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Thread: Possible reason for brain-size reduction since the Pleistocene

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    Possible reason for brain-size reduction since the Pleistocene

    A much better explanation than the aspersions towards farming:

    The brain is the most complex organ in the human body. Now, a new study has brought us closer to understanding some of its evolution. It shows that human brains decreased in size approximately 3,000 years ago. By studying ants as models to illustrate why brains may increase or decrease in size, the researchers hypothesize that brain shrinkage parallels the expansion of collective intelligence in human societies.
    Studying and understanding the causes and consequences of brain evolution helps us understand the nature of humanity. It is well documented that human brains have increased in size over the course of our evolutionary history. Less appreciated is the fact that human brains have decreased in size since the Pleistocene. When exactly these changes happened, or why, was not well known.
    "A surprising fact about humans today is that our brains are smaller compared to the brains of our Pleistocene ancestors. Why our brains have reduced in size has been a big mystery for anthropologists," explained co-author Dr. Jeremy DeSilva, from Dartmouth College.

    To disentangle this mystery, a team of researchers from different academic fields set out to study the historical patterns of human brain evolution, comparing their findings with what is known in ant societies to offer broad insights.
    "A biological anthropologist and a behavioral ecologist and evolutionary neurobiologist began sharing their thoughts on brain evolution and found bridging research on humans and ants might help identify what is possible in nature," said co-author Dr. James Traniello, from Boston University.

    Their paper, published in Frontiers in Ecology and Evolution, sheds new light on the evolution of our brain.

    A recent size decrease

    The researchers applied a change-point analysis to a dataset of 985 fossil and modern human crania. They found that human brains increased in size 2.1 million years ago and 1.5 million years ago, during the Pleistocene, but decreased in size around 3,000 years ago (Holocene), which is more recent than previous estimates.
    "Most people are aware that humans have unusually large brains—significantly larger than predicted from our body size. In our deep evolutionary history, human brain size dramatically increased," said Traniello. "The reduction in human brain size 3,000 years ago was unexpected."

    The timing of size increase coincides with what is previously known about the early evolution of Homo and the technical advancements that led to; for example, better diet and nutrition and larger social groups.

    As for the decrease in brain size, the interdisciplinary team of researchers propose a new hypothesis, finding clues within ant societies.

    What could ants teach us about human brain evolution?

    "We propose that ants can provide diverse models to understand why brains may increase or decrease in size due to social life. Understanding why brains increase or decrease is difficult to study using only fossils," explained Traniello.
    Studying computational models and patterns of worker ant brain size, structure, and energy use in some ant clades, such as the Oecophylla weaver ant, Atta leafcutter ants, or the common garden ant Formica, showed that group-level cognition and division of labor may select for adaptive brain size variation. This means that within a social group where knowledge is shared or individuals are specialists at certain tasks, brains may adapt to become more efficient, such as decreasing in size.
    "Ant and human societies are very different and have taken different routes in social evolution," Traniello said. "Nevertheless, ants also share with humans important aspects of social life such as group decision-making and division of labor, as well as the production of their own food (agriculture). These similarities can broadly inform us of the factors that may influence changes in human brain size."
    Brains use up a lot of energy, and smaller brains use less energy. The externalization of knowledge in human societies, thus needing less energy to store a lot of information as individuals, may have favored a decrease in brain size.
    "We propose that this decrease was due to increased reliance on collective intelligence, the idea that a group of people is smarter than the smartest person in the group, often called the 'wisdom of the crowds,'" added Traniello.
    DeSilva concluded, "We look forward to having our hypothesis tested as additional data become available."

    https://phys.org/news/2021-10-human-...ize-years.html
    Here is the link to the study:

    When and Why Did Human Brains Decrease in Size? A New Change-Point Analysis and Insights From Brain Evolution in Ants

    Human brain size nearly quadrupled in the six million years since Homo last shared a common ancestor with chimpanzees, but human brains are thought to have decreased in volume since the end of the last Ice Age. The timing and reason for this decrease is enigmatic. Here we use change-point analysis to estimate the timing of changes in the rate of hominin brain evolution. We find that hominin brains experienced positive rate changes at 2.1 and 1.5 million years ago, coincident with the early evolution of Homo and technological innovations evident in the archeological record. But we also find that human brain size reduction was surprisingly recent, occurring in the last 3,000 years. Our dating does not support hypotheses concerning brain size reduction as a by-product of body size reduction, a result of a shift to an agricultural diet, or a consequence of self-domestication. We suggest our analysis supports the hypothesis that 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. Humans live in social groups in which multiple brains contribute to the emergence of collective intelligence. Although difficult to study in the deep history of Homo, the impacts of group size, social organization, collective intelligence and other potential selective forces on brain evolution can be elucidated using ants as models. The remarkable ecological diversity of ants and their species richness encompasses forms convergent in aspects of human sociality, including large group size, agrarian life histories, division of labor, and collective cognition. Ants provide a wide range of social systems to generate and test hypotheses concerning brain size enlargement or reduction and aid in interpreting patterns of brain evolution identified in humans. Although humans and ants represent very different routes in social and cognitive evolution, the insights ants offer can broadly inform us of the selective forces that influence brain size.

