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exclusively to the long lineal ancestors: this in is most cases scarcely ever possible; & we are forced in each case to look to organisms of the same group, or that is to the collateral descendants from the same parent-form, to see by analogy what variations are possible, & what forms may states of the structure have been transmitted from various stages of descent in an unaltered state or little altered condition. Amongst the existing vertebrata we find no nearly perfect but a small amount of gradation, in the structure of the eye, & amongst fossil species we can know nothing of it: & we in this great class we should have probably to as descend far beneath to lowest known fossiliferous stratum to discover the earlier stages by which the eye had has been perfected.

But in the Articulata, we can start from an optic nerve coated with pigment, without any other mechanism. We are here no more concerned

How a nerve is rendered comes to be sensitive to light hardly does not here concern us, more than how life first originated: but I may remark that several facts make me suspect that any sensitive nerve may be rendered sensitive to light, or to & likewise to those coarser vibrations of the air, which cause sound. However this may be, in the Articulata we can start from an optic nerve, coated with pigment, but without any other mechanisms; & from this low stage point, numerous gradations of for structure & perfection,

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Sect VI. Means of Transition

numerous cases could be given amongst the lower animals of the same organ with same animal performing wholly distinct functions; thus the stomach or intestines (as in larva of Dragon-fly & the fish Cobites) may respires & digests or excretes.

In the Hydra the animal may be turned inside out, & the exterior surface will then digest, & the stomach respire.

In such cases natural selection might easily specialise the whole or part of the organ to one function alone, if any advantages was thus gained. Again there are many cases of two wholly distinct organs in the same individual performing the same function: to give only one instance, there are fish with gills or branchiæ which thus breathe the air the air dissolved in the water, & at the same time have their se breathe free air in their swim-bladders, which are this latter organ is being divided by highly vascular membranes partitions, & has having a ductus pneumaticus to supply air.

In such cases, the one organ would perform its proper function, now could aid the other, while this other was becoming modified & perfected so as to do the work by itself; & then the first might disappear or become modified for some other & quite distinct purpose.

The illustration of the swim-bladder of fish is a good one because it well shows us the highly important fact that an organ originally constructed for one purpose, namely flotation, may be converted into one for a wholly different one purpose, namely respiration; (a) As All physiologists I believe admit that the swim-bladder of fish is strictly in position & structure is homologous with or "ideally similar" with the lungs of the higher vertebrate

[there are pin holes where the following slip, [folio 208](a), was attached to the back of this sheet]

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(a); in certain

[pencil note in the hand of Geoffrey Keynes:]

Two sheets of the first draft of
The Origin of Species.
Given me by Mrs Litchfield
23 August 1923
G L Keynes

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(a)

The swim-bladder it has also, I may add, been worked in as an accessory organ to the auditory organs of certain fish                   ; or part of the auditory apparatus has been worked in as a complement to the swim-bladder; for I do know which view is now generally held.

[Unlike the normal draft leaves of blue wove paper, this note is written on chain-lined cream laid paper. No visible watermarks. There are pin holes where this was pinned to the back of the preceding sheet, folio 208. Since at least when it was photographed in 1988 it has been glued to the left lower edge of folio 208]

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animals; in all its relation of position & structure, hence hence these seem to me to be no great difficulty in believing that natural selection has actually converted a swim-bladder into a lung or natural selection completing the stages of conversion, & making it organ exclusively as organ used for respiration.

