Herbert Spencer

by J. Arthur Thomson

Spencer made his position stronger by adducing what he calls negative evidence, namely those "cases in which traits otherwise inexplicable are explained if the structural effects of use and disuse are transmitted."

(1) First he refers to the co-adaptation of co-operative parts. With the enormous antlers of a stag there is associated a large number of co-adaptations of different parts of the body, and similarly with the giraffe's long neck and the kangaroo's power of leaping. Spencer argued that the co-adaptation of numerous parts cannot have been effected by natural selection, but might be effected by the hereditary accumulation of the results of use. The difficulty is to discover how much deep-seated co-adjustment can be effected by exercise even in the course of a long time, and the theory requires such data before it can be more than a plausible interpretation, with certain a priori difficulties against it. If an animal suddenly takes to leaping many individual adjustments to the new exercise will arise; if the animals of successive generations leap yet more freely, they will individually acquire more thorough adjustments up to a certain limit; meanwhile there may arise constitutional variations making towards adaptation to the new habit, and under the screen of the individual modifications these may increase from minute beginnings till they acquire selection-value. Professors Mark Baldwin, Lloyd Morgan, and Osborn, have all made the same useful suggestion that adaptive modifications acquired individually may act as the fostering nurses of constitutional variations in the same direction until these coincident variations are large enough in amount to be themselves effective.

(2) Secondly, Spencer dwelt upon the notably unlike powers of tactile discrimination possessed by the human skin, and sought to show that while these could not be interpreted on the hypothesis of natural selection or on the correlated hypothesis of panmixia, they could be interpreted readily if the effects of use are inherited. But the difficulty again is to get secure data. It is uncertain how much of the inequality in tactile sensitiveness is due to individual exercise and experience, though it is certain that tactility in little-used parts can be greatly increased by use. Nor is it certain how much of the apparent unlikeness in tactility is due to unequal distribution of peripheral nerve-endings and how much to specialised application of the power of central perception. As Prof. Lloyd Morgan says: "We do not yet know the limits within which education and practice may refine the application of central powers of discrimination within little-used areas. The facts which Mr Spencer adduces may be in large degree due to individual experience; discrimination being continually exercised in the tongue and finger-tips, but seldom on the back or breast. We need a broader basis of assured fact." Nor, it may be added, is the action of selection to be excluded.

(3) Spencer's third set of negative evidences was based on rudimentary organs which, like the hind limbs of the whale, have nearly disappeared. Dwindling by natural selection is here out of the question; and dwindling by panmixia, i.e. the diminution of a structure when natural selection ceases to affect its degree of development, "would be incredible, even were the assumptions of the theory valid." But as a sequence of disuse the change is clearly explained. Prof. Lloyd Morgan replies: "Is there any evidence that a structure really dwindles through disuse in the course of individual life? Let us be sure of this before we accept the argument that vestigial organs afford evidence that this supposed dwindling is inherited. The assertion may be hazarded that, in the individual life, what the evidence shows is that, without due use, an organ does not reach its full functional or structural development. If this be so, the question follows: How is the mere absence of full development in the individual converted through heredity into a positive dwindling of the organ in question?" Moreover, the convinced Neo-Darwinian is not in the least prepared to abandon the theory of dwindling in the course of panmixia, especially in the light which Weismann's conception of Germinal Selection has thrown on this process.

The inductive evidence in support of the conclusion that bodily modifications due to use or disuse or environmental influence can be as such or in any representative degree transmitted, is very weak. The so-called evidences are often anecdotal and vague, often irrelevant and fallacious, and those Spencer adduced are by no means convincing. Let us consider the question briefly from the a priori side.

The general argument against the hypothesis rests on a realisation of the continuity of the germ-plasm. For if the germ-plasm, or the material basis of inheritance within the germ-cells, be somewhat apart from the general life of the body, often segregated at an early stage, and in any case not directly sharing in the every day metabolism, then there is a presumption against the likelihood of its being readily affected in a specific manner by changes in the nature of the body-cells. The germ-cell is in a sense so apart that it is difficult to conceive of the mechanism by which it might be influenced in a specific or representative manner by changes in the cells of the body.

On the other hand, in many plants and lower animals, the distinction between body-cells and germ-cells is far from being demonstrably marked, and even in higher animals we cannot think of the germ-cells as if they led a charmed life uninfluenced by any of the accidents and incidents in the daily life of the body which is their nurse, though not exactly their parent. No one believes this, Weismann least of all, for he finds one of the chief sources of germinal variation in the nutritive stimuli exerted on the germ-plasm by the varying state of the body. The organism is a unity; the blood and lymph and other body-fluids form a common internal medium; various poisons may affect the whole system, germ-cells included; and there are real though dimly understood correlations between the reproductive system and the rest of the organism.

There are some who pretend to find in this admission "a concealed abandonment of the central position of Weismann," for if, they say, the germ-plasm is affected by changes in nutrition in the body, and if acquired characters affect changes in nutrition, then "acquired characters or their consequences will be inherited." But it is a quite illegitimate confusion of the issue to slump acquired characters and their consequences as if the distinction was immaterial. The illustrious author of the Germ-Plasm has made it quite clear that there is a great difference between admitting that the germ-plasm has no charmed life, insulated from bodily influences, and admitting the transmissibility of a particular acquired character, even in the faintest degree. The whole point is this: Does a change in the body, induced by use or disuse or by a change in surroundings, influence the germ-plasm in such a specific or representative way that the offspring will exhibit the same modification which the parent acquired, or even a tendency towards it? Even when we fully recognise the unity of the organism, or recognise it as fully as we know how, it is difficult to suggest any modus operandi whereby a particular modification in, say, the brain or the thumb can specifically affect the germinal material in such a way that the modification or a tendency towards it becomes part of the inheritance. Did we accept Darwin's provisional hypothesis of pangenesis according to which the parts of the body give off gemmules which are carried as samples to the germ-cells, the possibility of transfer might seem more intelligible. But Darwin's suggestion remains a pure hypothesis, and is admitted by none except in extremely modified form. In fairness, however, we must note how little we understand of the modus operandi of influences which certainly pass in the other direction, from the reproductive organs to the body; we must recall Prof. Lloyd Morgan's warning that although we cannot conceive how a modification might as such saturate from body to germ-cells, this does not exclude the possibility that it may actually do so.

