First, the extra digit does not provide a functional advantage. The digits are rarely fully formed or fully functional. Second, the extra digits can cause problems with daily activities. The digits can get in the way of the other fingers as there may be deviation of the extra digit. And, in addition, the extra digit can tether or cause deviation of the larger, more normal digit. So the extra digit likely does not help function and may actually make it worse.
The extra toes cause the additional problem of interfering with shoe wear. The extra toes widen the foot and can change loading patterns with walking or running. While this can be addressed with especially wide shoes, removal of the extra toe may be a more straightforward solution. Extra fingers cause a similar although less problematic issue- glove wear. Clearly, wearing gloves may be a challenge or may not be possible with an extra digit. However, given that in most places, shoes are typically worn and gloves are more optional, this is less of a problem for most patients.
|Polydactyly of the feet with deviation of the extra toes.|
There are also social considerations with the extra digits. The extra digits certainly look different and may be noticeable in public. Interestingly, a missing pinky is typically less noticeable than an extra pinky. There have been multiple studies on appearance and hand differences. One such study, whose lead author was Ann Nachemson, found that children with milder birth differences of the hand, such as patients with extra digits, had worse social interaction scores compared to more severely affected kids and 'normal' kids- see citation HERE. Another study showed that overall health related quality of life measures in children with limb reduction deficiencies were better than kids with other health conditions. However, 'unexpected attention and perceived physical appearance' affected scores. Citation.
Recently, there have been a few newsworthy reports regarding extra digits in the ancient world. The first is a white paper by Richard D. Barnett on "Polydactylism in the Ancient World". This PAPER reviews some interesting findings on polydactyly from centuries ago including the importance of which side was affected.
In addition, there are recent findings from Chaco Canyon, New Mexico from Pueblo culture. This National Geographic ARTICLE reviews the findings. "The findings, published today in American Antiquity, indicate that the society did not view six-toed individuals as supernatural, but this form of polydactyly did grant them exalted status in life and in death. 'We found that people with six toes, especially, were common and seemed to be associated with important ritual structures and high-status objects like turquoise,' says Crown, who is also a past National Geographic grantee."
Charles A. Goldfarb, MD
My Bio at Washington University