I will now sum up the results of this sketch of the rise and progress of palaeontology. The whole fabric of palaeontology is based upon two propositions: the first is, that fossils are the remains of animals and plants; and the second is, that the stratified rocks in which they are found are sedimentary deposits; and each of these propositions is founded upon the same axiom, that like effects imply like causes. If there is any cause competent to produce a fossil stem, or shell, or bone, except a living being, then palaeontology has no foundation;if the stratification of the rocks is not the effect of such causes as at present produce stratification, we have no means of judging of the duration of past time, or of the order in which the forms of life have succeeded one another. But if these two propositions are granted, there is no escape, as it appears to me, from three very important conclusions. The first is that living matter has existed upon the earth for a vast length of time, certainly for millions of years. The second is that, during this lapse of time, the forms of living matter have undergone repeated changes, the effect of which has been that the animal and vegetable population, at any period of the earth's history, contains certain species which did not exist at some antecedent period, and others which ceased to exist at some subsequent period. The third is that, in the case of many groups of mammals and some of reptiles, in which one type can be followed through a considerable extent of geological time, the series of different forms by which the type is represented, at successive intervals of this time, is exactly such as it would be, if they had been produced by the gradual modification of the earliest forms of the series. These are facts of the history of the earth guaranteed by as good evidence as any facts in civil history.
Hitherto I have kept carefully clear of all the hypotheses to which men have at various times endeavoured to fit the facts of palaeontology, or by which they have endeavoured to connect as many of these facts as they happened to be acquainted with.
I do not think it would be a profitable employment of our time to discuss conceptions which doubtless have had their justification and even their use, but which are now obviously incompatible with the well-ascertained truths of palaeontology.
At present these truths leave room for only two hypotheses.
The first is that, in the course of the history of the earth, innumerable species of animals and plants have come into existence, independently of one another, innumerable times.
This, of course, implies either that spontaneous generation on the most astounding scale, and of animals such as horses and elephants, has been going on, as a natural process, through all the time recorded by the fossiliferous rocks; or it necessitates the belief in innumerable acts of creation repeated innumerable times. The other hypothesis is, that the successive species of animals and plants have arisen, the later by the gradual modification of the earlier. This is the hypothesis of evolution; and the palaeontological discoveries of the last decade are so completely in accordance with the requirements of this hypothesis that, if it had not existed, the palaeontologist would have had to invent it.
I have always had a certain horror of presuming to set a limit upon the possibilities of things. Therefore I will not venture to say that it is impossible that the multitudinous species of animals and plants may have been produced, one separately from the other, by spontaneous generation; nor that it is impossible that they should have been independently originated by an endless succession of miraculous creative acts. But I must confess that both these hypotheses strike me as so astoundingly improbable, so devoid of a shred of either scientific or traditional support, that even if there were no other evidence than that of palaeontology in its favour, I should feel compelled to adopt the hypothesis of evolution. Happily, the future of palaeontology is independent of all hypothetical considerations. Fifty years hence, whoever undertakes to record the progress of palaeontology will note the present time as the epoch in which the law of succession of the forms of the higher animals was determined by the observation of palaeontological facts. He will point out that, just as Steno and as Cuvier were enabled from their knowledge of the empirical laws of co-existence of the parts of animals to conclude from a part to the whole, so the knowledge of the law of succession of forms empowered their successors to conclude, from one or two terms of such a succession, to the whole series; and thus to divine the existence of forms of life, of which, perhaps, no trace remains, at epochs of inconceivable remoteness in the past.
FOOTNOTES
(1) De Solidoiintra Solidum, p.5--"Dato corpore certa figura praedito et juxta leges naturae producto, in ipso corpore argumenta invenire locum et modum productionis detegentia."(2) "Corpora sibi invicem omnino similia simili etiam modo producta sunt."(3) Sir J. D. Hooker.
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