Other Instances of Persistent form.

More than that. At the very bottom of the Silurian series, in what is by some authorities termed the Cambrian formation, where all signs appear to be dying out—even there, among the few and scanty animal remains which exist, we find species of molluscous animals which are so closely allied to existing forms that at one time they were grouped under the same generic name. I refer to the well-known Lingula of the Lingula flags. It was subsequently, in consequence of some slight differences, placed in the new genus Lingulella. Practically it belongs to the same great generic group as the Lingula, which you will find at the present day upon the shores of Australia. And the same thing is exemplified if we turn to certain great periods of the earth's page 19 history—as, for example, throughout the whole of the mesozoic period. There are groups of reptiles which begin shortly after the commencement of this period, as the Ichthyosauria and the Plesiosauria, and they abound in vast numbers. They disappear with the chalk, and throughout the whole of that great series of rock they present no important modification. Facts of this kind are undoubtedly fatal to any form of the doctrine of Evolution which necessitates the supposition that there is an intrinsic necessity on the part of animal forms which once come into existence to undergo modification; and they arc still more distinctly opposed to any view which should lead to the belief that the modification in different types of animal or vegetable life goes on equally and evenly. The facts, as I have placed them before you, would obviously contradict directly any such form of the hypothesis of Evolution as laid down in these two postulates.

Now the service that has been rendered by Mr. Darwin to the doctrine of Evolution in general is this: that he has shown that there are two great factors in the process of Evolution, and one of them is the tendency to vary, the existence of which may be proved by observation in all living forms; the other is the influence of surrounding conditions upon what I may call the parent form, and the variations which are thus evolved from it. The cause of that production of variations is a matter not at all properly understood at present. Whether it depends upon some intricate machinery—if I may use the phrase—of the animal form itself, or whether it arises through the influence of conditions upon that form, is not certain, and the question may for the present be left open. But the important point is the tendency to the production of variations; then whether those variations shall survive and supplant the parent, or whether the parent form shall survive and supplant the variations, is a matter which depends entirely on surrounding conditions. If the surrounding conditions are such that the parent form is more competent to deal with them and flourish in them than the derived forms, then in the struggle for existence the parent form will maintain itself and the derived forms will be exterminated. But if, on the contrary, the conditions are such as to be better for the derived than for the parent form, the parent form will be extirpated and the derived form will take its place.

In the first case there will be no progression, no advance of type, through any imaginable series of ages; in the second place, there will be modification and change of form, and thus we see that the immense amount of evidence brought to show that things do in this way take place in Nature, puts us in such a place that the existence of these persistent types of life is no obstacle in the way of the theory of Evolution at all. Take the case of these scorpions to which I have just referred. No doubt since the carboniferous epoch conditions have existed such as existed then when scorpions flourished, in which they find themselves better off, more competent to deal with the difficulties in their way than any kind of variation from the scorpion type and for that reason the scorpion has persisted and has not been supplanted by any other form. And there is no reason in the nature of things why, as long as this world exists, if there be conditions more favourable to scorpions than any variation which may arise from them, these forms of life should not persist.