The History of Biological Theories

Many events contributed to this end. Roux was an eager advocate ; he defended the new science against all attacks, and founded a journal for the debates and discussions connected with it. He en- deavoured to set those who were engaged in building up the new theories free from practical difficulties. If he had made this subject a branch of physiology, calling it 'the Physiology of Development', as some wished, he would have prevented his followers, most of whom were recruited from the anatomists, from filling the Chairs of Anatomy in the universities. So he called his new science 'Develop- mental Mechanics', and claimed that it was a more modern and more exact branch of anatomy.

Nevertheless, developmental mechanics did not gain a firm foothold in Germany. The influence of Darwinism was, and still is, very profound; Roux, however, found numerous and active adherents in America. Develop- mental mechanics was principally concerned with the phenomena of regeneration, with the influence of physical and chemical agents on the form of the organism (the effect of light, heat, gravitation, of oxygen, of distilled water, of various poisons, &c.), and, we may add in many cases, with the phenomena of fertilization. Later on, under the influence of Driesch, this branch of biology has been led into new paths. After the war the German embryologist, Spemann, attacked the problem anew. He and his pupils carried out many original experiments, by which they sought to revivify Roux's ideas, and to show that there are, in the embryo, specific centres from which the differentiation of organs is controlled.

The work described above altered the centre of gravity of all that research which had been inspired by Darwin and Haeckel. Phylogeny was relegated to a second place, if not quite discarded. Genetic ideas were still pre- dominant, but these ideas assumed a more concrete form ; they were gradually merged in a science which dealt with visible changes in structure. WHAT Roux had done thus unwittingly and against his own intention, Hans Driesch carried out quite consciously and consistently. He renounced Darwinism. In his own special work he was Roux's pupil. He worked in the field of developmental mechanics, and at first he followed the methods and the ideas of his teacher. Later he became more independent, and to-day he is definitely opposed to his former teacher. Experimental researches into the problems of developmental mechanics formed the starting-point of all his work. He was interested above all in development. Explanation along genetic lines, the search for cause and effect, seemed to him the goal of all scientific endeavour.

The further Driesch went the more he freed himself from the bonds which bound him to the mechanistic views of the nineteenth century. He began by following those mechanistic views to their logical conclusion. Seeing that they are untenable, he became a convert to vitalism. As this failed to satisfy him, he then propounded his own vitalistic theory. In many respects Driesch differs from every other modern biologist. In all his writings, difficult as they are, we feel that he is endeavouring to avoid the garrulous superficiality which characterizes so many of them. He is trying to express the quintessence of being, to confine within the limits of speech the greatest and the most elusive truths. In the end he has come to agree with the views of that original interpreter and critic, Emanuel Kant.

Driesch marks the end of Darwinism. The world paid no heed to him, did not understand him, opposed him, sought for compromises, but Darwinism could not be saved. He raises the same objections to Darwinism as did Roux and Goebel, but expresses them more pointedly. His main charge is that it gives no rational insight into events. 'Even supposing that the theories are correct, what can it matter to us that, at the present moment, such and such forms are existing on our earth, and that they have followed one another in such and such a sequence ? This is a theory to which any inquirer into the more profound and more general aspects of Nature is absolutely indifferent indifferent because historical ideas which are limited by time and space form no part of his inquiry' (Die Biologie als selbstdndige Grundwissenscbaft, 1893).

He barely touches upon those questions so important to the Darwinists questions about the origin of species and the development of the organic world, and he no longer asks whether Natural Selection is all-powerful or only partly efficacious. Driesch asks instead, whether life is really nothing but a special combination of chemical and physical processes, or whether it is not governed by its own peculiar laws. His opponents, the upholders of the opposite view, had scarcely had time to collect their arguments against this suggestion that the biological sciences are absolutely different from all other sciences, when he was attacking the question again. He now presented it as a choice between a belief in a living and directing force and a belief that life is purely mechanical.

