One evolutionary mystery of late has been wisdom teeth. For many people (myself included), there is not enough room for incoming widsom teeth, so they must be extracted. But why would humans have evolved with teeth that they don't need?
One perspective is discussed here. The premise is that invention of cooking and tools has allowed us to create soft food, and to consume it in bite-sized pieces. In essence, we no longer need to rip food apart with our teeth as we would have millions of years ago. Thus, the decreased muscular load on the jaw, especially in childhood, leads to a smaller facial size - one too small for all its teeth.
Another perspective is that of Weston A. Price, a pioneering dentist who studied the teeth and facial structure of various cultures across the world. Price believed that modern diets cause poor facial and jaw development. He wrote a book featuring hundreds of photographs of native populations with full faces and healthy teeth. These populations generally consumed natural foods and had little or none of the modern processed foods. More information about his ideas can be found here.