Temperature Constancy Appears Key to Tropical Biodiversity

The tropics owe their stunning biodiversity to consistent year-round temperatures, not higher temperatures or more sunlight, according to a novel survey of insect diversity at different latitudes and at different points in the planet's history.

The finding, presented this week in the journal Paleobiology by researchers from Harvard University, Simon Fraser University, and Brandon University, may finally answer a question that has dogged scientists for centuries.

It also suggests, intriguingly, that the world is likely far less diverse today than it was tens of millions of years ago, when the entire Earth had consistent year-round temperatures, much like the modern tropics.

"The latitudinal diversity gradient has been recognized for 150 years as one of the most general observations in nature, and has produced more explanatory hypotheses than nearly any other observation," says co-author Brian D. Farrell, professor of biology at Harvard. "We show that when most of today's organisms were diversifying, up through the Eocene, the world lacked pronounced seasonality, more like today's tropics, even in areas where the temperature was low."

"It appears it's not the heat of the tropics that promotes diversity; it's the newer seasons of the temperate zone that depress diversity."

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