* Darwin begins THE ORIGIN OF SPECIES with a survey of his ideas, with the final edition also featuring a survey of their historical predecessors. The first chapter gives an overview of the variation of form of domestic animals, with chapter 2 providing a discussion of the similar variation in wild animals. That done, in chapter 3 Darwin showed that there was a struggle for existence among organisms, that more were born than could survive.
* The introduction to THE ORIGIN OF SPECIES reflects on the voyage around the globe Charles Darwin took on the British Royal Navy brig HMS BEAGLE from 1831 to 1836. The BEAGLE was on a survey mission, and Darwin was on board as a naturalist, performing observations at the ship's many stops. When he returned home to England, he began to assimilate his experiences and consider their implications, fleshing out his ideas for more than 20 years. As Darwin put it:
BEGIN_QUOTE:
When on board HMS BEAGLE, as naturalist, I was much struck with certain facts in the distribution of the inhabitants of South America, and in the geological relations of the present to the past inhabitants of that continent. These facts seemed to me to throw some light on the origin of species -- that mystery of mysteries, as it has been called by one of our greatest philosophers.
On my return home, it occurred to me, in 1837, that something might perhaps be made out on this question by patiently accumulating and reflecting on all sorts of facts which could possibly have any bearing on it. After five years' work I allowed myself to speculate on the subject, and drew up some short notes; these I enlarged in 1844 into a sketch of the conclusions, which then seemed to me probable: from that period to the present day I have steadily pursued the same object.
END_QUOTE
"From that period to the present day" was 15 years, and Darwin had not been at all idle during that time. In fact, he likely wouldn't have gone public in 1859 except for the fact that a young field naturalist named Alfred Russel Wallace had, by coincidence, sent Darwin a paper that echoed Darwin's own ideas. Darwin had to go public to maintain his priority; he was careful to state that Wallace had "arrived at almost exactly the same general conclusions that I have on the origin of species." Wallace appreciated that Darwin had built up a more substantial body of research on the concept, and was pleased at sharing the credit with Darwin.
In any case, after giving the background of THE ORIGIN OF SPECIES and praising his allies, Darwin got down to business:
BEGIN_QUOTE:
In considering The Origin Of Species, it is quite conceivable that a naturalist, reflecting on the mutual affinities of organic beings, on their embryological relations, their geographical distribution, geological succession, and other such facts, might come to the conclusion that each species had not been independently created, but had descended, like varieties from other species. ["Varieties" were another term for "breeds" or "races", with "varieties" usually referring to plants -- though Darwin wasn't entirely consistent in his usage, sometimes referring to "races" of cabbages.]
Nevertheless, such a conclusion, even if well founded, would be unsatisfactory, until it could be shown how the innumerable species inhabiting this world have been modified, so as to acquire that perfection of structure and co-adaptation which most justly excites our admiration. Naturalists continually refer to external conditions, such as climate, food, [and so on], as the only possible cause of variation.
In one very limited sense, as we shall hereafter see, this may be true; but it is preposterous to attribute to mere external conditions, the structure, for instance, of the woodpecker, with its feet, tail, beak, and tongue, so admirably adapted to catch insects under the bark of trees. In the case of the misseltoe, which draws its nourishment from certain trees, which has seeds that must be transported by certain birds, and which has flowers with separate sexes absolutely requiring the agency of certain insects to bring pollen from one flower to the other, it is equally preposterous to account for the structure of this parasite, with its relations to several distinct organic beings, by the effects of external conditions, or of habit, or of the volition of the plant itself.
END_QUOTE
Darwin chose as one of his first of many examples the woodpecker, an animal that most of his readers would find perfectly familiar. What he was pointing out with the woodpecker was that, while organisms were adapted to their conditions -- of course they were, if they weren't they would die out, which was something of a clue in itself -- their adaptations said nothing of how they had arrived at that state. He added that popular notions of the emergence of new species, in which "some bird had given birth to a woodpecker, and some plant to the misseltoe, and that these had been produced perfect as we now see them" were not real explanations either, since such events had never been observed, and it was hard to think of why they would. How could some arbitrary bird just somehow produce a woodpecker?
