"8. Every gemmule may multiply itself by a process of scission into any number of equivalent gemmules."
Mr. Darwin has published a short notice in reply to Professor Delpino, in _Scientific Opinion_ of October 20, 1869, p. 426. In this reply he admits the justice of Professor Delpino"s attack, but objects to the alleged necessity of the first subordinate hypothesis, namely, that the emission of gemmules takes place in all states of the cell. But if this is not the case, then a great part of the utility and distinction of pangenesis is destroyed, or as Mr. Lewes justly says,[225] "If gemmules produce whole cells, we have the very power which was p.r.o.nounced mysterious in larger organisms."
{215} Mr. Darwin also does not see the force of the objection to the power of self-division which must be a.s.serted of the gemmules themselves if Pangenesis be true. The objection, however, appears to many to be formidable. To admit the power of spontaneous division and multiplication in such rudimentary structures, seems a complete contradiction. The gemmules, by the hypothesis of Pangenesis, are the ultimate organized components of the body, the absolute organic atoms of which each body is composed; how then _can_ they be divisible? Any part of a gemmule would be an impossible (because a _less_ than possible) quant.i.ty. If it is divisible into still smaller organic wholes, as a germ-cell is, it must be made up as the germ-cell is, of subordinate component atoms, which are then the _true_ gemmules. This process may be repeated _ad infinitum_, unless we get to true organic atoms, the true gemmules, whatever they may be, and they necessarily will be incapable of any process of spontaneous fission. It is remarkable that Mr. Darwin brings forward in support of gemmule fission, the observation that "Thuret has seen the zoospore of an alga divide itself, and both halves germinate." Yet on the hypothesis of Pangenesis, the zoospore of an alga must contain gemmules from all the cells of the parent algae, and from all the parts of all their less remote ancestors in all their stages of existence. What wonder then that such an excessively complex body should divide and multiply; and what parity is there between such a body and a gemmule? A steam-engine and a steel-filing might equally well be compared together.
Professor Delpino makes a further objection which, however, will only be of weight in the eyes of Vitalists. He says,[226] Pangenesis is not to be received because "it leads directly to the negation of a specific vital principle, co-ordinating and regulating all the movements, acts, and functions of the individuals in which it is incarnated. For Pangenesis of the individual is a term without meaning. If, in contemplating an {216} animal of high organization, we regard it purely as an aggregation of developed gemmules, although these gemmules have been evolved successively one after the other, and one within the other, notwithstanding they elude the conception of the _real and true individual_, these problematical and invisible gemmules must be regarded as so many individuals. Now, that real, true, living individuals exist in nature, is a truth which is persistently attested to us by our consciousness. But how, then, can we explain that a great quant.i.ty of dissimilar elements, like the atoms of matter, can unite to form those perfect unities which we call individuals, if we do not suppose the existence of a specific principle, proper to the individual but foreign to the component atoms, which aggregates these said atoms, groups them into molecules, and then moulds the molecules into cells, the cells into tissues, the tissues into organs, and the organs into apparatus?"
"But, it may be urged in opposition by the Pangenesists, your vital principle is an unknown and irresolute _x_. This is true; but, on the other hand, let us see whether Pangenesis produces a clearer formula, and one free from unknown elements. The existence of the gemmules is a first unknown element; the propagative affinity of the gemmules is a second; their germinative affinity is a third; their multiplication by fission is a fourth--and what an unknown element!"
"Thus, in Pangenesis, everything proceeds by force of unknown elements, and we may ask whether it is more logical to prefer a system which a.s.sumes a mult.i.tude of unknown elements to a system which a.s.sumes only a single one?"
