Hey Osirus,
Glad to hear you're making progress with the Reading Comp book! I love that lesson. For anyone else following along, this question appears on page 160 of that book.
Good question on the Critical Reasoning style RC questions. These are interesting, as they blend the nature of a specific detail RC question (you need to know where to look to refresh the pertinent information) and a Critical Reasoning question (your logic is being tested over and above just your "reading comprehension" of the passage itself). I'd look at it, then, as a question in two parts:
1) First you need to refresh yourself on the detail or theory that is being questioned. Treat this like a Specific Detail question - if you use your mental outline of the organization of the passage to determine where that theory is being discussed, you can go back to make sure you're aware of the theory. (side note - I'd argue that most CR-style RC questions will ask you to strengthen or weaken a theory, so that's usually what you're looking for) Here, you nailed it with your description - I'd also add that the first paragraph of the passage is the one that breaks out the two theories - replacement (which is the one in question) and independent evolution.
2) Then think about the question itself, once you've identified the conclusion that you're weakening. Here, you're weakening the replacement theory. Well, one of the best ways to weaken one theory would be to strengthen the opposite theory, and answer choice B does just that - it gives support to independent evolution, which has already been juxtaposed with the replacement theory in the initial paragraph as the "other" theory. By strengthening the opposite theory, choice B weakens the replacement theory.
Overall, I'd look at these CR-based RC questions as acts in two parts. Your first job is to find and process the theory in question, then you can take it as a straight CR question from there. If you're noting within each paragraph what the purpose of each is, you'll pretty quickly be able to go back and find the theory you need.
Brian Galvin
GMAT Instructor
Chief Academic Officer
Veritas Prep
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