Confronting Student Misconceptions
in a Large Class - by Dan Udovic
Small group evolution handout
Listed below are several answers to the following question, taken from student answers on a past exam. For each response, indicate whether you think an evolutionary biologist would agree with it, and if not, why not.
QUESTION: Fossil evidence suggests that the ancestor of the modern-day bat resembled a shrew or mouse and could not fly. How can the evolution of bat wings from the paws of shrew-like ancestors be explained?
- Bats would be better adapted if they had wings, so gradually they developed them. Bats in each generation had better wings than their parents did.
PROBLEM: Lamarckian, goal-directed. Sounds like bats developed wings because they "wanted" or "needed" them (Lamarck's internal will (note: this is the instructor's annotation, it would not appear on the students' sheets).
- Because the environment of the shrew-like ancestors favored gliding or flying, mutant individuals arose that were able to glide. Selection favored these individuals, and eventually all of them could glide. Repeating this process led ultimately to modern day bats.
PROBLEM: Changes are not induced by the environment. Mutations are independent of selection pressures. Does this mean that selection is "random"? NO! Otherwise, this answer is close to satisfactory. It does describe the process of natural selection (differential survival and reproduction), and does describe how cumulative selection could lead to the evolution of a complex trait.
- The existence of structures as complex as a bat wing can not be explained by traditional evolutionary theory because structures like these are too complex to arise by chance.
PROBLEM: Assumption is that because there is no intelligent designer, that the process is solely "chance". Apply the same logic to motion of the planets. What is the probability that the Earth's motion, by chance, would form such a perfect and consistent ellipse around the sun? Ignores the power of cumulative selection.
- Because the shrew-like ancestors of bats needed to fly to catch food, nature allowed them to develop the ability to fly better and they turned into bats.
PROBLEM: Need does not direct change. If it did, then wouldn't nature always allow change that prevents extinction. What does it mean to say "Nature allowed"?
- The bat evolved wings in order to make it easier to catch its prey.
PROBLEM: Evolution is not goal-oriented. Who is "the bat", and is it capable of making conscious decisions about the future of the species? This statement just ignores the whole issue by not defining what "evolve" means. Is it like going to the grocery store to pick up some wings?
- The shrew-like ancestors of bats kept stretching the skin and arms while jumping from tree branch to tree branch because that would help them glide better and jump farther. Gradually, through continued use of their arms in this way, they developed into wings.
PROBLEM: Lamarckian inheritance of acquired traits, use and disuse of parts. Discussion in class indicates this statement may just be too vague. From one point of view, a Darwinian might agree with it, from a different point of view, a Lamarckian might also.
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