On the Origin of Species

“Although much remains obscure, and will long remain obscure, I can entertain no doubt, after the most deliberate study and dispassionate judgment of which I am capable, that the view which most naturalists entertain, and which I formerly entertained—namely, that each species has been independently created—is erroneous. I am fully convinced that species are not immutable; but that those belonging to what are called the same genera are lineal descendants of some other and generally extinct species.”

Here, Darwin boldly asserts his rejection of the (then-common) view that species were created independently of one another—or that, among other things, they didn’t evolve from common ancestors. In addition, he claims that species aren’t static forms, timelessly reiterating themselves in succeeding generations. Instead, they’re mutable iterations of dynamic processes. In Darwin’s time, this view was highly contentious within the scientific community and deeply upsetting to dominant Christian religious convictions.

“[…]namely, that we know nothing about the origin or history of any of our domestic breeds. But, in fact, a breed, like a dialect of a language, can hardly be said to have had a definite origin. A man preserves and breeds from an individual with some slight deviation of structure, or takes more care than usual in matching his best animals and thus improves them, and the improved individuals slowly spread in the immediate neighborhood. But as yet they will hardly have a distinct name, and from being only slightly valued, their history will be disregarded. When further improved by the same slow and gradual process, they will spread more widely, and will get recognized as something distinct and valuable, and will then probably first receive a provincial name.”

Darwin explains why the origins of specific domestic breeds are unknown and, more fundamentally, why speaking of a specific origin point for a breed makes little sense. Changes don’t inherently result from any intrinsic characteristic of a breed but instead from the attention of human breeders. Darwin uses the general ignorance about the origins of domestic breeds to introduce the problem of the origin of species more generally. Here, he outlines the typical historical (or prehistorical) process for naming a breed.

“But the mere existence of individual variability and of some few well-marked varieties, though necessary as the foundation for the work, helps us but little in understanding how species arise in nature. How have all those exquisite adaptations of one part of the organization to another part, and to the conditions of life, and of one distinct organic being to another being, been perfected? We see these beautiful co-adaptations most plainly in the woodpecker and mistletoe; and only a little less plainly in the humblest parasite which clings to the hairs of a quadruped or feathers of a bird; in the structure of the beetle which dives through the water; in the plumed seed which is wafted by the gentlest breeze; in short, we see beautiful adaptations everywhere and in every part of the world.”

Given that Darwin is investigating how species (and varieties) originate, he must necessarily uncover why creatures develop specific adaptations. He frequently reiterates that in the struggle for life, the main opponents (and occasionally allies) of an organism are other organisms. Sometimes, organisms co-adapt, or develop adaptations that alter their subtle relationships with other organisms or their physical surroundings. Viewing these adaptations in the context of a creature’s relationship to the environment is often more useful than simply focusing on the creature’s individual physiology.

“I have called this principle, by which each slight variation, if useful, is preserved, by the term Natural Selection, in order to mark its relation to man’s power of selection. We have seen that man by selection can certainly produce great results, and can adapt organic beings to his own uses, through the accumulation of slight but useful variations, given to him by the hand of Nature. But Natural Selection, as we shall hereafter see, is a power incessantly ready for action, and is as immeasurably superior to man’s feeble efforts, as the works of Nature are to those of Art.”

In this passage, Darwin compares natural selection, which subsequently becomes the book’s single most important concept, with domestic selection. In this characterization, domestic selection—that is, selection resulting from conscious human intervention—is an incomparably diminished version of the unconscious, endless process of natural selection. Breeders, Darwin writes, select for the specific resemblances in animals that may be of use to human motivations, whereas natural selection works to benefit the plant or animal itself. The impetus to change in domestic selection is external. The impetus to change in natural selection is internal and thus truer.

“In looking at Nature, it is most necessary to keep the foregoing considerations always in mind—never to forget that every single organic being around us may be said to be striving to the utmost to increase in numbers; that each lives by a struggle at some period of its life; that heavy destruction inevitably falls either on the young or old, during each generation or at recurrent intervals. Lighten any check, mitigate the destruction ever so little, and the number of the species will almost instantaneously increase to any amount.”

Darwin outlines one of the key principles of population control in the struggle for existence among competing lifeforms. Left unchecked by competitors, all lifeforms in time exponentially increase their numbers. Relationships between organisms are so tenuous and specific that small adaptations can tip the balance in a new direction.

