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Talk:Zoology (general)  [[Talk:Zoology/EBtext]] , and [[Talk:Zoology/EBtext_systematics]]
Talk:Zoology (general)  [[Talk:Zoology/EBtext]] , and [[Talk:Zoology/EBtext_systematics]]
This is the page for general talk, about the CZ article.  
This is the page for general talk, about the new CZ article.
==History of zoology==
 
Humans have been fascinated by the other members of the animal kingdom throughout history. In [[Europe]], they gathered up and treasured stories of strange animals from distant lands or deep seas, such as are recorded in the ''[[Physiologus]]'', in the works of [[Albertus Magnus]] (''[[On Animals]]'' and so on), and other such works. These accounts were characterised by great credulity, and the creatures can be described as “legendary”. This period was succeeded by the age of collectors and travellers, when many of the strange stories believed in were actually demonstrated as true by the living or preserved trophies being brought to Europe.
 
Verification by collecting of things, instead of the accumulating of reports, then became more common, and scholars developed a new faculty of minute observation. The early collectors of natural curiosities were the founders of zoological science, and to this day the [[naturalist]] traveller and his correlative, the [[museum curator]] and [[systematist]], play a most important part in the progress of zoology. Indeed, the historical importance of this aspect or branch of zoological science was previously so great that the name “zoology“ had until the beginning of the [[20th century]] been associated entirely with it, to the exclusion of the study of minute anatomical structure ([[anatomy]]) and function ([[physoiology]]). Anatomy and the study of animal mechanism, animal physics and animal chemistry, all of which form part of a true zoology, were excluded from the usual definition of the word by the mere accident that the zoologist had his museum but not his garden of living specimens as the botanist had; and, whilst the zoologist was thus deprived of the means of anatomical and physiological study - only later supplied by the method of preserving animal bodies in [[alcohol]] - the demands of [[medicine]] for a knowledge of the structure of the human animal brought into existence a separate and special study of [[human anatomy]] and [[human physiology|physiology]].
 
From these special studies of human structure the knowledge of the anatomy of animals has proceeded, the same investigator who had made himself acquainted with the structure of the human body desiring to compare with the standard given by human anatomy the structures of other animals. Thus [[comparative anatomy]] came into existence as a branch of inquiry apart from zoology, and it was only in the latter part of the [[19th century]] that the limitation of the word “zoology” to a knowledge of animals which expressly excludes the consideration of their internal structure was rejected by scientists. It is now generally recognised that it is mere tautology to speak of zoology and comparative anatomy, and that museum naturalists must give attention as well to the inside as to the outside of animals.
 
Scientific zoology really started in the [[16th century]] with the awakening of the new spirit of observation and exploration, but for a long time ran a separate course uninfluenced by the progress of the [[medicine|medical]] studies of anatomy and physiology. The active search for knowledge by means of observation and experiment found its natural home in the [[university|universities]]. Owing to the connection of medicine with these seats of learning, it was natural that the study of the structure and functions of the human body and of the animals nearest to man should take root there; the spirit of inquiry which now for the first time became general showed itself in the anatomical schools of the [[Italy|Italian]] universities of the 16th century, and spread fifty years later to [[University of Oxford|Oxford]].
 
In the [[17th century]], the lovers of the new philosophy, the investigators of nature by means of observation and experiment, banded themselves into academies or societies for mutual support and intercourse. The first founded of surviving European academies, the [[Academia Naturae Curiosorum]] ([[1651]]) especially confined itself to the description and illustration of the structure of plants and animals; eleven years later ([[1662]]) the [[Royal Society of London]] was incorporated by [[royal charter]], having existed without a name or fixed organisation for seventeen years previously (from [[1645]]). A little later the [[Academy of Sciences]] of [[Paris]] was established by [[Louis XIV]]. The influence of these great academies of the [[17th century]] on the progress of zoology was precisely to effect that bringing together of the museum-men and the [[physician]]s or [[anatomist]]s which was needed for further development. Whilst the race of collectors and systematisers culminated in the latter part of the [[18th century]] in [[Linnaeus]], a new type of student made its appearance in such men as [[John Hunter]] and other anatomists, who, not satisfied with the superficial observations of the popular “zoologists”, set themselves to work to examine anatomically the whole animal kingdom, and to classify its members by aid of the results of such profound study. Under the influence of the touchstone of strict inquiry set on foot by the [[Royal Society]], the marvels of [[witchcraft]], [[sympathetic powders]], and other relics of mediaeval superstition disappeared, whilst accurate observations and demonstrations of a host of new wonders accumulated, amongst which were numerous contributions to the anatomy of animals, and none perhaps more noteworthy than the observations, made by the aid of [[microscope]]s constructed by himself, of [[Leeuwenhoek]], the [[Netherlands|Dutch]] naturalist ([[1683]]), some of whose instruments were presented by him to the Society.
 