In I can indeed hardly doubt that the true lungs of all the higher air breathing vertebrata are actually a modified swim-bladder; that though animals animals having true lungs lungs have all descended by ordinary generation from an ancient parts aquatic prototype, of which we know nothing, furnished with a floating organs of respiration apparatus or swim-bladder. We can thus as I presume (B) understand the strange anomaly fact that every particle of food & drink which these animals swallowed by them we swallow has to pass over the orifice of the trachea, with some risk of falling into the lungs, notwithstanding the beautiful contrivance by which the glottis is closed. falling into or entering the lungs. In the higher animals vertebrata the branchiæ have wholly (a)

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the slits on the sides of the neck and course of the arteries, still marking in the embryo their former position

disappeared, but it is conceivable that the branchiæ might have been worked into some quite new use, also as the animals which bore them possessor slowly over became fitted to inhabit are [illeg] dwell on the land instead of under the water. In the same way as some [illeg] believe that the wings & wing-covers branchiæ & protecting dorsal of insects scales in annelids have are homologous with that [inner] once view have been converted from, the branchiæ & dorsal scales of annelids; & therefore on this our view

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(B), as I infer from Prof Owen's interesting description of their parts,

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capable of actual conversion have been converted from the one purpose to the other.)

(In considering transitions of organs, it is so important to bear this possibility of conversion from one purpose to another in mind, in mind that one organ originally fitted for one purpose may be converted fitted for into another wholly different one, that I will give one more instance. Pedunculated cirripedes have two minute folds of skin, called by me the ovigerous fræna, which serve through the means of a sticky secretion, to retain within the sack the sheets of eggs, until they are hatched; these cirripedes have no branchiæ, the whole surface of the body sack & body serving for this purpose end: the Balanidæ, on the other hand, apparently owing apparently to their better enclosed shell, have no ovigerous fræna, the sheets of eggs lying loose at the bottom of the sack; but they have large plicated branchiæ. Now I think it can be shown from I think no one will dispute that the ovigerous fræna in the one group family are strictly homologous with the branchiæ of the other group; indeed they graduate into each other; & therefore I cannot Therefore I do not doubt that the ovigerous fræna which no doubt like the rest of the sack must have served are also in some very small degree for respiration have been enlarged by natural selection, & losing their adhesive functions have been converted by mere increase in size & plication into branchiæ. If the pedunculated cirripedes had all become extinct; & they have already suffered far fewer extinction than the Balanidæ, who could would possibly have ventured imagined that a in this latter

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will, that sexual selection will have often largely modified external features to give one male an advantage over in fighting with another or in charming the females. Moreover, when a modification of structures has arisen from any of the above or other unknown causes, it may be taken advantage of other species with in newly acquired by the habits. or economy of its possessor.

To give a very few instances, better to show what I mean. illustrating these latter remarks. If green woodpeckers alone had existed; & we did not know that there were many black & pied kinds, I have no doubt daresay that we should have thought the green colour a beautiful adaptation to hide this tree-frequenting bird & that it might consequently have arisen through natural selection:; as it is, I have no doubt the colour is due to some quite distinct cause, probably to sexual selection. A trailing Java bamboo in the Malay Archipelago climbs the loftiest trees by exquisitely constructed hooks clustered around the ends of the branches; & these no doubt are of the highest service to the plant; but as we see nearly similar hooks in many ot trees, which are not climbers, & the hooks of the bamboo may may have probably arisen not from natural selection, but from unknown laws of growth, & when per subsequently have been taken advantage of it & even further modified improved, so as to serve for climbing.

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& the bamboo being modified has been thus become indeed a climber. The naked skin on the heads of vultures is generally looked at as a direct adaptation for wallowing in putridity; & so it may be; or it may possibly be due the effect of the direct action of putrid matter; but we should be very cautious in drawing such inferences, when we see the naked skin on the head of the clean-feeding male turkey. The open sutures in the heads of young mammals, has often been advanced as a beautiful adaptation for parturition; & no doubt it facilitates or may be indispensable for this act; but as we find open sutures in the heads of young birds & reptiles, which have to emerge escape only from a broken egg, we may infer that this structure has arisen from the laws of growth, & has been taken advantage of in the act of parturition in the higher animals.—

It is most necessary to try to be fully conscious of one's own ignorance on causes producing slight & unimportant variations; ; & nothing has seemed to me better for this purpose than to reflect on the breeds of our domestic animals in different countries,

