The author takes issue with a researcher's claim that humans are "innately aggressive." To undermine this claim, the author relies on the researcher's own evidence that certain peoples have been aggressive in the past but are currently peaceable. Based on this evidence, the author explains that our genes must only code for the potential for aggression, not aggression itself—otherwise it would be impossible for these peoples to be peaceable at any time. The author then uses this to dispute the researcher's use of the word "innate": according to the author, if "innate" can include behavior that is merely possible, then everything we do would be "innate" and the word would be meaningless.

We know that the author is seeking to weaken the researcher's claim. To do so, the author uses the researcher's own evidence to infer that the researcher's use of the word "innate" relies on a definition so broad as to be meaningless.

However, it's important to note that the correct answer might not line up exactly with this assessment of the argument. The correct answer might describe only part of the reasoning, or might be more or less abstract. The best way to be sure is to carefully check each element of a possible answer. If any part of an answer choice is wrong, that's enough to eliminate.