Mr. Darwin appears, by "Natural Selection," to destroy the reality of species, and by Pangenesis that of the individual. Mr. Lewes observes[227]
of the individual that "This whole is only a subjective conception which summarizes the parts, and that in point of fact it is the parts which {217} are reproduced." But the parts are also, from the same point of view, merely subjective until we come to the absolute organic atoms. These atoms, on the other hand, are utterly invisible, intangible; indeed, in the words of Mr. Darwin, inconceivable. Thus, then, it results from the theories in question, that the organic world is reduced to utter unreality as regards all that can be perceived by the senses or distinctly imagined by the mind; while the only reality consists of the invisible, the insensible, the inconceivable; in other words, nothing is known that really is, and only the nonexistent can be known. A somewhat paradoxical outcome of the speculations of those who profess to rely exclusively on the testimony of sense. "_Les extremes se touchent_," and extreme sensationalism shakes hands with the "das seyn ist das nichts" of Hegel.
Altogether the hypothesis of Pangenesis seems to be little, if at all, superior to anterior hypotheses of a more or less similar nature.
Apart from the atoms of Democritus, and apart also from the speculations of mediaeval writers, the molecules of Bonnet and of Buffon almost antic.i.p.ated the hypothesis of Pangenesis. According to the last-named author,[228]
organic particles from every part of the body a.s.semble in the s.e.xual 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 parents. In 1849 Professor Owen, in his treatise on "Parthenogenesis," put forward another conception. 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 {218} other mutilations are repaired. Such unused products of the germ-cell are also supposed to become located 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 taking part in the production of some distinct and definite tissue--a condition somewhat similar to that conceived by Professor Owen.
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 a.s.sumption of an innate power and tendency in each physiological unit, Mr. Darwin"s, on the other hand, requires 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 it can hardly be so, for Mr. Darwin considers that his gemmule has the innate power and tendency to build up 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 is the other. The difference is but one of degree, not of kind. Moreover, the one mystery in the case of the "physiological unit" explains all, while with regard to the gemmule, as we have seen, it has to be supplemented by other powers and tendencies, each distinct, and each in itself inexplicable and profoundly mysterious. [Page 219]
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 growth and transformation of the most minute and the simplest organisms, which themselves, by all reason and a.n.a.logy, owe their existence to immediate transformation from the inorganic world.
Thus, then, 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 a.n.a.lysed, 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 a.s.sociated them closely together, and, therefore, the refutation of Pangenesis may render it advisable for those who have hitherto accepted "Natural Selection" to reconsider that theory. [Page 220]
CHAPTER XI.
SPECIFIC GENESIS.
Review of the statements and arguments of preceding chapters.--c.u.mulative 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 princ.i.p.al 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, vertebrate limbs, the laryngeal structures of the newborn kangaroo, the pedicellariae 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. [Page 221]
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 sh.e.l.l-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 the third chapter, 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-kingdoms. A curious resemblance, though less in degree, has also been seen to exist between the auditory organs of fishes and of Cephalopods. Remarkable similarities between certain placental and implacental mammals, between the bird"s-head processes of Polyzoa and the pedicellariae of Echinoderms, between Ichthyosauria and Cetacea, with very many other similar coincidences, have also been pointed out.
Evidence has also been brought forward to show that similarity is sometimes directly induced by very obscure conditions, at present quite {222} inexplicable, _e.g._ by causes immediately connected with geographical distribution; as in the loss of the tail in certain forms of Lepidoptera and in simultaneous modifications of colour in others, and in the direct modification of young English oysters, when transported to the sh.o.r.e of the Mediterranean.
Again, it has been a.s.serted that certain groups of organic forms seem to have an innate tendency to remarkable developments of some particular kind, as beauty and singularity of plumage in the group of birds of paradise.
It has also been contended that there is something to be said in favour of sudden, as opposed to exceedingly minute and gradual, modifications, even if the latter are not fortuitous. Cases were brought forward, in Chapter IV., such as the bivalve just mentioned, twenty-seven kinds of American trees simultaneously and similarly modified, also the independent production of pony breeds, and the case of the English greyhounds in Mexico, the offspring of which produced directly acclimated progeny.
