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In the two decades preceding the establishment of plate tectonics theory, G. G. Simpson wrote a series of papers that refuted the paleobiogeographic evidence purportedly requiring direct continental connections. So cogent was his rebuttal that drift proponents thereafter downplayed the past distribution of fossils.

Simpson presented several different arguments. He restricted his discussion to Cenozoic mammals with whose evolutionary history he was most familiar; he challenged the accuracy of the proponents舗 data; he criticized their methodology, both with respect to its undue appeal to authority and its lack of parsimony; he used his own “coefficient of faunal similarity” to show that present-day mammal distributions on dispersed continents are comparable to those for Tertiary continents; and perhaps most effective was his statistical argument that trans-oceanic dispersal of organisms, while highly improbable for a single event, is practically certain given the many opportunities for such events over geologic time spans. Simpson舗s objections arose from his own independently developed theory of historical biogeography which, by relying on mobile organisms dispersing across stable continents, was fully adequate to explain the paleobiogeographic data. Simpson thus regarded both drift theory and trans-oceanic land-bridges neither sufficient nor necessary to account for those data.

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