From William Henry Harvey 24 August 1860
Trin. Coll. Dublin—
Aug. 24. 1860
My dear Sir
I have taken advantage of the summer vacation to finish the reading of your book, & considering what has already passed between us on the subject, I feel bound to tell you that my opinions have been, at least modified.1 It is true that I cannot as yet (probably never shall) receive the theory of Natural Selection as a satisfying explanation of the Origin of species—but I am willing to admit that it explains several facts which are not otherwise easily to be accounted for. Until however something more is known of the inciting causes of the Variation & Correlation of Organs, which in Nature ever go hand in hand, I can only regard Natural Selection as one Agent out of several;—a handmaid or wetnurse—so to say—but neither the housekeeper, nor the mistress of the house.
So long as you deal in generalities I can usually follow your arguments assentingly. Many of the facts brought forward illustrate your general principles & fit well into the place assigned them. But unhappily, my assent is most ready in cases where your data are fewest! and I find that particular instances, intended to illustrate how Natural Selection has acted or might be supposed to act in certain cases, almost always incline me to withdraw my assent to the previous argument.
Thus, when—following your argument—I am half inclined to admit the successive development of species from species, I come to your Illustrations, instead of my faith in my teacher being confirmed, I am absolutely repelled, & forced to suspect some undetected flaw in his line of reasoning. For instance, the speculation on the bear & the whale, of which I dare say you have heard enough, simply made me laugh.2 But that on the Ostrich & a bustardlike-bird (p. 134), though less improbable, is almost as fanciful; for, if your previous statement of the reason why ground feeding birds have imperfect wings be a vera causa, it is just as likely that the Ostrich may be a decreasingly corpulent Dinornis3 acquiring wings in its efforts to escape from a recently selected Lion. The modern Ostrich assuredly does use its wings constantly, both in running, & in flapping its sides in hot weather.— Again, the imagined adaptation of the tube of the red-clover to the proboscis of an improved domestic bee (p. 95) seems to me referable to the times of the “may-bees” only;—and lastly (for it is useless to say more, since the result on my mind has been uniform), what you say (p. 392) of insular trees belonging to orders which elsewhere include only herbaceous species, seems to me to be unsupported by sufficient evidence. You cite no particular trees, & I may therefore be wrong in guessing that the Orders you allude to are Scrophularineæ& Compositæ; & the insular trees the Antarctic Veronicas & the arborescent Compositæ of S. Helena, Tasmania &c. But—in S. Africa, Halleria (a Scrophularinea) is often as large & woody as an apple tree; & there are several S. African arborescent Compositæ (Senecio & Oldenburghia).4 Besides, in Tasmania at least, the arborescent Composites are not found “competing with herbaceous plants alone, & growing taller & taller by overtopping them” & so being converted “first into bushes & ultimately into trees”; for the most arborescent of them all (Eurybia argophylla, the Musk-tree) grows, not among bushes & herbaceous plants but in Eucalyptus forests, where it forms an undergrowth to trees so hopelessly taller than itself that competition is impossible.5 And so of the S. African Halleria, which is a tree, among trees. What the conditions of the arborescent Gerania of the Sandwich Islands may be I am unable to say, or whether you allude to them. I cannot remember any other instances; nor can I accept your explanation in any of the cases I have cited.
The Chapters of your Essay that weigh most with me are the latter ones.— The fact of an orderly succession of forms throughout geological eras suggests the notion of an orderly transmutation of species successively from epoch to epoch.— The facts of geographical distribution, making allowance for residua, seem to me favourable on the whole to a theory of successive mutation; particularly as regards the biology of outlying, small islands.— The facts of Embryology & of morphology are favourable to belief in an intimate relationship of organism to organism throughout nature; & this relationship is explicable on the hypothesis of a community of descent: & though these facts are not contrary to a notion of separate creation they are unexplained by it.— But if Creation be the finished work of a single Divine Author a common-plan may be anticipated throughout; there will be a “wheel within a wheel”, the same idea endlessly repeated & endlessly diversified; the same results arrived at by innumerable different contrivances. There will thus arise, between the different organisms, graduated similarities & diversities, & these will suggest relationship; but the real blood-relationship may be no more than that between different patent contrivances for accomplishing the same end. Watt’s steam-engine is not necessarily the parent of all steamengines.—6 The major facts of classification therefore, the subordination of group to group, appear to me to be perfectly consonant with a theory of separate creation.