The contrast between Roux and Haeckel became, in the hands of Driesch, a contrast between the first and second halves of the nineteenth century we may even say, a contrast between the whole of modern science and the views of Aristotle. We have already described the embryological work which endeavoured to determine how the various tissues of the body are formed from the egg ; it assumed that, during segmentation, the characters of the future animal are separated, and enter the two daughter cells. As division proceeds, these characters become more and more separated, being apportioned to the various cells in an absolutely definite manner. His, Ray Lankester, Roux,

and Weismann upheld this theory, in its various modifica- tions; it is based upon the assumption that the whole organism is already contained within the egg. This assumption is contradicted, however, by the facts of regeneration, a phenomenon which is very intimately connected with the problem of the true nature of the organism. It becomes even more improbable in the light of Driesch's observations that from one isolated blasto- mere (in the case of the sea-urchins and other forms) a whole larva can develop; Roux's attempts to produce a half larva by killing one blastomere of a frog's egg were, it seems, very inexact. When the cells (and nuclei) of various stages in the segmenting sea-urchin are subjected to pressure, and so brought into thoroughly abnormal rela- tive positions, this does not necessarily prevent the forma- tion of a larva. Driesch pointed out later (and a number of scientists have confirmed this observation) that a whole larva can develop from fragments of an egg, if these are large enough and contain the nucleus. One or more cells can be isolated from the two-, four-, or eight-celled stage of the echinoderm embryo, and from each single cell, or each group of cells thus isolated, a whole larva can be produced ; again, from two eggs which have fused into one, only one normal larva is produced. 1

These observations led Driesch to formulate a new theory of development. Instead of the ordered pre-forma- tion which other workers had postulated, he suggested that there is a continued setting free of new structures. He called this hypothesis a theory of epigenetic or emergent volution. He suggested that the chemical structure of the egg is comparatively simple. The influence of the environ- 1 At first Driesch affirmed 'that any portion of the egg, as well as the whole egg in any position whatsoever, can produce a complete larva*, that 'the egg cannot, structurally, be built up out of different elements arranged in a specified and typical way*. Sec Die Lokalisation morpbogenetiscber Vorgdngc, 1899. Under criticism, he restricted this assertion, and admitted that there is a spatial structure which dominates development.

Many writers, particularly Jul. Schazel, have attacked Driesch's theories, from the mechanistic point of view. ment causes chemical change, which changes lead on to others, and so the process continues. If this picture is true, development is merely the liberation of a series of chemical processes which follow one another. This liberation de- pends on the one side upon the chemico-physical structure of the egg, and on the other upon the influence of the environment.

These processes are absolutely different from inorganic processes, for they are in their essence teleological. 'The processes of ontogeny, both in their form and their sequence, take place as if they were guided by an intelligence/ x The structure of the organism is characteristic of it, and it is causally inexplicable. It can only be judged teleo- logically. Later on Driesch abandoned this view, which he calls 'static teleology', and adopted in its place the ideas he calls 'dynamic teleology'. He himself has told us that he developed these ideas after a consideration of 'counter- reactions'. An answer to a question, for example, is just such a counter-reaction ; we cannot picture it as something merely mechanical for it is not merely a reaction; it is ideally related to the question which is the cause. Organic reactions involve similar responses. If a triton loses one of its feet, it responds to this 'cause' by forming a new one. The newly grown limb is formed on the pattern of the one which has been lost, and is similar to it in both size and shape. We may affirm that we 'understand' this re- action, even as we affirm that we 'understand' the answer to a question. But the unit which determines and directs the reaction is the normal and complete animal; this is obvious from a study of the processes of regeneration.

Driesch endeavoured to explain every biological problem in this manner. He collected and sifted all material that could possibly be used to illustrate his theory of 'reactions of response', or 'regulations', as he afterwards called them(Z)*V organischen Regulationeny 1901). He extended his theories 1 H. Driesch, Analytiscbe Tbeorie der organiscben Entwicklung, 1894. beyond the purely embryological processes, and made them include physiological and psychological phenomena, recording new experiments in their favour. We may quote a few examples of these processes of organic 'regulation 5 .