It was not until the [[19th century]] that the [[microscope]], thus early applied by [[Leeuwenhoek]], [[Malpighi]], [[Hook]], and [[Swammerdam]] to the study of animal structure, was perfected as an instrument, and accomplished for zoology its final and most important service. The perfecting of the microscope led to a full comprehension of the great doctrine of [[cell structure]] and the establishment of the facts - (1) that all organisms are either single corpuscles (so-called "cells") of living material (microscopic animalcules, ''etc.'') or are built up of an immense number of such units; (2) that all organisms begin their individual existence as a single unit or corpuscle of living substance, which multiplies by binary fission, the products growing in size and multiplying similarly by binary fission; and (3) that the life of a multicellular organism is the sum of the activities of the corpuscular units of which it consists, and that the processes of life must be studied in and their explanation obtained from an understanding of the chemical and physical changes which go on in each individual corpuscle or unit of living material or [[protoplasm]].
 
Meanwhile the [[astronomy|astronomical]] theories of development of the [[solar system]] from a [[gas]]eous condition to its present form, put forward by [[Kant]] and by [[Laplace]], had impressed men’s minds with the conception of a general movement of spontaneous progress or development in all nature. The science of [[geology]] came into existence, and the whole panorama of successive stages of the [[Earth]]’s history, each with its distinct population of strange [[animal]]s and [[plant]]s, unlike those of the present day and simpler in proportion as they recede into the past, was revealed by [[Cuvier]], [[Agassiz]], and others. The history of the [[crust]] of the earth was explained by [[Lyell]] as due to a process of slow development, in order to effect which he called in no cataclysmic agencies, no mysterious forces differing from those operating at the present day. Thus he carried on the narrative of orderly development from the point at which it was left by Kant and Laplace - explaining by reference to the ascertained laws of [[physics]] and [[chemistry]] the configuration of the Earth, its [[mountain]]s and [[sea]]s, its [[igneous rock|igneous]] and its [[stratified rock]]s, just as the [[astronomer]]s had explained by those same laws the evolution of the [[Sun]] and [[planet]]s from diffused [[gas]]eous matter of high temperature. The suggestion that living things must also be included in this great development was obvious.
 
The delay in the establishment of the doctrine of organic evolution was due, not to the ignorant and unobservant, but to the leaders of zoological and botanical science. Knowing the almost endless complexity of organic structures, realising that man himself with all the mystery of his life and consciousness must be included in any explanation of the origin of living things, they preferred to regard living things as something apart from the rest of nature, specially cared for, specially created by a [[god|Divine Being]]. Thus it was that the so-called “''Natur-philosophen''“ of the last decade of the [[18th century]], and their successors in the first quarter of the [[19th cetury|19th]], found few adherents among the working zoologists and botanists. [[Lamarck]], [[Treviranus]], [[Erasmus Darwin]], [[Goethe]], and [[Saint-Hilaire]] preached to deaf ears, for they advanced the theory that living beings had developed by a slow process of transmutation in successive generations from simpler ancestors, and in the beginning from simplest formless matter, without being able to demonstrate any existing mechanical causes by which such development must necessarily be brought about. They were met by the criticism that possibly such a development had taken place; but, as no one could show as a simple fact of observation that it had taken place, nor as a result of legitimate inference that it must have taken place, it was quite as likely that the past and present species of animals and plants had been separately created or individually brought into existence by unknown and inscrutable causes, and (it was held) the truly scientific man would refuse to occupy himself with such fancies, whilst ever centinuing to concern himself with the observation and record of indisputable facts. The critics did well; for the “''Natur-philosophen''”, though right in their main conception, were premature.
 
