In modern society, male and female villa has been out of balance, which has resulted in the existence of many single dogs. So what was the ratio of male and female 7000 years ago? According to US media, the gene of modern men shows that something strange happened between 5000 and 7000 years ago: most of the male population in Asia, Europe and Africa seems to have died one after another, leaving a huge gender ratio of 1:17 between men and women.
The so-called population bottleneck was first proposed in 2015, and researchers have been trying to find out the cause of this phenomenon ever since, according to a report published on June 6 on the interesting science website, why genes show that most men died one after another 7000 years ago. One hypothesis is that the decline of male population is caused by the ecological or climatic factors that mainly affect male offspring, while the other hypothesis suggests that the disappearance of male population is because some men have more power in society and thus have more children.
Now, a new paper, published May 25 in nature & middot; communications, offers another explanation: people living in patrilineal tribes, mainly men of the same lineage, may struggle with each other, once wiping out the entire male lineage.
According to Marcos & middot Feldman, a demographer at Stanford University, the lead author of the paper, the 1-to-17 ratio of men to women is "shocking because of its disparity. There must be another explanation.". According to their new explanation, the number of male population is not a sharp decline. Rather, the diversity of Y chromosome has declined due to the way people live in groups and fight with each other. In other words, it's not really a decrease in the number of men, it's just a decrease in the diversity between men.
In order to prove their theory, the researchers conducted 18 simulations, according to the report, in order to establish different hypotheses leading to the bottleneck, including factors such as Y chromosome variation, population competition and death. Their simulation shows that the war between patriarchal tribes may lead to this so-called "Y chromosome bottleneck" phenomenon, because members of each patriarchal tribe will have very similar Y chromosomes with each other. Therefore, if one tribe kills another, it also greatly reduces the chances of passing on the Y chromosome of the latter tribe to its offspring.
However, this bottleneck did not appear in the researchers' simulation of non patriarchal tribes. In addition, as mitochondrial DNA shows, there was no such bottleneck in the female population at that time. Mitochondrial DNA is a kind of DNA that can only be passed on from mother to child.
Feldman told interesting science: 'in the same group, women may come from anywhere. They may have entered the group as spoils after winning the war, or they may have lived in the local women before. '
The report pointed out that between 5000 and 7000 years ago, before human beings were about to enter into a larger social form and establish a large city, people still lived in groups in a small tribal way and engaged in small-scale farming. Chris Middleton Taylor Smith, an evolutionary geneticist at the Sanger Institute in the UK who was not involved in the study, told interesting science that it was a 'transition period between early farming with stone tools and later social farming with metal tools'.
But after this bottleneck period, 'you will see the rise of social organizations and the transformation of small societies into big cities, where people live in groups that are not so focused on maintaining the Y chromosome inheritance,' Feldman said. 'during this period, the male population has rebounded.