BIOLOGY. 89 BIOLOGY. problem of fitness or adaptation, the problem to which biology owes its independence among the sciences, has been a familiar one for ages, but it was only through the demonstration, by Wallace and Darwin, that the adjustive machinery of liv- ing organisms has come about gradually, through e.vtermination and sun'ival, in accordance with the mechanical principle of natural selection, that the possibility of a mechanical explanation of fitness was made clear. The discovery and demonstration of the sig- nificance of the survival of the fittest seems, to the writer, to be the foundation of scientific biology, and the greatest intellectual triimiph of the human mind. It has taught us that response, or the use of one event as a means of preparing for or predicting others — that distinctive at- tribute of living beings which, in its higher mani- festations, we know as human knowledge or sci- ence — admits of treatment by methods which do not differ in any essential or fundamental way from those that are employed in geologj' and astronomy and physics. It is only when we re- view, in the light of natural selection, the long history of Plato's question: Miat is science? What is it to know a thing? that we begin to comprehend the transcendent genius of Charles Darwin, and to grasp the significance of his con- tribution to human knowledge, and to attain to the beginnings of an adequate conception of its supreme intellectual value. This high estimation of the value of Damin's contribution to science does not meet the un- qualified approval of all biologists; many be- lieving that natural selection is only a minor factor in the evolution of living beings, or, at least, that we must search elsewhere for the origin of the raw material which it picks out and pre.se rses. We are told that since it is a merely negative process of sifting or weeding out, which does not produce, but only preserves, the fitness which exists, it does not show why there should be any fit to survive, but only how the unfit are ex- terminated. Without knowing why one horse is more fleet than another, or even why horses exist, breeders have increased the speed of horses by breeding from the most fleet ; just as a pack of wolves may increase it in nature, by destroying, generation after generation, all the horses they can run down. If, at every stage in the ancestry of horses, there has been need for greater speed, natural selection accounts for the whole history of this characteristic of horses, and even for the first vague beginnings of locomotion in .sedentary or floating animals, which may have found shel- ter from their enemies, or more abundant food, by those slight changes of place which may at first have been the incidental result of changes of shape. While it is obvious that a useful quality must exist before it can be useful, and before it can survive, and while no Darwinian holds natural selection to be an ultimate explanation of any- thing, in the metaphysic.il sense of the word ultimate, all admit that horses do differ among themselves in speed, and that each may reason- ably be expected to Iw more like its parents in speed than a horse selected at random. As no one disputes the existence of these prerequisites to improvement by selection, the declaration that nothing could come about through selection is childish. A living being is a being that responds to the stimulus of one event in such a way as to adjust its actions to other events of which, in course of nature, the stinmlus is the sign; and if all that have not thus responded have been ex- terminated in the struggle for existence, the ad- justments of the survivors is nothing more thaa might have been expected. Xo natural law is an agent. So far as human knowledge reaches, the laws of nature are nothing more than sunnuaries. of observed facts, joined to that confidence in the continuity of nature which leads us to expect that what has come about will continue to come about under like conditions. The rational basis for confidence in the continuity of nature seems to the writer to be found in the truth that we have survived and are in existence. Our con- fidence in the validity of science, and in the real existence of order in nature, is equal to, and identical with, our confidence in our own exist- ence. Natural selection seems to the writer to be a strictly scientific explanation of the fitness of living things, and they who assert that it is in- adequate because it fails to show why beneficial response should ever follow a stimulus, and thus furnish fitness to be selected, must remember that all science is inadequate in exactly the same degree. In no case does science tell us why natu- ral phenomena do occur in order, although it does tell us what order of events we may reason- ably expect. They who challenge the sufliciency of natural selection because it does not tell us why there should be any fitness to select, must find all science equally inadequate, although the common verdict of mankind is that scientific knowledge is very adequate and sufticient for all the needs of living things in that natural uni- erse in which we find ourselves, and of which we are constituent parts, even if it does fail to show us in nature any efficient cause for any- thing. The cuckoo that lays her eggs in strange nests gets the hard and exhausting and dangerous work of incubating done for her, whether it is imconsciously, or carelessly, or with forethought that she does so. The advantage is the same, no matter who or what it is that puts the eggs into the strange nest. After the foster-brothers of the nestling cuckoo are destroyed, it profits by the exclusive attention of its two nurses, and so long as the conduct of cuckoos conduces to the welfare of the race, cuckoos will increase and multiply to continue in the same course. We find worldly wisdom in the habits of cuckoos, and the immorality of their conduct is shocking to our refined sense of right : but. so long as the eggs are laid in suitable nests and are hatched, the result may be expected to come about, even if the birds have no more share in the worldly wis- dom than they have in the immorality. The biologist is sometimes told that since he does not know the individual history of any organism in the past, and is even less .ible to foresee that of any that may e.xist in the future, he only infers the fitness of living things for their environment from their survival, and can- not logically hold the descendants accounted for by the fitness of their ancestors: but it is our confidence in the continuity of nature, and not ability to say what it was that led to the survival of any individuiil organism in the past, which convinces us that the fittest have survived in the past, and that they will survive in the
