The Principles of Biology, Volume 1 (of 2)

We have before found our conceptions of vital processes made clearer by studying analogous social processes. In societies there is a mutual dependence of functions, essentially like that which exists in organisms; and there is also an essentially like reaction of functions on structures. From the laws of adaptive modification in societies, we may therefore hope to get a clue to the laws of adaptive modification in organisms. Let us suppose, then, that a society has arrived at a state of equilibrium analogous to that of a mature animal – a state not like our own, in which growth and structural development are rapidly going on, but a state of settled balance among the functional powers of the various classes and industrial bodies, and a consequent fixity in the relative sizes of such classes and bodies. Further, let us suppose that in a society thus balanced there occurs something which throws an unusual demand on one industry – say an unusual demand for ships (which we will assume to be built of iron) in consequence of a competing mercantile nation having been prostrated by famine or pestilence. The immediate result of this additional demand for iron ships is the employment of more workmen, and the purchase of more iron, by the ship-builders; and when, presently, the demand continuing, the ship-builders find their premises and machinery insufficient, they enlarge them. If the extra requirement persists, the high interest and high wages bring such extra capital and labour into the business as are needed for new ship-building establishments. But such extra capital and labour do not come quickly; since, in a balanced community, not increasing in population and wealth, labour and capital have to be drawn from other industries, where they are already yielding the ordinary returns. Let us now go a step further. Suppose that this iron-ship-building industry, having enlarged as much as the available capital and labour permit, is still unequal to the demand; what limits its immediate further growth? The lack of iron. By the hypothesis, the iron-producing industry, like all the other industries throughout the community, yields only as much iron as is habitually required for all the purposes to which iron is applied: ship-building being only one. If, then, extra iron is required for ship-building, the first effect is to withdraw part of the iron habitually consumed for other purposes, and to raise the price of iron. Presently, the iron-makers feel this change and their stocks dwindle. As, however, the quantity of iron required for ship-building forms but a small part of the total quantity required for all purposes, the extra demand on the iron-makers can be nothing like so great in proportion as is the extra demand on the ship-builders. Whence it follows that there will be much less tendency to an immediate enlargement of the iron-producing industry; since the extra quantity will for some time be obtained by working extra hours. Nevertheless if, as fast as more iron can be thus supplied, the ship-building industry goes on growing – if, consequently, the iron-makers experience a permanently-increased demand, and out of their greater profits get higher interest on capital, as well as pay higher wages; there will eventually be an abstraction of capital and labour from other industries to enlarge the iron-producing industry: new blast-furnaces, new rolling-mills, new cottages for workmen, will be erected. But obviously, the inertia of capital and labour to be overcome before the iron-producing industry can grow by a decrease of certain other industries, will prevent its growth from taking place until long after the increased ship-building industry has demanded it; and meanwhile, the growth of the ship-building industry must be limited by the deficiency of iron. A remoter restraint of the same nature meets us if we go a step further – a restraint which can be overcome only in a still longer time. For the manufacture of iron depends on the supply of coal. The production of coal being previously in equilibrium with the consumption; and the consumption of coal for the manufacture of iron being but a small part of the total consumption; it follows that a considerable extension of the iron manufacture, when it at length takes place, will cause but a comparatively small additional demand on the coal-owners and coal-miners – a demand which will not, for a long period, suffice to cause enlargement of the coal-trade, by drawing capital and labour from other investments and occupations. And until the permanent extra demand for coal has become great enough to draw from other investments and occupations sufficient capital and labour to sink new mines, the increasing production of iron must be restricted by the scarcity of coal, and the multiplication of ship-yards and ship-builders must be checked by the want of iron. Thus, in a community which has reached a state of moving equilibrium, though any one industry directly affected by an additional demand may rapidly undergo a small extra growth, yet a growth beyond this, requiring as it does the building-up of subservient industries, less directly and strongly affected, as well as the partial unbuilding of other industries, can take place only with comparative slowness. And a still further growth, requiring structural modifications of industries still more distantly affected, must take place still more slowly.

