An Introduction to Comparative Psychology
Chapter 19: Selective Synthesis in Evolution
C. Lloyd Morgan
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I SAID at the end of the last chapter, that in evolution we may see the continuous manifestation of a selective synthesis, which finds its expression in the primary laws of nature and of mind. Allusion has more than once in the course of this work been made to this synthetic tendency in nature; and towards the close of the chapter on Synthesis and Correlation I said that consciousness is essentially a synthetic unity, and that herein we might recognize the subjective aspect of that selective synthesis which we may discerning diverse forms throughout the objective world of nature. I here propose to deal, so far as can be done within reason able limits, with this selective synthesis. I shall endeavour to present a restatement of the fundamental traits which characterize evolution, and to indicate what I believe to be the essential solidarity of nature in all its modes, inorganic, organic, and conscious. It is, of course, true that the laws of inorganic development are not the same as the laws of organic development; and equally true that the study of mind introduces us to a new aspect of the developmental process. Notwithstanding these obvious differences, the evolution that sweeps through nature is, I believe, one and continuous. My chief concern here is with mental evolution, and it is towards this that I shall throughout be working. But I shall, nevertheless, devote a large share of my space to a consideration of the principles of evolution as they are exemplified first, under the simpler and more rigid conditions of inorganic nature, and then under the complex and plastic conditions of organic development.
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If we make a nearly saturated solution of chloride. of lead in hot water, and set the solution on one side to cool, we shall see after a while that myriads of minute acicular crystals of chloride of lead make their appearance and sink to the bottom of the vessel in which the solution is contained. Here is a simple case of development or evolution. Let us take note of some of the features it discloses. In the first place the crystals have a definite geometrical form, exhibit differential expansion under the influence of heat, and possess peculiar optical and electrical properties. In a word, the crystals are the result of a selective synthesis, special in its nature, and determinate in its products. Secondly, this selective synthesis can only manifest itself under appropriate environing conditions. If the water be hot, the crystals are not evolved; and if, after they have formed in a cooling solution, the vessel be again heated, the crystals will disappear. Thirdly, if we trace backward the evolution of one of these crystals, we reach a point, that at which the crystal began to form as such, where there is an apparent breach of continuity; by which I mean, not a gap or hiatus in the ascending line of development, but a point of new departure. Such new departures in development are illustrated in Fig. 2 1, which shows the volume-changes of the substance water under the uniform and continuous. application of heat. It will be seen that the line which diagrammatically represents these changes exhibits several points of new departure. Opinions differ as to the exact state in which the chloride of lead exists in the solution, but, what ever that state, there is a critical period when the chloride of lead in solution assumes the form of a solid crystal. Fourthly, it goes without saying that the requisite materials out of which the crystal can be built must be present.
The laws of crystalline synthesis have to a large extent been ascertained, and it is found that all known crystalline
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(340) forms fall naturally into certain well-defined groups. There is a remarkable definiteness and, so to speak, narrowness in the limitation of crystalline form. Quartz crystallizes in six-sided prisms capped with hexagonal pyramids, the angles between the faces being of constant value. Though this fundamental form may be modified by the development of additional minor planes, the range of variation is slight. Calcite crystallizes in a greater variety of forms, and there can be little doubt that each one of these is the strictly determinate outcome of crystalline synthesis under the existing conditions of the environment. We must thus regard each several variety of crystalline form as the joint product of what we may term an innate or inherent synthesis and the conditioning of the environment. Were such a crystal endowed with consciousness, we may well suppose that it would claim freedom to act in accordance with its inherent crystalline nature, except in as far as it was restrained by the inevitable conditions of its environment.
The same general principles are further illustrated in that form of selective synthesis which is shown in the production of chemical compounds. If electric sparks be made to pass between carbon points in an atmosphere of hydrogen, acetylene, a gas containing two atoms of carbon combined with two of hydrogen (C2H2), is formed. If this gas be mixed with hydrogen and caused to pass over spongy platinum, ethene, which has two atoms of carbon and six of hydrogen (C2H6), is produced. If the acetylene be passed through a red-hot tube, benzene (C6H6) is formed, together with small quantities of styrene (C8H8), napthalene (C10H8) and retene (C18H18). If, again, electric. sparks he caused to pass through a mixture of acetylene and nitrogen, hydrocyanic acid (HCN) is produced. Similar instances could be multiplied indefinitely. A mixture of carbon monoxide and hydrogen, when it is passed over spongy palladium, gives rise to formaldehyde (CH2O), and six molecules of this in presence of,
(341) calcium hydrate condense to form one molecule of a sugar called formose (C6H12O6). Once more, ethylene (C2H) combines with bromine to form a substance called ethylene dibromide, which in presence of potassium cyanide in solution gives rise to ethylene dicyanide ; this with water gives succinic acid (C4H6O4), a substance found in the turpentine of several species of pine.
