explains "Entwickelung" as a progress from simple to complex forms. He believes that in evolution there is a fundamental idea that "goes through all the forms of cosmic and animal development." A predecessor of von Baer had been the Frenchman, Lamarck. From von Baer, Herbert Spencer, about 1850, adopted the definition of evolution.

The hypothesis entered a new phase through Charles Darwin's epochmaking work: "The Origin of Species." The keynote of Darwin's theory is Natural Selection, by which term the development of all living forms is referred to the working of certain laws which in the reproduction of plants and animals preserved those individuals which were best fitted to survive the struggle for existence. The Darwinian theory may be summarized thus:

The Darwinian Hypothesis.

1. Every kind of animal and plant tends to increase in numbers in a geometrical progression.

2. Every kind of animal and plant transmits a general likeness, with individual differences, to its offspring.

3. Past time has been practically infinite.

4. Every individual has to endure a very severe struggle for existence, owing to the tendency to geometrical increase of all kinds of animals and plants, while the total animal and vegetable population (man and his agency excepted) remains almost stationary.

5. Thus, every variation of a kind tending to save the life of the individual possessing it, or to enable it more surely to propagate its kind, will in the long run be preserved and will transmit its favorable peculiarity to some of its offspring, which peculiarity will thus become intensified till it reaches the maximum degree of utility. On the other hand, individuals presenting unfavorable peculiarities will be ruthlessly destroyed (Survival of the Fittest), [tr. note: sic punctuation]

The basis of the theory then is that animals and plants multiply very rapidly and, second, that the offspring always vary slightly from the parents, though generally very closely resembling them. Mr. Alfred Russel Wallace says: "From the first fact or law there follows, necessarily, a constant struggle for existence; because while the offspring always exceeds the parents in number, generally to an enormous extent, yet the total number of living organisms in the world docs not, and can not, increase year by year. Consequently every year, on the average, as many die as are born, plants as well as animals; and the majority die premature deaths. They kill each other in a thousand different ways; they starve each other by some consuming the food that others want; they are destroyed largely by the powers of Nature—by cold and heat, by rain and storm, by flood and fire. There is thus a perpetual struggle among them which shall live and which shall die; and this struggle is tremendously severe, because so few can possibly remain alive—one in five, one in ten, often only one in a hundred or even in a thousand.

"Then comes the question, Why do some live rather than others? If all the individuals of each species were exactly alike in every respect, we could only say it is a matter of chance. But they are not alike. We find that they vary in many different ways. Some are stronger, some swifter, some hardier in constitution, some more cunning. An obscure color may render concealment more easy for some, keener sight may enable others to discover prey or escape from an enemy better than their fellows. Among plants the smallest differences may be useful or the reverse. The earliest and strongest shoots may escape the slug; their greater vigor may enable them to flower and seed earlier in a wet autumn; plants best armed with spines or hairs may escape being devoured; those whose flowers are most conspicuous may be soonest fertilized by insects. We can not doubt that, on the whole, any beneficial variations will give the possessors of it a greater probability of living through the tremendous ordeal they have to undergo. There may be something left to chance, but on the whole the fittest will survive." ("Darwinism" p. 7).

The same writer gives a probable instance of the working of Natural Selection in the origin of certain aquatic birds called dippers. He says: "An excellent example of how a limited group of species has been able to maintain itself by adaptation to one of these 'vacant places' in Nature, is afforded by the curious little birds called dippers or water-ouzels, forming the genus Cinclus and the family Cindidae of naturalists. These birds are something like small thrushes, with very short wings and tail, and very dense plumage. They frequent, exclusively, mountain torrents in the northern hemisphere, and obtain their food entirely in the water, consisting, as it does, of water-beetles, caddis-worms, and other insect-larvae, as well as numerous small fresh-water shells. These birds, although not far removed in structure from thrushes and wrens, have the extraordinary power of flying under water; for such, according to the best observers, is their process of diving in search of their prey; their dense and somewhat fibrous plumage retaining so much air that the water is prevented from touching their bodies or even from wetting their feathers to any great extent. Their powerful feet and long curved claws enable them to hold on to stones at the bottom, and thus to retain their position while picking up insects, shells, etc. As they frequent chiefly the most rapid and boisterous torrents, among rocks, waterfalls, and huge boulders, the water is never frozen over, and they are thus able to live during the severest winters. Only a very few species of dipper are known, all those of the old world being so closely allied to our British bird that some ornithologists consider them to be merely local races of one species; while in North America and the northern Andes there are two other species.

"Here, then, we have a bird, which, in its whole structure, shows a close affinity to the smaller typical perching birds, but which has departed from all its allies in its habits and mode of life, and has secured for itself a place in Nature where it has few competitors and few enemies. We may well suppose,* [[*Note characteristic phrase "We may suppose that,—." G.]] that, at some remote period, a bird which was perhaps the common and more generalized ancestor of our thrushes, warblers, wrens, etc., had spread widely over the great northern continent, and had given rise to numerous varieties adapted to special conditions of life. Among these some took to feeding on the borders of clear streams, picking out such larvae and mollusks as they could reach in shallow water. When food becomes scarce they would attempt to pick them out of deeper and deeper water, and while doing this in cold weather many would become frozen and starved. But any which possessed denser and more hairy plumage than usual, which was able to keep out the water, would survive; and thus a race would be formed which would depend more and more on this kind of food. Then, following up the frozen streams into the mountains, they would be able to live there during the winter; and as such places afforded them much protection from enemies and ample shelter for their nests and young, further adaptations would occur, till the wonderful power of diving and flying under water was acquired by a true land-bird." ("Darwinism," p. 81-82.)

Lines of Evidence.

The evolutionary hypothesis (both in its atheistic and theistic or
"Christian" form) is understood to rest on the following lines of proof:

i. Primary: The evidence of palaeontology (the study of fossil remains in the rocks). The surface of the earth underneath the top soil consists of layers of rock. Some of them are made up of lime deposits, others of the shells of shell-fish, others of sand-stone, others of dead trees of the