Charles Darwin objected to all attempts to reduce his theory of evolution to its doctrine of natural selection. "Natural selection has been the main but not the exclusive means of modification," he declared. …
Natural selection is generally held to result in adaptation, the shaping of an organism's form and behavior in response to environmental conditions to achieve enhanced reproductive success. …
For example, while it is true that some random mutations of genetic material produce attributes that enhance reproductive success and are thus favored by natural selection, and others produce harmful attributes that are weeded out, we now know from population genetics that most mutations fall into neither category. Research has revealed that neutral, nonadaptive changes account to a large extent for the evolution of DNA. Most substitutions of one unit of DNA for another within a population have no effect on reproductive success. These alterations often change the attributes of species, but their persistence from one generation to the next is not explainable by natural selection.
Additionally, the study of mass extinctions in paleontology has undermined the strict constructionist claim that natural selection can account for every species' success or failure. The extinction of the dinosaurs some 65 million years ago was probably caused by the impact of an extraterrestrial body. Smaller animal species are generally better able to survive the catastrophic changes in climate that we would expect to follow from such an impact, and mammals in the Cretaceous period were quite small because they could not compete on the large scale of the dominant dinosaurs. But while this scenario explains why dinosaurs died off and mammals fared relatively well, it does not conform to the strict constructionist view of the adaptive reasons for the success of species. For that view assumes that adaptations are a response to conditions that are already in place at the time the adaptations occur, and mammals could not have adapted in advance to conditions caused by the impact. In a sense, their success was the result of dumb luck.
The primary purpose of the passage is to
argue in favor of a recently proposed hypothesis
There is no “recently proposed hypothesis” that the author supports. Instead, she refutes the strict constructionists’ view.
summarize a contemporary debate
The author doesn’t merely summarize a debate between groups. Instead, she refutes the strict constructionists’ view, providing evidence to prove that they’re wrong.
demonstrate that a particular view is incorrect
The strict constructionists believe that natural selection explains all biological phenomena. The purpose of the passage is to demonstrate that
criticize the proponents of a traditional theory
The author criticizes a theory. But the strict constructionists have “recently risen to prominence;” they’re not proponents of a traditional theory.
explain why a particular theory is gaining popularity
The strict constructionists have “recently risen to prominence.” But the purpose of the passage is to disprove their theory, not to explain its popularity.
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