Then, in [[1859]], [[Charles Darwin]] placed the whole theory of organic evolution on a new footing, by his discovery of a process by which organic evolution can occur, and provided observational evidence that it had done so. This changed the attitudes of most exponents of the scientific method. Darwin's discoveries revolutionised the zoological and botanical sciences, by introducing the [[theory]] of [[evolution]] by [[natural selection]] as an explanation for the diversity of all animal and plant life. The subject-matter of this new science, or branch of biological science, had been neglected: it did not form part of the studies of the collector and systematist, nor was it a branch of anatomy, nor of the physiology pursued by medical men, nor again was it included in the field of microscopy and the cell theory. The area of biological knowledge which Darwin was the first to subject to scientific method and to render, as it were, contributory to the great stream formed by the union of the various branches, is that which relates to the breeding of animals and plants, their congenital variations, and the transmission and perpetuation of those variations. This branch of biological science may be called [[thremmatology]] - the science of [[breeding]]. Outside the scientific world, an immense mass of observation and experiment had grown up in relation to this subject. From the earliest times the [[shepherd]], the [[farmer]], the [[horticulturist]], and the “[[fancier]]” had for practical purposes made themselves acquainted with a number of biological laws, and successfully applied them without exciting more than an occasional notice from the academic students of biology. Darwin made use of these observations and formulated their results to a large extent as the laws of [[variation]] and [[heredity]]. As the breeder selects a congenital variation which suits his requirements, and by breeding from the animals (or plants) exhibiting that variation obtains a new breed specially characterised by that variation, so in nature is there a selection amongst all the congenital variations of each generation of a species. This selection depends on the fact that more young are born than the natural provision of food will support. In consequence of this excess of births there is a struggle for existence and a [[survival of the fittest]], and consequently an ever-present necessarily acting selection, which either maintains accurately the form of the species from generation to generation or leads to its modification in correspondence with changes in the surrounding circumstances which have relation to its fitness for success in the struggle for life,
structures to the service of the organisms in which they occur. It cannot be said that previously to Darwin there had been.any very profound study of teleology, but it had  been the delight of a certaifi type of mind—that of  the lovers of nature or naturalists par excellence, as ion’. they were sometimes termed—to watch the habits
 
of living animals and plants, and to point out the remarkable ways in which the structure of each variety of organic life was adapted to the special circumstances of life of the variety or species. The astonishing colours and grotesque forms of some animals and plants which the museum zoologists gravely described without comment were shown by these observers of living nature to have their significance in the economy of the organism possessing them; and a general doctrine was recognized, to the effect that no part or structure of an organism is without definite use and adaptation, being designed by the Creator for the benefit of the creature to which it belongs, or else for the benefit, amusement or instruction of his highest creature—man. Teleology in this form of the doctrine of design was never very deeply rooted amongst scientific anatomists and systematists. It was c~nsidered permissible to speculate somewhat vaguely on the subject of the utility of this or that startling variety of structure; but few attempts, though some of great importance, were made systematically to explain by observation and experiment the adaptation of organic structures to particular purposes in the case of the lower animals and plants. Teleology had, indeed, an important part in the development of physiology—the knowledge of the mechanism, the physical and chemical properties, of the parts of the body of man and the higher animals allied to him. But, as applied to lower and more obscure forms of life, teleology presented almost insurmountable difficulties; and consequently, in place of exact experiment and demonstration, the most reckless though ingenious assumptions were made as to the utility of the parts and organs of lower animals. Darwin’s theory had as one of its results the reformation and rehabilitation of teleology. According to that theory, every organ, every part, colour and peculiarity of an organism, must either be of benefit to that organism itself or have been so to its ancestors: i no peculiarity of structure or general conformation, no habit or instinct in any organism, can be supposed to exist for the benefit or amusement of another organism, not even for the delectation of man himself. Necessarily, according to the theory of natural selection, structures either are present because they are selected as useful or because they are still inherited from ancestors to whom they were useful, though no longer useful to the existing representatives of those ancestors. Structures previously inexplicable were now explained as survivals from a past age, no longer useful though once of value. Every variety of form and colour was urgently and absolutely called upon to produce its title to existence either as an active useful agent or as a survival. Darwin himself spent a large part of the later years of his life in thus extending the new teleology.
 
i A very subtle and important qualification of this generalization has to be recognized (and was recognized by Darwin) in the fact that owing to the interdependence of the parts of the bodies of living things and their profound chemical interactions and peculiar structural balance (what is called organic polarity) the variation of one single part (a spot of colour, a tooth, a claw, a leaflet) may, and demonstrably does in many cases entail variation of other parts— what are called correlated variations. Hence many structures which are obvious to the eye, and serve as distinguishing marks of separate species, are really not themselves of value or use, btit are the necessary concomitants of less obvious and even altogether obscure qualities, which are the real characters upon which selection is acting. Such correlated variations” may attain to great size and complexity without being of use. But eventually they may in turn become, in changed conditions, of selective value. Thus in many cases the difficulty of supposing that selection has acted on minute and imperceptible initial variations, so small as to have no selective value, may be got iid of. A useless “correlated variation “ may have attained great volume and quality before it is (as it were) seized upon and perfected by natural selection. All organisms are essentially and necessarily built up by such correlated variations.
 
