SAT Bio question on evolution

Test Preparation SAT Subject Test Preparation
1

<li>All of the following contribute to variation in a population EXCEPT
(A) mutation
(B) isolation
(C) sexual reproduction
(D) conjugation
(E) genetic drift</li>
</ol>

<p>The correct answer is (B) isolation…however I put (E) genetic drift. I know that drift refers to a change in the frequencies of a gene pool, but the reason why I steered away from isolation was because of founder effect. I guess this question rather refers to isolation of a population (so no alleles go in and out)?</p>

<p>Would I expect to see something on the test trickily worded like this? </p>

<li>Scientists believe that the giraffe originally had a short neck that has grown longer over time. The most likely explanation of this is which of the following?
I. Natural selection
II. Adaptive radiation
III. Divergent evolution</li>
</ol>

<p>(A) I only
(B) I and II only
(C) I and III only
(D) II and III only
(E) I, II and III</p>

<p>Correct answer is A, though I put C. Actually, I really don’t know why it can’t be adaptive radiation or divergent evolution? Some definitions of adaptive radiation say “development of new species to fill ecological niches” — obviously the giraffes with long necks are filling the tall tree niche. Other definitions specify that its rapid only…so that would rule it out i guess? Divergent evolution is when two populations of same species end up having different traits - well technically dont two populations emerge (a short neck and a long neck one) and the short neck one just died out?</p>

<p>These are from Barrons Test 1 btw.</p>

2

<p>the first question:
isolation is also taken as geographic isolation thus formation of different species.
so there would be variation with respect to the original population of the species.
genetic drift results in the change in the genetic pool.
so there is variation.
hence isolation is the correct answer.</p>

<p>well for the second question:
adaptive revolution occurs when individuals of a single species develop a slightly different characteristic to occupy different ecological niches.
but that isnt the case with respect 2 the giraffes.
unlike the finches on the Galapagos Islands we dont find giraffes of different ypes( here with respect 2 their necks)
so only natural selection is the correct option.</p>