October 2011 LSAT Section 4 Question 19
It can be inferred that the author of passage B would regard which one of the following as a mistaken assumption unde...
Replies

on May 5, 2020
Hello @NK848,I would refrain from using sufficient and necessary diagrams for passage A. Having said that, it is perfectly fine if you want to make a note to remind yourself of the relationship between replicating genes and altruistic behavior. I just want you to understand that this is not a sufficient/necessary relationship.
Your diagram, IRG ==> AB, states that interest in replicating genes guarantees altruistic behavior. Every time there is such an interest, altruistic behavior follows. This is too strong for what the passage says. Author A is simply proposing a theory to explain altruistic behavior.
Very rarely will I make sufficient and necessary diagrams on the reading comprehension section, but Passage B might be an exception. Your understanding of Author B's argument makes sense. She is saying we can only conclude that interest in replicating genes is the cause of altruism only if:
AB ---> IRG
However, the author argues that this is not the case. Therefore, we cannot conclude that interest in replicating genes causes altruism. Maybe altruism exists for its own sake.
In short, I would not use sufficient and necessary diagrams for "A explains B" or "B is caused by A." Look for your standard sufficient and necessary indicators like "only" or "always."
If your example said, "B is only caused by A," I would write B ---> A.
or
"A always causes B." A ---> B
on May 7, 2020
Thank you! I was trapped by the "only if" but your explanation makes sense.