Overcrowding of houses and rooms does not of itself prove the inmates to be underfed - the real test of overpopulation - for they may all be properly nourished, yet it is generally true that overcrowding and underfeeding go hand in hand. Shelter and food are both defective when poverty pinches. Indeed, house-rent is, in a way, a proof of overpopulation. At least, it is the penalty of being born poor. We can well imagine that among primitive cavemen, the strongest would secure the caves and not permit intruders unless paid for the privilege by service of some kind. The babies born in that cave, as soon as they grew to maturity, would have to find other shelter, if crowded out. Rent thus began, and has continued ever since, for few men can supply their children with houses. As in primitive times men raise offspring only to thrust them out like birds from a nest. As no young man can possibly earn enough to build his own house before marriage, it follows that rent is inevitable. Moreover, there were not enough caves for primitive man, and there have never been enough houses. In no part of the world is there a house or apartment for every possible family, and consequently matrimony and the raising of offspring is out of the reach of a certain percentage, which increases with the overpopulation. It is a physical impossibility to build houses to keep pace with increases of population, and indeed it is doubtful if the world is rich enough to do it, if it were possible. Moreover, the lower the man's efficiency the greater proportion of his wage is spent in rent; many of our poor pay out one-fourth of their income for shelter, but in primitive times it was still more. Here and there, in the rural districts of Europe, the peasantry are still existing like cave men. In Bulgaria, all the members of a family, and often several families, sleep in one room on mats spread on the floor. The Filipinos do the same, indeed, it is a universal phenomenon, and the primitive "dug-out" of our frontiers is practically the same as the majority of the medieval houses of England and Ireland - some of which are still in use.

* E. Ray Lankester, Quarterly Review, July, 1904. * Brooks Adams', "Civilization and Decay," p. 13.

* Ibid., p. 16. See also the dreadful details in Wallon's "Histoire de l'Esclavage".