6. Nature’s Mode of Producing Organic Forms.
The general process by which the higher and more elaborate forms of life, and eventually man himself, have been produced has been shown by Darwin to depend upon two important properties of living matter manifested in connexion with the multiplication of individuals. Living matter has a special property of adding to its bulk by taking up the chemical elements which it requires and building up the food so taken as additional living matter. It further has the power of separating from itself minute particles or germs which feed and grow independently, and thus multiply their kind. It is a fundamental character of this process of reproduction that the detached or pullulated germ inherits or carries with it from its parents the peculiarities of form and structure of its parent. This is the property known as Heredity. It is most essentially modified by another property—namely, that though eventually growing to be closely like the parent, the germ (especially when it is formed, as is usual, by the fusion of two germs from two separate parents) is never identical in all respects with the parent. It shows Variation. In virtue of Heredity, the new congenital variations shown by a new generation are transmitted to their offspring when in due time they pullulate or produce germs. Man has long been aware of this; and, by selecting variations of beasts, birds, or plants agreeable or useful to him, has intensified such variations and produced animals and plants in many features very unlike those with which he started.
It was Darwin’s merit to show that a process of selection which he called ‘Natural Selection’ must take place in the free untouched conditions under which animals and plants exist, and have existed for ages, on this globe. Both animals and plants produce germs, or young, in excess—usually in vast excess. The world, the earth’s surface, is practically full, that is to say, fully occupied. Only one pair of young can grow up to take the place of the pair—male and female—which have launched a dozen, or it may be as many as a hundred thousand, young individuals on the world. The property of Variation ensures that amongst this excess of young there are many differences. Eventually those survive which are most fitted to the special conditions under which this particular organism has to live. The conditions may, and indeed in long lapses of time must, change, and thus some variation not previously favoured will gain the day and survive. The ‘struggle for existence’ of Darwin is the struggle amongst all the superabundant young of a given species, in a given area, to gain the necessary food, to escape voracious enemies, and gain protection from excesses of heat, cold, moisture, and dryness. One pair in the new generation—only one pair—survive for every parental pair. Animal population does not increase: ‘Increase and multiply’ has never been said by Nature to her lower creatures. Locally, and from time to time, owing to exceptional changes, a species may multiply here and decrease there; but it is important to realize that the ‘struggle for existence’ in Nature—that is to say, among the animals and plants of this earth untouched by man—is a desperate one, however tranquil and peaceful the battlefield may appear to us. The struggle for existence takes place, not as a clever French writer[5] glibly informs his readers, between different species, but between individuals of the same species, brothers and sisters and cousins. The struggle between a beast of prey which seeks to nourish itself and the buffalo which defends its life with its horns is not ‘the struggle for existence’ so named by Darwin. Moreover, the struggle among the members of a species in natural conditions differs totally from the mere struggle for advancement or wealth with which uneducated writers so frequently compare it. It differs essentially in this—that in Nature’s struggle for existence, death, immediate obliteration, is the fate of the vanquished, whilst the only reward to the victors—few, very few, but rare and beautiful in the fitness which has carried them to victory—is the permission to reproduce their kind—to carry on by heredity to another generation the specific qualities by which they triumphed.
It is not generally realized how severe is the pressure and competition in Nature—not between different species, but between the immature population of one and the same species, precisely because they are of the same species and have exactly the same needs. From a human point of view the pressure under which many wild things live is awful in its severity and relentless tenacity. Not only are new forms established by natural selection, but the old forms, when they exactly fit the mould presented as it were for competitive filling, are maintained by the same unremitting process. A distinctive quality in the beauty of natural productions (in which man delights) is due to the unobtrusive yet tremendous slaughter of the unfit which is incessantly going on, and the absolute restriction of the privilege of parentage to the happy few who attain to the standard described as ‘the fittest.’