Theodore Roosevelt (1858–1919). Through the Brazilian Wilderness. 1914.
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| distribution of many forms of life, past and present, offers problems which with our present paleontological knowledge we are wholly unable to solve. If we consider only the biological facts concerning some one group of animals it is not only easy but inevitable to conclude that its distribution must be accounted for by the existence of some former direct land bridge extending, for instance, between Patagonia and Australia, or between Brazil and South Africa, or between the West Indies and the Mediterranean, or between a part of the Andean region and northeastern Asia. The trouble is that as more groups of animals are studied from the standpoint of this hupothesis the number of such land bridges demanded to account for the existing facts of animal distribution is constantly and indefinitely extended. A recent book by one of the most learned advocates of this hypothesis calls for at least ten such land bridges between South America and all the other continents, present and past, of the world since a period geologically not very remote. These land bridges, moreover, must, many of them, have been literally bridges; long, narrow tongues of land thrust in every direction across the broad oceans. According to this view the continental land masses have been in a fairly fluid condition of instability. By parity of reasoning, the land bridges could be made a hundred instead of merely ten in number. The facts of distribution are in many cases inexplicable with our present knowledge; yet if the existence of widely separated but closely allied forms is habitually to be explained in accordance with the views of the extremists of this school we could, from the exclusive study of certain groups of |