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quence of the want of scientific investigations fitted to guide the public mind. So far as a general conclusion has gained assent, men show no reluctance to accept the clear logical inferences following from the investigation of nature.
Among these results is rejection of fixedness of species as implying impossibility of deviation from a single normal type of structure. The possibility of adaptive changes being granted, the absolute fixedness of species in the rigid sense formerly acknowledged is abandoned. How great the modification of view must be, is much more difficult to decide, and hardly admits of exact statement. There is certainly no denial of distinction of species, nor can such denial ever find acceptance, whatever be the advance of theory, for the distinctions are so broad as to render this impossible. But the whole work of classification of the different orders of animal life, exceedingly difficult in any case, has been rendered much more perplexing in consequence of the accumulation of evidence favoring the doctrine of evolution. What can properly be regarded as the origin of a new species, and what as a mere modification or advance in a species already recognized, are questions for which it is difficult to find an exact answer. The theory of the "origin of species" by natural selection seems placed in an awkward perplexity as to what constitutes origin of a new order of life. And this difficulty must be regarded as a constant attendant on the scheme of thought, since "adaptive changes" must be of slow progress, and historically obscure, inasmuch as a succession of very slight differences must contribute to a general result. In this way it may even become matter of keen discussion what actually constitutes organic advance. Mr. Darwin admits serious difficulty at this point. He says, "Here we enter on a very intricate subject, for naturalists have not defined to each other's satisfaction what is meant by an advance in organization." * Thus there is dispute among competent authorities as to which may properly be considered the highest order of plants, and which the highest order of fishes. On the other hand, it is comparatively easy to decide among the more highly organized animals, when an advance is made, by reference to increased complexity in structure, or provision of separate organs for ac
complishment of distinct functions. These considerations, however, suffice to indicate how many and complicated are the subjects requiring to be examined on evidence, and adjusted in their relations to each other, before it can be possible to get beyond surmise, in order to formulate a complete scientific theory. That "adaptive changes" by natural law of evolution are not only possible, but that they frequently occur under observation, admits of no question; but whether this includes changes of structure such as imply origin of species may still be subject of grave doubt. The alterations made by Mr. Darwin in successive editions of his book, from the first edition in 1859, to the sixth edition in 1872,* introduced, as he explains, "according as the evidence has become somewhat stronger or weaker," are sufficient to suggest that a vast amount of work remains to be done before a well-defined theory can be formulated. While there is universal agreement as to the possibility of " adaptive changes" to which Mr. Darwin provisionally restricted his theory on account of the investigations of
* It may be well to mention here that the third American edition is from the fifth English edition.
Nageli as to plants, and those of Broca as to animals, there is much diversity of opinion concerning the wider application of the theory of evolution. This diversity arises in part from the varying estimate of the value of evidence as now accumulated, and in part from the varying conception of the completeness of our records of the ancient history of organism as presented by geology. There is as yet no general consensus of opinion, nor is there likely to be for a long time to come. Mr. Darwin himself is sufficiently cautious and faithful to observational methods, to admit that there are serious difficulties, of some of which he ventures only to say that they " are greatly diminished," while some have disappeared. Other writers, such as Hasckel, with greatly less caution, and with much greater alacrity in leaping over chasms, are prepared to go much further and faster than Darwin. Many more are exceedingly doubtful as to the scientific value of the evidence at command, being, as Mr. Darwin has said, "much shaken in their former belief." * And of many it must be said that they are convinced that the evidence is far from warranting the con
* Origin qf Species, 6th ad., p. 289.
elusion that all organized existence can be traced to "only a few forms," or to "one," according to the alternatives suggested by Darwin in the closing sentence of his book.
Waiving, then, meanwhile, as the state of scientific evidence warrants us to do, the question of the probable number of primordial forms in which organized existence appeared, there is at least another definite result to be recorded as following from even a modified recognition of a theory of development, that is the rejection of belief in the simultaneous origin of all species or orders of animal life existing now in the world. The scientific conception of the history of animal life is, that there has been a historical progression in the appearance of animals, in so far as lower orders took precedence of higher, while the higher have shown large power of adaptation to the circumstances in which they have been placed. In accordance with the whole principles regulating the relations of religion and science, religious men, scientific and non-scientific, will readily acquiesce in this modification of general belief, as largely favored by evidence which geology supplies, and supported by testimony drawn