In the United States, approximately 70% of homes contain pets, and many owners have more than one pet.1 According to the 2021–2022 American Pet Products Association National Pet Owners Survey, 35% of pet owners in the United States own a cat.¹ There are 94.2 million cats, compared with 89.7 million dogs. The American Veterinary Medical Association estimated 25.4 million households owned a cat in 2017–2018, estimating approximately 1.8 cats per household.² Although the estimate of pet owners is slightly different in the two surveys, the trends are the same: cats are a popular companion animal in the United States. In the United Kingdom, a survey conducted in 2011 estimated about 10 million cats and 11.5 million dogs within the country.³ Worldwide, domestic cats are gaining in popularity in some countries, perhaps being pets more conducive to the modern lifestyle, and, as the cat’s status upgrades from mere pet to family member, cat health care has become a common family value.

In tandem with human migrations, cats have traveled around the world, generally to work as vermin control on boats and farms; thus, their population has generally been unrestricted. Co-migrations with humans have resulted in large feral cat populations in both highly populated cities and remote islands that have, or previously had, human occupation.⁴ Because cats, as non-native species, severely threaten some native wildlife species,⁵ their management is a matter of significant debate, even though the resulting feral populations are due to human negligence. Many cats from feral populations are captured and transferred to shelters. People are increasingly concerned about the welfare of cats in shelters, and shelter managers must balance kill versus no-kill strategies to ensure adequate population control.

Currently, cats continue to travel the world but more commonly as our valued companions, thus contributing less to feral populations. Although migrant cats confuse the identity of a population’s original genetic composition, the origins of the domestic cat can be traced to the dawn of human civilization by following human migrations back through time and sampling the random-bred, remote, and feral cat populations of the world.

The domestic cat, Felis catus (also known as Felis silvestris catus), is one of 41 species in the cat family Felidae, subfamily Felinae, a member of the Felis lineage. The Felis lineage is composed of three African–Asian felid species including Felis nigripes (Black-footed cat), Felis margarita (Sand cat), and Felis chaus (Jungle cat). The lineage is also comprised of species more closely identified as “wildcats” in which the subspecies designations are somewhat contentious. Beside the domestic cat, three small felids that may be the progenitors or at least have some current genetic contributions to the domestic cat, including Felis lybica (African wildcat), Felis silvestris (European wildcat), and Felis bieti (Chinese desert cat) complete the lineage.6 The domestic cat and the wildcat species can interbreed, producing fertile hybrids; thus, their demarcation as subspecies and even distinct species are disputed. Because the common housecat is a domesticated derivative, the name F. catus has been adopted, which does not clearly denote the genetic relationship to progenitor wildcats or their subspecies.⁷ Population geneticists tend to use the term Felis silvestris catus for the domestic cat. The relationship of the African, European, and two Asian wildcats is also somewhat controversial; historically, 21 subspecies are defined. Other than the South African subspecies of African wildcat, Felis lybica cafra, most species of wildcat and their associated subspecies may be the progenitors of domestic cat populations,^8,9 with F. lybica having the most scientific support. The African wildcat definitely influenced the origins of the domestic cat;⁸ however, detailed examinations of other wildcat species and subspecies have not been possible because of poor access to appropriate samples. For two wildcat subspecies, European and Scottish wildcats, introgressions with domestic cats may be an ongoing process.^10,11 This threatens the existence of “pure” wildcat populations in Europe and the United Kingdom, although neither subspecies is thought to have contributed to the original domestication of the cat. Conservation efforts to protect the wildcat populations in Scotland, Italy, the Iberian Peninsula, and other regions fight the encroachment of domestic cats—household pets that may be returning to feral states, obscuring and perhaps reversing the domestication process and producing “hybrid swarms.”¹²

Cats likely participated actively in their own domestication; humans and felines developed a symbiotic, commensal, mutual tolerance. Several independent sites of early civilizations are known to have developed between 8000 and 3000 BCE, including the Huang He River region of China, the Indus Valley in Pakistan, and the Fertile Crescent region, which extends from Iraq, into Turkey, south along the Levant region of the Mediterranean coast, and, arguably, into the Nile Valley of Egypt. As humans made the transition from hunter–gatherers to the more sedentary lifestyle of the farmer and permanent settlements developed, villages produced refuse piles and grain stores, attracting mice and rats, a primary prey species for the small wildcat. To obtain these easy meals, bold wildcats perhaps began to tolerate humans, and humans accepted the cat because of its utility in vermin control.

Arguably, the domestication of the cat can be considered incomplete and in flux, because abandoned cats and feral populations can quickly adapt to a wildcat lifestyle.^13,14 The cat has behavioral and social attributes recalcitrant to domestication, such as being highly agile and a mainly solitary species; these very traits may be part of the reason that many humans find cats so fascinating and endearing. A combination of self-selection by the cat and selection by humans has led to a variety of aesthetically pleasing coat colors and traits specific to domesticated cats and behaviors that are conducive to companionship. A comprehensive review of cat coat color frequencies, such as those performed in Great Britain, have corroborated cat migrations and human selection preferences by indicating clines of higher and lower coat color frequencies across the world. These clines suggest some degree of controlled breeding or selection by humans, which probably began with the cat seeking human affection and companionship in the Fertile Crescent region and later became more systematic with the first controlled cat breeding programs, possibly in Egypt.¹⁵

