Because the native salmon

Answer choices

1. A

   Correct45% picked this

   Neither of the two populations of sockeyes has interbred with the

   Why this is right

   This rules out some OTHER WAY that their genetics would have changed. If the deep lake sockeye mated with the native salmon, then the result would be fish that have 1/2 sockeye genes, 1/2 native genes. If this were happening in the deep lake, but not the shallow lake, then 80 years later we'd see the deep lake sockeye have a different genetic makeup, since there would now be a lot of native salmon genes mixed into their [ahem] gene pool. This answer doesn't totally rule out interbreeding as the explanation for the genetic change (maybe some of the sockeye interbred with an animal other than the native salmon), but it's incredibly unlikely if not impossible that it happened with a different animal. Usually two species are defined as distinct because they can't interbreed. So salmon should only be able to interbreed with other salmon, one would think. If interbreeding didn't change the genetic makeup, then we're more likely to accept the author's explanation that adaptation changed the genetic makeup.

   Skill tested: Strengthen · how this choice captures the argument's function is the move to repeat next time.

   45%
2. B

   No Impact30% picked this

   When the native salmon in Lake Clearwater were numerous, they comprised two distinct populations that

   Citing a parallel between sockeye and native in terms of the fact that the deep lake crew doesn't associate with the shallow lake crew isn't doing anything for us in terms of ruling out an Alternate Explanation or boosting the plausibility of the Author's Explanation.

   30%
3. C

   No Impact10% picked this

   Most types of salmon that inhabit lakes spend part of the time in shallow water and

   We don't really care what most types of salmon do. The fact that most salmon would hang out in both parts of the lake, whereas sockeye are segregating themselves into two camps, doesn't rule out an Alternate Explanation for the genetic change nor does it help the Author's Explanation.

   10%
4. D

   Opposite (if anything)12% picked this

   One of the populations of sockeyes is virtually identical genetically to the sockeyes originally

   This answer potentially weakens, since the author's conclusion is that "each population has adapted genetically to its distinct habitat". This answer makes it seem like one of the two populations has not adapted genetically to its habitat. It sounds like their DNA is basically the same as when they were dumped there in 1940.

   12%
5. E

   No Impact3% picked this

   The total number of sockeye salmon in the lake is not as large as the number of native salmon

   The total number of fish in the lake doesn't help us assess the causal mystery behind why the two populations of sockeye now have different genetic makeups.

   3%