Why is the human brain so big?

For decades, researchers have been arguing about this, and various theories have emerged. Some people have proposed the “social brain hypothesis”, thinking that the evolution of a larger brain can help us manage the increasingly complex social life; others have proposed the “high energy consumption organization hypothesis”, thinking that carnivorous allows the brain to evolve at the cost of the intestine; The research suggests that social challenges such as cooperative hunting or sharing cultural knowledge promote the expansion of the human brain; in addition, a mathematical model that explains the evolution of the human brain also finds that the environment has a stronger influence…

Discover genes controlling brain size
Over the past 3 million years, the evolution of the brain has played an important role in our species’ ability to think, solve problems, and develop culture. However, the genetic changes behind our human brain evolution are elusive. In 2018, two research teams simultaneously discovered the gene family that makes humans evolve such incredible brains-NOTCH2.

Over the past three million years, this gene family has acted as a catalyst for the evolution of the human brain. The genome where the gene is located has been found to be related to neurodevelopmental diseases in the past, and it plays an important role in the development of the human cerebral cortex by delaying the differentiation of stem cells into neurons. In the long run, this leads to more neurons overall. This gene is also unique to humans (even human close relatives are not) and is highly expressed in cerebral cortical stem cells.

A replication error was discovered in a distant ancestor between 8 million and 14 million years ago resulting in “extra large chunks of DNA”, researcher David Hausler of the University of California, Santa Cruz and Howard Hughes Medical Research Institute The doctor said that he is a senior author of one of the new studies.

This special gene called NOTCH2NL produces proteins and is involved in converting neural stem cells into cortical neurons. NOTCH2NL increases the number of neocortical neurons where advanced cognitive functions reside. Over time, a bigger and stronger brain has been created.

“Our brain is mainly enlarged by the expansion of certain functional areas of the cerebral cortex, which is the basis for us to become human.” Dr. Hausler said, “The most exciting scientific problem I can think of, There is nothing like discovering and decoding the mysterious genetic changes that make us our own.”

Hausler said: “This is the first human-specific gene known in the first basic way to control brain size.”

After discovering that only human cells carry the NOTCH2NL gene, Hausler’s team began to compare gene expression during the development of human and macaque brains.

It doubled before the brain capacity increased dramatically
Partial copies of NOTCH2 are inserted into the genome by replication. This occurs in ancient ape species, which are the common ancestors of humans, chimpanzees and gorillas. This partial replication is a non-functional “pseudogene” that still exists in the chimpanzee and gorilla genomes.

However, in the human lineage, when additional NOTCH2 DNA is copied to its location, the pseudogene “resurrects” and produces a functional gene. This new gene will be repeated several times and will generate 4 related NOTCH2NL genes.

One of the four NOTCH2NL genes seems to be a non-functional pseudogene, but the other three are active genes, which are the active genes that direct the production of the original NOTCH 2 protein truncates.

The researchers explained: “When we compared genes expressed in stem cell-derived models during human and cynomolgus monkey brain development, we realized that we could detect NOTCH2NL in human cells, but not in cynomolgus monkey cells.”

“Looking at the DNA, we did not find it on the orangutan, only the truncated, inactive versions were found on our nearest relatives, gorillas and chimpanzees.”

“The evolutionary history of the reconstructed NOTCH2NL gene suggests that a process called gene conversion may be responsible for repairing the non-functional version of NOTCH2NL, which originally appeared as a partial replication of an important neurodevelopmental gene NOTCH2.”

The team believes that this repair effect only occurs in humans, about 3 to 4 million years ago, about the same time as the fossil records show that the human brain began to expand, that is, we separated millions of other apes Years later. But before we separated from the common ancestor of Neanderthals, NOTCH2NL repeated twice.

Dr. Hausler and his colleagues studied what happens when NOTCH2NL is not expressed: They removed NOTCH2NL from human stem cells and used it to grow a cortex called organic matter. The study found that organic compounds produced in NOTCH2NL-depleted stem cells differentiate more quickly, but the resulting organic compounds are smaller.

“If you lose NOTCH2NL, it will cause premature differentiation of cortical stem cells into neurons, but at the same time, very important stem cell banks will also be depleted,” Frank Jacob, a member of the Dr. Hausler team and a researcher at the University of Amsterdam Dr. Si said.

The duplication or deletion of the genomic region known as 1q21.1 is known to cause macrocephaly or microcephaly, respectively, and is associated with a range of neurodevelopmental disorders, including hyperactivity disorder, autism spectrum disorder and intellectual disability. Since NOTCH2NL is an evolutionary trade-off between the brain and the susceptibility to 1q21.1 disease, the researchers quickly pointed out that there are also many healthy variations here.