But there are other facts of classification which certainly favour the view of mutation, & these are what you have most enlarged on in the early chapters. The tendency of forms to vary; the impossibility of distinguishing between species & variety; in many cases the difficulty of drawing a clear line between genus & genus, order & order, class & class, & even between the vegetable & animal kingdoms;—these are difficulties to the believer in separate acts of creation & are perhaps the strongest evidence in favour of a doctrine of mutation. But it does not therefore necessarily follow that the mutation has been effected through “natural selection” alone.
For some years back I have contented myself in believing in the absolute creation of “natural species” as distinguished from “book-species”; allowing “book-species” to have originated by variation within limits. But I must freely confess that my “natural species” are purely ideal, & never can be absolutely made plain to the senses. It is for such species as these that Mr. Hopkins contends in Frazers Magazine.7
At p. 484. you state your belief “that animals have descended from at most only 4 or 5 progenitors, & plants from an equal or lesser number”;—and you admit that analogy suggests that “all organic beings may have descended from some one primordial form, into which life was first breathed by the Creator”. Now, if you admit 4 or 5, or even but one, primal organisms, you admit so many “natural species”, in the same ideal sense that I have been accustomed to do. The difference between us at starting is merely as to the number of originally created forms; a difference in degree & not one in kind. We both believe that Life was first given by the Creator. Hitherto I have believed in thousands of “natural species”; nor do I yet see any absurdity in so believing. I may yet be driven back, by evidence, step by step, as you have been, into the narrows, & back even to one primordial form; but so long as we hold that form to have been “created”, we cannot be said to be infidels. To my mind there is no more difficulty in believing in 50, or 500 or 5000 absolute acts of creation, than in believing in one solitary creative act;—nor do I see greater difficulty in believing in many successive acts than in few or many simultaneous acts; but you seem to feel a difficulty in both these cases. What has once occurred, may occur more than once.
Again, at p. 483, you ask, “Were all the infinitely numerous kinds of animals & plants created as eggs or seed, or as full grown”? To this it is sufficient to reply; was your primordial organism, or were your 4 or 5 progenitors created as egg, seed or full grown? Neither theory attempts to solve this riddle, nor yet the riddle of the Omphalos.
In a former letter I troubled you with a few remarks on the geological difficulties of the Theory,8 & I have still something to say under this head.
Granting the highly developed condition of Silurian fossils we are driven to seek for the “primordial form” in some much earlier bed, “long before the first bed of the Silurian was deposited”. At p. 285, you calculate the denudation of the Weald at 306,662,400 years, or at the lowest 150 to 100 millions of years. We shall not trouble ourselves to compute thereby the enormous length of the post-silurian epoch (from the present year, back to the date of the first silurian bed);—but let us endeavour to conceive, guided by palæontological evidence, the probable length of the pre-silurian-organic period, from the lowest bed, back to the bed of the Primordial Form. Little as we know of Silurian Animals we know at least that they were greatly diversified, many of them highly organised, and probably very far removed from a “primordial form”, & if we could fully unveil the buried world of that era, it would probably compel us to push back our “primordial” some millions of centuries further than the known evidence now obliges us to do.
But how is palæontological evidence to be applied so as to compute a probable lapse of time? Granting that species & genera divaricate in the manner explained by your diagram of divarication,9 we may observe the number of fossiliferous beds through which well marked & nearly allied genera extend; remaining mutually distinct below, and undivaricated above. Taking the group of Mollusca, I find, among the fragmentary evidence collected by the palæontologist, that between 20 & 30 molluscan genera which have numerous living species, are represented by fossil species in Silurian strata, & considering our very small acquaintance with Silurian fossils I think this a large number. I cannot doubt that many other genera which at present seem to fail a little above the Silurian will yet be traced down into it. Every fresh discovery will add to the lapse of time, required to gather in the divarications to a primordial.
