Splotchy Cats Show Why It’s Better to Be Female

If you’ve never really noticed the wide range of colors that can adorn the domestic cat, you might want to spend some time skimming through the official color charts of the Cat Fanciers Association website. According to the association, which claims to maintain the largest registry of pedigreed cats, cats can come in seal lynx and mackerel tabby, chinchilla silver and cream smoke, blue-patched and blue point. There are mitted cats and van cats, as well as more obvious cats that you might actually be able to picture in your mind, like “green-eyed white.” (Here is a very detailed poster showing much of the complexity in distinguishing breeds.)

This Crayola box of fur is enabled by just a handful of genes, leveraged by a long history of human breeders obsessed with getting the rarest or most beautiful or most striking combinations. But in that world of cat possibility, perhaps the strangest and most interesting of all is the common calico cat. All calicos (and all tortoiseshells) have blotches of black and orange fur. They are also almost always female. The reason why has to do with a genetic phenomenon that gets down to the very roots of what it means to be female.

It was only a bit more than a hundred years ago that biologists realized that