Herbert Spencer

by J. Arthur Thomson

A Digression.—Here we must digress a little to compare Spencer's conception of physiological or constitutional units with Weismann's conception of the Germ-Plasm. According to Weismann, there is in the nuclei of the germ-cells a distinctive physical basis of inheritance, the germ-plasm. It is the vehicle of the hereditary qualities, the architectural substance which enables the germ-cell to build up an organism; it has an extremely complex and at the same time persistent structure. Following a hypothesis of De Vries, he supposed that the readily stainable nuclear bodies (the chromosomes or idants) consist of a colony of invisible self-propagating vital units or biophors, each of which has the power of expressing in development some particular quality. He supposed that these biophors are aggregated into units of a higher order, known as determinants, one for each structure of the body which is capable of independent variation. These determinants are supposed to be grouped together in ids, each of which is supposed to possess a complete complement of the specific characters of the organism and also to have an individual character. The ids are arranged in linear series to form the visible idants or chromosomes, which will be slightly different from one another according to the individualities of the component ids. When the fertilised egg-cell develops, it gives rise (1) to somatic cells which carry with them part of the germ-plasm, and differentiate to form the body, and (2) to the germ cells which reserve part of the germ-plasm in an unchanged state, and eventually give rise in appropriate conditions to new individuals and their germ-cells.

Spencer refused to accept the contrast between body-cells and germ-cells as expressing a fact, and referred for his reasons to the numerous cases in which small pieces of a plant or polyp may grow into an entire organism. But when he represented Weismann as maintaining that the "soma contains in its components none of those latent powers possessed by those of the germ-plasm," he did not do justice to the comprehensive theory of the "Germ-plasm." For Weismann assumes that in certain cases the body-cells, even though differentiated, may carry with them some residual unused-up germ-plasm.

When a lizard regrows a lost tail—effectively responding to a casualty which has been common for untold generations—Weismann interprets the mechanism of this as due to a reserve of tail-determinants resident at or near the place of breakage, and localised there as the result of a long-continued process of selection. A chamæleon does not regenerate its tail, and this may be interpreted in terms of the selection-theory, since the chamæleon with its tail coiled up or embracing a branch has not been, in the course of its evolution, subjected to the frequently recurrent casualty which has beset most other lizards. Spencer said, "We cannot arbitrarily assume that wherever a missing organ has to be reproduced there exists the needful supply of determinants representing that organ," but Weismann made no such arbitrary assumption. Many organs are lost which are not regenerated, even when, as far as materials or differentiation are concerned, it would be easy to replace them. Why the everywhere present uniform physiological units that Spencer believed in should not replace them, we do not know; but if the distribution of regenerative determinants has been wrought out by selection, we understand the facts.

Spencer said that the hypothesis of a supply of determinants lying latent at or near the seat of injury, and able to reproduce the missing part in all its details, and to do this several times over, was "a strong supposition." We venture to think that the hypothesis that the same result is achieved by the "physiological units," which are all of the same kind, is a weak supposition. Spencer said: "Reproduction of the lost part would seem to be a normal result of the proclivity towards the form of the entire organism." But it is difficult to see why "proclivity of the physiological units towards the form of the entire organism" should bring about the regeneration of a tail here and a head there, a claw here and an eye there. But Spencer was too acute a thinker not to feel that if the theory of regenerative determinants was "incompetent," his own theory, which interpreted regeneration as due to the activity of physiological units, "with a proclivity towards the organic form of the species," did not cover the facts; e.g. the establishment of "false-joints," where the ends of a broken bone failing to unite remain movable one upon the other. Therefore he suggested a qualification of his hypothesis.

In "the social organism," it is often seen that the components of an aggregate "have their activities and arrangements mainly settled by local conditions." "A local group of units, determined by circumstances towards a certain structure, coerces its individual units into that structure." In an emigrant settlement, "individuals are led into occupations and official posts, often quite new to them, by the wants of those around—are now influenced and now coerced into social arrangements which, as shown perhaps by gambling saloons, by shootings at sight, and by lynchings, are scarcely at all affected by the central government. Now the physiological units in each species appear to have a similar combination of capacities. Besides their general proclivity towards specific organisation, they show us abilities to organise themselves locally; and these abilities are in some cases displayed in defiance of the general control, as in the supernumerary finger or the false joint. Apparently each physiological unit, while having in a manner the whole organism as the structure which, along with the rest, it tends to form, has also an aptitude to take part in forming any local structure, and to assume its place in that structure under the influence of adjacent physiological units" (Principles of Biology, revised edition, i. p. 364).