Now in each of these cases, and in thousands of other such cases with which chemistry makes us acquainted, we see that the new compound is due to a selective synthesis of the atoms, and that it has a definite and determinate composition. Not every collocation of atoms of carbon and hydrogen can coalesce to form a synthetic molecule; C2H2, C2H4, C2H6, are possible under the known laws of synthesis, but CH, CH2, CH3, CH5, C2H, C2H3, C2H5 and so forth, are, according to our present knowledge, impossible compounds. Secondly, this selective synthesis can only occur under suitable environing conditions. It is the function of experiment to ascertain the conditions under which synthesis can be effected. In the case of complex molecules, it is found to be quite impossible to produce them by a direct bringing together of the elements of which they are composed. They have to be built up by a series of successive steps or stages, the special conditions appropriate for each of these steps having to be ascertained by experiment. In this way many substances which are formed under organic conditions by animals or plants have now been produced in the laboratory, but many others cannot be so produced. We do not know ,the requisite stages, or have not learned the conditions under which the successive syntheses can occur. Here, again, we may notice, what we saw to be true of the development of crystals, that if we trace back the evolution of a chemical compound we reach a point, that at which the synthesis begins to take place, where there is an apparent breach of continuity, in the sense in which this phrase was
(342) before used. If the vapour of sulphur be passed over redhot charcoal, a volatile compound, carbon disulphide, is produced, which may be condensed into a heavy, colourless liquid. This liquid has altogether new properties, different from those of either sulphur or carbon. It is a definite and determinate product of selective synthesis. Between the physical condition of the elements before synthesis and that of the compound after synthesis there is an apparent breach of continuity. There does not appear to be a gradual and insensible change from the physical properties of the elements to the physical properties of the compound, but at the critical moment of the constitution of the compound there seems to be a new departure.
Selective synthesis of a definitely determinate nature; the controlling conditions of the environment ; apparent breaches of continuity in what we may term the curve of development: these, then, are some of the teachings of inorganic nature.
But it is possible that some of my readers are by this time beginning to exclaim:-- What has all this to do with Comparative Psychology ? I would ask them to bear with me. In the meanwhile, I may say somewhat in explanation of the central aim and purpose of this chapter. There are two opposing schools of psychologists. On the one hand are the Empiricists. They appear to be completely content with descriptive psychology. Laying great stress on the facts of association, they describe the genesis of psycho-logical states as a continuous process of aggregation under the conditions of association. They do not appear to recognize-or in any case they lay little stress on-an underlying law of synthesis. Anxious to base their psychology on the results of biological research, and catching up from evolutionists the watchword "environment," they are apt to regard psychological genesis as wholly the result of the conditioning effects of the environment, and make the individual mind a mere puppet in the hands of circum-
(343) stances. Allying themselves with the physiologists, they seem to regard consciousness as the mere spectator of a series of physiological changes in nerve-tissue. On the other hand are those whom we may term the Apperceptionists. For them the selective synthesis is the essential and central feature in mental development; the environmental circumstances are subsidiary. But they contend that this selective activity, to which they apply the term " apperception,''[1] is something sui generis, and peculiar to mind, something which is not found elsewhere in nature. "In the physical world," says Professor Mark Baldwin, "we find no such unifying force as that known in psychology as the activity of apperception." Now, according to the view adopted in this work, the Empiricists are right in their contention that the study of psychology should, so far as the conditions of the case admit, be brought in line with the study of branches of objective science; are right in utilizing to the full the results of general biology and of special nerve physiology; but are wrong in laying the main stress on the environment, to the entire, or almost entire, neglect of a law of intrinsic selective synthesis',--while the Apperceptionists, on the other hand, are right in -insisting on the central importance of selective synthesis in psychology ; are right in laying stress on the activity of the conscious subject; but are wrong in supposing that this selective synthesis is something sui generis, and peculiar to the activity of mind. Hence it becomes my duty-to bring out, as clearly as I can, the real existence of this selective synthesis, -- not as a mysterious "principle," but as a legitimate inference from the observed facts, -and also to show that this synthetic
(344) activity is universal or. common to all known aspects of nature, and nowise restricted to the realm of mind. And I do not see how I can hope to show this without a consideration of the phenomena of evolutional development in the inorganic sphere, as well as in biology and psychology.