Looking for genes unique to active humans
Another research team was led by developmental biologists Pierre Van der Hegen and Wibkuluwen of Brooks University. They arrived at NOTCH2NL from a related direction, using the original tissue to find human-specific genes that were active during fetal brain development. .

Van der Haigen said: “For us researchers, it is very important to understand the factors that cause the brain (especially the cerebral cortex) to become larger during human development and evolution. Given the relatively rapid evolution of the human brain , It is easy to guess that newly evolved, human-specific genes may help us shape the brain in a species-specific way”

Finding human-specific genes related to brain development has proved challenging because it is difficult to distinguish it from other species. Therefore, the team developed a new RNA sequencing analysis method, which is specifically used to detect the specificity and sensitivity of human-specific genes in embryonic tissues. This allows researchers to identify 35 human-specific genes active in the development of the human cerebral cortex, including the NOTCH2NL gene family.

They focused their attention on NOTCH2NL because its ancestral gene, NOTCH 2, plays an important role in controlling whether the cortical stem cells produce neurons or regenerate more stem cells. They found that artificial expression of NOTCH2NL in mouse embryos can increase the number of progenitor cells in the mouse cerebral cortex.

After testing an in vitro cortical development model based on human pluripotent stem cells, the researchers found that NOTCH2NL can significantly increase the number of cells in the culture, thereby generating more neurons.

“A stem cell has three possibilities for differentiation: regenerating two progenitor cells, generating two neurons, or generating a progenitor cell and a neuron. What NOTCH2NL does is to slightly change this decision possibility to make stem cells easier Progenitor cells are generated, and this will eventually increase the number of neurons.” Dr. van der Hegen said.

To better understand the role of these genes in humans, scientists have established an in vitro model of cortical development from human pluripotent stem cells to explore the function of NOTCH2NL. In this model, they found that NOTCH2NL can significantly increase the number of cortical stem cells, which in turn produces more neurons. This feature is expected to distinguish between human and non-human cortical neurogenesis.

We still have a lot of things we don’t understand about NOTCH2NL. What is clear so far is that NOTCH2NL plays an important role in the evolution of the human brain. It may partially answer that ancient question-the reason why we became humans is because of a gene mutation that happened millions of years ago, and this mutation made us smart.

Social challenges drive higher intelligence
NOTCH2NL helps our ancestors’ brains grow larger, but from a metabolic point of view, brain tissue is expensive. Dr. Maurizio Gonzalez Ferrero, a mathematical evolutionary biologist at the University of St Andrews in Scotland, said: “The brain accounts for 4% of the body’s weight but consumes 20% of the energy.”

There must be something that has driven the evolution of bigger and more expensive brains. Three competitors have emerged: social challenges (including cooperation and competition), ecological challenges (finding food, avoiding predators) and cultural challenges (ability to share acquired knowledge and skills).

Most researchers believe that social challenges have driven the emergence of higher intelligence, but these models are largely untestable.

In the May 2018 issue of Nature, Gonzalez Ferrero and his colleague Andy Gardner showed for the first time a computing tool used to understand what drives the human brain to become more Big. Gonzalez Ferrero said that their method is more complicated than its method, but it is also based on actual numerical operations. Our goal is not just to study why our brains get bigger, but why they become so big.

Gonzalez Ferrero said: “This is based on empirical evidence and has actual metabolic costs, so it is also easier to test.”

They studied the energy consumption of different tissues, as well as body size. The growth of any component requires increased energy, but this is a trade-off: increasing brain volume can also improve skills, but a larger, more energy-intensive brain will reduce energy in other parts of the body, such as reproductive tissue.

The new model produced multiple scenarios, each with different combinations of challenges. Gonzalez Freiro believes that the need for social intelligence-the main assumption is the most important, but the fact is the opposite. What he calls an “arms race” is competition between more and more intelligent individuals, and the results are counterproductive.

He said: “It will make your brain bigger, but they (in terms of metabolism) are too costly.”

On the contrary, the study found that the most likely explanation for our brain-to-body ratio is the 60% ecological challenge, 30% cooperation and 10% competition among groups. Social intelligence theorists are still skeptical of these results, but Gonzalez Ferrero pointed out: “We are not tied to any specific assumptions, we are only providing a tool.” He is already planning to perfect this tool . The initial model did not consider the cultural intelligence hypothesis, and he hoped to incorporate the cultural intelligence hypothesis into the model.

