Darwiniana; essays and reviews pertaining to Darwinism

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the okigin of species by means of natural

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(AmEEICAN JOtTKNAL OF SCIENCB AND AkTS, MaVCTl, 1S60.)

This book is already exciting mnch attention. Two American editions are announced, through which it will become familiar to many of our readers, before these pages are issued. An abstract of the argument — for " the whole volume is one long argument," as the author states — is unnecessary in such a case ; and it would be difficult to give by detached extracts. For the volume itself is an abstract, a prodromus of a detailed work upon which the author has been laboring for twenty years, and which " will take two or three more years to complete." It is exceedingly compact ; and although useful summaries are appended to the several chapters, and a general recapitulation con-

^ " On the Origin of Species by Means of Natural Selection, or the Preservation of Favored Races in the Struggle for Life," by Charles Darwin, M. A., Fellow of the Royal, Geological, Linnsean, etc., Societies, Author of " Journal of Researches during H. M. S. Beagle's Voyage round the World." London : John Murray. 1859. 502 pp., post 8vo.

D. H. HILL LIBRARY North Carolina State Collega

10 LARWINIANA.

tains the essence of the whole, yet much of the aroma escapes in the treble distillation, or is so concentrated that the flavor is lost to the general or even to the scientific reader. The volume itself — ^the proof -spirit — ^is just condensed enough for. its purpose. It will be far more widely read, and perhaps will make deeper impression, than the elaborate work might have done, with all its full details of the facts upon which the author's sweeping conclusions have been grounded. At least it is a more readable book : but all the. facts that can be mustered in favor of the theory are still likely to be needed.

Who, upon a single perusal, shall pass judgment upon a work like this, to which twenty of the best years of the life of a most able naturalist have been devoted ? And who among those naturalists who hold a position that entitles them to pronounce summarily upon the subject, can be expected to divest himself for the nonce of the influence of received and favorite systems ? In fact, the controversy now opened is not likely to be settled in an off-hand way, nor is it desirable that it should be. A spirited conflict among opinions of every grade must ensue, which — to borrow an illustration from the doctrine of the book before us — may be likened to the conflict in ISTature among races in the struggle for life, which Mr. Darwin describes ; through which the views most favored by facts will be developed and tested by " Natural Selection," the weaker ones be destroyed in the process, and the strongest in the long-run alone survive.

The duty of reviewing this volume in the American Journal of Science would naturally devolve upon

TEE ORIGIN OF SPECIES. H

the principal editor, whose wide observation and profound knowledge of various departments of natural history, as well as of geology, particularly qualify him for the task. But he has been obliged to lay aside his pen, and to seek in distant lands the entire repose from scientific labor so essential to the restoration of his health— a consummation devoutly to be wished, and confidently to be expected. Interested as Mr. Dana would be in this volume, he could not be expected to accept its doctrine. Yiews so idealistic as those upon which his " Thoughts upon Species " ^ are grounded, will not harmonize readily with a doctrine so thoroughly naturalistic as that of Mr. Darwin. Though it is just possible that one who regards the kinds of elementary matter, such as oxygen and hydrogen, and the definite compounds of these elementary matters, and their compounds again, in the mineral kingdom, as constituting species, in the same sense, fundamentally, as that of animal and vegetable species, might admit an evolution of one species from another in the latter as well as the former case.

Between the doctrines of this volume and those of the other great naturalist whose name adorns the title-page of this journal [Mr. Agassiz], the widest divergence appears. It is interesting to contrast the two, and, indeed, is necessary to our purpose ; for this contrast brings out most prominently, and sets in strongest light and shade, the main features of the theory of the origination of species by means of l^atural Selection.