“As man can produce and certainly has produced a great result by his methodical and unconscious means of selection, what may not nature effect? Man can act only on external and visible characters: nature cares nothing for appearances, except in so far as they may be useful to any being. She can act on every internal organ, on every shade of constitutional difference, on the whole machinery of life. Man selects only for his own good; nature only for that of the being which she tends […] How fleeting are the wishes and efforts of man! How short his time! And consequently, how poor will his products be, compared with those accumulated by nature during whole geological periods. Can we wonder, then, that nature’s productions should be far ‘truer’ in character than man’s productions; that they should be infinitely better adapted to the most complex conditions of life, and should plainly bear the stamp of far higher workmanship?”

Here, Darwin again develops the difference between natural and domestic selection, describing the latter as a mere shadow of the former. He implicitly adopts a metaphysical/epistemological hierarchy between internal, structural/constitutional differences and external appearances. Because natural selection develops primarily through internal changes, it’s truer to the essential task of survival. The survival of domesticated species, and the adjoining breeding programs, has comparably little relationship to the domesticated species’ existence. This kind of selection is, in a sense, less true because it’s externally and arbitrarily imposed.

“Natural selection can act only by the preservation and accumulation of infinitesimally small inherited modifications, each profitable to the preserved being; and as modern geology has almost banished such views as the excavation of a great valley by a single diluvial wave, so will natural selection, if it be a true principle, banish the belief of the continued creation of new organic beings, or of any great and sudden modification in their structure.”

Darwin frequently compares natural selection theory to the discoveries of geology, which reveal the extremely slow processes of interconnected changes and formations. Long-term, dynamic systems of change replace sudden upheaval as the standard orientation by which explanations of natural phenomena unfold. He hopes for this to overturn the prevailing 19th-century theory on the spontaneous, or instantaneous, creation of organisms. In Darwin’s view, we should everything in nature in terms of slow, steady—not sudden or immediate—change.

“As buds give rise by growth to fresh buds, and these, if vigorous, branch out and overtop on all sides many a feebler branch, 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.”

Darwin often uses a tree metaphor to explain the branching arms of species diversification from common parentage. As individuals undergo mutation, and species subsequently diversify according to the laws of natural selection, they branch off in various evolutionary directions. Eventually, like the dead branches of a tree, the intermediate varieties that link a species to its prehistoric parent usually become extinct.

“When we see any part or organ developed in a remarkable degree or manner in any species, the fair presumption is that it is of high importance to that species; nevertheless the part in this case is eminently liable to variation. Why should this be so? On the view that each species has been independently created, with all its parts as we now see them, I can see no explanation. But on the view that groups of species have descended from other species, and have been modified through natural selection, I think we can obtain some light.”

As in many other cases throughout the book, Darwin attempts to explain natural phenomena via natural selection instead of the prevalent theory of the time—independent creation of each species. Darwin systematically attempts to undercut this paradigm by revealing its impotence compared to natural selection. Thus, he shows that his theory has much greater explanatory power—that greater evidence supports it.

“On the ordinary view of each species having been independently created, why should that part of the structure, which differs from the same part in other independently-created species of the same genus, be more variable than those parts which are closely alike in the several species? I do not see that any explanation can be given. But on the view of species being only strongly marked and fixed varieties, we might surely expect to find them still often continuing to vary in those parts of their structure which have varied within a moderately recent period, and which have thus come to differ.”

Again, Darwin points to natural selection theory’s greater explanatory power than independent creation theory. In this case, the value of natural selection theory derives from a fundamental reconceptualization of “species.” Darwin redefines species such that they aren’t essentially distinct from varieties (but instead exist on a continuum) and thereby undercuts a basic definition on which independent creation theory depends.

“He who believes in separate and innumerable acts of creation will say that in these cases it has pleased the Creator to cause a being of one type to take the place of one of another type; but this seems to me only restating the fact in dignified language. He who believes in the struggle for existence and in the principle of natural selection, will acknowledge that every organic being is constantly endeavoring to increase in numbers; and that if any one being vary ever so little, either in habits or structure, and thus gain an advantage over some other inhabitant of the country, it will seize on the place of that inhabitant, however different it may be from its own place.”

Under natural selection theory, all organisms endeavor to increase the number of their species and thereby strive to propagate widely. The slightest change in an organism’s physical constitution, instinct, or other characteristic can eventually have a profound impact on its success and the success of its competitors. For example, a successful adaptation might lead to an organism’s overtaking another species in some geographical area. Darwin notes that people may gloss over these facts by rewriting them in language that makes species success appear to be the product of divine intervention. Darwin has strong scientific, philosophical, and dispositional aversions to this “dignified language.”

