Polydactyly (or polydactylism) is a scientific term for having extra digits (fingers or toes) beyond the number than is considered normal for the majority of the population. Extra toes are not always present in the same number on both feet or among individuals; this irregularity has caused some concern about the genetic fitness of this trait and its impact within a population. Polydactyly has been found in mammals (including humans), birds and reptiles. Few examples are found in the wild, but they do occur.
Some people view any structural difference as a “flaw” and therefor undesirable. Show standards are influenced by what people expect to see in an animal. Enthusiasts don’t want to reproduce such a disqualifying flaw in their breeding stock. We aren’t there yet with crested geckos or any other reptiles. However, most of us strive to breed for the nicest-looking geckos and to some, and an extra toe is just plain weird.
There is a lot of misunderstanding around these extra toes. Some see anything like this as a suspicious product of inbreeding. Through a bit of research, we believe that the forms of polydactyly seen in crested geckos are really just a random mutation that, while heritable, is not a reflection of inbreeding. Keepers are breeding thousands of these geckos a year, and mutations are bound to appear more often. That doesn’t necessarily mean that the rate of occurrence is changing. However, because there is a strong genetic link that is heritable, we do understand the caution many breeders feel regarding this trait.