Furthermore, I am anxious to draw a distinction which is, I think, too much lost sight of, but which is serviceable both in psychology, and in other branches of science,namely, that between primary or intrinsic laws of nature, and secondary or extrinsic laws. Let it be once for all understood, that by law I mean the generalized statement of observed fact, or of legitimate inference from observed fact. The tendency of carbon to unite with sulphur is due to a primary or intrinsic law, and when they combine they are typically free so to do. And in all cases where natural inherent tendency is fulfilled without let or hindrance, we should speak of freedom. This is, indeed, the very essence of our idea of freedom, that the body or system of which this attribute is predicated is free to carry out the tendencies of its inherent nature. Unfortunately, false, and often hazy, conceptions have tended not only to obscure this truth, but even to lead to its denial. For if we conceive of, the primary laws of nature as something external to phenomena and controlling them, then the sulphur and carbon are no longer free to combine, but do so under the compulsion of an external law. Regarding as I do the primary laws of nature as intrinsic and inherent (not external and compulsive), and any system exhibiting its own inherent activity as typically free, I distinguish these intrinsic laws from the extrinsic laws Which summarize the conditioning effects of environment. Freedom is intrinsic ; but all forms of constraint are extrinsic. The individual, man or animal or crystal, is free in so far as it acts in accordance with its inherent intrinsic nature ; it is under constraint in so far as its activity is thwarted by the extrinsic influence of environing conditions.
(345) These considerations should be borne in mind in any discussion of the free-will question. All natural law is determinate; hence there is no real conflict between determinism and freedom as above defined.
Now the selective synthesis which we have seen to be a factor in evolution is an intrinsic or primary law of nature; while the conditioning effects of the environment are secondary or extrinsic laws. Both are determinate, both are essentially natural. And it is my object to show that both are recognizable in evolution, in all its phases, inorganic, organic, and psychological.
I have spoken of the selective and synthetic tendency as active, and in the seventeenth chapter (P. 314) have laid some stress on this activity. That all the multitudinous natural operations we see around us, the changes and transformations of energy, give evidence of an activity of some sort and somewhere, can scarcely be called in question. But we are too apt to conceive this activity as external to and exercised upon natural objects ; and to talk of the constraining action of natural law as if this action were something external and controlling. It is distinctive of the monistic interpretation of nature, that the activity is regarded as intrinsic or inherent in and not external to, the happenings which we call natural.
In passing now from inorganic development to o rganic development, the first question that arises is:-- Can the inr organic have given origin by natural processes to the organic? It seems tolerably certain that the synthesis of living protoplasm has not yet been effected in a test-tube ; but he who bases upon this fact the assertion that the natural synthesis of protoplasm is impossible, would seem to have a somewhat overweening confidence in the test-tube. All that the failure to produce protoplasm in the laboratory shows, is that we have not yet learned, and perhaps may never learn, the stages of synthesis and the appropriate conditions under
(346) which the synthesis may take effect. I, for one, am not prepared to accept the verdict of the test-tube as finally conclusive. Whether the natural synthesis of protoplasm without the aid of already formed protoplasm is going on now anywhere in the wide world I- do not know but I but I believe that it has so taken place at some period or periods of the earth's history. The present existence of protoplasm shows that there is a synthetic, tendency for certain widely spread elements to combine in this way; nay more, the rapidity and vigour of organic growth show how exceedingly strong is the tendency. It is true that, so far as observation goes, this vigorous synthesis cannot now occur, unless a fragment of living protoplasm be present to initiate the new growth. But this does not nullify the fact of the existing synthetic tendency, Now one may well suppose that, not withstanding the strength of this tendency, the complete sequence of appropriate conditions for the successive stages of the synthesis is of the rarest occurrence; may even have occurred only at a certain stage of the earth's history. If it be said that the properties of protoplasm indicate a new departure, and that there is apparently no continuity of curve between the properties of the inorganic and the organic, this may be readily admitted, and regarded as a marked instance of what we have already seen to be a not unusual feature of development.