As a matter of fact, Spencer has himself suggested a modus operandi—as already outlined. The constitutional units are supposed to circulate; when they come to a modified organ and visit its modified constitutional units, they are supposed to be themselves impressed; they are supposed to be "eventually gathered into sperm-cells and germ-cells," which thus come to bear the "superposed traits" resulting from modification. But, as we have seen, the difficulty is to find any basis in fact on which these assumptions can rest. Indeed, they are contradictory to well-established physiological facts.

Inconceivability.—In reference to the difficulties which beset theories of heredity, Spencer remarks:—

"If it is said that the mode in which functionally-wrought changes, especially in small parts, so affect the reproductive elements as to repeat themselves in offspring, cannot be imagined—if it be held inconceivable that those minute changes in the organ of vision which cause myopia can be transmitted through the appropriately modified sperm-cells or germ-cells; then the reply is that the opposed hypothesis presents a corresponding inconceivability. Grant that the habit of a pointer was produced by selection of those in which an appropriate variation in the nervous system had occurred; it is impossible to imagine how a slightly different arrangement of a few nerve-cells and fibres could be conveyed by a spermatozoon. So too it is impossible to imagine how in a spermatozoon there can be conveyed the 480,000 independent variables required for the construction of a single peacock's feather, each having a proclivity towards its proper place. Clearly the ultimate process by which inheritance is effected in either case passes comprehension; and in this respect neither hypothesis has an advantage over the other."

Let us consider what Spencer has said in regard to "inconceivability." Most ova are very minute cells, often microscopically minute, and a spermatozoon may be only 1/100,000th of the ovum's size—inconceivably minute, but yet exceedingly real and potent. We cannot conceive how a complex inheritance made up of numerous contributions is potentially contained in such small compass, and yet in some form it must be. Similarly, we cannot conceive how the pin-head like brain of the ant contains all the ant's "wisdom."

Those who find it difficult to believe that items so minute as the germ-cells can have room for the complexity of hereditary organisation which seems to be a necessary postulate may be reminded of three things: (1) They should recall what students of physics have told us in regard to the fineness, or, from another point of view, the coarse-grainedness of matter. They tell us that the picture of a Great Eastern filled with framework as intricate as that of the daintiest watches does not exaggerate the possibilities of molecular complexity in a spermatozoon, whose actual size is usually very much less than the smallest dot on the watch's face.

(2) It should be remembered that in development one step conditions the next, and one structure grows out of another, so that there is no need to think of the microscopic germ-cells as stocked with more than initiatives. (3) It should be remembered that every development implies an interaction between the growing organism and a complex environment without which the inheritance would remain unexpressed, and that the full-grown organism includes much that was not as such inherited, but has been individually acquired as the result of nurture or external influence.

Now, returning to Spencer, we find that by an extraordinary argument he concludes that the number of determinants required for the development of a single feather in the peacock's tail must be 480,000, and he points to the inconceivability of these being contained, along with much else of course, in the spermatozoon. We are not at present concerned with the precise number of determinants, but we can see no reason why a spermatozoon should not contain millions if they were needed. The inconceivability is a general one; it is due to the difficulty of imaging the complexity of matter.

But the inconceivability of a particular modification of the nose affecting the germ-cells in a specific and representative way is a different kind of inconceivability. It is due to our being unable to imagine any reasonable modus operandi consistent with our knowledge of the structure and metabolism of the organism. As we have seen and emphasised Spencer does himself suggest a modus operandi, but it seems to us to make unwarranted assumptions, and is for that reason to us "inconceivable."

A Priori Argument.—But Spencer advanced an a priori argument to strengthen the position which he felt bound to hold—the transmissibility of acquired characters. "That changes of structure caused by changes of action must be transmitted, however obscurely, appears to be a deduction from first principles—or if not a specific deduction, still, a general implication. For if an organism A, has, by any peculiar habit or condition of life, been modified into the form A', it follows that all the functions of A', reproductive function included, must be in some degree different from the functions of A." [This, we venture to think, must depend on the nature and amount of the modification.] "An organism being a combination of rhythmically-acting parts in moving equilibrium, the action and structure of any one part cannot be altered without causing alterations of action and structure in all the rest." [The appreciability of the change will depend on the amount and nature of the modification, and on the intimacy of the correlation subsisting in the organism. Dislodging a rock may alter the centre of gravity of the earth, but it does not do so appreciably.] "And if the organism A, when changed to A', must be changed in all its functions; then the offspring of A' cannot be the same as they would have been had it retained the form A." [Assuming that is to say that the change in the physiological units of the body affects the physiological units in the germ-cells.] "That the change in the offspring must, other things equal, be in the same direction as the change in the parent, appears implied by the fact that the change propagated throughout the parental system is a change towards a new state of equilibrium—a change tending to bring the actions of all organs, reproductive included, into harmony with these new actions." [It seems to us to pass the wit of man to conceive how or why an improved equilibrium in the use of the hand should involve any corresponding or representative change of equilibrium in the germ-cells.]