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Tropical diversity came with time

Species in the richly diverse tropics don't evolve any faster than do species in temperate zones, researchers report.

Rather, the tropics accumulated its astounding abundance of species largely because life has thrived there so long.

Why the low latitudes teem, flutter, buzz, and slither with so much more diversity than the temperate zones do is a long-standing question. Biologists have proposed a rich abundance of hypotheses, notes John Wiens of the State University of New York at Stony Brook. In the 1990s, several researchers devised versions of what Wiens calls the tropical-conservation hypothesis. It argues that many of the tropics' species-rich lineages originated there and were slow in colonizing the temperate zones that have killer winters. Thus, life in the tropics has had longer to diversify.

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