[AlotOfReading]

We don't know.

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)

[andrewflnr]

I hadn't heard the term "spandrel" before, especially not in this context. Makes sense, though. https://en.wikipedia.org/wiki/Spandrel_(biology)

[rirze]

I personally dislike the definitions here-- traits and genetic changes are, by default, unattributed to external pressures. They don't "arise" from the environment, rather the environment selects for traits through survival/reproduction, if applicable.

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.

[andrewflnr]

Technically yes, kind of, but if a feature is truly unaffected by the environment, then there's no particular reason it would get fixed, and you have to make the rather shaky assumption that it became widespread purely by chance. Most features have some cost, and the simplest explanation for that feature being widespread is that it has some counteracting benefit that leads to it being selected for. That's a reasonable first hypothesis, to say the least, which means the "spandrel" hypothesis makes sense as the less common special case.

[rirze]

> Most features have some cost

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.

[andrewflnr]

Blood types aren't fixed across the population. It's kind of a tricky question which of our points they make a better example for. :D

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.

[gyomu]

Didn't a lot of other great apes evolve intelligence similar to ours, but we more or less drove them all to extinction?

[shakna]

Less than more. Most of the early hominids crossbred. For as much violence as there was, there was also a lot of sex.

Less extinction, and more evolution.

[AlotOfReading]

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.

[nylonstrung]

The burial sites of Homo Naledi suggest they had developed burial rituals and primitive art which would mean non-Sapiens hominids were likely smarter than previously believed

[david-gpu]

The subject of Homo Naledi is very controversial. Take it with a grain of salt.

[Gravityloss]

it's interesting to think that since humans got established, becoming too intelligent became a disadvantage? Like there's a glass ceiling.

[zmmmmm]

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 ...

[dsign]

Came here to say this, but you did it for me :-) . I truly believe there's a more than 50% chance the vast history of hominids ends this century.

[Ekaros]

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.

[8bitsrule]

> Human brains are expensive in terms of energy

I dunno ... 10 bits/second ain't so lavish...

[dotancohen]

Perhaps, but 1/3 of your blood supply is expensive.

[energy123]

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.

[actionfromafar]

There are huge reserves of the population where contraception isn't a thing. There are so many people alive today, that evolving out intelligence is really hard to imagine. Perhaps in some kind of far future science fiction "robots spoonfeeding drooling humanoids" scenario.

[strogonoff]

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.

[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...

[Rediscover]

> ... vocal cord development ...

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.

[Mitochondriac]

Semi-aquatic environments make sense if you look at our brains dependency on DHA (seafood is a rich source) and the hypothesis that our fingers get wrinkly in water after a while to improve grip.

[usrnm]

Aren't we a lot more evolved for hunting animals on foot? The whole thing with us losing our fur and sweating with the whole body, adaptations to running and throwing stuff, all of this makes us better hunters, but not necessarilly fushermen.

[m0llusk]

The two go together. Living with water requires control of breathing. Hunting animals on land requires strong endurance and probably also an ability to carry water.

[AlotOfReading]

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.

[strogonoff]

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.

[KurSix]

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...

[anal_reactor]

I'm a huge fan of the hypothesis that:

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

[ChrisGreenHeur]

all of this applies to monkeys

[anal_reactor]

Yes but we were first

[ekianjo]

How about if we were the only apes to not fear fire as much and discovered that we get much more nutrients by cooking stuff?

[AlotOfReading]

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.

[Theodores]

The cooking hypothesis is not well known, however, from what I understand, this was when we went from having big guts and average brains to small guts and big brains. The fossil record of primates is far from complete, but roughly speaking, we have been eating cooked food for a million years.

The stone tools that predate this by a few million years reinforce the cooked food hypothesis in this 'chicken or egg' situation.

[bigbrained124]

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.