—Charles Darwin, The Origin of Species
Recently, I got into a familiar sort of argument with a Christian whom I love and respect very much. We got arguing about evolution, and it soon became clear we were two non-experts arguing passionately about a topic which neither of us fully understood. The most obvious problem was that neither of us had actually read Charles Darwin’s The Origin of Species.
Inspired by our argument, and my own ignorance of a topic which I consider very important, I decided to finally read Darwin’s famous book, take careful notes, and write a book report on what I learned. It took me about three weeks, but I have finally finished the book and my report on it, which I now present to you, dear reader, in the interest of fostering understanding and better-informed arguments.
Chapter 1: Variation Under Domestication
Darwin begins his argument by looking at domesticated animals and plants, which humans have changed over the course of generations to suit their needs. Breeders and horticulturalists have managed to “create” and sustain a great variety of breeds of plants and animals for human use through the power of selection and careful choosing of desirable traits in dogs, sheep, crops, cattle, pigeons, etc. Darwin did extensive experiments with pigeons, which he painstakingly kept, bred, cross-bred, and studied, and concluded that all varieties of pigeon probably descended from the rock pigeon (Columba livia).
In the process of “artificial selection” (by man), some breeds are preserved and others are discarded, depending on their usefulness to man. The breeding and cultivation of a great variety of domestic species shows an enormous potential for change and inheritance. The point of this first chapter is to show that animals display a great potential for change and variability within species. Domestic/artificial selection proves this. From the simple form of the wolf have descended all the diverse dog breeds we see today, for example.
Chapter 2: Variation Under Nature
Then, Darwin extends this idea of the potential for variation under domestication to the potential for variation in nature. He finds, through numerous examples, that there is great variation within species, so much so that naturalists disagree over what counts as a species, and what is a “variety.” He gives the example of two prominent scientists whose views differ markedly on the number of plant species in England. A Mr. Babington names 251 species, while Mr. Bentham names only 112! Darwin notes, “I was much struck how entirely vague and arbitrary is the distinction between species and varieties.”
These differences, like the twelve known varieties of oak trees, blend into each other in a graduated series. Darwin concludes: “I look at the term ‘species’ as one arbitrarily given for the sake of convenience.” The point of this chapter is that in nature, as under domestication, there is enormous variety even within “species”, and this is an important point to establish in Darwin’s slowly building argument for this theory.
Chapter 3: Struggle for Existence
So we see that variability exists in nature, but how do we account for the incredible diversity of life across the planet? The answer, Darwin reasoned, is the struggle for existence. Nature may appear pleasant and beautiful to us, but nature is also a battlefield, a brutal, competitive, and unrelenting struggle for survival among creatures. This struggle for existence follows from the high rate at which all organisms tend to increase. As more individuals are produced than can survive, there must in every case be a struggle for existence, and much destruction.
To test the rate of reproduction vs. survival of creatures, Darwin conducted an experiment: “On a piece of ground three feet long and two wide, dug and cleared, and where there could be no choking from other plants, I marked all the seedlings of our native weeds as they came up, and out of the 357 no less than 295 were destroyed, chiefly by slugs and insects.” Many more plants were destroyed than survived, and this turns out to be the rule in nature.
Given the fact that there are limited resources in nature, and competition among species for those resources, any variation of a creature, however slight, if it benefits an individual in the struggle for survival, will tend to the preserve that individual, and these traits will 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 born, a limited number can survive. So, the struggle for existence favors organisms best adapted to their environment, and this creates the diversity of life, filling each niche of a complex and ever-changing system.
Chapter 4: Natural Selection
Just as human breeders “select” creatures which they prefer, nature can be said to “select” creatures best suited to their environment. This is called “Natural Selection” and it is the crux of Darwin’s theory. Given the constant struggle for life, and the ever-changing conditions on earth over its vast history, each slight modification in an organism which favors its survival, will tend to be preserved and passed onto its offspring. If man can produce such marked changes in dog breeds over a few hundred years, what changes might nature produce over millions of years, on a constantly changing planet (climate, geography), filled with a constant competition for survival among creatures?