An organism may gradually accustom itself to certain poisons it then possesses what is called 'acquired im- munity'. If the poison is administered in ever-increasing doses the organism learns to produce certain anti-toxins which render the poison innocuous. This production of anti-toxins which are not produced by the organism in normal circumstances is a regulatory process by means of which life is maintained. A willow twig planted in the earth forms adventitious roots, and regulates its growth and form in such a way that a normal plant is produced. Crabs with stalked eyes will regenerate their eyes if these are removed; they form an antenna in place of an eye, however, if the eye ganglion which lies in the eye-stalk is removed as well. Here the crab reacts to the injury in two different ways ; these can still be regarded as 'regulated' reactions.

Such observations led Driesch to formulate a dynamic interpretation of Weismann's theories. Weismann's idea was that the characteristics of the organism are pre-formed in the egg, existing there as tiny particles. Quite apart from the impossibility of picturing 'lung-breathing' or 'four-footedness', for instance, as embodied in little parti- cles, this theory gives us no insight into the processes at work, no picture of the gradual development of those fea- tures which are characteristic of the organism. Driesch, too, imagines that these characteristics exist in the body, but as possibilities only, endowed with an impulse to- wards self-realization. The egg, and every embryonic cell, possesses a 'prospective power', i. e. a capacity to develop definite characters ; the prospective power of the egg will lead to the development of the whole organism. A sufficiently large piece of an echinoderm egg, if it contains the nucleus ; one of the two, or four, or eight blastomeres of the echinoderm embryo all these have the same

prospective power. The ectoderm and endoderm of the echinoderm have different prospective powers, for, if isolated, they can only reproduce their own kind. The blastula cells of the echinoderm, on the other hand, are all of equal power. Delving deeper into these ideas of 'prospective power', and of 'organic regulation', Driesch was led on to the view that life is 'a law unto itself, that it stands alone and apart from the processes of the inorganic world.

After the decline of naturalism, the theory held was that there is no essential difference between the animate and the inanimate; that life is only a very complicated chemico-physical process a machine-like process, where the word 'machine' is used in its most generalized sense, to imply a multiplicity of processes occurring in space and time. Driesch discarded this mechanistic theory of life, and opposed to it a 'dynamic-vitalism', a theory of the 'autonomy of living processes'. He gives four proofs, which are intended to demonstrate that this theory is the only possible one, and that the mechanistic theory is untenable.

His first argument is as follows : If development could only follow one fixed path, it would be possible to think of the egg as a highly complicated machine, which, by the interaction of its separate parts, is able to produce the complete organism. But any one cell of the two-, four-, or eight-celled blastula can give rise to a whole embryo. Similar cells may produce very dissimilar products ; while, on the other hand, the same structures may be produced in various ways. Thus one cell of the four-celled blastula gives rise to quite different organs, according as one, two or three of the blastula cells are removed. These facts do not agree with our conception of a machine. Consequently there must be a factor at work in organic development which is neither physical nor chemical but vital.

Driesch derived his second argument from the facts of development, such as are furnished by a study of the blastula of the echinoderm. This is formed by the con- tinued division of the egg. And yet each of its cells (or groups of cells) can function instead of that egg. There is, however, no conceivable machine which can continually divide, and of which each part is equivalent to the original machine; therefore the egg is absolutely different in nature from a machine.