On returning from this analogy, we see more clearly the truth that any considerable member of an animal organism, cannot be greatly enlarged without some general reorganization. Besides a building up of the primary, secondary, and tertiary groups of the subservient parts, there must be an unbuilding of sundry non-subservient parts; or, at any rate, there must be permanently established a lower nutrition of such non-subservient parts. For it must be remembered that in a mature animal, or one which has reached a balance between assimilation and expenditure, there cannot (supposing general conditions to remain constant) be an increase in the nutrition of some organs without a decrease in the nutrition of others; and an organic establishment of the increase implies an organic establishment of the decrease – implies more or less change in the processes and structures throughout the entire system. And here, indeed, is disclosed one reason why growing animals undergo adaptations so much more readily than adult ones. For while there is surplus nutrition, it is possible for specially-exercised parts to be specially enlarged without any positive deduction from other parts. There is required only that negative deduction implied in the diminished growth of other parts.

§ 70. Pursuing the argument further, we reach an explanation of the third general truth; namely that organisms, and species of organisms, which, under new conditions, have undergone adaptive modifications, soon return to something like their original structures when restored to their original conditions. Seeing, as we have done, how excess of action and excess of nutrition in any part of an organism, must affect action and nutrition in subservient parts, and these again in other parts, until the re-action has divided and subdivided itself throughout the organism, affecting in decreasing degrees the more and more numerous parts more and more remotely implicated; we see that the consequent changes in the parts remotely implicated, constituting the great mass of the organism, must be extremely slow. Hence, if the need for the adaptive modification ceases before the great mass of the organism has been much altered in its structure by these ramified but minute reactions, we shall have a condition in which the specially-modified part is not in equilibrium with the rest. All the remotely-affected organs, as yet but little changed, will, in the absence of the perturbing cause, resume very nearly their previous actions. The parts that depend on them will consequently by and by do the same. Until at length, by a reversal of the adaptive process, the organ at first affected will be brought back almost to its original state. Reconsidering the above-drawn analogy between an organism and a society, will enable us better to recognize this necessity. If, in the case supposed, the extra demand for iron ships, after causing the erection of some additional ship-yards and the drawing of iron from other manufactures, were to cease; the old dimensions of the ship-building trade would be quickly returned to: discharged workmen would seek fresh occupations, and the new yards would be devoted to other uses. But if the increased need for ships lasted long enough, and became great enough, to cause a flow of capital and labour from other industries into the iron-manufacture, a falling off in the demand for ships, would much less rapidly entail a dwindling of the ship-building industry. For iron being now produced in greater quantity, a diminished consumption of it for ships would cause a fall in its price, and a consequent fall in the cost of ships: thus enabling the ship-builders to meet the competition which we may suppose led to a decrease in the orders they received. And since, when new blast-furnaces and rolling-mills, &c., had been built with capital drawn from other industries, its transference back into other industries would involve great loss; the owners, rather than transfer it, would accept unusually low interest, and an excess of iron would continue to be produced; resulting in an undue cheapness of ships, and a maintenance of the ship-building industry at a size beyond the need. Eventually, however, if the number of ships required still diminished, the production of iron in excess would become very unremunerative: some of the blast-furnaces would be blown out; and as much of the capital and labour as remained available would be re-distributed among other occupations. Without repeating the steps of the argument, it will be clear that were the enlargement of the ship-building industry great enough, and did it last long enough to cause an increase in the number of coal-mines, the ship-building industry would be still better able to maintain itself under adverse circumstances; but that it would, though at a more distant period, end by sinking down to the needful dimensions. Thus our conclusions are: – First, that if the extra growth caused by extra activity in a particular industry has lasted long enough only to remodel the proximately-affected industries; it will dwindle away again after a moderate period, if the need for it disappears. Second, that a long period must be required before the re-actions produced by an enlarged industry can cause a re-construction of the whole society, and before the countless re-distributions of capital and labour can again reach a state of equilibrium. And third, that only when such a new state of equilibrium is eventually reached, can the adaptive modification become a permanent one. How, in animal organisms the like argument holds, need not be pointed out. The reader will readily follow the parallel.