The ordinary and generally-received view assumes the independent, specific creation of each kind of plant

* Article in this Journal, vol. xxiv., p. 305.

and animal in a primitive stock, wliicli reproduces its like from generation to generation, and so continues the species/ Taking the idea of species from tins perennial succession of essentially similar individuals, tke chain is logically traceable back to a local origin in a single stock, a single pair, or a single individual, from wliicb all the individuals composing the species have proceeded by natural generation. Although the similarity of progeny to parent is fundamental in the conception of species, yet the likeness is by no means absolute ; all species vary more or less, and some vary remarkably — partly from the influence of altered circumstances, and j)artly (and more really) from unknown constitutional causes which altered conditions favor rather than originate. But these variations are supposed to be mere oscillations from a normal state, and in ^N^ature to be limited if not transitory ; so that the primordial differences between species and species at their beginning have not been effaced, nor largely obscured, by blending through variation. Consequently, whenever two reputed species are found to blend in l^ature through a series of intermediate forms, community of origin is inferred, and all the formes, however diverse, are held to belong to one species. Moreover, since bisexuality is the rule in Nature (which is practically carried out, in the long-run, far more generally than has been suspected), and the heritable qualities of two distinct individuals are mingled in the offspring, it is supposed that the general

sterility of hybrid progeny interposes an effectual barrier against tlie blending of the original species by crossing.

From this generally-accepted view the well-known theory of Agassiz and the recent one of Darwin diverge in exactly opposite directions.

That of Agassiz differs fundamentally from the ordinary view only in this, that it discards the idea of a common descent as the real bond of union among the individuals of a species, and also the idea of a local origin — supposing, instead, that each species originated simultaneously, generally speaking, over the whole geographical area it now occupies or has occupied, and in perhaps as many individuals as it numbered at any subsequent period.

Mr. Darwin, on the other hand, holds the orthodox view of the descent of all the individuals of a species not only from a local birthplace, but from a single ancestor or pair ; and that each species has extended and established itself, through natural agencies, wherever it could ; so that the actual geographical distribution of any species is by no means a primordial arrangement, but a natural result. He goes farther, and this volume is a protracted argmnent intended to prove that the species we recognize have not been independently created, as such, but have descended, like varieties, from other species. Yarieties, on this view, are incipient or possible species : species are varieties of a larger growth and a wider and earlier divergence from the parent stock ; the difference is one of degree, not of kind.

The ordinary view — rendering unto Caesar the

14 BARWINIANA.

things that are Cgesar's — looks to natural agencies for the actual distribution and perpetuation of species, to a supei-natural for their origin.

The theory of Agassiz regards the origin of species and their present general distribution over the world as equally primordial, equally supernatural; that of Darwin, as equally derivative, equally natural.

The theory of Agassiz, referring as it does the phenomena both of origin and distribution directly to the .Divine will — thus removing the latter with the former out of the domain of inductive science (m which efficient cause is not the first, but the last word) —may be said to be theistic to excess. The contrasted theory is not open to this objection. Studying the facts and phenomena in reference to proximate causes, and endeavoring to trace back the series of cause and effect as far as possible, Darwin's aim and processes are strictly scientific, and his endeaV^r, whether successful or futile, must be regarded as a legitimate attempt to extend the domain of natural or physical science. For, though it well may be that "organic forms have no physical or secondary cause," yet this can be proved only indirectly, by the failure of every attempt to refer the phenomena in question to causal laws. But, however originated-, and whatever -bo thought of Mr. Darwin's arduous undertaking in this respect, it is certain that plants and animals are subject from theij^ birth to physicaf influences, to which they have to accommodate themselves as they can. How "ritefallyTFey''are'^born to'Trouble," and how incessant and severe the struggle for life generally is, the present volume graphically describes. Few will deny that sucli influences must liave gravely affected the range and the association of individuals and species on the earth's sui'face. Mr. Darwin thinks that, acting upon an inherent predisposition to vary, they have sufficed even to modify the species themselves and produce the present diversity. Mr. Agassiz believes that they have not even affected the geographical range and the actual association of species, still less their forms ; but that every adaptation of species to climate, and of species to species, is as aboriginal, and therefore as inexplicable, as are the organic forms themselves.

