How terrible is reproductive isolation in nature?

The history of life on Earth is 4 billion years old, and countless species have evolved during this long evolutionary history of life. Due to genetic mutation, chromosomal variation, and genetic recombination, the original life has been differentiated into various branches on the path of evolution, resulting in new species and gradually forming a variety of creatures.

In such a wide range of species, there is a common phenomenon that only organisms of the same species can normally reproduce and continue the species; and reproductive isolation between different species. Reproductive isolation means that under natural conditions, different species are either unable to mate or are unable to produce offspring after mating, or the offspring that are born are unable to reproduce properly. For example, although a horse and a donkey can give birth to a mule, the mule is incapable of reproduction.

Reproductive isolation exists between all species, whether human or animal. Reproductive isolation prevents the exchange of genes between different species, ensuring the stability and diversity of the species. So, why can't different species combine? Why do some people say that reproductive isolation is terrible? Is there reproductive isolation between humans and all living things?

Why do some people say reproductive isolation is scary

Most of the species are very different from each other in many aspects, such as physiology, geographic distribution, and behavior. It is obvious that mating between species in this case is impossible, and reproductive isolation is created before fertilization.

And some species can mate with each other behaviorally, but due to chromosomal differences, it will result in the sperm and eggs of both not being able to combine to form fertilized eggs, and will not be able to produce offspring.

And two species with close kinship and high similarity, due to similar chromosome number, chromosome structure, chromosome shape, and size, crossbreeding under artificial intervention, there is a certain chance to produce hybrid species. However, even if the hybrid offspring can be born successfully, the hybridization leads to genetic defects that make their survival rate low, and they can no longer continue to mate to produce new offspring. This type of situation is reproductive isolation after fertilization, and the offspring produced will be hybrid sterility, hybrid decay, or even hybrid non-viability. This is perhaps the scary part of reproductive isolation.

For example, the combination of horse and donkey produces a mule that grows up healthy, but the mule is infertile. This is because the horse's chromosomes are 64, while the donkey's chromosomes are 62, even if the combination of horse and donkey can produce offspring "mule", but the number of chromosomes of the mule is only 63, and if the number of chromosomes is odd, the germ cells can not carry out normal mitosis, there is no way to reproduce the next generation, and the combination of horse and donkey process It is also very difficult to combine horse and donkey, and the success rate is low, so until now mule has not formed its independent species.

For example, male lions and female tigers can crossbreed to give birth to lion-tiger beasts; male tigers and female lions can crossbreed to produce tiger-lion beasts. But even in captivity, the successful conception rate of lions and tigers is only 1% to 2%, and even successful conception survival rate is extremely low, there will be low immunity, disease, and early death of the problem. Because of genetic defects, lions and tigers are often too large and overwhelming; tigers and lions are smaller but have more genetic defects.

From the genetic level, both lions and tigers have 38 chromosomes, and the offspring of these two crosses also have 38 chromosomes, so lions and tigers are fertile. However, the chromosome match between lions and tigers is not high, resulting in unstable genetic traits in the offspring lions and tigers, so there will be low immunity and a short life span. Moreover, both male lions and tigers are not fertile, and only female individuals have some fertility, thus occasionally producing hybrid second-generation lions and tigers (father: lion, mother: lion and tiger) or tigers and tigers (father: tiger, mother: lion and tiger), but the second-generation beasts that give birth have genetic defects and have a short life span and cannot give birth. Therefore, since the offspring born to lions and tigers are also not fertile, there is also reproductive isolation between the two.

The next generation of any cross-species breeding is either physically defective or unable to reproduce offspring, and humans are currently unable to break this boundary.

Is there reproductive isolation between humans and all living things?

All humans currently existing in the world, whether black, white, yellow, or other kinds of skin color, belong to the same species, and the only species existing under the genus Homo sapiens.

Humans and chimpanzees belong to the same primate family Hominid, a genus of humans and a genus of chimpanzees, both evolved separately on the path of evolution only about 6 million years ago.

In the 1820s, before the discovery of genes, Soviet biologist Ila Ivan tried to secretly conduct "human-ape hybrid" experiments at the Soviet Summit ape breeding base, wanting to try to remove sperm from chimpanzees, and through artificial insemination, making chimpanzee sperm and human female The volunteers were then kept in strict isolation after the experiment. However, for a variety of reasons, the experiment did not go ahead and ended in vain!

Such an experiment not only violates the biological laws of nature, but is also ethically and morally intolerable. The reason why Ivan was able to carry out such crazy research is rumored to be because the Soviet Union at that time wanted to obtain a group of strong and controllable "soldiers" like apes, to improve their combat power and secure their "great power status". So it was hoped that through "human-ape hybridization", a new species of "ape-man" would be created that had both human intelligence and the strong physique of a chimpanzee.

However, we now know that, from a genetic point of view, although the two species have a genetic similarity of up to 99%, humans have 46 chromosomes, and chimpanzees have 48 chromosomes, it is conceivable that if they can mate, even if they can produce offspring, it is also a hybrid with 47 chromosomes, chromosomes are odd, so do not have the ability to reproduce. So there reproductive isolation between humans and chimpanzees is obvious.

And in the process of human evolution, a human genus in addition to our homo sapiens, there have been very many human species, such as Neanderthals, Slovenians, Heidelberg, etc.. Some of these human species had existed on Earth at the same time as Homo sapiens for some time, and there was a certain overlap of living space. At that time, the reproductive isolation between Homo sapiens and other species had not been fully formed.

The results of genetic sequencing show that, so far, the majority of European and Asian people still have about 1% to 2% of the genes from Neanderthals. Although the Neanderthals have been extinct for a long time, the influence of this part of the gene on modern man is difficult to remove. Some modern research, that many modern human diseases, such as depression, type 2 diabetes, smoking more addictive, obesity, and other health problems, are related to the Neanderthal genes left in our bodies.

Conclusion

The purpose of reproductive isolation is to retain good genes so that the offspring of each species can survive and develop more healthily and stably and this natural protection mechanism guarantees genetic stability and diversity. Imagine if there was no reproductive isolation among all species, the world would be in chaos, and all species could mate with each other, which would lead to a series of problems and break the biological chain. In this way, reproductive isolation is not terrible, no reproductive isolation is really "terrible".