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more especially in the less civilised countries, where there has been little artificial selection. Not but what I am convinced, th as previously explained, that there hardly exists a race of man so barbarous that they have not probably in some degree influenced modified by occasional & unconscious selection their domestic animals. In the case of the races of man himself, the difficulty rises to a climax, for artificial selection is here quite eliminated. In our domestic animals, careful observers are convinced that a damp climate affects the growth of the hair, & that with the hair the growth of the horns is correlated, & mountain breeds of all our animals differ from the lowland breeds & a mountainous country, would probably affect through are greater use the hinder limbs, & possibly even the form of the pelvis; & then by the law of homotypic homologous variation, the front front limbs & even the head would might would probably be affected. The shape, also, of the pelvis might even affect by pressure in the womb the shape of the head. The laborious breathing of in high regions would, we have some reason to believe, would affect the size of the chest, & again correlation would come into play. Animals kept by savage races in different countries, would often have to live largely by a struggle for life their own subsistence, & would be exposed to much a certain extent to natural selection; & individuals

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with slightly different constitutions would succeed under different climates. There is some reason to believe that constitution & colour are correlated & a good observer states that in cattle susceptibility to the attacks of flies is correlated with colour; as is liability to the poison of certain plants.

But we are far too ignorant to speculate on the these subject, relative importance of the various influences; & I have alluded to them only to show that if we are unable to account for the the such differences characters, which distinguish our domestic breeds in different countries, & which nevertheless we generally admit have arisen during the course of ordinary generations, we ought not to lay much stress on our ignorance of the precise precise cause of analogous differences between true species. I will here say nothing on the origin of the races of Man, which are so strongly marked; I think I can see some little light chiefly through sexual selection of a particular kind, but without entering on copious details, my reasoning would appear quite frivolous.—

The foregoing remarks lead me to say a few words on the protest lately [illeg] made by some naturalists that against the doctrine that every part & detail of structure has been created for the good of the organism: its possessor. They believe that a

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multitude of details have been created for beauty or in the eyes of man, or for mere variety. These latter Such a doctrines are is absolutely opposed to our theory. Yet I fully admit that each in many parts are of no direct use to their possessors. Physical conditions probably have had some little effect on structure, quite independently of any good thus gained. [illeg] those gained: c Correlation of growth has no doubt had played a most important part, but then the and a change modification of structure a which was of use to the possessor will have often has entailed other & diversified changes, will generally have been of no direct use; but not injurious So reversion may cause characters now useless to reappear at the present day, though they may have formerly been so, useful; or only may formerly only have arisen from due to correlations of growth or be due to or to the direct action of physical conditions. The effects of sexual selection, when resulting giving only beauty in the eyes of the other sex, can only be called useful only in rather a forced sense & b But by what is far the most important consideration, is that in every organism the main & fundamental part of the structure of every organism must be organic being is due to inheritance; & therefore often of no special use, yet will to each species at the present time; though each species undeniably is well fitted for its place in nature. Thus we can hardly believe that the webbed feet web between the toes of the upland goose or of the frigate bird

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, though we may most easily err on both sides, that some other contrivances are much less perfect. Can we consider the sting of the wasp or bee perfect, which, when used against many attacking animals, cannot be withdrawn owing to the backward serratures & so inevitably causes the the death of the bee or wasp of the insects by tearing out t its viscera? If

If we look back at the sting of a as a boring organ, modified but not perfected, furnished beautifully & therefore serrated as in so many members of the same great order, modified but not perfected, with the poison originally adapted to cause galls, , intensified, we can perhaps understand this anomaly of its use so often causing the insect's own death;

f For if on the whole it be its use the power of stinging be useful to the community it will fullfil the requirements of natural selection. If we admire the truly wonderful power of scent by which the males of many insects find the females; can we admire the production for this single purpose of even by the thousands of drones,: for this single purpose ; which are utterly useless to the community for any other purpose good, & which are ultimately slaughtered by their industrious but sterile sisters. It may be difficult, but we ought to admire the savage intuitive hatred of the Queen-Bee, which compels urges her instantly to destroy the young queens, her daughters, as soon as born, or herself to perish in the contest combat; for

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