Figure 1 Phylogenetic tree inferred from human fossils
Is multi-regional origin theory wishful thinking?
Humans have gone through a long evolutionary process, from Homo ergaster to H. Neanderthalensis, and finally to H. sapiens sapiens about 65,438+million years ago, that is, today's modern humans. There is no dispute in academic circles that the first humans may have appeared in Africa 5 to 7 million years ago. However, how did modern humans develop? This issue has always aroused widespread interest in academic circles, and the debate continues. At present, there are two main views on the origin of modern human beings: African origin theory and multi-regional origin theory. Both hypotheses believe that Homo erectus originated from Homo erectus in Africa and moved out of Africa to Eurasia about 654.38+0 million years ago. According to the African origin theory, modern human beings originated from the second migration in Africa 654.38 billion years ago, and completely replaced the ancient species in other regions after leaving Africa. The multi-regional origin theory, also known as the independent origin hypothesis, holds that human beings all over the world have independent origins, that is, Homo erectus in Africa, Heidelberg, Neanderthals and Homo erectus in East Asia have independently evolved into several major species (subspecies) of modern human beings.
Since the African origin theory was first put forward in the late 1980s, it has been supported by many archaeological evidences. However, a large number of human fossils have been unearthed in East Asia, including Chinese mainland. These fossils have the same shape and are widely distributed in this area. Therefore, many archaeologists and paleoanthropologists question the hypothesis of African origin. They think that there is an evolutionary process of "Homo erectus → Early Homo sapiens → Modern Man" in Asia and Africa, so they think that the origin of modern human beings is multi-regional. From 65438 to 0987, Rebecca Kan and others put forward the famous "Eve Hypothesis" by studying the maternal mitochondrial DNA polymorphism, which opened the prelude to exploring prehistoric human history with genetic methods. Eve hypothesis and genetic analysis of European Neanderthals support the hypothesis of African origin. Therefore, this view has caused an uproar in archaeology and paleontology, which makes East Asia, including Chinese mainland, the most concerned area to verify the pattern of human origin.
It is worth noting that the multi-regional origin theory is also difficult to solve the evolutionary paradox. In biological evolution, a large number of species often appear under good living conditions, and when the environment changes, a large number of species become extinct. Therefore, the species eliminated are the vast majority, and the few survive. In the past 6.5438+million years, the harsh living environment in several periods in Eurasia was enough to eliminate ancient species with almost the same viability as other animals. Why do all ethnic groups have to survive, instead of following the evolutionary elimination law equally with other creatures? After the separation of the two species, the gap must be getting bigger and bigger with the passage of time. But according to the multi-regional origin, human beings are very strange. Even though there is no species difference among Homo erectus, early Homo sapiens and late Homo sapiens, the gap between them has not widened, and it has narrowed during the period of 6.5438+0 million years, and even the gap of 6.5438+0 million years is not enough to cause reproductive segregation among all races. Humans also violate the law of evolutionary distance in a maverick way. We can't help asking, is the evolutionary path outlined by the multi-regional origin theory too wishful thinking?
Second, the ancestry of modern people from Africa.
Eve theory has caused many controversies, but with the continuous maturity of gene technology, these controversies have been settled. Using genetic technology to study the evolution of human population is to trace the approximate time and route of the origin and migration of human population by using some genetic markers. At present, the most ideal genetic marker for studying the evolution and migration of early human beings is generally recognized as SNP marker (NRY)4 of non-recombination segment of Y chromosome. This is because there is only one non-recombination region of paternal Y chromosome in human body, which can effectively eliminate the heterozygosity interference of exchange recombination. At the same time, the mutation rate of SNP is low, which can be inherited more stably and faithfully record evolutionary events. In addition, because the sewall wright of haploid Y chromosome is only 1/4 of autosomal locus, it is easy to produce population-specific haplotypes.
In 200 1 year, underhill et al. of Stanford University obtained 13 1 haplotype composed of 2 18 NRY loci on Y chromosome by denaturing high performance liquid chromatography (DHPLC) analysis, which was applied to 1062 representative individuals in the world. This is the most widely used genetic marker in the study of human evolution and origin. The distribution of these 2 18 NRY polymorphisms in representative populations in various regions of the world clearly shows the approximate cluster tree of modern human population.
Fig. 2 NRY chromosome haplotype tree (maximum reduction)
Figure 2 shows the system tree from top to bottom, which represents the time of branch generation. Obviously, the earliest branches all occurred in the African population, and then they were divided into Europe and Asia. The division between the United States and Australia occurred under the division of Asia. This shows that human beings have differentiated from African populations to European and Asian populations, and the American and Australian populations originated from Asian populations. This is the "Adam Theory" confirmed by the "Eve Theory". According to the mutation rate, it took Africans more than100000 years to differentiate into Eurasian.
