Polydactyly was and still is a common trait in the Maine Coon breed. The word polydactyly derives from the Greek word polydaktylos (poli = very, many, daktylos = finger) and describes the physical anomaly in man and animals with more fingers than the wild type of the given species. The polydactyl Maine Coon originally contributed much of the gene pool (40% according to The FIFe Breed Council MCO and Henning Mueller-Rech, 2011/2012), and consequently polydactyls are part of the pedigree of most Maine Coon cats of today. But the disqualification from the shows led to the exclusion of many polydactyl Maine Coons from reproduction. Polydactyly is inherited as an autosomal dominant trait with high penetrance (Danforth 1947; Lettice et al. 2008, Hamelin 2011), and can therefore be easily selected in breeding. Polydactyly is not found only in Maine Coon cats. It is common in cats along the east coast of North America (the United States and Canada) and also in England. Lloyd (1985) examined over 5000 cats in 35 populations in eastern Canada and the northeastern United States and found that 0-8% of the cats in these different populations were polydactyls. The famous author Ernest Hemingway had nearly 200 cats who lived with him between his two houses in Key West, Florida and Cuba, many of them six-fingered polydactyls. Today 40-50 descendants of these cats still live in the Hemingway home and museum in Key West.
Polydactyly poses no problem for the well-being of the cat (Lange et al. 2014, Hamelin et al. 2017) and should be considered an innocent phenotypic variant of the breed. In general, polydactyly is not a handicap and does not cause negative effects in cats. Except in rare cases it can be affected by nail growth. The large legs of polydactyl Maine Coons are often compared to snowshoes and some claim that they facilitate walking on snow. The large legs are also designed to help the cat climb and hunt more efficiently. Today polydactyl Maine Coons can be bred and registered within CFA, New Zealand Cat Fancy Inc. (NZCF), The International Cat Association (TICA) and Cat Fanciers's Federation (CFF). The NZCF was the first to accept polonactyl Maine Coon cats in the show ring, making it eligible for championship status alongside the traditional Maine Coons (January 2009) (PolyTrack Newsletter 2009). TICA has followed this example and has accepted polydactyl Maine Coons for the championship since May 2015 (TICA web page). FIFe has gone in the opposite direction and recently (January 2014) banned the breeding and registration of polydactyl Maine Coons.