Because my anatomy course is for art students, its content is designed almost entirely around the human body's superficial structures-- mostly muscles and bony landmarks-- that dictate the external human form. But occasionally (well, OK, often) we go off on random tangents during which students asks about other anatomical structures or physiological processes. And I have to admit, these random questions are one of my favorite parts of the class.
One subject that comes up often is that of human vestigial anatomical structures. Vestigial structures are those that had a purpose in earlier evolutionary forms of ourselves, but now have little or no function. As evolution allows us, as a species, to slowly adapt to our environment and our circumstances, certain structures become unnecessary. With each generation these structures become slightly less prominent, until they are slowly phased out altogether. Our vestigial structures (and reflexes, for that matter) are those which still remain in some form but no longer serve much of a purpose. One example is our coccyx bone, which is the remains of what use to be caudal vertebrae, or bones of a tail.
Here is a nice summary of ten vestigial traits that still occur in humans today. Enjoy, and I will be back soon with a new posterior torso post as well as more news about my new project!