No one has a firm grasp as to why the middle finger, the impedicus, is the longest finger on each hand.
This Latin word, in translation, means impudent, bold, and immodest, but points us in the wrong direction in solving this mystery, as the name, and the lewd（下流的） gestures commonly made with this finger, in no way explain its length.
The impedicus itself has a Latin name for being the longest, which is mesaxonic, meaning middle axis. Mesaxonic lends a little more assistance in the quest for an explanation for the middle finger's length.
Evolutionary physiologists cling to the symmetry theory, based upon their studies of the evolutionary reasons for the inner workings of animals' bodies. Experts in this field hold that the longer third finger is most likely a vestige of our ancestors' paws, and state the need for balance as the primary reason for its length.
Their esteemed colleagues, evolutionary morphologists（形态学者）, who study the evolutionary aspects of the shape and of the structures of bodies, also adhere to the theory of symmetry, but tack an additional aspect onto this theory, one they refer to as the "geometry of closing." The geometry of closing is merely scientific jargon for the fact that when the hand closes to form a fist, all fingers touch the palm of the hand at the same time. This way, when they grasp an object, they all share the work equally. Simply put, the fingers on our hands differ in length, because this particular shape works so well, and has done so for millions of years.
Anthropologists, in general, disagree with the balancing act behind the theory of symmetry. Their underlying reason for disputing this theory is that, in their studies of human evolution, they have encountered other primates, man's closest, hairiest relatives, who have longer fourth fingers. Anthropologists, however, do not pose a counter theory to the most commonly held one. Until they do, the theory of symmetry wins hands down!