Let us now take note of some of the more salient phenoinena presented by living matter. It is in its chemical nature exceedingly complex, highly stored with energy, and very unstable. It is semi-fluid, viscid, and possesses mobility. It is capable of growth by assimilation, and of disintegration under the stress of comparatively slight stimuli or changes in the environment. It divides by fission ,into small individual units or cells, in each of which there is generally a central differentiated portion, the nucleus. There can be no question that this protoplasmic material, whether
(347) it be regarded as a single chemical substance, or as a group of analogous substances, is a product of- selective synthesis; and there can be little doubt that the differentiation of the nucleus within the cell is a, further result of selective synthesis, though how this was brought about we are not at present able to say. 'Furthermore, we may affirm with little fear of contradiction that, interesting and important as are the structure and composition of this living substance, it is chiefly in virtue of its being a vehicle for orderly transformations of energy that we describe it as living. Here, in fact, is where the organic differs most markedly from the inorganic. When the crystals of chloride of lead are formed in a cooling solution, there is a redistribution of energy; when the carbon and hydrogen combine to give rise to acetylene, or the carbon and sulphur to form carbon, disulphide, changes in the distribution and mode of occurrence of energy occur. But in protoplasm, owing to the power of continuous assimilation and concomitant. disintegration, there is a continuous series of transformations and redistributions of energy ; and it is just herein that one of the characteristics of, life lies. We study the substance of living things, not only to learn what it is, but also to understand what it does.
In the unicellular organisms, or those which are constituted by a single cell, there are wide differences in the complexity of the structure of this cell. Some, like the amoeba, are comparatively simple; others, like the vorticella, show not a little differentiation; within the substance of yet others, exquisitely formed and delicately sculptured skeletons of silica or carbonate of lime are produced. That the more differentiated form- have been evolved from the less differentiated forms is part of the evolutionary assumption . But how? There can be little question that here, as on the lower plane of inorganic development, the two factors, an intrinsic synthetic tendency and a constraining and conditioning environment, are operative. It is difficult to
(348) assign the due value to each. When, however, we consider the exquisitely fashioned frustules of the diatom, the beautiful basket-work of the radiolarian tests, or the delicately chiseled calcareous shells of the foraminifera, we are unable to assign their conditioning to any probable mode of action of the environment.' Nor -have we any reason to 'suppose that the possession of those particular forms and modes of sculpturing which we observe, affords any security against elimination by the stress of inorganic conditions, by enemies, or by competition. We seem, therefore, justified in supposing that the primary factor is here the most important, and that these exquisite skeletons are the result of selective synthesis. If this be so, then the various types of frustules, to take the diatom as an example, must be regarded as determinate, synthetic products analogous to the crystalline forms displayed by calcite. But how different are the determinate forms displayed under organic conditions from those which are displayed under inorganic conditions!
It is true that the tests of radiolarians may show, in the basal ground-plan of their structure, some indications of continuity With the crystalline forms of quartz; but it is only on careful analysis that any trace of similarity of type is disclosed, so completely is it hidden and masked by the profound modifications impressed on the silica by the organic, conditions of its production.
If now we pass from these skeletal products of certain unicellular organisms to the protoplasmic structure of such forms as vorticella, stentor, or paramecium, with its not inconsiderable differentiation, and if we ask concerning this how far it is due to selective synthesis, and how far to the conditioning effect of the environment, our difficulties seem to increase. In either case the numerous forms that are, as a matter of fact, presented. to our study must be due, on the hypothesis of evolution, to variation; and this variation must arise out of the inherent nature of the organic material
(349) or some part of it, reacting under the stress of environing forces. The essential question, therefore, is whether the variations so arising are indeterminate or determinate. Are the forms we observe entirely the result of the natural selection of adaptive variations, through the elimination of an indefinite number of non-adaptive variations? or are they the result of the natural selection of adaptive variations from' among those presented -by determinate synthesis, numerous perhaps, but not indefinitely numerous? In other words, have we, when we reach this stage of evolution, got rid, for good and all, of determinate products of selective synthesis, and have we henceforth to deal with indeterminate, variations in any or all directions ? The question is a biological one, and most difficult to decide by observation. But, if the skeletons of certain unicellular organisms be regarded as the results of determinate variation, it would seem not unreasonable to assume that the differentiated structure of a vorticella or paramoecium is also the no-doubt naturally selected result of determinate synthesis. For it must be remembered, that the, protoplasmic structure of vorticella, no less than the sculptured frustule of a diatom, is the visible expression of an intrinsic activity under the partial control of environing conditions.