The third argument was based on an analysis of be- haviour. In the actions of men and of animals experiences are combined to form ideas. This implies a process which is anything but mechanical. It is true that we can picture a machine which is able to collect experiences, as is a phonograph, but it lacks the power of combining those experiences, as a man combines the words he has learnt, in order to express new ideas. The fourth argument against the theory of mechanical action is derived from the study of the physiology of the brain. If a portion of the brain is removed its functions are performed, after a time, by another part of the brain which had not hitherto undertaken that work. The basis of action is therefore not a hard and fast mechanical or constructional relationship existing in the nervous centres of the brain. 1

The idea of entelechy was formulated by Aristotle. He believed that this conception would enable him to harmo- nize the idealism of Plato and the facts of actual experience. According to Plato we must distinguish between two distinct worlds. The world of eternal reality is known by the mind, but there is a world of continual change which we know through the senses. Snow, an animal, a rose, represent ideas which underlie the separate and transitory natural objects known to experience. These ideas exist in the mind, pre-formed, and we remember them when we consider the world around us. Aristotle accepted this theory of ideas, but not the theory of two worlds. He taught, for instance, that a definite plant, which I now have

1 Driesch's Vitalism is expounded most simply in his Der Vitalismus als Gescbicbte und als Lebre .1905. before me, is only a transitory phenomenon, which does not represent any idea in the outer world, but forms merely a passing stage in the realization the embodiment of that plant. The analogy of the architect is the most appropriate one. He builds the house according to a plan ; this plan is realized in the house. It is characteristic of the plan (which was conceived in the mind) that it is not made up of separate parts, that it occupies no space, that it cannot be perceived by the senses ; that it is, in short, an idea which dominates the construction.

In order, however, properly to understand the Aristo- telian conception of entelechy, we must not think of the idea as separated from the fabric. In considering living objects this error is a very natural one; when a plant is produced from the seed a highly complicated structure is realized. Here it is the idea of the plant which controls the structure, regulates the supply of power and of build- ing material, repairs injuries, and gets rid of obstructions. This something which makes the life of every single organism a reality, Aristotle (and Driesch with him) calls entelechy. Entelechy is no mechanism, it is nothing spatial, for it is not in the seed ; it cannot be asserted that one part of it is here and another there, but it is, like the plan conceived in the mind, everywhere at once. If a branch is broken off a plant, the entelechy remains whole, for the plant can reproduce that branch ; if a new branch of the same kind is grafted on to a plant, its entelechy grows on as a uniform whole ; if four cuttings of the plant are planted in the earth, we do not get four new entelechies but merely four repetitions of the same process.

Entelechy is, therefore, an agent with definite capacities. Its power is revealed in development, in the regulation and execution of physiological and mental processes. Its capacities are made manifest by the manner in which these are executed. It is comparable with physical and chemical constants. As the constants for iron show how this sub- stance expands with heat, according to the general laws of expansion, how it conducts electricity, what is its

specific gravity, &c., so its entelechy is characteristic of the manner in which a definite organism acts. The in- organic constants likewise have no spatial significance ; it would be quite useless to investigate how in any piece of iron the colour, gravity, specific heat, &c., are distributed, since they are present in every particle of the iron ; they therefore do not represent any extensive, but rather an intensive reality, like entelechy. The difference between Aristotle's and Driesch's con- ceptions of entelechy lies firstly in the manner in which the two men arrived at the idea. Aristotle, starting from Platonic metaphysics, sought for a road to objective reality. Driesch, starting from biological reality, sought to give it a strictly logical expression. For this reason Aristotle's conception of entelechy was a very much wider one than that of Driesch. It included the creations of the artist, and even the facts of inanimate nature, while Driesch merely applied the idea to biological processes. Secondly, Driesch's conception of nature was a quantita- tive one, while Aristotle was content with the qualitative view (for the Aristotelian entelechies were qualities). Driesch also leaves undecided the question whether ente- lechy, as the creative agent, is to be contrasted with dead and passive matter as something absolutely different from it (as Aristotle thought, when he separated matter and form).

