It cannot then be well denied that the astronomers and geologists have made it exceedingly probable that this earth on which we live has been brought to its present condition by passing through a succession of changes from an original state of great heat and fluidity, perhaps even from a mixture mainly consisting of gases; that such a body as the planet Jupiter represents one of the stages through which it has passed, that such a body as the moon represents a stage toward which it is tending; that it has shrunk as it cooled, and as it shrank has formed the elevations which we call mountains, and the depressions which contain the seas and oceans; that it has been worn by the action of heat from within and water from without, and in consequence of this action presents the appearance when examined below the surface of successive strata or layers; that different kinds of animal and vegetable life have followed one another on the surface, and that some of their remains are found in these strata now; and that all this has taken enormous periods of time. All this is exceedingly probable, because it is the way in which, as Laplace first pointed out, under well-established scientific laws of matter, particularly the law of gravitation and the law of the radiation of heat, a great fluid mass would necessarily change. And the whole solar system may and probably did come into its present condition in this way. It certainly could have been so formed, and there is no reason for supposing that it was formed in any other way.
Once more, if we begin, as it were, at the other end, and trace things backwards from the present, instead of forwards from the remote past, it cannot be denied that Darwin's investigations have made it exceedingly probable that the vast variety of plants and animals have sprung from a much smaller number of original forms.
In the first place, the unity of plan which can be found pervading any great class of animals or plants seems to point to unity of ancestry. Why, for instance, should the vertebrate animals be formed on a common plan, the parts of the framework being varied from species to species, but the framework as a whole always exhibiting the same fundamental type? If they all descended from a common ancestor, and the variations were introduced in the course of that descent, this remarkable fact is at once accounted for. But, in the second place, observation shows that slight variations are perpetually being introduced with every successive generation, and many of these variations are transmitted to the generations that follow. In the course of time, therefore, from any one parent stock would descend a very large variety of kinds. But if, in the third place, it be asked why this variety does not range by imperceptible degrees from extreme forms in one direction to extreme forms in the other, the answer is to be found in the enormous prodigality and the equally enormous waste of life and living creatures. Plants and animals produce far more descendants than ever come even to such maturity as to reproduce their kind. And this is particularly the case with the lower forms of life. Eggs and seeds and germs are destroyed by millions, and so in a less but still enormous proportion are the young that come from those that have not been destroyed. There is no waste like the waste of life that is to be seen in nature. Living creatures are destroyed by lack of fit nourishment, by lack of means of reproduction, by accidents, by enemies. The inevitable operation of this waste, as Darwin's investigation showed, has been to destroy all those varieties which were not well fitted to their surroundings, and to keep those that were. One species of animal has been preserved by length of neck, which enabled it to reach high-growing fruits and leaves; another by a thicker skin, which made it difficult for enemies to devour; another by a colour which made it easier to hide. One plant has been preserved by a bright flower which attracted insects to carry its pollen to other flowers of its kind; another by a sweet fruit which attracted birds to scatter its seed. Meanwhile other animals and plants that had not these advantages perished for the lack of them. The result would be to maintain, and perpetually, though with exceeding slowness, more and more to adapt to the conditions of their life, those species whose peculiarities gave them some advantage in the great struggle for existence.
Here again we have the working of known laws of life, capable of accounting for what we see. And the high probability cannot be denied that by evolution of this kind the present races of living creatures have been formed. And to these arguments the strongest corroboration is given by the frequent occurrence, both in plants and animals, of useless parts which still remain as indications of organs that once were useful and have long become useless. Animals that now live permanently in the dark have abortive eyes which cannot see, but indicate an ancestor with eyes that could see. Animals that never walk have abortive legs hidden under their skin, useless now but indicating what was useful once. Our knowledge no doubt in this as in any other province of nature is but the merest fraction of what may be known therein. But there is no evidence whatever to show that what we have observed is not a fair sample of the whole. And so taking it, we find that the mass of evidence in favour of the evolution of plants and animals is enormously great and increasing daily.
Granting then the high probability of the two theories of Evolution, that which begins with Laplace and explains the way in which the earth was fitted to be the habitation of living creatures, and that which owes its name to Darwin and gives an account of the formation of the living creatures now existing, we have to see what limitations and modifications are necessarily attached to our complete acceptance of both.