What Darwin did see was that animals and plants domesticated by humans had been reshaped, sometimes almost out of recognition, from their wild ancestors, and a thorough investigation of the variation of organisms under domestication might well have insights into the variation of organisms in the wild.
Variation was only part of the equation, however. Darwin had been influenced by the work of the English economist Thomas Malthus, whose ESSAY ON THE PRINCIPLE OF POPULATION, published in 1798, suggested that organisms are capable of breeding until they outstrip their food supply, inevitably leading to competition for resources. Those members of a species whose variations gave them an edge in the struggle for existence would tend to prosper, while those with variations that were a disadvantage would gradually die out:
BEGIN_QUOTE:
As many more individuals of each species are born than can possibly survive; and as, consequently, there is a frequently recurring struggle for existence, it follows that any being, if it vary however slightly in any manner profitable to itself, under the complex and sometimes varying conditions of life, will have a better chance of surviving, and thus be naturally selected.
END_QUOTE [Darwin's italics]
Plant and animal breeders used selective breeding or "artificial selection" to enhance features they desired in livestock or crop plants; all Darwin was saying was that the environment itself could perform a similar process, driving gradually improved adaptation through what he called, in contrast to artificial selection, "natural selection".
Darwin realized that there might be skepticism that natural selection could account for elaborate organs such as the eye or the equally elaborate patterns of instinctive behavior of animals. He believed that these issues could be addressed, and that the evidence from cross-breeding or "hybridization" of different varieties and species; from the fossil record; from the geographical distribution of different species; and from the structural similarities or "affinities" between different species all helped support his argument. The rest of THE ORIGIN OF SPECIES explored these issues in detail.
At the end of the introduction Darwin concluded, in a confident but characteristically cautious fashion:
BEGIN_QUOTE:
Although much remains obscure, and will long remain obscure, I can entertain no doubt, after the most deliberate study and dispassionate judgement 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, in the same manner as the acknowledged varieties of any one species are the descendants of that species. Furthermore, I am convinced that Natural Selection has been the main but not exclusive means of modification.
END_QUOTE
BACK_TO_TOP* The final edition of THE ORIGIN OF SPECIES included a preface in which Darwin fussily made sure that credit was given where credit was due. The idea of evolution of species was not at all new, and the notion of natural selection had even been considered well before the publication of THE ORIGIN OF SPECIES. Darwin was, however, the first to come up with a coherent theory based on such concepts, and flesh it out in persuasive detail.
Darwin identified as first in the list of prophets with honor the French naturalist Jean-Baptiste Pierre Antoine de Monet, Chevalier de Lamarck, who had published several influential documents on his evolutionary concepts a half-century earlier. Darwin noted that Lamarck's works upheld "the doctrine that species, including man, are descended from other species" and that Lamarck was a pioneer in "arousing attention to the probability that all change in the organic, as well as the inorganic world, being the result of law, and not of miraculous interposition."
Lamarck believed that species evolved, and that they did so through their "needs and strivings" and the "inheritance of acquired characteristics". A giraffe stretched its neck to reach the leaves on the higher branches of trees; it passed its longer neck down to its descendants, whose "needs and strivings" then resulted in a still longer neck. Today, Lamarck is mostly remembered for his concept of "inheritance of acquired characteristics", which we know is wrong. Any scheme at the biochemical level that would be able to "read" the physical changes in an organism during its lifetime and then encode them so they could be passed on to descendants would be very elaborate; we know a great deal about biochemistry these days, and there's no trace of any such elaborate system.
There is some, often disputed, evidence for the inheritance of acquired characteristics in certain fine-print cases; and in the 21st century, we have acquired a deep appreciation of how the "microbiome" -- the community of microorganisms that live on and in us, mostly in the lower digestive tract, being passed down from mother to offspring -- influence our evolution. However, even giving Lamarck the benefit of the doubt, he was still generally wrong. However, Lamarck not only promoted the idea of evolution of organisms, he also was one of the first to propose a mechanism by which it might happen.
In 1813, an American doctor named William Charles Wells had published a paper that would prove extremely perceptive in hindsight, neatly anticipating THE ORIGIN OF SPECIES. As Darwin put it:
BEGIN_QUOTE:
In this paper [Wells] distinctly recognizes the principle of natural selection, and this is the first recognition which has been indicated; but he applies it only to the races of man, and to certain characters alone. After remarking that negroes and mulattoes enjoy an immunity from certain tropical diseases, he observes, firstly, that all animals tend to vary in some degree, and, secondly, that agriculturists improve their domesticated animals by selection [...]