    https://www.frontiersin.org/articles...21.742639/full

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    Interesting theory, outsourcing. :)

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    I wonder why, if their hypothesis is correct, it only happened around 1000 BCE? Did society change dramatically around that time?

    Fwiw, I always hypothesized that gradually, over a much longer span of time, we evolved to make the brain more efficient, and thereby requiring less energy. That could happen by increasing connectivity. Perhaps also certain parts of the brain decreased, not all of it, i.e. the limbic "id" part of the brain, while the pre-frontal lobe either stayed the same or grew.

    There's recently been quite a lot of research showing that in extreme cases of addiction the pathways between the pre-frontal cortex and the limbic system are "out of whack" to use a non-scientific term. In a more extreme case, say, of criminals, I wonder if it's not just the pathways, but might the limbic part of the brain actually be larger than in average people?

    If I could live another lifetime, I think it's brain research that I would pursue. I think the answer to why so many things plague us might be there.


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    I suppose that human brain size didn't suddenly decrease everywhere on Earth at the same time. It would be interesting to compare the evolution across various regions and types of societies (HG, Neolithic, Bronze Age, Iron Age / rural vs urban) to help determine the underlying cause.
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    Damn stupid steppe people ! Oh, wait....

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    Quote Originally Posted by bigsnake49 View Post
    Damn stupid steppe people ! Oh, wait....
    I don't understand the joke. Steppe people also had division of labor as pastoralists. They weren't very naturalistic, in fact they deforested vast areas to make it more like the steppe.

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    Also, didn't hunter-gatherers exterminate all of the mega fauna? Civilizations were inevitable. In a way the elimation of this game made man explore other survival strategies

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    Quote Originally Posted by Jovialis View Post
    I don't understand the joke. Steppe people also had division of labor as pastoralists. They weren't very naturalistic, in fact they deforested vast areas to make it more like the steppe.
    Glad I wasn't the only one who didn't get it.

    Indeed, they burnt down many forests in the sort of slash and burn agriculture we see in the Amazon today. Neolithic people planted and planted the same areas over and over again, and drained the soil of its nutrients. It took a long time to figure out how to use crop rotation and even how to use animal fertilizer in the right way. The Paleolithic people did extinguish the mammoths and other large game, so humans had to develop new tools with different arrow points and started hunting smaller game.

    Oh, wait, I get the smart aleck remark now. It's because I pointed out that Corded Ware didn't have metallurgy. It doesn't mean they were dumb; it just means their culture wasn't as advanced as other cultures of their time in terms of metallurgy etc. or pottery for that matter, or wrist guards etc. Are we supposed to lie and say they were? That's the world we live in today; forget about reading the archaeology papers and basing conclusions on them as well as genetics. There's no objectively discernible truth; there's just the truth we want to promulgate through propaganda. Sorry, I don't roll that way; never did. I don't care who gets offended; I follow the data wherever it leads.

    They didn't owe their dominance of Central Europe to a "superior" culture technologically. It's just that their pastoralist life style happened to be better suited to the prevailing climate conditions. If place X wasn't fertile and covered with grass they could move elsewhere. Of course, the plague didn't much help the Neolithic farmers. Still, Yamnaya and Corded Ware and Bell Beaker didn't make as much of an impact on Southern Europe did they? For the Balkans that had to wait for the fall of the Roman Empire and another plague. Are we supposed to pretend the Slavs who entered the Balkans and even Greece had a superior, more advanced civilization than the one they replaced? Is that how population genetics is supposed to be pursued?.

    Snide comments don't take the place of reasoned, informed debate.

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    ^^Also it seems lost on some people that it was division of labor that facilitated the decrease of brain size, not specifically farming.

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    Yes, division of labor is a key component, but I believe the overarching factor (even though the paper says there's no support for it) is (self) domestication.