First, then, at the very meeting point of these two evolutions we have the important fact that all the evidence that we possess up to the present day negatives the opinion that life is a mere evolution from inorganic matter. We know perfectly well the constituents of all living substances. We know that the fundamental material of all plants and all animals is a compound called protoplasm, or that, in other words, organic matter in all its immense variety of forms is nothing but protoplasm variously modified. And we know the constituent elements of this protoplasm, and their proportions, and the temperatures within which protoplasm as such can exist. But we are quite powerless to make it, or to show how it is made, or to detect nature in the act of making it. All the evidence we have points to one conclusion only, that life is the result of antecedent life, and is producible on no other conditions. Repeatedly have scientific observers believed that they have come on instances of spontaneous generation, but further examination has invariably shown that they have been mistaken. We can put the necessary elements together, but we cannot supply the necessary bond by which they are to be made to live. Nay, we cannot even recall that bond when it has once been dissolved. We can take living protoplasm and we can kill it. It will be protoplasm still, so far as our best chemistry can discover, but it will be dead protoplasm, and we cannot make it live again; and as far as we know nature can no more make it live than we can. It can be used as food for living creatures, animals or plants, and so its substance can be taken up by living protoplasm and made to share in the life which thus consumes it; but life of its own it cannot obtain. Now here, as it seems, the acceptance of the two evolutions lands us in acceptance of a miracle. The creation of life is unaccounted for. And it much more exactly answers to what we mean by a miracle than it did under the old theory of creation before Evolution was made a scientific doctrine. For under that old theory the creation of living creatures stood on the same footing as the creation of metals or other inorganic substances. It was part of that beginning which had to be taken for granted, and which for that reason lay outside of the domain of Science altogether. But if we accept the two evolutions, the creation of life, if unaccounted for, presents itself as a direct interference in the actual history of the world. There could have been no life when the earth was nothing but a mass of intensely heated fluid. There came a time when the earth became ready for life to exist upon it. And the life came, and no laws of inorganic matter can account for its coming. As it stands this is a great miracle. And from this conclusion the only escape that has been suggested is to suppose that life came in on a meteoric stone from some already formed habitable world; a supposition which transfers the miracle to another scene, but leaves it as great a miracle as before.
Nor, if it was a miracle, can we deny that there was a purpose in it worthy of miraculous interference. For what purpose can rank side by side with the existence and development of life, the primary condition of all moral and spiritual existence and action in this world? In the introduction of life was wrapped up all that we value and all that we venerate in the whole creation. The infinite superiority, not in degree only, but in kind, of the living to the lifeless, of a man to a stone, justifies us in believing that the main purpose of the creation that we see was to supply a dwelling-place and a scene of action for living beings. We cannot say that the dignity of the Moral Law requires that creatures to be made partakers in the knowledge of it, and even creatures of a lower nature but akin to them, must have been the results of a separate and miraculous act of creation. But we can say that there is a congruity in such a miracle, with the moral purpose of all the world, of which we are a part, that removes all difficulty in believing it. Science, as such, cannot admit a miracle, and can only say, 'Here is a puzzle yet unsolved.' Nor can the most religious scientific man be blamed as undutiful to religion if he persists in endeavouring to solve the puzzle. But he has no right to insist beforehand that the puzzle is certainly soluble; for that he cannot know, and the evidence is against him.
Secondly, if we look at the Darwinian theory by itself, we see at once that it is incomplete, and the consideration of this incompleteness gravely modifies the conclusion which would otherwise be rightly drawn from it, and which, indeed, Darwin himself seems disposed to draw. For the theory rests on two main pillars, the transmission of characteristics from progenitor to progeny, and the introduction of minute variations in the progeny with each successive generation. Now, the former of these may be said to be well established, and we recognise it as a law of life that all plants and animals propagate their own kind. But the latter has, as yet, been hardly examined at all. Each new generation shows special slight variations. But what causes these variations? and what determines what they shall be? In Darwin's investigations these questions are not touched. The variations are treated as if they were quite indefinite in number and in nature. He concerns himself only with the effect of these variations after they have appeared. Some have the effect of giving the plant or animal an advantage in the struggle of life; some give no such advantage; some are hurtful. And hence follows the permanent preservation or speedy destruction of the plants and animals themselves. But we are bound to look not only to their effects but to their causes, if the theory is to be completed. And then we cannot fail to see that these variations in the progeny cannot be due to something in the progenitors, or otherwise the variations would be all alike, which they certainly are not. They must, therefore, be due to external circumstances. These slight variations are produced by the action of the surroundings, by the food, by the temperature, by the various accidents of life in the progenitors. Now, when we see this, we see also how gravely it modifies the conclusions which we have to draw concerning the ancestry of any species now existing. Let us take, for instance, the great order of vertebrate animals. At first sight the Darwinian theory seems to indicate that all these animals are descended from one pair or one individual, and that their unity of construction is due to that fact; but if we go back in thought to the time at which the special peculiarities were introduced which really constituted the order and separated it from other animals, we see that it is by no means clear that it originated with one pair or with one individual, and that, on the contrary, the probabilities are the other way. Although the separation of this order from the rest must have taken place very early, it cannot well have taken place until millions of animals had already come into existence. The prodigality of nature in multiplying animal life is fully acknowledged by Darwin, and that prodigality is apparently greatest in the lowest and most