IIUC human intelligence is not in evolutionary equilibrium; it’s been increasing pretty rapidly (by the standards of biological evolution) over the course of humanity’s development, right up to “recent” evolutionary history. So difficulty-of-improving-on-a-system-already-optimized-by-evolution isn’t that big of a barrier here, and we should expect to see plenty of beneficial variants which have not yet reached fixation just by virtue of evolution not having had enough time yet.
(Of course separate from that, there are also the usual loopholes to evolutionary optimality which you listed—e.g. mutation load or variants with tradeoffs in the ancestral environment. But on my current understanding those are a minority of the available gains from human genetic intelligence enhancement.)
While cultural intelligence has indeed evolved rapidly, the genetic architecture supporting it operates through complex stochastic development and co-evolutionary dynamics that simple statistical models miss. The most promising genetic enhancements likely target meta-parameters governing learning capabilities rather than direct IQ-associated variants.
Longer:
You make a good point about human intelligence potentially being out of evolutionary equilibrium. The rapid advancement of human capabilities certainly suggests beneficial genetic variants might still be working their way through the population.
I’d also suggest this creates an even more interesting picture when combined with developmental stochasticity—the inherent randomness in how neural systems form even with identical genetic inputs (see other comment response to Yair for more detail). This stochasticity means genetic variants don’t deterministically produce intelligence outcomes but rather influence probabilistic developmental processes.
What complicates the picture further is that intelligence emerges through co-evolution between our genes and our cultural tools. Following Heyes’ cognitive gadgets theory, genetic factors don’t directly produce intelligence but rather interact with cultural infrastructure to shape learning processes. This suggests the most valuable genetic variants might not directly enhance raw processing power but instead improve how effectively our brains interface with cultural tools—essentially helping our brains better leverage the extraordinary cultural inheritance (language among other things) we already possess.
Rather than simply accumulating variants statistically associated with IQ, effective enhancement might target meta-parameters governing learning capabilities—the mechanisms that allow our brains to adapt to and leverage our rapidly evolving cultural environment. This isn’t an argument against genetic enhancement, but for more sophisticated approaches that respect how intelligence actually emerges.
(Workshopped this with my different AI tools a bit and I now have a paper outline saved on this if you want more of the specific modelling frame lol)
IIUC human intelligence is not in evolutionary equilibrium; it’s been increasing pretty rapidly (by the standards of biological evolution) over the course of humanity’s development, right up to “recent” evolutionary history.
Why do you believe that? Do we have data that mutations that are associated with higher IQ are more prevalent today than 5,000 years ago?
The best and most recent (last year) evidence based on comparing ancient and modern genomes seems to suggest intelligence was selected very strongly during agricultural revolution (a full SD) and has changed <0.2SD since AD0 [for the populations studied]
It seems that the evolutionary pressure for intelligence wasnt that strong in the last few thousand years compared to selection on many other traits (health and sexual selected traits seem to dominate).
Edit: it would take some effort to dig up this study. Ping me if this is of interest to you.
The evidence I have mentally cached is brain size. The evolutionary trajectory of brain size is relatively easy to measure just by looking at skulls from archaeological sites, and IIRC it has increased steadily through human evolutionary history and does not seem to be in evolutionary equilibrium.
(Also on priors, even before any evidence, we should strongly expect humans to not be in evolutionary equilibrium. As the saying goes, “humans are the stupidest thing which could take off, otherwise we would have taken off sooner”. I.e. since the timescale of our takeoff is much faster than evolution, the only way we could be at equilibrium is if a maximal-under-constraints intelligence level just happened to be exactly enough for humans to take off.)
There’s probably other kinds of evidence as well; this isn’t a topic I’ve studied much.
If humans are the stupidest thing which could take off, and human civilization arose the moment we became smart enough to build it, there is one set of observations which bothers me:
The Bering land bridge sank around 11,000 BCE, cutting off the Americas from Afroeurasia until the last thousand years.
Around 10,000 BCE, people in the Fertile Crescent started growing wheat, barley, and lentils.
Around 9,000-7,000 BCE, people in Central Mexico started growing corn, beans, and squash.
10-13 separate human groups developed farming on their own with no contact between them. The Sahel region is a clear example, cut off from Eurasia by the Sahara Desert.
Humans had lived in the Fertile Crescent for 40,000-50,000 years before farming started.
Here’s the key point: humans lived all over the world for tens of thousands of years doing basically the same hunter-gatherer thing. Then suddenly, within just a few thousand years starting around 12,000 years ago, many separate groups all invented farming.
