The first group of facts consists of the great powers of increase of all organisms and the circumstance that, notwithstanding this great yearly increase, the actual population of each species remains stationary, there being no permanent increase. Now, these two facts were recognized by Buffon, but though, of course, known to all subsequent writers, were fully appreciated or thought out to their logical results by none of them. Lamarck, so far as I can ascertain, took no notice of them whatever. Darwin has given illustrations of these facts in Chapter IV. of the _Origin of Species_, and I have added others in the second chapter of my _Darwinism_. That the population of each species remains stationary, with, of course, considerable fluctuations, is both a matter of observation and of reasoning. The powers of increase of all creatures are so great that if there is in any country room and food for a larger number of any species they will be produced in a year or two. It is impossible, therefore, to believe that, in a state of nature, where all kinds of animals and plants have lived together as they best could for thousands of years, there can be any important difference in their numbers from year to year or from century to century. Now, it is as a consequence of these two indisputable facts that the struggle for existence necessarily results. For if every year each pair of animals or each plant produces only ten young animals or plants, and this is very far below the average, and if the adult life of these is taken at ten years, again below the average of the higher plants and animals, then, unless some of the parents die, the whole of the offspring must die off every year; or, in other words, only as many young can survive as are necessary to replace the old ones that die. Hence the deaths must always (on the average and in the long run) equal the births. This terrible yearly destruction is an absolutely certain fact, as well as an inevitable result of the two preceding facts, and it is said to be due to the struggle for existence. This struggle is manifold in its nature. Individuals of the same species struggle together for food, for light, for moisture; they struggle also against other species having the same wants; they struggle against every kind of enemy, from parasitic worms and insects up to carnivorous animals; and there is a continual struggle with the forces of nature—frosts, rains, droughts, floods, and tempests.