Remember my preference

  
About the Book

Table of Contents

Part I

Part II

Part III

Part IV



     

Part IV:  The Fitness of Living Things: Dauermodifications

Chapter 1

How Is Fitness Acquired?

     THOSE WHO live nearest to nature never cease to wonder at the fitness of living things. Until man intrudes, nature seems replete with evidences of wise design. Every creature is equipped with all the structures, all the skills, and all the instincts necessary for its own continuance as part of the web of life. Man alone appears to be an alien and a disturber.
     The concept of nature as "red in tooth and claw," which Tennyson introduced in his poem In Memoriam some ten years before Darwin published his Origin of Species, is increasingly being viewed today as a travesty of the natural order. Probably the only reason it has survived so long is that those who contributed most to reinforce it by their writings, including Darwin himself, derived too much of their knowledge of animal behaviour by observing them in captivity. In the wild there is inevitably some shedding of blood, but we now know that cruelty per se is almost entirely absent. Death is avoided by all living things, and they do not seem to live in fear of death, except where man intrudes.
     Structurally animals are extraordinarily sensitively fitted for the kind of lives they live. To the Christian this is evidence of wise design, but to the unbeliever it seems to demand some other explanation. In many cases where the element of fitness is truly extraordinary, it becomes extremely difficult to see how it could come about purely by chance.
     One of the earlier students of nature who sought to account for this fitness without any direct appeal to supernatural intervention was Jean Baptiste Lamarck (1744 - 1829). In his Philosophie zoologique, published in 1809, he reasoned that any animal could adjust itself structurally to improve its fit with the environment and
pass on the
 advantageous adjustment to its descendants. By a process akin to compound interest, each

     pg.1 of  7     

generation improved upon the fitness of the previous one and thus all living creatures constantly enhanced their chances of survival not by a process of elimination of the unfit, but by improving their own fitness. This natural ability was resident within the constitution of all living things. It was not a conscious goal-seeking which might be confused with some form of teleology, but simply part of the stuff of living. The important thing was that every gain was inherited. "Lamarckianism" came to be defined simply as "the inheritance of acquired characteristics," and the acquired characteristics were modifications of structure resulting to the benefit of the organism from the direct influence of the environment.
     In Darwin's time, Lamarckianism was very widely accepted by those who by disposition sought an explanation of fitness without appeal to supernatural agency. Curiously, Darwin did not himself feel happy about it. He sought for and found what he considered a better explanation in the multiple concepts of Natural Selection, the Struggle to Survive, and the Survival of the Fittest. In Darwin's view, Lamarckianism was unrealistic, mystical, and not adequately borne out by the facts. He saw the elimination of the unfit as a much more likely and verifiable principle of improvement of a species. He did not reject the inheritance of acquired characteristics, but he questioned whether characteristics were ever acquired by the mechanism Lamarck envisioned.
     In the course of time, however, Darwin himself gradually shifted his position in this respect, and it is interesting to observe the change in his thinking as reflected in his own written observations. In 1861 he wrote: (1)

     My greatest trouble is not being able to weigh the direct effects of the long continued action of changed conditions of life without any selection, against the action of selection on mere accidental (so to speak) variability. I oscillate much on this head, but generally return to my belief that the direct action of the conditions of life has not been great. At least this direct action can have played an extremely small part in producing all the numberless and beautiful adaptations in every living creature.

But one year later, on 24 November 1862, Darwin wrote to Sir Joseph D. Hooker: (2)

     I hardly know why I am a little sorry, but my present work is leading me to believe rather more in the direct action of physical conditions. I presume I regret it because it lessens the glory of Natural Selection and is so confoundedly doubtful.

1. Charles Darwin: Life and Letters, edited by Francis Darwin, Murray, London, 1888, vol. II, p.369, in a letter to T. Davidson dated 30 April.
2. Ibid., p.390.

     pg.2 of  7     

     Darwin reflected upon the matter and became convinced enough that ten years later, when he published the sixth edition of his Origin of Species he observed: (3)

     Species have been modified . . . chiefly through natural selection of numerous, successive, slight, favourable variations, aided in an important manner by the inherited effects of use and disuse of parts; and in an unimportant manner . . . by the direct action of external conditions. . . .  It appears that I underrated the frequency of these latter forms of variation as leading to permanent modificaions of structure independently of natural selection.

