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Parallel Paths: A Study in Biology, Ethics, and Art. T. W. Rolleston
Читать онлайн.Название Parallel Paths: A Study in Biology, Ethics, and Art
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isbn 4064066202972
Автор произведения T. W. Rolleston
Жанр Документальная литература
Издательство Bookwire
“Vital phenomena are essentially bound up with the living protoplasm. No other substance exhibits a similar series of remarkable and varied phenomena, such as we may compare with the attributes of life. As both physics and chemistry have been restricted to the investigation of lifeless bodies, any attempt to explain vital phenomena solely by chemical and physical laws could only be induced by a false conception of their real significance, and must lead to fruitless results. The physical attributes of air, water, and of the glasses and metals made use of in physical apparatus, can never explain qualities like nutrition, respiration, growth, irritability and reproduction.”
And Wilson concludes his work by the admission that
“the study of the cell has on the whole seemed to widen rather than to narrow the enormous gap that separates even the lowest forms of life from the inorganic world.”47
“The lowest observed forms of life” would have been a more exact way of stating the fact.
Many questions of detail will occur to the reader at this point, which he will find answered in the pages of Weismann or other investigators. Here we must confine ourselves to what has a distinct bearing on the objects of this study. One of the points which may be briefly touched on is the question how it comes that two germ cells, once having passed through their maturation divisions, cannot fuse and form a new being; nor can two sperm cells. Were this possible we might have ‘self-fertilization,’ and virginal conception or parthenogenesis, whenever two germ cells in the ovary of a female animal or in that of a plant happened to come into contact. But since the object of fusion is the union of (more or less) unlike, and not closely related, elements, we find that even when a kind of self-fertilization occurs, as in some plants, the sperm or pollen cells are differentiated visibly, and probably still more invisibly, from the germ cells. But, apart from this, the object of preventing the union of reproductive cells of the same sex is mechanically attained by a very curious device. The cell-organ by which division is carried out is the centrosome. But in the course of the two maturation divisions of the germ cell, that cell loses its centrosome, which seems to be absorbed into the protoplasmic substance of the cell when once its task is accomplished. No fusion of any number of such cells can therefore lead to any further change or growth, for growth is based on cell division, and the centrosome is the organ of division. The sperm cell, on the other hand, does not lose its centrosome; it retains it to form the organ of division for the new cell after conjugation. But, reduced as it is to little more than a bare nucleus without any envelope of nutritive matter, the sperm cell cannot support the intense vital activity called for in the initial stages of the life of a new being, and therefore sperm cells, like the germ cells, though for a different reason, would be incapable of mutual conjugation, even if the element of mutual attraction existed among them.
Another point of interest is the question of the determination of sex. The known facts afford a strong corroboration of the general theory of reproduction outlined above. It has not been ascertained, nor is it, perhaps, ascertainable, whether the sperm cells of the male contain in their chromatin a preponderance of male, while the germ cells provide chiefly the female determinants.48 However this may be, it is certain that determinants which severally control the formation both of male and of female structure are always present in every combination of the sperm and germ cells, those which exhibit the greatest energy and vitality probably prevailing in the determination of the sex of the future being. This accounts at once not only for the cases (rare in the higher animals) of actual hermaphroditism, when the sex is really indistinguishable, but for the universal occurrence in all male animals of rudimentary female organs (such as mammæ) and in all females of rudimentary male organs. Both sets of determinants are always present; the more powerful prevail, but the weaker have a deflecting influence on the total result. When the primary sexual characters of the embryo are determined, they appear to communicate a stimulus which starts into activity the appropriate secondary characters, such as colouring and other modifications not directly sexual. An extraordinary case, which I take from Beddard’s Animal Coloration,49 is that of a chaffinch which was found to have on the left side of its body the plumage of a hen bird and on its right that of a cock. On dissection the meaning of this freak of physiology was revealed. The bird was an hermaphrodite, having the female organs of generation on the left side of its body and the male on the right. Hermaphroditism is not in itself a very uncommon phenomenon in birds (though here it is a monstrosity, not, as in slugs and snails, a natural and useful condition); but the way in which in this instance it governed the distribution of colour is most peculiar; and of course it strongly reinforces Weismann’s conception of distinct determinants for the various details of bodily structure.50
This brings us to the recognition of a competition among determinants which is an important, indeed a cardinal, feature in Weismann’s theory of evolution. He makes, as I am forced to believe, an illegitimate and extravagant use of it, but the principle may really exist and be operative without furnishing the master-word to the riddle of organized being. The master-word, as I shall try to show, is nature’s will to live. But before going fully into this argument, let us fix in our minds the rationale of those processes of elementary organic life which have been described in this chapter. Protoplasmic life may be supposed to have originated, and perhaps to be still originating, in certain molecular combinations of matter. In other words, the combination, when it took place, developed certain peculiar forces through which it was enabled to maintain itself and to grow, by the processes called assimilation and nutrition. These forces, then, were potentially present in nature before the molecules combined to evoke them. They are among the latent powers of life. They waited, ready to be called into action when the required external form should be arrived at in the play of molecular energy. Life first originated, no doubt, in unconnected and inconceivably small units of protoplasm. Between the units thus formed and their combination into the elaborate structure which we now know a cell to be—packed as full of varied energies, it has been said, as an ironclad is of machinery—there is evidently a very wide gap. All we know is that when we have got the cell, we find it in possession of a complex apparatus for subdivision, which, taken together with the faculties of nutrition and growth, enable any one cell to multiply indefinitely by producing replicas of itself. To life and growth, then, has been added the faculty for multiplication. Here we strike on a veritable mystery. Why should any new movement ever take place? Why should a cell ever divide in two? We can only say that it is its property to do so.51 It does so because it is alive. Did this property first arise as one of a multitude of aimless movements—the only one which ensured permanence and multiplicity to the organisms which exhibited it? If so, then Nature, at the time when life began on the earth, behaved in a manner most unlike that in which she behaves at present. If we are to interpret the processes hidden in the remote past by the light of what we see at present, we shall conclude that, at bottom, the will to live made molecular action—and the same force incorporated itself in the combinations which originated protoplasmic life, ordered the structure of the cell, and gave it the need and the power to multiply. Nature is for ever changing, for ever straining after new life, after more life.
Having arrived at the cell with its powers of division, the next step was the power of conjugation between cells with their interchange of vital substance, bringing about, in Weismann’s words, “a wealth and diversity of organic architecture which without it would have been unattainable.” It takes place by means of physical energies, but the process is entirely inexplicable unless we assume that it exists to satisfy a need, a Drang, for life. And this need, although of course it displays itself in physical processes, is not in itself a physical process. At the very beginnings of structural life, if not before it, we are obliged to pass beyond physics in order to comprehend physical phenomena. Whenever we find an aggregate of living units, such as a Pandorina colony, living with a communal life which is other than the sum-total of the lives of the individual units, we are in presence at once of the necessity for a metaphysical conception, to render intelligible the unity in diversity which we perceive.
The response of living protoplasm to the