Because the native salmon in Lake Clearwater had nearly disappeared, sockeye salmon were introduced in 1940. After be...

Irina on August 17, 2019

@Minerva,

This is a strengthen question, meaning the correct answer choice will support the conclusion and the rest of the answer choices will weaken or have no impact on the validity of the conclusion. The argument tells us that a genetically uniform group of sockeye salmon split into two distinct populations that do not interbreed, one inhibiting deep areas of the lake and the other - shallow. The populations now differ genetically, so some researchers hypothesize that each has adapted genetically to its distinct habitat.

(A) Neither of the populations of sockeyes has interbred with the native salmon.

Correct. This fact tells us that the changes in the genetic makeup are not due to interbreeding with other species of salmon. Rejecting this alternative hypothesis strengthens our hypothesis that genetic changes are indeed due to adaptations to their new habitats.

(B) When the native salmon in Lake Clearwater were numerous, they comprised two distinct populations that did not interbreed.

Incorrect. This fact alone is insufficient to infer anything about the introduced salmon, it is equally plausible that the native populations did not interbreed because of their distinct habitat rather than differences in genetic make up, and in that case, this fact will weaken rather than strengthen the argument.

(C) Most types of salmon that inhabit lakes spend part of the time in shallow water and part in deeper water.

Incorrect. This statement is about other types of salmon not sockeye salmon in this particular lake and is thus irrelevant to the conclusion.

(D) One of the populations of sockeyes is virtually identical genetically to the sockeyes originally introduced in 1940.

Incorrect. This fact weakens the conclusion, if the population is genetically identical to the one originally introduced, it means no genetic adaptations occurred contrary to the hypothesis.

(E) The total number of sockeye salmon in the lake is not as large as the number of native salmon had been many years ago.

Incorrect. This fact is irrelevant, the argument is about the genetic makeup not the population size of the introduced salmon.

Does this make sense?

Let me know if you have any further questions.