Scientific Essay
***This essay is subject to change
People and cats cooperate more than 7000 years. The original cats have been changed up to now due to different wild and domestic circumstances. Domestic cats are called Felis sylvestris catus according to binomial nomenclature. Like other members of Felidae family which includes tiger, lion, puma, cheetah and etc., domestic cats are characterized by supple, low-slung bodies, finely molded heads, long tails that aid in balance, and specialized teeth and claws that adapt them admirably to a life of active hunting. Domestic cats possess other features of their wild relatives in being basically carnivorous, remarkably agile and powerful, and finely coordinated in movement. [britannica].
Nowadays, The International Cat Association recognizes 58 breeds of cats which were established by artificial selection. Breed is a group of animals, usually domesticated, that share common features such as appearance, behavior and etc., and their establishment is an example of artificial selection i.e. the driving force of breed development is mediated by human beings rather than nature. People are able to select, amplify and emphasize certain feature of organisms. Actually, there are two modes of artificial selection, weak and strong. First one is mediated only by postzygotic properties. However, second mode uses both prezygotic and postzygotic properties.
So, we can consider artificial evolution as a facilitated small-range evolution simulation. Once Darwin stated in his work, “The variation of animals and plants under domestication”, that the evolution of any type can only work where variation present. This means that evolution occurs in case if primary material, an organism, has enough genetic diversity for adapting to new circumstances. The strong artificial selection is often accompanied by strict restriction in spouses’ choice which means that target organisms with feature of interest mate only with each other in order to establish feature in a group. This phenomenon of mating between closely related organisms is called inbreeding. In general, this process has two main issues about future perspective of a breed. First of all, it increases the genetic disease rate due to lowered genetic variation. Effects of recessive alleles which cause disorders are, naturally, hindered by dominant alleles and prevent the disease flow. However, inbred individuals have higher chances of suffering from recessive allele-mediated genetic diseases. The second issue has larger scale, and it is related to whole breed. Pure breed organisms tend to have lowered genetic variation in their genomes. This decreases their potential to adapt to new circumstances. Here, we can mention Darwin’s quote, “the power of selection absolutely depends on the variability of organic beings”.
Many people worry about the future of pure breed cats, about their lowered genetic variance and health problems. In this case, we can consider this issue from two perspectives, breed and species. These days 58 distinct breeds are established, and each of them is characterized by certain properties like size, color, behavior, longevity and so forth. Firstly, we discuss genetic variation among one breed members. Here we can see low genetic variance in comparison with random-bred cats. In study that I observed, scientists derived information from 1100 individuals, representing 17 random bred populations from different countries and 22 breeds, and they used heterozygosity and allelic richness for determining the genetic diversity. As a result, the average heterozygosity in pure breeds is 0.51 and allelic richness is 2.74, whereas, the average heterozygosity and allelic richness in random bred populations are 0.65 and 3.41, respectively. [Table 1, The ascent of cat breeds: Genetic evaluations of breeds and worldwide random-bred populations]. This data demonstrates that individuals inbreeding decreases genetic variance and consequently it can be negatively interpreted meaning that pure breed individuals have lower genetic flexibility and potential. These cats are prone to various genetic diseases and less adaptive to changes. So, inbreeding is negative from the point of view of pure breeds. However, according to the second perspective which is based on species, Felis catus, we can claim that inbreeding brings positive effects, too. Even though the genetic variation decreases among members of a single breed, the overall variation maintain. In my opinion, the genetic variation even increased due to human’s activities. In table 1, we can see that heterozygosity and allelic richness values of wild cats are higher than those of pure bred cats. This is quite expected result. However, these values are lower in wild cats than in random-bred domestic cats (in wild cats: Ho=0.53 and all. richness=3.36; in random-bred domestic cats: Ho=0.65 and all. richness=3.41) which means that random-bred domestic cats have higher genetic variation.
After all I have a hypothesis that explains the results above. Random-bred domestic cats have no restrictions about their mating partners and no restrictions about geography. In common sense, people don’t appreciate random-bred cats because they are excessively many and don’t have any special features. That’s why, people don’t regulate their mating partners. Secondly, human beings are highly developed organisms who learned to move from one location to the other. This capability is advantageous for cats as well. They can move from one country to another, from one continent to another. In general, wild cats don’t have this opportunity.
In conclusion, I would like to point out that life is dynamic process and standard of one day doesn’t matter on the next. For example, today we say that inbreeding is a concern that harms cats now, but after some time certain breeds can possess special feature that will fulfill life’s requirements. By saying this, I mean that inbreeding is harmful for pure breed cats, but it is advantageous for species, Felis catus, as a whole. Everything depends on a perspective through which you consider an issue.
References:
Direct link to Table 1: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2267438/table/T1/
The ascent of cat breeds: Genetic evaluations of breeds and worldwide random-bred populations, Monika J. Lipinski a, Lutz Froenicke a, Kathleen C. Baysac a, Nicholas C. Billings a,, Christian M. Leutenegger b, Alon M. Levy c, Maria Longeri d, Tirri Niini e, Haydar Ozpinar f, Margaret R. Slater g, Niels C. Pedersen b, Leslie A. Lyons https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2267438/
Genetic analysis shows low levels of hybridization between African wildcats (Felis silvestris lybica) and domestic cats (F. s. catus) in South Africa
Genetic diversity of dog breeds: within-breed diversity comparing genealogical and molecular data
