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Darwin's On the Origin of Species: A Modern Rendition

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Charles Darwin’s most famous book On the Origin of Species is without question, one of the most important books ever written. While even the grandest works of Victorian English can prove difficult to modern readers, Darwin wrote his text in haste and under intense pressure. For an era in which Darwin is more talked about than read, Daniel Duzdevich offers a clear, modern English rendering of Darwin’s first edition. Neither an abridgement nor a summary, this version might best be described as a "translation" for contemporary English readers. A monument to reasoned insight, the Origin illustrates the value of extensive reflection, carefully gathered evidence, and sound scientific reasoning. By removing the linguistic barriers to understanding and appreciating the Origin, this edition aims to bring 21st-century readers into closer contact with Darwin’s revolutionary ideas.

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1 Variation under Domestication

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IN CONSIDERING THE INDIVIDUALS OF A DOMESTICATED plant or animal variety, it is striking that they are generally more diverse than those belonging to varieties or species in the wild. The vast diversity of domesticated organisms, which have varied under many different climates and treatments, suggests that greater variability results from the conditions under which domestication occurs – conditions unlike those encountered by the parent species in the wild. This variability may partly be connected with excess food, as proposed by Andrew Knight. It seems clear that organisms must be exposed to a new environment over several generations for it to cause appreciable variation, and once organization begins to vary, it usually continues to do so for many generations. There is no case of a variable organism ceasing to be variable under domestication. Established domesticated plants such as wheat still often yield new varieties, and animals domesticated long ago are still capable of rapid improvement or modification.

 

2 Variation in Nature

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BEFORE APPLYING THE PRINCIPLES FROM THE LAST CHAPTER to living things in the wild, we need to establish whether or not they too are subject to variation. A proper treatment of this topic would involve a long catalog of dry facts, but I will reserve this for my future work. And I won’t discuss the various definitions of “species,” because no one definition satisfies all naturalists, even though everyone vaguely knows what it means. Generally, the term includes an unknown element of a distinct act of creation. “Variety” is almost as difficult to define, but in this case community of descent is often implied even though it can rarely be proven. There are also monstrosities – by which I mean considerable structural deviations that are either harmful or useless to the species and not usually propagated – but these graduate into variations. Some authors use the term “variation” in a technical sense to indicate an un-inheritable modification resulting from environmental conditions, but the dwarfed shells of brackish Baltic waters, dwarfed plants of alpine summits, and the thickened fur of animals living far north might be inherited for at least a few generations, and in such cases I would call the form a variety.

 

3 The Struggle for Existence

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BEFORE DISCUSSING THE STRUGGLE FOR EXISTENCE, I NEED to show how it is relevant to natural selection. As mentioned in the previous chapter, individual organisms in the wild vary from one another. (I am not aware that this has ever been disputed.) It is not important whether a multitude of doubtful forms are called “species,” “sub-species,” or “varieties.” For example, what rank the two or three hundred doubtful British plants are entitled to hold is immaterial if the existence of any well-marked varieties is accepted. The existence of individual variability and of well-marked varieties is a necessary foundation, but does not help explain how species arise. How have all the exquisite adaptations of one part of the organization to another and of living things to their environments – including other living things – been perfected? We see beautiful coadaptations in the woodpecker and mistletoe, in the humblest parasite that clings to the hairs of a quadruped or the feathers of a bird, in the structure of a beetle that dives through water, and in the plumed seed that is wafted by the gentlest breeze. In short, we see beautiful adaptations in every part of the organic world.