Driesch used this idea of entelechy to build up his psychological theories. In these, too, his ideas were very closely akin to those of Aristotle. He does not believe in a psychology of consciousness, for he holds that we cannot affirm anything objective in regard to consciousness, since it is purely subjective. The only proper subject of psycho- logical study is the organism in action. Similar features underlie the phenomena of behaviour (both of men and animals) and the phenomena of development. In both cases the actions are directed towards a certain end. In neither case can we think of them as purely mechanical, for they are directed by an idea. Let us take the case of

a dog who is making for home. All his movements are co- ordinated by and subordinated to his aim to reach home. He avoids obstacles, finds the shortest path, and makes use of all his previous experience. The application which he makes of those earlier experiences is controlled by the special object which he wishes to attain. His progress is directed by something which is very analogous to the entelechy which controls and directs development. This something, which is very real, though intangible, and which is known only to the mind, was called 'psychoid' by Driesch. 'Psychoid' is already present in the newly born ; it takes the form of an 'urge' towards action. This 'urge' is endowed with knowledge ; this is clearly revealed in the first movements of the new-born animal. This innate urge and innate knowledge, which precedes all experience, were called by Driesch primary purpose and primary knowledge. Later on, when the organism has accumulated experiences, it regulates its activities according to these ; such experi- ences constitute its 'secondary purpose' and 'secondary knowledge'.

There have been many complaints of the obscure style of Driesch's writings. Why are they considered so difficult to read ? Why have so few scientists attempted to discuss or to criticize the principles underlying his theories ? The cause is not to be sought in Driesch's style, but in his peculiar mode of thought. It was said by Coleridge that every man is born either a Platonist or Aristotelian. Driesch is a Platonist, if he believes in intuition, if his objective thinking is by means of plastic pictures. He is an Aristotelian, if his convictions depend upon 'proof. The difference can only be partially expressed by the deceptive words 'abstract' and 'concrete'. Platonic ideas are very 'abstract' ; nevertheless they are, in general, much more comprehensible, and much nearer to reality than are the ideas of Aristotle and this in spite of the fact

that Aristotle's ideas are much more concrete, dealing with such concrete themes as dynamics and 'energeia'. Among modern writers Kant, Lotze, Darwin, Weis- mann, and Roux are to be numbered among the unimagi- native 'proof-seekers', while Goethe and Schopenhauer may be cited as important disciples of the opposite school. The writings of the intuitive thinkers are very much easier to read. We do not have to search for each idea at the end of a troublesome proof; it is there, in every sentence, in every word. The only purpose of the detailed exposition is to give to this idea logical form, to define its shape and delimit its contour. In contrast with this, the scientist who deals in 'proofs' is not expounding an idea : he is seeking for 'truth', and is striving to distinguish truth from error. In this endeavour he employs nothing but logic, and for this purpose he strives to 'prove' that it must be so, and not otherwise. For this reason his thought seems to us to be very abstract. In his 'proof there is nothing that can appeal to the imagination, while his appeals to the under- standing, his constant demands upon it, make us feel unsafe. We involuntarily fear the false inference that may be lurking somewhere, hidden from us. Driesch is a 'proof-seeker' par excellence. His earliest theoretical work was very characteristic of his whole method. He began by inquiring in how far biology can be treated mathematically, that is, can adopt the methods of the most logical of the sciences, one closely akin to logic. In a second theoretical investigation, he asserted that no really fruitful natural science is possible without a definite theory of knowledge, and turned his whole attention to the relationship between causality and teleology a subject which is pure logic.

He attacked the usual methods of biological classifica- tion, asserting that they 'lacked that character of inevitable- ness' which is possessed by a geometric class by, for example, the geometric group of regular bodies. He tells us that he once believed in the mechanistic theory, but that he discovered his error when he attempted to follow out this theory to its logical conclusion. In this way he had ultimately been led to declare himself a dynamic vitalist. When he has arrived at this position he begins to question himself anew is he right in his conclusions ? To this question he himself gives the answer :

'Such questionings are impossible and they should never be formulated, either now or in the future. No new line of approach to these problems is possible. This is implied in our admission of the fact that the idea of "necessary connexion" is an a priori logical necessity' ('Kritisches und Polemisches,' BioL ZentralbL 1902). He has become a vitalist; he does not claim to have presented this view in any new manner, but he believes he has demonstrated that it is the only theory which is intellectually possible.