But let us take Patella & Chiton, two well-marked & nearly allied Silurian genera, having numerous modern as well as ancient species. The fossil Chitons have the same number of valves, similarly arranged & sculptured as their modern congeners, & except the subgenera Chitonellus & Cryptochiton, neither very different from the type, I know of no generic divarication. Now if Chiton & Patella, littoral shells, living side by side on the same rocks, have continued with the same habits, the same organization, generically undivaricated since the first bed of the silurian was deposited; may not these same two genera go down through lower strata with the same habits, the same organization & generically disunited to some indefinitely distant primal sea, before a tendency to coalesce exhibit itself; & may they not then go down through an equally indefinite but probably much longer period before an animal half-patella & half-chiton, the common progenitor of both will be found? But suppose us to have reached this Chitona-patella: can we believe it to be the common progenitor of all Mollusca? Certainly not, for Chiton & Patella are far removed from the lowest of the Molluscan series.— But to hunt back for a common progenitor of Molluscs through supposed forks of an imaginary family-tree would be a very hopeless task, and when at length, after fresh myriads of centuries we had traced this parent of Mollusca, we should have to go still further down, & probably to an equally remote era before the common progenitor of Mollusca & Articulata were found;—& this low organism might still be myriads of centuries removed from your ultimate Protozoon.
By your theory, the changes from generation to generation are infinitessimal; & to the continued accumulation of such changes through vast periods is due the present diversified condition of the organic world. But till I began this conjectural calculation I had no conception of the smallness of an infinitessimal generic difference. Judging now by the differences which may have modified the organization of Chiton & other molluscan genera during the whole post-silurian epoch, I can only liken each small cyclical divergence to the distance between two of the striæ on some microscopic test-object! Well may those naturalists who believe in the cyclical fixity of a variable type be forgiven when they see so large, so ancient & so widely diffused a genus as Chiton is so persistently slow in its progressive development. I am tempted to think that “festina lente” ought still to be our motto, in receiving a theory of unlimited divarication.
Moreover, we must bear in mind, that as, in imagination, we descend through pre-silurian beds toward our first organism, many circumstances conspire to render every successive step slower & slower. For you tell us that higher & more improved forms alter quicker, but low, unimproved forms endure longest & alter most slowly. We know how long Chiton & other molluscan genera have endured & flourished, & how slowly they have altered, if altered at all, in organization. In every step below them therefore we must allow still longer periods of stability, still slower cycles of change.— Besides, at every step downwards, we encounter fewer & fewer forms; hence, there will be less & less “struggle for life” in a continually thinner & thinner population. “Natural Selection” consequently will become feebler & feebler, as the “Struggle for life” diminishes; & this latter, it seems to me, must cease altogether long before the era of your Protozoon be arrived at.
But granting that we are at length arrived at the bottom of the well & have secured our “primordial form”, just as it was “created”. What was it like?— It is plain that it must have belonged to the Protozoa; for it is the original protozoon itself. Besides, as it united in itself the undeveloped Animal & Vegetable ideas, it could not be higher in organization than the simplest animal & vegetable soldered together. A pair of nucleated cells, combined into an atom of sarcode, would answer to this description. But the size of each cell might be as large as you please. The largest cells known in the Vegetable Kingdom occur among the Algæ; those of Valonia Forbesii are sometimes as big as a pigeon’s egg. But remembering the enormous bulk of the animals of the early world, & that the earliest types of each group are the most gigantic, I think we may (if necessary) make the cells of our primal organism as big as plum-puddings—or as balloons. There is nothing necessarily to limit the size but the tenacity of cellulose & sarcode, & that might vary almost indefinitely.
But probably the enormous size suggested may be objected to, & there is nothing compelling us to any size. The organization must have been simple, but the size is an open question. Whatever was the size, large or small, the production of the first organism was a stupendous miracle. The “flashing up of elemental atoms into living tissue” (p. 483) which then occurred is doubtless as wonderful as the creation of a new world.10 For, however brought about, this is what took place. Certain atoms of carbon, oxygen, hydrogen & azote, changing into cellulose & protoplasm, became a living body, endowed with growth; capable, by feeding, of changing mineral atoms into more cellulose & protoplasm; having an instinct to turn to the light & perhaps the germs of indefinitely progressive instincts; and above all, possessing a procreative power, enabling it to transmit from generation to generation of similar organisms, throughout all time, similar powers & capacities. This first organism in fact possessed distinct personality; hence (my reason assures me) the Power that called it into being & endowed it with secondary powers must be a Personality, & not merely “a law or laws acting around us.” And as every organism in Nature has its personality, so, whether every one were separately created, or the higher derived through the lower, we require a personal, creative or moulding Power alike in all cases. Secondary (or physical) laws suffice for all the phenomena of the inorganic world, but life is made up of contingencies which physical laws, unmodified by personal Agency, will not always meet.