END_QUOTE
Darwin then provided a citation directly from Wells:
BEGIN_QUOTE:
[What is done by agriculturists] by art, seems to be done with equal efficacy, though more slowly, by nature, in the formation of varieties of mankind, fitted for the country which they inhabit. Of the accidental varieties of man, which would occur among the first few and scattered inhabitants of the middle regions of Africa, some one would be better fitted than others to bear the diseases of the country. This race would consequently multiply, while the others would decrease; not only from their in ability to sustain the attacks of disease, but from their incapacity of contending with their more vigorous neighbours.
The colour of this vigorous race I take for granted, from what has been already said, would be dark. But the same disposition to form varieties still existing, a darker and a darker race would in the course of time occur: and as the darkest would be the best fitted for the climate, this would at length become the most prevalent, if not the only race, in the particular country in which it had originated.
END_QUOTE
The implication in this quote that dark skin color was linked to resistance against tropical disease was off target, since the skin color had little or nothing to do with resistance against disease; dark skin simply provided greater protection against the hot tropical sun. Wells' general thinking, however, was completely on target. People from tropical regions who didn't have resistance to the diseases common there died off, leaving fewer descendants than those who remained healthy and created populations with a resistance to those diseases. White-skinned Europeans who hadn't lived in tropical environments had not acquired resistance to such diseases through the same ugly winnowing of their ancestors, and Europeans suffered badly when they went to the tropics in those days.
Other noteworthies in Darwin's list included:
That was the only mention of Spencer in THE ORIGIN OF SPECIES, but he would become the godfather of a movement known as "Social Darwinism", in which the concept of "survival of the fittest" -- originally Spencer's phrase, not Darwin's, though Darwin came to like it -- was applied to human society. Ruthless capitalists, imperialists, and fascists would find Social Darwinism attractive, interpreting it as a "scientific" justification for the far older "predator ethic" or "might makes right".
Social Darwinism would eventually be discredited. Fortunately, Darwin himself never endorsed the concept, finding Spencer's work to be more speculative generalities than serious science, and explicitly rejected the dodgy idea that evolutionary science could be used as the basis of moral principle. However, true to his ideas, Darwin did think that moral principles might well be the product of natural selection, writing in his later book DESCENT OF MAN that natural selection "may be safely [regarded as the source of] the social instincts which afforded the basis for the development of the moral sense."
In any case, THE ORIGIN OF SPECIES said little about the ethical implications of evolutionary ideas one way or another. If evolution by natural selection was the way the world actually worked -- and Darwin believed the evidence showed that it was -- then it was a fact that had to be accepted, like it or not. Valid ethical arguments might be raised over the implications of that fact, but they could not alter the fact in the slightest. To anyone who had protested, centuries earlier, against the idea that the Earth went around the Sun instead of the reverse, the only answer was: It moves nonetheless.
BACK_TO_TOP* Chapter 1 of THE ORIGIN OF SPECIES considered the variation of domesticated organisms. As Darwin pointed out, there was considerable variation among domesticated organisms, with new varieties continuously being produced by plant and animal breeders even among organisms that had been domesticated for a long time:
BEGIN_QUOTE:
No case is on record of a variable being ceasing to be variable under cultivation. Our oldest cultivated plants, such as wheat, still often yield new varieties: our oldest domesticated animals are still capable of rapid improvement or modification.
END_QUOTE
At least as far as had been observed for domesticated species, variability wasn't something that organisms eventually "ran out of". As far as the origins of that variability went, Darwin could only offer vague generalities: "I am strongly inclined to suspect that the most frequent cause of variability may be attributed to the male and female reproductive elements having been affected prior to the act of conception."
That was true as far as it went, but it didn't go very far. Ironically, the initial basis for understanding this variability was established in a paper published in 1866, only seven years after the first publication of THE ORIGIN OF SPECIES, by a Catholic monk named Gregor Johan Mendel, born in Moravia, now part of the Czech Republic. Mendel's paper focused on the breeding of pea plants, showing that the various "traits" of the pea plant -- color of flowers, color of peas, height, and so on -- seemed to reside in discrete "factors", as Mendel called them. It was as though these factors were cards in a deck, with different "hands" dealt to the pea plants from generation to generation.
