Fossil evidence and genetic analysis show that human beings originated in Africa. The earliest human ancestor is considered to be an ancient anthropoid ape. They parted ways with chimpanzees, distant relatives of human beings, about 6.5 million years ago. About 2 million years ago, Australopithecus africanus evolved into Homo erectus and gradually spread all over the world. The famous Beijingers are one of Homo erectus. They came to northern China about 700,000 years ago and lived there until about 200,000 years ago. People once thought that Beijingers were the ancestors of China people, but genetic analysis showed that they were only close relatives of human beings. In fact, our ancestors had never seen such close relatives, because modern Homo sapiens did not come to East Asia until about 40,000 years ago, when Beijingers had been extinct for many years.
There is also a "European ape-man" in Europe, similar to Peking man. This is a subspecies of Homogeneous-Neanderthals. They began to settle in Europe about 200,000 years ago, and gradually spread around, south to Siberia and south to today's Middle East. Unlike Beijingers, Neanderthals became extinct about 30,000 years ago. Don't underestimate the age gap. We should know that modern Homo sapiens walked out of Africa and entered Europe through the Middle East 50,000 to 80,000 years ago, so the ancestors of human beings should have met their Neanderthal relatives.
Now that relatives have met, it is natural to ask a question: Have they communicated with each other? If there was communication, was it a kind cooperation or a life-and-death fight? Archaeological evidence shows that there seems to be no large-scale war between the two, but the more specific form of communication is unknown. Just then, scientists discovered that several Neanderthal skeletons found in caves in Vindiga, Croatia, were well preserved and could be used to sequence the Neanderthal genome. Thus, in 2006, German scientists took the lead in measuring the sequence of 654.38+100,000 "letters" (nucleotides) and drew two conclusions: First, Neanderthals were not the ancestors of human beings. Second, there is no gene exchange between them.
The magazine Science published on May 7th this year overturned this conclusion. SvantePaabo, a professor of evolutionary anthropology at the Max Planck Institute in Germany, and his huge international research team published an article saying that they successfully measured the sequence of 4 billion "letters" with a new DNA sequencing technology, and concluded through computer analysis that Neanderthals once had gene communication with humans!
These two achievements are extremely difficult and highly technical. First of all, such an ancient bone must contain a lot of bacteria, and DNA pollution is inevitable. The old method is to achieve the purpose of sequencing by DNA amplification, but this amplification is easy to amplify bacterial pollution. This is also the reason why the "dinosaur gene" sequence detected by Chen in that year was later proved to be mostly contaminated by bacteria. The new method adopted by Professor Papo does not need DNA amplification, and the required gene sequence can be accurately detected even when the bacterial contamination reaches 99.8%.
Secondly, even with this new method, there are inevitably many errors in the measured gene sequence. How to judge whether Neanderthals had gene communication with modern people? This work was completed by Dr. Richard green, who graduated from the Department of Mathematics. Dr Green designed a complicated algorithm to compare the genome sequence of Neanderthals with that of five women from southern Africa, western Africa, Europe, Papua New Guinea (located in South Asia) and China, and finally reached this conclusion.
Dr. Green counted the differences between Neanderthal genome and modern genome. If Neanderthals didn't communicate with modern people, then Neanderthals' genomes should be as different as those of five modern people. But Dr. Green found that the genome sequence of Neanderthals was more different from that of two Africans than that of three other Africans. According to this algorithm, as long as our ancestors had several sexual exchanges with Neanderthals, it was enough to explain this difference.
Dr. Green also calculated that the time of gene exchange occurred between 50,000 and 80,000 years ago, that is, the time when humans first walked out of the African continent. Dr. Green even calculated the location where the gene exchange took place, about in the Middle East today, which was more in line with the situation at that time.
By analyzing the number and location of gene exchange, Dr. Green calculated that 1%~4% of the modern human genome came from Neanderthals, but there is no indication that these foreign genes played a key role in human evolution.
However, Dr. Green mentioned in his paper that this algorithm has defects. If Neanderthals and modern humans both evolved from a unique group of Homo erectus, this algorithm will not work. However, Dr. Green doesn't think this hypothesis holds, it only has mathematical significance.
This research is of great significance and has aroused great repercussions internationally. If it is finally proved to be correct, it shows that human beings are not all descendants of a single ethnic group, but are mixed with some "close relatives" genes. Did this mixture promote human evolution? What effect does it have on the human body? Let's wait and see. ⑥2