 

4 Natural Selection

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HOW DOES THE STRUGGLE FOR EXISTENCE INFLUENCE VARIAtion? Does selection – so potent in human hands – apply in nature? I think it does, most effectively. Recall the strength of heredity and the endless peculiarities in domesticated organisms, and to a lesser extent in wild organisms. (Under domestication the whole organization becomes somewhat plastic.) Also recall the complex and close-fitting relationships of all organisms to one another and to their physical environments. If variations useful to humans have occurred, then surely variations useful to each organism in the great and complex battle of life also sometimes occur in the course of thousands of generations. Accepting this and adding that many more individuals are born than can possibly survive, can it be doubted that those with even a slight advantage will have the best chance of surviving and propagating their kind? Moreover, it is certain that even slightly detrimental variations are destroyed. I call this preservation of favorable variations and rejection of detrimental variations “natural selection.” Variations that are neither useful nor detrimental are not affected by natural selection and remain a fluctuating element, perhaps as observed in so-called polymorphic species.

 

5 Variation

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IN EARLIER CHAPTERS I SOMETIMES IMPLIED THAT VARIAtions are due to chance. Of course this is completely incorrect, but it illustrates our ignorance of the causes of variation. Some authors believe that the reproductive system functions in creating offspring that are similar to the parents and in generating individual differences or slight structural deviations, but the great frequency of variability and monstrosity under domestication suggests that structural deviations somehow result from the environment endured by parents and their ancestors over several generations. I remark in chapter 1 that the reproductive system is particularly susceptible to environmental changes. (Proving this requires a long catalog of facts that cannot fit here.) The varying and plastic condition of offspring results mainly from the functional disturbance of the reproductive system in parents, with the reproductive elements seemingly affected before fertilization.1 It is unknown why a disturbed reproductive system should cause this or that part of an organism to vary more than usual. We can nevertheless occasionally catch hints and recognize that there must be some cause for each structural deviation, however slight.

 

6 Difficulties with the Theory

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LONG BEFORE ARRIVING AT THIS POINT IN MY WORK, A CROWD of difficulties will have occurred to the reader. Some are so grave that they stagger me to this day, but most are only apparent, and even the real ones are not fatal to my theory. These difficulties and objections can be categorized into the following groups:

1. If species have descended from other species by fine gradations, why aren’t there countless transitional forms everywhere? Why isn’t all nature a confusion instead of species being distinct, as they are?

2. Is it possible that an animal such as, for example, the bat, could have descended from another animal with entirely different habits? Can natural selection produce organs of slight importance, such as the giraffe’s tail, which is used to shoo flies, but also produce wonderfully structured organs, such as the eye, with its barely understood and inimitable perfection?

3. Can instincts be acquired and modified through natural selection? Can the marvelous instinct of bees to make cells, practically anticipating the discoveries of mathematicians, be explained?

 

7 Instinct

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INSTINCT COULD HAVE BEEN WORKED INTO PREVIOUS CHAPters, but I thought it would be better to treat it separately, especially because an instinct as wonderful as that of the honeybee making the cells of its hive may have occurred to many readers as sufficiently challenging to overthrow my whole theory. I must premise that my theory has nothing to do with the origin of primary mental powers, just as it has nothing to do with the origin of life itself; this discussion is concerned only with the diversity of instincts and other mental qualities of animals within a class.

I will not try to define instinct. Several distinct mental capacities are commonly embraced by the term, but everyone knows what is meant by instinct impelling a cuckoo to migrate and lay her eggs in other birds’ nests. An action that in humans would require experience, when performed by animals (especially young ones) and by many individuals in the same way without their knowing its purpose is usually said to be instinctive. But none of these characteristics of instinct is universal. As Pierre Huber expresses it, a small dose of reason or judgment is often involved even with animals low on the scale of nature.

 

8 Hybrids

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NATURALISTS GENERALLY MAINTAIN THAT THE OFFSPRING of crosses from between different species are specially endowed with sterility to prevent the confusion of all organisms. At first this seems probable, because species within a region would hardly remain distinct if they were to cross freely. The importance of the fact that hybrids are generally sterile has recently been underrated by some writers. But for the theory of natural selection, hybrid sterility is a particularly important problem, because sterility cannot possibly be useful to a hybrid and therefore cannot be acquired by the preservation of successive degrees of profitable sterility. However, I hope to show that sterility is not a specially acquired or endowed quality, but a by-product of other acquired qualities.

