How do hybrids dominate the earth step by step?
Written by | Tang Bo (National Animal Gene Research Center of China Agricultural University)
When the box office of the domestic science fiction film " Wandering Earth " exceeded 4 billion yuan, many movie fans still remember the American fantasy movie " Aquaman " released more than two months ago. At present, the global box office of the movie has exceeded US$1.13 billion, of which the Chinese market contributed about US$300 million, ranking among the top 20 most popular movies in global history.
In the story told by "Aquaman", the queen of Atlantis and an American lighthouse guardian fell in love and gave birth to a boy Arthur. With the help of Princess Mela ( Aome's fiancée), Arthur fought against her younger brother Aome who wanted to rule the ocean and annex the land, and finally defeated the powerful Aomeman and became the Seaman who commanded the seven seas.
Arthur Curry
For Pure Haisheng's younger brother Oum, Arthur is just a "mix" of half-land and half-season. Om did not take his elder brother Arthur seriously at first, but it was Arthur, a bastard who defeated himself, took back the throne, and even hugged the beauty. Such stories are common in Chinese and foreign myths and legends and literary works. Although they are fictional, they contain profound scientific principles, that is, the performance of hybrids is sometimes better than that of purebreds.
Since the Austrian priest and father of modern genetics Gregor Mendel discovered this law of life through pea experiments, geneticists and breeders have cultivated a series of hybrid crops and new animal varieties. Hybrids have become the main force in agricultural production. It is these hybrids that feed such a huge population and countless domestic animals on the earth. It goes without saying that plants and animals are the ones. Even humans themselves, thanks to their hybrid advantages, have been able to prosper and evolve and become the master of the earth.
Today, let’s talk about the history of human “hybrid” development.
Going out of Africa
Somewhere in Africa about 7 million years ago, human ancestors parted ways with apes, and began a unique evolutionary path of making tools, walking upright, being able to talk, and telling stories. After
, human ancestors such as Australopithecus, talented people and craftsmen gradually spread to the entire Africa; either due to food deficiency or the instinct of animal curiosity, more than 1 million years ago, the truly standing Homo erectus began to step out of Africa and advance towards the Eurasian continent. These Homo erectus included Yuanmou people, Lantian people and Beijing people who lived on the vast land of China. However, these early humans who walked out of Africa became extinct one after another, and were not the direct ancestors of modern humans.
For decades, most scientists who study the history of human evolution believe that modern humans originated from a single group left behind somewhere in southern Africa. About 200,000 years ago, this branch of humans began to evolve rapidly and became the direct ancestor of modern humans, namely Homo sapiens. However, this theory is being challenged by some new discoveries.
In June 2017, an international research team led by Dr. Jean-Jacques Hublin from the Max Planck Institute for Evolution of Anthropology in Germany published two important papers back-to-back in the journal Nature. They discovered a skull of Homo sapiens 315,000 years ago in a cave in northern Africa. This not only pushed the history of modern humans forward 100,000 years, but also speculated that Homo sapiens did not originate from a single source in southern Africa, but was mixed with different races spread across multiple regions of Africa. In other words, before leaving Africa, Homo sapiens began to "hybridize" and the descendants of such "hybrid" can go out of Africa and every corner of the earth.
After thirty or three hundred thousand years of reproduction and survival in Africa, these modern human ancestors, like earlier human ancestors, were unable to break free from the temptation of curiosity and food, and kept trying to get out of Africa. Finally, 50,000 years ago, a small group of modern human ancestors were lucky to achieve unprecedented victory.
The reason why modern human ancestors achieved evolutionary success was not only due to their own efforts, but also the help of Homo erectus descendants who had walked out of Africa in the early days, including the contribution of genes.About 50,000 to 100,000 years ago, modern human ancestors walked out of Africa and first encountered some mysterious races evolved from Homo erectus, familiar with and adapted to the environment of the Eurasian continent, and started a love and killing with these mysterious races for thousands of years, which made us who are lonely in the human race today.
fell in love with the big-headed Needetts in
1856, three years ago, when Darwin published "The Origin of Species ", in a quarry in Neanderth Valley 12 kilometers east of Dusseldorf, Germany, quarrymen found a human-shaped skull and some bones during their operations. Archaeologists identified this as an extinct remains, and scientists called this species " Neanderthal ". Later archaeologists excavated hundreds of Neanderthal remains from Europe and the Middle East.
Neanderthals have obvious differences in anatomy from early Homo sapiens. They have thick limbs, strong bodies, and light-colored skin. What's more special is that their brain capacity is even larger than those of modern human ancestors. They can make stone tools, use fire, and may have evolved into certain cultures, such as burying relatives.
modern human skull and Neanderthal skull (Photo source: theverge.com)
Neanderthal skull Picture source: wiki
Scientists have been arguing about the status of Neanderthals in taxonomics. Some people believe that Neanderthals belong to a completely different race from Homo sapiens, while others believe that Neanderthals also belong to Homo sapiens, which is a subspecies below it. And most scientists generally believe that Neanderthals have no genetic contribution to modern humans until the first Neanderthal genome sketch was released in 2009.