Who shall decide between such extreme views so ably maintained on either hand, and say how much of truth there may be in each ? The present reviewer has not the presumption to undertake such a task. Having no prepossession in favor of naturalistic theories, but, struck with the eminent ability of Mr. Darwin's work, and charmed with its fairness, our humbler duty will be performed if, laying aside prejudice as much as we can, we shall succeed in giving a fair account of its method and argument, offering by the way a few suggestions, such as might occur to any naturalist of an inquiring piind. An editorial character for this article must in justice be disclaimed. The plural pronoun is employed not to give editorial weight, but to avoid even the appearance of egotism, and also the circumlocution which attends a rigorous adherence to the impersonal style.

We have contrasted these tw^o extremely divergent theories, in their broad statements. It must not be inferred that they have no points nor ultimate results in common.

In tlie first place, tliey practically agree in upsetting, each in its own way, the generally-received definition of species, and in sweeping away the ground of their objective existence in ^Nature. The orthodox conception of species is that of lineal descent : all the descendants of a common parent, and no other, constitute a species ; they have a certain identity because of their descent, by which they are supposed to be recognizable. So naturalists had a distinct idea of what they meant by the term species, and a practical rule, which was hardly the less useful because difficult to apply in many cases, and because its application was indirect : that is, the community of origin had to be inferred from the likeness ; such degree of similarity, and such only, being held to be conspecific as could be shown or reasonably inferred to be compatible with a common origin. And the usual concurrence of the whole body of naturalists (having the same data before them) as to what forms are species attests the value of the rule, and also indicates some real foundation for it in Nature. But if species were created in numberless individuals over broad spaces of territory, these individuals are connected only in idea, and species differ from varieties on the one hand, and from genera, tribes, etc., on the other, only in degree ; and no obvious natural reason remains for fixing upon this or that degree as specific, at least no natural standard, by which the opinions of different naturalists may be correlated. Species upon this view are enduring, but subjective and ideal. Any three or more of the human races, for example, are species or not species, according to the bent of the naturalist's mind. Darwin's theory brings us the otlier way to the same result. In his view, not only all the individuals of a species are descendants of a common parent, but of all the related species also. Affinity, relationship, all the terms which naturalists use figuratively to express an underived, unexplained resemblance among species, have a literal meaning upon Darwin's system, which they little suspected, namely, that of inheritance. Varieties are the latest offshoots of the genealogical tree in " an unlineal " order ; species, those of an earlier date, but of no definite distinction ; genera, more ancient species, and so on. The human races, upon this view^, likewise may or may not be species according to the notions of each naturalist as to what differences are specific ; but, if not species already, those races that last long enough are sure to become so. It is only a question of time.

How well the simile of a genealogical tree illustrates the main ideas of Darwin's theory the following extract from the summary of the fourth chapter shows :

" It is a truly wonderful fact — the wonder of which we are apt to overlook from familiarity— that all animals and all plants throughout all time and space should bcrelated to each other in group subordinate to group, in the manner which we everywhere behold — namely, varieties of the same species most closely related together, species of the same genus less closely and unequally related together, forming sections and sub-genera, species of distinct genera much less closely related, "and genera related in diiferent degrees, forming sub-families, families, orders, sub-classes, and classes. The several subordinate groups in any class cannot be ranked in a single file, but seem rather to be clustered round points, and these round other points, and so on in almost endless cycles. On the view that each species has been independently created, I can see no explanation of this great fact in the classification of all organic beings ; but, to the best of my judgment, it is explained through inheritance and the complex action of natural selection, entailing extinction and divergence of character, as we have seen illustrated in the diagram.

