For a long time, the development of a larger brain capacity has been seen as a sign 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, enters a plateau stage, and finally stops developing. However, this is not the case. Our brain has shrunk, and the lost brain tissue is the size of a lime." De Silva's team's calculations show that over the past thousands of years, The human brain capacity has rapidly decreased by about 10%, and the related research paper has been published in the Swiss journal "Ecology and Evolutionary Frontiers". So, what are the reasons for shrinking the human brain? Will a smaller human brain have an impact on its function? The human brain has quietly shrunk, and Discovery magazine in the United States reported that the average size of the human brain is shrinking, starting tens of thousands of years ago. In the past 100000 years, the average brain capacity of Homo sapiens has decreased by about 40%. The Chadian Sahelanthropus tchadensis, who lived approximately 4 million years ago and is considered to represent the oldest ancestor of humanity, had 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 (Lucy and her contemporaries) was around 500 milliliters. By 1 million years ago, some Homo erectus had a brain capacity exceeding 1000 milliliters. About 130000 years ago, the average brain capacity of Neanderthals (with a sample size range of 1172-1740 milliliters) and Homo sapiens (1090-1175 milliliters) 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 human brain capacity been constantly increasing? No! Measurements conducted on a population of 122 individuals show that the brain capacity of modern adults ranges from 900-2100 milliliters, with an average global human brain capacity of 1349 milliliters, which is smaller than the brain capacity of human Stone Age ancestors. The calculations by De Silva's research team also show that over the past 150000 years, the average capacity of the human brain has remained approximately 1450 milliliters. But over the past few thousand years, this value has rapidly decreased by about 10% to 150 milliliters. They used fossil and modern specimen data to determine that this shrinkage of the human brain occurred between 3000 and 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 men and women has decreased by about 10% (157 milliliters) and about 17% (261 milliliters), respectively. Why does human brain capacity shrink when collective intelligence plays a role? Some researchers believe that the brain is the most important part of the human body