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and progress from the most ancient times. The following table may be taken to outline roughly our present knowledge of the facts :—

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However, many of these fully-developed types appear suddenly and unheralded in the geological strata, so that a gradual change from less perfect to better developed forms is not proved. But naturalists appeal to factors of immigration and to the incompleteness of the data as yet observed. This contention receives support from the present distribution of living organisms, inasmuch as they are found to be closely connected with the distribution of fossils and the geological record of the strata. Take, for instance, the existing mammals of South America: two groups can be readily made out, one of exclusively indigenous animals (e.g., the monkeys and marmosets), and a second one containing animals which are closely related to those which now live, as they formerly lived, in North America. The geology of the Isthmus shows that South America was formerly cut off from the northern continent, and in the strata which represent this state of isolation, not a single fossil has been found that was ancestral to the second group of mammals; while ancestral remains of the latter are to be found in the strata succeeding the union of the two continents. Migration and ancestral development, it is maintained, are clearly demonstrated.

Analogous evidence is obtained from the fauna of islands. The continental islands, which can be shown geologically to have formed part of the continent (e.g., Great Britain, Madagascar, Borneo, Sumatra, and Java), share in its fossils and present forms, and this in proportion as the separation took place in more or less recent epochs. The Oceanic Islands, on the other hand, although fully capable of sustaining life, have only been populated by chance

migration, such as drift-wood and wind-storms may carry with them. Thus spiders, flies, bugs, beetles, butterflies, and lizards abounded in Krakatoa shortly after the great eruption of 1883, which buried all life under a deep layer of volcanic debris; but no land mammals (except bats, which are often carried immense distances by strong gales) are to be found in those parts which have not been artificially introduced by man.

(3) Embryology, difficult as it is in its interpretation and liable to abuse, still affords additional evidence which is claimed by naturalists for the theory of descent. It reveals the fact that all forms begin as unicellular organisms, and pass through stages which are hardly distinguishable one from another in the various types. The number of stages also, in individual development, is proportional to the complexity of the adult form. Thus, not only such widely divergent animals as fishes, amphibians, reptiles, birds, and mammals exhibit the same plan of development, before reaching their adult form, but also this development seems to show stages corresponding to its grade in the scale of complexity. For example, the embryo of a mammal has gillpouches, skeletal supports, arteries, and veins and heart, like a fish; at a later stage its structure is that of the lung-fishes.

Further, embryology helps to connect the various orders, which are not shown to be related by the evidence already outlined, e.g., the segmented worms and the shell-fish possess closely similar types of larvae; the lancelet and tunicates are shown to be linked with vertebrates as well as invertebrates.

Such is the bare outline of the copious evidence which scientists consider to be explained by the theory of descent. If, they argue, the existing animals and plants had been created as they are now, all these facts would be mere puzzles. If, however, the existing types are transformations of more primitive organism, then it is possible to connect all these converging lines of argument into an intelligent whole.

It is essential to note that this theory does not in any way exclude creation; indeed Cuvier and Agassiz, who upheld special creation and immutability of species, were forced to admit a systematic creative plan to explain the palaeontological data then known.

Secondly, it should be kept in mind that what scientists

propose here is a theory, held, it is true, to be most probable, but as yet unproved-some say unprovable-and, from the very nature of the case capable of modification or even rejection, should future evidence and research demand it. Indeed, it is significant that an eminent professor in zoology-however isolated he may be could say, 'The more deeply I pursued the alleged evidence for it (this theory), and sought to gain through special investigations some essential proof of the genetic relationships of animals, the more clearly I recognized that the theory is a seductive romance, which deceptively pretends to give results and explanations, rather than a doctrine built upon positive foundations.'1 In fact, no indubitable cases of species formation, i.e., of transformation from one species to the other, have been observed.