The multicellular organisms differ from those which are unicellular, not merely and not chiefly in that they are composed of many cells, but in the fact that there are differentiations among the cells with differences of function; and that the differentiated structures and functions are so integrated and co-ordinated as to conspire to form a unity, both structurally and functionally. Among them reproduction is either by fission, -- that is, is, the division of the organism into two or more, as in some worms; or by budding, as in many zoophytes ; or by the detachment of eggs which generally have to be, but in' some cases need. not be, fertilized. In sexual reproduction, to which alone we can here
(350) refer, the egg so detached is a single cell - but it is, so to' speak, a representative cell. It contains the potentiality (to use this word for the present to express our comparative ignorance of the structure and energy in virtue of which the cell has this power), -- it contains, I say, the potentiality of developing under -appropriate conditions into an organism. like that from which the cell was detached. This it is which makes the human ovum or sperm the most marvellous speck of matter in the known universe. Confining our attention therefore to the higher animals, we may say that each individual, with its tens of thousands of co-ordinated cells and cell-activities, takes its origin from a single cell, the nu lens of which contains germinal matter derived from two separate individuals. There can be no question therefore that within this cell, and probably within its nucleus, is contained the potentiality of the complex organism into which it develops. Here, then, it is that all variation must take its origin. In technical phrase, variation is germinal in origin, but somatic (from soma, the body) in expression.
The question here again arises how this variation in the germinal matter may be caused. It is clear that the extrinsic action of natural selection, through the elimination of relative failures, can have played but an indirect part in the origin of variations. Given favourable variations, natural selection ,may account for survival. It cannot account for their presence and origin. Variation is germinal in origin, but somatic in expression. It is on this somatic expression in the bodily organization that natural selection takes effect; and it -is only in so far as these organisms are the bearers of germinal cells capable of reproducing similar individuals, that natural selection is effective on the race. Each individual carries, in the germinal matter, the secret of its structure and energy. If it perish through elimination, or if it be prevented from taking any share in the continuance of the race, its germinal secret perishes with it.
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We seem, then, forced to conclude that the variations which take their origin in germinal matter must be intrinsic, and rather called forth by, than produced by, influences brought to bear upon it from without. If so, we must again ask, Are the variations determinate or indeterminate ? According to one school of biologists; the variations are frequently determinate, and arise in a manner that is easily understood. If any part of the somatic structure of an organism is modified during the life of that organism, this "acquired character" affects the germinal matter -in such a way that a similar modification is developed in the offspring which arise- from that germinal matter. Thus, in so far as a man improves his physique or his brain-power by careful training, lie is impressing his germinal matter with a potentiality of similar development. Those who hold this view have not as yet been able either to establish the fact of such inheritance of acquired characters beyond question, or to suggest such an explanation of the manner in which the influence affects the germinal matter, as to satisfy their critics, who contend that no such origin of determinate variations has been proved or is probable. According to the opposing view, all variations arise endogenously within the germ-plasm; and there is no transference to the germ-plasm of exogenous variations taking their origin in somatic modifications. 'If this be so, we are thrown back upon such influences, acting on the germinal nuclear Matter, as nutrition, climate, and tile nature of the medium in which the organism lives, in so far as this can affect the germinal matter in its sheltered position within the body, and upon the general effect of the organic environment of the somatic cells and their products. These influences may give rise to indeterminate variations, or to variations which are determinate. In the former case, we may say that chance offers an indefinite number of fortuitous variations to the winnowing process of natural selection. In the latter case, we may say
(352) that selective synthesis offers a definite number of determinate variations to the eliminating agencies of life's struggle. The observations of Schmankewitsch appear to show, that by gradually altering the salinity of the water in which certain brine-shrimps live, one species can be transformed into another species differing determinately in the form of the tail-lobes and the character of the spines they bear. Pupae of a Texan species of the Saturnia were brought in 1870 to Switzerland and kept there during the winter. The moths which emerged from the cocoons were completely Texan in character, and laid eggs; the caterpillars were fed on the leaves of Juglans regia (the Texan form feeding on Juglans nigra); and the moths which resulted from this development were possessed of new and determinate characters such as to justify, it would seem, their being regarded as different species. Now here it is difficult to say whether the difference was called forth by some action on the germinal matter or on the cells which developed therefrom. But, in either case, the apparently determinate nature of the change is to be noted It appears to me that the recorded experience of breeders shows that the material offered to artificial selection is not the result of fortuitous but rather of determinate variation. As Darwin said, " There are two factors : namely, the nature of the organism, and the nature of the conditions. The former seems to be much the more important." I am therefore disposed to believe that the factor that I have termed selective synthesis is still operative in the case of the multicellular organism. It is, no doubt, indefinitely more complex than it is in the case of inorganic development, or even of the development of the exquisite markings on the frustules of diatoms. But this increasing complexity is just what a study of the lower phases of development would lead one to expect.