"The afiinities of all the beings of the same class have sometimes'been represented by a great tree. I believe this simile largely speaks the truth. The green and budding twigs may represent existing species; and those produced during each former year may represent the long succession of extinct species. At each period of growth all the growing twigs have tried to branch out on all sides, and overtop and kill the surrounding twigs and branches, in the same manner as species and groups of species have tried to overmaster other species in the great battle for life. The limbs divided into great branches, and these into lesser and lesser branches, were themselves once, when the tree was small, budding twigs ; and this connection of the former and present buds by ramifying branches may well represent the classification of all extinct and living species in groups subordinate to groups. Of the many^twigs which flourished when the tree was a mere bush, only two or three, now grown into great branches, yet survive and bear all the other branches ; so with the species which lived during long-past geological periods, very few now have living and modified descendants. From the first growth of the tree, many a limb and branch has decayed and dropped ofi"; and these lost branches of various sizes may represent those whole orders, families, and genera, which have now no living representatives, and which are known to us only from having been found in a fossil state. As we here and there see a thin, straggling branch springing from a fork low down in a tree, and which by some chance has been favored and is still alive on its summit, so we occasionally see an animal like the Ornithorhynchus or Lepidosiren, which in some small degree connects by its afiinities two large branches of life, and which has apparently been saved from fatal competition by having inhabited a protected station. As buds give rise by growth to fresh buds, and these, if vigorous, Ijranch out

THE ORIGIN OF SPEGIE8. 19

and overtop on all sides many a feebler brancli, so by generation I believe it has been with the great Tree of Life, which fills with its dead and broken branches the crust of the earth, and covers the surface with its ever-branching and beautiful ramifications."

It may also be noted that there is a significant correspondence between the rival theories as to the main facts employed. Apparently every capital fact in the one view is a capital fact in the other. The difference is in the interpretation. To run the parallel ready made to our hands : ^

"The simultaneous existence of the most diversified types under identical circumstances, .... the repetition of similar types under the most diversified circumstances, .... the unity of plan in otherwise highly-diversified types of animals, .... the correspondence, now generally known as special homologies, in the details of structure otherwise entirely disconnected, down to the most minute peculiarities, .... the various degrees and different kinds of relationship among animals which (apparently) can have no genealogical connection, .... the simultaneous existence in the earliest geological periods, . •. . . of representatives of all the great types of the animal kingdom, .... the gradation based upon complications of structure which may be traced among animals built upon the same plan ; the distribution of some types over the most extensive range of surface of the globe, while others are limited to particular geographical areas, .... the identity of structures of these types, notwithstanding their wide geographical distribution, .... the community of structure in certain respects of animals otherwise entirely different, but living within the same geographical area, .... the connection by series of special structures observed in animals widely scattered over the surface of the globe,. . . . the definite relations in which animals stand to the surrounding world, .... the relations in which individuals of the same

^ Agassiz, " Essay on Classification ; Contributions to Natural History," p. 132, et seq.

20 DABWINIANA.

species stand to one another, .... the limitation of the range of changes which animals undergo during their growth, ... * the return to a definite norm of animals which multiply in various ways, .... the order of succession of the different types of animals and plants characteristic of the different geological epochs, .... the localization of some types of animals upon the same points of the surface of the globe during several successive geological periods, .... the parallelism between the order of succession of animals and plants in geological times, and the gradation among their living representatives, .... the parallelism between the order of succession of animals in geological times and the changes their living representatives undergo during their embryological growth,^ t • • • t^^ combination in many extinct types of characters which in later ages appear disconnected, in different types^ .... the parallelism between the gradation among animals and the changes they undergo during their growth, .... the relations existing between these different series and the geographical distribution of animals, .... the connection of all the known features of Nature into one system — "

In a word, the whole relations of animals, etc., to surrounding Nature and to each other, are regarded under the one view as ultimate facts, or in their ultimate aspect, and interpreted theologically ; under the other as complex facts, to be analyzed and interpreted

^ As to this, Darwin remarks that he can only hope to see the law hereafter proved true (p. 449); and p. 338: "Agassiz insists that ancient animals resemble to • a certain extent the embryos of recent animals of the same classes ; or that the geological succession of extinct forms is in some degree parallel to the embryological development of recent forms. I must follow Pictet and Huxley in thinking that the truth of this doctrine is very far from proved. Yet I fully expect to see it hereafter confirmed, at least in regard to subordinate groups, which have branched off" from each other within comparatively recent times. For this doctrine of Agassiz accords well with the theory of natui-al selection."

scientifically. The one naturalist, perhaps too largely assuming the scientifically unexplained to be inexplicable, views the phenomena only in their supposed relation to the Divine rnind. The other, naturally expecting many of these phenomena to be resolvable imder investigation, views them in their relations to one another, and endeavors to explain them as far as he can (and perhaps farther) through natural causes.

