Hypotheses for ongoing evolution of muscles of the upper extremity.

There are organs and muscles in the human body that may be considered rudimentary in that they have insignificant or undetermined function. Several such muscles are found in the upper extremity. In this review, four muscles that appear to be undergoing evolutionary changes are discussed: flexor digitorum superficialis to the fifth finger, anconeus, palmaris longus, and anconeus epitrochlearis. The present study synthesizes, advances and extends previously described work about these muscles and extends the hypotheses and concludes that: (a) the flexor digitorum superficialis to the fifth finger is currently under adaptive evolution, (b) the anconeus has currently stabilized its evolution and is serving as a transient stability augmenter during a short portion of the human lifespan, and (c) the entire distal upper extremity is currently in the process of undergoing evolutionary change. Understanding of these muscles and their evolutionary context is important for understanding of impact on function, dysfunction, treatment and future research. Published by Elsevier Ltd.