Two sets of observation, to a large extent fundamentally different, are often confused in discussions of this subject: the sterility of two species when crossed, and the sterility of hybrids produced from a cross of two species.1

 

9 The Imperfection of the Geological Record

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IN CHAPTER 6 I LISTED THE MAIN OBJECTIONS TO THE IDEAS presented in this book. Most of them have now been discussed. One – the distinctness of species and the fact that they do not blend together via countless transitional links – is an obvious difficulty. I have given reasons as to why such links cannot be observed in places that would seem to favor their existence (i.e., large continuous areas with a graduated environment). I tried to show that the survival of each species depends more on the presence of already-defined species than on climate, and this significant aspect of the environment does not graduate away like heat or moisture. I also tried to show that intermediate varieties exist in smaller numbers than the forms they connect and are therefore generally beaten out and exterminated during further modification and improvement. The main cause for the lack of many existing intermediate links is the very process of natural selection, through which new varieties continually replace their parent forms. However, this extermination acts on a massive scale, so the number of intermediate varieties that has ever existed must be enormous. Why, then, isn’t every geological formation and stratum full of extinct intermediate links? Geology does not reveal a finely graded chain of organisms, and this is perhaps the gravest objection to my theory. The explanation lies in the extreme imperfection of the geological record.

 

10 The Succession of Organisms in the Geological Record

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NEW SPECIES HAVE APPEARED VERY SLOWLY, ONE AFTER ANother, both on the land and in the waters. Sir Charles Lyell shows that evidence for this in Tertiary stages is compelling, and every year tends to fill up the blanks. In some of the most recent beds, only one or two species have since gone extinct, and only one or two are new species having appeared for the first time in that specific location, or as far as we know, on earth. (“Recent” is a relative term. They would seem very old if described in actual years.) If Philippi’s observations in Sicily are correct, the successive changes in the marine inhabitants there have been many and most gradual. Secondary formations are more fragmented, but as Bronn remarks, neither the appearance nor disappearance of their now-extinct species is simultaneous in each formation.

Species in different genera or classes have not changed at the same rate or to the same extent. The oldest Tertiary beds sometimes yield shells of mollusks that still exist, surrounded by the shells of extinct species. Falconer gives a similar case from the sub-Himalayan deposits; he found the fossil of an extant crocodile species surrounded by many strange and now lost mammals and reptiles. The Silurian Lingula differs only slightly from living species in the same genus, while most of the other Silurian mollusks and all the crustaceans have changed greatly. Land dwellers seem to change more quickly than those of the sea – a recent find in Switzerland provides a striking example – because organisms high on the scale of nature may change more quickly than those low on the scale, although there are exceptions. As Pictet remarks, the rate at which life on earth changes does not correspond to the succession of geological formations; between any two successive formations, the various life forms rarely change in exactly the same degree. However, upon comparison of all but the most closely related formations, all species are found to have changed. And finally, once a species disappears from the face of the earth, it never reappears. All of these observations agree with my theory.

 

11 The Geographical Distribution of Life

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THE SIMILARITIES AND DIFFERENCES AMONG ORGANISMS across the earth cannot be explained by climate or other physical conditions. Almost every author who has recently studied the subject comes to this conclusion. The American continent alone would suffice to prove the point. Excluding the polar regions, there is a fundamental division in geographical distribution between the New World and the Old World. Despite this division, the vast American continent includes very diverse conditions: humid regions, arid deserts, lofty mountains, grassy plains, forests, marshes, lakes, and great rivers, all across wide temperature ranges. There is hardly an environment in the Old World that has no parallel in the New (at least as closely as the same species would require).1 The conditions of the Old and New Worlds are parallel – and yet the organisms are wildly different.

