Three thousand years ago, why did the human brain become mysteriously smaller?

▎The editing brain of WuXi AppTec's content team is the most complex organ in the human body
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In our nearly 6 million years of evolutionary history, the size of the human brain has almost quadrupled
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However, previous studies have found that human brain capacity has shrunk in history
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What is causing the shrinkage of the human brain? When and why did these changes happen? It has always been a big mystery that has plagued anthropologists
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 Recently, scientists have put forward this hypothesis by observing the ant model: The evolutionary pattern of the human brain is affected by collective intelligence
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In other words, a society with a high degree of information sharing and efficient division of labor makes the human brain reduce its size in order to save metabolic costs
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 ▲The paper was published in the "Frontiers in Ecology and Evolution" magazine (picture source: screenshot of the paper page) "A surprising fact about humans today is that the brains of the ancestors of the Pleistocene (2.
588 million-11.
17 million years ago) compared to our brains smaller
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However, we do not know, why then would the human brain mystery reduced in volume
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"co-author, Dr.
Jeremy DeSilva from Dartmouth College (Dartmouth College) explains
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 To solve this mystery, an interdisciplinary research team integrating biological anthropologists, behavioral ecologists and evolutionary neurobiologists set out to explore the evolutionary history of the human brain
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 ▲The evolutionary trajectory of the ancient human brain (picture source: reference [1]) First, the researchers conducted a change point analysis on a data set of 985 fossils and modern human skulls
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The researchers found that the brains of ancient humans had enlarged at two points during the Pleistocene 2 million years and 150 years ago
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In the past 100,000 years, the size of the human brain remained stable until it suddenly shrank 3,000 years ago
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 Scientists have further discovered that the increase in the size of the human brain coincides with the trajectory of early human evolution and technological progress in the archaeological record
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For example, when the human brain is enlarged, humans have obtained better diet changes (such as using fire to cook food), and a larger community size
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 So why did the human brain shrink mysteriously later? The co-author of the paper, Dr.
James Traniello from Boston University, said: "In our complex evolutionary history, the size of the human brain has increased rapidly
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Therefore, the reduction in the size of the human brain 3,000 years ago is even more apparent.
Unexpected
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" ▲ Inferring the time of several changes in human brain capacity during evolution (picture source: reference [1]) Ants have become a key model for anthropologists to study the role of sociality in brain evolution
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Ants and human society are different, but they are very similar in many important aspects, such as group size, collective intelligence, division of labor, and food production (agriculture), which can help scientists understand the underlying factors that affect the evolution of the human brain
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Therefore, the interdisciplinary research team found clues through the ant society
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 For the worker ants of a variety of ants (Oecophylla weaver ant, Atta leaf-cutting ant or Formica common garden ant), the researchers analyzed their brain size, structure, and energy usage calculation models and patterns, and found the size of the brain.
May selectively adapt to group-level cognition and division of labor
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Image source: https://commons.
wikimedia.
org/wiki/File:Ant_Receives_Honeydew_from_Aphid.
jpg#/media/File:Ant_Receives_Honeydew_from_Aphid.
jpg The research and analysis results mean that in a knowledge-sharing social group, the reduction of human brain capacity is Due to increased reliance on collective wisdom
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Researchers believe that group cognition reduces the need for neural structure in certain aspects of supporting individual intelligence and decision-making
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 In ants, there is evidence that the increase in brain size increases the cost of metabolism
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A brain with a smaller capacity requires less energy
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Humans began to share knowledge highly 3,000 years ago, and social knowledge is externalized, so that individuals do not need to store a lot of information.
The human brain may shrink its brain capacity in order to become more efficient
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 Specifically, as the size of the group increases, the complex interaction between humans and the social environment has led to an increase in the demand for the brain
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However, due to the metabolic needs of the brain, there may be limitations in the feedback loop between the size of the social network and the structure of the brain
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If the adaptive group response generated by group decision-making, that is, "collective wisdom", exceeds the cognitive accuracy and speed of individual decision-making, then the size of the human brain may be reduced in order to save metabolic costs
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 Another study, through a multidisciplinary modeling method, really proved that individuals with relatively small brains can achieve the same level of behavioral performance as individuals with large brains but living alone through social interaction
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 Scientists look forward to the emergence of more data to verify the hypothesis in the future
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 References: [1] DeSilva,JM, et, al.
(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.
https://doi.
org/10.
3389/fevo.
2021.
742639[2] When and why did human brains decrease in size 3,000 years ago? New study may have found clues within ants.
Retrieved October 22, 2021, from https://www .
newswise.
com/articles/when-and-why-did-human-brains-decrease-in-size-3-000-years-ago-new-study-may-have-found-clues-within-ants[3 ] Human Brains Decreased in Size 3,000 Years Ago, New Study Says.
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