But does the one really exclude the other ? Does the investigation of physical causes stand opposed to the theological view and the study of the harmonies between mind and [N'ature ? More than this, is it not most presumable that an intellectual conception realized in J^ature would be realized through natural agencies ? Mr. Agassiz answers these questions afiarmatively when he declares that '^ the task of sciencejs to investigate what has been done^"toTnc[uire if possible hoio it has teen done^ rather than to ask what is possible for the Deity, since we can hiow that onlyhy what actually exists / " and also when he exter ds the argument for the intervention in l!Tature of a creative mind to its legitimate application in the inorganic world; w^hich, he remarks, "considered in the same light, would not fail also to exhibit unexpected evidence of thought, in the character of the laws regulating the chemical combinations, the action of physical forces, etc., etc." ^ Mr. Agassiz, however, pronounces that "the connection between the facts is only intellectual " — an opinion which the analogy of the inor-

* Op: cit., p. 131. — One or two Bridgewater Treatises, and most; modern works upon natural theology, should have rendered the evi-. dences of thought in inorganic Nature not " unexpected." 2 ganic worlclj just referred to, does not confirm, for there a material connection between the facts is justly held to be consistent with an intellectual — and which the most analogous cases we can think of in the organic world do not favor ; for there is a material connection between the grub, the pupa, and the butterfly, between the tadpole and the frog, or, still better, between those distinct animals which succeed each other in alternate and very dissimilar generations. So that mere analogy might rather suggest a natural connection than the contrary; and the contrary cannot be demonstrated until the possibilities of Mature under the Deity are fathomed.

But, the intellectual connection being undoubted, Mr. Agassiz properly refers the whole to " the agency of Intellect as its first cause." In doing so, however, he is not supposed to be offering a scientific explanation of the phenomena. Evidently he is considering only the ultimate ivhy, not the proximate why or how.

ISTow the latter is just what Mr. Darwin is considering. He conceives of a physical connection between allied species ; but we suppose he does not deny their intellectual connection, as related to a supreme intelligence. Certainly we see no reason why he should, and many reasons why he should not. Indeed, as we contemplate the actual direction of investigation and speculation in the physical and natm'al sciences, we dimly apprehend a probable synthesis of these divergent theories, and in it the ground for a strong stand against mere naturalism. Even if the doctrine of the origin of species through natuml selection should prevail in our day, we shall not despair ; being confident that the genius of an Agassiz will be found equal to the work of constructing, upon the mental and material foundations combined, a theory of N^ature as theistic and as scientific as that which he has so eloquently expounded.

To conceive the possibility of '' the descent of species from species by insensibly fine gradations" during a long course of time, and to demonstrate its compatibility with a strictly theistic view of the universe, is one thing ; to substantiate the theory itself or show its likelihood is quite another thing. This brings us to consider what Darwin's theory actually isj and how he supports it.

That the existing kinds of animals and plants, or many of them, may be derived from other and earlier kinds, in the lapse of time, is by no means a novel proposition. I^ot to speak of ancient speculations of the sort, it is the well-known Lamar ckian theory. The first difficulty which such theories meet with is that in the present age, with all its own and its inherited prejudgments, the whole burden of proof is naturally, and indeed properly, laid upon the shoulders of the propounders ; and thus far the burden has been more than they could bear. From the very nature of the case, substantive proof of specific creation is not attainable ; but that of derivation or transmutation of species may be. He who affirms the latter view is bound to do one or both of two things : 1. Either to assign real and adequate causes, the natural or necessary result of which must be to produce the present diversity of species and their actual relations ; or, 2. To show the general conformity of the whole body of facts to sucli assumption, and also to adduce instances explicable by it and inexplicable by the received view, so perhaps winning om- assent to the doctrine, through its competency to harmonize all the facts, even though the cause of the assumed variation remain as occult as that of the transformation of tadpoles into frogs, or that of Coryne into Sarzia.

