As all good teachers know, students will work much harder for extra-credit points than at the assigned task. I like to take advantage of this convenient trait in my introductory course on evolution. Once my students — nonscience majors at a midwestern land-grant university — understand the basic terms, I offer additional points for answering the questions I really want them to investigate. Find a dozen differences between the skeletons of a chimpanzee and a human being, I challenge them; tell me how a human female skeleton differs anatomically from a male.
The male and female skeletons I display are exemplary in their difference, and since most students should be able to guess what that difference is if they don’t already know, I usually feel confident that the final answer is a giveaway. I say usually because seven years ago, the first time I taught the course, I got a surprising answer that still crops up with alarming regularity. Five minutes into the lab period, a young woman announced that she could answer the question without even examining the human skeletons.
I waited silently for her to explain that the female pelvis is shaped slightly differently from the male’s, with a larger opening for childbearing. That part was the giveaway. The real purpose of the exercise was to make her prove her conjecture with measurements — to translate the theory to practice. I also wanted her to explain why this sexual dimorphism — that is, this sexually determined physical difference — is not nearly so pronounced in nonhuman primates, such as chimpanzees.
She spoke: Males have one fewer pair of ribs than females.
I was totally unprepared for her answer. My mandible dropped. After a moment’s reflection, I realized she must be referring to the biblical story in which God creates Eve from one of Adam’s ribs. My student was someone who believed in the literal truth of the Bible, and it was her religious belief, not her previous knowledge of human anatomy, that made her so sure of her answer. This was going to be a challenge.
