Page:Encyclopædia Britannica, Ninth Edition, v. 24.djvu/869

Rh ZOOLOGY 819 the transmission (as Lamarck would have supposed) of a more and more weakened and structurally impaired eye to the offspring in successive generations, until the eye finally disappeared. But this instance is really fully ex plained by the theory of natural selection acting on con genital fortuitous variations. Many animals are thus born with distorted or defective eyes whose parents have not had their eyes submitted to any peculiar conditions. Sup posing a number of some species of Arthropod or Fish to be swept into a cavern or to be carried from less to greater depths in the sea, those individuals with perfect eyes would follow the glimmer of light and eventually escape to the outer air or the shallower depths, leaving behind those with imperfect eyes to breed in the dark place. A natural selection would thus be effected. In every succeeding generation this would be the case, and even those with weak but still seeing eyes would in the course of time escape, until only a pure race of eyeless or blind animals would be left in the cavern or deep sea. Experiments and inquiries with regard to this subject are in progress; amongst those who have occupied themselves with it are August Weismann of Freiburg and E. B. Poulton of Oxford. It has been argued that the elaborate structural adapta tions of the nervous system which are the corporeal correla tives of complicated instincts must have been slowly built up by the transmission to offspring of acquired experience, that is to say, of acquired brain structure. At first sight it appears difficult to understand how the complicated series of actions which are definitely exhibited as so-called &quot; instincts &quot; by a variety of animals can have been due to the selection of congenital variations, or can be otherwise explained than by the transmission of habits acquired by the parent as the result of experience, and continuously elaborated and added to in successive generations. It is, however, to be noted, in the first place, that the imitation of the parent by the young possibly accounts for some part of these complicated actions, and, secondly, that there are cases in w-hich curiously elaborate actions are performed by animals as a characteristic of the species, and as sub serving the general advantage of the race or species, which, nevertheless, can not be explained as resulting from the transmission of acquired experience, and must be supposed to be due to the natural selection of a fortuitously developed habit which, like fortuitous colour or form variation, happens to prove beneficial. Mr Poulton has insisted upon the habits of &quot; shamming dead &quot; and the combined posturing and colour peculiarities of certain caterpillars (Lepidopterous larva?) which cause them to resemble dead twigs or similar surrounding objects. The advantage to the animal of this imitation of surrounding objects is that it escapes the pursuit of (say) a bird which would, were it not deceived by the resemblance, attack and eat the cater pillar. Now it is clear that preceding generations of cater pillars cannot have acquired this habit of posturing by experience. Either the caterpillar postures and escapes, or it does not posture and is eaten ; it is not half eaten and allowed to profit by experience. We seem to be justified in assuming that there are many movements of stretching and posturing possible to caterpillars, and that some cater pillars had a congenital fortuitous tendency to one position, some to another, and, finally, that among all the variety of habitual movements thus exhibited one has been selected and perpetuated because it coincided with the necessary conditions of safety, since it happened to give the caterpillar an increased resemblance to a twig. The view that instinct is the hereditarily fixed result of habit derived from experience has hitherto dominated all inquiry into the subject, but we may now expect to see a renewed and careful study of animal instincts carried out with the view of testing the applicability to each in stance of the pure Darwinian theory without the aid of Lamarckism. The whole of this inquiry has special importance in regard to mankind, since the great questions of influence of race and family as opposed to the influence of education are at issue. If pure Darwinism is to be accepted, then education has no value in directly affecting the mental or physical features of the race, but only in affecting those of the individual. Were acquired characters really and fully transmitted, then every child born would inherit the know ledge of both its parents more or less completely, and from birth onwards would be able to add to its inherited stock, so that the progress of the race in mental acquirements would be prodigiously more rapid than it is. On the other hand, peculiarities of mind and body established in a race or a family acquire increased significance, for they cannot be got rid of by training, but are bound to reappear if the stock which exhibits them is allowed to breed. It seems that the laws of thremmatology may eventually give to mankind the most precise directions, not only as to how to improve the breeds of plants and animals, but as to how to improve the human stock. It is not a little re markable that the latest development of zoological science should favour that respect to breeding which is becoming less popular than it was, and should tend to modify the current estimate of the results of education. The relation of Darwinism to general philosophy and of Relation the history of zoology to philosophical doctrines is one of of zo - the most interesting chapters which might be written on *? tc the subject of this article. It belongs, however, rather to so ,,i iv- the history of philosophy than to that of zoology. Undoubt edly the conceptions of mankind at different periods of history with regard to cosmogony, and the relations of God, nature, and man, have had a very marked influence upon the study of zoology, just as in its turn the study of zoology has reacted upon those conceptions. In this, as in other phases of mental development, the Develop- ancient Greeks stand out in the most striking manner as ment f possessing what is sometimes called the modern spirit. tl e l , The doctrine of evolution is formulated in unmistakable tiou terms by Heraclitus and other philosophers of antiquity. Not only so, but the direct examination of nature, includ ing the various forms of animal life, was practised by Aristotle and his disciples in a spirit which, though not altogether free from prejudice, was yet far more like that which actuated the founders of the Royal Society less than three hundred years ago than anything which was mani fested in the two thousand years intervening between that date and the time of Alexander the Great. The study of zoology in the Middle Ages was simply a fantastic commentary on Aristotle and the records of animals in the various books of the Bible, elaborated as part of a peculiar system of mystic philosophy, which has more analogy with the fetichism and totem worship of savage races than with any Greek or modern conceptions. So far as philosophy affected the study of zoology in the beginning of the modern period, its influence was felt in the general accept ance of what has been called the Miltonic cosmogony, namely, that interpretation of the Mosaic, writings which is set forth by the poet Milton, and of which the character istic is the conception of the creation of existing things, including living things, nearly or just as they are, by a rapid succession of &quot; fiats &quot; delivered by an anthropo morphic Creator. It was not until the end of the 18th century that Schelling (as quoted above) conceived that unity of nature and general law of development which is now called the doctrine of evolution. In England Erasmus Darwin (Zoonomia, published in 1794-96), in France Lamarck (Philosophic Zoologigue,