Heterogenesis

“ If influences capable of directly or indirectly producing changes operate on any particular stage of development, these changes are always transmitted to the same stage. Upon this metamorphosis depends. In a precisely similar manner changes which operated periodically on certain generations (1, 3, 5, for instance) are transmitted to these generations only, and not to the intermediate ones. Upon this depends heterogenesis. ”

“ In seeking answers to these questions, we inquired whether there are common to both Homogenesis and Heterogenesis, any conditions under which alone sperm-cells and germ-cells arise and are united for the production of new organisms; and we reached the conclusion that, in all cases, they arise only when there is an approach to equilibrium between the forces which produce growth and the forces which oppose growth. ”

“ Besides insuring a structural fitness between each kind of organism and its circumstances, the working of "natural selection" also insures a fitness between the mode and rate of multiplication of each kind of organism and its circumstances. We may, therefore, without any teleological implication, consider the fitness of homogenesis and heterogenesis to the needs of the different classes of organisms which exhibit them. ”

“ In Heterogenesis, on the other hand, we have the birth of dissimilar products, the beginning of a new branch from a "life-tree," in which the offspring have no tendency to assume the parental type. This occurs, for instance, where the protoplasmic matter of an animal or of a vegetal cell becomes modified and resolved into Bacteria. ”

“ Manifestly the favourable and unfavourable conditions recurring in combinations that are rarely twice alike, cannot be met by any regularly recurring form of heterogenesis; and it is interesting to see how survival of the fittest has established a mixed form. ”

“ Heterogenesis may thus be defined either in accordance with my proposal or in the manner hitherto adopted, since it may be regarded as more morphological than the cyclical succession of differently formed sexual generations; or, with Claus, as the succession of different sexual generations, “living under different conditions of existence”—a definition which applies in all cases to seasonal dimorphism. Varying conditions of existence, in their widest sense, are the result of the action of different climates ”

“ Since these generations have been exposed to the alternating influence of the summer and winter temperature a periodical dimorphism has been developed—a regular cycle of dissimilar generations. It has already been asserted that the consecutive generations of a species comport themselves with respect to heredity in a manner precisely similar to that of the ontogenetic stages, and at the same time such succeeding generations point out the parallelism between metamorphosis and heterogenesis. ”

“ We have just been led to the comprehension of heterogenesis by cyclical heredity, by the fact that a cycle is produced whenever a series of generations exists under regularly alternating influences.87 In this cycle newly acquired changes, however minute in character at first, are only transmitted to a later, and not to the succeeding generation, appearing only in the one corresponding, i.e. ”

“ Every differentiation of structure being a result of some difference in the relations of the parts to the agencies acting on them, it follows that the more multiplied and more unlike the agencies, the more varied must be the differentiations wrought. Hence the change from a state of homogeneity to a state of heterogeneity, will be marked in proportion as the environing actions to which the organism is supposes it is only are complex. ”

“ The connexion which we noted between heterogeneity of structure and heterogeneity of function—a connexion made so familiar by experience as to appear scarcely worth specifying—is clearly a necessary one. It follows from the general truth that in proportion to the heterogeneity of any aggregate, is the heterogeneity it will produce in any incident force (First Principles, § 156) . The energy continually liberated in the organism by decomposition, is here the incident force; the functions are the variously modified forms produced in its divisions by the organs they pass through ”

“ This formation of molecules more and more heterogeneous during terrestrial evolution, has been accompanied by increasing heterogeneity in the aggregate of compounds of each kind, as well as an increasing number of kinds; and this increasing heterogeneity is exemplified in an extreme degree in the compounds, non-nitrogenous and nitrogenous, out of which organisms are built. So that the classes, orders, genera, and species of chemical substances, gradually increasing as the Earth has assumed its present form, increased in a transcendent degree during that stage which preceded the origin of life. ”

“ Grant that each organism is at the outset relatively homogeneous and that when complete it is relatively heterogeneous, and it necessarily follows that development is a change from the homogeneous to the heterogeneous—a change during which there must be gone through all the gradations of heterogeneity that lie between these extremes. ”

“ In evolution heterogeneity is a constant measure of progress, hence the laws stating the variety of effects producible from given elements have a direct interest and value. These are the laws of combination and permutation. Combinations, mathematically, are groups where the presence and not the position of an element counts for difference—thus B C A and B A C are the same combination but different permutations. As additions are made to the elements, combinations increase in geometrical progression with 2 as constant factor. ”

“ I name these facts to illustrate the truth that any kind of arrangement stands in the way of rearrangement; and that this must be true of organization, which is one kind of arrangement. When, during the evolution of a living body, its component substance, at first relatively homogeneous, has been transformed into a combination of heterogeneous parts, there results an obstacle, always great and often insuperable, to any considerable change of structure; the more elaborate and definite the structure the greater is the resistance it opposes to alteration. ”