The human brain may change in the future
Recent social and workplace changes may even drive the recent upward trend in autism cases. Simon Barron Cohen, director of the Autism Research Center at Cambridge University, wants to know whether the increase in autism cases is partly blamed on “type matching”, where people choose people who resemble them as spouses. People with autism spectrum disorders usually pay more attention to details and have more analytical skills. Nowadays, they may find it easier to find a partner they like more than they used to. Barron Cohen pointed out that in the late 1950s, only 2% of the graduates of MIT were women, and now the ratio reaches 50%. He is developing a study to test whether the type-selection pairs that exist in people who are susceptible to autism will increase their chances of having children with autism.

The human brain has now become a unique cognitive machine in the world, and it is likely to undergo greater changes in the future. Stephen Pique, a Harvard experimental psychologist who studies language and brain evolution, said that the environment we are in is essentially a “cognitive environment.” In a study, Wiley found that the genes that control glucose metabolism in the human brain are one of the most recently evolved genes. It may be this evolution that has made the human brain twice as big as the chimpanzee, the species closest to us.

The first mixed race between different ancient human populations
The researchers found the genome of a young girl who lived about 90,000 years ago from a fragment of bone about two centimeters long found in Denisova’s cave in Siberia. The researchers named her “Denny”. Although this bone is only two centimeters, it has made major discoveries after research.

DNA analysis showed that the “Danny” girl was a direct mixed-race child from two extinct ancient human populations-Neanderthals (mother side) and Denisovan (father side). And these two ancient human populations and our modern humans do not belong to the same evolutionary branch. Although geneticists have previously discovered evidence of inter-human genus hybridization, researchers have for the first time discovered the first generation of different ancient human populations.

The first artist on earth is not human
We often lament the wisdom and creativity of humans in ancient civilizations, and we can’t help but imagine who the first artist on earth is. However, the University of Southampton in the United Kingdom, the Max Planck Institute in Germany, the University of Barcelona in Spain, and other research groups used the latest uranium and thorium dating methods to jointly explore the authorship of the previously discovered Spanish cave mural sites. After research, it was discovered that the first artist on earth was not a human, but a Neanderthal. Prior to this, Neandertals were widely described as barbaric and inferior races without aesthetic and cognitive abilities; however, the findings of these cave paintings show that our modern humans are not the first people on Earth to be able to deal with symbolic thinking and possession Self-conscious complex Kochi creature.

Ancient human “children” can walk upright more than 3 million years ago
Our modern bipeds can effectively walk on two legs, but evolved arboreals cannot. Precisely, in our origin story, when did the transition from tree life to terrestrial life take place has always been a matter of debate among ancient anthropologists. Many researchers believe that Alfa apes lived in East Africa between 3 and 4 million years ago and were the first fully bipedal ancestors.

However, in the July 2018 issue of “Science Progress”, American researchers analyzed the foot bone fossils of a 2.5-year-old female young apes of the Australopithecus afarensis about 3.31 million years ago, which is about the size of a human thumb It was discovered in the Dikika area of ​​Ethiopia in 2002.

The study found that many structural features of the young ape’s foot indicate that she can walk upright, and its inner wedge bone protrudes, which can be used to help climb trees.

The most famous representative of Australopithecus afarensis is “Lucy” unearthed in Ethiopia in 1974. She lived about 3.2 million years ago. Some scholars previously believed that the Australopithecus afarensis almost completely walked on two feet, but there are also studies suggesting that they are partially inhabiting trees, and “Lucy” may have died due to injury from falling off the tree. This may mean that younger Alfa individuals will roam the trees to avoid predators, but once they reach adulthood, they will spend time on the ground foraging.

Our expansion story
Researchers agree that the earliest primitive people-the primate branch-appeared in Africa. But after that, things became a little blurry. In particular, the map of when and how humans spread on the old continent has been changing. These discoveries opened up a “new” path for our ancestors and distant relatives.

Israel
The story about the origins of modern humans is constantly being modified, but in general, Homo sapiens first appeared in what we now call Ethiopia, and some descendants who remained in East Africa evolved into modern Homo sapiens about 100,000 years ago . Data published in Science in January 2018 shows that from the anatomical point of view, part of the jaw of a modern human can be traced back to 177,000 to 194,000 years ago. This is the oldest skeletal evidence of humans outside Africa, which is more than 50,000 years earlier than the early estimates of Homo sapiens appearing on the African continent.

The researcher’s lead researcher Isreel Heskowitz said: “Although all the anatomical details of the Misilia fossils are completely consistent with modern humans, some features are similar to those of Neanderthals and other human groups. Remains. This shows that although Africa is the origin of our species, some of our features must have evolved outside Africa.

