Saturday, November 19, 2022

Recent evolution in human brain size

 


Human brain size remained stable from 300,000 to 60,000 years ago. It then diversified, becoming larger in some populations and smaller in others. This was when modern humans were spreading out of Africa and into new environments in Eurasia.

 

 

With the end of the last ice age, some 10,000 years ago, northern hunting peoples found themselves in a new environment. Men could no longer pursue herds of wandering reindeer over the vast steppe-tundra. They now had to hunt over shorter distances, and the game would be smaller and more varied. Meanwhile, women now had opportunities for gathering fruits, berries, roots, and other small food items. They thus turned toward food gathering, while men moved into the formerly female domain of crafts, kiln operation, and shelter construction. Cognitive demands were thus changing. Men no longer had to store huge amounts of spatiotemporal data when tracking prey, and women were losing their dominance of artisanal work (Frost 2019).

 

The post-glacial period also brought an apparent decrease in brain size. Henneberg (1988) found that male brains shrank by 9.9% and female brains by 17.4% between the ice age and modern times. He attributed the decrease to a reduction in body size. In a reanalysis of Henneberg's data, Hawks (2011) showed that the reduction in body size explains only one-fifth to one-seventh of the decrease in brain size. He also showed that the declining ratio of brain size to body size did not affect all populations equally. In fact, it can be securely demonstrated only for Europeans and Chinese. No decline is discernable for Nubians, the only non-Eurasian population for which we have a large cranial sample.

 

In a recent analysis of cranial data, DeSilva et al. (2021) argue that brain size began to decrease with farming and the rise of larger, more complex societies. They argue more specifically that the decrease was due to an increasing ability to store knowledge externally either in written form (on tablets, paper, or parchment) or in the brains of scribes, skilled tradesmen, and other knowledge workers. People no longer had to rely solely on their own brains to store the knowledge they needed:

 

 […] the recent decrease in brain size may instead result from the externalization of knowledge and advantages of group-level decision-making due in part to the advent of social systems of distributed cognition and the storage and sharing of information. (DeSilva et al. 2021, p. 1)

 

That hypothesis has been challenged by Villmoare and Grabowski (2022). Because farming was adopted at different times in different populations, they argue that DeSilva et al. (2021) should have analyzed the cranial data on a regional basis. But this was not done:

 

Since this transition [to farming] occurred at different times across the globe, rather than over a single 3–5 ka year period, under the hypothesis of DeSilva et al. (2021) we should detect the change in different modern human populations at different times. However, the dataset of DeSilva et al. (2021) is not organized to test the hypothesis in this fashion. Populations from around the globe are lumped together, with only 23 crania sampled over what we would argue to be a critical window with regards to their hypothesis, 5–1 ka, and coming from Algeria, England, Mali, China, and Kenya, among other locations. Later modern human samples are focused on Zimbabwe (at 1.06 ka), the Pecos Pueblo sample from the United States (1 ka), and finally, 165 crania (28% of the total sample) are from Australian pre-Neolithic hunter-gatherer populations and dated in DeSilva et al. (2021) to 100 years ago. (Villmoare and Grabowski 2022, p. 2)

 

The cranial dataset suffers from other problems:

 

In that same dating category [100 years ago], 307 (53% of the total sample) are from unspecified Morton Collection crania, where we have no way of knowing how many may be from pre-Neolithic and post-Neolithic populations. We also observe that the sample of DeSilva et al. (2021) generates a modern human mean of 1,297 cc in the final 100-year category, which is well below other published estimates of contemporary world-wide modern mean human cranial capacity that range from ?1,340 cc up to ?1,460 cc. (Villmoare and Grabowski 2022, p. 2)

 

When Villmoare and Grabowski (2022) reanalyzed the cranial data for the last 300,000 years, they found a very different picture:

 

[…] our analyses showed no changes in brain size associated with the transition to agriculture during the Holocene. Overall, our conclusion is that, given a dataset more appropriate to the research question, human brain size has been remarkably stable over the last 300 ka. (Villmoare and Grabowski 2022, p. 4).

 

Actually, their reanalysis shows that brain size remained stable from 300,000 to 60,000 years ago. It then diversified, becoming larger in some populations and smaller in others. This was when modern humans were spreading out of Africa and into new environments in Eurasia (see chart at top of post).


