Jason Ali and Jonathan Aitchison have recently published a paper in the Journal of Biogeography about how sea level changes have likely influenced the evolution of many species in the Galapagos. During the Ice Ages, sea levels likely changed by as much as 144m below present, dramatically changing the Galapagos landscape. Many of the central islands, that are now separate, would have been joined together removing the geographic barriers that foster speciation. This idea helps to explain why a single species of several taxonomic groups (such as lava lizards and snakes) is found in the central islands while the outer islands tend to each have their own species. Basically the outer islands have always been isolated whereas the inner ones have been joined in the recent geologic past.
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