That organic types should be comparatively stable, might be anticipated on the hypothesis of Evolution. The structure of any organism being a product of the almost infinite series of actions and reactions to which ancestral organisms have been exposed; any unusual actions and reactions brought to bear on an individual, can have but an infinitesimal effect in permanently changing the structure of the organism as a whole. The new set of forces, compounded with all the antecedent sets of forces, can but inappreciably modify that moving equilibrium of functions which all these antecedent sets of forces have established. Though there may result a considerable perturbation of certain functions – a considerable divergence from their ordinary rhythms – yet the general centre of equilibrium cannot be sensibly changed. On the removal of the perturbing cause the previous balance will be quickly restored: the effect of the new forces being almost obliterated by the enormous aggregate of forces which the previous balance expresses.

§ 71. As thus understood, the phenomena of adaptation fall into harmony with first principles. The inference that organic types are fixed, because the deviations from them which can be produced within assignable periods are relatively small, and because, when a force producing deviation ceases, there is a return to something like the original state; proves to be an invalid inference. Without assuming fixity of species, we find good reasons for anticipating that kind and degree of stability which is observed. We find grounds for concluding, a priori, that an adaptive change of structure will soon reach a point beyond which further adaptation will be slow; for concluding that when the modifying cause has been but a short time in action, the modification generated will be evanescent; for concluding that a modifying cause acting even for many generations, will do but little towards permanently altering the organic equilibrium of a race; and for concluding that on the cessations of such cause, its effects will become unapparent in the course of a few generations.

CHAPTER VI.
INDIVIDUALITY

§ 72. What is an individual? is a question which many readers will think it easy to answer. Yet it is a question that has led to much controversy among Zoologists and Botanists, and no quite satisfactory reply to it seems possible. As applied to a man, or to any one of the higher animals, which are all sharply-defined and independent, the word individual has a clear meaning: though even here, when we turn from average cases to exceptional cases – as a calf with two heads and two pairs of fore-limbs – we find ourselves in doubt whether to predicate one individuality or two. But when we extend our range of observation to the organic world at large, we find that difficulties allied to this exceptional one meets us everywhere under every variety of form.

Each uniaxial plant may perhaps fairly be regarded as a distinct individual; though there are botanists who do not make even this admission. What, however, are we to say of a multiaxial plant? It is, indeed, usual to speak of a tree with its many branches and shoots as singular; but strong reasons may be urged for considering it as plural. Every one of its axes has a more or less independent life, and when cut off and planted may grow into the likeness of its parent; or, by grafting and budding, parts of this tree may be developed upon another tree, and there manifest their specific peculiarities. Shall we regard all the growing axes thus resulting from slips and grafts and buds, as parts of one individual or as distinct individuals? If a strawberry-plant sends out runners carrying buds at their ends, which strike root and grow into independent plants that separate from the original one by decay of the runners, must we not say that they possess separate individualities; and yet if we do this, are we not at a loss to say when their separate individualities were established, unless we admit that each bud was from the beginning an individual? Commenting on such perplexities Schleiden says – "Much has been written and disputed concerning the conception of the individual, without, however, elucidating the subject, principally owing to the misconception that still exists as to the origin of the conception. Now the individual is no conception, but the mere subjective comprehension of an actual object, presented to us under some given specific conception, and on this latter it alone depends whether the object is or is not an individual. Under the specific conception of the solar system, ours is an individual: in relation to the specific conception of a planetary body, it is an aggregate of many individuals." … "I think, however, that looking at the indubitable facts already mentioned, and the relations treated of in the course of these considerations, it will appear most advantageous and most useful, in a scientific point of view, to consider the vegetable cell as the general type of the plant (simple plant of the first order). Under this conception, Protococcus and other plants consisting of only one cell, and the spore and pollen-granule, will appear as individuals. Such individuals may, however, again, with a partial renunciation of their individual independence, combine under definite laws into definite forms (somewhat as the individual animals do in the globe of the Volvox globator²⁵). These again appear empirically as individual beings, under a conception of a species (simple plants of the second order) derived from the form of the normal connexion of the elementary individuals. But we cannot stop here, since Nature herself combines these individuals, under a definite form, into larger associations, whence we draw the third conception of the plant, from a connexion, as it were, of the second power (compound plants – plants of the third order). The simple plant proceeding from the combination of the elementary individuals is then termed a bud (gemma), in the composition of plants of the third order."

