The tropics being then completely, absolutely and forever out of the question as spheres for colonization, what is the good of our new move? Are we simply streaming to a new environment merely to perish and thin out the home country, as our elder brethren did in India, Java, Northern Africa, Greece and Rome thousands of years ago? Is it merely to thin out New England to make the stay-at-homes safer? As long as we are even now producing enough food and other necessaries for almost double our present population, and as there will be further increases, we can well dismiss the necessity for thinning out. The flow is toward America.

Two conditions, each subject to law, answer the question. In the first place, certain products of the tropics are now necessary for our existence. This is one of a group of phenomena which must be explained in full or we will fail to realize the importance, indeed the vital necessity, of "The White Man's Burden." It may thus be stated - the higher the civilization, the more numerous become the necessities of existence. That is, the higher the type, or the more intricate the machine, the more it needs for survival. Luxuries of one age are the necessities of the next.* There is no end of illustrations, many of which, no doubt, will present themselves to every man in his own particular sphere so that it would be a waste of time to mention them. The longer we live as a race, the more we require to keep us alive, because we ourselves are different. If we returned to the life of a savage we would promptly die of exposure or starvation, for we could not eat the food of our ancestors of a few thousands years ago. Evolution means enfeeblement and a more intricate human machine for which more care is necessary.

* Prof. Ira Remsen, of Johns Hopkins University, says (Science, January 1, 1904): "Things that are not dreamed of in one generation become the necessities of the next generation. Many thousands of workmen are now employed and millions of dollars are invested, in the manufacture of dye-stuffs that were unknown a few years ago".

This law is only a corollary of the law of selection. Man survived by reason of the favorable variations. His hair, for instance, disappeared because the least hairy were better fitted to survive rapid changes of temperature, one day cold, another hot, etc. Thus, clothing became a necessity, while once it was a mere ornament or luxury, and though we now need protection from cold, we are not degenerate, but a higher evolution with more needs - indeed the only type which could survive - the fittest. Horses need hair in then natural state, but it is too much for active exercise in civilization, and they are healthier if clipped and blanketed when idle. We can go on through the whole list of modern needs and follow up the same law. Hence, the fittest types are those with intelligence enough to survive by their avoidance of the causes of death. Great musculature is a nuisance and takes up too much time and nourishment to keep it healthy, and the less muscular types have the advantage in modern life. We now have machinery for brute force. The weaker prehistoric men on horseback were superior to the muscular fellows, too stupid to train horses. Intelligent weaklings are the best types, for certain situations, and, indeed, they actually put the most robust in dangerous places - soldiers, sailors and policemen - and kill them off. Machinery of all sorts, then, is a modern necessity to aid our incompetent muscles.