Molecular Anthropology and African Theory of Human Origin

Molecular anthropology technology is widely used in anthropology and archaeology, and plays an increasingly important role in the origin and evolution of human beings, human migration and communication, kinship between people, archaeological identification and so on. 1987, the article "Mitochondrial DNA and Human Evolution" by three molecular biologists (R.L. Kan, M. Si Tong King and A.C. Wilson) from the University of California, Berkeley was published in the British magazine Nature. They selected 147 women whose ancestors came from Africa, Europe, Asia, the Middle East, Papua New Guinea and Australia, and successfully extracted mtDNA from the placenta cells of babies after delivery, analyzed its sequence, and drew a phylogenetic tree according to the analysis results. It can be inferred that the measured infant mtDNA can trace all modern people back to a woman who lived in Africa about 290,000 ~10.4 million years ago, with an average of 200,000 years ago. She is the "grandmother" of people living in every corner of the earth today. Then, according to the mutation rate of mtDNA, the approximate time for African population to differentiate into other populations in the world is calculated, which is about 6.5438+0.8 million years to 90,000 years, with an average of about 6.5438+0.3 million years ago. It is believed that about10.3 million years ago, a group of descendants of this "grandmother" left their hometown of Africa, migrated and spread to all parts of the world, gradually replacing the early Homo sapiens, that is, the descendants of indigenous Homo erectus living there, and then settled in all parts of the world, gradually evolving into what we are now. This is the famous "Eve Hypothesis" of the origin of modern people.

In 2000, underhill of Stanford University in the United States used denaturing high performance liquid chromatography technology to analyze and obtain the 13 1 haplotype composed of 2 18 non-recombination sites on Y chromosome, studied the world's 1062 representative male individuals, and drew the phylogenetic tree according to the analysis results. The results of Y-DNA phylogenetic tree are very similar to those of mtDNA phylogenetic tree. Other modern people in the world, such as Europeans and Asians, originated from Africa, while modern people in the United States and Australia originated from Asians. This is the Adam Hypothesis which is compatible with the Eve Hypothesis. Similarly, according to the mutation rate of Y-DNA, it is estimated that the approximate time for African population to differentiate into other populations in the world is 140000 ~ 40000 years, with an average of about 60000 years ago.

1In July, 1997, the American weekly Science published an article, which caused an uproar in academic circles. M. Krings, a molecular biologist at the University of Munich in Germany, etc. , extracted and amplified the mtDNA of Neanderthal fossils about 60,000 years ago discovered in Neanderthal Canyon in Dü sseldorf, Germany in 1856, and sequenced the extracted DNA. It is found that there is a 12 fragment in the mtDNA sequence of Nigerians, which is completely different from that of modern people. The mtDNA of Nigerians is outside the variation range of modern people, and the calculated differentiation time is more than 300 thousand years. Historically, Nigerians and modern people have coexisted within 654.38 million+years. If there is a direct genetic relationship between the two races, the difference should not exceed 654.38+ million years. It can be inferred that Nigerians can't be the direct ancestors of modern humans. They didn't pass on their blood to modern humans at all, but just became a sideline in the history of human evolution. This result supports the hypothesis that modern people originated in Africa [7]. This scientific discovery was once rated as one of the top ten scientific and technological achievements in the world from 65438 to 0997. Later, another scientist successfully extracted mtDNA sequences from Neanderthal fossils unearthed in the Caucasus and Croatia, and also concluded that Neanderthals were not related to modern people.

Chu Jiayou and others 14 American scholars 1998 published an article in PNAS, which also supported the view that modern people originated in Africa. They used 30 autosomal microsatellite loci (DNA sequences consisting of 2-6 base repeat units) to analyze the genetic structure of 28 East Asian populations, including the Han population in China and the northern and southern populations of ethnic minorities. The research results support the hypothesis that modern China people also originated from Africa. People think that modern China people entered Chinese mainland from Southeast Asia, not from Central Asia. However, due to the small sample size, weak population representation, high mutation rate of microsatellite loci and some limitations in tracing distant events, the work of Chu Jiayou and others cannot convincingly prove that East Asians originated in Africa.

1999, Su Bing and others used a set of Y chromosome haplotypes consisting of 19 Y-SNPs, with a total of 925 individuals, who came from Han and ethnic minorities in China provinces, as well as Northeast Asia, Southeast Asia, Africa, America and Oceania, to systematically study the origin and migration of modern East Asians, including various populations in China. The results showed that all Y-SNP haplotypes in modern East Asian population, including China, came from late mutation, while the early type only existed in Africa. Therefore, people think that all modern East Asians come from an ancient type of Africa. Moreover, East Asians migrated from Southeast Asia to the south of China, then moved northward, and gradually spread to various areas in China and Northeast Asia, which may completely replace the indigenous people who lived there and become new residents in this area.

For these modern people who migrated from Africa after a long journey, did they completely replace the original aborigines living on the East Asian continent to become new residents in East Asia, or did they have some degree of integration with the local aborigines, and both of them have made genetic contributions to us now? This problem has also aroused great interest of many scientists. They are based on the assumption that modern people who migrated from Africa did not completely replace the local natives in the group, and the local natives may have a small number of genes inherited. On the basis of the above experiments, they will expand the sample size in East Asia to see the possible contribution rate of these local aborigines or the possibility of incomplete substitution. In which population are these genes likely to remain in modern times?

In 200 1 year, Ke Yuehai et al. studied the typing of three Y chromosome haplotypes, M89, M 130 and YAP, on a random sample of nearly 12 000 men in various regions of China. The selected Y chromosome non-recombination region mutants M89, M 130 and YAP are all from another Y chromosome haplotype M 168. The mutation M 168 is a representative mutation site for human beings to go out of Africa and spread to other areas outside Africa. M 168 is the most direct evidence that modern humans originated in Africa alone. Except in Africa, no mutant individuals older than M 168 were found in other regions. The results of this study showed that all the 10,000 samples had one of three mutations, namely M89, M 130 and YAP. No individual was found to carry any type other than the above three Y-SNP mutations, nor were any two or more mutations found in M89, M 130 and YAP at the same time, which was different from other regions of the world except Africa. All 65,438+02,000 samples from China carried the "genetic trace" of the M 168 mutant from Africa. Therefore, the evidence of Y chromosome does not support the hypothesis that modern people in China originated independently, but supports the hypothesis that modern people in East Asia, including China, originated in Africa.

Since then, there have been some genetic studies, especially the extensive study of East Asian population by using various genetic markers and typing methods such as Y chromosome, mitochondrial DNA, autosome and single nucleotide polymorphism. The results prove that modern people in East Asia have the same characteristics of African descent. According to the variation rate of Y-DNA haplotypes, it is estimated that about 60,000 ~/kloc-0.8 million years ago, the earliest modern people who left Africa first entered the south of East Asia through Southeast Asia, and gradually spread northward to the East Asian continent with the end of the East Asian Ice Age. The other branch gradually entered the Pacific islands from the Southeast Asian continent along the southeast coast to the east.