The first line of proof, successfully carried out, would establish derivation as a true physical theory ; the second, as a sufficient hypothesis.

Lamarck mainly undertook the first line, in a theory which has been so assailed by ridicule that it rarely receives the credit for ability to which in its day it was entitled. But he assigned partly unreal, partly insufficient causes ; and the attemj)t to account for a ^progressive change in species through the direct influence of physical agencies, and through the appetencies and habits of animals reacting upon their structure, thus causing the production and the successive modification of organs, is a conceded and total failure. The shadowy author of the " Yestiges of the Natural History of Creation " can hardly be said to have undertaken either line, in a scientific way. He would explain the whole progressive evolution of ISTature by virtue of an inherent tendency to development, thus giving us an idea or a word in place of a natural cause, a restatement of the proposition instead of an explanation. Mr. Darwin attempts both lines of proof, and in a strictly, scientific spirit ; but the stress falls mainly upon the first, for, as he does assign real causes, he is bound to prove their adequacy.

It should be kept in mind that, while all du-ect proof of independent origination is attainable from the nature of tlie case, the overthrow of particular schemes of derivation has not established the opposite proposition. The futility of ' each hypothesis thus far proposed to account for derivation may be made apparent, or unanswerable objections may be urged against it ; and each victory of the kind may render derivation more improbable, and therefore specific creation more probable, without settling the question either way. New facts, or new arguments and a new mode of viewing the question, may some day change the whole aspect of the case. It is with the latter that Mr. Darwin now reopens the discussion.

Havino; conceived the idea that varieties are incipient species, he is led to study variation in the field where it shows itself most strikingly, and affords the greatest facilities to investigation. Thoughtful naturalists have had increasing grounds to suspect that a reexamination of the question of species in zoology and botany, commencing with those races which man knows most about, viz., the domesticated and cultivated races, would be likely somewhat to modify the received idea of the entire fixity of species. This field, rich with various but unsystematized stores of knowledge accumulated by cultivators and breeders, has been generally neglected by naturalists, because these races are not in a state of nature ; whereas they deserve particular attention on this very account, as experiments, or the materials for experiments, ready to our hand. In domestication we vary some of the natural conditions of a species, and thus learn experimentally what changes are within the reach of vary ing conditions in Xatni'e. TVe sejDarate and protect a favorite race against its foes or its competitors, and tbns learn what it miglit become if Katm^e ever afforded it equal opportunities. Even when, to subserve human uses, we modify a domesticated race to the detriment of its native vigor, or to the extent of practical monstrosity, although we secure forms which would not be originated and could not be pei^etuated in free ISTature, yet we attain wider and juster views of the possible degree of variation. "We perceive that some species are more variable than others, but that no species subjected to the experiment persistently refuses to vary ; and that, when it has once begun to vary, its varieties are not the less but the more subject to variation. "ISTo case is on record of a variable being ceasing to be variable under cultivation." It is fair to conclude, from the observation of plants and animals in a wild as well as domesticated state, that the tendency to vary is general, and even universal. Mr. Darwin does " not believe that vaiiability is an inherent and necessary contingency, under all circumstances, with all organic beings, as some authors have thought." 1^0 one supposes variation could occur under all circumstances ; but the facts on the whole ^ imply a universal tendency, ready to be manifested under favorable circumstances. In reply to the assumption that man has chosen for domestication animals and plants having an extraordinary inherent tendency to vary, and likewise to withstand diverse climates, it is asked :