The old doctrine of types, which was used by the philosophically minded zoologists (and botanists) of the first half  of the 19th century as a ready means of explaining the failures and difficulties of the doctrine of design, fell into its proper place under the new dispensation. The adherence to type, the favourite conception. of the transcendental morphologist, was seen to be nothing more than the expression of one of the laws of thremmatology, the persistence of hereditary transmission of ancestral characters, even when they have ceased to be significant or valuable in the struggle for existence, whilst the so-called evidences of design which was supposed to modify the limitations of types assigned to Himself by the Creator were seen to be adaptations due to the selection and intensification by selective breeding of fortuitous congenital variations, which happened to prove more useful than the many thousand other variations which did not survive in the struggle for existence.
 
Thus not only did Darwin’s theory give a new basis to the study of organic structure, but, whilst rendering the genera,1 theory of organic evolution equally acceptable and EMedS of necessary, it explained the existence of low and simple Da~In’s forms of life as survivals of the earliest ancestry of theo,y
 
more highly complex forms, and revealed the classi- tiPOfl
 
fications of the systematist as unconscious attempts ZOO Ogy. to construct the genealogical tree or pedigree of plants and animals. Finally, it brought the simplest living matter or formless protoplasm before the mental vision as the startingpoint whence, by the operation of necessary mechanical causes, the highest forms have been evolved, and it rendered unavoidable the conclusion that this earliest living material was itself evolved by gradual processes, the result also of the known and recognized laws of physics and chemistry, from material which we should call not living. It abolished the conception of life as an entity above and beyond the common properties of matter, and led to the conviction that the marvellous and exceptional qualities of that which we call “living “ matter are nothing more nor less than an exceptionally complicated development of those chemical and physical properties which we recognize in a gradually ascending scale of evolution in the carbon compounds, containing nitrogen as well as oxygen, sulphur and hydrogen as constituent atoms of their enormous molecules. Thus mysticism was finally banished from the domain of biology, and zoology became one of the physical sciences—the science which seeks to arrange and discuss the phenomena of animal life and form, as the outcome of the operation of the laws of physics and chemistry.
 
A subdivision of zoology which was at one time in favour is simply into morphology and physiology, the study of form and structure on the one hand, and the study ofthe activities and functions of the forms and structures of zooon the other. But a logical division like this is not necessarily conducive to the ascertainment and remembrance of the historical progress and present significance of the science. No such distinction of mental activities as that involved in the division of the study of animal life into morphology and physiology has ever really existed: the investigator of animal forms has never entirely ignored the functions of the forms studied by him, and the experimental inquirer into the functions and properties of animal tissues and organs has always taken very careful account of the forms of those tissues and organs. A more instructive subdivision must be one which corresponds to the separate currents of thought and mental preoccupation which have been historically manifested in western Europe in the gradual evolution of what is to-day the great river of zoological doctrine to which they have all been rendered contributory.
 
== Branches of zoological study ==
 
It must recognize the following five branches of zoological study:—
 
I. Morphography.—The work of the collector and systematist:
 
exemplified by Linnaeus and his predecessors, by Cuvier, Agassiz, Haeckel.
 
2. Bionomics.—The lore of the farmer, gardener, sportsman, fancier and field-naturalist, including thremmatology, 01 the science of breeding, and the allied teleology, or science of organic adaptations: exemplified by the patriarch jacob, the poet Virgil, Sprengel, Kirby and Spence, Wallace ann Darwin.
 
3. Zoo-Dynamics, Zoo-Physics, Zoo-Chemistry.—The pursuit of the learned physician,—anatomy and physiology: exemplified by Harvey, Hailer, Hunter, Johann Muller.
 
4. Plasmology.—The study of the ultimate corpuscles of living matter, their structure, development and properties, by the aid of the microscope; exemplified by Malpighi, Hook, Schwann, Kowalewsky.
 
5. Philosophical Zoology.—General conceptions with regard to the relations of living things (especially animals) to the universe, to man, and to the Creator, their origin and significance:
 
exemplified in the writings of the philosophers of classical antiquity, ar,d of Linnaeus, Goethe, Lamarck, Cuvier, Lyell, I-I. Spencer and Darwin.
 
