Field of Science

Six digit cat

Today a very affectionate cat walked up to my son and me as we were walking back from basketball practice. He wanted a lot of attention, and I noticed he had very peculiar front paws.

He really wanted some company, so my son and I obliged.

As I took a closer look, I realized he had six claws on each front paw. Looked like double thumbs. Nice!

I ran inside and got my camera, and tried to take some pictures for documentation, but they weren't good enough to show the six digits. I then held up his paws pretty firmly. He was good enough not to put his claws in my flesh, even though he clearly didn't much care to be constrained like that. I think he understood that this was a very important scientific investigation. No anthropomorphism here, I swear.

Click images to enlarge in order to see both claws on the thumb.

So why does he have six digits? Well, it could be a developmental "defect", even though I hesitate to even call it a defect - he was clearly doing very well, and my fitness assay was inconclusive (I didn't see any offspring). In that case, his kittens wouldn't have six. More interesting, if was a genetic "defect", then it could be heritable. Wouldn't that be cool? With some human artificial selection, the trait might even become established (i.e., appear in non-vanishing numbers, without going to fixation, i.e., the whole population sharing the trait). I hope he already had offspring, because he looked neutered, the poor thing. If true, that would be a real waste.


  1. Here's some evidence that polydactyly is inherited.

  2. So, apparently this is quite common. This wiki page has lots of photos, and explains that the trait is genetically inherited, and that the gene responsible is called Pd (for polydactyl).

    The trait is autosomal dominant with complete penetrance (for the buffs).

  3. yep,

    this is normally caused by what is called a homeotic transformation. Something existing becomes repeated, or somehow reitterated. Could also have something to do with broken polarity with the "anlage". Check out Drosophila and homeosis, there a tons of similar phenotypes from antenapedia, over wingless, to eyes in the antennas. Insects appeat to be way more modular in terms of development than vertebrates.
    Cheers Arend

  4. Polydactyly runs in many breeds. I own a polydactyl Pixie Bob -- double dew claws (ie. "thumbs") on the front paws, and single dew claws on the rear (normally absent). By coincidence, we had him in for a checkup the other day, and there was another poly in the waiting room. I have seen and handled a kitten with *triple* dew claws on the front -- it looked like he had a small auxiliary paw, with pad and three toes, sticking out the side of his leg.

  5. I'd agree calling it a "defect" may be off. Years ago my brother had a poly cat (extra digit on each paw) named Zeke and with the extra dew claw his front paws were like a baseball glove and he got quite adept at catching things 'one-pawed' among his digits and picking things up with them even if he couldn't penetrate them with his claws. Zeke was also able to cling, upside down, to the roof of a cage made of chickenwire. Unfortunately for science but fortunately for the habitability of my Mom's house, Zeke was neutered.

  6. Of course, polydactyly exists in humans too (who can forget the six-fingered man "who killed my father, prepare to die!"). But did you know that a genetic change can also cause a loss of digits in an otherwise perfectly looking human hand? Steen Rasmussen's son has two hands like that, and you really have to count in order to notice it. Now, of course, our non-believing friends tell us that mutations can never give rise to big adaptive changes. Why don't these mutations convince them?

  7. My son's cat has paws like that - like giant oven mitts. Thanks for the post - a very cooperative cat, I'd say.


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