Without a doubt, humans, chimpanzees, and other organisms share similar features. An early explanation was that these features reflect similar designs because they serve similar purposes. Then evolutionary theory hypothesized that similar features were explained by (and are evidence for) descent from a common ancestor. Which explanation matches the evidence?

A nurse who worked with me would pleasantly call in patients by saying, “Mr._____, it’s checkup time!” Periodic checkups are good. As an Air Force physician taking care of combat pilots, I cared about all areas of their health—including their marriages.