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Difficulty: MediumEvaluating the Impact of New Evidence

### Mammoth Population Decline

Scientists debate the primary cause of the woolly mammoth’s extinction at the end of the Pleistocene epoch.

Hypothesis 1
The extinction was driven by rapid climate warming, which altered the vegetation of the mammoth's habitat. The dry, grassy steppe-tundra transitioned into wet, nutrient-poor shrublands and forests, which could not support the dietary needs of large herbivores like mammoths.

Hypothesis 2
The extinction was caused by human overhunting. As human populations expanded across northern regions, their advanced hunting tools and strategies allowed them to hunt mammoths at rates far exceeding the species' natural reproduction rates, driving them to extinction.

New Evidence
Researchers analyzed woolly mammoth fossils and plant pollen from sediment layers on a remote Siberian island. They found that a major decline in the mammoth population occurred over a 500500-year period during which grass pollen levels dropped by 80%80\% and shrub pollen levels increased. The earliest human artifacts on the island date to 1,0001,000 years after the mammoth population had already completely disappeared.

Based on this new evidence, which of the following statements best describes the impact of the findings on the two hypotheses?

  1. A
    The evidence undermines the climate-driven vegetation change explanation while strengthening the human overhunting explanation.
  2. B
    The evidence supports both the climate-driven vegetation change explanation and the human overhunting explanation.
  3. The evidence strengthens the climate-driven vegetation change explanation while undermining the human overhunting explanation.Answer
  4. D
    The evidence has no effect on the climate-driven vegetation change explanation but weakens the human overhunting explanation.

Answer

The evidence strengthens the climate-driven vegetation change explanation while undermining the human overhunting explanation.
The correct answer is the option stating that the evidence strengthens the climate-driven vegetation change explanation while undermining the human overhunting explanation. This is because the evidence of an 80%80\% reduction in grass pollen coincides with the decline of the mammoth population, directly supporting the habitat change model. Concurrently, the finding that humans did not inhabit the island until 1,0001,000 years after the mammoths had gone extinct directly refutes the human hunting model for this population.

Step-by-Step Solution

1
Analyze the core claim of Hypothesis 1 and Hypothesis 2.
Hypothesis 1 claims extinction was due to climate-driven vegetation shifts (loss of grasses). Hypothesis 2 claims extinction was due to human overhunting.
Understanding the core assertions of both viewpoints is required before evaluating new data.
2
Evaluate the impact of the plant pollen data on Hypothesis 1.
The new data shows a major decline in mammoth population occurred alongside an 80%80\% drop in grass pollen. This directly supports the idea that loss of grasses (their food source) led to their decline, strengthening Hypothesis 1.
Aligning experimental evidence of food scarcity with the predictions of the habitat-change hypothesis.
3
Evaluate the impact of the human artifact timeline on Hypothesis 2.
The mammoth population disappeared 1,0001,000 years before humans arrived. Since humans were not present during the decline, they could not have driven the extinction on this island, weakening Hypothesis 2.
Using chronological evidence to determine if a hypothesized cause could have physically occurred.

Key Concept

Evaluating the Impact of New Evidence
Estimated Time:1m 30s
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Topics

Evaluating the Impact of New Evidence

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