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Even if the few cases put forward by evolutionists could be proved to be absolute new productions of species, they are too few, even if multiplied a hundredfold, to be advanced as an objective' proof of the real descent by transformation of the millions of species known to science. The theory of descent does connect in a rational manner all the facts of nature which naturalists have grouped together under the titles of 'homology,'' palaeontological succession,' ontogeny,' and 'geographical distribution,' outlined above, but it does not explain all, nor, in fact, the most important parts of the facts known, e.g., the sudden appearance of the Cambrian fauna, the origin of the fishes in Silurian strata, the existence of highly specialized types from earliest times, the lack of imperfect ancestral systems to the rich forms of post-Silurian flora, the fact that the fundamental structures of types' persist throughout, though these may differ considerably one from another. 'Never before has it become so notorious as in the last decade how little there is in this theory that is universally accepted, as appears when the most obvious questions are asked regarding the course of development and its efficient causes.' &

Hence, many naturalists would postulate a common origin of all living organisms, not from one ancestral type, but from several, so as to account more readily for the numerous missing links in the evolutionary descent. This

1 Albert Fleischmann, Prof. at Erlangen, in his Die Descendenztheorie, p. iii. Leipzig, 1901.

2 Steinmann, Die Abstammungslehre, pp. 1, 2. Leipzig, 1908.

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would leave a possibility open, namely, that what naturalists call species' are not true species in the strict sense of the term, but the modified varieties of species as yet unrecognized. As a matter of fact, naturalists admit that the term 'species' as used in natural history is a very vague and elastic concept, dependent more on the subjective whims of the classifying zoologist than on a uniform objective standard of essential properties.

While all naturalists accept and are agreed as to the significance of the theory of descent, there is at the present time a heated controversy with regard to the causes which produce the evolutionary transformations and the reasons why the progressive graduations met with in fossils do not present those irregularities which should be expected from chance productions, but progress instead in one direction only, and appear to be teleological in character.

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Darwin had formulated, modestly enough, the principle of natural selection or the survival of the fittest' Spencer put it, without however, stating anything about the origin of fitness.' Before his epoch-making enunciation, Lamarck (1744-1829) had stated that an orderly and progressive evolution was due to transmission of acquired characters; while Buffon (1707-1788) and Erasmus Darwin (1731-1802) had recognized other influences at work in the modification of existing types, such as adaptation to environment, the use and disuse of organs. De Vries brought to light again the discovery of Mendel, that variation occurred along definite lines, not by any ever-present fluctuating variations in the struggle for existence, but by spontaneous and sudden changes, on which the other factors would act as selective guides, or like a sieve, determining which varieties were to live and which to die.

The discussion has been obscured by the further issues as to the nature and the origin of life: whether life is a mere physico-chemical process; whether evolution is the result of causo-mechanical agency between the sensitive organism and its surroundings, or whether it is not rather the outcome of inherent forces which are only stimulated to action by environmental influences, and are not caused by them.

That there is absolutely no scientific evidence for spontaneous generation cannot be called into question at the present day; indeed, the researches of Pasteur and his

collaborators and the whole science of pathology and preventive medicine go to confirm this, its fundamental axiom, omne vivum e vivo. Even if spontaneous generation were a proved fact, the question of the origin of life would still remain an open one from the scientific point of view, until the disputed sufficiency of physico-chemical processes to explain all the phenomena of life were settled. It should be noted that these two principles do not pertain solely to biology, but fall within the sphere of psychological science, especially as biology ignores completely all differences in psychic activities in the zoo-phytic groupings.

The debate remains open, for though the experimental evidence seems to be in favour of the indivisibility and distinctness of unit species-characteristics, still the causomechanical theory of selectionists is not considered to have been proved untenable.

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From a zoological point of view, man is an animal, and it is natural that zoologists should seek to find man's place in the zoological scale, and to inquire how far he can be made to fit in with existing evolutionary theories. As far as his anatomical structure is concerned, the human organism is obviously related to the higher apes. So much so that the structural differences between the higher apes and their lower types are greater than the structural differences between themselves and man. Some zoologists have, therefore, maintained that man is but an ape-the highest ape known. But zoology ignores completely psychic factors which do not come within its scope, and therefore zoology is incompetent to judge of the significance of such factors. Even if the body of man had been exactly similar to that of an ape, the psychic factors would be sufficient to show that similarity of bodily form does not necessarily argue to identity of whole individuality-much more so when the bodily differences themselves, slight as they are from a zoological point of view, are those demanded by the all-important subservience to the psychic factors.

Assuming that anatomically man is related to the higher apes, the next point to decide is (4) whether there is any evidence of evolution in the human organism, and (B) whether this evolution has proceeded from ape-like ancestors or otherwise.

(4) The arguments adduced for the evolution of mankind are the same as those shown above for the theory of

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