Third, the origin of modern people in East Asia
There has been a lot of controversy about the origin of East Asians. Many paleoanthropologists still insist that East Asia is also the birthplace of modern people, but genetic research increasingly does not support this view.
From 65438 to 0998, Chu Jiayou and others used 30 autosomal microsatellite loci to analyze the genetic structure of 28 East Asian populations, including the northern and southern populations of Han nationality. These results support that modern China people originated in Africa and entered Chinese mainland via Southeast Asia. Because of the high mutation rate of microsatellite loci, there are some limitations in the study of long-standing human evolution events and population migration, so the data from East Asia cannot convincingly rule out the hypothesis of multi-regional origin.
1999, Su Bing et al. 7 used a set of Y chromosome haplotypes consisting of 19 Y-SNPs, covering all populations in East Asia and the Pacific, and systematically studied the origin and migration of East Asian populations including China. This study will overcome the regret caused by the use of autosomal microsatellite markers and the small sample size in Chu Jiayou's research. The sample size of the study is 925 people, including individuals of ethnic minorities and Han nationality in various provinces of China, groups in Northeast Asia, Southeast Asia and groups in Africa, America and Oceania.
Fig. 3 Migration route of Homo sapiens in late East Asia
Among the 16 haplotypes composed of 19 loci, half of them are endemic to East Asian populations. This obvious group specificity provides an ideal tool for studying population migration and gene exchange between people. It is found that the genetic diversity of southern population is higher than that of northern population, and the genetic diversity of each population decreases in turn according to non-Han population in Southeast Asia, southern Han population, northern Han population and northern non-Han population. Moreover, the haplotypes in the south include all species in the north. This single gradient pattern implies an important message, because the mutation occurred much earlier than the migration event, and these mutations were not formed after the migration, so the migration should be in the direction of decreasing gradient. This reveals that humans began to enter East Asia from the south. Haplotypes in Southeast Asia almost cover all the specific haplotypes in China and East Asia, so Southeast Asia may be the first stop for people who migrated from Africa to East Asia in the early days. From there, the ancestors of China people entered the south of China from Southeast Asia, and then crossed the Yangtze River into the north. This finding is consistent with the haplotype distribution of mitochondrial DNA.
In the analysis of Y chromosome polymorphism in East Asian population, it is found that two key mutation sites are closely related to the African origin and subsequent migration of East Asian population. All Y-SNP haplotypes of modern East Asians come from late mutation, and the early type is unique to African populations. Therefore, it is considered that all the 739 East Asian individuals observed are from Africa, which reveals that the groups coming out of Africa may completely replace the local groups in East Asia, and this possibility can only be confirmed by further expanding the sample size of East Asian people. It is true that East Asia is very special in geological history. It is considered that the climate during the Ice Age can still adapt to the survival and reproduction of large mammals in southern China, and the ancient human fossils in China have the characteristics of continuity. Although the evidence is still controversial, it is undeniable that a few China "aborigines" (Homo sapiens, an early Homo sapiens) 6.5438 million years ago and "new immigrants" (Homo sapiens, a late Homo sapiens) who came to China from Africa via Southeast Asia later became the ancestors of modern China people.
In 2000, Ke Yuehai and others used three ancient Y-SNPs, M89, M 130 and YAP, to study the genotyping of nearly12,000 male random samples from all over China. Its purpose is to investigate the possibility of incomplete substitution, even if it exists, on the basis of expanding the sample size in East Asia. The selected three Y chromosome polymorphisms M89, M 130 and YAP are three mutation types based on M 168. It is considered that M 168 is a variant of human beings in Africa, and its original form only appears in East Africans. Modern people and some Africans except Africa have the mutant of M 168. M 168 is the most direct evidence that modern human singles originated in Africa. No examples of individuals with mutations above M 168 have been found outside Africa. The results of this study show that more than 10,000 samples have one of three mutants, namely M89, M 130 and YAP. No other types of Y-SNP mutations were found in individuals, and no mutations of M89, M 130 and YAP were found in individuals at the same time. This result is consistent with the genotyping results in other parts of the world except Africa. Therefore, the research shows that the evidence of Y chromosome does not support the hypothesis of multi-regional origin, which may play a very small role in the origin of modern people in China.
