Tired than a horse, the donkey who lost his home, and the mule whose name was set for a humble life, what kind of suffering did he have?
"Bamboo blossoms and mules become pregnant, and eventually they will bring destruction to themselves." This sentence that has been circulating for thousands of years, it is easy to see the strange part of it: how can a mule actually get pregnant? And if you get pregnant, you will die?
mule
<h1 class= "pgc-h-arrow-right" > mule birth and "infertility"</h1>
As for whether mules will give birth, we can actually use common sense to answer: no. Because mules belong to interspecific hybrids, "interspecific hybridization" refers to cross-species fertility, and the products of their birth cannot even be regarded as an independent "species".
As the offspring of horses and donkeys, mules folded 64 and 62 chromosomes into 63. Normal animals are diploid organisms, simply put, chromosomes are even numbers, but mules have an odd number of chromosomes, which causes its germ cells to be unable to meiosis normally, and naturally cannot conceive and reproduce offspring.
In fact, the original interspecific hybridization is not so easy to succeed, because there is reproductive isolation between different species, also known as reproductive barrier, which is an important definition to distinguish species, so that organisms of different species cannot mate and procreate. If there is no reproductive isolation between the two species, even if they seem to have a large gap, they can only be regarded as different "subspecies" under one species; on the contrary, animals that look alike can directly indicate that they are two different species once reproductive isolation occurs.
There have been many experiments in history with such "similar" hybridizations between species. In the last century, a Soviet expert Ivanov did an experiment with chimpanzees, but he spent all the money and did not succeed, and eventually the experiment was forced to terminate due to many factors such as human morality; some people tried to cross with lions and cats with the same number of chromosomes, and the end was also unsuccessful.
But the mule is really a "strange flower", it is not only a rare successful product of interspecific hybridization, but also coincidentally inherits the comprehensive advantages of parents. Horses are easier to tame but "squeamish", donkeys are "temperamental" but can bear weights, mules are docile and can carry, eat relatively little, and live longer than their parents' 25 to 30 years, can reach 50 years, and their economic level is simply the only choice for rural areas.
However, in the beginning, to produce mules, people had to lock up horses and donkeys together and expect them to "have a long-term relationship", a process that was very difficult, often took years, and was not necessarily successful, because there was little sexual attraction between different species in reproductive isolation, but now under the operation of artificial insemination, mules have become easy to give birth.
So why does hybridization with chimpanzees, lions and cats fail, while horses and donkeys succeed? Are horses and donkeys the same species?
That's not true. Humans and chimpanzees have evolved over millions of years and have long been two different animals, chimpanzees have 48 pairs of chromosomes, while humans have only 46 pairs, and the shape of chromosomes is also very different. As for lions and cats, although they have the same number of chromosomes, the difference in body size is too large, and they themselves have a physiological isolation.
Chromosomal comparison of humans (top) and chimpanzees (bottom).
Although horses and donkeys are both part of the genus Makoe, they are divided into wild horse species and African wild donkey species. Their hybridization is successful because the size of the race itself and the morphology of the chromosomes are relatively similar, and even many are homologous, such as: donkey's 2 chromosome and horse's 1 chromosome, donkey's 13th and horse's 11th, donkey's 14th and horse's 13th, and donkey's 16th and 25th add up to correspond to the 5th of the horse. Isn't this like the "gap" that evolutionary laws have left specifically for the birth of mules?
<h1 class="pgc-h-arrow-right" > mules really can't reproduce? </h1>
The mule is a creature that can be said to be both unfortunate and lucky, although it is tired, but its birth and survival are full of miracles, and even the "infertile" point is likely to be overturned.
As we mentioned above, mules have only 63 odd chromosomes, and if this 63 is a pattern of subtracting one from 2×32, it is basically impossible to survive. But the mule's chromosome is the 32 +31 pattern, which is simply that the parents take out half of the chromosome, and the 31 side is odd, so there must be a chromosome that is not a twosome, but a threesome.
This means that it does not have a single free superfluous chromosome, but all chromosomes tend to be randomly separated and freely combined. If the trisomy chromosome is combined with an animal of the same genus, the mule will become pregnant normally. This, in turn, creates its fertility, although the probability is extremely low, less than one in ten million.
In 2017, a farmer surnamed Qiu in Weichang Mongol Autonomous County, Hebei Province, discovered that his mother mule had given birth to a mule. The whole village was surprised and excited, but also worried that this "abnormally produced" little mule was sick, but it was not only able to stand and walk, but even ask for breast milk, everything was no different from normal.
This case illustrates that mules are possible to procreate, and not only that, mules even have "sexual desires.". In order to prevent mules from riding horses and donkeys at the sight of horses and donkeys, causing chaos in the village, the owners usually "castrated" the male mules. The process is relatively inhumane, but fortunately, the mule is tenacious, as long as it eats well, drinks and recuperates for a period of time, it can return to normal.
It is worth thinking about, as a hybrid species, the mule itself has no hope of breeding offspring, but nature allows it to retain its reproductive instincts.
< h1 class="pgc-h-arrow-right" > mule pregnancy is good or bad? </h1>
We don't know what mules think, but mule pregnancy and childbirth is not necessarily a good thing for most humans.
"Mule inability to give birth" can almost be regarded as the solidification of human common sense, we look at the example, we can know that mules not only have the probability of pregnancy, but also after giving birth to "mother and child health", rumors are not self-defeating, but for people earlier in the times, mule pregnancy is a big rebellious, contrary to heavenly reason, out of fear, people will put pregnant mother mules to death.
In 1997, there were also mule pregnancies in California, which were reported by the media, and as the influence expanded, more and more people called for the killing of female mules and mules. We can guess that there must be more than one such event.
Other domestic livestock are pregnant, and people can think of the appreciation of property and rejoice; while mules are born to serve, die for service, and have a very small probability of conceiving offspring in their lives, but they have to be disposed of as ominous things, and the saying that "pregnancy must die" is really bitter.
However, scientists have the opposite attitude towards this, not only do they not think that mule foals are "damned", but even feel that this matter has a high research value in genetics, and mules themselves are also a practical "good foal", if they can achieve intraspecific reproduction, it will form an excellent industrial chain.
They have tried to double the number of mules' chromosomes and tried to make a fuss about the sperm of male mules, but they have failed, and human research on mule foals is still obstructed and long.
Imagine if our study of mule fertility is successful in the future, then mules will become the world's first interspecific hybrid animal that not only transcends the reproductive isolation of parents' generations, but also produces offspring on its own. Will it create new concepts in biology, bringing us more and more surprises and miracles? Everything can only be seen in the future.