Why can't Asian elephants and African elephants?

Hybridization is the reproductive behavior of two different species. In nature, different animals rarely cross because of the restriction of reproductive isolation between species. Reproductive isolation is the reproductive barrier of species, which refers to the mechanism that two geographically close species will not mate or will not mate successfully. In the definition of reproductive isolation, it is difficult to mate successfully, including that the germ cells cannot combine after mating, and it is difficult for the germ cells to develop into embryos after combining, and the offspring are almost infertile after producing offspring. Although we often say that mules are the product of cross between donkeys and horses, it does not mean that donkeys and horses have broken through reproductive isolation, because mules are highly infertile.

Different subspecies of the same species are not restricted by reproductive isolation, such as Siberian tiger and Bengal tiger, African leopard and Far East leopard, which can breed normally. The secret of hybridization between Asian lion and African lion, Asian elephant and African elephant is actually hidden in their differences.

Asian elephants and African elephants have no chance to meet in the natural environment, so they were geographically isolated at first, which led to their chance to meet only in the zoo. Because elephants are standard in zoos, there are a large number of them, so it is very common for Asian elephants and African elephants to take pictures together in zoos, which makes them break the original geographical isolation.

However, despite this, there are only a handful of successful cases of hybridization between Asian elephants and African elephants, and most of the hybrids either have no offspring or die soon after birth. For example, at Chester Zoo in England, a hybrid elephant named "Morty" was born. Its father is a male African elephant and its mother is a female Asian elephant, but there are spots.

There used to be a hybrid elephant in Beijing Zoo. Although he did not die young, he was still infertile as an adult. Obviously, this is the result of reproductive isolation. Moreover, through low success rate and high mortality rate, there is serious reproductive isolation between the two elephants. Why? The answer lies in the genetic differences between the two elephants.

Although both Asian elephants and African elephants are elephants, they are not as simple as subspecies of elephants. Although they have the same ancestor, they have been divided for too long. According to the current research, Asian elephants and African elephants may have evolved respectively more than 5 million years ago.

There is no gene communication for such a long time, and their habitats are very different, which makes their genetic differences surpass the interspecific differences and rise to the intergeneric differences. Therefore, African elephants belong to the elephant family, and Asian elephants belong to the elephant family. Their differences are just like lions and clouded leopards.

In reproductive isolation, the success rate of cross-species hybridization is already very low. For example, the probability that lions and tigers can successfully give birth to tigon is less than one in ten thousand, let alone rise to genus and decline geometrically. Among the known vertebrates, except birds, sheep and goats (sheep and goats), cross-species hybridization ended in failure.

From a genetic point of view, Asian elephants are actually closer to extinct mammoths. They belong to different species of the same subordinate, just like lions and tigers, while African elephants are close relatives of the extinct ancient ling image and belong to different species of the same subordinate.

Moreover, although there is only one species (four subspecies) of Asian elephants, there are two different species of African elephants: African grassland elephants and African forest elephants, and there has been no gene exchange between them for at least several hundred thousand years. Therefore, these two African elephants also exist as different species, and there is reproductive isolation between them like donkeys and horses.