So genetic research, especially the Y chromosome, proves that modern people in East Asia and Africa have the same origin. About 18000-60000 years ago, the earliest modern people who walked out of Africa entered the south of East Asia, and then gradually entered the East Asian continent with the end of the East Asian Ice Age. Another migration route is to start from the Southeast Asian continent and gradually enter the Pacific Islands eastward.
Up to now, a series of genetic studies on modern people in East Asia, including Chinese mainland, have made up for the lack of information on the origin of modern people in East Asia. At the same time, a wide range of genetic markers and typing methods such as mitochondrial, autosomal and Y chromosome microsatellite markers and single nucleic acid polymorphism have been used to study the East Asian population. The results show that modern people in East Asia are from Africa and support the hypothesis of African origin 10.
Fig. 4 Fossil faults revealed by the age distribution of human fossils found in East Asia.
The multi-regional origin hypothesis queries East Asia on the basis of a large number of fossils and archaeological remains found in East Asia, especially in Chinese mainland. 1 1. However, in the most important fossil evidence, fossil faults did appear in East Asia, including China, and it was in the critical period of the origin of modern people, that is, between 4-65438+ million years. The genetic explanation holds that the fault on this fossil is not accidental, but caused by the extinction of a large number of biological species in East Asia during this period, because the human fossil fault 65438+ million years ago is roughly consistent with the existence time of Quaternary Ice Age in this area. The possible reason for this phenomenon is that the existence of Quaternary glaciers 5000-65438+ ten thousand years ago made it difficult for most biological species in East Asia, including Chinese mainland, to survive in this period. After the end of the Ice Age, modern people who originated in Africa and crossed Southeast Asia from south to north and entered Chinese mainland became new residents of this territory.
Estimation of Tetradifferentiation Age —— Genetic Distance Showed by ——STR
In order to estimate the age of early modern people entering China, Su Bing et al. genotyped individuals with three microsatellite markers DYS389, DYS390 and DYS39 1 pair 12. In this study, 160 individuals with M 122 mutation were screened and analyzed.
According to the ancestor sewall wright (Ne), the mutation rate of microsatellite markers (μ) and the number of mutations accumulated in the population (V), there is a formula for calculating the age of population differentiation events:
t = -Ne ln( 1-V/Ne μ)
This formula is applicable to the population 13, which has experienced a strong bottleneck effect and produced rapid growth, that is, a small number of people differentiated from the mother population and then proliferated into subgroups. For the estimation of sewall wright in the formula, it is generally believed that the sewall wright of modern men is 5000- 10000. Because the genetic diversity of Asian population is less than that of African population, the effective number of Asian male population is 750-2000, the mutation rate is 0. 18%, and 20 years is the first generation.
Fig. 5 Origin and migration of Han and Tibetan nationalities.
It is concluded that the age of M 122c mutation is about 18000-60000 years ago in all the populations with M122 mutation studied, and the division between them is calculated as 5000 years (this age is calculated by DYS390). Generally speaking, it is very difficult to accurately estimate the age of ancient human population migration and gene mutation from the perspective of genetics, because the deviation caused by the estimation of sewall wright and mutation rate in the above formula directly affects the results, but making such an age estimation is consistent with the findings of physique morphology and archaeology in teeth, stone tools and fossils. Archaeological research shows that the unique Sino-Dont tooth pattern of North Asians covering northern China occurred 18000-25000 years ago, which evolved from Sino-Dont tooth pattern in Southeast Asia, which is consistent with the lower age limit M 122C calculated by our formula. In addition, recent archaeological studies in Siberia, Lake Baikal and Altai Mountain show that the human stone civilization in this area appeared 25,000-45,000 years ago. If Siberia and the whole East Asian group originated in Africa and migrated from Southeast Asia, then modern humans should have entered East Asia before the emergence of the Stone Age civilization in North Asia. It is considered that the estimated upper age limit of M 122C mutation is closer to the fact of 60,000 years ago. Therefore, it is considered that180,000-60,000 years is the age when early modern people moved to East Asia and caused bottleneck effect. Based on this, the study holds that with the gradual disappearance of the Ice Age, modern people of African descent entered East Asia from the south about 60,000 years ago, and gradually migrated northward in the next tens of thousands of years, covering Chinese mainland, North China and Siberia. About 8500 years ago, after a long period of ignorance, the earliest Chinese civilization represented by Yangshao culture began to sprout in the middle and upper reaches of the Yellow River.