I have spoken of the nuclear matter of the germ as containing the potentiality of developing into an organism like
(353) the parent. Dr Weismann has recently made an attempt to suggest a structural basis of this potentiality. The attempt is from the nature of the case speculative, but the speculation runs on scientific lines. I cannot, of course, here discuss or even describe Dr Weismann's views. Suffice it to say, that he suggests the possible or probable existence of biological units of progressive complexity, which he terms biophors, determinants, and ids These give actuality in the germ to its potentialities of development; and they may well be regarded, from our standpoint, as the structural expression of determinate selective synthesis. Dr Weismann is of opinion that the cause of hereditary variation must be due to the direct "effect of external influences on the biophors and determinants. "We are," he says, "undoubtedly justified in attributing the cause of variation to the influence of changed external surroundings." It is not, however, quite clear whether he regards the variations so produced as determinate in direction or not. But he forcibly states his belief that we cannot possibly attribute the immense number of adaptations to rare fortuitous variations occurring only once. " The necessary variations from which transformations arise by means of selection must," he says, "in all cases be exhibited over and over again by many individuals." If the variations are not indeterminate, but the outcome of selective synthesis, the occurrence of such variations as are exhibited over and over again by many individuals would be what we should naturally expect.
Granting all Dr Weismann's assumptions, the manner in which the determinants and biophors are distributed throughout the organism during the process of development remains an unsolved riddle. Of this Dr Weismann himself is fully aware. He is far too honest an inquirer into truth to attempt to gloss over our present ignorance.
It seems to me that the problem of development will have to be attacked in the direction- rather of energy than of
(354) structure. We must regard the living organism, nay even the fertilized egg-cell, not only as a piece. of mechanism but also as a piece of going mechanism. I remember one seeing a lecturer build up a number of -gyroscope top's into a compound system of spinning parts. So long as they continued spinning the system was stable; as the spinning died down the system fell to pieces. It is the spin of life that somehow effects the distribution of structure; and different eggs develop into different animals in virtue of a inherited difference of their vital spin. Cell-division cannot be a matter of structure only ; it must be a matter of what I am speaking of as spin -- a term which must not be interpreted too literally. When the organisin has been built up into its several parts, composed of differentiated cells, the spin of each -ell must in large degree be dependent on, and conditioned by, the spin of neighbouring cells which constitute its immediate environment, and must in turn influence that of those cells; and thus the spin of the entire group is a co-ordinated and integrated spin, conditioned as a whole by the general environment of the aggregate.
What I before termed the potentiality of the fertilized egg cell, we may now regard as a definite biophoral or other structure, which is the vehicle of a particular and specialized, vital spin. I am inclined to regard the vital spin as that upon which the more stress will ultimately be laid; the spin determining the development of structure, rather than the structure determining the nature of the spin. Starting, that is to say, with a particular and specialized spin in the fertilized egg, then, given an adequate supply of material fitted for assimilation, the evolution of the indefinitely more complex and co-ordinated spin of the differentiated cells of the adult organism follows, and is manifested to our eye as a structural product, the functional activities of the organism being the net result of specialized co-ordinations of vital
(355) spin. The analogy of mechanics may mislead us. We make machines with a co-ordinated mechanism to effect certain transformations of energy, and thus regard the structure as determining the nature of the output of energy. But in nature the machines are not made, but develop, and their structures are determined by the modes of energy of which they are the vehicle. On the view of evolution developed in this chapter the transformations of energy involved in the complex vital spin are due, primarily, to inherent and determinate selective synthesis of the vital molecular vibrations which constitute the spin, and secondarily, to the conditioning of the spin in harmony with the environment.
The vital molecular movements and transformations of energy reach their acme of delicate co-ordination in the brain of the higher vertebrates ; and there they are associated with the phenomena of consciousness. We thus pass from organic evolution to mental evolution.