It is unnecessary to follow in this article all these subjects, since the
 
== Zoology since Darwin ==
 
Darwin may be said to have founded the science of bionomics, and at the same time to have given new stimulus and new direction to morphegraphy, physiology, and plasmology, by uniting them as contrbutories to one common biological doctrine—the doctrine of organic evolution—itself but a part of the wider doctrine of universal evolution based on the laws of physics and chemistry. The immediate result was, as pointed out above, a reconstruction of the classification of animals upon a genealogical basis, and an investigation ef the individual development of animals in relation to the steps of their gradual building up by cell-division, with a view to obtaining evidence of their genetic relationships. On the other hand, the studies which occupied Darwin himself so largely subsequently to the publication of the Origin of Species, viz, the
 
explanation of animal (and vegetable) mechanism, colouring, habits, &c., as advantageous to the species or to its ancestors, are only gradually being carried further. The most important work in this direction has been done by Fritz MUller (Für Darwin), by Herman MUller (Fertilization of Plants by Insects),
 
by August Wcismann (memoirs translated by Meldola) by Edward B. Poulton (see his addresses and memoirs published in the Transactions of the Entomological Society and elsewhere), and by Abbot Thayer (Concealing Coloration in the Animal Kingdom, Macmillan & Co. 1910). In. the branch of bionomics, however, concerned with the laws of variation and heredity (thremmatology), there has been considerable progress. In the first place, the continued study of human population has thrown additional light on some of the questions involved, whilst the progress of microscopical research has given us a clear foundation as to the structural facts connected with the origin of the egg-cell and sperm-cell and the process of fertilization.
 
Great attention has been given lately to the important experiments upon the results of hybridizing certain cultivated varieties of plants which were published so long ago as I 865, by the Abbé Mendel, but failed to attract notice until thirty-five years later, sixteen years after his death (see MENDELISM). Mendel- Mendel’s object was to gain further knowledge as to Ism, the result of mixing by cross-fertilization or interbreeding two strains exhibiting diverse characters or structural features. The whole question as to the mixture of characters in offspring thus produced was—and remains—very imperfectly observed. Mendel’s observations constitute an ingenious attempt to throw light on the matter, and in the opinion of some biologists have led to the discovery of an. important principle. Mendel made his chief experiments with cultivated varieties of the self-fertilizing edible pea. He selected a variety with some one marked structural feature and crossed it with another variety in which that feature was absent. Instances of his selected varieties are the tall variety which he hybridized with a dwarf variety, a yellow-seeded variety which he hybridized with a green-seeded variety, and again a smooth-seeded variety which he hybridized with a wrinkle-seeded variety. In each set of experiments he concentrated his attention on the one character selected for observation. Having obtained a first hybrid generation, he allowed the hybrids to self-fertilize, and recorded the result in a large number of instances (a thousand or more) as to the number of individuals in the first, second, third and fourth generations in which the character selected for experiment made its appearance. In the first hybrid generation formed by the union of the reproductive germs of the positive variety (that possessing the structural character selected for observation) with those of the negative variety, it is not surprising that all or nearly all the individuals were found to exhibit, as a result 01 the mixture, the positive character. In subsequent generations produced by self-fertilization of the hybrids it was found that the positive character was not present in all the individuals, but that a result was obtained showing that in the formation of the reproductive cells (ova and sperms) of the hybrid, half were endowed with the positive character and half with the negative. Consequently the result of the haphazard pairing of a large number of these two groups of reproductive cells was to yield, according to the regular law of chance combination, the proportion I PP, 2PN, INN, where P stands for the positive character and N for its absence or negative character—the positive character being accordingly present in three-fourths of the offspring and absent from onefourth. The fact that in the formation of the reproductive cells of the hybrid generation the material which carries the positive quality is not subdivided so as to give a half-quantity to each reproductive cell, but on the contrary is apparently distributed as an undivided whole to half only of the reproductive cells and not at all to the remainder, is the important inference from Mendel’s experiments. Whether this inference is applicable to other classes of cases than those studied by Mendel and his followers is a question which is still under investigation. The failure of the material carrying a positive character to divide so as to distribute itself among all the reproductive cells of a hybrid individual, and the limitation of its distribution to half only of those cells, must prevent the “swamping” of a newly appearing character in the course of the inter-breeding of those individuals possessed of the character with those which do not possess it. The tendency of the proportions in the offspring of rPP, 2PN, INN is to give in a series of generations a regular reversion from the hybrid form PN to the two pure races, viz, the race with the positive character simply and the race with the total absence of it. It has been maintained that this tendency to a severance of the hybrid stock into its components must favour the persistence of a new character of large volume suddenly appearing in a stock, and the observations of Mendel have been held to favour in this way the views of those who hold that the variations upon which natural selection has acted in the production of new species are not small variations but large and “ discontinuous.” It does not, however, appear that “large” variations would thus be favoured any more than small ones, nor that the eliminating action 01 natural selection upon a.n unfavourable variation could be checked.
 
