THE QUARTERLY JOURNAL OF SCIENCE. JULY, 1868. I. DARWIN AND PANGENESIS. It is nearly ten years since the most important work on biological science which has ever been published, namely, the Origin of Species,' issued from the press; and during the long interval, interrupted, we regret to say, by bodily illness, the well-known author of that work has been accumulating further evidence in favour of his theory, which he now gives to the world. So far, his detailed information relates almost entirely to animals and plants under domestication;* and although the work in which it is contained forms a continuation of the argument in favour of the derivative origin of species, it does not conclude the consideration of the subject; and we are promised, first, a work upon the variability of organic beings in a state of nature; secondly, one upon the difficulties opposed to the theory of natural selection; and, finally, one in which it is apparently intended by the author to give a résumé of the whole subject, and wherein he will “try the principle of natural selection, by seeing how far it will give a fair explanation of the several classes of facts alluded to."t We confess that these announcements have taken us a little by surprise; for seeing that the esteemed author of these works, extant and promised, is already about sixty years of age, and that ten years have elapsed between the appearance of his introductory treatise and the one now before us, which is by no means the most important of the series, he must have sufficient faith in his own. theory of the "survival of the fittest" to anticipate the extension of his brilliant career to at least the age of ninety. All we can say is, that we hope his expectations may be realized, and that the accumulation of knowledge and thought in the meantime may enable The Variation of Animals and Plants under Domestication.' By Charles Darwin, M.A., F.R.S., &c. In two vols., with illustrations. Murray, 1868. + Ibid., vol. i., p. 9. VOL. V. Y P him to bequeath to mankind a biological theory which shall bear the test of future ages, and firmly secure the pedestal of fame upon which the reputation of its author is already elevated. It may be within the memory of some of our readers, that about six years after the appearance of the 'Origin of Species '-when, therefore, sufficient time had elapsed to enable all classes of thinkers to express their views upon the Darwinian theory-we ventured to review the state of scientific opinion upon the subject, and to add such original thoughts as that review had suggested to us; * and as we find in the work before us many attempts to explain difficulties which at that time appeared to us to militate against the unqualified acceptance of the Darwinian doctrine, we may be pardoned for once more touching upon them, with a view to consider whether those obstacles have been removed in the present work, or whether they still impart to the hypothesis an imperfection which needs to be supplied before it can be converted into a well-acknowledged biological guide for all ages. It appeared to us at that time, as it has to many others, that the author claimed for what he terms "natural selection," powers to modify old species as well as render permanent the character of new ones, thus implying intelligence and every other attribute requisite for that purpose; and we sought to show that the author himself had not formed a clear conception of what "natural selection" is able to accomplish. We quoted one of his remarks, that "it" (natural selection)" can modify the egg, seed, or young, as easily as the adult;" but endeavoured to show, by collateral quotations, that the author rather considered the "conditions of life" as the causes which induce variability, and that then "natural selection" accumulates those variations when they are profitable for the animal. Now, as by "natural selection" the author meant the part played by nature (the conditions of existence by which the living form is surrounded) analogous to man's operations in selecting and training animals under domestication; so, just as we might say of any change in the nature of an animal, "fattening" or "crossing" has effected it, instead of "the breeder has effected it by fattening or crossing;" we must not be too nice in our distinction of terms, and we must regard "Nature," the "conditions of existence," "natural selection," as in so far one and the same great power favouring the continued existence of certain types, and even in some degree modifying those types, just as the breeder modifies his domesticated animals. But even granting to the author the utmost licence in the use of terms, we could not then, and cannot now, help being drawn insensibly to the conclusion that the departure from any existing type results in the * "Darwin and his Teachings: "Quarterly Journal of Science,' April, 1866. + Origin of Species,' 3rd edition (1861), p. 144, par. 2. main from a change in the reproductive organs of the animal; and it appears to us that whilst in his earlier work the author laid too little stress upon this obscure phase of his subject, it has haunted him throughout the present work; and though he still attributes to the external conditions of existence the chief influence in modifying species (or even varieties), we find his expressions much more clear concerning the agency which immediately operates to bring about this modification, for he says:-" The causes which induce variability act on the mature organism, on the embryo, and, as we have good reason to believe, on both sexual elements before impregnation has been effected.” * Now this is what may be called a much clearer declaration of principle than we have hitherto had from the author; and, leaving out of sight the question of the amount of variability which can by any means be brought about, we find that virtually, according to his views, the nature of the living form is decided at its very conception. For, whether the most widely diverging characters have been secured, as in the author's favourite illustration, the pigeon, or some "spontaneous" variation has sprung up, or some peculiarity has been lost sight of for one or more generations and has suddenly reappeared, in every case, and especially in the latter, the reproductive elements, or one of them, must, according to the author's views, have been the acting or perpetuating agency. In order to account for this marvellous property of the germ, the author has supplied us with a provisional hypothesis, "pangenesis," and has sought to explain how the sexual elements operate upon the fabric of which they serve as the basis. But there still remains a wide subject untouched; and that is, whether and in what degree the reproductive organs