I don’t find it plausible that this happened because humans everywhere suddenly evolved to be smarter at the same time across 10+ isolated populations. That’s not how advantageous genetic traits tend to emerge, and if it was the case here, there are some specific bits of genetic evidence I’d expect to see (and I don’t see them).
I like Bellwood’s hypothesis better: a global climate trigger made farming possible in multiple regions at roughly the same time. When the last ice age ended, the climate stabilized, creating reliable growing seasons that allowed early farming to succeed.
If farming is needed for civilization, and farming happened because of climate changes rather than humans reaching some intelligence threshold, I don’t think the “stupidest possible takeoff” hypothesis looks as plausible. Humans had the brains to invent farming long before they actually did it, and it seems unlikely that the evolutionary arms race that made us smarter stopped at exactly the point we became smart enough to develop agriculture and humans just stagnated while waiting for a better climate to take off.
I do agree that the end of the last glacial period was the obvious immediate trigger for agriculture. But the “humans are the stupidest thing which could take off model” still holds, because evolution largely operates on a slower timescale than the glacial cycle.
Specifics: the last glacial period ran from roughly 115k years ago to 12k years ago. Whereas, if you look at a timeline of human evolution, most of the evolution from apes to humans happens on a timescale of 100k − 10M years. So it’s really only the very last little bit where an ice age was blocking takeoff. In particular, if human intelligence has been at evolutionary equilibrium for some time, then we should wonder why humanity didn’t take off 115k years ago, before the last ice age.
In particular, if human intelligence has been at evolutionary equilibrium for some time, then we should wonder why humanity didn’t take off 115k years ago, before the last ice age.
Yes we should wonder that. Specifically, we note
Humans and chimpanzees split about 7M years ago
The transition from archaic to anatomically modern humans was about 200k years ago
Humans didn’t substantially develop agriculture before the last ice age started 115k years ago (we’d expect to see archaeological evidence in the form of e.g. agricultural tools which we don’t see, while we do see stuff like stone axes)
Multiple isolated human populations independently developed agriculture starting about 12k years ago
From this we can conclude that either:
Pre-ice-age humans were on the cusp of being able to develop agriculture, and an extra 100k years of gradual evolution was sufficient to bump them over the relevant threshold
There was some notable period between 115k and 12k years ago where the rate of selective pressure on humans substantially strengthened or changed direction for some reason. Which might correspond to a very tight population bottleneck:
IIUC human intelligence is not in evolutionary equilibrium; it’s been increasing pretty rapidly (by the standards of biological evolution) over the course of humanity’s development, right up to “recent” evolutionary history. So difficulty-of-improving-on-a-system-already-optimized-by-evolution isn’t that big of a barrier here, and we should expect to see plenty of beneficial variants which have not yet reached fixation just by virtue of evolution not having had enough time yet.
(Of course separate from that, there are also the usual loopholes to evolutionary optimality which you listed—e.g. mutation load or variants with tradeoffs in the ancestral environment. But on my current understanding those are a minority of the available gains from human genetic intelligence enhancement.)
TL;DR:
While cultural intelligence has indeed evolved rapidly, the genetic architecture supporting it operates through complex stochastic development and co-evolutionary dynamics that simple statistical models miss. The most promising genetic enhancements likely target meta-parameters governing learning capabilities rather than direct IQ-associated variants.
Longer:
You make a good point about human intelligence potentially being out of evolutionary equilibrium. The rapid advancement of human capabilities certainly suggests beneficial genetic variants might still be working their way through the population.
I’d also suggest this creates an even more interesting picture when combined with developmental stochasticity—the inherent randomness in how neural systems form even with identical genetic inputs (see other comment response to Yair for more detail). This stochasticity means genetic variants don’t deterministically produce intelligence outcomes but rather influence probabilistic developmental processes.
What complicates the picture further is that intelligence emerges through co-evolution between our genes and our cultural tools. Following Heyes’ cognitive gadgets theory, genetic factors don’t directly produce intelligence but rather interact with cultural infrastructure to shape learning processes. This suggests the most valuable genetic variants might not directly enhance raw processing power but instead improve how effectively our brains interface with cultural tools—essentially helping our brains better leverage the extraordinary cultural inheritance (language among other things) we already possess.
Rather than simply accumulating variants statistically associated with IQ, effective enhancement might target meta-parameters governing learning capabilities—the mechanisms that allow our brains to adapt to and leverage our rapidly evolving cultural environment. This isn’t an argument against genetic enhancement, but for more sophisticated approaches that respect how intelligence actually emerges.
