Number and Origin of Clamshell Tools Found at Different Levels Below the Surface in Neanderthal Cave
| Depth of tools found below surface in cave (meters) | Tools made from clamshells that Neanderthals collected from the beach | Tools made from clamshells that Neanderthals harvested from the seafloor |
|---|---|---|
| 2–3 | 7 | 0 |
| 3–4 | 99 | 33 |
| 4–5 | 2 | 0 |
| 5–6 | 18 | 7 |
| 6–7 | 1 | 0 |
Studying tools unearthed at a cave site on the western coast of Italy, archaeologist Paola Villa and colleagues determined that prehistoric Neanderthal groups fashioned tools from shells of clams that they harvested from the seafloor while wading or diving or that washed up on the beach. Clamshells become thin and eroded as they wash up on the beach, while those on the seafloor are smooth and sturdy, so the research team suspects that Neanderthals prized tools made with seafloor shells. Although the number of tools varies sharply among depth intervals, the team concluded that seafloor-shell tools were relatively scarce in every layer containing both tool types, supporting the idea that seafloor shells were more challenging to obtain, noting that ______
Which choice most effectively uses data from the table to support the research team’s conclusion?
For table-based command-of-evidence questions, translate every scope word in the claim—such as “each,” “overall,” or “among”—into a specific comparison. Then verify both the numerator and denominator of every statistic in the choices; a plausible percentage may use the wrong comparison group even when its arithmetic is internally correct.
Hints
Focus on the claim’s scope
Identify the layers in which both kinds of tools occur. The claim must be supported separately for each of those layers.
Determine the correct denominators
For each relevant row, add the beach-shell and seafloor-shell counts to find the total number of tools in that layer.
Verify every statistic
Some choices may divide one tool type by the other or mistake one category’s count for a layer total. Check each stated proportion against the table.
Step-by-step Explanation
Identify the claim’s scope
The team claims that seafloor-shell tools were relatively scarce in every layer containing both tool types. Evidence must therefore compare seafloor-shell tools with all tools in each relevant layer separately.
Calculate the layer totals
Both tool types occur at depths of 3–4 meters and 5–6 meters. The totals are tools at 3–4 meters and tools at 5–6 meters.
Check the denominators
The seafloor-shell shares are and . Values such as and approximately result from dividing the seafloor-shell counts by the beach-shell counts, not by the total number of tools in each layer.
Select the complete evidence
The correct choice reports that at 3–4 meters, 33 of 132 tools were made from seafloor shells, and at 5–6 meters, 7 of 25 were. These accurate within-layer comparisons show that seafloor-shell tools were a minority in both relevant layers.