Journal of Genetics 48: 164-175 (1947)
THE PROBLEM OF NON-HEREDITARY ADAPTIVE MODIFICATIONS
(COINCIDENT OR ORGANIC SELECTION)
By V. S. KIRPICHNIKOV
Institute of Cytology, Histology and Embryology and Institute of Zoology,
Academy of Science, U.S.S.R., Moscow-Leningrad
Recent years witnessed the rise of renewed interest in the question of the interrelation of non-hereditary adaptive modifications and natural selection. Among the large number of papers published on this subject, those printed in Russian occupy a significant place. The problems discussed by the Russian scientists are of considerable importance in clarifying the theory of evolution. A review of these papers may be of general interest. In this connexion it may be in place to give a brief outline of the development of the problems concerned.
I. THE HYPOTHESIS OF COINCIDENT AND ORGANIC SELECTION
|*Cit. after Baldwin (1902)|
Towards the end of the last century Lloyd Morgan (1896), Osborn (1896, 1897). and Baldwin (1896,* 1902) simultaneously and independently of one another proposed a new hypothesis of the selection of coincident variations or, as Osborn and Baldwin termed it, of organic selection. This hypothesis was supported by Poulton, Wallace, Gulick, and can be summarized as follows:
Individual plasticity is the property of all organisms. According to Morgan and Baldwin plasticity is acquired in the struggle for life as the result of natural selection. According to Osborn it is an inherent quality of living matter, the property of protoplasm. Osborn found it impossible to explain in any other way the experimentally established ability for adaptation to conditions of life not only unusual for the existing forms, but for their ancestors as well.
The plasticity of organisms is expressed in the form of change in habits and of morphological, adaptive alterations. Habit alters the structure of the organism including such basic organs as the skeleton, the circulatory system, etc.
If individual adaptive modifications happen to be present, those among the numerous divers congenital variations will be favoured that are coincident with a given useful modification. Such variations will gradually accumulate. If the conditions that called forth the given plastic modification are continued for a considerable period, the accumulation of coincident variations will progress slowly, but inevitably.
According to Lloyd Morgan and Baldwin this accumulation is the result of the extinction of all variations going in other directions and the preservation of all coincident variations. Since they enhance non-hereditary change and supplement its shortcomings. From Osborn's point of view the accumulation of hereditary variations similar to modifications has nothing to do with selection, but takes place automatically since all other variations are eliminated.
The plastic (phenotypical) adaptations will be substituted by hereditary ones. Non-hereditary alterations of habit and structure acquire phylogenetic significance. As an illustration Lloyd Morgan refers to alterations that take place in bone structure. Certain individuals reveal an increased growth of bone structure as the result of increased function and of the influence of contiguous parts in an altered environment and with the acquisition of new habits. This may be qualified as a plastic modification. After such an alteration congenital variations leading also to an intensified bone development will no longer be eliminated. Moreover they will also be accumulated due to their usefulness since they enhance the plastic modification. The accumulating hereditary variations will finally effect a similar strengthening of the bone structure which had been hitherto the result of habitual use, that is, had been due to the plasticity of the organism.
|CybeRose note: This is the pseudo-Lamarckian position. In fact, Lamarck wrote, "whatever the environment may do, it does not work any direct modification whatever in the shape and organisation of animals."|
Baldwin points to the fact that organic selection not only stabilizes modifications but further expands plasticity in the same direction (see also Gulick, 1905). According to Baldwin organic selection attains first rate importance in evolution because of the existence of broad and complex accommodations of a general nature. Detto (1904) likewise refers to such modifications, indicating that selection creates comparatively non-specific reaction systems which account for the existence of a 'modification reserve' (see also Lukin, 1942). Thus Osborn's 'self-adaptation' in an unusual environment can be easily explained without resorting to the inherent plasticity of the protoplasm.
Gulick (1905) likewise supports the hypothesis of the selection of coincident variations and calls it 'coincident selection'. He particularly stresses the significance of the isolating influence of modifications which hamper free cross-breeding. Lately, this particular role of modifications has been discussed in works on ecological isolation among birds (Promptov, 1934a,b, 1936; Hogben, 1940), on biological races of insects (Thorpe, 1940), races of fish Kirpichnikov, 1933; L. S. Berg, 1934) and many others. Muller (1942) has analysed the question in detail and illustrated his arguments with examples of temperature modifications in Drosophila.
Huxley (1942) cites numerous cases in which there is a non-hereditary barrier for cross-breeding at the first stage of divergent evolution.
The hypothesis of coincident selection proposed by the early American authors was gradually forgotten in the years that followed. Baur (1922) and other well-known apologists talk of individual plasticity only as the result of natural selection. Turesson 1922) concludes that non-hereditary differences are substituted at the very earliest stages of the formation of new races and ecotypes by similar hereditary changes. Thellung (1930) refers to a corresponding replacement, and explains it by the fact that hereditary variations are more specialized and require less energy for the development of the character. All these remarks are of a casual nature and are not in any way connected with the views of Lloyd Morgan and his contemporaries. Only in 1935 did this problem once more become the object of discussion, particularly in Russian works. In his latest very interesting book Huxley (1942) lays much stress on the principle of Baldwin and Lloyd Morgan's organic selection.
II. 'INDIRECT SELECTION' AND THE FIXATION OF MODIFICATIONS
ACCORDING TO KIRPICHNIKOV
In a paper on the problem of race-formation in fishes (Kirpichnikov, 1933) and especially in succeeeding papers (1935, 1940) an attempt is made to give a general analysis of the origin and the significance of non-hereditary adaptive modifications in the formation of species and in evolution (the hypothesis of 'indirect selection').
|*Further on in the text this capacity will be termed 'adaptability'.|
Not only are constant morphological changes often present and play an important role, being particularly essential to immobile plants (see also Schmalhausen, 1941), but small regulatory, functional and morphogenetic ones also. In higher forms of animals, habits (conditional reflexes) become particularly significant (see, for instance, Krushinsky, 1944. 1946).
'Growth' modifications in fishes serve as an excellent illustration of how completely one modification can effect an organism. Fluctuations in water temperature as well as in the quantity of food in the water lead to serious changes in the rate of growth and differentiation. This leads to changes in the size of the fish at maturity and in the final stages of growth. Changes in the interrelations between the rate of growth and differentiation also influence the process of maturation itself, the quantity of sexual products, the form and. proportions of the body. Finally, the number of 'quantitative' characters is changed (Hubbs, 1926. 1940; Kirpichnikov, 1933, 1940, 1943, 1945; Gabriel, 1944, etc.). Such an all-round reaction favours adaptivity to new conditions and opens the road for future adaptation to changing environment.
The existing parallelism of hereditary (systematic) and non-hereditary variability in nature points to the significance of the latter in speciation. There are many cases when closely related species and subspecies of plants and animals differ inherently from one another by characters that are easily altered by external conditions.
The stabilization of non-hereditary variations in speciation is the result of selection. and not due to the direct inheritance of acquired characters. The relation between the organism and its environment, which is unbalanced when the latter is altered, becomes readjusted through selection. Thus 'the curves of adaptivity' are moved in the direction of the changing environment. These curves express the alterations in viability of the individual observed when there are fluctuations in certain ecological factors in nature.
Selection in this case is most intensive when it concerns the less plastic but the most vital structures of the organism. Organs or