The experiments of Born and others have shown that fragments of a young tadpole may go on developing to some extent after they are cut off, and that the undifferentiated rudiment of a limb may be successfully grafted on to another tadpole. "In brief, we may say that each part is in chief measure autogenous." "Though all parts are composed of physiological units of the same nature, yet everywhere, in virtue of local conditions and the influence of its neighbours, each unit joins in forming the particular structure appropriate to its place." This conclusion is very interesting when compared with that reached more inductively by many embryologists (of the so-called epigenetic school), namely, that what a blastomere or cleavage-cell of an egg does, is determined by its intra-embryonic environment, by its relations, both statical and dynamical, to the whole organisation of which it forms a part. As Driesch puts it: "The relative position of a blastomere in the whole determines in general what develops from it; if its position be changed, it gives rise to something different; in other words, its prospective value is a function of its position." But those who assume heterogeneous determinants do not thereby exclude what truth there may be in this view that what an early blastomere does is a function of its inter-relations.

But let us consider how much Spencer puts to the credit of his "constitutional units." (1) They carry within them the traits of the species and even some of the traits of the ancestors of the species, the traits of the parents and even some of the traits of their immediate ancestors, and the congenital idiosyncrasies of the individual itself. In this they resemble the germ-plasm. (2) They "must be at once in some respects fixed and in other respects plastic; while their fundamental traits, expressing the structure of the type, must be unchangeable, their superficial traits must admit of modification without much difficulty; and the modified traits, expressing variations in the parents and immediate ancestors, though unstable, must be considered as capable of becoming stable in course of time." Again they resemble the germ-plasm. (3) Once more, "we have to think of these physiological units (or constitutional units as I would now re-name them) as having such natures that while a minute modification, representing some small change of local structure, is inoperative on the proclivities of the units throughout the rest of the system, it becomes operative in the units which fall into the locality where that change occurs." Here they part company from the germ-plasm, except in so far as it may be said that the development of the distributed determinants is in part dependent on local conditions. (4) Finally, since Spencer supposed "an unceasing circulation of protoplasm throughout an organism," such that "in the course of days, weeks, months, years, each portion of protoplasm visits every part of the body"—a wild assumption—"we must conceive that the complex forces of which each constitutional unit is the centre, and by which it acts on other units while it is acted on by them, tend continually to re-mould each unit into congruity with the structures around: superposing on it modifications answering to the modifications which have arisen in these structures. Whence is to be drawn the corollary that in the course of time all the circulating units—physiological, or constitutional if we prefer so to call them—visit all parts of the organism; are severally bearers of traits expressing local modifications; and that those units which are eventually gathered into sperm-cells and germ-cells also bear these superposed traits."

This theory—which is not unlike a combination of Darwin's pangenesis with De Vries's neo-pangenesis—is very significant, for it discloses Spencer's hypothesis as to the modus operandi of the transmission of acquired characters. But there is unfortunately no factual warrant for the assumption that the constitutional units visit one another in various corners of the body, getting impressions as they go, or for the assumption that they are eventually gathered into the germ-cells—an assumption which shows how far Spencer deliberately stood from the conception of the continuity of the germ-plasm. Even if we suppose an organism to undergo numerous modifications in different parts of its body, as a plant may do when it is transferred from the Alps to the lowlands; even if we suppose the constitutional units—which are all of one kind—to circulate and become bearers of the traits expressing local modifications, we have to face other questions: do they all become remoulded in relation to all the modifications? or do some become remoulded in relation to one modification and some in relation to another? or do all the modifications so hang together that one kind of alteration impressed upon the constitutional units covers them all? The difficulties of the conception of constitutional-units certainly do not seem less than the difficulties of the conception of specific determinants.

Even to the general reader, who is not concerned with the problem of the mechanism of inheritance and development, who has a shrewd suspicion that it is one of those things no fellow can understand, our digression should be interesting, for it illustrates Spencer's fertility of invention and his adroitness in lugging in one hypothesis after another to eke out a theory which in its first statement appears to be very simple. It is instructive to observe how the constitutional units at first so harmlessly simple, grow under the conjurer's hands until they become more marvellous than Clerk Maxwell's "sorting demons."

But it is more instructive still to hear the conclusion of the whole matter. "At last then we are obliged to admit that the actual organising process transcends conception. It is not enough to say that we cannot know it; we must say that we cannot even conceive it. And this is just the conclusion which might have been drawn before contemplating the facts. For if, as we saw in the chapter on "the Dynamic Element in Life," it is impossible for us to understand the nature of this element—if even the ordinary manifestations of it which a living body yields from moment to moment are at bottom incomprehensible; then still more incomprehensible must be that astonishing manifestation of it which we have in the initiation and unfolding of a new organism." "Thus all we can do is to find some way of symbolising the process so as to enable us most conveniently to generalise its phenomena; and the only reason for adopting the hypothesis is that it best serves this purpose."