“ Incipient modifications are developed and defined in different ways by different circumstances, and the parts of a living being are brought into closer reciprocal relations, and thus welded into a coherent organic whole. This is what Mr Spencer means when he says that evolution implies a transition from "an indefinite incoherent homogeneity to a definite coherent heterogeneity": [108] the whole process being interconnected in such a way that these different aspects of it—definiteness, coherence, heterogeneity—increase together and imply one another. ”

“ Each of these modifications is a change of the molecule into equilibrium with its environment—an adaptation, as it were, to new surrounding conditions to which it is subjected; as through Evolution in general. Larger or more integrated aggregates are successively generated; as through Evolution in general. More complex or heterogeneous aggregates are so made to arise, one out of another; as through Evolution in general. A geometrically increasing multitude of these larger and more complex aggregates so produced, at the same time results; as through Evolution in general. ”

“ With advancing integration there went that advancing heterogeneity implied by inclusion of the several classes of inorganic phenomena and the several classes of super-organic phenomena in the same category with organic phenomena. And then the indefinite idea of progress passed into the definite idea of evolution, when there was recognised the essential nature of the change, as a physically determined transformation conforming to ultimate laws of force. ”

“ XIV, that an essential characteristic of Evolution is the integration of parts, which accompanies their differentiation—an integration shown both in the consolidation of each part, and in the union of all the parts into a whole. Hence, animate bodies having greater co-ordination of parts than inanimate ones must exhibit greater co-ordination of changes; and this greater co-ordination of their changes must not only distinguish organic from inorganic aggregates, but must, for the same reason, distinguish higher organisms from lower ones, as we found that it did. ”

“ But while the entire assemblage of societies thus fulfils the law of evolution by increase of heterogeneity,--while within each of them contrasts of structure, caused by differences of environments and entailed occupations, cause unlikenesses implying further heterogeneity, we may infer that the primary process of evolution--integration--which, up to the present time, has been displayed in the formation of larger and larger nations, will eventually reach a still higher stage, and bring yet greater benefits. ”

“ That tendency towards greater heterogeneity which is given to an organism by disturbing its environment, is helped by the tendency which every modification has to produce other modifications—modifications which must become more numerous in proportion as the organism becomes more complex. Lastly, among the indirect and involved manifestations of this tendency, we must not omit the innumerable small irregularities of structure which result from the crossing of dissimilarly-modified individuals. ”

“ The ultimate structural state accompanying that ultimate functional state towards which an organism tends, both individually and as a species, may be deduced from one of the propositions set down in the opening section of this chapter. We saw that the limit of heterogeneity is arrived at whenever the equilibration of any aggregate becomes complete—that the re-distribution of matter can continue so long only as there continues any motion unbalanced. ”

“ If, from late stages in the Earth's history, we run back, and find the lines of chemical evolution continually converging, until they bring us to bodies which we cannot decompose, may we not suspect that, could we run back these lines still further, we should come to still decreasing heterogeneity in the number and nature of the substances, until we reached something like homogeneity? ”

“ And it cannot become perfectly definite until its units are aggregated into a compact whole. That is to say, the acquirement of definiteness is simply a concomitant of complete union of the elements constituting each component division. Thus, Evolution is characterized not only by a continuous multiplication of parts, but also by a growing oneness in each part. And while an advance in heterogeneity results from progressive differentiation, an advance in definiteness results from progressive integration. ”

“ Besides that orderly heterogeneity which distinguishes organisms, there is the disorderly or chaotic heterogeneity, into which a loose mass of inorganic matter lapses; and at present no reason has been given why the homogeneous germ of a plant or animal should not lapse into the disorderly instead of the orderly heterogeneity. ”

“ In reality, however, it is quite conceivable that the idea of a descent may prove correct, and possibly the idea of an evolution of the species will have to be replaced by that of a heterogenetic generation, or by the theory that certain groups in the organic system are originated [29] by heterogenetic generation, and others by evolution; and so the evolution theory must share with the theory of heterogenetic generation, or of a metamorphosis of germs. ”

“ In the series of organisms we should thus find a succession of states like those which constitute the history of the individual, with this difference, that in the individual we can make out the link which connects the primitive homogeneity with the final heterogeneity, while in the series of organisms all we can do is to connect, with a considerable degree of probability, the hypothetical starting-point with the positive goal. ”

“ Unless we deny the persistence of force, we must admit that the lapse of an organism's structure from an indefinitely homogeneous to a definitely heterogeneous state, must be cumulative in successive generations, if the forces causing it continue to act. And for the like reasons, the increasing assemblage of individuals arising from a common stock, is also liable to lose its original uniformity; and, in successive generations, to grow more pronounced in its multiformity. ”

“ If there is a mode of integration which necessarily subjects the united individuals to unlike sets of incident forces, and does this with complete uniformity from generation to generation, it is to be inferred that the united individuals will become unlike. They will severally assume such different functions as their different positions enable them respectively to carry on with the greatest advantage to the assemblage. This heterogeneity of function arising among them, will be followed by heterogeneity of structure ”