The animal kingdom presents still greater difficulties. When, from sundry points on the body of a common polype, there bud out young polypes which, after acquiring mouths and tentacles and closing up the communications between their stomachs and the stomach of the parent, finally separate from the parent; we may with propriety regard them as distinct individuals. But when in the allied compound Hydrozoa, we find that these young polypes continue permanently connected with the parent; and when by this continuous budding-out there is presently produced a tree-like aggregation, having a common alimentary canal into which the digestive cavity of each polype opens; it is no longer so clear that these little sacs, furnished with mouths and tentacles, are severally to be regarded as distinct individuals. We cannot deny a certain individuality to the polypedom. And on discovering that some of the buds, instead of unfolding in the same manner as the rest, are transformed into capsules in which eggs are developed – on discovering that certain of the incipient polypes thus become wholly dependent on the aggregate for their nutrition, and discharge functions which have nothing to do with their own maintenance, we have still clearer proof that the individualities of the members are partially merged in the individuality of the group. Other organisms belonging to the same order, display still more decidedly this transition from simple individualities to a complex individuality. In the Diphyes there is a special modification of one or more members of the polypedom into a swimming apparatus which, by its rhythmical contractions, propels itself through the water, drawing the polypedom after it. And in the more differentiated Physalia various organs result from the metamorphosis of parts which are the homologues of individual polypes. In this last instance, the individuality of the aggregate is so predominant that the individualities of its members are practically lost. This combination of individualities in such way as to produce a composite individual, meets us in other forms among the ascidians. While in some of these, as in the Clavelina and in the Botryllidæ, the animals associated are but little subordinated to the community they form, in others they are so combined as to form a compound individual. The pelagic ascidian Doliolum is an example. "Here we find a large individual which swims by contractions of circular muscular bands, carries a train of smaller individuals attached to a long dorsal process of the test. These are arranged in three rows: those constituting the lateral row have wide mouths and no sexual organs or organs of locomotion – they subserve the nutrition of the colony, a truth which is illustrated by the fact that as soon as they are properly developed the large individual (the mother) loses her alimentary canal;" while from the median row are eventually derived the sexual zoids.

On the hypothesis of Evolution, perplexities of this nature are just such as we might anticipate. If Life in general commenced with minute and simple forms, like those out of which all organisms, however complex, now originate; and if the transitions from these primordial units to organisms made up of groups of such units, and to higher organisms made up of groups of such groups took place by degrees; it is clear that individualities of the first and simplest order would merge gradually in those of a larger and more complex order, and these again in others of an order having still greater bulk and organization. Hence it would be impossible to say where the lower individualities ceased and the higher individualities commenced.

§ 73. To meet these difficulties, it has been proposed that the whole product of a single fertilized germ shall be regarded as a single individual; whether such whole product be organized into one mass, or whether it be organized into many masses that are partially or completely separate. It is urged that whether the development of the fertilized germ be continuous or discontinuous (§ 50) is a matter of secondary importance; that the totality of living tissue to which the fertilized germ gives rise in any one case, is the equivalent of the totality to which it gives rise in any other case; and that we must recognize this equivalence, whether such totality of living tissue takes a concrete or a discrete arrangement. In pursuance of this view, a zoological individual is constituted either by any such single animal as a mammal or bird, which may properly claim the title of a zoon, or by any such group of animals as the numerous Medusæ that have been developed from the same egg, which are to be severally distinguished as zooids.

