Facts and fancies in modern science / Studies of the relations of science to prevalent speculations and religious belief

by Sir John William Dawson

The latter is a process not open to observation within the time at our command—purely hypothetical, therefore, and of which the possibility remains to be proved; while the causes on which it must depend are necessarily altogether different from those at work in ontogenesis, and the conditions of a long series of different kinds of animals, each perfect in its kind, are equally dissimilar from those of an animal passing through the regular stages from infancy to maturity. The similarity, in some important respects, of ontogenesis to phylogenesis was inevitable, provided that animals were to be of different grades of complexity, since the development of the individual must necessarily be from a more simple to a more complex condition. On any hypothesis, the parallelism between embryological facts and the history of animals in geological time affords many interesting and important coincidences. Yet it is perfectly obvious that the causes and the conditions of these two successions cannot have been the same. Further, when we consider that the embryo-cell which develops into one animal must necessarily be originally distinct in its properties from that which develops into another kind of animal, even though no obvious difference appears to us, we have no ground for supposing that the early stages of all animals are alike; and when we rigorously compare the development of any animal whatever with the successive appearance of animals of the same or similar groups in geological time, we find many things which do not correspond—not merely in the want of links which we might expect to find, but in the more significant appearance, prematurely or inopportunely, of forms which we would not anticipate. Yet the main argument of Haeckel's book is the quiet assumption that anything found to occur in ontogenetic development must also have occurred in phylogenesis, while manifest difficulties are got rid of by assuming atavisms and abnormalities.

A third characteristic of the method of the book is the use of certain terms in peculiar senses, and as implying certain causes which are taken for granted, though their efficacy and their mode of operation are unknown. The chief of the terms so employed are "heredity" and "adaptation." "Heredity" is usually understood as expressing the power of permanent transmission of characters from parents to offspring, and in this aspect it expresses the constancy of specific forms; but, as used by Haeckel, it means the transmission by a parent of any exceptional characters which the individual may have accidentally assumed. "Adaptation" has usually been supposed to mean the fitting of animals for their place in nature, however that came about; as used by Haeckel, it imports the power of the individual animal to adapt itself to changed conditions and to transmit these changes to its offspring. Thus in this philosophy the rule is made the exception and the exception the rule by a skilful use of familiar terms in new senses; and heredity and adaptation are constantly paraded as if they were two potent divinities employed in constantly changing and improving the face of nature.

It is scarcely too much to say that the conclusions of the book are reached almost solely by the application of the above-mentioned peculiar modes of reasoning to the vast store of facts at command of the author, and that the reader who would test these conclusions by the ordinary methods of judgment must be constantly on his guard. Still, it is not necessary to believe that Haeckel is an intentional deceiver. Such fallacies are those which are especially fitted to mislead enthusiastic specialists, to be identified by them with proved results of science, and to be held in an intolerant and dogmatic spirit.

Having thus noticed Haeckel's assumptions and his methods, we may next shortly consider the manner in which he proceeds to work out the phylogeny of man. Here he pursues a purely physiological method, only occasionally and slightly referring to geological facts. He takes as a first principle the law long ago formulated by Hunter, Omne vivum ex ovo—a law which modern research has amply confirmed, showing that every animal, however complex, can be traced back to an egg, which in its simplest state is no more than a single cell, though this cell requires to be fertilized by the addition of the contents of another dissimilar cell, produced either in another organ of the same individual or in a distinct individual. This process of fertilization Haeckel seems to regard as unnecessary in the lowest forms of life; but, though there are some simple animals in which it has not been recognized, analogy would lead us to believe that in some form it is necessary in all. Haekel's monistic view, however, requires that in the lowest forms it should be absent and should have originated spontaneously, though how does not seem to be very clear, as the explanation given of it by him amounts to little more than the statement that it must have occurred. Still, as a "dualistic" process it is very significant with reference to the monistic theory.

Much space is, of course, devoted to the tracing of the special development or ontogenesis of man, and to the illustration of the fact that in the earlier stages of this development the human embryo is scarcely distinguishable from that of lower animals. We may, indeed, affirm that all animals start from cells which, in so far as we can see, are similar to each other, yet which must include potentially the various properties of the animals which spring from them. As we trace them onward in their development, we see these differences manifesting themselves. At first all pass, according to Haeckel, through a stage which he calls the "gastrula," in which the whole body is represented by a sort of sac, the cavity of which is the stomach and the walls of which consist of two layers of cells. It should be stated, however, that many eminent naturalists dissent from this view, and maintain that even in the earliest stages material differences can be observed. In this they are probably right, as even Haeckel has to admit some degree of divergence from this all-embracing "gastræa" theory. Admitting, however, that such early similarity exists within certain limits, we find that, as the embryo advances, it speedily begins to indicate whether it is to be a coral-animal, a snail, a worm, or a fish. Consequently, the physiologist who wishes to trace the resemblances leading to mammals and to man has to lop off one by one the several branches which lead in other directions, and to follow that which conducts by the most direct course to the type which he has in view. In this way Haeckel can show that the embryo Homo sapiens is in successive stages so like to the young of the fish, the reptile, the bird, and the ordinary quadruped that he can produce for comparison figures in which the cursory observer can detect scarcely any difference.