Besides these, the case of the Normandy pigs, of _Datura tatula_, and also of the black-shouldered peac.o.c.k, have been spoken of. The teeth of the labyrinthodon, the hand of the potto, the whalebone of whales, the wings of birds, the climbing tendrils of some plants, &c. have also been adduced as instances of structures, the origin and production of which are probably due rather to considerable modifications than to minute increments.
It has also been shown that certain forms which were once supposed to be especially transitional and intermediate (as, _e.g._, the aye-aye) are really by no means so; while the general rule, that the progress of forms has been "from the more general to the more special," has been shown to present remarkable exceptions, as, _e.g._, Macrauchenia, the Glyptodon, and the sabre-toothed tiger (Machairodus).
Next, as to specific stability, it has been seen that there may be a {223} certain limit to normal variability, and that if changes take place they may be expected _a priori_ to be marked and considerable ones, from the facts of the inorganic world, and perhaps also of the lowest forms of the organic world. It has also been seen that with regard to minute spontaneous variations in races, there is a rapidly increasing difficulty in intensifying them, in any one direction, by ever such careful breeding.
Moreover, it has appeared that different species show a tendency to variability in special directions, and probably in different degrees, and that at any rate Mr. Darwin himself concedes the existence of an internal barrier to change when he credits the goose with "a singularly inflexible organization;" also, that he admits the presence of an _internal_ proclivity to change when he speaks of "a whole organization seeming to have become plastic, and tending to depart from the parental type."
We have seen also that a marked tendency to reversion does exist, inasmuch as it sometimes takes place in a striking manner, as exemplified in the white silk fowl in England, _in spite of_ careful selection in breeding.
Again, we have seen that a tendency exists in nature to eliminate hybrid races, by whatever means that elimination is effected, while no similar tendency bars the way to an indefinite blending of varieties. This has also been enforced by statements as to the prepotency of certain pollen of identical species, but of distinct races.
To all the preceding considerations have been added others derived from the relations of species to past time. It has been contended that we have as yet no evidence of minutely intermediate forms connecting uninterruptedly together undoubtedly distinct species. That while even "horse ancestry"
fails to supply such a desideratum, in very strongly marked and exceptional kinds (such as the Ichthyosauria, Chelonia, and Anoura), the absence of links is very important and significant. For if every species, without{224} exception, has arisen by minute modifications, it seems incredible that a small percentage of such transitional forms should not have been preserved.
This, of course, is especially the case as regards the marine Ichthyosauria and Plesiosauria, of which such numbers of remains have been discovered.
Sir William Thomson"s great authority has been seen to oppose itself to "Natural Selection," by limiting, on astronomical and physical grounds, the duration of life on this planet to about one hundred million years. This period, it has been contended, is not nearly enough on the one hand for the evolution of all organic forms by the exclusive action of mere minute, fortuitous variations; on the other hand, for the deposition of all the strata which must have been deposited, if minute fortuitous variation was the manner of successive specific manifestation.
Again, the geographical distribution of existing animals has been seen to present difficulties which, though not themselves insurmountable, yet have a certain weight when taken in conjunction with all the other objections.
The facts of h.o.m.ology, serial, bilateral and vertical, have also been pa.s.sed in review. Such facts, it has been contended, are not explicable without admitting the action of what may most conveniently be spoken of as an _internal_ power, the existence of which is supported by facts not only of comparative anatomy but of teratology and pathology also. "Natural Selection" also has been shown to be impotent to explain these phenomena, while the existence of such an internal power of h.o.m.ologous evolution diminishes the _a priori_ improbability of an a.n.a.logous law of specific origination.
All these various considerations have been supplemented by an endeavour to show the utter inadequacy of Mr. Darwin"s theory with regard to the higher psychical phenomena of man (especially the evolution of moral conceptions), and with regard to the evolution of individual organisms by the action{225} of Pangenesis. And it was implied that if Mr. Darwin"s latter hypothesis can be shown to be untenable, an antecedent doubt is thus thrown upon his other conception, namely, the theory of "Natural Selection."