The essential questions for our consideration are -- (1.) Is there selective synthesis in mental development? (2.) What is the nature of the conditioning environment in mental evolution ? (3.) Is variation determinate or indeterminate ? (4.) Are there apparent breaches of continuity in mental development? (5.) Is mental development dependent on natural selection through elimination ? (6.) Is it necessary that we should believe in the inheritance of acquired characters ?
In reply to the first of these queries, Is there selective synthesis in mental development? it appears to me that the psychologist is bound to answer that there is. And I would remind the reader of what was said concerning the externality of the object as presented in vision. I look up from my page and have an impression of a book at a certain distance from me. In psychological analysis it is found that the impression is the result of the coalescence of cer-
(356) -tain retinal sensations with certain motor sensations derived from the eye muscles and the apparatus of accommodation. It appears to me obvious that no mere commingling of disparate sensations could give the out-thereness of the impression, but that when the motor sensations coalesce with the retinal sensations they enter into a synthesis which has -a new and determinate character. It would seem that just as the raw material of life is the product of selective synthesis, so too is the raw material of sentience dependent upon an analogous process; and that it is inconceivable that the elements of sentience should give rise to consentience and consciousness by-mere fortuitous grouping, without the play of that selective synthesis which sweeps, as I believe, through the whole ascending curve of evolution, inorganic, organic, and psychical. In any case, psychology, so far as I am able to interpret its teaching, proclaims the fact that selective synthesis is of the very essence of mental development.
Passing to our second question, we have seen in the lower phases of inorganic and organic evolution how important a part the environment plays in conditioning development. The products of selective synthesis must be in harmony with the environment, if they are to exist and persist. What, then, is the environment in mental development? We must here distinguish between the environment of the co-ordinated system of ideas which constitutes the complex mental synthesis of the individual mind, and the environment of the several units which are the elements in this synthesis. The mental synthesis is -the correlate of the integrated spin of a vast number of brain-molecules ; the results of this integrated spin must be in harmony with the general environment; but the spin of any subordinate group of cells must also be in harmony with the spin of the surrounding groups which constitute its immediate environment. So the mental system of the individual must be in sufficient
(357) harmony with the surrounding social and other environment to enable the man in whom it occurs to escape elimination by competition or by enemies and to elude temporary elimination in the prison or the madhouse. On the higher plane of intellectual thought it must, in order to be fruitful and not barren, be fitted to resist the elimination of adverse criticism. Within the system itself the environment of any constituent idea or ideal is wholly psychical. This is obvious enough in the higher region of intellectual ideas, -and of moral and aesthetic ideals. But it is also true in the domain of sense. For there is no test beyond and behind -that of practical experience ; and practical experience is psychical. Hence it follows, that any product of mental synthesis must, in order to make good its existence, be in congruity with the mental system in which it develops, Its psychical spin is conditioned by the co-ordinated psychical spin of the whole system. I am thinking out a problem and a solution flashes across my mind through some subtle association by similarity. But it has to stand the test of the environment. If it be not in congruity with all I know of the subject it cannot find a permanent place in my system of ideas: it is eliminated through incongruity. Contradictories cannot co-exist in the same synthesis. The advance of science is on this wise. The thinker assimilates all that is best in the work of his precursors, and by observation and experiment brings in fresh stores of facts; a congruous system takes form in his mind, all that is incongruous therewith being eliminated; and for after thinkers the result of his thought is part of the environment which they must assimilate, and which through the rigorous application of scientific -method and verification they must hand on in a more highly developed condition through the further elimination of incongruities.
Whether the variations that occur in mental faculty are determinate or indeterminate in their direction (our third
(358) question), it is hard to decide. Are there definite types of character ? or are what we regard as such types merely convenient categories under which we class individuals who are indefinitely variable? Is genius the result of a fortunate commingling of inherited aptitudes, or is it a product of selective synthesis, a crystalline gem of rarest purity and symmetry? I am inclined to believe that the variations are determinate, the definite products of selective synthesis and that mental evolution proceeds along lines which are determined by the intrinsic laws of mind, just as a crystal is evolved along lines which are determined by the intrinsic laws of crystallization. But there can be little doubt that, as we advance from the simpler to the complex, the rigidity and narrowness of the synthesis give place to far greaterplasticity and freedom. The determinate possibilities of synthesis are in brain and mind indefinitely increased, and thus, from the very multiplicity of determinate variations, their definitely synthetic nature is liable to escape our observation.