     In the first edition of his Origin of Species (1859, chap.6, p.256), Darwin had said that natural selection is "in some cases" aided by the use and disuse of parts and "slightly affected" by the direct influence of the environment. In the sixth edition (1872, p.167) the words "in some cases" had become "in many cases," and "slightly affected" had become simply "affected." Four years later, in 1876, Darwin wrote in a letter to Moritz Wagner: (4)

     In my opinion the greatest error which I have committed has been not allowing sufficient weight to the direct action of the environment, i.e., food, climate, etc., independently of natural selection. . . .  When I wrote the Origin and for some years afterwards I could find little good evidence of the direct action of the environment; now there is a large body of evidence.

     Finally, in 1877, in a letter to Melchior Neumayer dated 9 March, he wrote concerning an example of direct influence of the environment reported by his correspondent.  "It is by far the best case which I have ever met with showing the direct influence of life on the organism." (5)
     But his common-sense logic and the evidence he accumulated in support of natural selection were persuasive enough that they prepared the way for the final overthrow of Lamarckianism an overthrow completed by the experiments of Auguste Weismann (1843-1914).
     It had long been recognized that modification of a parent body by artificial means had no effect upon the offspring. Circumcision, for example, had been practiced for thousands of years without leading to a race of congenitally circumcised male children. The operation still had to be performed in every generation.  Still

3. Darwin, Charles, The Origin of Species by means of Natural Selection, Murray, London, 6th edition, 1872, chap.15, p.42l.
4. Charles Darwin: Life and Letters, edited by Francis Darwin, Murray, London, 1888, vol. III, p.159.
5. Ibid., vol. II, p.232.
 

     pg.3 of  7     


there was a possibility that the modification was not effectively passed on because only the father of the next generation was involved, and not the mother. If some comparable gross modification of the mother had been repeated over the same period of time, the results might have been different. However, it had been customary in China for many centuries to bind the feet of female infants in the upper classes of society. Small feet were considered beautiful. Yet here again there was no evidence that the modification was becoming inheritable. Clearly, modifying the male or the female in such ways, even after centuries of repetition, did not affect the germinal stream in any way, since no influence upon subsequent generations had ever been observed.
     In an attempt to determine whether inheritance of such modifications or acquired characters would occur if both sexes were modified in the same way, Weismann cut off the tails of experimental mice of both sexes, male and female, for many generations: he still found that such a modification did not become inheritable. Thus Julian Huxley remarked upon the apparent immunity of living organisms against all experimental attempts to modify their characteristic form in a way that would be self-perpetuating, underscoring the fact that there seems to be no direct effect of the environment upon the germ plasm. In 1938 Huxley observed, (6)

     Can the hereditary constituents be permanently changed by environment? It is clear that theoretically it should be possible to induce such changes. The hereditary constitution is seen to be something material which only our lack of knowledge prevents us from defining chemically; and as such it must be possible for us to alter it. The remarkable fact, however, is its stubbornness in resistance in alteration.
     Sixty-nine generations of flies bred in the dark a nd yet no alteration in their eyes or their instincts with regard to light. Ninety generations in an attempt to cause their resistance to heat by acclimatization and selection without result. . . .
    In spite of all the work that has been done, we have only established that to a great many apparent outward influences the germ plasm is quite unresponsive.

     Admittedly this was written four decades ago, but subsequent research has only reinforced the conclusion. Insofar as the germ plasm and nuclear genes are concerned, the results are still negative. No experimental modification of the body cells seems capable of bringing about inheritable changes in the nuclear genes of the organism. As some wag is reported to have said when referring to the negative results of Weismann's
 
6. Huxley, Sir Julian, "Inheritance of Acquired Characteristics" in Essays in Popular Science, Penguin, Harmondsworth, England. 1938, pp.36-37. 

