May 2, 2006
Another one for the intelligent designers to explain:
Scientists believe they have cracked one of the most enduring mysteries since Charles Darwin returned from the Galapagos islands: why is there such a variety of life in the tropics?
The bunching up of much of the world’s biodiversity along the equatorial regions contrasts with the rapid drop-off in organisms that eke out a living in more temperate and polar regions. But well-known as the pattern is, a full explanation has so far proved elusive.
Scientists have proposed that evolution, the natural process that saw modern life develop out of a primitive broth, speeds up at the equator, so more species are able to flourish there. One theory is that creatures living along the equator are more likely to evolve into different species for two reasons: firstly, they have a higher rate of metabolism, which leads to more genetic mutations; secondly, they have shorter generations, so genetic changes can be rapidly passed down.
… [Shane Wright, a plant geneticist at the University of Auckland,] tested the theory by counting up the number of genetic mutations in a collection of closely related plants. The pairs were picked so that one variety lived along the equator while the other lived at a higher latitude. Species showing a high number of mutations are more likely to pass genetic changes on to the next generation, and through natural selection ultimately give rise to new species.
The study, which looked at varieties of conifers, flowering plants and other tree varieties, found that on average equatorial plants evolved at twice the rate of more temperate species. In one case, a plant evolved 13 times faster than a close relative living in a temperate climate.
… Dr Wright said the study supported the idea that the equator was home to the lion’s share of the world’s species because organisms there respond to the warm conditions by speeding up their metabolism and reproducing faster.
… The finding explains why 4 billion years of evolution has given rise to biodiversity hotspots in rainforests, including Brazil’s Atlantic forest, which is believed to be home to millions of insect species, 20,000 plant species and more than 1,000 species of vertebrate.
Of course, it doesn’t explain much if you think the Earth is a few thousand years old.
Unless, that is, you’re Michael Behe. In Darwin's Black Box: The Biochemical Challenge to Evolution, he argued that evolutionary anomalies could “have been placed there by the designer… for artistic reasons, to show off, for some as-yet undetectable practical purpose, or for some unguessable reason.” Well, there’s no doubt that many parts of the tropics are aesthetically pleasing to the point of showing off.
Back in the real world, Dr. Wright’s study is being published in the Proceedings of the National Academy of Sciences.
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