“To suppose that the eye, with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest possible degree. Yet reason tells me, that if numerous gradations from a perfect and complex eye to one very imperfect and simple, each grade being useful to its possessor, can be shown to exist; if further, the eye does vary ever so slightly, and the variations be inherited, which is certainly the case; and if any variation or modification in the organ be ever useful to an animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, though insuperable by our imagination, can hardly be considered real.”

Opponents of natural selection theory often cite the eye in their arguments. Darwin understands why. The eye is an organ that inspires awe. Still, Darwin notes that properly understanding and rationally applying the theory can address any difficulty our imagination may have in believing the eye is a product of natural selection. Darwin repeatedly notes that slow processes of change can yield incredible results, like the eye.

“It may be difficult, but we ought to admire the savage instinctive hatred of the queen-bee, which urges her instantly to destroy the young queens her daughters as soon as born, or to perish herself in the combat; for undoubtedly this is for the good of the community; and maternal love or maternal hatred, though the latter fortunately is most rare, is all the same to the inexorable principle of natural selection.”

In natural selection, organisms unconsciously select for behaviors that help propagate the species or community. Sometimes this yields behavioral results that we might find morally repugnant, like the “maternal hatred” with which queen bees attack their female offspring. From the viewpoint of the bee colony, however, this is a good thing because it maintains collective stability and uniformity. Darwin notes that the process of natural selection can be brutal or even seemingly amoral.

“He must be a dull man who can examine the exquisite structure of a comb, so beautifully adapted to its end, without enthusiastic admiration. We hear from mathematicians that bees have practically solved a recondite problem, and have made their cells of the proper shape to hold the greatest possible amount of honey, with the least possible consumption of precious wax in their construction.”

In his extended analysis of the structure of bees’ honeycombs, Darwin expresses great admiration for them and the unconscious process of natural selection that resulted in the beehive and honeycomb. Through steady modification, nature produced an extremely efficient system that, economically speaking, can’t be improved. Darwin adds that admiration for such natural phenomena is highly desirable.

“Beyond this stage of perfection in architecture, natural selection could not lead; for the comb of the hive-bee, as far as we can see, is absolutely perfect in economizing wax. Thus, as I believe, the most wonderful of all known instincts, that of the hive-bee, can be explained by natural selection having taken advantage of numerous, successive, slight modifications of simpler instincts; natural selection having by slow degrees, more and more perfectly, led the bees to sweep equal spheres at a given distance from each other in a double layer, and to build up and excavate the wax along the planes of intersection.”

Just as Darwin defends the human eye as the product of natural selection, he defends the honeycomb, which, he holds, has adapted to a point of perfection. Thus, from the viewpoint of the honeybee, natural selection has reached its final form. Bee colonies couldn’t more efficiently and precisely achieve their purpose, so natural selection to further update construction of the honeycomb is unnecessary.

“A man must for years examine for himself great piles of superimposed strata, and watch the sea at work grinding down old rocks and making fresh sediment, before he can hope to comprehend anything of the lapse of time, the monuments of which we see around us.”

Darwin often uses the geological record as a model for his views on biological development and the genealogical history of organisms. He focuses largely on the temporal dimensions of evolutionary change, which, he notes, require significant practice to understand. The world is an ancient place, and the products of natural selection reached their present forms over extremely long periods of time. Just as the geologist must study rocks for years to comprehend Earth’s age, the biologist must study natural history to understand natural selection.

“But we continually over-rate the perfection of the geological record, and falsely infer, because certain genera or families have not been found beneath a certain stage, that they did not exist before that stage. We continually forget how large the world is, compared with the area over which our geological formations have been carefully examined; we forget that groups of species may elsewhere have long existed and have slowly multiplied before they invaded the ancient archipelagoes of Europe and of the United States. We do not make due allowance for the enormous intervals of time, which have probably elapsed between our consecutive formations—longer perhaps in some cases than the time required for the accumulation of each formation.”

Many of Darwin’s contemporaries look to the geological record to disprove natural selection theory. For many reasons, especially the significant gaps and limitations of the fossil record, Darwin finds this rebuttal misguided. He thinks that people tend to focus too intently on the known sliver of the fossil record and are therefore prone to ignore how slight and insignificant that record is compared to the vastness of history, the imperfections of sedimentary remains, and the multitude of fossils yet undiscovered. Darwin consistently and vigorously objects to imprecise reasoning.

“I look at the natural geological record, as a history of the world imperfectly kept, and written in a changing dialect; of this history we possess the last volume alone, relating only to two or three countries. Of this volume, only here and there a short chapter has been preserved; and of each page, only here and there a few lines.”

