June 24, 2021

I, Science

The science magazine of Imperial College

Welcome to The Dog & Pony Show! Let’s talk about cats.

Not all cats are created equal. A couple of days ago, the BBC posted an article about a pair of polydactyl kittens. (If you’re wildly picturing a chimera of cat and pterosaur, you’ve headed off in the wrong direction. Come back.) Polydactyly is an anatomical anomaly in which a hand or foot (or paw) has more than the usual number of digits – which is of course five for humans, but five on the front feet, including the dewclaw, and only four on the back for cats. Occasionally, the extra digits can form an entire sub-paw.

Polydactyly appears to be both a relatively common condition in cats – or at least certain breeds of cat – and a relatively common source of news for the BBC: links to two other stories about cats with supernumerary toes accompany the latest post. This week’s kittens, Ned and Fred, have an extra eight and 10 toes, respectively. Last month an entrepreneurial cat named Daniel, from Wisconsin, USA, put his 28 toes to good use by getting people to donate a dollar per toe in a fundraiser for a local animal rescue centre.

Henry VIII’s second wife, Anne Boleyn, is rumoured to have had an extra digit. But this is probably due to an unflattering description written 50 years after her death by the C16th propagandist Nicholas Sanders, a man as influential as he was unreliable: “It is said she had a projecting tooth under the upper lip, and on her right hand six fingers. There was a large wen under her chin, and therefore to hide its ugliness she wore a high dress covering her throat”. Sanders does not paint a pretty picture.

In cats though, an extra toe on each front foot often gives the cute impression of thumbs – as with this adorable little gremlin – and there are many polydactyl-cat enthusiasts. Ernest Hemingway was a fan and his former home in Florida is now a museum of sorts and home to about 50 cats, half of which are polydactyl and all descended from cats belonging to the writer. Indeed, polydactyl cats are occasionally referred to as ‘Hemingway cats’.

As Hemingway’s legacy suggests, though polydactyly can occur by itself, it more commonly appears as a congenital anomaly, inherited as an autosomal single dominant trait of the Pd gene. This, and the observation that the east coast of North America centred around Boston has an especially high proportion of polydactyl cats, has led to the idea that most, if not all, of these cats are descendants of extra-toed cats brought over on ships from the UK – apparently because they were considered lucky by sailors. (In other parts of Europe, polydactyl cats were largely wiped out – apparently because they were considered unlucky by everyone else.)

The Straight Dope tells me that an article in Cornell University’s Cat Watch in 1998 looked at studies that suggested the polydactyl trait may indeed be traceable to cats arriving in Boston by ship. But we’ll have to set that against a 2008 study by geneticists who found that the polydactyly in the cats they looked at in the US and in the UK can be caused by different genetic mutations, suggesting that the extra toes originated in more than one place independently.

Whatever its origin, polydactyl cats are now being bred in the US to preserve the trait. Once barred from cat shows, breeds such as the Polydactyl Maine Coon are now recognised by TICA (The International Cat Association) and a New Traits class introduced to official shows to cater for them. To get a polydactyl kitten you just need one of the parents to carry the trait, making it relatively easy to select for. The only problem for the cat – except in extreme cases, where too many toes can impair mobility – is that untrimmed extra claws might twist and dig into the skin. Odd as a six-toed cat may sound, it’s certainly no stranger than selecting for squashed noses or baldness.

Image: flickr | pumbamama