Saudi Arabia Central Province
For more than a decade, a team of archaeologists and anthropologists has been searching for evidence in the Arabian desert to prove that some of the earliest members of humanity once crossed the green spaces that used to be there. Researchers published a report in the journal Nature Ecology and Evolution in April 2018. The finger bone is about 85,000 years old and is the oldest anatomically modern human fossil found in the Arabian Peninsula. Based on the animal bones, stone tools, and sediments at the same location, the research team believes that it is located next to a freshwater lake that has water all year round, surrounded by semi-arid grasslands, and prey everywhere: this is an attraction for early hunting collectors Camp, they believe these people have lived here for a while.

New discoveries support the idea that early modern people spread to Eurasia earlier and more frequently than many people thought.

Atiklan Parkham, India
A long time ago, right now in South India, early humans demonstrated the innovative capabilities that Silicon Valley tech wizards envy. Over time, ancient inventors gave up bulky hand axes and choppers and switched to smooth thin stones to cut things and make spears.

At the same time, modern human ancestors on the African continent also started a similar renewal activity. However, it is surprising that archaeologists found traces of the tool replacement period in the soil layer of the Pakkam site in Attila, India. The tool replacement of this site may have occurred 250,000 years ago, or it may have been 385,000 years ago, which is much earlier than other sites in India. This means that the origin of culture in India in the middle Paleolithic period was 100,000 years earlier. Although no human bones were found, a large amount of stone evidence from 385,000 years ago indicates that Homo sapiens left Africa much earlier than people thought. However, other researchers believe that these tools are not so advanced and may be made by another, older species.

Shangchen Ruins in China
In the area of ​​Lantian Village, Xi’an, Shaanxi Province, a Chinese and foreign team led by Zhu Zhaoyu, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, discovered a Shangli site, an early Pleistocene paleolithic site. The 96 stone tools found in the site were analyzed through a series of field measurements and experimental tests, and it was found that these stone tools had been 2.12 million years old at the earliest. In other words, humans have left Africa at least as early as 2.12 million years ago, which is about 270,000 years earlier than the previously proposed era.

They were found along with the bones of deer and other animals, but no human fossils. However, an excavation in 1964 found a partially erect human skull from 1.63 million years ago.

The polls released by the think tanks of the United States, Germany and France on June 30 show that after the new crown epidemic era, more Europeans and Americans regard China as a big country.

According to Agence France-Presse, the US-based German Marshall Foundation, the German Bertelsmann Foundation, and the Montaigne Institute of France surveyed 1,000 people each in the United States, Germany, and France this year, from January 9 to 22. Sunday, May 11-19. The results show that the new crown epidemic has caused more and more Westerners to view China as a top power, while the US’s leading position is declining.

The poll found that since the new crown epidemic, people’s awareness of China’s influence has increased significantly. Before the epidemic, people agreed that the United States is the most influential country in the world, and China and the European Union are almost tied for second. After the crisis, the United States is still considered the most influential, but China’s influence has increased significantly. The survey found that by comparing the data from January and May, the proportion of French respondents who believe that China is the most influential country in the world has increased from 13% to 28%, and that of German respondents has increased from 12% to 20%. Respondents rose from 6% to 14%. People interviewed in the United States, France and Germany still believe that the United States is the most influential country, but its influence has weakened. In France, the proportion of respondents who believe that the United States is the world’s largest country fell from 67% in January to 55% in May. Similar changes have taken place in German data.

The head of the German Marshall Foundation, Martin Quinceis, said on the 30th that before the new crown crisis, China’s impact on the world was an abstract concept, “When you think about the dependence on Chinese masks and medical equipment, this concept changes. Be very specific.” Quincys expects this to have a lasting impact. He said that the change in concept transcends intergenerational and political boundaries. “It looks more structural than just a quick response to the crisis.”

Agence France-Presse said that although China is considered increasingly influential, the survey found that the majority of respondents in Germany and France believe that their country should adopt a tougher attitude toward Beijing on issues such as climate warming, human rights and cybersecurity . French interviewees most want to adopt a tougher attitude towards China. Americans are the least willing to take stricter measures, but this may be because the United States has confronted China more than its European allies, especially in the area of ​​trade and security.

In recent years, the United States and the European Union have adopted a tougher attitude toward China, and public opinion has followed suit. Especially after the new crown crisis, many Americans, French and Germans now hold a negative view of China’s rising influence. Specifically, in the January survey, nearly half of the respondents in all three countries considered China’s rising influence to be negative. After the outbreak, the proportion increased by 10 percentage points or more.

The survey also revealed that a relative loser in the New Crown crisis was the European Union. Before the outbreak, the French and Germans firmly believed that the European Union’s influence ranked second in the world, surpassing China. After the epidemic, more French and American respondents believe that China has more influence than the EU, while more Germans still think that the EU has more influence than China.