(Reprinted from popular science)

We all know that humans have 23 pairs of chromosomes, but this conclusion was not established until the 50s of the last century, when it was thought that humans had 24 pairs of chromosomes - this is a careless and irresponsible study. Coincidentally, this conclusion correctly reflects the chromosome numbers of other apes.

Humans were still one with chimpanzees about 5 million years ago, so what caused our ancestors to lose a pair of chromosomes and completely part ways with their primate compatriots?

The 24th pair of chromosomes disappeared

It is surprising that humans do not have 24 pairs of chromosomes. Our ancestors of apes, modern chimpanzees, gorillas and other apes were loyal fans of chromosomes, with the exception of humans, which may be one of the genetic proofs that made us human.

With the completion of the Human Genome Project, researchers have mapped out a detailed blueprint of 23 pairs of human chromosomes and compared them to chimpanzee chromosomes. In the latest analysis, scientists at the University of Washington in the United States published data showing that chromosome 2, the second largest chromosome in humans, was formed by the merger of two chromosomes of Australopithecus. Scientists have earlier speculated that human chromosome 2 may have been formed by the merger of two chromosomes of Australopithecus. In this detailed analysis of chromosome 2, the scientists found conclusive evidence of chromosome fusion: at a certain location on chromosome 2, there is a DNA-encoded duplication with the characteristics of a centromere, and the centromere is the center point of the chromosome when it is mitotic, and each chromosome may have only one centromere.

Scientists therefore judged that this location was a remnant of the centromere of one of the chromosomes before the fusion of the two chromosomes. But why did the two chromosomes of Australopithecus suddenly merge into one, and how drastic an evolutionary act of such a large movement would have had on our ancestors in the first place?

Adventurous chromosomal modification

Even today, with the rapid development of genetic engineering, it is difficult to imagine that an existing species can be transformed into a completely new organism that is extremely adaptable to the environment by discarding and fusing chromosomes. In the new generation millions of years ago, it was reasonable to assume that our ancestors had committed this risky act just to better adapt to the natural environment!

The struggle of human ancestors to survive in the past 5 million years can be described as a thrilling adventure of life. The DNA of mitochondria in human cells can trace the origins of female ancestors, indicating that we have a common mother, and the same conclusion can be drawn from the DNA mutation on the male Y chromosome. This single ancestor may not indicate that the mutation occurred in only one person, but it allows us to imagine how great the pressure to survive was at the beginning of the transformation, so that only this single bloodline remained.

Adam and Eve lived in arid East Africa, which was less like the Garden of Eden, and resolutely broke with the rest of their ape brothers, leading to reproductive isolation and a new hairless ape that walked upright.

Although the bold changes of our ancestors are extremely unsafe, but, as the financial world often says, high risk, high return, our ancestors through such adventures, or helpless measures, and many large and small genetic modifications since then, have become modern humans, and become the most successful species of adaptation to the environment. We have to admire the courage of our ancestors, who, after a lot of attempts and failures, and overcoming various bottlenecks, finally achieved what they wanted and presented the wonderful present day.

But how did such an innovative change come about, and how did it come about and how did it come about? Scientists have been trying to trace ancient genes, and now they have created an ancient gene from 530 million years ago by combining two key proteins in the genes of modern mice that evolved from ancient genes. This reversal process is very gratifying, and the evolution at the molecular level is beginning to take shape, and the fusion event of human chromosome 2, which has cracked even more changes, seems to be dawning.

Posthuman species without a Y chromosome

Nowadays, there are many kinds of organisms, and the number of chromosomes varies greatly, and it is clear that the fusion and disappearance of biological chromosomes are always going on. Therefore, we can't help but wonder if similar events will continue to occur among the 23 pairs of chromosomes that humans have, and who will be the next chromosome that unfortunately disappears.

Scientists have found that the Y chromosome of human males is likely to be the next victim.

Millions of years ago, there were about 1,500 genes on the Y chromosome, but now there are only 40 left.

Because the Y chromosome is unique to males, it cannot be recombined with the paired chromosome, nor can it be corrected, and a large number of mutations are produced and accumulated in the process of division and replication from generation to generation, so that one functional gene is destroyed due to mutations. In fact, there is a strict set of correction programs for errors in DNA replication in cells, but no one can say why the Y chromosome is still "depleted".

But one thing is for sure, the process will not stop. Because the Y chromosome is constantly losing genes, so that human males are in an embarrassing situation, men can come to the world thanks to this Y chromosome, and the continuous disappearance of genes makes men have the possibility of extinction as a whole, as for the female X chromosome, for some reason there is no change.

Scientists speculate that if the Y chromosome disappears completely along with the man, it will be replaced by a new, more complete species of humans, and that the creature "human" will become a completely new species after another risk-taking behavior, which we can call postmodern humans. Imagine what postmodern people would have been like at that time, and what impact it would have on the entire material world.