Mendel's work was ignored at the time. Darwin never even heard of the paper, and in fact it wasn't until the beginning of the 20th century that other researchers duplicated Mendel's work, to then rediscover his paper. Over the following decades, biologists acquired a working understanding of the mechanisms of inheritance, or "heredity", realizing that the "code" for an organism resided in the threadlike "chromosomes" in the heart of a cell; and then determining that the active element of the chromosomes was a long, chainlike molecule named "deoxyribonucleic acid (DNA)". A DNA molecule consists of a long double spiral chain, resembling a twisted ladder, with information encoded by the arrangement of four different types of molecular subunits, or "bases". The DNA molecules in the chromosomes are divided into functional blocks, called "genes", that correspond to Mendel's factors; the sum of all the information encoded in the chromosomes of any particular organism is referred to as that organism's "genome".
Much of the variability observed by plant and animal breeders was caused by the shuffling of genes from the parents in the course of breeding. The shuffling ensured a great deal of variation, with the variation enhanced by the fact that genes sometimes underwent "mutations" or spontaneous modifications of their coding, producing "mutant" organisms with features never seen before in their ancestry.
Selective breeders of Darwin's time knew nothing of these matters, but they were able to observe plants and animals, spot desireable traits, and then work to breed those organisms to propagate those traits. It was not always easy to do, since sets of traits, both wanted and unwanted, tended to be propagated together; and it was also difficult to get a variety to "breed true" so that the desired traits uniformly appeared in successive generations. As Darwin pointed out, there was also variation in organisms that seemed to arise after conception -- as we know now, the processes of development in the growth of an organism are complicated and can be affected by the environment, meaning that two organisms that started out with exactly the same genome would not grow up to be perfectly identical.
Darwin, always painfully thorough, was perfectly up-front about his lack of understanding of the rules of inheritance, writing:
BEGIN_QUOTE:
The laws governing inheritance are quite unknown; no one can say why the same peculiarity in different individuals of the same species, and in individuals of different species, is sometimes inherited and sometimes not so; why the child often reverts in certain characters to its grandfather or grandmother or other much more remote ancestor; why a peculiarity is often transmitted from one sex to both sexes or to one sex alone, more commonly but not exclusively to the like sex.
END_QUOTE
In any case, the variability of domesticated organisms was obvious beyond reasonable dispute. Dogs were a spectacular example, ranging in form from greyhounds to bulldogs to mastiffs to pekinese. Nobody could credibly deny that they were derived from wild ancestors, such as wolves or foxes -- incidentally, we know today from comparisons of wolf and dog DNA that all dogs are descended from wolves, in fact all dogs are more closely related to wolves than coyotes are. There was no way most dogs could survive in the wild -- and so they had to be human cultivations, all derived from a set of common wild ancestors.
Incidentally, Darwin got that fact wrong in chapter 1, saying that he didn't believe that "all our dogs have descended from one wild species." Obviously, even he found it too wild to think it plausible that so much variation could have been obtained from a single source; although Darwin's modern critics accuse him of unrestrained imagination, in many cases his error was that he wasn't imaginative enough.
Darwin was particularly intrigued by one domesticated organism, the pigeon. As he wrote: "Believing that it is always best to study some special group, I have, after deliberation, taken up domestic pigeons." He fell in love with the birds, and his enthusiasm shows with the obvious pride in which he wrote: "I have associated with several eminent fanciers, and have been permitted to join two of the London Pigeon Clubs." However, they were also an excellent choice for experimental subjects, being relatively easy to rear, able to mature and breed rapidly, and in particular exhibiting a vivid and wide range of variation. Darwin elaborated at length on the diversity in form of the pigeon:
BEGIN_QUOTE:
Compare the English carrier and the short-faced tumbler [pigeons], and see the wonderful difference in their beaks, entailing corresponding differences in their skulls. The carrier, more especially the male bird, is also remarkable from the wonderful development of the carunculated skin about the head, and this is accompanied by greatly elongated eyelids, very large external orifices to the nostrils, and a wide gape of mouth. The short-faced tumbler has a beak in outline almost like that of a finch; and the common tumbler has the singular and strictly inherited habit of flying at a great height in a compact flock, and tumbling in the air head over heels.
