Thumb cats. Mitten cats. Hemingway cats. Boxing cats. Six-toed cats. They’re called by all sorts of names, but the true name for the phenomenon that gives these cats such unique feet is polydactyly.

The word comes from Greek roots — “poly” meaning many and “daktylos” meaning digits. And true to form, all polydactyl cats have more than the standard number of toes on each foot. A typical cat has five toes on each front foot and four toes on each back foot, for a total of 18. The Guinness World Record for number of toes is 28. That’s a lot of cute little jellybeans!

Cats with extra toes are most commonly seen in southwestern England, Wales, and on the East Coast of North America — in the U.S. as well as Canada. It’s believed this is because polydactyl cats were very popular as ships’ cats, for their extraordinary hunting ability and also perhaps because they were seen as good luck talismans.

There is a bit of controversy about whether the mutation originated in North America or in England, but researchers and folklorists generally agree that it spread widely via cats carried on ships originating in Boston. Not only that, but the prevalence of polydactyly in various other ports seems to relate to the establishment of trade between those ports and Boston.

However, there’s an interesting twist to this folklore when it comes to genetics. Polydactyly is caused by one of a number of genetic mutations. For a while, researchers believed they’d isolated a single mutation responsible for extra digits on kitty feet, but with more study, they discovered that there are several genes that seem to cause different types of polydactyl mutations. They also found that polydactyl cats in England had a different genetic variant than those in North America, so it seems that both sides of the polydactyly origin debate are right — even if the North American variant did spread farther than the British and Welsh variant.

There is another condition similar to polydactyly in that it produces extra toes. However, this condition, known as radial hypoplasia, doesn’t just cause extra “thumbs” like the standard polydactyl mutation. It causes a cat to be born with numerous extra toes on the paw itself. Although they’re awfully cute, it’s a bad idea to breed cats with radial hypoplasia because it will eventually result in cats who have severe disabilities such as underdeveloped or twisted front legs.

These days, polydactyly seems pretty evenly spread out among all breeds and non-purebred cats — but at one time, almost 40 percent of Maine Coons were polydactyls. However, because polydactyly is seen as a defect according to breed standards, it has been largely bred out of Maine Coons destined for the show ring. However, some breeders are breeding polydactylism back into the Maine Coon.

As most mitten-cat lovers know, author Ernest Hemingway was particularly fond of polydactyl cats; that love affair began when a ship captain gave him a white six-toed cat named Snowball. To this day, the Hemingway house and museum in Key West, Florida, hosts nearly 50 of Snowball’s descendants, about half of whom are polydactyls.

Do you have a polydactyl cat? How many toes does yours have? Show your boxing-cat love in the comments!