Through the metaphor of a lost book with a smattering of imperfectly recovered lines of text, Darwin emphasizes the failures and limitations of the geological/fossil record. Again, he emphasizes the folly of attempting to assert definitive knowledge of the natural, genealogical history of species with such little information. Instead of glossing over the enormous gaps in the record, we ought to accept our ignorance, wait for further data, and understand that the record isn’t a master key to natural history. The closest we can come is his driving concept: natural selection.

“As the accumulation of each formation has often been interrupted, and as long blank intervals have intervened between successive formations, we ought not to expect to find, as I attempted to show in the last chapter, in any one or two formations all the intermediate varieties between the species which appeared at the commencement and close of these periods; but only moderately long as measured geologically, closely allied forms, or, as they have been called by some authors, representative species; and these we assuredly do find. We find, in short, such evidence of the slow and scarcely sensible mutation of specific forms, as we have a just right to expect to find.”

In this passage, Darwin progresses beyond defensively dismissing the value of the fossil record toward a positive account of its slight value in buttressing natural selection theory. Whereas his contemporaries often used the fossil record to dismiss natural selection, Darwin finds that when considering it appropriately (including its gaps), the fossil record provides useful supporting evidence of natural selection. This is one of many instances in which Darwin’s careful adherence to precise scientific and logical methodology reveals the clarity of his thinking.

“But the wide distribution of fresh-water plants and of the lower animals, whether retaining the same identical form or in some degree modified, I believe mainly depends on the wide dispersal of their seeds and eggs by animals, more especially by fresh-water birds, which have large powers of flight, and naturally travel from one to another and often distant piece of water. Nature, like a careful gardener, thus takes her seeds from a bed of a particular nature, and drops them in another equally well fitted for them.”

Another common criticism of Darwin’s theory appeals to the bizarreness of geographical distribution of certain species. If natural selection is a true principle of biological history, the odd distribution of similar species across portions of the globe seems, at first glance, inexplicable. Darwin uses his knowledge of freshwater birds and other creatures to discount these worries. In addition, he provides speculative histories of seed distribution to explain the spread of plants across time and place.

“The ingenuity and utility of this system are indisputable. But many naturalists think that something more is meant by the Natural System; they believe that it reveals the plan of the Creator; but unless it be specified whether order in time or space, or what else is meant by the plan of the Creator, it seems to me that nothing is thus added to our knowledge. Such expressions as that famous one of Linnaeus, and which we often meet with in a more or less concealed form, that the characters do not make the genus, but that the genus gives the characters, seem to imply that something more is included in our classification, than mere resemblance. I believe that something more is included; and that propinquity of descent—the only known cause of the similarity of organic beings—is the bond, hidden as it is by various degrees of modification, which is partially revealed to us by our classifications.”

In the penultimate chapter, “Mutual Affinities of Organic Beings,” Darwin discusses the problems of taxonomy and species classification. He notes that all organic beings are part of one system of divergences and interrelations. Taxonomic organization shouldn’t group organisms together based solely on shared resemblances because this doesn’t support the underlying principle that unifies the creatures. Instead, taxonomic organization should be based on “propinquity of descent”—that is, closeness of kinship or shared ancestral history. This manner of organization reflects an adherence to the principle of natural selection.

“Rudimentary organs may be compared with the letters in a word, still retained in the spelling, but become useless in the pronunciation, but which serve as a clue in seeking for its derivation. On the view of descent with modification, we may conclude that the existence of organs in a rudimentary, imperfect, and useless condition, or quite aborted, far from presenting a strange difficulty, as they assuredly do on the ordinary doctrine of creation, might even have been anticipated, and can be accounted for by the laws of inheritance.”

The strange phenomena of rudimentary organs (parts of an organism that are of little or no use and may be diminished in size and value) is inexplicable from the viewpoint of independent creation. From Darwin’s viewpoint, on the other hand, they’re easily explicable and even provide insight into a creature’s evolution. This is one of many problems in biology that Darwin uses to reveal the vast explanatory power of natural selection theory compared to the independent creation paradigm that most of his contemporaries accepted.

“I should infer from analogy that probably all the organic beings which have ever lived on this earth have descended from some one primordial form, into which life was first breathed.”

Although he implicitly states this idea throughout the book, Darwin draws this (radical) conclusion only at the end. Darwin notes that it’s quite possible, especially given a natural system in which all life forms share common parentage, that all life on Earth has a single origin. Even though most people today may tacitly hold this view, it directly countered the predominant scientific (and religious) views of Darwin’s mid-19th century counterparts. He alludes to this only once (and very briefly), presumably because of its revolutionary implications, which most at the time considered imprudent and incautious to fully embrace.