Why Animals do not Race-Mix
Race-mixing / Hybridization is so rare in the animal kingdom that there isn’t even a lot of research available about where or how this eventually happens as a natural, self-determined phenomenon. Most animal species live within geographical boundaries, in specific climates and in every biome and environment there is a chain or hierarchy of predators and predated, Nature is designed in such a way that hybridization between different species of animals barely ever happens in very few cases (so the current literature says). Adaption to various different environments, hierarchies and food chains, predators and predated animals and many other factors have made race-mixing among animals nearly impossible to happen naturally.
A few hybrid species do exist however, and the reason in most cases is because humans have “created” them for research purposes, in order to see what happens when two species of different animals combine, something which otherwise happens extremely rarely in nature. Examples of this are the liger, mule, zorse, coywolf etc. Interestingly, what has been discovered is that most hybrid animals are in most cases infertile, unable to reproduce [1]:
“In short, hybrid animals are infertile because they don’t have viable sex cells, meaning they can’t produce sperm or eggs. This is the case because the chromosomes from their different species parents don’t match up.”
Needless to say, such hybrid animals cannot survive for a long time in nature.
This is to be expected, as different species of animals with different evolutionary traits and pathways are not compatible, therefore a forced hybridization between different species can result in offspring that are genetically “mutated” so to say, specimens that carry “genetic diseases” such as infertility due to genetic incompatibility of the parents, although there are also instances where hybrid offspring may outperform parents in physical characteristics (strength, size, stamina, speed etc). There are also cases of supposed “successful” hybrid examples between what is claimed to be very distinct species, for example the hybrid between the rose-breasted grosbeak and the carlet tanager [2]:
“The birds aren’t exactly cousins, or even close relatives. Mulvihill suspects the species may be separated by more than 10 million years of divergent evolution.”
But is that accurate? At a closer look, we observe that the two species of birds are part of the same family,
Cardinalidae, and according to Wikipedia [3]:
“Membership of this family is not easily defined by a single or even a set of physical characteristics, but instead by molecular work.”
Therefore is difficult to tell how the two species “divergently evolved” to the claimed scale when they are part of the same family with very similar breeding behavior and patterns, same dwelling areas, similar diets etc. [4] [5]. If anything, these two species are a lot more similar than they are different, therefore higher potential of genetic compatibility in case of mating. 10 million years of “divergent evolution” did not seem to incur major differences between the two birds, in fact there are hardly any major differences between them. Perhaps National Geographic’s claim is just exaggerated.
On another note we have seen above that ligers are a “man-made” hybrid between lions and tigers. Based on taxonomic classification, not only that lions and tigers are part of the same family, Felidae, but they are part of the same subfamily and genus. Therefore, theoretically they are even closer related than rose-breasted grosbeak and the scarlet tanager. Yet ligers are still known among hybrid animals to suffer from infertility and likely other genetic complications due to parent incompatibility. Taxonomically there is a greater variation between the two bird species than between tigers and lions, yet the later produces offspring that according to available (rather limited) research seem to be more prone to infertility and other imbalances compared to the birds’ hybrid. Something doesn’t seem to add up.
Rose-breasted Grosbeak (left) - Scarlet Tanager (right)
In reality, breeding between different species is a gambling, prone to chance. The offspring can either be healthy and “better” in some aspects, depending on the compatibility of the parents, whilst in other cases the offspring can suffer from genetic conditions, as documented by a study posted in the scientific journal PLOS Biology [6]:
“Crosses between closely related species give two contrasting results. One result is that species hybrids may be inferior to their parents, for example, being less fertile [1]. The other is that F1 hybrids may display superior performance (heterosis), for example with increased vigour [2]. Although various hypotheses have been proposed to account for these two aspects of hybridisation, their biological basis is still poorly understood [3].”
Indeed, the science of hybridization is very poorly understood, mostly because is a new science that has never preoccupied humans until recent times when hybridization between humans became a sort of political agenda, although not very visible for obvious reasons. Unfortunately, as any other area of activity, science has also been hijacked by those that pay the money and therefore science can be used in some ways as a form of programming where such research on animal hybridization can suggest the idea that there is nothing wrong or unnatural in hybridization between humans because it occurs in nature, although the complications here are obvious. Similar to hybrid animals, there are complications between “hybrid” people as well, as explained in other articles.
A very interesting example is provided by United States Department of Agriculture, where they raise the issue of loss of integrity of native populations of cutthroat trouts in areas populated with non-native rainbow trouts [7]:
“Among the many issues associated with introductions of nonnative aquatic species is the likelihood of hybridization with native species. An oft-mentioned example in western North America involves cutthroat trout, a cold-water fish that was once much more abundant and widespread, and rainbow trout, a popular sportfish also indigenous to parts of the West but widely introduced elsewhere. Where cutthroat trout are native and rainbow trout introduced, hybrids between the two species often appear, levels of hybridization sometimes persist or grow, and the incidence of hybridization can spread. Managers worry that mixing of these species will inevitably and irreversibly lead to the formation of hybrid swarms in which all fish are hybrids and the genetic integrity of native populations is lost, undermining conservation efforts (...)”
Do we see this elsewhere? To most people it should beg the question why they don’t think the same about humans.