Nature is very magical, in order to ensure the genetic integrity and continuity of species, a barrier is set up between species, that is, organisms across species cannot reproduce.
However, there are always some species that break through the barriers set up by nature, achieve cross-species "communication", and also reproduce offspring, the most representative of which are horses and donkeys, and after doing something that cannot see the light, "mules" are born.
However, although horses and donkeys can give birth to "mules", it is not as simple as you think.
Branches began to form 40 million years ago
Although horses and donkeys belong to the same order of Odd Hoof, they are related to zebras, rhinoceroses and tapirs. About 40 million years ago, due to changes in the earth's environment, Archaeopteryx gradually diverged into two branches: one evolved into a horse, and the other evolved into a donkey and zebra.
Although horses and donkeys share a common ancestor, they survive in different environments and have evolved some different characteristics. Horses are more adapted to the grasslands where food is abundant and the territory is wide. In order to adapt to the environment of the grassland, the body structure of the horse has also changed, becoming longer legs and forelimbs that are more conducive to running.
Whereas, donkeys are more suitable for relatively barren places, like arid deserts and semi-arid mountain environments. In order to adapt to this environment, donkeys have also evolved personality traits such as hardiness, drought tolerance, and hunger tolerance.
In addition to this, in order to adapt to this environment, the body structure of donkeys, like horses, has changed, and in order to reduce energy expenditure, the body has become short and the legs have begun to become shorter.
Although horses and donkeys share a common ancestor, it can be seen from the time that it is very long, tens of millions of years old, which is enough time to give birth to many new species.
For example, humans evolved from Australopithecus 6 million years ago, and chimpanzees, which are closest to humans, have completely become two species after 6 million years of evolution, and the two species can no longer be genetically fused and communicated.
So why did it take tens of millions of years for horses and donkeys to fuse and communicate genes across species?
Why can horses and donkeys be genetically fused across species?
We are all aware of the fact that the purpose of reproduction is to continue genes, either through self-replication or through gene fusion.
The vast majority of animals carry and transmit genetic information in the body of the chromosome, which is a linear DNA molecule, each chromosome contains many gene fragments of proteins, which are used to perform cellular functions and determine the shape of the organism.
Therefore, in the process of gene fusion of species, chromosomes are extremely important. If you want to communicate across species and give birth to offspring, the first problem is to solve the problem of chromosomes.
There are 64 chromosomes in horses and 62 chromosomes in donkeys, and although there are slight differences in the number of chromosomes, this is not the main factor in determining whether genes can communicate.
Another factor is whether the chromosomes are similar in structure and arrangement, if the species is homologous from an evolutionary tree, although the number of chromosomes is slightly different, but the chromosome arrangement and structure are similar, it can also be fused to produce offspring.
In addition to horses and donkeys, there are also lions and tigers, and genetic exchange can also be carried out across species.
Speaking of which, there is also a problem, that is, humans and chimpanzees are close relatives, the genetic similarity reaches about 98%, and the chromosomal difference is not large, the number of human chromosomes is 46, and the number of chimpanzee chromosomes is 48, but humans cannot merge with chimpanzees genetically.
The main point is that humans have evolved very quickly, and although humans and chimpanzees have only been diverging for millions of years, they have evolved faster than horses and donkeys have evolved in tens of millions of years.
For this reason, humans are very different from chimpanzees in chromosome arrangement and structure, and although the two are homologous, at the chromosomal level, they are already more different than many homologous animals. This means that the two systems are incompatible, which is why humans cannot communicate with chimpanzee genes.
Although it is possible to reproduce across species, it is not as simple as people think
Although horses and donkeys can reproduce across species, this is not allowed by the laws of nature after all, and it belongs to breaking the barriers set by nature, so there is also a price to pay.
Horses have 64 chromosomes and donkeys have 62 chromosomes, and when the chromosomes are arranged and combined and the structure is similar, offspring are born, also known as "mules".
Because of the genetic characteristics inherited from horses and donkeys, mules are not only physically strong like horses, but also able to bear hardships and stand hard work like donkeys, which is a very successful model of gene fusion.
However, the number of chromosomes of the mule that inherits the genes of the two is also taken as the average of the two, that is, 63. If the chromosomes are singular here, there is a serious consequence.
Because chromosomes need to be arranged in pairs in the process of transmitting information. However, because they are singular chromosomes, mules are abnormal during meiosis and cannot pair chromosomes correctly. As a result, mules are unable to reproduce offspring, and are only one-time creatures that cannot perpetuate their genes.
From here, I have to sigh at the miracle of nature, although horses and donkeys can have a short genetic fusion, which seems to break the barrier, but they can't really break through that barrier, and only allow a short exchange, that is, to be able to give birth to a generation.