BASIC BOOKS, JANUARY 2014Baobab trees crossed the Indian Ocean, perhaps as seeds drifting on marine currents. Iguanas from the New World travelled thousands of miles over the Pacific to reach Fiji and Tonga, probably by hitching rides on natural rafts of vegetation. A small carnivorous sundew plant somehow made it from Australia to the top of a sheer-sided mesa in northern South America. Frogs, traditionally considered hopeless ocean voyagers, traversed seas from mainland habitats to colonize the islands of São Tomé and Príncipe, the Seychelles, the Philippines, Sulawesi, and the West Indies. Crocodiles, burrowing lizards, rodents, and monkeys dispersed to the Americas from Africa via the Atlantic.
All of these improbable journeys, and many others, are now supported by genetic evidence as well as other data. As I describe in my book The Monkey’s Voyage, these cases collectively represent a major sea change in the field of biogeography, from a view in which distributions broken up by oceans were typically explained by the fragmentation of landmasses through continental drift to a more balanced perspective that recognizes the great importance of natural ocean crossings. Recent molecular-clock studies, in particular, have often refuted hypotheses that invoke continental drift in favor of relatively recent long-distance oceanic dispersal. For those of us who were raised thinking of continental breakup as the default explanation for such piecemeal distributions, the geographic history of living things has been turned ...