The runt is a bird of great size, with long, massive beak and large feet; some of the sub-breeds of runts have very long necks, others very long wings and tails, others singularly short tails. The barb is allied to the carrier, but, instead of a very long beak, has a very short and very broad one. The pouter has a much elongated body, wings, and legs; and its enormously developed crop, which it glories in inflating, may well excite astonishment and even laughter.
The turbit has a very short and conical beak, with a line of reversed feathers down the breast; and it has the habit of continually expanding slightly the upper part of the oesophagus. The Jacobin has the feathers so much reversed along the back of the neck that they form a hood, and it has, proportionally to its size, much elongated wing and tail feathers. The trumpeter and laugher, as their names express, utter a very different coo from the other breeds.
The fantail has thirty or even forty tail-feathers, instead of twelve or fourteen, the normal number in all members of the great pigeon family; and these feathers are kept expanded, and are carried so erect that in good birds the head and tail touch; the oil-gland is quite aborted. Several other less distinct breeds might have been specified.
[...] Altogether at least a score of pigeons might be chosen, which if shown to an ornithologist, and he were told that they were wild birds, would certainly, I think, be ranked by him as well-defined species. [...] Great as the differences are between the breeds of pigeons, I am fully convinced that the common opinion of naturalists is correct, namely, that all have descended from the rock-pigeon (Columba livia), including under this term several geographical races or sub-species, which differ from each other in the most trifling respects.
END_QUOTE
Domestic pigeons could be easily crossbred even when the mates had very different features, suggesting they were all closely related and derived from common stock. No wild pigeons resembled exotic domestic pigeons in their unusual features, and though the domestication of pigeons stretched back into vague antiquity -- Darwin noted they were mentioned in Egyptian writings from 3000 BCE -- it strained credibility to think that there had once been such exotic pigeons in the wild, with humans domesticated a range of such breeds, which then all conveniently went extinct. Darwin's conclusion was that all the wild variation in breeds of domestic pigeons had been derived from one, repeat one, wild species, the rock pigeon.
On surveying the range of forms of domestic organisms in general, it was much more a simple observation than a brilliant stroke of insight to see that these organisms had been cultivated through the careful supervision of selective breeders, working patiently on their subjects over numerous generations:
BEGIN_QUOTE:
[When] we compare the dray-horse and race-horse, the dromedary and camel, the various breeds of sheep fitted either for cultivated land or mountain pasture, with the wool of one breed good for one purpose, and that of another breed for another purpose; when we compare the many breeds of dogs, each good for man in very different ways; when we compare the game-cock, so pertinacious in battle, with other breeds so little quarrelsome, with "everlasting layers" which never desire to sit, and with the bantam so small and elegant; when we compare the host of agricultural, culinary, orchard, and flower-garden races of plants, most useful to man at different seasons and for different purposes, or so beautiful in his eyes, we must, I think, look further than to mere variability.
We cannot suppose that all the breeds were suddenly produced as perfect and as useful as we now see them; indeed, in several cases, we know that this has not been their history. The key is man's power of accumulative selection: nature gives successive variations; man adds them up in certain directions useful to him. In this sense he may be said to make for himself useful breeds.
The great power of this principle of selection is not hypothetical. [...] Breeders habitually speak of an animal's organisation as something quite plastic, which they can model almost as they please. [...] That most skilful breeder, Sir John Sebright, used to say, with respect to pigeons, that "he would produce any given feather in three years, but it would take him six years to obtain head and beak."
END_QUOTE
The breeders did not create the variation; they simply exploited the variation inherent in the species they were working with, and in many cases their breeding activities simply exploited some unexpected and interesting variation with no particular goal in mind. As Darwin pointed out, the pigeon breeders who produced the ancestors of the fantail had no concept of the ultimate result of their work; they simply noticed that some pigeons had extra tailfeathers, found them amusing, and kept selectively breeding such pigeons until, generations later, the pigeons had extravagant tails. Much the same has been done by goldfish breeders, coming up with fancy variants with double tails or bubble eyes.
