(2) Similarly, the theory makes no allowance for the increased efficiency which may come with increased population, because increase of population makes possible better coöperation. As we have already seen, coöperation and division of labor in a society depend upon the size of the group to a certain extent, that is, the larger the group there is for organization the better can be the organization and division of labor in that group. Every increase of population, therefore, opens up new and superior ways of applying labor; and coöperation and the division of labor make it possible for men to do more as a group than they could possibly accomplish working as individuals. Improved means of coöperation, therefore, operate very much the same way in human society in controlling nature as new inventions. (3) The theory of Malthus makes no allowance for the general law of animal fertility, which is that as the rate of individual evolution increases the rate of reproduction decreases. Of course, Malthus's theory antedates this law of animal fertility, which was first stated by Herbert Spencer. Some scientists declare that this law does not apply within the human species, and it must be admitted that it is not yet certain that it does. As we have already seen, however, the lower and less individualized classes in human society reproduce much more rapidly than the upper or more individualized classes. Increase of food supply, of wealth, and so on, does not necessarily mean increase of population, and the fatal error in Malthus's theory is that he assumes that wherever food increases population always increases also. (4) The overpopulation which Malthus feared, so far from being an evil, has been shown by the labors of Darwin to be the condition essential to the working of the process of natural selection in the human species. Overpopulation, at least until artificial selection arrives, is not an evil, but a good in human society. Without it there would not be sufficient elimination of the unfit in human society to prevent wholesale social degeneration. Even with artificial selection, however, some overpopulation would be necessary for the working of any scheme of selection. We must conclude, then, that Malthus's theory, either as an explanation of the growth of modern populations or as an implied practical ethical doctrine, is of no value whatever.