Most people think that brain evolution happens in a linear fashion: it grows, then goes into a plateau, and finally stops developing, but that's not the case. Measurements of 122 populations show that the brain volume of modern adults is 900-2100 milliliters, and the average human brain volume worldwide is 1349 milliliters, which is smaller than the brain volume of human Stone Age ancestors.
◎ Liu Xia, reporter of this newspaper
The development of a larger brain capacity has long been seen as a sign of increased intelligence and the ability of humans to "rule" the planet. In the last 2 million years of human evolution, the capacity of the human brain has increased nearly 4 times. But there is growing evidence that sometime after the end of the last ice age, the human brain became smaller.
Jeremy de Silva, a professor of paleoanthropology at Dartmouth College in the United States, said: "Most people think that brain evolution happens in a linear way: it keeps growing, then goes into a plateau, and finally stops developing, but this is not the case, our brain shrinks, and the lost brain tissue is the size of a lime." De Silva's team calculated that human brain capacity has rapidly declined by about 10 percent over the past few thousand years, according to the research paper published in the Swiss journal Frontiers in Ecology and Evolution.
So, what causes the shrinkage of the human brain? Does the smaller human brain have an impact on its function?
The human brain "quietly" became smaller
The American magazine "Discovery" pointed out in the 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 volume of Homo sapiens has decreased by about 40%.
Living about 4 million years ago, the Sahelanthropus tchadensis, thought to represent humanity's oldest ancestor, has a brain volume of about 350 milliliters. After that, the human brain volume began to increase. From about 4 million years ago to about 2 million years ago, the brain capacity of Australopithecus australopithecus ("Lucy" and its contemporaries) was about 500 ml. By 1 million years ago, some Homo erectus had a brain volume of more than 1,000 milliliters. About 130,000 years ago, the average brain volume of Neanderthals (specimens with brain volume ranged from 1172-1740 ml) and Homo sapiens (1090-1175 ml) reached 1500 ml. It is worth noting that human body size has not changed substantially since the time of Homo erectus, so the increase in brain capacity has been largely unrelated to body size growth.
But has human brain capacity been increasing? Non also! Measurements of 122 populations show that the brain volume of modern adults is 900-2100 milliliters, and the average human brain volume worldwide is 1349 milliliters, which is smaller than the brain volume of human Stone Age ancestors.
De Silva's team also calculated that the average human brain volume has remained at about 1450 milliliters over the past 150,000 years. But over the past few thousand years, that number has rapidly dropped by about 10 percent to 150 milliliters. Using fossil and modern specimen data, they determined that this shrinkage of the human brain occurred 3,000 to 5,000 years ago.
In addition, a paper published in the journal Human Biology in 1988 analyzed the skulls of more than 12,000 Homo sapiens from Europe and North Africa. Studies have shown that over the past 10,000 years, brain volume in men and women has declined by about 10 percent (157 ml) and about 17 percent (261 milliliters), respectively.
Collective intelligence comes into play
Why is the human brain volume shrinking?
Some researchers believe that the brain is the most energy-consuming organ in the human body, and although the brain now accounts for only 2% of human body weight, it consumes nearly a quarter of energy. By inventing ways to store information externally: cave art, writing, digital media, the human brain has reduced its capacity somewhat.
Chris Stringer, a paleoanthropologist at the Natural History Museum in London, and Christopher Cork, a neuroscientist at the Allen Institute, said in an interview with the Wall Street Journal on September 8 that books, personal devices and the Internet are used as information stores, which is likely to exacerbate the trend of shrinking brain capacity. Chris Stringer said: "Our brains don't need to work as hard as before, so they're getting smaller. ”
The Discover report pointed out why the human brain capacity has become smaller? Perhaps the most convincing hypothesis is that Homo sapiens underwent "self-domestication." The term derives from the human understanding of animal domestication. Compared with their wild ancestors, domesticated species such as sheep and dogs differ in many physical and behavioral characteristics, such as being tame, less timid, and smaller brains.
Humans may have domesticated themselves as well: in the Stone Age, cooperative, level-headed individuals were more likely to survive and reproduce than aggressive individuals. These tendencies are influenced by genes that also influence human physical characteristics, including body size and brain size. Over time, this self-domestication in humans has led to smaller brains.
Using fossil and modern specimen data, De Silva's team determined 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 suggest that complex social structures may play a role in brain volume reduction.
They speculate that the cooperation of human social organizations has greatly increased in the last 3,000 years, and collective intelligence has come into play. James Trañello, a professor of biology at Boston University and one of the co-authors of the De Silva team's research paper, explains that a group of people is smarter than the smartest person in the group. It's a bit like the Chinese proverb "Three stinkers are better than Zhuge Liang". So, in general, if you live in a group, you will solve problems faster, more effectively, and more accurately than if you were alone.
According to De Silva, humans are so social that each individual no longer needs to know everything. As David Giri, a cognitive scientist at the University of Missouri, explains: Increasingly complex societies do not require humans to master a variety of survival skills like humans in primitive societies. Based on this, some functions of the human brain are gradually degraded, and the brain capacity is reduced.
The functions are becoming more and more developed
Does shrinking of the human brain affect its function?
"Losing part of the brain doesn't have much impact on its function." Qiu Zilong, a researcher at the Songjiang Research Institute of Shanghai Jiao Tong University School of Medicine, told Science and Technology Daily: "There is a certain redundancy in the human brain, and sometimes even if a part is lost, it does not have much impact on its overall function. ”
He further explained that from a neuroscientific point of view, the human brain does have some redundancy - some "idle space". For example, clinically, some children who have suffered severe brain damage and undergo brain surgery to remove part of their brain can still return to normal function as they age. In addition, some people with epilepsy have 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 critical 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, and it takes tens of thousands of years to change significantly. Since ancient times, human beings have created a series of splendid civilizations, a series of high-precision technology, 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."
New Zealand scientist James Flynn found that in the process of continuous evolution, human IQ is also increasing, 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 function is more and more developed." ”
Humans have brains that are unique on Earth, but intelligent minds did not begin out, they are the result of millions of years of human development and evolution in the process of evolution. At present, the human brain is still evolving silently, what surprises will it bring us in the future? Let's wait and see!
Source: Science and Technology Daily