BACK_TO_TOP* Having pointed to the obvious variability of domesticated organisms, in chapter 2 of THE ORIGIN OF SPECIES, Darwin then argued that species in nature demonstrated a similar variability. It seemed a reasonable enough idea, and he had mentioned in the previous chapter that there was no strong reason to suspect that domesticated species were inherently more or less variable than wild ones:
BEGIN_QUOTE:
It has often been assumed that man has chosen for domestication animals and plants having an extraordinary inherent tendency to vary, and likewise to withstand diverse climates. I do not dispute that these capacities have added largely to the value of most of our domesticated productions; but how could a savage possibly know, when he first tamed an animal, whether it would vary in succeeding generations, and whether it would endure other climates?
Has the little variability of the ass or guinea-fowl, or the small power of endurance of warmth by the reindeer, or of cold by the common camel, prevented their domestication? I cannot doubt that if other animals and plants, equal in number to our domesticated productions, and belonging to equally diverse classes and countries, were taken from a state of nature, and could be made to breed for an equal number of generations under domestication, they would vary on an average as largely as the parent species of our existing domesticated productions have varied.
END_QUOTE
That was essentially all that Darwin really needed to say about the matter. There were plenty of examples of wild organisms that were obviously very similar, while featuring a wide range of variation -- for example garter snakes, which all look alike except in terms of a diversity in coloration, changing from locale to locale. Darwin felt that a wide range of such examples could be provided, but being unwilling to go to too much length, he instead engaged in a discussion of the distinction between "species" and "varieties".
Chapter 2 has a sketchy, somewhat digressive feel to it, and indeed Darwin himself described it as "short & dry" in an 1859 letter listing the chapter titles of THE ORIGIN. Variability of organisms in nature was easily observed; there's no good reason to doubt it. Take any reasonable bird-watcher's guide and look up, say, seagulls, and there's a range of variations on the seagull theme -- seagulls with differences in markings, size, minor features. Given the variability of domesticated species, would it seem preposterous to think that wild seagulls might well be variations that shared common ancestors, just as did domestic pigeons? If not, then what real explanation could be provided for the variations? Were the different seagulls just made that way? That less explains the matter than simply shrugs it off.
The example of seagulls is no unusual exception, either. Given almost any wild organism -- mice, frogs, hummingbirds, oak trees -- there is a similar range of variation. Organisms are not at all like mass-produced machines, with individuals being far more variable than items in any production batch of a machine. That range of variation makes neatly categorizing organisms difficult. Cats and dogs are clearly distinct species, they can't be crossbred, but what about different types of cats? Housecats and tigers can't be crossbred, but housecats can crossbreed with some wildcats. The important thing is the evident variation, and quibbling over whether a set of organisms amounted to different species or varieties of a same species was of less importance. In fact, in the next chapter Darwin commented:
BEGIN_QUOTE:
It is immaterial for use whether a multitude of doubtful forms be called species or sub-species or varieties; what rank, for instance, the two or three hundred doubtful forms of British plants are entitled to hold, if the existence of any well-marked varieties be admitted.
END_QUOTE
The impression is that Darwin was simply trying to defuse potential objections to his theory based on legalistic nitpicking about the distinction between species and varieties. That having been done, he moved on to more substantial matters.
BACK_TO_TOP* Early in chapter 3 of THE ORIGIN OF THE SPECIES, Darwin re-introduced his concept of evolution by natural selection:
BEGIN_QUOTE:
Owing to [the] struggle for life, any variation, however slight and from whatever cause proceeding, if it be in any degree profitable to an individual of any species, in its infinitely complex relations to other organic beings and to external nature, will tend to the preservation of that individual, and will generally be inherited by its offspring. The offspring, also, will thus have a better chance of surviving, for, of the many individuals of any species which are periodically born, but a small number can survive.
I have called this principle, by which each slight variation, if useful, is preserved, by the term of 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.
END_QUOTE [italics added]
Darwin here solidly chained the concept of artificial selection of domestic organisms performed by human breeders to selection of wild organisms by nature. Not only did Darwin see natural selection as a workable concept, he saw it as more effective than artificial selection, at least over the long run. In natural selection, the breeder was the Grim Reaper, choosing between the survival and extinction of a species. Human breeders might not always be alert or diligent, but the Grim Reaper never tired, never missed anything important to the survival of an organism.