When the authors looked more narrowly at the last 30,000 years, they found no discernable change in mean brain size or in variation around the mean. They did not attempt a regional analysis. That’s a pity because DeSilva et al. (2021) may have been right within a more limited context, specifically that of complex Eurasian societies. We still have John Hawks’ finding that brain size decreased in Eurasians after the last ice age. But when exactly? Immediately after the ice age? Or during the much later increase in social complexity?

 


Today, more than a decade later, John Hawks has still not published that paper in a journal. When I asked him why, he replied: "I did not feel it was necessary to pursue formal journal publication for this, because I did not think it fit well into the journals at the time." Yet, at that time, the paper was exciting a lot of interest. This is what he wrote on his blog:

 

I've had a dozen requests from colleagues to cite the paper (which anyone is welcome to do by using the arXiv number). I also had two great interactions with colleagues who had comments and suggestions on the preprint, which I am now incorporating into a revision. (Hawks 2012)

 

He might have had trouble publishing the paper in a top-tier journal. But the main problem lay elsewhere. Once it got published, some academics might have viewed him the wrong way. Perhaps not, but why take the risk? Why risk opportunities for getting funding and invitations to work on big projects with big names?

 

Those are questions that many anthropologists end up asking themselves. I have no easy answer, other than to say that you can never control what other people think of you. You only get to own your own thoughts, not those of others.

 

References

 

DeSilva, J. M., Traniello, J. F. A., Claxton, A. G., and Fannin, L. D. (2021). When and why did human brains decrease in size? A new change-point analysis and insights from brain evolution in ants. Frontiers in Ecology and Evolution 9: 742639. https://doi.org/10.3389/fevo.2021.742639

 

Frost, P. (2019). The Original Industrial Revolution. Did Cold Winters Select for Cognitive Ability? Psych 1(1): 166-181. https://doi.org/10.3390/psych1010012

 

Hawks, J. (2011). Selection for smaller brains in Holocene human evolution. arXiv:1102.5604 [q-bio.PE] https://arxiv.org/abs/1102.5604  

 

Hawks, J. (2012). Spreading preprints in population biology. John Hawks Weblog, August 1. https://johnhawks.net/weblog/topics/meta/population-biology-arxiv-callaway-2012.html

 

Henneberg, M. (1988). Decrease of human skull size in the Holocene. Human Biology 60: 395-405. https://www.jstor.org/stable/41464021

 

Villmoare, B. and M. Grabowski. (2022). Did the transition to complex societies in the Holocene drive a reduction in brain size? A reassessment of the DeSilva et al. (2021) hypothesis. Frontiers in Ecology and Evolution 10: 963568. https://doi.org/10.3389/fevo.2022.963568

26 comments:

Pumpkin Person said...

Because farming was adopted at different times in different populations, they argue that DeSilva et al. (2021) should have analyzed the cranial data on a regional basis. But this was not done

And even if it were, I see no reason to believe the decline in brain size was caused by evolution and not by malnutrition/disease associated with agriculture. Too bad they don't have polygenic scores for brain size. Then using ancient DNA they could see if the brain size decline was truly genetic or merely nutritional. Given the rapid recovery of brain size and height to ice age levels in just the last 100 years, I'm inclined to believe it's the latter:

http://www.iapsych.com/iqmr/fe/LinkedDocuments/lynn1990.pdf

Anonymous said...

this PUmpkin guy above is a complete idiot he barely understands what he is talking about. ive been commenting on his blog for 4 years and he just uses the same descriptions for things that he started with.

it would be in your best interest not to entertain him he doesnt have any scientific reputability!

Anonymous said...

Pumpkin Person is not even smart enough to hold an intelligent conversation with anyone.

Santocool said...

Sedentarzation has accentuated the behavioral domestication of much of the human population, and domestication is related to the comparatively smaller brain.

Anonymous said...

Santo is even smarter than Pumpkin...i wonder who isnt!

Peter Frost said...

Pumpkin,

Two points:

- The decline didn't happen in all populations that adopted farming.
- The increase in brain size had already started two hundred years ago in Germany and the U.S.:

Jantz and Jantz (2016) and Jellinghaus et al. (2018) found an increase in brain size from at least 1800 in Germans and 1820 in white Americans. When I asked John Hawks, he attributed this reversal to improvements in nutrition and a reduction of childhood disease. That, too, was what I thought, initially.