Researchers have also done a lot of work to estimate the age of population differentiation in the world. In March this year, Alan R. Templeton summarized the research results in this field (14). Because different gene mutations recorded different events, he found that modern people walked out of Africa more than once. A small number of people left Africa at least 840,000 to 420,000 years ago. According to the estimation of mitochondria and Y chromosome, most human beings walked out of Africa from 654.38+05,000 to 80,000 years ago, and then there were several population refluxes and further expansion. Different from the fact that modern people completely replaced ancient humans, groups of modern people who went out of Africa merged with each other to form a modern world crowd.
Five Essentials Analysis of Population Sources
When genetics studies the pedigree of human beings to a fine level, it is difficult to find clues to discover complex human groups. Linguistic research systematically classifies people with its detailed materials and objective and rigorous methods, which provides the most ideal clues for genetic research. The population in East Asia is mainly divided into six systems: Sino-Tibetan language family, Altai language family, Dong-Tai language family, Miao-Yao language family, South Asian language family and Austronesian language family, among which Sino-Tibetan language family is undoubtedly very important. In particular, the origin of Sino-Tibetan language family and the relationship between Sino-Tibetan language family and Tibeto-Burman language family have aroused widespread concern in academic circles. In 2000, Qian Yaping et al. 15 and Su Bing et al. 16 reported the genetic research of different language families of Sino-Tibetan language family respectively. The results show that the ancestors of Sino-Tibetan language families originally came from the south of East Asia. About 20,000 to 40,000 years ago, a language family with M 122 mutation on Y chromosome finally reached the middle and upper reaches of the Yellow River basin, and then. The population growth made it necessary for this group to expand their new residence, which led to the division of the two language families about 5000-6000 years ago. One subgroup, known as the pre-Tibeto-Burman language family, left the Yellow River basin, moved west and south, and finally settled in the north and south of the Himalayas. This migration is along the famous "Tibet-Burma Corridor", which starts from the upper reaches of the Yellow River, reaches Qinghai Province in the west and reaches the Himalayas in the south. Among them, the Jingpo language branch has been going south, crossing the Himalayas to today's Myanmar, Bhutan, Nepal, northeastern India and northern Yunnan Province. After mixing with a group with YAP mutation from Central Asia or Southwest Siberia on a large scale, Tibetan language spread to the Himalayas and eventually spread throughout Tibet. Burmese, Yi and Karen languages reached the northwest of Yunnan in the south and finally reached Vietnam, Laos and Thailand. During these 5,000 years, another language family, the Chinese language family, mainly expanded eastward and southward, and finally settled in various regions of China.
The origin of Austronesian language family is also a matter of great concern to academia and the public. People of this language family are distributed in the islands and continental margins of the Pacific Ocean and the Indian Ocean. There are two popular hypotheses about the origin of Polynesian people on Pacific islands. The first is called the "express train" hypothesis, which holds that a rapid migration from the south of China to the east 4000-5000 years ago, the first stop reached Taiwan Province Province, and then reached the Pacific islands including Polynesia, that is, Polynesia originated in Taiwan Province Province. The second hypothesis holds that Micronesia nearby is the origin of Polynesia. In 2000, Su Bing and others 17 denied the above two hypotheses by using the results of Y chromosome research, and thought that some modern humans in Southeast Asia arrived in Taiwan Province Province, and some entered the Pacific Islands and arrived in Polynesia before 1500 years ago (this may be the farthest migration of prehistoric humans). The two migrations are irrelevant, and the genetic vector distance is also completely opposite.
Recent research has provided more and more detailed group data, which makes the relationship between the six lineages in East Asia gradually emerge. According to the latest data from the Modern Anthropology Research Center of Fudan University, the relationship between these six systems is likely to conform to the following structure.
Fig. 6 Possible relationships among population systems in East Asia
Although the genetic relationship between Australian indigenous groups and East Asians (including Austronesian-speaking Pacific islands) is unclear, evidence from Y chromosome and autosome shows that they migrated independently from Africa.
It can be seen that the study of Y chromosome can analyze many fine structures. In contrast, the mitochondrial data is much inferior. The two most commonly used fragments in mitochondria are D-loop and V region, but the mutations of these two fragments are very old and existed before humans left Africa. The standard sequence of CRS over D ring is the most common in Europe, but it also accounts for more than 10% in southern China. Other sequence types only have general racial classification significance. There are 9bp repeats in V region, which can be divided into type I, type II and type III according to the number of repeats. Type ⅱ is the most common, type ⅲ is rare, and the proportion of type ⅰ is relatively significant. Among East Asians, I-type is less in the north, more in the south of the Yangtze River, less in the south, and the Pacific Ocean has increased sharply. It's hard to explain anything. Therefore, mitochondria are rarely used for structural analysis of local populations.