A good deal of confusion has arisen in the ‘discussions of this latter topic, owing to defective nomenclature. By some writers the word “mutation” is applied only to large and suddenly appearing variations which are found to he capable of hereditary transmission, whilst the term “ fluctuation “ is applied to small variations whether capable of transmission or not. By others the word “fluctuation.” is apparently applied only to those small “acquired” variations due to the direct action of changes in food, moisture and other features of the environment. It is no discovery that this latter kind of variation is not hereditable, and it is not the fact that the small variations, to which Darwin attached great but not exclusive importance as the material upon which natural selection operates, are of this latter kind. The most instructive classification of the ‘ variations” exhibited by fully formed organisms consists in the separation in the first place of those which arise from antecedent congenital, innate, constitutional or germinal variations from those which arise merely from the operation of variation of the environment or the food-supply upon normally constituted individuals. The former are “innate” variations, the latter are “superimposed” variations (so-called “ acquired variations “). Both innate and superimposed variations are capable of division into those which are more and those which are less obvious to the human eye. Scarcely perceptible variations of the innate class arc regularly and invariably present in every new generation of every species of living thing. Their greatness or smallness so far as human perception goes is not of much significance; their real importance in regard to the origin of new species depends on whether they are of value to the organism and therefore capable of selection in the struggle for existence. An absolutely imperceptible physiological difference arising a~s a variation may be of selective value, and it may carry with it correlated variations which appeal to the human eye but are of no selective value themselves. The present writer has, for many years, urged the importance of this consideration.
 
The views of de Vries and others as to the importance of “saltatory variation,” the soundness of which was still by no means generally accepted in 1910, may be gathered from the articles MENDELISM and VAR1ATION~ A due appreciation of the far-reaching results of “ correlated variation “ must, it appeals, give a new and distinct explanation to the phenomena which are referred to as “large mutations,” ‘“ discontinuous variation “ and “ saltatory evolution.” Whatever value is to be attached to Mendel’s observation of the breaking up of self-fertilized hybrids of cultivated varieties into the two original parent forms according to the formula “ 1PP, 2PN, I NN,” it cannot be considered as more than a contribution to the extensive investigation of heredity which still remains to be carried out. The analysis of the specific variations of organic form so as to determine what is really the nature and limitation of a single “ character “ or “individual variation,” and whether two such true and strictly defined single variations of a single structural unit can actually “blend” when one is transmitted by the male parent and the other by the female parent, are matters which have yet to be determined. We do not yet know whether such absolute blending is possible or not, or whether all apparent blending is only a more or less minutely subdivided “mosaic” of non-combinable characters of the parents, in fact whether the combinations due to heredity in reproduction are ever analogous to chemical compounds or are always comparable to particulate mixtures. The attempt to connect Mendel’s observation with the structure of the spermcells and egg-cells of plants and animals has already been made. The suggestion is obvious that the halving of the number of nuclear threads in the reproductive cells as compared with the number of those present in the ordinary cells of the tissues—a phenomenon which has now been demonstrated as universal—may he directly connected with the facts of segregation of hybrid characters observed by Mendel. The suggestion r&luires further experimental testing, for which the case of the parthenogenetic production of a portion of the offspring, in such insects as the bee, offers a valuable opportunity for research.
 
Another important development of Darwin’s conclusions deserves special notice here, as it is the most distinct advance Var! a- in the department of bionomics since Darwin’s own tion, writings, and at the sa1ne time touches questions of fundamental interest. The matter strictly relates to the consideration of the “ causes of variation,” and is as follows. The fact of variation is a familiar one. No two animals, even. of the same brood, are alike: whilst exhibiting a close similarity to their parents, they yet present differences, sometimes very marked differences, from their parents and from one another. Lamarck had put forward the hypothesis that structural alterations acquired by (that is to say, superimposed upon) a parent in the course of its life are transmitted to the offspring, and that, as these structural alterations are acquired by an animal or plant in consequence of the direct action of the environment, the offspring inheriting them would as a consequence not unfrequently start with a greater fitness for those conditions than its parents started with. In its turn, being operated upon by the conditions of life, it would acquire a greater development of the same modification, which it would in turn transmit to its offspring. In the course of several generations, Lamarck argued, a structural alteration amounting to such difference as we call” specific “ might be thus acquired. The familiar illustration of Lamarck’s hypothesis is that of the giraffe, whose long neck might, he suggested, have been acquired by the efforts of a primitively short-necked race of herbivores who stretched their necks to reach the foliage of trees in a land where grass was deficient, the effort producing a distinct elongation in the neck of each generation, which was then transmitted to the next. This process is known as “direct adaptation “; and there is no doubt that such structural adaptations are acquired by an animal in the course of its life, though such changes are strictly limited in degree and rare rather than. frequent and obvious.
 
