The trait of polydactyl (also known as supernumerary fingers) is an inherited trait and these occurrences have been carefully documented for centuries. Some extreme cases include: an instance of 13 fingers on each hand and 12 toes on each foot, an infant at the Htel-Dieu in Paris in 1687 which had 40 digits, ten on each member, a woman who had six fingers and two thumbs on each hand, and another who had eight toes on one foot.
The Foldi family (pictured above) was first written of in the 1896 publication Anomalies and Curiosities of Medicine. The family of Foldi, part of the Hyabites tribe living in Arabia, confine their marriages to their tribe and they all have 24 digits.
The inhabitants of the village of Eycaux in France, at the end of the last century, had nearly all supernumerary digits either on thier hands or feet. Being isolated in an inaccessible and mountainous region, they had intermarried for many years and perpetuated the anomaly.
It is surprising that the trait of extra digits is not all that uncommon. In fact, it is estimated that about one in three thousand Europeans are born with an extra finger or toe.
The trait is even more common in Africa, with about one in three hundred displaying the trait.
The French mathematician Pierre Louis Moreau de Maupertuis (1968-1758) wrote about a doctor he knew named Jacob Ruhe who not only had six fingers and toes – but so did his most of his family including his grandmother, three siblings and two of his children. The Russian Geneticist E.O. Manoiloff published a paper in 1931 on one Viaceslav Michailovic de Camio Scipion who was able to document his multi-digit lineage back over six centuries.