Central Asians' Expansion to Europe and America
For the genetic research on the origin and migration of American people outside Eurasia and East Asia, two important areas are Central Asia and Siberia. Spencer Wells' (18) research on Eurasia shows that Central Asia is the region with the highest genetic diversity in Eurasia population. This area is the birthplace of two major waves of migration, one to Europe in the west and the other to America in the east. Among all the Eurasian populations studied, the Central Asian population is the oldest population in Eurasia, with the highest genetic diversity, especially the Uzbek population, with a very consistent haplotype frequency.
After the Central Asian Group moved northward to Siberia, one of them moved eastward to America. According to the research of Su Bing 19, the ancestor of American group is Siberian group. The diversity of Y chromosome types in Siberia is higher than that in America, which is consistent with the research results of Douglas C. Wallace and others in 1985. There are two migrations from Siberia to America, the first from southern Siberia to most parts of America, and the second from eastern Siberia to North America, which can be called a two-step model. 1986, J. H.Greenberg and others put forward a three-step migration model on the origin of American population based on language, teeth and genetics, and distinguished the origins of Indians, Na-Dennes and Eskimos-Aleutians. The research evidence of mitochondria supports this model. In 2020, Su Bing and others found that M 130T is a unique allele in Asia, widely distributed in East Asia, with the highest frequency in Siberia's Lower amur river Basin and the Sea of Okhotsk. M 130T originated in East Asia, passed through Chinese mainland, arrived in Siberia before 15000, and finally entered the southern group of America 2 1.
After the Central Asian Group moved northward to Siberia, one of them moved westward to Europe. It is generally believed that the present ethnic groups in Europe were formed in the Paleolithic Age (about 45,000 years ago) and the Neolithic Age (about 10000 years ago) and migrated from the Near East to Western Europe and Northern Europe.
To sum up, a series of studies on Eurasian and American groups show that Central Asia is the ancestor of Siberian, American and some European groups. After the Central Asian Group moved northward to Siberia, one moved eastward to America and the other moved westward to Europe. These conclusions should be further compared and verified with the data of mitochondrial and autosomal loci.
Seven sections
Although a lot of genetic evidence supports the hypothesis of African origin, there is still a lot of work to be done to finally reveal the origin and migration of modern human beings, and a lot of conclusive evidence from fossils is needed to support it, and the doubts need to be explained from archaeology and paleoanthropology. Moreover, genetics itself has many different views and research conclusions about the origin of modern human beings in Africa. In 2000, Max Ingman of Uppsala University in Sweden and others studied 53 groups from different regions, races and cultures through mitochondrial DNA diversity, and cluster analysis found that modern people really originated in Africa. However, the research by Alan Thorne of Australian National University in 200 1 and 1 shows that modern humans did not directly originate from the same African ancestor, as is generally believed, but may have evolved from ancient humans in different regions. 1974 successfully extracted mitochondrial DNA from human remains about 60,000 years ago near Mungo Lake, New South Wales, southeast Australia, which is the oldest DNA extracted from ancient human remains so far. After analyzing the extracted DNA mitochondria, it is found that it has no genetic relationship with ancient DNA found in other parts of the world, which is considered to have originated from early modern humans in Africa. This result shows that the evolutionary route of early modern people in Australia is independent of that of ancient Africans. Inman's new discovery questioned the popular theory of "going out of Africa" in academic circles. They put forward a new theory of modern human origin, which is called "regional continuity". They think that Homo erectus originated in Africa has been migrating to other areas outside Africa for the past 65438+500 million years, and formed different branches. These branches evolved into modern people in Africa, Europe, East Asia and West Asia through hybrid breeding 654.38+0.5 billion years ago.
It can be seen that the origin of modern human beings may be much more complicated than imagined. Scholars in genetics and archaeology will continue to argue and explore in this field, but this will not affect our confidence in finally revealing the magnificent prehistoric human history in the near future.
To annotate ...
1 Ian tattersall: "We humans are never alone", Science, No.5, 2000, p.8-14.
2 Wu Xinzhi et al., Human Evolution in China (Oxford: Oxford University Press,1995); Ann Gibbons, Homo erectus in Java: A 250,000-year anachronism, Science, Vol.274, No.5294 (1996):1841-42; Wu Xinzhi: Research and Prospect of Paleontology in China in the 20th Century, Journal of Anthropology No.3 (18), pp. 165-7 1; Wu Xinzhi: Evolution of Ancient Humans in China, Journal of Anthropology, Vol.9, No.4, 3 12-2 1 p.
Why is there a "wave of closure" in educational institutions?
Because of the competitive pressure.
People's living standards are getting higher a