A c.u.mulative argument thus arises against the prevalent action of "Natural Selection," which, to the mind of the Author, is conclusive. As before observed, he was not originally disposed to reject Mr. Darwin"s fascinating theory. Reiterate endeavours to solve its difficulties have, however, had the effect of convincing him that that theory as the one or as the leading explanation of the successive evolution and manifestation of specific forms, is untenable. At the same time he admits fully that "Natural Selection" acts and must act, and that it plays in the organic world a certain though a secondary and subordinate part.
The one _modus operandi_ yet suggested having been found insufficient, the question arises, Can another be subst.i.tuted in its place? If not, can anything that is positive, and if anything, what, be said as to the question of specific origination?
Now, in the first place, it is of course axiomatic that the laws which conditioned the evolution of extinct and of existing species are of as much efficacy at this moment as at any preceding period, that they _tend_ to the manifestation of new forms as much now as ever before. It by no means necessarily follows, however, that this tendency is actually being carried into effect, and that new species of the higher animals and plants are actually now produced. They may be so or they may not, according as existing circ.u.mstances favour, or conflict with, the action of those laws.
It is possible that lowly organized creatures may be continually evolved at the present day, the requisite conditions being more or less easily supplied. There is, however, no similar evidence at present as to higher forms; while, as we have seen in Chapter VII., there are _a priori_ considerations which militate against their being similarly evolved. {226}
The presence of wild varieties and the difficulty which often exists in the determination of species are sometimes adduced as arguments that high forms are now in process of evolution. These facts, however, do not necessarily prove more than that some species possess a greater variability than others, and (what is indeed unquestionable) that species have often been unduly multiplied by geologists and botanists. It may be, for example, that Wagner was right, and that all the American monkeys of the genus cebus may be reduced to a single species or to two.
With regard to the lower organisms, and supposing views recently advanced to become fully established, there is no reason to think that the forms said to be evolved were new species, but rather reappearances of definite kinds which had appeared before and will appear again under the same conditions. In the same way, with higher forms similar conditions must educe similar results, but here practically similar conditions can rarely obtain because of the large part which "descent" and "inheritance" always play in such highly organized forms.
Still it is conceivable that different combinations at different times may have occasionally the same outcome just as the multiplications of different numbers may have severally the same result.
There are reasons, however, for thinking it possible that the human race is a witness of an exceptionally unchanging and stable condition of things, if the calculations of Mr. Croll are valid as to how far variations in the eccentricity in the earth"s...o...b..t together with the precession of the equinoxes have produced changes in climate. Mr. Wallace has pointed out[229] that the last 60,000 years having been exceptionally unchanging as regards these conditions, specific evolution may have been {227} exceptionally rare. It becomes then possible to suppose that for a similar period stimuli to change in the manifestation of animal forms may have been exceptionally few and feeble,--that is, if the conditions of the earth"s...o...b..t have been as exceptional as stated. However, even if new species are actually now being evolved as actively as ever, or if they have been so quite recently, no conflict thence necessarily arises with the view here advocated. For it by no means follows that if some examples of new species have recently been suddenly produced from individuals of antecedent species, we ought to be able to put our fingers on such cases; as Mr.
Murphy well observes[230] in a pa.s.sage before quoted, "If a species were to come suddenly into being in the wild state, as the Ancon sheep did under domestication, how could we ascertain the fact? If the first of a newly-born species were found, the fact of its discovery would tell nothing about its origin. Naturalists would register it as a very rare species, having been only once met with, but they would have no means of knowing whether it were the first or the last of its race."
But are there any grounds for thinking that in the genesis of species an _internal_ force or tendency interferes, co-operates with and controls the action of external conditions?
It is here contended that there are such grounds, and that though inheritance, reversion, atavism, Natural Selection, &c., play a part not unimportant, yet that such an internal power is a great, perhaps the main, determining agent.