Direct genetic evidence for cat–human interactions can now be more readily interpreted. Ancient DNA studies are demonstrating the association of cats over space and time. Bones from cats in human dwellings demonstrate when coat colors appeared that are associated with domestication and controlled breeding. The genetic signatures in the cat’s mitochondrial DNA can track their populations of origin, such as Egypt or the Near East, and demonstrate their diaspora around the world. Thus, cats are actually a proxy for human migration patterns.^16–18

The creation of cat breeds has been a significantly different process than breed development in other companion animal and agricultural species. These nuances are important for an understanding of the appropriate genetic tools, resources, and techniques that will be the most beneficial and efficient for cat genetic research and health programs (see Chapter 51: The Feline Genome and Clinical Implications). Random-bred and feral cats represent the overwhelming majority of cats throughout the world, not fancy cat breed populations, although most genetic studies have focused on cat breeds to date. Considering the worldwide distribution of cats, the United States likely has the highest proportion of pedigreed cats. However, the proportion of pedigreed versus random-bred cats is still fairly low; only 10% to 15% of feline patients at the University of California, Davis Veterinary Medicine Teaching Hospital are pedigreed cats.¹⁹ A general understanding of cat breed development and a more in-depth understanding of the limited number of foundation cat breeds will help the veterinarian predict health care problems on the basis of each patient’s genetic background. The knowledge of cat breed relationships also helps the veterinarian prioritize differential diagnoses for health care management.

Some of the earliest descriptions of different “types” of cats were documented in Siam (current day Thailand) by monks during the Ayutthaya period (1350–1767). Korats, Burmese, and Siamese were clearly defined according to their coat colors. These colorations define the same cat breeds today. The naturalist Georges-Louis Leclerc (Comte de Buffon; 1707–1788) described “races” of domestic cats, identifying some of the current breeds, such as the Angora and the Chartreux, based on coat coloration and fur length. Early taxonomists used coat colors to define domestic cats according to their different variants and subspecies. The aesthetic value of coat color and type variants led to competitive showing and breeding. The first documented cat show that judged cats on their aesthetic value occurred in London, England, at the Crystal Palace in 1871. This competition presented only a handful of breeds, including the British, Persian, Abyssinian, Angora, and Siamese. Thus, these early documented cat breeds likely represented genetically distinct populations insofar as strict breeding programs were not established at the time.

Within a few years, cat shows began taking place in the United States, and the homegrown Maine Coon cat was added as a specific breed. The Maine Coon developed from western European random-bred cats that had traveled to the New World with the pilgrims and colonial settlers. By the early 1900s, several cat fancy registries were established, and stricter breeding practices were developed. In contrast, a wealth of dog breeds were well-established by the 20th century, having been in development for several hundred years. A variety of cattle and horse breeds also existed, domesticated from various regional wild populations of the world. Several modern encyclopedic volumes pertaining to the domestic cat list approximately 50 to 80 cat breeds worldwide. However, most breeds were developed in the past 50 years, and many listed breeds did not develop into viable populations; some no longer exist, in fact.

Another major difference between cats and other domesticated species lies in the selection process for cat breeds. Cats were originally, and continue to be, selected for aesthetic traits, such as coat colors and fur types, which are mainly single-gene traits. Cats performed their required function, vermin control, naturally. Dog breeds, however, have been selected for morphologies that support diverse functions and behaviors. The breeds of agricultural species are selected for meat and milk quality and quantity. These behavioral and production traits involve complex interactions among many genes, which suggests that more selection has been applied to the genome of dogs, cattle, pigs, and chickens than to the genome of the domestic cat. Less selection likely results in more genetic diversity for cats, which may mean comparatively fewer health problems for cats than for other species.

However, significant distinctions are now apparent among the structural morphologies of current cat breeds. On one end of the spectrum is the cobby and robust body of the Persian, which has extreme brachycephalia; on the other extreme is the slender and fine body of the Siamese, which has extreme dolichocephalia. The severity of these extremes, particularly in facial structure, has led to certain feline health problems^20–23 and resulted in criticism of the cat fancy. A greater emphasis on selection, drawing on more complex genetic interactions, may lead to more health concerns.

Today’s most common cat breeds and their genetic relationships are listed in Table 50.1. Most international cat fancy associations, such as the Cat Fanciers’ Association (CFA), The International Cat Association (TICA), the Governing Council of the Cat Fancy (GCCF), and the Fédération Internationale Féline (FIFe), recognize approximately 35 to 41 cat breeds, although a few breeds dominate the census of the registries. Persian cats and related breeds (e.g., Exotic Shorthairs, a shorthaired Persian variety) are among the most popular cat breeds worldwide and represent most pedigreed cats. However, registrations for Ragdolls, Siberians, and Maine Coons are more recently increasing. Although not all cats produced by breeders are registered (perhaps only 20% to 30%) the CFA, one of the largest cat registries worldwide, registers tens of thousands of pedigreed cats annually. Common breeds having at least 1000 annual registrants are the Abyssinian, Maine Coon, and Siamese. Other popular breeds include the Birman and Burmese, which are more prevalent in some countries, such as the United Kingdom. Most of these popular breeds also represent the oldest and most established cat breeds worldwide.

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