And here I must observe that if we allow a Self-originated, Supernatural Power to have once acted as above described, we cannot presume to limit the further working of that Power. If the derived generative force of animal or plant may act an indefinite number of times, must not the primary Generating Force be held capable of acting an indefinite number of times? Hence I see no theoretical reason for limiting the number of originally created forms, either as to their variety among themselves or as to the number of individuals of each kind that may have been simultaneously or successively called into being. Neither is it of any theoretical consequence whether they were created as eggs or as adults; for the Power that could call a living tissue from the dust, must be held capable of, at will, calling up an egg or an adult.
To return to our primordial form; let us see what becomes of him on the theory of natural selection. By theory we have made him the simplest in structure; the feeblest in divaricating tendency (because “unimproved”) & there is a probability in favour of his being of small size. By theory also he is alone in the world, because every species starts from a solitary individual or pair. Now granting a high rate of increase to such a being we may safely allow myriads of years or perhaps of centuries to roll by before the world could have been so fully stocked with undivaricated protozoa that there should have arisen any “struggle for life”. Millions of ordinary protozoa may congregate without crowding in a cubic foot of water; how many million millions would it require to overstock a primæval, universally extended Ocean?— “Variability” if solely depending on “conditions of life” could effect but little, for protozoic forms flourish equally well on arctic-snows, in temperate & tropical rivers & seas & in thermal springs. They are the simplest of organisms, & the simpler an organism is, the less is it affected by “conditions of life”. Any attempt therefore to set “natural selection” in action under such circumstances appears to me to be impossible.
I have endeavoured, by theory, to overcome this difficulty; but granting that “Growth”, & “Reproduction” are ordinarily in each animal or plant fixed-average quantities; and considering that “Variability” arising from conditions of life, from use & disuse, is feeble or wholly inoperative in a being placed and constituted as our protozoon; and that a “Struggle for life” is all but impossible to conceive; I have exhausted your Productive “Laws” (p. 490) & have no resource left but to call up the Unknown Laws of Variation, those namely which cause an Organism “to sport” or diversify itself unexpectedly.— Natural Selection, no doubt, is ready to take advantage of such contingent variations, but cannot be said either to explain, or to originate them. If therefore these are necessary, at starting, to set natural selection in motion, we are surely calling up a wholly different Agency to any set forth in your theory.
For once that we call in Unknown Laws of Variation, “Growth” will no longer be a fixed-average quantity, but may be supposed to vary indefinitely either in the same being or in its immediate progeny, as we see illustrated by sponges & the lower algæ. The Protozoon may be supposed as plastic as an Amoeba. Hence divarication from the original Protozoon may immediately commence, & even be rapid, but would be disorderly or monstrous but for another unexplained Law, “the correlation of Organs”.
By the help of Divarication & Correlation acting together we arrive at the symmetrical diversity of organisms, so obvious in all around us; and with “Reproduction” ever multiplying individuals, & “Inheritance” seizing on & perpetuating new variations, we may conceive the Earth to be rapidly peopled with diversified & diversifying forms. And these may have been originated, & have gone on divaricating for long ages before a “Struggle for Life” shall have brought Natural Selection into being. Whilst we have Instruments at command so powerful as “Unknown Laws” (of Variation & Correlation) we no longer feel hopelessly crushed by the weight of 50 or 500 post-silurian epochs, for we see that, time being allowed, we shall at length emerge from the abyss. But without calling in these Unknown & Unexplained laws, organic nature, if it originated in a single “primordial form” appears to me to be doomed to perennial sameness. The primordial form, like the Protococcus nivalis, would have reproduced its own likeness from the dawn of life to the present day. Mere lapse of time can effect no change whatever.
But what are these “Unknown Laws of Variation”; what this “Correlation of Organs”? My reason tells me that they are probably fresh revelations of the same Supernatural Power which originated our “primordial form”, and endowed it with its reproductive, & all its other powers. Organic nature, from beginning to end, is a continued miracle, & this is true on both theories; whether each species has been separately created, or whether the past & present conditions of the organic world have arisen by successive divarications of a primæval germ. Every living atom bears its witness to an Everliving, Superintending, Upholding, & Contriving Intelligence. In every variation from type, in every correlation of parts, there are evidences of Creative Power, such as no secondary agency, like that of Natural selection accounts for; and I think also there are evidences of one Great Design, beginning at the simplest elementary form, & culminating in the “fearfully & wonderfully made” framework of man.
