Human somatic cells contain 23 pairs of chromosomes, while primates with the same ancestor as humans mostly have 24 pairs of chromosomes. How this evolutionary result came about is not yet clear, but current research also Shows that the number of chromosomes in humans can change.
Human cells contain 23 pairs of chromosomes. Modern scientists cannot give you a complete answer as to why there are this number, because this is the result of evolution. In the era of human civilization and modern science, it is enough to observe When it comes to chromosomes, humans have this number of chromosome pairs, 22 pairs of autosomes plus 1 pair of sex chromosomes. The length of the X sex chromosome is much longer than the Y sex chromosome. The Y sex chromosome is only related to male gender determination. There is the key gene SRY for male formation.
According to research on mammalian pedigrees, gene sequencing, and gene mutation rates (genetic molecular clocks), humans and primates have a certain blood relationship, but humans and them are reproductively isolated, and primates are not. Animals generally have 24 pairs of chromosomes. This situation seems contradictory. Is it possible to lose one pair of chromosomes inexplicably? Although the specific process is not yet clear, scientists have found based on genetic mutation rates and other studies that the human Y chromosome has shortened a lot in the past few million years and may disappear in the future. Could it be that men will not exist at that time? , human beings will become extinct? Not necessarily.
In the era of human evolution, humans actually did not only have genetic exchanges with human populations. In the era when apes evolved into humans, humans still maintained certain genetic exchanges with many human evolutionary branches. Comparatively What is clear is that Neanderthals and other human races that were in the same era as the ancestors of modern humans, they and humans were unable to have genetic exchanges due to geographical isolation, and during the process of human migration, there were people who encountered them. Opportunities, and modern genetic testing also shows that people outside Africa also contain Neanderthal genes to a certain extent, indicating that hybridization between different populations in the history of human evolution may have contributed some genes to humans.
Going further, we can talk about distant hybridization. This kind of situation is relatively rare in nature. Because of the difference in chromosome number, distant hybridization generally produces offspring with reproductive capacity, but the female individuals produced by the hybridization They can still maintain a certain reproductive capacity. Crossing them with animals from their parents will also lead to differences in the genetic traits of the offspring from those of their parents, because of the presence of genes in organelles such as mitochondria.
The specific role of distant hybridization in evolution is still not fully determined, because the evolutionary history of organisms on earth has lasted too long, but human evolution is a dynamic and continuous process. During human evolution and other The human branch has genetic exchanges, and may also have genetic exchanges with slightly more distant species, thus forming the current number of chromosomes in humans. Modern research shows that the human Y sex chromosome is gradually shortening. This does not mean that men will disappear in the future, but it may mean that humans in the future will form a new way of determining sex.
The change in the number of chromosomes in humans may be due to their own mutations or the influence of other factors such as distant hybridization. In short, it is the result of evolution. Now we have observed that modern humans have 23 Regarding chromosomes, in fact, ordinary people basically don’t need to ask why, because there are so many observed.