Before plate tectonics became an accepted idea in geology, Lyell’s doctrine of uniformitarianism still ruled supreme (see my review of Cataclysms: A New Geology for the Twenty-First Century for a short introduction). A corollary was that the continents supposedly had always been where they are now. One observation scholars had to explain away was that the same fossils occur on both sides of the various oceans. Looking at maps, some people noticed the thin strip of land connecting North and South America and concluded that land bridges must have formed and sunk beneath the waves at just the right times in history to enable migrations (see Four Revolutions in the Earth Sciences: From Heresy to Truth for more details). As explained in The Tectonic Plates are Moving!, we know better nowadays. Nevertheless, the concept of land bridges is still alive and well today, and palaeobotanist Alan Graham here introduces five of them, exploring their effects on biogeography, climate, and human history.

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