and time). The earth and solar system is just a vivarium of galactic scale. Several "glass wall" mechanisms were placed to ensure we are separated from the rest of the universe, like the oort cloud.
Somewhere out there in the universe are humans living freely outside the glass wall.
As time goes on, the glass walls tend to age and occasionally the "cracks" allows external lifeforms (aliens) to slip past the protection layer, much like how insects or parasites would occasionally slip past any opening.
With this in mind, there would be two types of aliens/visitors to our enclosure: (1) lifeforms that are similar to humans in terms of size and biological complexity but more technologically advanced and (2) our protectors who are incomprehensibly larger and more complex than any life on earth. This isn't as outlandish as it seems to be considering there are stars that are million times larger than our own sun.
This sheer difference in scale might as well make the protectors exist in a different dimension. This explains why people would say that aliens were here all this time, but from another dimension. Technically they are here, but more accurately to say the protectors surround us.
Occasionally protectors would step in to prevent mankind from destroying their own enclosure, much like a terrarium owner would reach into the enclosure to remove unwanted organisms. Frequent unidentified sightings on nuclear sites is the protectors' way of peeking and reaching a "hand".
It remains to be seen if humanity would one day evolve to outgrow the enclosure.
We destroyed the many other humanoid/intelligent species, who did compete with us.
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.
which is the point. They were not evolved from the same species of land animal.
How much of the intelligence gap is culture and communication that lets us educate ourselves and compound knowledge vs biology? Homo lived for thousands and thousands of years with the same level of development as other apes
And they still are alongside us right now. Which to me is fascinating.
The other apes are intelligent enough for their niche. At some point in humanity's past, the environment was harsh enough that the less intelligent ones died.
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 ;)
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)
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?
No I mean absolutely zero contact with or help from modern (say since the last 10,000 years) human civilization.
I mean literally giving birth in a forest and then raising the baby there without ever speaking a word around it or showing it any tools etc.
(this assumes that it will survive to 1-2 years old without any fatal sickness etc. but let's say that the mother/parents will get just enough "outside" help to make sure it does, but the baby itself is not to come in contact with any tech or language)
Every one of our evolutionary ancestors was the best human yet, just like we are.
No no no, I don't mean going from already intelligent/sentient/sapient to MORE intelligent….
I mean, going from the levels of intelligence/awareness we see in insects → fish → chickens and cattle → monkeys/apes → what we consider "actual" intelligence as seen in humans.
Evolution of anything is obviously not some simple boolean switch: It's not like one day you're a full fish and the next day you give birth to an amphibian with legs.
But how would the gradual evolution of intelligence look and feel like?
Going from what we consider animals to be, to having awareness and introspective thoughts and future planning?
Is it like, do you have just 1 thought per day at first,
or can only count up to 3 for a few thousand years,
only plan for up to 1 day ahead, and remember that plan for only a few hours…
And when do all the clearly self-destructive things kick in, that we Modern Humans™ do that obviously harm individuals and the species? :)
Humans have the gift of understanding, but our lives are filled with things we either don’t really understand or that we have an illusion of understanding. Of course, we wonder “why does evil exist?” whereas cats wonder “when is dinnertime?”
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.