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. Nonetheless, a group of self-proclaimed strict constructionist Darwinians has recently risen to prominence by reducing Darwin’s theory in just this way. These theorists use the mechanism of natural selection to explain all biological phenomena; they assert that natural selection is responsible for every aspect of every species’ form and behavior, and for the success or failure of species in general.
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. If the strict constructionists are right, the persistence of every attribute and the survival of every species are due to such adaptation. But in fact, nature provides numerous examples of attributes that are not adaptations for reproductive success and of species whose success or failure had little to do with their adaptations.
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 author would be most likely to agree with which one of the following statements?
(A) Natural selection is responsible for almost none of the characteristics of existing species.
(B) The fact that a species flourishes in a certain environment is not proof of its adaptation to that environment.
(C) Only evolutionary changes that provide some advantage to a species are transmitted to subsequent generations.
(D) Large animal species are generally unable to survive in harsh environmental conditions.
(E) Natural selection is useful for explaining the form but not the behavior of most species.
A. This answer overstates the author’s argument by implying that natural selection is responsible for no changes, which is stronger than the author’s actual point that natural selection isn’t responsible for all changes.
B. Correct. It aligns with the information in paragraph 4, which explains that mammals flourished after the asteroid strike despite not being adapted to the new environment, suggesting that not all evolutionary changes are driven by adaptation.
C. This contradicts the passage, specifically lines 29-31, which state that most changes do not have an inherent advantage or disadvantage, so this answer doesn’t reflect the author’s point accurately.
D. The passage distinguishes between "catastrophic" conditions and "harsh" conditions, so while large animals might struggle in catastrophic situations, the answer misinterprets the distinction between the two terms.
E. This answer is misleading because it references form and behavior without providing the context or distinction between them that the passage would likely offer, thus trying to trick you based on keywords that are not used correctly in this case.
