What are the primary drivers that caused selection pressure for intelligence in humans?

post by Towards_Keeperhood (Simon Skade) · 2024-11-07T09:40:20.275Z · LW · GW · No comments

This is a question post.

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  Answers
    7 TsviBT
    5 RHollerith
    4 Ape in the coat
    1 Towards_Keeperhood
None
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I just read the wikipedia article on the evolution of human intelligence, and TBH I wasn't super impressed with the quality of the considerations there.

I currently have 3 main (categories of) hypotheses for what caused selection pressure for intelligence in humans. (But please post an answer if you have other hypotheses that seem plausible!):

("H" for "hypothesis")

My prior intuitive guess would be that H1 seems quite a decent chunk more likely than H2 or H3. However, there's a possibly very big piece of evidence for H3: Humans are both the smartest land animals and have the best interface for using tools, and that would seem like a suspicious coincidence.

Any pieces of evidence or considerations are welcome, even if you don't have something close to a full answer!

(A main motivation for why I ask this is evaluating whether orcas might be smarter than humans [LW · GW]. (Where it seems to me like orcas have selection pressure for H1 and H2 but not H3.) So if you have more relevant considerations for that, e.g. why being selected on tool use in particular might cause human brains to generalize for being good at abstract problem solving, those would also be very appreciated!)

  1. ^

    The outwitting (e.g. cheating by having sex with someone of higher status while getting away with your spouse raising the child) could happen sub-consciously and would not necessarily need to be reflectively endorsed as what the person thinks are their values/desires.

Answers

answer by TsviBT · 2024-11-08T05:27:01.438Z · LW(p) · GW(p)
  • Fighting wars with neighboring tribes
  • Extractive foraging
  • Persistence hunting (which involves empathy, imagination (cf cave paintings), and tracking)
  • Niche expansion/travel (i.e. moving between habitat types)
  • In particular, sometimes entering harsh habitats puts various pressures
  • Growing up around people with cultural knowledge (advantage to altriciality, language, learning, imitation, intent-sharing)
  • Altriciality demands parents coordinate
  • Children's learning ability incentivizes parents to learn to teach well

etc.

There's a whole research field on this FYI.

↑ comment by Richard_Kennaway · 2024-11-08T10:11:20.797Z · LW(p) · GW(p)

Or briefly, intelligence is good for everything.

Replies from: TsviBT
↑ comment by TsviBT · 2024-11-08T13:49:16.736Z · LW(p) · GW(p)

Intelligence also has costs and has components that have to be invented, which explains why not all species are already human-level smart. One of the questions here is which selection pressures were so especially and exceptionally strong in the case of humans, that humans fell off the cliff.

↑ comment by Towards_Keeperhood (Simon Skade) · 2024-11-08T07:52:40.539Z · LW(p) · GW(p)

Thanks!

What's the ect? Or do you have links for where to learn more? (What's the name of the field?)

(I thought wikipedia would give me a good overview but your list was already more useful to me.)

Replies from: TsviBT
↑ comment by TsviBT · 2024-11-08T08:06:16.689Z · LW(p) · GW(p)

IDK, fields don't have to have names, there's just lots of work on these topics. You could start here https://en.wikipedia.org/wiki/Evolutionary_anthropology and google / google-scholar around.

See also https://www.youtube.com/watch?v=tz-L2Ll85rM&list=PL1B24EADC01219B23&index=556 (I'm linking to the whole playlist, linking to a random old one because those are the ones I remember being good, IDK about the new ones).

answer by RHollerith · 2024-11-13T06:27:12.271Z · LW(p) · GW(p)

It's also important to consider the selection pressure keeping intelligence low, namely, the fact that most animals chronically have trouble getting enough calories, combined with the high caloric needs of neural tissue.

It is no coincidence that human intelligence didn't start rising much till humans were reliably getting meat in their diet and were routinely cooking their food, which makes whatever calories are in food easier to digest, allowing the human gut to get smaller, which in turn reduced the caloric demands of the gut (which needs to be kept alive 24 hours a day even on a day when the person finds no food to eat).

answer by Ape in the coat · 2024-11-08T19:19:26.100Z · LW(p) · GW(p)

I suspect that runaway sexual selection played a huge part.

↑ comment by Towards_Keeperhood (Simon Skade) · 2024-11-08T19:29:01.783Z · LW(p) · GW(p)

thanks. Can you say more about why?

I mean runaway sexual selection is basically H1, which I updated to being less plausible. See my answer here [LW(p) · GW(p)]. (You could comment there why you think my update might be wrong or so.)

Replies from: Ape in the coat
↑ comment by Ape in the coat · 2024-11-09T05:56:46.386Z · LW(p) · GW(p)

I think that first some amount of intelligence in our ancestors evolved as necessary for survival as species - therefore explaining the "coincidence" of intelligence being useful for it - but then it was brought up to our current level as a runaway process. Because nothing other than a runaway process would be enough.

The thing is, ancestral hominids do not need this level of intelligence for survival purpose. Pack hunting, minor tool making, stamina regeneration, and being ridiculously good at throwing things is enough to completely dominate the ancestral environment. But our intelligence didn't stop at this level, so something else has to be pushing it forward.

And sexual selection is the most obvious candidate. We already have examples of animals with ridiculously overdeveloped traits, due to it, up to the point where they actively harmful to the survival of an individual. We know that humans have extremely complicated mating rituals. At this point, the pieces just fall together.

Replies from: Simon Skade
↑ comment by Towards_Keeperhood (Simon Skade) · 2024-11-09T10:29:28.666Z · LW(p) · GW(p)

Thanks!

