In nature, many animals have reproductive isolation , but strangely, there is no reproductive isolation between humans. Whether it is black people, white people or yellow people, they can intermarry freely and produce healthy offspring. So the question is, why hasn't humans formed reproductive isolation?
The recent common ancestor of humans
The reason why humans do not have reproductive isolation is actually because we split up late and people living in different places have been engaged in small-scale intermarriage.
According to existing hypotheses, biomolecular science has given evidence of human origin in Africa. We know that all men have an Y chromosome . Since the Y chromosome only exists in men and does not in women, this also means that the Y chromosome is passed down from generation to generation by men's ancestors. Scientists can track the Y chromosomes of everyone in the world, and then analyze the conditions such as their genetic mutation rate and how big the difference is, and analyze the recent common ancestor of men.
The results show that the closest common ancestor of all men on earth is
Although there is no chromosome similar to the Y chromosome in women, don’t forget that humans were originally developed from fertilized eggs, and mitochondrial exists in fertilized eggs, and DNA in mitochondrial completely comes from the mother.
Scientists can also judge women's recent common ancestors by conditions such as the DNA mutation rate of mitochondria. It turns out that the common ancestor of all women today is a woman from .14 million years ago from Africa, and she was also named "mitochondrial Eve".
To put it more, the reason why "Y chromosome Adam" and "mitochondrial Eve" did not live in the same era is because there were many people in the same period of their lives. It is just that these people have not lived until now for various reasons. Only the genes of the two of them are relatively strong and have continued to this day.
Why does humans not have reproductive isolation
From the mitochondria Eve and Y chromosome Adam, we can see that humans separated very late. After all, the most recent common ancestor of all men in the world came from 60,000 years ago. About 60,000 years later, humans began to leave Africa, but at that time there were many other races living in the world, such as: Neanderthal , Florian , Denisovans, etc. Homo sapiens met them after leaving Africa and had gene exchange with them.
study found that except for Africans, all races in other regions contain 1%-4% of Neanderthal genes. In my country and the Oceania region, we found that we contain 1%-2% of Denisovan gene.
From this we can see that humans do not have a single species originated. It is very likely that after leaving Africa, they had genetic exchanges with local races and produced offspring.
. Because the local race evolved in the local area for a long time, a part of the genes that adapt to local life have accumulated in the body. For example: Scientists believe that the reason why people on the Qinghai-Tibet Plateau can live on the plateau is because they have a certain Denisovan gene in their bodies.
Although humans have integrated genes such as Denisovans and Neanderthals, the proportion of genes in these races in the human body is small, and most of the genes in our bodies are still from Homo sapiens in Africa. Moreover, in the process of human evolution, humans have been conducting reproductive communication through trade, business, fleeing and migration, etc. Therefore, there is no reproductive isolation between humans. On the contrary, because the transportation is convenient now, communication between humans in the world is more convenient than ever, so humans will not form reproductive isolation in the future.
The reason why animals form reproductive isolation, such as horses and donkeys, is that they are separated for a long enough time during the evolution process and have not had gene communication, which leads to the accumulation of a large number of different genes during the evolution, so that hybrids are infertile, forming a complete reproductive isolation.
However, reproductive isolation is not black or white. Some organisms are two species, but they can also form healthy offspring. For example, Indochina tigers can cross-breed with South China tigers to give birth to offspring.
summary
Nowadays, all people are Homo sapiens. Although when Homo sapiens walked out of Africa, Homo sapiens who lived in different places merged the local original genes, this gene did not allow us to form reproductive isolation. The appearance of skin color is just a different living conditions of the local people and the evolved response measures. Therefore, no black, white or yellow people have reproductive isolation.
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