Question 125·Hard·Inferences
Archaeologist María R. Sánchez recently reexamined settlement layers in Mexico’s Tehuacán Valley. Earlier studies had proposed that the marked intensification of maize agriculture there about 4,000 years ago was a desperate response to increasing aridity. Sánchez’s team, however, measured oxygen-isotope ratios in speleothem (cave-stalagmite) samples that span the period and found that it was noticeably wetter than both earlier and later phases. Pollen counts from nearby lake sediments corroborate the wetter conditions, showing a surge in moisture-loving tree species. These findings suggest that _____
Which choice most logically completes the text?
For "Which choice most logically completes the text?" questions, paraphrase the setup and track how the new evidence affects the earlier claim. Here, decide whether the new climate data supports or weakens the drought-response explanation. Choose an answer that matches the passage’s limited implication (it wasn’t driven by declining rainfall) and avoid choices that introduce new causal mechanisms or claims about dating that the text never establishes.
Hints
Focus on the contrast
Look at what earlier studies proposed about maize agriculture and climate, and then see how Sánchez’s findings compare. Does the new evidence support or weaken the earlier idea?
Use the phrase "These findings suggest that"
Ask yourself: given that the period was wetter and moisture-loving trees increased, what broad conclusion about the reason for the surge in maize agriculture is most reasonable?
Watch out for new, unsupported topics
Eliminate any answer choices that bring in ideas not mentioned in the passage (for example, claims about precise dating errors or detailed social/ecological mechanisms that the text doesn’t state).
Stay within the passage’s scope
The passage only talks about one specific earlier explanation (response to aridity) and the new climate evidence. The correct answer should stick closely to that, not go beyond it.
Step-by-step Explanation
Restate the setup in your own words
Earlier researchers claimed that maize farming intensified about 4,000 years ago because the climate was getting drier, so people had to farm more as a "desperate response." Sánchez reexamined the evidence for climate at that time.
Identify what the new evidence shows
Sánchez’s team used oxygen-isotope ratios from stalagmites and pollen from lake sediments. Both lines of evidence point to the same thing: the time of intensified maize agriculture was wetter than both earlier and later periods, and moisture-loving trees increased.
Figure out how the new evidence affects the old explanation
If maize farming increased during a wetter period, then it probably was not a desperate reaction to increasing aridity (dryness). The new data undercut that original explanation, but they do not say exactly what did cause the change.
Match this logical conclusion to the best choice
We need a choice that says, in effect, "the intensification of maize agriculture likely wasn’t caused by declining rainfall," without introducing new, unsupported claims. The best match is: the surge in maize agriculture in the Tehuacán Valley was probably motivated by factors other than declining rainfall.