How does the human brain "lose"?, Over thousands of years, brain capacity has decreased by about 10%

Most people believe that brain evolution occurs in a linear manner: it continues to grow, then enters a plateau period, and finally stops developing, but this is not the case. According to measurements conducted on a population of 122 individuals, the brain capacity of modern adults ranges from 900 to 2100 milliliters, while the average global human brain capacity is 1349 milliliters, which is smaller than the brain capacity of our ancestors during the Stone Age.

For a long time, the development of a larger brain capacity has been regarded as a symbol of human intelligence enhancement and the ability to "rule" the Earth. In the last two million years of human evolution, the capacity of the human brain has increased nearly four times. But more and more evidence suggests that at some point after the end of the previous glacial period, the human brain became smaller.

Jeremy de Silva, a professor of paleoanthropology at Dartmouth College in the United States, said, "Most people believe that brain evolution occurs in a linear manner: it continues to grow, then enters a plateau period, and finally stops developing, but the fact is that our brain has shrunk, and the lost brain tissue is the size of a lime." De Silva's research team's calculations show that over the past few thousand years, human brain capacity has rapidly decreased by about 10%, and related research papers have been published in the Swiss journal "Frontiers of Ecology and Evolution".

So, what are the reasons for shrinking the human brain? Will shrinking the human brain have an impact on its function?

The human brain has quietly become smaller

The American magazine Discovery pointed out in a report that the average size of the human brain is shrinking, which began tens of thousands of years ago. Over the past 100000 years, the average brain capacity of Homo sapiens has decreased by about 40%.

The Chadian Shah people, who lived about 4 million years ago and are considered to represent the oldest ancestors of humanity, have a brain capacity of approximately 350 milliliters. Afterwards, the human brain capacity began to increase. From approximately 4 million years ago to approximately 2 million years ago, the brain capacity of the Southern Ape was around 500 milliliters. By one million years ago, some Homo erectus had a brain capacity exceeding 1000 milliliters. About 130000 years ago, the average brain capacity of Neanderthals and Homo sapiens reached 1500 milliliters. It is worth noting that since the era of Homo erectus, there has been no substantial change in human body size, so most of the increase in brain capacity is not related to body size growth.

But has the human brain capacity been constantly increasing? No way! According to measurements conducted on a population of 122 individuals, the brain capacity of modern adults ranges from 900 to 2100 milliliters, while the average global human brain capacity is 1349 milliliters, which is smaller than the brain capacity of our ancestors during the Stone Age.

The calculation by the De Silva research group also shows that over the past 150000 years, the average capacity of the human brain has remained around 1450 milliliters. But over the past few thousand years, this value has rapidly decreased by about 10%, reaching 150 milliliters. They used fossil and modern specimen data to determine that this shrinkage of the human brain occurred 3000-5000 years ago.

In addition, a paper published in the journal Human Biology in 1988 analyzed the skulls of over 12000 Homo sapiens from Europe and North Africa. Research has shown that over the past 10000 years, the brain capacity of males and females has decreased by approximately 10% and 17%, respectively.

The collective wisdom plays a role

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 only accounts for 2% of human body weight, it consumes nearly a quarter of its energy. By inventing methods for storing information externally, such as cave art, writing, and digital media, the human brain capacity has been reduced.

Chris Stringer, a paleoanthropologist at the Natural History Museum in London, England, and Christopher Kirk, a neuroscientist at the Allen Institute in the United States, said in an interview with the Wall Street Journal on September 8 that books, personal devices and the Internet were used as information storage, which may have exacerbated the trend of shrinking brain capacity. Chris Stringer said, "Our brain doesn't need to work as hard as before, so it's getting smaller."

A report from Discovery magazine suggests that why does human brain capacity decrease? Perhaps the most convincing assumption is that Homo sapiens have experienced "self domestication". This term originates from human understanding of animal domestication. Compared to their wild ancestors, domesticated species such as sheep and dogs have many differences in physical and behavioral characteristics, such as domestication, less timidity, and smaller brains.

Perhaps humans have also domesticated themselves: in the Stone Age, individuals who were good at cooperation and had a calm mind were more likely to survive and reproduce than aggressive individuals. These tendencies are influenced by genes, which can also affect human physical characteristics, including body size and brain size. Over time, human self domestication has led to a smaller brain.

The De Silva team used fossil and modern specimen data to determine that the shrinkage of the human brain occurred 3000-5000 years ago, which was a prosperous period of ancient civilizations in North Africa, the Middle East, and South America. They believe that complex social structures may play a role in reducing brain capacity.

They speculate that cooperation among human social organizations has greatly increased in the past 3000 years, and collective intelligence has begun to take effect. James Tranello, one of the co authors of the research paper by the De Silva team and a biology professor at Boston University in the United States, explained that a group of people are even smarter than the smartest person in this group. This is a bit like the Chinese proverb "Three stinky cobblers are better than Zhuge Liang.". So, generally speaking, if you live in a group, solving problems will be faster, more effective, and more accurate than when you are alone.

De Silva stated that human sociality is so strong that every individual no longer needs to know everything. As cognitive scientist David Gilly from the University of Missouri explained, the increasingly complex society eliminates the need for humans to master multiple survival skills like in primitive societies. Based on this, some functions of the human brain are gradually deteriorating, and the brain capacity is shrinking accordingly.

The functions are becoming increasingly advanced

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

"Losing a portion of the brain does not have a significant impact on its function," said Qiu Zilong, a researcher at the Songjiang Research Institute of Shanghai Jiao Tong University School of Medicine, to a reporter from Science and Technology Daily. "The human brain has a certain degree of redundancy, and sometimes even if a portion is lost, it does not have a significant impact on its overall function."

He further explained that from a neuroscience perspective, there is indeed some redundancy in the human brain - some "idle space". For example, in clinical practice, some children's brains are severely injured, and after undergoing brain surgery to remove a portion of the brain, their brain can still recover normal function as they age. In addition, some epilepsy patients have had their brains partially removed and are still able to live normally.

"It can be seen that the brain has some redundancy in function. If the loss is not in a critical area, it does not actually affect the overall functioning of the brain," said Qiu Zilong.

He pointed out that the evolution of the human brain is a slow process that takes tens of thousands of years for significant changes to occur. Since ancient times, humans have created a series of brilliant civilizations and advanced technologies, all of which can indicate that humans are becoming increasingly intelligent. Moreover, intelligence tests have also proven that the human brain is becoming increasingly developed.

After studying human intelligence, New Zealand scientist James Flynn found that in the process of continuous evolution, human intelligence is also constantly improving, and this phenomenon is also known as the Flynn effect.

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

Human beings possess a unique brain on Earth, but their intelligent minds are not inherent in the beginning. They are the result of millions of years of human evolution and development. At present, the human brain is still silently evolving. What surprises will it bring us in the future? Let's wait and see!