Whether such acquired characters can be transmitted to the next generation is a separate question. It was not proved by Larnarck that they can be, and, indeed, never has been proved by actual observation. Nevertheless it has been assumed, and also indirectly argued, that such acquired characters must be transmitted. Darwin’s great merit was that he excluded from his theory of de’velopment any necessary assumption of the transmission of acquired characters. He pointed to the admitted fact of congenital variation, and he showed that congenital variations are arbitrary and, so to speak, non-significant.
 
Causes of Their causes are extremely difficult to trace in detail, congeni- but it appears that they are largely due to a “shaking talvar!a- up” of the living matter which constitutes the fertilized germ or embryo-cell, by the process of mixture in it of the substance of two cells—the germ. cell and the sperm-cell—derived from two different individuals. Other mechanical disturbances may assist in this production of congenital variation. Whatever its causes, Darwin showed that it is all-important. In some cases a pair of animals produce ten million offspring, and in such a number a large range of congenital variation is possible. Since on the average only two of the young survive in the struggle for existence to take the place of their two parents, there is a selection out of the ten million young, none of which are exactly alike, and the selection is determined in nature by the survival of the congenital variety which is fittest to’ the conditions of life. Hence there is no necessity for an assumption of the perpetuation of direct adaptations. The selection of the fortuitously (fortuitously, Transthat is to say, so far as the conditions of survival are mission concerned) produced varieties is sufficient, since it of  is ascertained that they will tend to transmit those ~dr~fl_ characters with which they themselves were born, herited although it is not ascertained that they could transmit charcharacters acquired on the way through life. A simple illustration of the difference is this: a man born with four fingers only on his right hand is ascertained to be likely to transmit this peculiarity to some at least of his offspring; on the other hand, there is not the slightest ground for supposing that a man who has had one finger chopped off, or has even lost his arm at any period of his life, will produce offspring who are defective in the slightest degree in regard to fingers, hand or arm. Darwin himself, influenced by the consideration of certain classes of facts which seem to favour the Lamarckian hypothesis, was of the opinion that acquired characters are in some cases transmitted. It should be observed, however, that Darwin did not attribute an essential part to this Lamarckian. hypothesis of the transmission of acquired characters, but expressly assigned to it an entirely subordinate importance.
 
The new attitude which has been taken since Darwin’s writings on this question is to ask for evidence of the asserted transmission of acquired characters. It is held f that the Darwinian doctrine of selection of fortuitous congenital variations is sufficient to account for all cases, that the Lamarckian hypothesis of transmission cf acquired characters is not supported by experimental evidence, and that the latter should therefore be dismissed. Weismann has also ingeniously argued from the structure of the egg-cell and sperm-cell, and from the way in which, and the period at which, they are derived in the course of the growth of the embryo from the egg—from the fertilized egg-cell—that it is impossible (it would be better to say highly improbable) that an alteration in parental structure could produce any exactly representative change in the substance of the germ or sperm-cells.
 
The one fact which the Lamarckians can produce in their favour is the account of experiments by Brown-Séquard, in which he produced epilepsy in guinea-pigs by section of the large nerves or spinal cord, and in. the course of which ~he was led to believe that in a few rare instances the artificially produced epilepsy and mutilation of the nerves was transmitted. This instance does not stand the test of criticism. The record of Brown-Séquard’s original experiment is not satisfactory, and the subsequent attempts to obtain similar results have not been attended with success. On the other hand, the vast number of experiments in the cropping of the tails and ears of domestic animals, as well as of similar operations on man, are attended with negative results. No case of the transmission of the results of an injury can be produced. Stories of tailless kittens, puppies and calves, born from parents one of whom had been thus injured, are abundant, but they have’, hitherto entirely failed to stand before examination.
 
Whilst simple evidence of the fact of the transmission of an acquired character is wanting, the a priori arguments in its favour break down one after another when discussed. The very cases which are advanced as only to be explained on the Lamarckian assumption are found on examination and experiment to be better explained, or only to be explained, by the Darwinian principle. Thus the occurrence of blind animals in caves and in the deep sea was a fact which Darwin himself regarded as best explained by the atrophy of the organ. of vision in successive generations through the absence of light and
 
1 Weismann, Vererbung, &c. (1886).
 
consequent disuse, and 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 explained (as the present writer has shown) by the theory of natural selection acting on congenital fortuitous variations. It is definitely ascertained that many animals are thus born with distorted or defective eyes whose parents have not had their eyes submitted to any peculiar conditions. Supposing 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 he 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.
 
