If once that ice were melted off--ah, well, there is much virtue in an _if_. Still, Mr. Alfred Russel Wallace seems to suggest somewhere that the sun is gradually making inroads even now on those great glacier-sheets of the northern cap, just as we know he is doing on the smaller glacier-sheets of Switzerland (most of which are receding), and that in time perhaps (say in a hundred thousand years or so) warm ocean currents may once more penetrate to the very poles themselves. That, however, is neither here nor there. The fact remains that we of Northern Europe live to-day in a cramped, chilled, contracted world; a world from which all the larger, fiercer, and grander types have either been killed off or driven south; a world which stands to the full and vigorous world of the Eocene and Miocene periods in somewhat the same relation as Lapland stands to-day to Italy or the Riviera. This being so, it naturally results that if we want really to understand the history of life, its origin and its episodes, we must turn nowadays to that part of our planet which still most nearly preserves the original conditions--that is to say, the Tropics. And it has always seemed to me, both _a priori_ and _a posteriori_, that the Tropics on this account do really possess for every one of us a vast and for the most part unrecognised educational importance. I say 'for every one of us,' of deliberate design. I don't mean merely for the biologist, though to him, no doubt, their value in this respect is greatest of all. Indeed, I doubt whether the very ideas of the struggle for life, natural selection, the survival of the fittest, would ever have occurred at all to the stay-at-home naturalists of the Linnaean epoch. It was in the depths of Brazilian forests, or under the broad shade of East Indian palms, that those fertile conceptions first flashed independently upon two southern explorers. It is very noteworthy indeed that all the biologists who have done most to revolutionise the science of life in our own day--Darwin, Huxley, Wallace, Bates, Fritz Mueller, and Belt--have without exception formed their notions of the plant and animal world during tropical travels in early life. No one can read the 'Voyage of the _Beagle_,' the 'Naturalist on the Amazons,' or the 'Malay Archipelago' without feeling at every page how profoundly the facts of tropical nature had penetrated and modified their authors' minds. On the other hand, it is well worth while to notice that the formal opposition to the new and more expansive evolutionary views came mainly from the museum and laboratory type of naturalists in London and Paris, the official exponents of dry bones, who knew nature only through books and preserved specimens, or through her impoverished and far less plastic developments in northern lands. The battle of organic evolution has been waged by the Darwins, the Huxleys, and the Muellers on the one hand, against the Cuviers, the Owens, and the Virchows on the other.