But, then, the reversal would surely have been stronger in women than in men. If brain size had decreased twice as much in women, shouldn't the rebound have been twice as strong in women? Yet this is not what we see in the brain size of Americans born from 1820 to 1990: "Both sexes changed, but female change was less pronounced than male change" (Jantz and Jantz 2016). In Germans born between 1800 and 1950, no clear sex difference was observable in the magnitude of this change over time (Jellinghaus et al. 2018).

Both Jantz and Jantz (2016) and Jellinghaus et al. (2018) are skeptical that these changes could be explained by improvement in nutrition or reduction of childhood disease. Infant mortality is a good proxy for both, and it did not begin to decline until circa 1900. At the very least, the increase in brain size should have accelerated during the twentieth century, yet it didn't (Jellinghaus et al. 2018).

http://evoandproud.blogspot.com/2019/07/why-did-brain-size-decrease-after-ice.html

Anonymous said...

awesome job of putting this pseudointellectual (Pumpkin) in his place Peter!

Pumpkin Person said...

Peter, thanks for the reply.

No hypothesis perfectly explains all the data, especially given the incompleteness of the archeological record, but what's the alternative? Are we to believe there was selection for smaller brains during the Holocene (at the same time & place that you've argued there was selection for higher IQ)? And if that doesn't strain credibility enough, there was suddenly selection for bigger brains in the last few hundred years, at the same time you've argued there was a decline in genetic IQ:

http://evoandproud.blogspot.com/2022/09/the-great-decline.html

Seems too paradoxal. But hopefully we'll soon get polygenic scores for brain size from ancient DNA.

Sean said...

Wrangham notes that de-domesticated animals like the Dingo get back most of their ancestral wild characteristics with the exception of a larger cranium. He seems to think large brains in that context are something to do with intra-species competition (aggression). Hawks is a bit politically correct about Neanderthals and in my opinion he assumed their huge heads were a sign of intelligence. The first human skull we have with impacted wisdom teeth is from at least 13,000 years ago (Magdalenian 'Girl'). Sexual selection reducing the whole head size?

Peter Frost said...

Pumpkin,

The correlation between IQ and brain size is 0.40. Brain size reflects not only cognition but also non-cognitive functions, such as information storage. Northern hunting peoples have to store huge quantities of spatial and temporal coordinates when tracking prey. This is largely because hunting distance increases with increasing distance from the equator. The prey are more spread out and tend to be more mobile.

When the ice age ended, some 10,000 years ago, northern hunters were now in a forested environment where hunting distance was shorter. So they had to store less spatiotemporal data in their brains. And brain size decreased (what you don't use, you lose).

There is an alternate theory. With the rise of civilization, knowledge could be stored on external media, and mental activity could be delegated to specialized knowledge workers. Each individual no longer had to be a cognitive jack of all trades.

Those are just theories. Maybe I'm wrong. Maybe you're wrong. Maybe we're both wrong.

As for ancient DNA, a team led by Michael Woodley examined data from ancient DNA retrieved at sites in Europe and central Asia, specifically the frequency of alleles associated with high educational attainment. They found that those alleles gradually became more and more frequent over the time frame of the DNA samples: 4,560 to 1,210 years ago.

Woodley, M.A.; Younuskunju, S.; Balan, B.; Piffer, D. Holocene selection for variants associated with general cognitive ability: comparing ancient and modern genomes. Twin Res Hum Genet 2017, 20, 271-280, doi:10.1017/thg.2017.37

Again, we should not assume a high correlation between cognition and brain size. It's only 40%. Brain size may have decreased while cognitive ability increased.

Sean,

Has John Hawks done any research on human brain size recently?

Santocool said...

Decreased brain size may also be related to increased selective pressure for domestication or social conformity, which happened with the emergence of complex/verticalized societies, not just with cognitive diversification by specialization.

Based on the assumption that domesticated species tend to have smaller brains than their non-domesticated counterparts.

I am referring to the Neolithic period. Of course, after many centuries, new selective pressures for the increase of the brain, of its sophistication, then, of intelligence, has happened.

Anonymous said...

Santo and Peter just put the Pumpkin in his place! Pumpkin is a pseudoscientist with little cognitive remarkability. let him fail! let him suffer!

Santocool said...

A conspiratorial possibility coming from the psychopath Elon Musk:

To flood Twitter with man-made climate change deniers, resulting in the prevalence of this narrative and the continued destruction of the natural environment for short-term profits.