It is a remarkable fact that it was overlooked alike by the supporters and opponents of Lamarck’s views until pointed out by the present writer (Nature, 1894,’p. 127), that the two statements called by Lamarck his first and second laws are contradictory one of the other. Lamarck’s first Jaw asserts that a past history of indefinite duration is powerless to create Ethica- a bias by which the present can be controlled. He bility. declares that in spite of long-established conditions and correspondingly evoked characters new conditions will cause new responsive characters. Yet in the second Ltw he asserts that these new characters will resist the action of yet newer conditions or a reversion to the old conditions and be maintained by heredity. If the earlier characters were not maintained by heredity why should the later be? If a character of much longer standing (certain properties of height, length, breadth, colour, &c.) had not become fixed and congenital after many thousands of successive generations of individuals had developed it in response to environment, but gave place to a new character when new moulding conditions operated on an individual (Lamarck’s first law), why should we suppose that the new character is likely to become fixed and transmitted by mere heredity after a much shorter time of existence in response to environmental stimulus? Why should we assume that it will be able to escape the moulding by environment (once its evoking cause is removed) to which, according to Lamarck’s first law, all parts of organisms are subject? Clearly Lamarck gives us no reason for any such assumption, and his followers or latter-day adherents have not attempted to do so. His enunciation of his theory is itself destructive of that theory. Though an acquired or “superimposed ‘ character is not transmitted to offspring as the consequence of the action of the external agencies which determine the “acquirement,” yet the tendency to react to such agencies possessed by the parent is transmitted and may be increased and largely developed by survival, if the character developed by the reaction is valuable. This newly discovered inheritance of “variation in the tendency to react” has a wide application and has led the present writer to coin the word “educability.” It has application to all kinds of organs and qualities, but is of especial significance in regard to the development of the brain and the mental qualities of animals and of man (see the jubilee volume of the Soc. de Biologie, 1899, and Nature, 1900, p. 624).
 
It has been argued that the elaborate structural adaptations of the nervous system which are the corporeal correlatives of Theo,:y complicated instincts must have been slowly built oltrans- up by the transmission to offspring of acquired cxmission perience, that is to say, of acquired brain structure.
ICS. At first sight it appears difficult to understand how the complicated series of actions which are definitely
exhibited as so-called “instincts” 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, ai~d 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 which curiously elaborate actions are performed by animals as a characteristic of the species, and as subserving 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 pr-ove beneficial. Such cases are the habits of “shamming dead” and the combined posturing and colour peculiarities of certain caterpillars (Lepidopterous larvae) which cause them to resemble dead twigs or similar surroundingobjects. 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 caterpillar. Now it is clear that preceding generations of caterpillars 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 caterpillars had a congenital fortuitous tendency to one position, some to another, and, finally that among all the variety of habitual Inovements 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 long 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 instance of the pure Darwinian theory without the aid of Lamarckism.
 
Nothing can be further from the truth than the once favourite theory that instincts are the survivals of lapsed reasoning processes. Instincts, or the inherited structural mechanisms of ‘the nervous centres, are in antagonism to the results of the reasoning process, which are not capable of hereditary transmission. Every higher vertebrate animal possesses the power of forming for itself a series of cerebral mechanisms or reasoned conclusions based on its individual experience, in proportion as it has a large cerebrum and has got rid of or has acquired the power of controlling its inherited instincts. Man, compared with other animals, has the fewest inherited Record mental mechanisms or instincts and at the same time ~ the the largest cerebrum in proportion to the size of his Past. body. He builds up, from birth onwards, his own mental mechanisms, and forms more of them, that is to say, is more “educable,” and takes longer in doing so, that is to say, in growing up and maturing his experience, than any other animal. The later stages of evolution leadifig from his ape-like ancestors to man have consisted definitely in the acquirement of a larger and therefore more educable brain by man and in the consequent education of that brain. A new and’ most important feature in organic development makes its appearance when we set out the facts of man’s evolutional history. It amounts to a new and unprecedented factor in organic development, external to the organism and yet produced by the activity of the organism upon which it permanently reacts. This factor is the Record of the Past, which grows and develops by laws other than those affecting the perishable bodies of successive generations of mankind, and exerts an incomparable influence upon the educable brain, so that man, by the interaction of the Record and his educability, is removed to a large extent from the status of the organic world and placed in a new and unique position, subject to new laws and new methods of development unlike those by which the rest of the living world is governed. That which we term the Record of the Past comprises the “taboos,”

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