All this has long been known, and has been regarded as a wonderful evidence of the homology or unity of plan which pervades nature, and as constituting man the archetype of the animal kingdom—the highest realization of a plan previously sketched by the Creator in many ruder and humbler forms. It also teaches that it is not so much in the mere bodily organism that we are to look for the distinguishing characters of humanity as in the higher rational and moral nature.

But Haeckel, like other evolutionists of the monistic and agnostic schools, goes far beyond this. The ontogeny, on the evidence of analogy, as already explained, is nothing less than a miniature representation of the phylogeny. Man must in the long ages of geological time have arisen from a monad, just as the individual man has in his life-history arisen from an embryo-cell, and the several stages through which the individual passes must be parallel to those in the history of the race. True, the supposed monad must have been wanting in all the conditions of origin, sexual fertilization, parental influence, and surroundings. There is no perceptible relation of cause and effect, any more than between the rotation of a carriage-wheel and that of the earth on its axis. The analogy might prompt to inquiries as to common laws and similarities of operation, but it proves nothing as to causation.

In default of such proof, Haeckel favors us with another analogy, derived from the science of language. All the Indo-European languages are believed to be descended from a common ancestral tongue, and this is analogous to the descent of all animals from one primitive species. But unfortunately the languages in question are the expressions of the voice and the thought of one and the same species. The individuals using them are known historically to have descended by ordinary generation from a common source, and the connecting-links of the various dialects are unbroken. The analogy fails altogether in the case of species succeeding each other in geological time, unless the very thing to be proved is taken for granted in the outset.

The actual proof that a basis exists in nature for the doctrine of evolution founded on these analogies, might be threefold. First. There might be changes of the nature of phylogenesis going on under our own observation, and even a very few of these would be sufficient to give some show of probability. Elaborate attempts have been made to show that variations, as existing in the more variable of our domesticated species, lead in the direction of such changes; but the results have been unsatisfactory, and our author scarcely condescends to notice this line of proof. He evidently regards the time over which human history has extended as too short to admit of this kind of demonstration. Secondly. There might be in the existing system of nature such a close connection or continuous chain of species as might at least strengthen the argument from analogy; and undoubtedly there are many groups of closely allied species, or of races confounded with true specific types, which it might not be unreasonable to suppose of common origin. These are, however, scattered widely apart; and the contrary fact of extensive gaps in the series is so frequent, that Haeckel is constantly under the necessity of supposing that multitudes of species, and even of larger groups, have perished just where it is most important to his conclusion that they should have remained. This is, of course, unfortunate for the theory; but then, as Haeckel often remarks, "we must suppose" that the missing links once existed. But, thirdly, these gaps which now unhappily exist may be filled up by fossil animals; and if in the successive geological periods we could trace the actual phylogeny of even a few groups of living creatures, we might have the demonstration desired. But here again the gaps are so frequent and so serious that Haeckel scarcely attempts to use this argument further than by giving a short and somewhat imperfect summary of the geological succession in the beginning of his second volume. In this he attempts to give a continuous series of the ancestors of man as developed in geological time; but, of twenty-one groups which he arranges in order from the beginning of the Laurentian to the modern period, at least ten are not known at all as fossils, and others do not belong, so far as known, to the ages to which he assigns them. This necessity of manufacturing facts does not speak well for the testimony of geology to the supposed phylogeny of man.

In point of fact, it cannot be disguised that, though it is possible to pick out some series of animal forms, like the horses and camels referred to by some palæontologists, which simulate a genetic order, the general testimony of palæontology is, on the whole, adverse to the ordinary theories of evolution, whether applied to the vegetable or to the animal kingdom. This the writer has elsewhere endeavored to show; but he may refer here to the labors of Barrande, perhaps unrivalled in extent and accuracy, which show that in the leading forms of life in the older geological formations the succession is not such as to correspond with any of the received theories of derivation.[2] Even evolutionists, when sufficiently candid, admit their case not proven by geological evidence. Gaudry, one of the best authorities on the Tertiary mammalia, admits the impossibility of suggesting any possible derivation for some of the leading groups, and Saporta, Mivart, and Le Conte fall back on periods of rapid or paroxysmal evolution scarcely differing from the idea of creation by law, or mediate creation, as it has been termed.