On February 12, 2009, an international research team led by Svante Pääbo, the Max Planck Institute for Evolutionary Anthropology in Germany announced that they had deciphered the first sketch of the Neanderthal genome. These genomic DNA was extracted from three small bones belonging to different Neanderthals, unearthed from the Wendiga Cave in the north of Croatia. The genome information of Neanderthals has a total of about 2 billion base pairs, accounting for about 60% of its entire genome. What shocked the world even more is that scientists found that the European and Asian populations actually contain 1 to 4% of the genomic information unique to Neanderthals, while African indigenous people do not contain it, indicating that modern people had had intercourse with Neanderthals after leaving Africa, and these intercourse descendants became the ancestors of modern people. Scientists chose to release the Neanderthal genome sketch they drew on February 12, mainly to commemorate the 200th anniversary of the birth of Darwin, the founder of evolution. In May 2010, details of Neanderthal genome sketches were officially published in the journal Science.
Neanderthal skull and Professor Svante Pabo (Photo source: Washington Post )
Four years later, the research team dug out a Neanderthal toe bone from a cave called Denisova in the Altai Mountains, southern Siberia, Russia, and extracted genomic DNA from it, measured the entire genome of the Altenides, and found that the modern human genome contains only 1.5-2.1% of Neanderthal genetic information. In 2017, a previous paper in the journal Science believed that Neanderthal genetic information accounts for slightly higher proportion of East Asian genomes than Western Europeans. 2.3 to 2.6% of the genomes of Middle East sub-genomes originated from Neanderthals, while Neanderthal contributions to the Western European genomes were only 1.8 to 2.4%.
Scientists speculate that Neanderthals lived in Eurasia about 400,000 to 40,000 years ago, while early modern humans walked out of Africa about 50,000 years ago. Many studies have shown that it was 50,000 to 60,000 years ago that early modern humans had just stepped out of Africa and embarked on the land of the Middle East when they met Neanderthals living nearby. Both sides may have lived together in the Eurasian continent for up to 5,000 years. There is no direct evidence for whether there is a large-scale conflict between the two sides, but by comparing the genetic information of ancient humans, scientists speculate that Neanderthals and early modern humans love each other and have mixed feelings.
In 2015, Dr. Fu Qiaomei from the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences, as the first author, wrote in the journal Nature that researchers analyzed the early modern human DNA of males about 40,000 years unearthed from Romanian , and found that the proportion of Neanderthal genome information in the genome of this modern human is as high as 9%. In other words, the man's great-great-grandparents may be one of the Neanderthals. This is also the early modern humans who have so far discovered a close relationship with Neanderthals.
In fact, early modern humans not only accepted the genetic gifts of Neanderthals, but also successfully passed their genetic information to Neanderthals 100,000 years ago. In February 2016, researchers from international groups such as the Max Planck Institute for Evolutionary Anthropology in Germany announced in the journal Nature that in the genome of a female Neanderthal in a remote cave in the Altai Mountains in Russia, they detected the genetic information unique to modern human ancestors for the first time. It is speculated that a small group of modern human ancestors had had a mixed relationship with East Asian Neanderthals 100,000 years ago, but later these modern human genetic information disappeared without a trace.
colludes with the mysterious "Denisovans"
However, it is not only Neanderthals who have genetic communication with the ancestors of modern humans. Let us return to the Altai Denisova Cave located on the junction of Russia, China and Mongolia mentioned earlier. Not only did Neanderthals live here, but also protected the ancestors of modern humans, and a mysterious race lived in it.
Just a month before the first Neanderthal genome sketch was published in Science, a team led by Svanter Parbo of the Max Planck Institute for Evolutionary Anthropology and Anatoli P. Derevianko of the Russian Academy of Sciences wrote in Nature that they had discovered another new extinct race. Researchers performed a genetic analysis of mitochondrial DNA on a small piece of finger bone that was dug out from the Denisova cave two years ago. They extracted mitochondrial DNA from this small bone fragment and sequenced it. By comparing it with the mitochondrial DNA of early modern humans, Neanderthals, bonobos and chimpanzees, they were surprised to find that this small bone fragment belonged to neither early modern humans nor Neanderthals, nor bonobos or chimpanzees. Further analysis found that the owner of this small bone fragment shared the same ancestor as early modern humans and Neanderthals 1 million years ago. Therefore, researchers speculated that this small bone fragment belongs to an extinct new race.
At the end of 2010, the research team further analyzed the genomic DNA of this phalanx and inferred that this new race is close to Neanderthals, and may have been a family 640,000 years ago, while the evolution of the differences with modern Africans may be 840,000 years ago.
Molars that determine the identity of the "Denisovan" (Photo source: David Reich et al., 2010)
Soon after, researchers dug out other bone pieces of different individuals in the same cave, all of which have a genetic background similar to this new race, so they call it "Denisovan".
