Human brain capacity has decreased by about 10% over thousands of years. How did the brain get "lost"?

    Most people think that brain evolution occurs in a linear fashion: it keeps growing, then reaches a plateau, and finally stops growing, but this is not the case. Measurements of 122 people showed that the brain volume of modern adults is 900-2100 milliliters, and the global average human brain volume is 1349 milliliters, which is smaller than the brain volume of our Stone Age ancestors.

    The development of larger brains has long been seen as a sign of humans' increased intelligence and ability to "dominate" the earth. In the last 2 million years of human evolution, the capacity of the human brain has increased nearly four times. But there is growing evidence that the human brain shrank sometime after the last ice age.

    Jeremy DeSilva, a professor of paleoanthropology at Dartmouth College in the United States, said: "Most people think that brain evolution occurs in a linear way: it keeps growing, then reaches a plateau, and finally stops developing, but in fact No, our brains shrank and we lost brain tissue the size of a lime." Calculations by De Silva's research team show that over the past thousands of years, human brain size has declined rapidly by about 10%. Relevant research papers were published in the Swiss journal Frontiers in Ecology and Evolution.

    So, what causes the human brain to shrink? Will the shrinking of the human brain affect its function?

    The human brain is "quietly" getting smaller

    The American "Discover" magazine pointed out in a report that the average size of the human brain is shrinking, and this shrinkage began tens of thousands of years ago. Over the past 100,000 years, the average brain size of Homo sapiens has decreased by about 40%.

    Sahelanthropus tchadensis, which lived about 4 million years ago and is considered to represent the oldest ancestor of humans, had a brain volume of about 350 milliliters. After that, human brain size began to increase. From about 4 million years ago to about 2 million years ago, the brains of Australopithecus apes ("Lucy" and her contemporaries) were about 500 milliliters. By 1 million years ago, some Homo erectus had brain volumes exceeding 1,000 milliliters. About 130,000 years ago, the average brain volume of Neanderthals (specimens ranged from 1172 to 1740 ml) and Homo sapiens (1090 to 1175 ml) reached 1500 ml. Notably, human body size has not changed substantially since the time of Homo erectus, so increases in brain size have mostly been independent of increases in body size.

    But is human brain capacity constantly increasing? No! Measurements of 122 people showed that the brain volume of modern adults is 900-2100 milliliters, and the global average human brain volume is 1349 milliliters, which is smaller than the brain volume of our Stone Age ancestors.

    Calculations by De Silva's research team also show that over the past 150,000 years, the average human brain capacity has basically remained at about 1,450 milliliters. But over the past few thousand years, this value has rapidly dropped by about 10%, to 150 milliliters. Using fossil and modern specimen data, they determined that this shrinkage of the human brain occurred between 3,000 and 5,000 years ago.

    In addition, a 1988 paper published in the journal Human Biology analyzed more than 12,000 Homo sapiens skulls from Europe and North Africa. Research shows that over the past 10,000 years, the brain volume of men and women has decreased by about 10% (157 ml) and about 17% (261 ml), respectively.

    Collective intelligence comes into play

    Why does human brain capacity shrink?

    Some researchers believe that the brain is the most energy-consuming organ in the human body. Although the brain currently accounts for only 2% of human body weight, it consumes nearly a quarter of energy. The human brain has lost some capacity by inventing ways to store information externally: cave art, writing, digital media.

    Chris Stringer, a paleoanthropologist at the Natural History Museum in London, and Christopher Coker, a neuroscientist at the Allen Institute in the United States, said in an interview with the Wall Street Journal on September 8 that books, The use of personal devices and the Internet as storage for information is likely exacerbating the trend of shrinking brain size. "Our brains don't have to work as hard as they used to, so they get smaller," Chris Stringer said.

    A report in "Discover" magazine pointed out why the human brain size has become smaller? Perhaps the most convincing hypothesis is that Homo sapiens experienced "self-domestication." The term originates from human understanding of animal domestication. Domestic species such as sheep and dogs differ in many physical and behavioral traits compared to their wild ancestors, including being docile, less timid, and having smaller brains.

    Humans may have also domesticated themselves: During the Stone Age, cooperative, level-headed individuals were more likely to survive and reproduce than aggressive ones. These tendencies are influenced by genes, which also influence human physical characteristics, including body shape and brain size. Over time, this self-domestication of humans resulted in smaller brains.

    De Silva's team used fossil and modern specimen data to determine that the shrinkage of the human brain occurred between 3,000 and 5,000 years ago, a period of prosperity for ancient civilizations in North Africa, the Middle East, and South America. They believe that complex social structures may play a role in shrinking brain size.

    They speculate that the cooperation of human social organizations has been greatly enhanced in the past 3,000 years, and collective intelligence has begun to play a role. James Traniello, a co-author of the study by De Silva's team and a professor of biology at Boston University, explained that a group of people is smarter than the smartest person in the group. This is a bit like the Chinese proverb "Three Stooges are better than Zhuge Liang". So, generally speaking, if you live in a group, you will solve problems faster, more efficiently, and more accurately than if you are alone.

    De Silva said humans are so social that each individual no longer needs to know everything. As David Geary, a cognitive scientist at the University of Missouri, explains: Increasingly complex societies mean that humans no longer need to master a variety of survival skills like humans in primitive societies. Based on this, some functions of the human brain have gradually deteriorated, and brain capacity has shrunk.

    Functions are becoming more and more developed

    Will shrinking the human brain have an impact on its function?

    "Losing part of the brain will not have much impact on its function." Qiu Zilong, a researcher at the Songjiang Research Institute of Shanghai Jiao Tong University School of Medicine, told a reporter from Science and Technology Daily: "There is a certain redundancy in the human brain. Sometimes even if a part is lost, it will affect the overall function." It doesn’t have much impact on functionality.”

    He further explained that from a neuroscientific perspective, the human brain does have a certain amount of redundancy—some “idle space.” For example, in clinical practice, some children who have suffered severe brain trauma and undergo brain surgery to remove part of their brain can still return to normal functions as they grow older. In addition, some patients with epilepsy have had part of their brain removed and can still live normally.

    "It can be seen that there is some redundancy in the function of the brain. If the loss is not a key part, it does not affect the function of the entire brain." Qiu Zilong said.

    He pointed out that the evolution of the human brain is a slow process, with significant changes taking tens of thousands of years. Since ancient times, human beings have created a series of splendid civilizations and a series of sophisticated technologies, which can show that human beings are getting smarter and smarter. "Moreover, IQ tests also prove that the human brain is becoming more and more developed."

    After studying human IQ, New Zealand scientist James Flynn found that in the process of continuous evolution, human IQ is also constantly improving. This phenomenon is also named the "Flynn effect."

    Qiu Zilong emphasized: "The size of the human brain is not the most important, as long as the functions become more and more developed."

    Human beings have unique brains on earth, but human beings’ intelligent minds did not exist at the beginning. They are the result of millions of years of development and evolution during the course of human evolution. At present, the human brain is still evolving silently. What surprises will the future bring us? let us wait and see!


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