Result: planet Earth becomes progressively uninhabitable, even if it takes some more time, and this leads scientists to develop technologies related to long-range space travel, aiming at the arrival of our ''sapiens'' species to Mars and the possibility [some say, unlikely] of colonization.

Pumpkin Person said...

The correlation between IQ and brain size is 0.40.

And the correlation between IQ and polygenic education scores is only 0.3, yet you use them to infer population IQ trends. And you're fully justified because at the population level the correlation is much stronger. The same is true for brain size.

Brain size reflects not only cognition but also non-cognitive functions, such as information storage.

I would classify information storage as a type of cognition but your point still stands.

Northern hunting peoples have to store huge quantities of spatial and temporal coordinates when tracking prey. This is largely because hunting distance increases with increasing distance from the equator. The prey are more spread out and tend to be more mobile.

But if brain size decreased because selection pressures for spatial memory relaxed in the Holocene, why did brain size suddenly bounce back in the last hundred years or so? You don't buy the nutrition/health hypothesis so did the industrial revolution rapidly select for spatial & temporal storage?


There is an alternate theory. With the rise of civilization, knowledge could be stored on external media, and mental activity could be delegated to specialized knowledge workers. Each individual no longer had to be a cognitive jack of all trades.

Again, that only explains why brain size decreased in the Holocene; it's doesn't explain why it made almost a full recovery in the industrial revolution. The only theory that explains both in my humble opinion is nutrition/health.


Those are just theories. Maybe I'm wrong. Maybe you're wrong. Maybe we're both wrong.

Absolutely

As for ancient DNA, a team led by Michael Woodley examined data from ancient DNA retrieved at sites in Europe and central Asia, specifically the frequency of alleles associated with high educational attainment. They found that those alleles gradually became more and more frequent over the time frame of the DNA samples: 4,560 to 1,210 years ago.

In my opinion this makes it even less likely that the Holocene brain size decline was genetic, because genes for brain size and genes for education likely overlap considerably, making it unlikely they were selected for in opposite directions. So I think a nutritional explanation fits the data better, especially since malnutrition is thought to have shrunk body size & life during the Holocene span too prompting Jared Diamond to call it the worst mistake humans ever made:

https://www.discovermagazine.com/planet-earth/the-worst-mistake-in-the-history-of-the-human-race

Santocool said...

What i understood, human brain became more rich in complexity despite its size's decrease. It's like losing in quant but gaining in qual.

Also would be important to know how brain size varied throught different human pre historic human populations, probably less because were little communities, and after sedentarization/emergence of "civilized" societies, way more socially verticalized and densely populated, probably a reflect of a bigger genetic diversity/inequalities.

Maybe "elites" retained most of previous brain size while it decreased among lower classes due to comparatively worse nutrition and also to the selection for tamed and/or less intelligent/critical thinkers individuals.

Anonymous said...

Pumpkin is a know-nothing! He is a fraud!

Peter Frost said...

Santocool,

I've heard people say that domesticated animals have smaller brains. Do you have a source?

I think Elon Musk is primarily concerned about the trend toward increasing ideological conformity in the U.S.

Pumpkin,

"And the correlation between IQ and polygenic education scores is only 0.3, yet you use them to infer population IQ trends."

No, the correlation between IQ and educational attainment is 0.5:

"When intelligence and educational outcomes—often assessed as years of full-time education or as highest achieved qualification, and also by school grades or educational achievement test scores—are measured at about the same time, a typical correlation is ∼0.5."

Ian J Deary, Wendy Johnson, Intelligence and education: causal perceptions drive analytic processes and therefore conclusions, International Journal of Epidemiology, Volume 39, Issue 5, October 2010, Pages 1362–1369, https://doi.org/10.1093/ije/dyq072

Anyway, you're committing a Tu Quoque fallacy. "You say my argument sucks, but you made another argument that also sucks!"

"why did brain size suddenly bounce back in the last hundred years or so?"

Brain size in Germans and Americans has been increasing for at least the last two hundred years. I say "at least" because we lack good data. It increased because population growth was being driven by the higher fertility of the middle class, and that fertility was predicated on success at tasks like calculating, writing, budgeting, planning, etc.

"it's doesn't explain why it made almost a full recovery in the industrial revolution."

I'm not sure that "industrial revolution" applies to the early period of the American and German data. To a large extent, we are talking about proto-industrial farmers and artisans who were entering a more dynamic economic environment with more cognitive challenges.