Of course, this was describing the concept in the most stark and brutal terms. Although the concept of natural selection did feature as a significant component the raw struggle for survival between predator and prey, Darwin pointed out that it was subtler than that, there was more to it than just vicious competition:
BEGIN_QUOTE:
I should premise that I use the term Struggle for Existence in a large and metaphorical sense, including dependence of one being on another, and including (which is more important) not only the life of the individual, but success in leaving progeny.
END_QUOTE
Note how Darwin commented that "success in leaving progeny" was more important than survival of the individual. The "struggle for existence" might be better seen as the "struggle to create the next generation". A plant with flowers that were more attractive to pollinators -- brighter colors, stronger smell -- than the flowers of other plants of the same species was likely to be more successful in producing offspring.
It didn't even have to be more than slightly more successful. After Darwin's time, biologists would examine the cumulative effects of such a "selective advantage" and mathematically show that the gradual accumulation of offspring with such an advantage would result, in a few hundred or thousand generations, in their complete domination of the population of their species. That is exactly the same power as compounded interest on a bank account, but applied for vast millenniums of time.
* The struggle for existence was an obvious consequence of the fact that organisms will reproduce until they outstrip their food supply:
BEGIN_QUOTE:
A struggle for existence inevitably follows from the high rate at which all organic beings tend to increase. Every being, which during its natural lifetime produces several eggs or seeds, must suffer destruction during some period of its life, and during some season or occasional year, otherwise, on the principle of geometrical increase, its numbers would quickly become so inordinately great that no country could support the product.
Hence, as more individuals are produced than can possibly survive, there must in every case be a struggle for existence, either one individual with another of the same species, or with the individuals of distinct species, or with the physical conditions of life. It is the doctrine of Malthus applied with manifold force to the whole animal and vegetable kingdoms; for in this case there can be no artificial increase of food, and no prudential restraint from marriage. Although some species may be now increasing, more or less rapidly, in numbers, all cannot do so, for the world would not hold them.
END_QUOTE
Organisms replicate at a rate that, if left unchecked, would lead to open-ended population growth. If two mice were bred and doubled their numbers in a year, then if the process were continued without culling, within about 60 years, mice would completely carpet the Earth, and within about 30 more years the mass of mice would exceed that of the entire planet. That simply cannot happen. Larger animals may reproduce much more slowly, but that doesn't change the situation -- sooner or later, the growth in their populations will be curtailed. Darwin knew that when conditions were very favorable to a species, it could undergo a population boom, its numbers growing rapidly:
BEGIN_QUOTE:
In looking at Nature, it is most necessary to [never] 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. The face of Nature may be compared to a yielding surface, with ten thousand sharp wedges packed close together and driven inwards by incessant blows, sometimes one wedge being struck, and then another with greater force.
END_QUOTE
The checks on numbers were competition for food, predation, climate change, and epidemics in a "web of complex relations" between organisms -- Darwin's "ten thousand sharp wedges" being one of the most memorable notions in his work. Incidentally, Darwin makes a comment here that seems a bit puzzling to a modern reader, pointing out that some epidemics were due to parasitic worms and so represented an adversarial struggle between parasite and host. It comes as something of a surprise to realize that, since the pathogen theory of infectious disease was not commonly accepted in Darwin's era.
Looking ahead to later chapters, Darwin pointed out that this struggle for existence was linked to the features of organisms:
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A corollary of the highest importance may be deduced [ -- ] namely, that the structure of every organic being is related, in the most essential yet often hidden manner, to that of all other organic beings, with which it comes into competition for food or residence, or from which it has to escape, or on which it preys.
This is obvious in the structure of the teeth and talons of the tiger; and in that of the legs and claws of the parasite which clings to the hair on the tiger's body. But in the beautifully plumed seed of the dandelion, and in the flattened and fringed legs of the water-beetle, the relation seems at first confined to the elements of air and water. Yet the advantage of plumed seeds no doubt stands in the closest relation to the land being already thickly clothed by other plants; so that the seeds may be widely distributed and fall on unoccupied ground. In the water-beetle, the structure of its legs, so well adapted for diving, allows it to compete with other aquatic insects, to hunt for its own prey, and to escape serving as prey to other animals.
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