(Workshopped this with my different AI tools a bit and I now have a paper outline saved on this if you want more of the specific modelling frame lol)
Why do you believe that? Do we have data that mutations that are associated with higher IQ are more prevalent today than 5,000 years ago?
The best and most recent (last year) evidence based on comparing ancient and modern genomes seems to suggest intelligence was selected very strongly during agricultural revolution (a full SD) and has changed <0.2SD since AD0 [for the populations studied]
It seems that the evolutionary pressure for intelligence wasnt that strong in the last few thousand years compared to selection on many other traits (health and sexual selected traits seem to dominate).
Edit: it would take some effort to dig up this study. Ping me if this is of interest to you.
The evidence I have mentally cached is brain size. The evolutionary trajectory of brain size is relatively easy to measure just by looking at skulls from archaeological sites, and IIRC it has increased steadily through human evolutionary history and does not seem to be in evolutionary equilibrium.
(Also on priors, even before any evidence, we should strongly expect humans to not be in evolutionary equilibrium. As the saying goes, “humans are the stupidest thing which could take off, otherwise we would have taken off sooner”. I.e. since the timescale of our takeoff is much faster than evolution, the only way we could be at equilibrium is if a maximal-under-constraints intelligence level just happened to be exactly enough for humans to take off.)
There’s probably other kinds of evidence as well; this isn’t a topic I’ve studied much.
If humans are the stupidest thing which could take off, and human civilization arose the moment we became smart enough to build it, there is one set of observations which bothers me:
The Bering land bridge sank around 11,000 BCE, cutting off the Americas from Afroeurasia until the last thousand years.
Around 10,000 BCE, people in the Fertile Crescent started growing wheat, barley, and lentils.
Around 9,000-7,000 BCE, people in Central Mexico started growing corn, beans, and squash.
10-13 separate human groups developed farming on their own with no contact between them. The Sahel region is a clear example, cut off from Eurasia by the Sahara Desert.
Humans had lived in the Fertile Crescent for 40,000-50,000 years before farming started.
Here’s the key point: humans lived all over the world for tens of thousands of years doing basically the same hunter-gatherer thing. Then suddenly, within just a few thousand years starting around 12,000 years ago, many separate groups all invented farming.
I don’t find it plausible that this happened because humans everywhere suddenly evolved to be smarter at the same time across 10+ isolated populations. That’s not how advantageous genetic traits tend to emerge, and if it was the case here, there are some specific bits of genetic evidence I’d expect to see (and I don’t see them).
I like Bellwood’s hypothesis better: a global climate trigger made farming possible in multiple regions at roughly the same time. When the last ice age ended, the climate stabilized, creating reliable growing seasons that allowed early farming to succeed.
If farming is needed for civilization, and farming happened because of climate changes rather than humans reaching some intelligence threshold, I don’t think the “stupidest possible takeoff” hypothesis looks as plausible. Humans had the brains to invent farming long before they actually did it, and it seems unlikely that the evolutionary arms race that made us smarter stopped at exactly the point we became smart enough to develop agriculture and humans just stagnated while waiting for a better climate to take off.
I do agree that the end of the last glacial period was the obvious immediate trigger for agriculture. But the “humans are the stupidest thing which could take off model” still holds, because evolution largely operates on a slower timescale than the glacial cycle.
Specifics: the last glacial period ran from roughly 115k years ago to 12k years ago. Whereas, if you look at a timeline of human evolution, most of the evolution from apes to humans happens on a timescale of 100k − 10M years. So it’s really only the very last little bit where an ice age was blocking takeoff. In particular, if human intelligence has been at evolutionary equilibrium for some time, then we should wonder why humanity didn’t take off 115k years ago, before the last ice age.
Yes we should wonder that. Specifically, we note
Humans and chimpanzees split about 7M years ago
The transition from archaic to anatomically modern humans was about 200k years ago
Humans didn’t substantially develop agriculture before the last ice age started 115k years ago (we’d expect to see archaeological evidence in the form of e.g. agricultural tools which we don’t see, while we do see stuff like stone axes)
Multiple isolated human populations independently developed agriculture starting about 12k years ago
From this we can conclude that either:
Pre-ice-age humans were on the cusp of being able to develop agriculture, and an extra 100k years of gradual evolution was sufficient to bump them over the relevant threshold
There was some notable period between 115k and 12k years ago where the rate of selective pressure on humans substantially strengthened or changed direction for some reason. Which might correspond to a very tight population bottleneck:
source: Robust and scalable inference of population history from hundreds of unphased whole-genomes
Note that “bigger brains” might also not have been the adaptation that enabled agriculture.