SAT Reading and Writing: Chelonibia Barnacles Transition
A hard Digital SAT transition question about Chelonibia testudinaria barnacles. Pick the transition that signals the new research undermines the prior passive-displacement explanation.
Question
Long thought to be sessile (immobile), adult Chelonibia testudinaria, barnacles that adhere to sea turtle shells, have been observed to shift slightly in position over time—a phenomenon that has been attributed to the barnacles’ passive displacement by water currents. ______ a research team found that adult C. testudinaria moved toward the heads of their sea turtle hosts and thus against the prevailing water flow, behavior consistent with self-initiated locomotion.
Which choice completes the text with the most logical transition?
Step-by-Step Solution
Distinguish the phenomenon from the explanation, then match the transition.
1Track what the passage actually claims.
Sentence 1 offers one specific explanation for why the barnacles shift over time: passive displacement by water currents.
Sentence 2 reports the research team’s finding: the barnacles moved against the prevailing water flow, in a way consistent with self-initiated locomotion.
Moving against the current is not what passive displacement would produce. The new evidence therefore weakens — does not support — the explanation given in sentence 1.
2Separate the phenomenon from the explanation.
The phenomenon is the observed shifting in position. That part is real and not in dispute — the research team observed the shifting too.
The explanation is the proposed cause: passive displacement. That is what the new evidence challenges.
Whichever transition you pick has to operate on the explanation, not on the phenomenon.
3Test each transition against that relationship.
A. “Confirming this hypothesis” reverses the logic — the research disproves the hypothesis, it does not confirm it.
B. “Undermining this explanation” precisely names what the evidence does. It targets the explanation, and weakens it.
C. “Drawing a similar conclusion” suggests the new finding agrees with the prior reasoning. It does the opposite.
D. “Contrary to this phenomenon” sounds like a contrast, but the phrase “this phenomenon” points at the shifting itself — and the research confirms the shifting. It is contrary to the explanation, not to the phenomenon.
4Choose B and read the sentence back to confirm.
“Undermining this explanation, a research team found that adult C. testudinaria moved toward the heads of their sea turtle hosts and thus against the prevailing water flow…”
The transition correctly signals that the upcoming evidence weakens the passive-displacement explanation. The answer is B.