You, and your ancestors, have spent thousands of years adapting to the eternal darkness of caves buried as much as a kilometer below the surface of the earth. You've lost your eyes. You've lost your pigmentation. You're all in for the stgyian blackness. Then, the rules are changed. You find yourselves closer to the surface. It's warmer. The darkness turns to light. But, is it too late? Are you locked in to your subterranean lifestyle?Research with cave-dwelling scorpions suggests that you can get your evolutionary money back. The scorpion Family Typhlochachtidae includes a number of species found in Mexican caves. Although all show adaptations for life in caves, several live closer to the surface and show a more generic body form than those found at greater depths. In work led by Lorenzo Prendini of the American Museum of Natural History and to be published in Cladistics, researchers developed a phylogeny based on 195 morphological characters and discovered that three shallow-living, morphologically unspecialized species are descended from specialized deep-dwelling species. This runs counter to the predictions of "Dollo's Law", which suggests that selection leading to the develoment of highly specialized traits is not reversible.
Prendini suggests that the evolutionary flexibility of scorpions may play a role - they are, after all, among the oldest extant invertebrate groups. On a more speculative note, he also suggests that the "new" surface dwellers may have been able to come up out of the dark when the Chicxuluxb asteroid wiped out the competition some 65 million years ago.
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