On rare occasions, humans are born with tails — real functioning tails that can even be “wagged” via voluntary muscles contractions in response to emotional stimuli. Although the birth of a baby with a tail is frightening for parents and typically requires surgery, the remarkable human tail is an important part of the even more remarkable tale of our origins—namely evolution.
Human tails are part of the evolutionary baggage that we carry in our bodies, leftover from our ancestors. As we evolved through time, responding to different environmental pressures, natural selection pruned and edited, making our ancestors better at some things—like talking—while ignoring skills and characteristics that became less relevant in new contexts—like smelling. Unfortunately, natural selection has no mechanism to eliminate useless features, but traits that become irrelevant can atrophy or get co-opted for some other task since there is no longer a disadvantage when those features show up in a weakened form.
Originally posted on The Daily Beast on June 1, 2014.