Maine coons have many traits that set them apart from other cats, such as large size, a square jaw, and often feet with six or more toes. But sometimes these traits have been artificially preserved — and, in some cases, exaggerated — through artificial selection. (Image credit: Sergei Ginak/Getty Images)

Of the more than 600 million cats across the globe, less than 10% belong to a specific breed. But are these purebred cats the result of human intervention, or did some develop naturally?

The answer is more complicated than it might seem. According to Leslie A. Lyons, a cat geneticist at the University of Missouri College of Veterinary Medicine, most cat breeds developed in the past 140 years as a result of human selection for specific physical traits.

According to Sarah Hartwell, a cat genetics hobbyist and founder of the cat resource MessyBeast, the progenitors of natural breeds form under the same conditions as wild species do.

"Natural breeds could be considered a step along the road to speciation," she told Live Science. In most cases, they form as a result of environmental adaptation. In Western Russia, cold and snowy conditions favored thick-furred, big-boned cats that became the foundation of the Siberian forest cat breed. In Southeast Asia and the coastal areas of the Indian Ocean, warm and humid conditions favored short-haired, slender-bodied, big-eared cats that set the stage for the Abyssinian.

Siberian forest cats are a "natural" cat breed, meaning they are descended from cats that evolved without human intervention. (Image credit: vvvita/Getty Images)

In some cases, natural breeds begin as a result of geographic isolation. This phenomenon, known as the founder effect, occurs when a gene that is not advantageous to the animals' survival spreads because the population has a small, isolated gene pool. On the Isle of Man (a self-governing British Crown Dependency in the Irish Sea), a mutation that caused a short tail spread as a result of inbreeding, resulting in the ancestors of the Manx cat. Unfortunately, Manx cats can suffer from spinal defects due to this tail mutation.

Although the ancestors of natural breeds evolved under natural conditions, modern-day cats of these breeds are not so "natural" anymore.

"All breeds, no matter what species, have human influence," Lyons told Live Science. According to a study in the journal Animal Genetics that she co-authored, the selective breeding of cats has increased exponentially in the past century, which, in turn, has removed the environmental pressures that shaped natural breeds.

Manx cats have short tails that spread as a result of inbreeding long ago. (Image credit: slowmotiongli/Getty Images)

The Manx breed, for example, likely would have died out naturally due to a lack of genetic diversity and the detrimental effects of the short-tail mutation. In the modern day, the breed is still widespread as a result of intentional breeding by humans. However, there are some who are trying to eliminate it.

"The thought is to retire this breed, or find a way to make them healthier," Lyons told Live Science. "Maybe we [work toward] a tailed Manx."

Some of the once-natural breeds are more closely connected to their roots than others are. Modern Siberian cats, for example, are genetically and physically similar to their ancestors because breeders regularly bring in new cats, found as strays or as pets in the breed's home region, to add to breeding programs.

Although the Russian blue cat's ancestors originated naturally, selective breeding and crossbreeding have made modern Russian blues genetically and physically different from their ancestors, and from each other. (Image credit: Nailia Schwarz/Alamy)

Other breeds have been altered both genetically and physically from their original appearance. Russian blues, for example, were crossbred with Siamese cats to prevent the breed's extinction after World War II, and breeders have since divided them into specific "types" that look different from the original cats.

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So yes, "natural" cat breeds do exist, but they are not entirely natural. The traits that are quintessential of a Maine coon purchased from a breeder — such as large size, square jaw, and often feet with six or more toes — may resemble the Maine coons discovered back in the 1800s, but they have been preserved — and, in some cases, exaggerated — through artificial selection.

"It all depends on popularity and what people prefer," Lyons told Live Science. "One lineage of cats might become very popular and change what the breed looks like, and then it might swing back another direction depending on the next new craze."

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Katherine Irving is a freelance science journalist specializing in wildlife and the geosciences. After graduating from Macalester College, where she wrote screenplays, excavated dinosaur bones and vaccinated wolves, Katherine dove straight into internships with Science Magazine and The Scientist. She now contributes to the Science Magazine podcast and loves reporting about the beautiful intricacies of our planet.

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