“Hybrid” describes the offspring of two different species. Some people use reproductive tests to identify species. Thus polar bears (Ursus maritimus) are a different species than grizzly bears (Ursus arctos horribilis) because they don't normally reproduce together in the wild. However, we have discovered that, on rare occasions, these species have bred in the wild producing hybrid cubs. The offspring of such unions are called a “pizzly” if the father were a polar bear and a “grolar bear” if the father were a grizzly. Either way, the simple fact that these different species do occasionally hybridize in the wild undermines the use of a reproductive test to identify a species.
I've always favored using morphology to identify a species. Once a population has enough traits in common that they can all be identified as belonging to the same group, then they earn the moniker of species. Thus bears with large bodies, white fur, long necks, and pointed faces are “polar bears”; bears with smaller bodies, brown fur, short necks, and flat faces are “grizzly bears.” Admittedly that definition has it's own difficulties but at least it acknowledges the fact that identifying a species is more subjective than objective. It also dispels the mistaken impression that species are absolutely distinct and don't reproduce together.
The term “hybrid” is a sort of misnomer and gives a false impression of the importance of reproduction between different species. Hybridization is so common that I'm surprised that a reproductive test is even considered as a possible way to distinguish one species from another. The reproductive boundaries are crossed frequently in the wild and are absurdly common in captivity. Let's look at a few of the more interesting ones.
We've already talked about pizzly/grolar bear hybrids but there have been many crossovers between other bear “species” (usually in zoos): a Malayan Sun bear and a sloth bear, a sloth bear and an Asiatic black bear, a black bear and a spectacled bear, and a black bear and a sun bear.
Cat hybrids are fairly well known but the number of combinations is still remarkable. Lions + tigers is especially common; the offspring are called either ligers (lion fathers) or tigons (tiger fathers). Other examples among the Panthera genus include lion/leopard hybrids, lion/jaguars, tiger/jaguars, tiger/leopards, and jaguar/leopard. The features exhibited among the cubs of these unions sometimes blend the parents' features so well they appear to be Photoshopped together.
Horse and donkeys have been bred for centuries to produce mules. However, in spite of their differing chromosomes, horses call also reproduce with zebras (zorse) and zebras can breed with donkeys (zeedonks). The offspring of these combinations are almost always sterile.
Domestic cows can breed with buffalo (beefalo).
Camels can breed with llamas (camas).
Wolves can breed with domestic dogs (wolf dogs) and with coyotes (coywolves).
Besides mammal species, fish also hybridize. A while back, I blogged about hybrids between the Australian black-tip shark and the common black tip shark. Scientists called that “evolution in action” but I won't go into that now. It again represents the fact that the boundaries between species is not a reproductive one. Hybridization also occurs among birds, insects, and especially plants. Again, there are far more examples than I can begin to address in a single blog post.
Speciation and hybrization are especially relevant to an understanding of creation. The Bible says that God created animals “according to their kind” (Genesis 1). When Noah entered the Ark, he had “kinds” of animals on board with him. There are millions of known species and perhaps millions more undiscovered. However, the vast majority of these millions include bacteria, plants, algae, fungi, and insects. Noah did not have to make accommodations for any of these (though many probably did make their way on the Ark).
According to Wikipedia, there are only about 62,305 species of vertebrate animals. About ½ of these are fish and another 10% are amphibians. Noah did not have to provide for these either. That leaves less than 25K vertebrate species Noah had to concern himself with (never mind that some of the mammals and reptiles are also marine dwelling). So, does this mean that Noah had to take 50K animals on the Ark (a male and female of each species)? Hardly. We've already seen that “species” aren't distinct. There are eight species of bears but Noah did not have 16 bears on the Ark; he had 2. There are 41 cat species but Noah did not have 82 cats on the Ark; he had 2. Ditto for the many species of dogs, cattle, squirrels, deer, parrots, ducks, etc.
I've heard varying estimates of the number of animals Noah would have had to have on the Ark in order account for the number of species we have today. Some estimates are as low as 3,000 while others range as high as 15,000. Even the highest estimates are far less than the “millions of animals” caricature used by evolutionists to criticize the Flood event.
“Species” is a label we use for convenience. Though I sometimes chide evolutionists about it, I really don't have a problem with the term; I only object to the idea that when populations specieate that they have somehow “evolved.” The ancestral kinds on the Ark were necessarily genetically diverse. The descendants of the original Ark-kinds (cats for example) have adapted to their various ecological niches around the world. The resulting populations are called “species” (lions, tigers, lynxes, ocelots, cheetahs, etc). Each one possesses different combinations of features already present in the original kind. When the different species hybridize, they merely recombine the same features in new ways. We could potentially get new species but we won't get new kinds.