Polydactyly – the presence of extra fingers and toes – is especially common in cats. And it’s all thanks to Ernest Hemingway and Sonic the Hedgehog.
Most cats have five toes on each front paw and four toes on each rear paw, for a total of 18 toes. Polydactyl cats have more: the record is 28 toes total. That’s a lot of toes! (The human with the most toes, born in India in 2010, had a measly 20 toes in all.)
Ernest Hemingway was a big fan of polydactyl cats and actually collected them. About fifty descendants of those cats still live in a former house of his in Florida. According to Wikipedia, fully half of those cats have excess toes.
Where does feline polydactyly come from? Well, it’s all thanks to a mutation in a gene that regulates the gene Shh. Shh is crucial for animal growth: the protein encoded by Shh influences brain structure and development, as well as teeth, lungs, arms, legs, fingers, toes, and a whole bunch more. Problems with this gene can also cause embryos to develop many little bumps, making them look a little like a baby hedgehog… and so the protein produced by Shh is known as Sonic hedgehog.
I’m not even kidding – that’s its actual official scientific name. There are a few equally odd protein names out there, including one named after Pikachu, but maybe that’s a post for another time.