I agree that sexual selection is a thing - that it's the reason for e.g. women sometimes having unnecessarily large breasts.

But I think it gets straightened out over long timescales - and faster the more expensive the trait is. And intelligence seems ridiculously expensive in terms of metabolic energy our brain uses (or childbirth motality).

A main piece that updated me was reading anecdotes in Scott Alexander's Book review of "The Secret of our success" [LW · GW] where I now think that humans did need their intelligence for survival. (E.g. 30 year old hunter gatherers perform better at hunting etc than hunter gatherers in their early 20s, even though the latter are more physically fit.)

Replies from: Ape in the coat
↑ comment by Ape in the coat · 2024-11-11T11:50:16.376Z · LW(p) · GW(p)

30 year old hunter gatherers perform better at hunting etc than hunter gatherers in their early 20s, even though the latter are more physically fit.

I'm not sure how it's relevant. Older hunters are not more intelligent, they are more experienced. Moreover, your personal hunting success doesn't necessary translates into your reproductive success - all the tribe will be enjoying the gains of your hunt and our ancestors had a strong egalitarian instinct. And even though higher intelligence improves the yields of your labor, it doesn't mean that it creates strong enough selection pressure to outweighs other factors.

But I think it gets straightened out over long timescales - and faster the more expensive the trait is.

It doesn't have to happen for a species who is already dominating their environment. As for them it can be the most dominant factor determining inclusive genetic fitness.

And if the trait, the runaway sexual selection is propagating, is itself helpful in competition with other species, which is obviously true for intelligence, there is just no reason for such straightening over a long timescale.

Replies from: Simon Skade
↑ comment by Towards_Keeperhood (Simon Skade) · 2024-11-11T12:44:12.844Z · LW(p) · GW(p)

I'm not sure how it's relevant.

I thought if humans were vastly more intelligent than they needed to be they would already learn all the relevant knowledge quickly enough so they reach their peak in the 20s.

And if the trait, the runaway sexual selection is propagating, is itself helpful in competition with other species, which is obviously true for intelligence, there is just no reason for such straightening over a long timescale.

I mean for an expensive trait like intelligence I'd say the benefits need to at least almost be worth the costs, and then I feel like rather attributing the selection for intelligence to "because it was useful" rather than "because it was a runaway selection".

Replies from: Ape in the coat
↑ comment by Ape in the coat · 2024-11-11T13:22:59.727Z · LW(p) · GW(p)

I thought if humans were vastly more intelligent than they needed to be they would already learn all the relevant knowledge quickly enough so they reach their peak in the 20s.

There is a difference between being more intelligent than you need for pure survival and being so intelligent that you can reach the objective ceiling of a craft at early age.

I mean for an expensive trait like intelligence I'd say the benefits need to at least almost be worth the costs, and then I feel like rather attributing the selection for intelligence to "because it was useful" rather than "because it was a runaway selection".

The benefit is in increased inclusive genetic fitness. A singular metric that encorparates both success in competition with other species and with other members of your species due to sexual selection. If the species is already dominating the environment then the pressure from the first component compared to the second decreases. 

That's why I'm attributing the level of human intelligence in large part to runaway sexual selection. Without it, as soon as interspecies competition became the most important for reproductive success, natural selection would not push for even grater intelligence in humans, even though it could improve our ability to dominate the environment even more.

Replies from: Simon Skade
↑ comment by Towards_Keeperhood (Simon Skade) · 2024-11-11T16:21:24.915Z · LW(p) · GW(p)

If the species is already dominating the environment then the pressure from the first component compared to the second decreases. 

I agree with this. However I don't think humans had nearly sufficient slack for most of history. I don't think they dominated the environment up until 20000years [1]ago or so, and I think most improvements in intelligence come from earlier.

That's why I'm attributing the level of human intelligence in large part to runaway sexual selection. Without it, as soon as interspecies competition became the most important for reproductive success, natural selection would not push for even grater intelligence in humans, even though it could improve our ability to dominate the environment even more.

I'm definitely not saying that group selection lead to intelligence in humans (only that group selection would've removed it over long timescales if it wasn't useful). However I think that there were (through basically all of human history) significant individual fitness benefits from being smarter that did not come from outwitting each other, e.g. being better able to master hunting techniques and thereby gaining higher status in the tribe.

 

  1. ^

    Or could also be 100k years, idk

answer by Towards_Keeperhood · 2024-11-08T17:52:13.217Z · LW(p) · GW(p)

My prior intuitive guess would be that H1 seems quite a decent chunk more likely than H2 or H3.

Actually I changed my mind.

Why I thought this before: H1 seems like a potential runaway-process and is clearly about individual selection which has stronger effects than group selection (and it was mentioned in HPMoR).

Why I don't think this anymore:

  • It would also be incredibly huge coincidence if intelligence mostly evolved because of social dynamics but happened to be useful for all sorts of other survival techniques hunters and gatherers use. See e.g. Scott Alexander's Book review of "The Secret of our success" [LW · GW].
  • If there was only individual benefits for intelligence but it was not very useful otherwise then over long timelines group selection[1] would actually select against smarter humans because their neurons would use up more metabolic energy.

However, there's a possibly very big piece of evidence for H3: Humans are both the smartest land animals and have the best interface for using tools, and that would seem like a suspicious coincidence.

I think this is not a coincidence but rather that tool use let humans fall into an attractor basin where payoffs of intelligence were more significant.

  1. ^

    I mean group selection that could potentially be on a level of species where species go extinct. Please lmk if that's actually called differently.

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