Once or twice in your essay you object to our attributing to the Creator a way of working similar to that of intelligent man. At p. 188, speaking of the structure of the eye, you say,— “Have we any right to assume that the Creator works by intelligent powers like those of man”?— We have at least some reason for “assuming” that He possesses such powers; for how has man acquired them but through His gift? Nor do I think it presumption to believe that the Infinite Intelligence is ever acting, everywhere throughout creation. And if not, whence arise those wondrous correlations, beginning with the balanced movements of the spheres, & penetrating every particle of matter? Are they merely coincidences? Or, do they come through natural-selection?—
Do not suppose me to mean that I consider you to deny a Superintending Providence. Your admission of a created germ of life, & the quotation from Bishop Butler,11 explanatory of the word natural (“what is natural requires & presupposes an intelligent agent to render it so”) show that you admit a Supernatural Agency. But it seems to me that in developing the theory of natural selection & referring every operation in nature to it, the underworking Power is too generally lost sight of as an element in the problem, & that the continual mention of “usefulness” is the only evidence of theism that the work supplies;—because, an appreciation & perpetuation (or selection) of the “useful” presupposes a vigilant & intelligent agent. I do not suppose you to say, for instance, (p. 235) that “nature” is no more conscious than the reforming bees of the saving of wax effected by “sweeping equal spheres at a given distance from each other in a double layer” &c. There is abundant evidence of intelligence somewhere; either among the bees (which we do not think) or Above & around the bees. But it is surely no explanation to say, as you often do: “If so & so were useful to any animal in its struggle for life, it would be easy for natural selection, by slow degrees, more & more perfectly, to fit the creature to its peculiar habits, & endow it with such & such instincts;”—as in the case of the Ant & the Bee, whose instincts, supposed to be acquired through inheritance, are transmitted through successive communities of neuters! You seem to me to be merely asserting this trueism; Nature or the Author of Nature, can easily effect any preconceived design, & form & endow any creature, as He pleases. Nothing is really explained by saying “it would be easy” “if it were useful”. And when we strike off such “explanations” as these, with which the book abounds, the facts of organisation explained by natural selection will be very seriously diminished.—
If there be any part of the theory of natural selection more firmly established than another, it is what we may call the law of the strongest. Dominant races throughout nature will gradually drive out feeble races; “the weakest will go to the wall”.12 In applying this universally recognised principle you strongly insist that improved races will continually supplant unimproved, & hence you deduce the gradual progress of organic nature from the simple primordial forms up to man. We know what an “improved” race among domestic animals means; we know how it is manufactured, how disseminated & how preserved from degenerating; but we also know that it is feebler in constitution & less fitted to conquer in the struggle for life than its unimproved progenitor. Artificially “improved” races could never become dominant, if neglected by man. It is of importance to your theory therefore to determine whether, in Nature, the most dominant races are also the organically improved races? Unless I mistake your meaning you seem very generally, so to argue, & many of your readers understand you to contend for one continued progress onward, from the monad to the man, accomplished by the continual extinction of less improved forms, by dominant improved varieties.