"In my opinion this makes it even less likely that the Holocene brain size decline was genetic, because genes for brain size and genes for education likely overlap considerably, making it unlikely they were selected for in opposite directions."

Debate is a two-way process. Please listen to the other side. My argument was that the early Holocene decline was due to a decrease in hunting distance and a consequence decrease in the need to store huge quantities of spatiotemporal data. That's not really cognitive ability, and the decline would probably not show up in PGS data.

Santocool said...

https://www.science.org/content/article/tamer-cow-smaller-brain#:~:text=Following%20the%20pattern%20of%20other,of%20the%20Royal%20Society%20B%20.


https://phys.org/news/2022-01-brain-size-decreased-domesticated-cats.html

The first two results on google...



You're kidding, right?

Where is this ideological conformity?

Here, in Brazil, it's divided, do you call it just conformity?

And for a more Positive or Negative side?

Santocool said...

''Compare a wild boar with a domestic pig and you may notice a few key differences, including the fact that the pig will likely have a smaller head—and brain—than the boar. Scientists have known for decades that domesticated animals like sheep, pigs, cats, and dogs have smaller brains than their wild counterparts—part of what scientists refer to as "domestication syndrome." Now, the first large-sale study of brain sizes across cattle breeds reveals a new wrinkle: Breeds that tolerate more interaction with humans have smaller brains than those that live more independent lives.''

Sean said...

Peter, I don't follow Hawks any more, but as I recall he was always very reluctant to admit to great intelligence differences between human species (Neanderthal and Sapiens), so it is hardly a new thing for him to steer clear of those issues in far less clearly demarcated taxa.

Neanderthals had no tents or even clothes so they could not wander far from their caves, unlike the Steppe Tundra hunters in pursuit of the worlds most mobile animal, and reindeer herds are also extremely unpredictable because they like to head into the wind. Yet Neanderthals had very much larger brains. Inuit do have large brains admittedly.

Anonymous said...

Pumpkin is a blind crazed buffoon. he thinks he can get away with being rude etc. to people. you would be doing us all a favor of if you stopped being so arrogant Pumpkin!

Pumpkin Person said...

No, the correlation between IQ and educational attainment is 0.5

I said polygenic education scores, not education itself. Even if the IQ vs education correlation were entirely mediated by genes, polygenic scores currently exclude rare variants and non-additive effects and thus only crudely measure the education genotype.


So even though phenotypic education (in a given society) better predicts phenotypic IQ than phenotypic brain size does; phenotypic brain size arguably better predicts genotypic IQ than polygenic education scores do

Anyway, you're committing a Tu Quoque fallacy. "You say my argument sucks, but you made another argument that also sucks!"

No I think both phenotypic brain size and polygenic education scores are strong measures of POPULATION IQ, but poor measures of INDIVIDUAL IQ.


Brain size in Germans and Americans has been increasing for at least the last two hundred years. I say "at least" because we lack good data. It increased because population growth was being driven by the higher fertility of the middle class, and that fertility was predicated on success at tasks like calculating, writing, budgeting, planning, etc.


Well it's increased 0.46 SD in America since WWII. Given the 0.4 correlation between IQ and brain size, you'd have to argue that selection for IQ over just the post-war period increased IQ by 0.46 SD/0.4 = 1.15 SD despite fertility trends over that period being considered dysgenic, mutation load on the rise and reaction time and polygenic education scores perhaps decreasing. We'd also expect the brain size increase to exceed the height increase if it were driven by IQ selection but instead we see the opposite.

Santocool said...

https://www.scientificamerican.com/article/mind-control-parasite-makes-wolves-effective-pack-leaders/#:~:text=Wolves%20infected%20with%20a%20common,strike%20out%20on%20their%20own.

‘Mind Control’ Parasite Makes Wolves Effective Pack Leaders

The parasite Toxoplasma gondii can change the behavior of infected wolves in ways that make them more likely to be pack leaders'

Santocool said...

https://www.youtube.com/watch?v=Fe88ckTWyTU

What is the average IQ of Nauru

Santocool said...

https://www.youtube.com/watch?v=0o1PXeFEcL0&list=WL&index=7

Autism: An evolutionary perspective, Professor Simon Baron-Cohen, 1st Symposium of EPSIG, 2016

Anonymous said...

Peter keep blogging! your blog is great! Pumpkin is a trash human being he deserves to suffer he has no intellect dont let him con you into anything!