In the southern hemisphere, parts of Australia, South Africa, and western South America between the 25th and 35th southern parallels share similar environments, yet their inhabitants could not be more different. South American organisms south of the 35th parallel and those north of the 25th necessarily face considerably different climates, yet they are more closely related to one another than to the organisms of Africa or Australia under nearly the same climates. (Analogous observations could be listed for ocean dwellers.)

 

12 The Geographical Distribution of Life, Continued

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LAKES AND RIVER SYSTEMS ARE SEPARATED FROM ONE another by barriers of land, so it might seem obvious that freshwater species do not range across many bodies of water and that because the sea is an even greater barrier, they would never spread to distant regions. But actually the reverse is true. Not only do many freshwater species from quite different classes have enormous ranges, but interrelated species prevail throughout the world! When I first collected freshwater insects, shelled mollusks, and other freshwater species in Brazil, I remember being surprised at their similarity to those in Britain, and at the dissimilarity of the surrounding terrestrial organisms.

The capacity of freshwater organisms to range widely may be unexpected, but in most cases it can be explained by their being adapted to make short and frequent migrations from pond to pond or stream to stream – a tendency for wide dispersal follows as an almost necessary consequence. I can here consider only a few cases. With respect to fish, I believe that the same species never occurs in freshwater on widely separated continents. But within one continent, individual species range widely and almost capriciously: two river systems can have some fish in common and some different. A few observations favor the possibility that they occasionally spread by “accidental” means; for example, live fish are sometimes dropped by whirlwinds in India, and fish eggs remain viable after their removal from water. However, I attribute the dispersal of freshwater fish mainly to minor changes in land level within the recent period that caused rivers to flow into one another. Examples could also be given of this result brought about by floods without any changes in level. The loess of the Rhine reveals considerable changes in level within a very recent geological period when the surface was inhabited by still-extant terrestrial and freshwater shelled mollusks. The remarkable difference between fish on opposite sides of continuous mountain ranges, which must have parted river systems and prevented them from intertwining since an early period, suggests the same conclusion.

 

13 Affinities between Organisms: Morphology, Embryology, and Rudimentary Organs

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FROM THE FIRST DAWN OF LIFE, ALL ORGANISMS HAVE resembled one another in descending degrees, so they can be classed into groups subordinate to groups. This classification is not arbitrary like the grouping of stars into constellations. Its meaning would have been straightforward if one group had been fitted exclusively to land and another to water, one to feed on flesh, another on vegetation, and so on. The reality of nature is very different, with members of even the same subgroup commonly having different habits. In chapters 2 and 4, on variation and natural selection, respectively, I attempted to show that widely ranging, highly diffused, and common species, dominant within large genera, vary the most. The varieties – the insipient species – produced in this way ultimately become new and distinct species, and these tend to produce other new and dominant species through inheritance. As a consequence, large groups, generally with many dominant species, tend to continue increasing indefinitely. I also tried to demonstrate that the varying descendants of each species strive to occupy as many different places as possible in the environment, resulting in a constant tendency for their characteristics to diverge. This conclusion is supported by studying the great diversity of life forms competing closely in any small area and by considering certain observations about naturalization.

 

14 Summary and Conclusion

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AS THIS ENTIRE BOOK IS ONE LONG ARGUMENT, IT MAY BE convenient to briefly review the main observations and inferences.

I do not deny that many and serious objections can be advanced against the theory of descent with modification by means of natural selection, and I have endeavored to grant them full force. At first it seems very difficult to believe that complex organs and instincts are perfected by the accumulation of countless minor variations and not by means superior to, though analogous with, human reason. This difficulty may seem beyond our imagination, but it cannot be real if we accept the following: (1) Gradations leading to the perfection of any organ or instinct, each one good for its individual possessor, do exist or could have existed. (2) All organs and instincts are ever so slightly variable. (3) There is a struggle for existence during which each profitable deviation of structure or instinct is preserved. I do not think the validity of these propositions can be disputed.

 

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