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Biology 155: How would you evaluate these explanations of Darwin’s Ideas?

Unfortunately, even today there is considerable confusion about Darwin’s theory of natural selection and how it works. People often mis-state Darwin’s ideas in a teleological way, implying that organisms evolve certain traits because they need them. On the contrary, evolution doesn’t “care” what organisms need- those individuals that have traits that help them survive or reproduce pass on those traits. Those individuals that don’t have those traits die. As a result, we need to be careful about how we state our understanding of evolution and evolutionary theory.

To test understanding of Darwin’s ideas, this question was included on an exam:

Four student answers to the question are given. Based on what you know about Darwinian evolution and natural selection, evaluate and grade how well each answer represents Darwin’s ideas. For any answer that does not receive full credit (4 points) be sure to indicate why points were lost.

Student 1. Darwin saw that populations increased faster than the ability of the land to support them could increase, so that individuals must struggle for limited resources. He proposed that individuals with some inborn advantage over others would have a better chance of surviving and reproducing offspring and so be naturally selected. As time passes, these advantageous characteristics accumulate and change the species into a new species.

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Student 2. Darwin’s theory of evolution explains how new species arise from already existing ones. In his mechanism of natural selection, organisms with favorable traits tend to survive and reproduce more successfully, while those that lack the traits do not. Beneficial traits are passed on to future generations in this manner, and a new species will be created in the end!

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Student 3. Descent with modification using natural selection was Darwin’s attempt at explaining evolution. An organism is modified by its surroundings, activities, and lifestyle so that it evolves traits that it requires to be successful in its environment.. These modifications, by natural selection, make the organism better suited to its life.

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Student 4. Darwin’s theory states that organisms can become modified by environmental conditions or use or disuse of features and that the modifications can be passed on to succeeding generations. He proposes that nature selects for a characteristic that would be beneficial to the survival of the organisms and that organisms would pass on this trait.

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