Admitting it to be very desirable that there should be words for expressing these relations and this equivalence, it may be objected that to apply the word individual to a number of separate living bodies, is inconvenient: conflicting so much, as it does, with the ordinary conception which this word suggests. It seems a questionable use of language to say that the countless masses of Anacharis Alsinastrum (now Eloidea canadensis) which, within these few years, have grown up in our rivers, canals, and ponds, are all parts of one individual: and yet as this plant does not seed in England, these countless masses, having arisen by discontinuous development, must be so regarded if we accept the above definition.

It may be contended, too, that while it does violence to our established way of thinking, this mode of interpreting the facts is not without its difficulties. Something seems to be gained by restricting the application of the title individual, to organisms which, being in all respects fully developed, possess the power of producing their kind after the ordinary sexual method, and denying this title to those incomplete organisms which have not this power. But the definition does not really establish this distinction for us. On the one hand, we have cases in which, as in the working bee, the whole of the germ-product is aggregated into a single organism; and yet, though an individual according to the definition, this organism has no power of reproducing its kind. On the other hand, we have cases like that of the perfect Aphis, where the organism is but an infinitesimal part of the germ product, and yet has that completeness required for sexual reproduction. Further, it might be urged with some show of reason, that if the conception of individuality involves the conception of completeness, then, an organism which possesses an independent power of reproducing itself, being more complete than an organism in which this power is dependent on the aid of another organism, is more individual.

§ 74. There is, indeed, as already implied, no definition of individuality that is unobjectionable. All we can do is to make the best practicable compromise.

As applied either to an animate or an inanimate object, the word individual ordinarily connotes union among the parts of the object and separateness from other objects. This fundamental element in the conception of individuality, we cannot with propriety ignore in the biological application of the word. That which we call an individual plant or animal must, therefore, be some concrete whole and not a discrete whole. If, however, we say that each concrete living whole is to be regarded as an individual, we are still met by the question – What constitutes a concrete living whole? A young organism arising by internal or external gemmation from a parent organism, passes gradually from a state in which it is an indistinguishable part of the parent organism to a state in which it is a separate organism of like structure with the parent. At what stage does it become an individual? And if its individuality be conceded only when it completely separates from the parent, must we deny individuality to all organisms thus produced which permanently retain their connexions with their parents? Or again, what must we say of the Hectocotylus, which is an arm of the Cuttle-fish that undergoes a special development and then, detaching itself, lives independently for a considerable period? And what must we say of the larval nemertine worm the pilidium of which with its nervous system is left to move about awhile after the developing worm has dropped out of it?

To answer such questions we must revert to the definition of life. The distinction between individual in its biological sense, and individual in its more general sense, must consist in the manifestation of Life, properly so called. Life we have seen to be, "the definite combination of heterogeneous change, both simultaneous and successive, in correspondence with external co-existences and sequences." Hence, a biological individual is any concrete whole having a structure which enables it, when placed in appropriate conditions, to continuously adjust its internal relations to external relations, so as to maintain the equilibrium of its functions. In pursuance of this conception, we must consider as individuals all those wholly or partially independent organized masses which arise by multicentral and multiaxial development that is either continuous or discontinuous (§ 50). We must accord the title to each separate aphis, each polype of a polypedom, each bud or shoot of a lowering plant, whether it detaches itself as a bulbil or remains attached as a branch.

By thus interpreting the facts we do not, indeed, avoid all anomalies. While, among flowering plants, the power of independent growth and development is usually possessed only by shoots or axes; yet, in some cases, as in that of the Begonia-leaf awhile since mentioned, the appendage of an axis, or even a small fragment of such appendage, is capable of initiating and carrying on the functions of life; and in other cases, as shown by M. Naudin in the Drosera intermedia, young plants are occasionally developed from the surfaces of leaves. Nor among forms like the compound Hydrozoa, does the definition enable us to decide where the line is to be drawn between the individuality of the group and the individualities of the members: merging into each other, as these do, in different degrees. But, as before said, such difficulties must necessarily present themselves if organic forms have arisen by insensible gradations. We must be content with a course which commits us to the smallest number of incongruities; and this course is, to consider as an individual any organized mass which is capable of independently carrying on that continuous adjustment of inner to outer relations which constitutes Life.