In the towns dotted across Britain’s Isle of Man, you can sometimes spy a particularly eye-catching resident. It is a cat seemingly like any other, only missing something: its tail.

The animal has captured the hearts of pet owners both on the island and much further afield. In fact, there are now far more Manx cats in North America than on the island where they originated.

How they came to lose their tails in the first place remains a bit of a mystery – but the answer lies in a genetic mutation.

In 2013, one gene was shown to have four possible mutations that can lead to a tailless Manx cat. All four mutations are specific to the Manx – other tailless or bob-tailed cats carry different mutations responsible for the trait.

The study’s co-author Leslie Lyons, a cat expert and geneticist at the University of Missouri – Columbia, went to the Isle of Man herself to collect samples from Manx cats. The mutations were present there, meaning all Manx cats must have come from tailless cats on the island, which have lived there for hundreds of years.

Isle of Man resident Sara Goodwins, author of the book A De-tailed Account of Manx Cats, notes that the first linguistic reference to tailless cats on the Isle of Man appears in the mid-18th Century. Before that, since there was no special word for them, Goodwins says that it was unlikely they were present in any significant number.

Since cats use their tails for balance when running and jumping, and to communicate body language, it seems odd that some should lack them. Lyons says she cannot think of any natural advantage to being without a tail. Instead, the gene likely has been passed on mainly through selective breeding by humans, a process called “novelty selection”.

Although the gene that carries these mutations is dominant, making it easy enough to pass on, there is an interesting quirk: if an unborn cat inherits the gene from both parents rather than just one, it will likely die in the womb. That is why the gene that causes the cats to have no tail has been nicknamed, darkly, “the lethal gene”.

“You never see these babies born, or they never develop,” says Lyons. “That means there is a high selection against this mutation.”

Even when the gene is inherited from just one parent, it is not necessarily benign. Manx cats can suffer from health issues related to having too few vertebrae in the lower or lower-middle part of their spines, like incontinence and in some cases even lameness.

For this reason, some breeders will not try to preserve the gene, while others have specialised in trying to breed Manx cats with healthier spines.

The introduction of problematic traits in domesticated animals is a phenomenon that is gradually becoming better understood.

For example, a 2016 study of dogs suggested that small domestic populations led to the accumulation of harmful genes in animals that were selectively bred for certain physical features, such as colour or shape of the head.

Even more troubling is a practice called “docking”, in which the tails of young cats and dogs are surgically removed so that they appear to have been born without tails. The process is banned as a cosmetic measure in the UK, except for working dogs used by the police and armed services.

However, Manx owners say that their breeding has not just caused them to lose their tails, but other feline characteristics, too. “A Manx cat will go for a walk with you,” says Goodwins. “Most cats hate water but Manx cats like swimming.”

It is not clear why they behave this way.

Goodwins’ personal theory is that the Manx genome was influenced by the introduction of Scandinavian cat breeds to the Isle of Man when Vikings arrived there over a millennium ago. Today’s Norwegian forest cats, which share some of the Manx’s doglike characteristics, are likely descended from cats that Vikings kept.

However, Lyons says that she is not aware of any genetic evidence that would back up Goodwins' idea.

“They’re not similar to one another [genetically], but they are similar to random bred cats,” she says. The Manx genome is like the Norwegian forest cat’s only in the sense that they are both highly diverse: if a cat has been bred from many different breeds, it will “match” with a Manx simply because the two share diverse genomes.

The Manx cat, then, may be an oddity but it reveals much about our attitudes towards domesticated animals. As our understanding of genetics has improved, so has our understanding of the Manx.

Whether it will be deemed ethical to preserve Manx mutations in the future is unclear. But the cat certainly has, against all the odds, survived and thrived, even far from its native shores.

For a humble islander without a tail, the Manx has – if nothing else – certainly travelled well.

This story is a part of BBC Britain – a series focused on exploring this extraordinary island, one story at a time. Readers outside of the UK can see every BBC Britain story by heading to the Britain homepage; you also can see our latest stories by following us on Facebook and Twitter.