    After animals, it was only a matter of time before people began "farming" their brethren, and thus Civilization was born. In old books I've seen it flat-out stated that civilization = "When man domesticates himself." I've never heard this in school or in modern works though.

    Farming/Livestock-->growing population-->storable surplus commodities-->ruling class to manage it all-->armies to protect the ruling class' loot-->religion to control the masses...Soon a group of people would become itself like a functional human: one class the "brain," another the feet, another the fingers....

    This "person" would trade and interact with other "persons" resulting in more commodities that needed even more control and even more specialized jobs down the chain. And soon "families" (empires) appeared etc. etc.

    It's not hard to imagine the exponential explosion of a pyramidal class-labor structure with enormous, increasing masses of "one trick pony" workers at the bottom. And in Nature, if you don't use it, you lose it. Hence reduction in brain size.

    My support? I don't have much LOL But:

    Domesticated animals (who only have to worry about a few tasks and have their basic needs taken care of by others) always have smaller brains than their wild kin.

    3000 years is in the time frame of the earliest civilizations.

    As an aside, given the ant study, what do you think the Internet/technology and the modern flow of information are going to do to our brains? I doubt it'll be good.

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    I'm not pessimistic about any of this. Smaller brains does not equal being dumber. The article said smaller brains are more efficient.

    Just like the way a tiny smart phone is superior to the huge clunky computers of the past.

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    But also, let's say bigger brains do equal more intelligence (they don't). The knowledge within civilization is more plentiful than any one human can retain, even someone with an extremely high IQ. Furthermore, who is to say the people at the top are self-domesticating? I think it is rather they are domesticating those beneath them, while those at the top are free to be the jack of all trades and master of them all. Aristotle wrote about this in his book Politica. Those beneath serve, while the elite are free to pursue higher callings.

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    Quote Originally Posted by Jovialis View Post
    I don't understand the joke. Steppe people also had division of labor as pastoralists. They weren't very naturalistic, in fact they deforested vast areas to make it more like the steppe.
    The joke is because I have steppe in my heritage so I was making fun of myself. I actually have all three major group in my admix: 55% Farmer, 22% Hunter Gatherer and 23% Metal Age Invader.

    As far as decrease in brain size I would think that pastoralists & hunter gatherers do not need to use their brains as much as farmers. Farmers are face with challenges from weather to pests to wild animals eating their crops to protecting their crops from invaders in addition to figuring out what to plant where and when. Meeting challenges and problem solving is what intelligence is all about.

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    Quote Originally Posted by bigsnake49 View Post
    The joke is because I have steppe in my heritage so I was making fun of myself. I actually have all three major group in my admix: 55% Farmer, 22% Hunter Gatherer and 23% Metal Age Invader.

    As far as decrease in brain size I would think that pastoralists & hunter gatherers do not need to use their brains as much as farmers. Farmers are face with challenges from weather to pests to wild animals eating their crops to protecting their crops from invaders in addition to figuring out what to plant where and when. Meeting challenges and problem solving is what intelligence is all about.
    This was mine, I made a thread about it a couple years ago. However, some posters explain that there are some issues with it.

    https://www.eupedia.com/forum/thread...ncient-Origins

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    It was organized religion (I think)

    Maybe, once civilization started, outsourcing grew.
    If you read carefully you'll realize that it says brain size started shrinking since the Ice Age. Which absolutely coincides with the begining of sedentary societies.

    But going again to the 3,000 YBP date, the only things that I can think of, are the end of the Egyptian New Kingdom, Micenic Greece, Assyrian Empire...
    And their substitution by the Classical Ancient Empires such as: Greece, Alexander the Great, Rome, Persia, unified China, India... Also Greek philosophy, Judaism(the Bible), Confucianism, Taoism, Vedas...

    All those new political entities and ideologies/ religions are those who arose after the brain diminished in size.
    There are not minor changes, particularly the idological one. Basically a lot of our thinking, has its roots there.

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    Quote Originally Posted by Jovialis View Post
    I'm not pessimistic about any of this. Smaller brains does not equal being dumber. The article said smaller brains are more efficient.
    Just like the way a tiny smart phone is superior to the huge clunky computers of the past.
    I'm going to repost this, because bigger brains do not necessarily equal smarter as stated in the OP article. Again, just like the way a smart phone is more advanced than a rocket ship from the 1960s.

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    Quote Originally Posted by Jovialis View Post
    I'm going to repost this, because bigger brains do not necessarily equal smarter as stated in the OP article. Again, just like the way a smart phone is more advanced than a rocket ship from the 1960s.
    It is the number of connections in the brain rather than the size that determines intelligence.

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