A hundred years ago the French scientist Cuvier, who gave much time to the study of the fossils of extinct mammals, presented the “cataclysmal” explanation of their end. They were destroyed by sudden great geologic changes. To us, perhaps, these changes seem to have ignored certain other animals in a most disquieting way. Cuvier was at a disadvantage, of course, for he was working in a Bible-ridden world which had to accept the Book of Genesis as fact. Even as late as 1887, Henry H. Howorth wrote in _The Mammoth and the Flood_: These facts ... prove in the first place that a great catastrophe or cataclysm occurred at the close of the Mammoth period, by which that animal, with its companions, were overwhelmed over a very large part of the earth’s surface. Secondly, this cataclysm involved a very wide-spread flood of water, which not only killed the animals but also buried them under continuous beds of loam or gravel. Thirdly, that the same catastrophe was accompanied by a very great and sudden change of climate in Siberia, by which the animals which had previously lived in fairly temperate conditions were frozen in their flesh underground and have remained frozen ever since.[24] In the hundred years since Koch found a mammoth and a spear point in Missouri we have learned little that is definite about the reasons for the extinction of mammoth, mastodon, camel, horse, sloth, and the rest. We merely know that they died out as the glaciers began to melt. The most natural guess for either scientist or amateur is that change of climate was the lethal factor. Yet we know that many of them had already survived drastic changes of climate and lived through interglacials as well as glacials in the Great Ice Age. Further, how do we account for the survival of deer, antelope, fox, rabbit, moose, beaver, bear, and so many other animals? How could climate be so selective? If the dire wolf died, why not the timber wolf? If the short-faced bear, why not the grizzly? If one form of rabbit and three forms of antelope, why not all rabbits and all antelopes? If disease instead of climate was the great eliminator—as some have suggested—we face the same dilemma. The mysteries of extinction are so many and so baffling that it is small wonder no book in English has been written on the subject. Since 1906, when Henry Fairfield Osborn summed the matter up in his paper of fifty-odd pages, “The Causes of Extinction of Mammalia,” Eiseley credits only two theories with contributing anything new to the discussion. One is the hypothesis of Sewall Wright and his co-workers that when an animal was greatly reduced in numbers it would suffer fatally from inbreeding.[25] This, however, leaves us still searching for what reduced its numbers so radically.