Such appears to me to be the general drift of your argument; but the chapters on “use & disuse” allow for occasional retrogression. They teach us, that if an animal, through profitable use of its limbs has risen, in successive generations, from a very low to a very high organization; its degenerating descendants, subjected to changed conditions of life, which would cause them gradually, in successive generations, to lose the formerly acquired habit, & the organs fitted to those habits, may descend in the scale of being to the state of the unimproved original from which the race ascended. The blind animals, vertebrate & invertebrate of the Kentucky caverns illustrate such retrogressions. You suppose these animals to have “slowly migrated, by successive generations, from the outer world into the deeper & deeper recesses of the caves” (p. 138); and we see that they have already gone so far back as to have lost the eyes which their progenitors had acquired (through natural selection, as all eyes have arisen (p. 136)), and to have had their bodies considerably correlated with their new habitats. Now, they have only to go still further back, and after successive migrations & generations their descendants may lose every acquired organ, one by one, till they revert to a protozoic form. But how can we certainly tell that they are migrating inwards, deeper & deeper into the caves? May they not, on the contrary, be migrating outwards, seeking the light, as almost all known organisms instinctively do;—and if so, they are animals in progress, acquiring, not losing organs. Their imperfect eyes are nascent, not obliterated eyes. And in the case of the blind-rat, with its well formed though sightless eyeballs we have an animal almost ready for emergence?13
But to return to the dominant races: are these the improved or the unimproved in organization? Viewing organic nature in its widest aspect I think it is unquestionable that the truly dominant races are not those of high, but those of low organization. The simpler any animal’s structure is, the less is it dependent on outward conditions; hence, the better is it fitted to conquer in the struggle for life, & to perpetuate its kind to a remote posterity. Cryptogamic plants & invertebrate animals, natures scavengers, are the most dominant and persistent races of the world. The Protococcus nivalis is probably one of the oldest inhabitants of the world, younger only than the snow; and the P. pluvialis, which scarcely differs, is equally persistent wherever rain water habitually rests, & these two may be called dominant. But as they are harmlessly dominant, we do not heed them. Other animals & plants of low organization by the ravages they cause, teach man himself that his domination over nature is by sufferance of a Higher Power. The Botrytis which so nearly destroyed the potatoe; the Oidium which has ruined the vinegrowers throughout the world; these, and the locust & the caterpillar, the tapeworm & its kindred, with the innumerable army of intestinal worms & of animal & vegetable parasites, these are the true dominant races; the Lords of creation that never struggle for life and that fear no evil. They have nothing to lose by any chance, short of the anihilation of the world, & if the theory of natural selection be true, they have every thing to win.
The law of the strongest therefore most forcibly applies to the wholly unimproved races; in a less degree to those higher in the scale; and gradually diminishes upwards as organization, & sensibility to outward conditions encrease. I object therefore to its being made a vera causa of the evolution of organization. It only applies where a peculiar organization, combined with strength of constitution & adaptability to circumstances, gives an animal an advantage over its fellows: but in this case I think the dominancy will depend more on the strength of constitution & power of adaptation than on the organization. For we see improved & unimproved races (like the humble & domestic bees) flourishing together without one supplanting the other; & if the humble bee, notwithstanding its wasteful habits, have greater strength of constitution & less susceptibility to varying climate than the domestic bee, it will eventually win.
I have already far transgressed the proper bounds of a letter, & yet have a few more words to say.
When you suppose one species to pass, by insensible degrees into another, so many facts of variation support your view that it does not seem very improbable; but where a generic limit has to be passed, bearing in mind how persistent generic differences are, I think we require a saltus (it may be a small one) or real break in the chain, namely, a sudden divarication.14 I know you account for genera by the dropping out of supposed intermediate infinitessimals. But we know also that sudden divarications do sometimes occur in nature; and it is possible that they may be even necessary consequences of repeated & long-continued infinitessimal changes. The tower of Pisa may be infinitessimally receding from its perpendicular for centuries, & may at last, the point of balance being passed, come down bodily with a crash. I have sometimes amused myself, when looking through a kaleidoscope, by turning it so as to make it indicate genera & species. Starting with any pattern of figure, by very slow turning of the tube you may get successively a great many modifications of the figure, without any radical change in the pattern, thus illustrating several species of one genus. But when you have turned the tube so far as to cause such a displacement of the fragments of glass as makes them topple over, a perfectly new pattern will suddenly start up & may then by further slow turning be modified, till it in turn shall topple over. Of course this is merely a possible illustration of the gradual succession of species & genera, if they arise by smaller & greater divarications.
You object, I know, very strongly to abrupt changes. But as there are volcanoes & sudden displacements in the mineral world, there may also be abrupt divarications in the organic. Some of the facts of metamorphosis, particularly that of the Cirrhipedes (p. 441) which for a special purpose suddenly acquire & as suddenly lose their compound eyes & natatory legs; and every similar fact that indicates a special interference of Creative intelligence implies at least a break in the series of changes. Nor can I divest myself of the belief that there is a real break between every established species (however originated), & that that break implies the interference of a First Cause. The line of unfertile hybridity offers us some evidence of such breaks; anatomical structure, in cases where the plan of organization is reversed, will probably furnish more exact evidence. The change from hairs to feathers seems a sudden one, inexplicable on the hypothesis that intermediate links have dropped out. The change from coniferous wood-tissue & no ducts to ordinary wood-tissue with ducts, seems also sudden. And so do other changes that imply contrariety or polarity.
