The upper incisors or tusks were very much longer than in the modern species, being from ten to twelve feet long, and sometimes curved up and back so as to form an almost complete circle. As these tusks continue to grow throughout life, their enormous length is, I take it, a proof of much greater longevity and thus of greater vitality than in the cases of the modern species. The latter is simply a degenerate. And so I might go on with the Edentates, the Ungulates, the Rodents, the Carnivores, etc., for the same thing must be said of all. As Sir William Dawson[86] remarks: "Nothing is more evident in the history of fossil animals and plants of past geological ages than that =persistence or degeneracy are the rule= rather than the exception.... We may almost say that all things left to themselves =tend to degenerate=, and only a new breathing of the Almighty Spirit can start them again on the path of advancement." In spite of the long popular views of Cuvier, every modern scientist admits that the great lion and hyena of the Pleistocene are identical with the living species of Africa. Many say the same thing of the fossil bear as compared with the modern brown bear and the grizzly, though, as Dana remarks of all three, lion, hyena, and bear, "these modern kinds are dwarfs in comparison." I quote again from Dana: "Thus the brute races of the Middle Quaternary on all the continents exceeded the moderns greatly in magnitude. Why, no one has explained."[87] This was in 1875. In the last edition of his "Manual," published shortly after his death, he has this to say in addition: "A species thrives best in the region of fittest climate. =In the Pleistocene, the fittest climate was universal.= Geologists have attributed the extinction of most of the species and the dwindling of others to the cold of the Reindeer epoch. It is the only explanation yet found, though seemingly insufficient for the Americas." (p. 1016.)