I was just taking a test in which there was a question that I found very dubious:

"50 people from USA move to a remote island. Which of the following causes the largest change in frequencies of alleles:

Natural selection or Genetic drift?"

 

Doesn't it really depend on whether the conditions are particularly harsh on the island or not? Making natural selection more likely the harsher the conditions?

 

The short answer is that you're right, and it would depend. The long answer is that this applies to the vast majority of similar test questions and you have to assume any details not given aren't especially important. It's one of the assumptions you have to make in order to take most tests. The goal of the test question is not to teach you the information but to make sure you understand it.

 

In this case, most people who understand the relationship between genetic drift and population size will realize what the question is asking and will get the right answer. This means the question works as a test of knowledge, even if it doesn't cover every possible outlier scenario.