Passing now to our fourth question, Are there apparent breaches of continuity in mental development? I am disposed to answer that such apparent breaches there are. The step from mere sentience to consentience probably involved such a breach or new departure in the develop mental curve. The step from consentience, or senseexperience, to reflection and thought certainly involves, in my judgment, such a new departure. The curve of the development of sense-experience and intelligence pursues a smooth upward course. But when the perception of relations is introduced there is a point of new departure. If tile dividing line between sense-experience and conceptual thought is to be drawn, on the basis of the data at present open to our observation, between the lower Primates and man, then we may say that there is an apparent breach of continuity at this stage of mental evolution analogous to
(359) the apparent breach of continuity between the inorganic and the organic stages of the evolutionary process. This is the view to which I myself incline. 'But we have seen that such apparent breaches of continuity are natural incidents in the ascending curve of evolution. If, therefore, they do thus occur in mental evolution, this does but serve to bring this phase of development into line with the inorganic and organic phases.
At the same time it should be clearly grasped that these apparent breaches of continuity are to be regarded as merely incidental to the conditions under which the phenomena are presented to our observation. The breach between the liquid and the vaporous states of water holds good only under the normal conditions of pressure. On these conditions it is contingent. Could we only in other matters, as has been the case with liquid and vapour through the classical researches of Andrews and others, find the appropriate conditions, every apparent breach of continuity would probably disappear. We are constrained to believe that evolution as a process is essentially one and continuous. By which we mean that nowhere ..is there evidence of supernatural interference ab extra. It is imperative to distinguish with due care between the results of empirical observation and their interpretation on a deeper plane of philosophic thought, The apparent breaches of continuity are empirical, and are incidental only to the limiting conditions of phenomenal presentation.
To the question, Is mental development in all its phases entirely, or even mainly, dependent on natural selection through elimination ? I reply with an emphatic no. I do not of course deny that in the animal world, and in human society to a less degree, it has been the function of intelligence and reason to enable the organism so to guide its -actions as to resist elimination, to live out its full span of life and to procreate its kind; and that those organisms in which
(360) intelligent adaptation was inadequate to these purposes have again and again suffered the penalty of elimination leaving others fitter than them in possession of life's field. But I see no evidence to show that commanding intellect, mathematical or scientific ability, -artistic genius or lofty moral ideas, are attributable solely to natural selection through elimination.[2] In his essay upon "The Musical Sense in Animals and Man," Dr Weismann says:-" Talents for music, art, poetry, and mathematics do not contribute .towards the preservation of the human species, and therefore cannot have arisen by the operation of natural selection." He suggests that as the dexterity of the hand was evolved for other purposes than piano-playing, but has been utilized by man for this purpose, so faculty, which was evolved for other purposes, may by man have been devoted to mathematics, art, or poetry. I see no reason for disagreeing with this contention ; but at the same time I submit that the development of definite and self-consistent artistic, musical, poetic, and ethical ideals demands an explanation which is nowhere given in Dr Weismann's essay. Such explanation is afforded, if they be regarded as the results of inherent activities which are selective and synthetic in their nature.
Lastly we come to the question, Is it necessary to our conception of mental development that we should believe in, the inheritance of acquired characters? Much of the essay of Dr Weismann, to which I have just alluded, is devoted to the consideration of this question with special reference to musical faculty. He concludes that such inheritance of acquired faculty is neither proved nor necessary to an adequate interpretation of the facts. In this I am disposed to agree with him ; though I am not prepared at present to
(361) assert that such inheritance is impossible. The vital spin in the germinal cells may possibly be in some way influenced by the somatic spin around them ; or the spin of the biophors derived from specialized determinants may influence in an analogous manner the spin of the similar determinants in the germinal cells. Be this as it may, it appears to me that if, as I have above contended, the development of definite and self-consistent artistic, ethical, and other ideals is due to selective synthesis, under the conditioning restraints of a Psychical environment, we have herein all that can reasonably be required by any one who is content to adopt air interpretation of nature, including Psychical nature, based on the principles of evolution. An activity which is selective and synthetic is disclosed throughout all the operations of nature, and in psychology is an essential factor in mental development. But there is no evidence that this activity is peculiar to psychology, and there is no evidence that it is external to, and not naturally inherent in, the phenomena which it is the business of empirical psychology to describe.
