Изображения страниц

the sexual secretions, and by their union build up the embryo, each particle taking its due place, and occupying in the offspring a similar position to that which it occupied in the parent. In 1849 Professor Owen, in his treatise on "Parthenogenesis," put forward another idea. According to this, the cells resulting from the subdivision of the germ-cell preserve their developmental force, unless employed in building up definite organic structures. In certain creatures, and in certain parts of other creatures, germ-cells unused are stored up, and by their agency lost limbs and other mutilations are repaired. Similar unused products of the germ-cell are also supposed to become situate in the generative products.

According to Mr. Herbert Spencer, in his "Principles of Biology," each living organism consists of certain so-called "physiological units." Each of these units has an innate power and capacity, by which it tends to build up and reproduce the entire organism of which it forms a part, unless in the meantime its force is exhausted by its contributing to the production of some distinct and definite tissue-a condition somewhat similar to that conceived by Professor Owen.1

Now, at first sight, Mr. Darwin's atomic theory appears. to be more simple than any of the others. It has been objected, that while Mr. Spencer's theory requires the assumption of an innate power and tendency in each physiological unit, Mr. Darwin's, on the other hand, re

1 Mr. Spencer, however, holds that so long as the process of growth and multiplication by gemmation goes on actively, so that the aggregates and their units, in a continual state of change, are not held in such constant relation as to bring about an equilibrium between the form of the one and the polarities of the other, the process of growth and multiplication may go on without limit.

quires nothing of the kind, but explains the evolution of each individual by purely mechanical conceptions. In fact, however, it is not so. Each gemmule, according to Mr. Darwin, is really the seat of powers, elective affinities, and special tendencies as marked and mysterious as those possessed by the physiological unit of Mr. Spencer, with the single exception that the former has no tendency to build up the whole living, complex organism of which it forms a part. Some may think this an important distinction, but such can hardly be the case, for Mr. Darwin considers that his gemmule has the innate power and tendency to increase and transform itself into the whole living, complex cell of which it forms a part; and the one tendency is, in principle, fully as difficult to understand, fully as mysterious, as the other. The difference is but one of degree, not of kind. Moreover, the one conception in the case of the "physiological unit" explains all, while with regard to the gemmule, as we have seen, its power of growth has to be supplemented by other powers and tendencies, each distinct, and each in itself inexplicable and profoundly mysterious.


That there should be physiological units possessed of the power attributed to them, harmonizes with what has recently been put forward by Dr. H. Charlton Bastian; who maintains that under fit conditions the simplest organisms develop themselves into relatively large and complex ones. This is not supposed by him to be due to any inheritance of ancestral gemmules, but to direct

1 As this sheet of the second edition is passing through the press, a work has appeared written by Dr. H. Charlton Bastian, and entitl "The Modes of Origin of Lowest Organisms." London and New York: Macmillan and Co.

growth and transformation of the most minute and the simplest organisms, which themselves, by all reason and analogy, owe their existence to immediate transformation from the inorganic world.

On the whole, then, we seem justified in asserting that there are grave difficulties in the way of the reception of the hypothesis of Pangenesis, which moreover, if established, would leave the evolution of individual organisms, when thoroughly analysed, little if at all less mysterious or really explicable than it is at present.

As was said at the beginning of this chapter, “Pangenesis" and "Natural Selection" are quite separable and distinct hypotheses. The fall of one of these by no means necessarily includes that of the other. Nevertheless, Mr. Darwin has associated them closely together, and, therefore, the refutation of Pangenesis may render it advisable for those who have hitherto accepted "Natural Selection" to reconsider their acceptance of that theory.



Review of the statements and arguments of the preceding chapters.— Cumulative argument against predominant action of "Natural Selection." — Whether anything positive as well as negative can be enunciated.—Constancy of laws of nature does not necessarily imply constancy of specific evolution.-Possible exceptional stability of existing epoch.-Probability that an internal cause of change exists.-Innate powers must be conceived as existing somewhere or other. -Symbolism of molecular action under vibrating impulses.—Professor Owen's statement.-Statement of the author's view.-It avoids the difficulties which oppose "Natural Selection."-It harmonizes apparently conflicting conceptions.-Summary and conclusion.

HAVING now severally reviewed the principal biological facts which bear upon specific manifestation, it remains to sum up the results, and to endeavour to ascertain what, if anything, can be said positively, as well as negatively, on this deeply interesting question.

In the preceding chapters it has been contended, in the first place, that no mere survival of the fittest accidental and minute variations can account for the incipient stages of useful structures, such as, e.g., the heads of flat-fishes, the baleen of whales, limbs of vertebrates, the laryngeal structures of the new-born kangaroo, the pedicellaria of Echinoderms, or for many of the facts of mimicry, and especially

those last touches of mimetic perfection, where an insect not only mimics a leaf, but one worm-eaten and attacked by fungi.

Also, that structures like the hood of the cobra and the rattle of the rattlesnake seem to require another explanation.

Again, it has been contended that instances of colour, as in some apes; of beauty, as in some shell-fish; and of utility, as in many orchids, are examples of conditions which are quite beyond the power of Natural Selection to originate and develop.

Next, the peculiar mode of origin of the eye (by the simultaneous and concurrent modification of distinct parts), with the wonderful refinement of the human ear and voice, have been insisted on; as also, that the importance of all these facts is intensified through the necessity (admitted by Mr. Darwin) that many individuals should be similarly and simultaneously modified in order that slightly favourable variations may hold their own in the struggle for life, against the overwhelming force and influence of mere number.

Again, we have considered, in Chapter III., the great improbability that from minute variations in all directions, alone and unaided, (save by the survival of the fittest), closely similar structures should independently arise; though, on a non-Darwinian evolutionary hypothesis, their development might be expected a priori. We have seen, however, that there are many instances of wonderfully close similarity which are not due to genetic affinity; the most notable instance, perhaps, being that brought forward by Mr. Murphy, namely, the appearance of the same eye-structure in the vertebrate and molluscous sub

« ПредыдущаяПродолжить »