Interspecies breeding (sometimes called cross breeding1) is the act of creating offspring from two different species. It should not be confused with the chimera which involves more of a Frankenstein-type process of gene splicing, cell modification, implantation, and embryo modification. While the creation and study of hybrid plants has been ongoing for hundreds of years, this writeup deals with hybrid species created by cross breeding in the animal kingdom - specifically mammals, however the concepts themselves cross these borders.

Disclaimer:
This writeup is about procreation - not intercourse. It is not about beastiality/bestiality, so look for your stories about human/animal and human/plant "relationships" elsewhere. I don't have any suggestions on where to look. Certainly not on E2.

Interspecies breeding is a very complex subject. Obviously it is not possible to mate any animal with any other animal to produce a strange new creature. If you've learned anything from South Park, you will know that "pig and elephant DNA just won't splice". It is commonly believed that for two species to be able to interbreed, they must have the same number of chromosomes. While this is true in most cases there are many exceptions. For example, a horse (64 chromosomes) and a zebra (44 chromosomes) can produce viable offspring. If the animals have a different number of chromosomes, the animal with the smaller number must be the male (e.g., a male zebra and a female horse could produce a foal, but a female zebra could not be impregnated by a male horse). What is most important is that the chromosomes that do match up are homologous. What determines this homology at the cellular level is beyond the scope of this writeup.

In general, cross bred animals are sterile. This is typically related to the fact that even if the chromosomes match up enough to create the offspring, there are still genetic problems that cause the hybrid to be unable to produce children. In cases where then animal can (medically) produce viable eggs or sperm; it again becomes a problem of matching chromosomes with some other species. This is not to say that no crossbred animal can mate, it is just rare.

Most cross breeding occurs between animals in the same Genus. There have been cases where offspring has been produced between animals in different genera but in the same family. However, this is uncommon, and has caused some scientists to question whether the classifications of these animals are correct in the current system.

Hybrid Examples

There are many examples of two species of animals that have/can/do produce offspring. A well known example of this is the mule. While not terribly creative, these new hybrid animals are usually named by combining the common names of the parents. When the male and female of both species can each be combined to form the hybrid, it is the name of the male that is used first. For clarification of this, see the examples below:

  • liger = male lion + female tiger
  • tigon or tiglon = male tiger + female lion
     
  • mule = male donkey + female horse
  • hinny = male horse + female donkey (jenny)
     
  • zorse = zebra + horse
  • zonkey or zebrass = zebra + donkey (ass)
  • cama = camel + llama
  • catalo or beefalo = buffalo + cattle
  • yakalo = yak + buffalo
  • wholphin = whale + dolphin (specifically a false killer whale and a bottlenose dolphin)
     
  • Toast of Botswana = goat + sheep
    Obviously this deserves some clarification. While a sheep can be impregnated by a goat, the kid/lamb is always stillborn... except in one case in the early 1990s. This animal was nicknamed the Toast of Botswana. Since it was the only one ever known to have lived, no other name has been given to a goat/sheep combination.
     
  • humanzee - there have been numerous reports of human/chimpanzee combinations, but none of these have been confirmed
  • several species of cats can be bred including: lion/leopard, lion/jaguar, puma/leopard, bobcat/lynx, caracal/serval
  • several species of canines including domestic dog/wolf, coyote/wolf, domestic dog/coyote
  • several species of monkeys and apes can interbreed
  • several species of deer and antelope can be interbred
  • several species of snakes can be crossbred
  • wild and domestic pigs can crossbreed
  • African elephant and Asian elephants are known to have bred once in the past

Interspecies Breeding in the Wild

It is quite clear that cross breeding occurs naturally. When horses and donkeys are kept together for long periods of time, eventually you will get a mule. Anyone who has had a male dog will probably know that it will hump damn near anything: male, female, or inanimate. Sex drive is part of the animal world, and when you can't be with the one you love, love the one you're with (my humble apologies to Stephen Stills).

Regardless, breeding between species is very uncommon in the wild. Ignoring chromosomal issues above, there are many more reasons for this including:

  • Mating rituals - For many animals, it can be extremely difficult for a male to be accepted by a female of the same species. A separate species has no chance.
  • Different habitats - Many animals that can mate don't live in the same regions naturally
  • Breeding/heat cycles - Different species do not often have the same mating seasons/breeding cycles (i.e., females are not in heat and/or males to not get the urge for sex)
  • Physical differences - while it may be possible to artificially inseminate a camel with llama sperm, the chances of such a small animal mounting such a large animal are slim
  • Chemical processes - sperm needs specific enzymes to penetrate the egg that may differ between species. This may not be possible outside a laboratory for many animals.
  • Immune systems - the immune system of the female may reject the sperm as a foreign body since it does not match the sperm of the female's species. See also human seminal plasma hypersensitivity.
  • Rejection - similar to above, and having the same problem with organ transplants in humans, the female body may reject the fetus before it comes to term.
  • Death - Miscarriages are a common occurrence with interspecies breeding. Even if the pregnancy comes to full term, stillbirths are also common. Lastly, if the animal is born alive it often has health problems and does not live long, or is abandoned by its mother.

1 Cross breeding is actually a much wider term. It can be used to refer to breeding two different stocks to improve the overall healthiness of both. For example, a dog breeder will cross breed his champion bitch with a male of the same breed from across the country. A farmer might use a bull from his neighbor's barn to impregnate his cows. These acts reduce inbreeding and can improve the pedigree or breeding population of animals.

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