     pg.4 of  7     


experiments, and with apologies to Shakespeare's Hamlet: "There is a divinity that shapes our ends, rough-hew them how we will."
     Now it is possible by deliberately damaging the nuclear genes to bring about inheritable modifications. But this kind of interruption of the normal development of an organism must be a comparatively rare event in nature, (7) and when it does occur it is even less likely that the effect will be beneficial. Indeed, there are many geneticists who believe that all gene mutations which result from this kind of interference with the normal development of the organism are harmful. Individuals carrying such harmful genes would tend to be eliminated in the natural course of events, simply because they are less fit.
     The amazing fitness of organisms within their own particular habitat demands an explanation. And the explanation must also account for the fact that living things seem to have a large capacity for adjustment to environmental pressures and seem to be able to pass on the benefit of these adjustments by inheritance to succeeding generations. Since experimentally it has not seemed possible to mimic nature in this respect by effecting changes on nuclear genes we must suppose either that there is some built-in mechanism of adjustment that is inheritable by some other means than nuclear genes, or that God has been at work creatively making these adjustments throughout the past.
     Certainly the fitness of things is everywhere manifest in nature and all the more manifest as the circumstances are more carefully examined. Since the environment tends to be in a state of flux, fitness must involve a similar flexibility. The ideal mechanism would be one which can capture and hold any successful adjustment made in one generation so that the next generation can build upon it. Wood Jones was one of those who argued strongly for this view, but despite his eloquence, current orthodoxy having rejected Lamarck did not allow him a hearing: he was arguing in favour of some form of inheritance of acquired characters. (8) He was arguing, in fact, in favour of the view that environmental pressures did have a direct effect on the development of living forms over successive generations and not merely an indirect effect through a process of natural selection by elimination of the less fit.

7. The very persistence of many forms over supposedly millions of years without significant change is evidence of this. The stability of many organisms over enormous periods of time is astonishing.
8. Jones, F. Wood, Trends of Life, Arnold, London, 1953, especially chap.12, p.128, "The Inheritance of Adaptations."
 

     pg.5 of  7     


   The negative evidence against the inheritance of acquired characters under experimental conditions in the laboratory is not always borne out by what goes on in nature. The contradiction may have been unresolved in the past, because current theory has demanded that nuclear genes provide the only pathway for inheritable factors and these genes are remarkably immune to the direct influence of environmental pressures, except those which are essentially damaging.
     But in the past few years a renewed interest in the possibility of another pathway whereby the environment might have a direct influence upon an organism responding in an inheritable way has led to the conclusion that there are probably carriers of inheritable material in the cytoplasm of the cell and not merely in the nucleus. These carriers, which have been termed Plasmagenes, are responsive to the direct action of the environment. This responsiveness appears to be somewhat delayed, so that the environmental pressure must be held constant over several generations to influence the plasmagenes. That the response of these extra-nuclear genes can be inherited through succeeding generations is demonstrated by the fact that the effect persists even when the original stimulus is removed. If the environment gradually reverts to its original nature, the modified organisms will continue to retain their altered form for several generations, and then they too revert.
     Thus the response of the organism to direct environmental pressure is demonstrated. Yet it is seen to be of such a nature that it retains its flexibility and is therefore able to adjust in either direction to its own advantage and pass on the adjustment to successive generations. In this way the mechanism contributes to the fitness of the organism without endangering it if the environmental pressure changes. This type of modification which continues for a limited time even when the stimulus which provoked it is removed has been termed a dauermodification.
     Such a mechanism serves the dual purpose of preserving the line in its purity and maintaining the species as such, while at the same time opening the way for a form of adjustment that allows a particular species to spread successfully into different habitats which it could not otherwise occupy. The nuclear genes therefore preserve the species as such: the plasmagenes preserve the local population as a variety.
     The difference between the conventional Darwinian view of natural selection and the view which is now beginning to crystallize, based on plasmagenic inheritance of acquired modifications, is this:  the former

     pg.6 of  7     


depended upon a process of selective elimination of the unfit, whereas the latter favours survival by inherited adaptation. Progress, identified as increasingly successful adaptation, no longer becomes a ruthless weeding out, but a demonstration of a sensitive mechanism specifically designed to guarantee exactly the opposite result, namely, an improvement in the chances of survival of every individual. It is in some sense a reflection of the benevolence of the Creator rather than of a pitiless eradication in the interests of efficiency at all costs.
     The older view of nature as ruthlessly efficient is therefore replaced by a more generous view, which holds that any disadvantaged species need not be eliminated but is provided with the means of contributing to the greater fitness of its descendants. This is achieved by passing on to these future generations the benefits of its own response to the environment even though these were not overtly expressed in its members at the time.
     It is as though the Lord has so designed the mechanism of inheritance in order that the "kinds" of Genesis will not be destroyed or blurred, while yet allowing modification which greatly increases the range of climate, altitude, food resources, and so forth, that the particular species can occupy. There are numerous illustrations of this type of response among plants and animals; and there are some striking illustrations of it for man himself. 

     pg.7 of  7     

 Copyright © 1988 Evelyn White. All rights reserved

Previous Chapter                                                                      Next Chapter



Home | Biography | The Books | Search | Order Books | Contact Us