This general state of balance, however, is able to go along with a lot of special balancings that seem largely independent of each other. It is important to remember this when we come a little later on to consider the instincts. All sorts of lesser systems prevail within the larger system represented by the individual organism. It is just as if within the state with its central government there were a number of county councils, municipal corporations, and so on, each of them enjoying a certain measure of self-government on its own account. Thus we can see in a very general way how it is that so much variation is possible. The selective organization, which from amongst the germinal elements precipitates ever so many and different forms of fresh life, is so loose and elastic that a working arrangement between the parts can be reached in all sorts of directions. The lesser systems are so far self-governing that they can be trusted to get along in almost any combination; though of course some combinations are naturally stronger and more stable than the rest, and hence tend to outlast them, or, as the phrase goes, to be preserved by natural selection. It is time to take account of the principle of natural selection. We have done with the subject of variation. Whether use and disuse have helped to shape the fresh forms of life, or whether these are purely spontaneous combinations that have come into being on what we are pleased to call their own account, at any rate let us take them as given. What happens now? At this point begins the work of natural selection. Darwin's great achievement was to formulate this law; though it is only fair to add that it was discovered by A.R. Wallace at the same moment. Both of them get the first hint of it from Malthus. This English clergyman, writing about half a century earlier, had shown that the growth of population is apt very considerably to outstrip the development of food-supply; whereupon natural checks such as famine or war must, he argued, ruthlessly intervene so as to redress the balance. Applying these considerations to the plant and animal kingdoms at large, Darwin and Wallace perceived that, of the multitudinous forms of life thrust out upon the world to get a livelihood as best they could, a vast quantity must be weeded out. Moreover, since they vary exceedingly in their type of organization, it seemed reasonable to suppose that, of the competitors, those who were innately fitted to make the best of the ever-changing circumstances would outlive the rest. An appeal to the facts fully bore out this hypothesis. It must not, indeed, be thought that all the weeding out which goes on favours the fittest. Accidents will always happen. On the whole, however, the type that is most at home under the surrounding conditions, it may be because it is more complex, or it may be because it is of simpler organization, survives the rest.