formless type of animal. There being, then, these many millions of living creatures in existence, the external surroundings introduce into them many variations, and among these the special variations to which the vertebrate type is due. It is quite clear that wherever the external surroundings were the same or nearly the same, the variations introduced would be the same or nearly the same. Now, it is far more probable that external surroundings should be the same or nearly the same in many places than that each spot should be absolutely unlike every other spot in these particulars. The beginnings of the vertebrate order would show themselves simultaneously, or at any rate independently, in many places wherever external conditions were sufficiently similar. And the unity of the plan in the vertebrata would be due, not to absolute unity of ancestry, but to unity of external conditions at a particular epoch in the descent of life. Hence it follows that the separation of animals into orders and genera and even into species took place, if not for the most part yet very largely, at a very early period in the history of organic evolution. Of course the descendants of any one of the original vertebrata might, and probably in not a few cases did, branch off into new subdivisions and yet again into further subdivisions, and we are always justified in looking for unity of ancestry among all the species. But it is also quite possible that any species may be regularly descended, without branching off at all, from one of the originals, and that other species that resemble it may owe the resemblance simply to very great similarity of external conditions. To find, for instance, the unity of ancestry between man and the other animals, it will certainly be necessary to go back to a point in the history of life when living creatures were as yet formless, undeveloped—the materials, as we may call them, of the animal creation as we now see it, and not in any but a strictly scientific sense, what we mean when we ordinarily speak of animals. The true settlement of such questions as these can only be obtained when long and patient study shall have completed Darwin's investigations by determining under what laws and within what limits the slight variations which characterise each individual animal or plant are congenitally introduced into its structure. As things stand the probabilities certainly are that a creature with such especial characteristics as man has had a history altogether of his own, if not from the beginning of all life upon the globe, yet from a very early period in the development of that life. He resembles certain other animals very closely in the structure of his body; but the part which external conditions had to play in the earliest stages of evolution of life must have been so exceedingly large that identity or close similarity in these external conditions may well account for these resemblances. And the enormous gap which separates his nature from that of all other creatures known, indicates an exceedingly early difference of origin.
Lastly, it is quite impossible to evolve the Moral Law out of anything but itself. Attempts have been made, and many more will no doubt be made, to trace the origin of the spiritual faculty to a development of the other faculties. And it is to be expected that great success will ultimately attend the endeavours to show the growth of all the subordinate powers of the soul. That our emotions, that our impulses, that our affections should have had a history, and that their present working should be the result of that history, has nothing in it improbable. There can be no question that we inherit these things very largely, and that they are also very largely due to special peculiarities of constitution in each individual. That large part of us which is rightly assigned to our nature as distinct from our own will and our own free action, it is perfectly reasonable to find subject to laws of Evolution. Much of this nature, indeed, we share with the lower animals. They, too, can love; can be angry or pleased; can put affection above appetite; can show generosity and nobility of spirit; can be patient, persevering, tender, self-sacrificing; can take delight in society: and some can even organise it, and thus enter on a kind of civilisation. The dog and the horse, man's faithful servants and companions, show emotions and affections rising as far as mere emotions and affections can rise to the human level. Ants show an advance in the arts of life well comparable to our own. If the bare animal nature is thus capable of such high attainments by the mere working of natural forces, it is to be expected that similar forces in mankind should be found to work under similar laws. We are not spiritual beings only, we are animals, and whatever nature has done for other animals we may expect it to have done and to be doing for us. And if their nature is capable of evolution, so too should ours be. And the study of such evolution of our own nature is likely to be of the greatest value. This nature is the main instrument, put into the grasp as it were of that spiritual faculty which is our inmost essence, to be used in making our whole life an offering to God. It is good to know what can be done with this instrument and what cannot; how it has been formed in the past, and may be still further formed for the future. It is good to study the evolution of humanity. But all this does not touch the spiritual faculty itself, nor the Moral Law which that faculty proclaims to us. The essence of that law is its universality; and out of all this development, when carried to its very perfection, the conception of such universality cannot be obtained. Nothing in this evolution ever rises to the height of a law which shall bind even God Himself and enable Abraham to say, 'Shall not the Judge of all the earth do right?' The very word right in this, its fulness of meaning, cannot be used.
Evolution may lead the creature to say what is hateful and what is loveable, what is painful and what is delightful, what is to be feared and what is to be sought; it may develope the sentiment which comes nearest of all to the sentiment of reverence, namely, the sentiment of shame; but it cannot reveal the eternal character of the distinction between right and wrong. Nay, there may be, as was pointed out in the last Lecture, an evolution in our knowledge even of the Moral Law, just as there is an evolution in our knowledge of mathematics. The fulness of its meaning can become clearer and ever clearer as generation learns from generation. But the principle of the Moral Law, its universality, its supremacy, cannot come out of any development of human nature any more than the necessity of mathematical truth can so come. It stands not on experience, and is its own evidence. Nor indeed have any of the attempts to show that everything in man (religion included) is the product of Evolution ever touched the question how this conception of universal supremacy comes in. It is treated as if it were an unauthorised extension from our own experience to what lies beyond all experience. This, however, is to deny the essence of the Moral Law altogether: that Law is universal or it is nothing.