“THE HIDDEN BOND OF CONNEXION”: COMMON DESCENT AS AN OBSTACLE TO TEACHING EVOLUTION TO COLLEGE UNDERGRADUATES

Charles Darwin presented two separate but related concepts in the Origin of Species. “Descent with modification” includes the idea that all life on Earth is genealogically related and the idea that life has changed over time. In teaching introductory geology and paleontology courses, given our area of expertise, we tend to emphasize concrete paleontological evidence for the concept of change over time. Our lectures are peppered with examples of evolutionary transitions documented by fossil intermediate forms. Arguments for common descent, such as homologous morphological and genetic structures, are often glossed over or assumed to be self-evident.

I have polled students taking my general education geology course, “Life Through Time”, over several semesters, both before we begin discussing evolution and at the end of the course. Even before we take up the subject of evolution, no students dispute the observation that organisms do change over time, though they might argue about the degree of change that is possible. However, when asked directly, the majority of students (52-74%) do not think that all life is genealogically related. Reasons for such skepticism include the conventional (e.g., differences between organisms are too large) and the novel (e.g., we diverged so long ago that we are no longer related, although we once were). The concept of common descent would appear to be a substantial obstacle to understanding evolution for most undergraduate students.

Anonymous pre- and post-topic polling shows that it is possible to improve student understanding of evolutionary concepts, for instance, that the fossil record provides evidence of change over time and that evolution is non-controversial within the scientific community. However, in its traditional format, the course has not been as successful in demonstrating the evidence that connects humans to other organisms. Indeed, few students substantially change their position on common misconceptions about evolution after taking the course, unless those misconceptions have been explicitly targeted with multiple lectures, assignments, and activities. By emphasizing and expanding on the arguments for common descent, students can substantially improve their understanding of evolution.