Denisovans are close relatives to Neanderthals, and about 17% of their genetic information comes from the latter. In August 2018, according to Nature, an international research team led by Viviane Slon and Svante Pääbo of the Max Planck Institute for Evolutionary Anthropology in Germany analyzed a small piece of bone from the Denisova Cave in the Altai Mountains of Russia. The bone belonged to a girl at least 13 years old 90,000 years ago. What is even more surprising is that her mother was a Neanderthal and her father was a Denisovan. This is the first time that scientists have discovered direct hybrid offspring of Neanderthal and Denisovans, indicating that it is very common for these different races to get mixed together after encountering.
The Denisovans and modern humans may be later than the Neanderthals, and their gene distribution is not as wide as the latter.The genetic information of the Denisovans is mainly retained in the genome of modern Asians. The Melanesian genome, which lives in the Pacific islands near Southeast Asia, contains 4 to 6% of the Denisovan genetic information. A 2016 study reduced this percentage to 1.1%, and it is speculated that there may be another extinct human that contributed genetic information. Other researchers have found that Denisovans contributed to the genomes of some Australians and Aboriginal people scattered on Southeast Asian islands, as well as the genomes of the continental East Asia and the Native Americans.
In March 2018, researchers from the University of Washington, Seattle and Princeton University wrote in the journal Cell that they used a new reference-free genome detection method to analyze 5,639 human genome sequences from Eurasia and Oceania, and found that the genetic information left by Denisovans in East Asian populations is quite different from that among South Asians and Oceania populations. Therefore, it is speculated that Denisovans have had at least two intercourses with modern humans, which makes the mixing of modern humans with other ancient humans more complicated.
So far, scientists have only found the remains of the Denisovans in the Denisovan caves in the Altai Mountains of Russia, and they are all small bone fragments, and their relatively complete remains have never been found. This makes it difficult for scientists to speculate on what the Denisovans look like, let alone issues such as living habits and living areas. But like Neanderthals, they kept their genetic information forever in part of the genome of modern humans by mixing with modern human ancestors, and brought unexpected benefits to these modern humans adapting to the environment and eventually becoming the master of the earth.
removes the false and retains the truth, transforms into a strong man
During the years of living with modern human ancestors, due to climate deterioration and other reasons, Neanderthals and Denisovans have also accumulated a large number of harmful gene mutations, which are inevitably passed on to their offspring who cross with modern humans. Although the gene gifts obtained from Neanderthals and Denisovans and other races are not all beneficial to modern humans, modern humans have gradually eliminated unfavorable genes in their not-so-long evolutionary history and preserved the favorable genes, so that they can climb the plateau, travel to Shanghai Island, travel around the world, and even explore the universe.
As we all know, when the ancestors of modern humans just left Africa 50,000 years ago, the Neanderthals and Denisovans had lived in Eurasia for more than 300,000 years, evolved strong adaptability to the local climate, food, pathogenic microorganisms and other environments, and finally formed some unique genotypes that were suitable for the environment. The mixing of modern humans with these ancient humans is conducive to introducing the corresponding favorable genotypes of these ancient humans. It can obviously help newcomers to quickly adapt to the environment, such as the cold climate in Europe, and then spread around the world.
Researchers from Shenzhen BGI Research Institute, University of California , and South China University of Technology and other institutions found that the reason why Chinese Tibetans can adapt to the high-altitude and low-oxygen environment of more than 4,000 meters in Tibet is probably because Tibetans inherited an EPAS1 gene mutant model related to hypoxia adaptation from the Denisovans or their close relatives. The research results were published in the journal Nature in July 2014.
Researchers from the Max Planck Institute for Evolutionary Anthropology in Germany analyzed the genome of 112,000 British people and found that some genes related to skin color, hair color, height, sleep patterns and even smoking conditions were from Neanderthals.
In October 2018, David Enard from the University of Arizona and Dmitri A. Petrov from the Stanford University reported in the journal Cell that during the intercourse, Neanderthals and ancient Homo sapiens not only spread viruses to each other, but also passed on the viral interacting protein (VIP) gene to the offspring of the two parties. VIP proteins have many functions, such as participating in immune responses, and can resist the invasion of specific viruses, especially RNA viruses. Due to gene mutations, some Neanderthal VIP proteins can fight the invasion of certain specific viruses, especially RNA viruses.In this way, Homo sapiens offspring who inherited Neanderthal VIP genes will gain resistance to more viruses, namely genetic adaptability, and can survive the subsequent large-scale plague, while those non-mixed offspring will be gradually eliminated. Forbes contributor Dr. Jennifer Raff vividly compares this phenomenon to the Neanderthals and ancient Homo sapiens both expel each other and provide antidotes to each other.
Neanderthals and modern ancestors have poisoned each other and provided each other with "anti-drugs" (Photo source: David Enard et al., 2018, Cell)
Although Neanderthals and Denisovans have completely extinct as human races, their love stories with modern human ancestors have been deeply engraved in our genome and can no longer be erased or erased.
References
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Thanks to Dr. Fu Qiaomei for reviewing and revisioning this article.
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