these were much older, because bronze was used long before iron was discovered. And lastly in some, tools of stone only have been found, some beautifully polished, but others rough and rude, showing that the men who used them must have been mere savages like the Australians now; and yet the oldest of these lake-villages have no bones of extinct animals in them, and therefore cannot be so ancient as those men whose tools were found in the cavern at Torquay and the sandpits of Abbeville, or as have since been found in England, Denmark, Germany, America, and indeed in almost all countries.

It is impossible, without a knowledge of geology, to realise how very long ago these last-mentioned men must have lived. But when I tell you that since their tools were buried in the rocks, there has been time for beds of immense thickness to be laid down little by little, as the Ganges is laying them down now; for parts of the French valleys to be gradually washed away, and their shape altered; for rivers to change their courses, and vast beds of peat to grow over the bottoms of the valleys; and, more than all, for whole races of animals which once lived to have died quite away from the face of the earth, you may perhaps form some idea of the long ages that man must have been upon our globe. This history, however, is so new and as yet so little understood, that it cannot be explained in a few pages. You will find all the proofs of it given in Sir Charles Lyell's work on the 'Antiquity of Man,' in which they were first collected in 1863; and you must remember the fact, that man is very ancient, as one of the great discoveries of the nineteenth century.

Chief Works consulted.-Lyell's 'Principles of Geology,' 'Elements of Geology,' 'Antiquity of Man;' Lubbock's 'Prehistoric Times ;' 'Quarterly Geological Journal,' vol. xxx. : Obituary of Agassiz.

CH. XL.

BIOLOGY.

419

CHAPTER XL.

SCIENCE OF THE NINETEENTH CENTURY (CONTINUED). Facts which led Naturalists to believe that the Different Kinds of Animals are descended from Common Ancestors-All Animals of each Class formed on one Plan-Embryological StructureLiving and Fossil Animals of a Country resemble each other Gradual Succession of Animals on the Globe-Links between Different Species-Darwin's Theory of Natural Selection-Wallace worked out the same Theory independently-Sketch of the Theory of Natural Selection-Selection of Animals by Man-Selection by Natural Causes-Difficulties in Natural History which are explained by this Theory-Foolish Prejudices against it-Concluding Remarks on the History of Science.

Facts which have led Naturalists to believe that the different kinds of Animals are descended from common Ancestors. We now come to the first attempt of any value which has ever been made, to explain how the different kinds of animals and plants have been produced. This question is so very difficult, and seems so much beyond our grasp, that we find very few people throughout the history of science who even tried to answer it. Aristotle, it is true, remarked that we can trace such a close resemblance between the different species, from the lowest plant up to the highest animal, as would seem to show they are related to each other (p. 16). Bonnet, too, thought that animals were developed from lower into higher forms (p. 202); and Lamarck, as we have seen, boldly suggested the same explanation (p. 391).

But people in general treated these as mere wild speculations, and were content to say that God had created animals, just in the same way as they said that the stars were created by Him, without pausing to consider how He has created them.

Since the time of Buffon and Linnæus, however, many new facts had gradually been brought to light about living animals; and fossil species had been dug out of the earth, showing that many different forms had lived upon our globe, one after the other; and these new discoveries led naturalists to speculate whether some clue might not be found to explain this long succession of living beings.

Then again, as naturalists spread all over the world and many new forms of animals and plants became known, it was found to be more and more difficult to separate the different species and to say which are and which are not descendants of one parent. Linnæus, as we have seen (p. 392), pointed this out in the case of plants, and wild roses are a very good example of it; for the different kinds run so much into each other that while one of our best botanists has divided them into seventeen species, another thinks that many of these must have come from the same parent, and that only five species can be distinguished. Again, among insects, the well-known naturalist, Mr. Bates, has shown that on the Amazons in South America it is often impossible to tell, among some families of butterflies, which are the same species and which keep apart from each other. Facts like these, of the relationship of living beings, had long been forcing themselves upon naturalists, and this was one of the reasons given by Lamarck for supposing animals to be all descended from a few simple forms.

All the Animals of each Class formed on the same

CH. XL.

DESCENT OF ANIMALS.

421

Plan. Another reason was that curious agreement in the bones of different animals which had become more and more noticed ever since the time of John Hunter, and which Geoffroy St.-Hilaire insisted upon so strongly. Why should the animals of one class (such as the vertebrate or backboned class) be formed all on one plan even to the most minute bones; so that the wing of a bat, the front leg of a horse, the hand of a man, and the flapper of a porpoise, are all made of the same bones, which have either grown together, or lengthened and spread apart, according to the purpose they serve? And, more curious still, why should some animals have parts which are of no use to them, but only seem to be there because other animals of the same class also have them. Thus the whale has teeth like the other mammalia, but they never pierce through the gum; and the boa-constrictor has the beginnings of hind legs hidden under its skin, though they never grow out. Here again it seemed extraordinary, if a boa-constrictor and a whale were created separately, that they should be made with organs which are quite useless; while, on the other hand, if they were descended from the same ancestor as other reptiles and mammalia who have teeth and hind legs, they might be supposed to have inherited these organs; just as, for example, a child sometimes has a mole or other mark upon its body in exactly the same place as its great grandfather had before it.

Embryos of Animals alike in Structure.-Another still more remarkable fact was that pointed out by Von Baer, that the higher animals, such as quadrupeds, before they are perfectly formed, cannot be distinguished from the embryos of other and lower animals, such as fish and reptiles. If animals were created separately why should a dog begin

like a fish, a lizard, and a bird, and have at first parts which it loses as it grows into its own peculiar form?

Living Animals of a Country agree with the Fossil ones.-These were facts entirely belonging to living creatures, but now others sprang up about fossil species which were equally puzzling. We know that certain animals are only found in particular countries; kangaroos and pouched animals, for example, in Australia; and sloths and armadillos in South America. Now it is remarkable that all the fossil quadrupeds in Australia are also pouched animals, though they are of different kinds and larger in size than those now living; and in the same way different species of sloths and armadillos are found fossil in South America; while in the rocks of Europe fossil mammalia are found, only slightly different in form from those which are living there now. Naturalists therefore asked themselves again-'Would it not seem likely that the living pouched animals of Australia and the sloths and armadillos of America are the descendants of the dead ones in the rocks, although they have in the course of long ages become rather different from them; while oxen, bears, wolves, &c., are also the descendants of those which are found buried in the rocks of Europe?

Gradual succession of Animals which have appeared upon the Globe.-—This seemed still more likely as the study of geology advanced, and it became clear that a gradual succession of higher and higher animals had appeared upon the globe. Thus, in the oldest rocks containing fossils, we find no monkeys, no quadrupeds, no reptiles, no amphibians such as our frogs, but only shells of marine animals, and a few bones of fishes, of kinds quite different from those now living. Then in rocks above these we find the fish becoming very abundant and varied, and higher still we meet with