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About 2 to 3 million years ago, a group of spiders from parts unknown let out long silk threads into the wind and set sail, so to speak, across the Pacific Ocean to Hawaii. These spiders were parasites of other spiders, invading their webs, snipping threads to steal insects that had been caught.
But there weren't many webs to rob on Hawaii when they arrived. So they expanded their repertoire, looking for other ways to survive by trapping and eating other spiders. A new species evolved from those first spiders, after finding a way to live on rocks. And then another species evolved to live under leaves. And then another. And then 11 more species. Charles Darwin first noted this phenomenon, called adaptive radiation, in the beaks of finches of the Galapagos Islands. His study of the finches' diversity led to his theory of evolution by natural selection. Yet today, much remains unknown about how adaptive radiation, and thus evolution, actually work. Hawaii is even more of a hotbed for biological diversification than the Galapagos due to its isolation.Image credit: George Roderick/University of California, Berkeley