are affected by certain psychical causes, with which neither "conditions of existence" nor yet" natural selection" have any immediate relation. This phase of the question must, however, be left for a moment unconsidered; and having referred to the crucial difficulty upon which we stumble when we regard the mode in which variation begins, we must next touch upon that other perplexing problem, hybridism, which is considered by the author's opponents to denote its limits, and to stand as an insuperable obstacle in the way of the acceptance of his theory. In our former notice of the author's works referred to above, we ventured to express the view that the phenomenon of hybridism should be regarded in the light of an occasional check placed by Providence upon the too rapid tendency to vary, which might arise even under the author's slow process, and might cause a reversion to the original stock, or a confusion of forms, totally subversive of all order in animated * Animals and Plants under Domestication,' vol. ii., p. 270. nature; and although such a view may be seized upon by the opponents of the theory as an admission that there is a limit to variation, and that therefore no new species can thus have been brought into existence (a corollary which by no means results from our proposition), yet we find that in the work before us the author quite concurs with our views, excepting that he seeks to explain how hybridism is affected by nature, whilst we contented ourselves with suggesting that Providence does bring about such results, without as yet seeing clearly by what means they are effected. He first compares the phenomena relating to this subject in domesticated animals with those in a state of nature:-" On the principle which makes it necessary for man, whilst he is selecting and improving his domestic varieties, to keep them separate, it would clearly be advantageous to varieties in a state of nature, that is, to incipient species, if they could be kept from blending, either through sexual aversion or by becoming mutually sterile. Hence it at one time appeared to me probable, as it has to others, that this sterility might have been acquired through natural selection. On this point we must suppose that a shade of lessened fertility first spontaneously appeared, like any other modification, in certain individuals of a species when crossed with other individuals of the same species, and that successive degrees of infertility, from being advantageous, were slowly accumulated."* The words italicized by us show that the author had thus only removed the difficulty a little farther from view than before, but he has now come to the conclusion that "species have not been rendered mutually infertile through the accumulative action of natural selection;' "that they have not been endowed through an act of creation with this quality;" but that "it has arisen incidentally during their slow formation in connection with other and unknown changes in their organization."† The word (again underlined by us) would lead one to think that the difficulty remains to the author pretty much where it was; but the context shows that he attributes the changes in the reproductive system leading to hybridism to a correlative variation in the whole living form, that is, that when the whole fabric changes, that portion of it which perpetuates the animal changes also, and the ultimate agency is again "pangenesis;" but then again he says, " Pangenesis does not throw much light on hybridism."‡ There is another view taken by the author, of the occurrence and effect of hybridism in nature, which deserves mention. He finds that when wild animals are at first domesticated, the sudden change in the surrounding conditions of their life renders them for a time infertile: "numerous facts," he says, "have been given, *Animals and Plants under Domestication,' vol. ii., p. 185. Ibid., p. 385. showing that when animals are first subjected to captivity, even in their native land, and although allowed much liberty, their reproductive functions are often greatly impaired or quite annulled;" but, on the other hand, crosses between varieties slightly modified render the offspring rather more fertile than otherwise. Now he believes that what occurs under domestication by a leap, is slowly proceeding in nature; for natura non facit saltum, and that infertility has been gradually proceeding from changed conditions of existence, extending over long ages, but resulting at length in as marked a difference as when the conditions have been suddenly changed from freedom to captivity. But here, again, whilst the author's results appear to be correctly stated, the parallel by which he seeks to explain the cause is unfortunate and inapplicable; for in the case of domestication a male and female of the same variety (or one of them) are suddenly rendered quite infertile, their "fertility becomes at once quite annulled;" whereas in nature the individuals of the same species remain quite fertile, inter se, whilst it is only when they come to be crossed with other species that the union is barren. But there is still another aspect of the question, in which a simple statement of facts alone gives to the theory of modification a large amount of weight. In seeking to show that the barrier of hybridism is not so formidable as his antagonists would make it appear, the author says: "The sterility of distinct species when first united, and that of their hybrid offspring, graduates by an almost infinite number of steps, from zero, when the ovule is never impregnated and a seed capsule is never formed, up to complete fertility. We can only escape the conclusion that some species are fully fertile when crossed, by determining to designate as varieties all the forms which are quite fertile. This high degree of fertility is, however, rare. Nevertheless, plants which have been exposed to unnatural conditions sometimes become modified in so peculiar a manner that they are much more fertile when crossed by a distinct species than when fertilized by their own pollen. Success in effecting a first union between species and the fertility of their hybrids depends in an eminent degree on the conditions of life being favourable. The innate sterility of hybrids of the same parentage and raised from the same seed-capsule often differs much in degree."† In our notice of the author's former work we charged him with making light of the difficulties of hybridism. The fact is, he was already in possession of a mass of information which justified his giving less weight to that phase of the question than we were disposed to do, for, in common with many other critics, we had been * Animals and Plants under Domestication,' vol. ii., p. 176 + Ibid., p. 179. |