Inigo Montoya: "I do not mean to pry, but you don't by any chance happen to have six fingers on your right hand?"
Man in Black: "Do you always begin conversations this way?"
In The Princess Bride (1987), a character named Inigo searches for a six-fingered man who had killed his father when he was a young boy. Although it is supposed to be comical, this variation is not as rare as one may think. In fact, according to the book, Endless Forms Most Beautiful by Sean B. Carroll, about 5 to 17 births out of 10,000 display this variation, known as polydactyly. Other well-known individuals who were born with polydactyly are Anne Boleyn, wife of King Henry VIII, and Antonio Alfonseca, a pitcher for the Marlins. However, it is important to note that this variation has a range of appearances including an extra flap or piece of skin on the side of the hand, individual bones, or duplication of the nail. This mutation has also been seen throughout many vertebrates including mice and chickens.
How might one obtain this variation? Commonly, polydactyly is either inherited or induced experimentally. In fact, scientists believe that there are similarities in the manner of developing this mutation between chickens and humans. However, most advances within this area were made when studying the fruit fly.
While Carroll terms these mutations as 'monsters' or 'mutants,' these variations have incredibly useful suggestions for the rules and process of development. This information can be used to describe the formation of all bodies and body parts of humans and other animals alike. By inducing experimental changes and observing the physical transformations in an organism, scientists are able to track certain genes and investigate how a change could lead to large (or no) effects in a structure.