I am therefore still strongly of the opinion that, whether all organisms originated in but a few primæval types or in a definite, but considerable, number of “natural species”—a question that at present must be left open—that the present aspect of nature is due, not to a succession of minute differences accumulated through inheritance & preserved by “natural selection”, but to renewed interferences with ordinary generation, which may be attributed either to “Variation & Correlation of Organs”, or to a superintending & moulding Intelligence:—& that these interferences may have caused either sudden or gradual changes in the previously moulded organisms. By admitting the possibility of sudden divarication we get rid of those perfectly innumerable forms of life which your hypothesis requires us to believe in, but of whose existence there is so little evidence either in existing nature or among fossils. But the whole subject is at present obscured by difficulties that no proposed hypothesis fully gets rid of. By directing attention to one set of phenomena your theory of natural selection finds favour, but turning to another set I am driven back nearly to my old ground; and then “natural selection” is to me but a new phrase signifying “the order of nature”, which may be further translated into “the will of God”, & then the theory dissolves into thin air.
As yet therefore I cannot subscribe myself your disciple, but I remain as heretofore | My dear Sir | very faithfully yours | W. H. Harvey
To | Charles Darwin Esq, F.R.S. | &c. &c &c
Sept. 20th. 1860 | Prof. Harvey in letter (p. 13) says [‘dominant’ del] the lowest forms, as protozoa, intestinal worms, & parasitic cryptogams are the dominant forms.— These are most [interl] widely spread, [‘which’ del] & I imagine have many species in groups, & are infinitely numerous in individuals which truly shows that [interl] they are dominant. *in fact they are so, otherwise they would not exist in numbers. [added] As far as number of individuals are concerned, I ought to have put in caution “relatively to size of individuals”. They probably are really highly dominant, for no doubt they keep down numbers of higher productions; or rather probably aid in keeping down certain forms.— To say that cryptogamic forms such as Botrytis are dominant over phanerogams, implies that if they did not exist, the number of phanerogams, would be larger in any country.
I doubt this, for the land is so thickly clothed with plants they could hardly exist. I daresay there would be change in proportions. Under artic climate, on mountains & barren heath where the higher cryptogams abound, they are to certain extent dominant & more heath or poor grasses would grow. So when he speaks of Protococcus being dominant, it can only be dominant under the conditions in which it can live. A few fish of one species is yet dominant over millions of infusoria & worms.— I must somehow show that when I talk of plants being dominant I refer only to those other plants, with which it comes in competition. But by dominant I in fact imply that the single species or group is increasing in numbers; can we believe this of low organisms? Again with respect to parasitic worms being dominant.; in a country fully stocked with mammals, would the number increase if no parasitic worms, perhaps they would, for then they would gain an advantage over insects & other vegetable feeders. No doubt parasitic worms are one check; especially when numbers increase. But we know of no case of animal not increasing in numbers, owing to such causes, if food abounds & there be no struggle for life *for food at certain seasons or [interl] with beasts of prey
Hence wide distribution, large groups—or [unlimit] numbers of individuals (disregarding size) do not make a group dominant looking to world or even to a single country, we must include under closely similar conditions, as inhabitants of water—or plants [drawing nourishment] from soil & breathing air—
The number of intestinal worms beat that of the species on which parasitic—many belong to large group— [‘ma’ del] ranges as widely & if inhabiting other species, may range wider; yet can hardly be said to be dominant over that species unless it exterminated it & then it would cause its own extermination, or unless it greatly reduced its numbers, irrespectively of other grass-feeders or carnivores with which it came into competition.
So grasshoppers [‘are’ del] may be dominant over herbaceous quadrupeds: & insects [above del ‘they’] no doubt are a highly dominant group.— The expression as used by me is relatively to allied forms; if of two species one cd resist intestinal worms better than other species, or live on food on which grass hoppers did not eat *as roots [interl], it would be in fact so far dominant.—
I suspect I have used expression, the dominant forms within each class.—
Second CD note:
Every group of organisms which exists in great numbers may be said to be a dominant group.— In Australia Marsupials are dominant mammals—not so [‘Ornithorynchus’ del] in world. My remarks on dominant forms chiefly relate to dominance over other members of the same group, or to those which come into direct competition with [‘it’ del] them.— Under simple conditions of life the lowest forms are often dominant.
Add [‘when’ del] dominant over other members of the same class which live in same region under [‘con’ del] similar conditions of life—or members of other classes with which the dominant forms come into competition or struggle for life
Continues earlier discussion, admitting his opinions have been modified. Still regards natural selection as one agent of several. States areas of disagreement.