The old belief that climatic stability accounts for the high level of species diversity in the Amazon River basin of South America emerged, strangely enough, from observations of the deep sea.
Topic
Why does the Amazon basin have such high species diversity? Competing explanations about climatic stability versus climatic fluctuations.
Framework
Old / New (the passage contrasts the old "stability hypothesis" with a newer "fluctuation/refuge hypothesis")
Main Point
The older idea that the Amazon’s exceptional diversity is due to a stable climate is now challenged by evidence for significant past climate fluctuations, which may actually better explain the diversity. (The "Most Valuable Sentence" is at the end of the passage: )
P1: The Stability Hypothesis for Diversity
The passage introduces the old idea: the Amazon, like the deep sea, is super diverse because its stable climate means few extinctions and plenty of time for new species to evolve. This was originally inspired by comparisons to deep-sea environments and is supported by some evidence of long-lasting species.
P2: Observed Problems with Stability Hypothesis
But more recently, researchers have noticed some weird patterns, like different bird species living in different areas even though the forest looks pretty much the same everywhere. This is puzzling if the whole Amazon has a stable climate and should be relatively uniform.
P3: Haffer’s Fluctuation/Refugia Hypothesis
Haffer offers a new explanation: during the ice ages, lowland Amazon areas got super dry, turning into near-deserts, while upland areas stayed wet and acted as refuges. Populations split up and evolved separately, increasing diversity. This process also helps explain the weird distributions seen today.