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After the article and video about the origin of human beings in East Asia were released, many netizens put forward the following reasons to defend the African origin of modern man:
"The East Asian origin theory cannot be justified, and South Africa people do not carry Nidan genes. That is to say, your children and grandchildren do not carry your genes, isn't that ridiculous? ”
"If humans were born in East Asia, Africans should have migrated from East Asia, and humans in Eurasia were mixed with Neanderthals, so how to explain that Africans do not have Neanderthal genes."
"Ethnic groups outside Africa are more or less mixed Neanderthal and/or Denisovan, but sub-Saharan South Africa has no such mixed ancestry. This only shows that Africa is the origin of Homo sapiens, otherwise you can't explain the existence of such facts. ”
In the past, some netizens used this reason to defend the theory that modern people came out of Africa, and these statements were changed to a more academic statement: "Eurasians have the Y-chromosome M186 mutation gene, but Africans do not, indicating that human beings originated in Africa." ”
This statement is also out of the implicit premise on which the African theory is based, that is, the conclusion that is only possible under the molecular clock hypothesis and the neutral theory: that is, the genes of species have always changed linearly in one direction and will not change backwards. Under this premise, it is concluded that a gene type is an ancestral type, and the genetic mutation forms an evolutionary type. Under this premise, the genotype of the San people in southern Africa, which has the highest upper limit of genetic diversity, was used as the root haplotype of the African theory, and the DNA evolutionary tree map of the modern human African theory was established.
Southern African San people
In fact, the genome contains a huge number of revertant mutations, and there are at least 1180 revertant mutations in the African model mitochondrial phylogenetic tree. A gene revert mutation is when a gene changes from A to B and then B to A. Genetic revertant mutations occur when a species reaches the upper limit of genetic diversity.
Therefore, in the case of the fact that there is an upper limit of genetic diversity and a genetic reverting mutation in humans, the existence of a certain mutated gene cannot be used as evidence of the ancestral or evolutionary type.
The expert explanation of this question by a human genetics expert gives this:
For example, the genome is assumed to contain an infinite number of mutation sites, mutations are neutral, can be divided into nascent and ancestral types, and there are no duplicate mutations, etc., according to these assumptions, in the base site of M168, T (M168T) is considered to be a nascent base, and G (M168G) is considered to be an ancestral base. However, if the mutation is not neutral and there is a repeat mutation (such as in the saturated state), it is impossible to distinguish the neonatal type from the ancestral type, then the fact that the Chinese all have M168T may be due to the physiological characteristics of East Asians, and M168G may be an African-specific mutation (M168T becomes M168G) that occurred after modern Asian humans entered Africa and crossed with African paleohumans. Therefore, the state and distribution of the M168 allele cannot be conclusive evidence for the African theory because of the uncertainty of the premise.
Out of East Asia says the Y chromosome (DNA) evolutionary tree
出东亚说线粒体（mtDNA)进化树
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