Comparing artificial vs. natural selection, Darwin writes, “Nature can act on every 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.” Thus, nature’s productions are far “truer” than mans, and are much better adapted to the complex conditions of life. Also, unlike artificial selection by man, natural selection is constantly working on every living organism all the time, rejecting that which is bad, preserving and adding up what is good. Most of this remains unseen to us, because we lack the time, ability, and patience to see it.
Then Darwin discusses another element of selection, which he calls “sexual selection.” This has to do with the struggle between males for the females. In this struggle, “victory will depend not on general vigor, but on having special weapons, confined to the male sex.” Darwin gives the example of female birds, which choose to mate with the most melodious or beautiful males, as in the case of the peacock. These female choices, over time, will result in real changes in the males.
Darwin also discusses how, sometimes, natural selection will act on two interconnected species at the same time, as in the case of flowers and bees. Flowers need to attract bees to pollinate them, so over time, those flowers which are most attractive to bees will tend to survive and reproduce. These kinds of interconnected relationships exist all throughout nature.
It’s important to note here that, under Darwin’s theory, “natural selection can act only by the preservation and accumulation of infinitesimally small inherited modifications, each profitable to the preserved being.” So, it’s not as though a giraffe gives birth to a man, or slime to a tree. This process happens slowly, and is guided not by chance, but by competition, variation, and ever-changing conditions of life.
The down side of this amazing process is that much extinction of organisms is inevitable: “I think it inevitably follows that as new species in the course of time are formed through natural selection, others will become rarer and rarer, and finally extinct…Each new variety or species, during the progress of its formation, will generally press hardest on its nearest kind, and tend to exterminate them. Hence all the intermediate forms between the earlier and later states, that is between the less and more improved state of a species, as well as the original parent-species itself, will generally tend to become extinct.”
Despite all the destruction, Darwin ends this (his longest and most important chapter) on a more positive note, describing “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.”
Chapter 5: Laws of Variation
While I was reading The Origin of Species, I also downloaded the audiobook, to re-listen to chapters I’d read as I walked around Fullerton. In his abridged audiobook of Origin of Species, Richard Dawkins omitted chapter 5: Laws of Variation, because it has been shown by modern science (specifically genetics) to be false.
In this chapter, Darwin sought to discover the actual mechanism that causes variation and inheritance in organisms. We now know that these variations are caused by genes and DNA, but when he was writing The Origin of Species, Darwin didn’t know about genetics, so he proposed some theories to explain the mechanism of variation, none of which turned out to be the case: the conditions of life, reproductive systems being affected, use and disuse of structures, correlation of growth (one organ changing affects another organ).
Darwin admitted, “Our ignorance of the laws of variation is profound.” He did have some notion of dominant vs. recessive traits, but didn’t understand why: “There is a tendency in the young of each successive generation to produce the long-lost character, and this tendency, from unknown causes, sometimes prevails.” I suspect Darwin would have been very pleased to learn about genes and DNA, as it explains the mechanism of his theory.
Chapter 6: Difficulties on Theory
In this chapter, Darwin begins to address difficulties/objections that people might raise against his theory, and they are pretty much still the standard objections people give. The first is: Why, if species have descended from other species by small gradations, do we not everywhere see innumerable transitional forms? This objection is still raised by some creationists today, and, in Darwin’s day, when much of the world remained to be explored by paleontologists, it was a valid objection. Since the publication of The Origin of Species, many more transitional forms have been discovered.
Darwin gave a few ideas about the lack of transitional forms in nature. For example, why don’t we see creatures that are half-human and half-ape? The reason we don’t see these creatures running around is because “the transitional varieties will generally have been exterminated by the very process of the formation and perfection of the new form.” These transitional forms should be exterminated and disappear sooner than the forms which originally linked them together. In college, I took a course on human evolution, and learned that many transitional hominid skeletons have since been discovered.
|Evolution of human skulls.|
Darwin wondered why we don’t find such creatures embedded in huge numbers in fossils. The answer is twofold: First, there needs to be specific conditions for the preservation of fossils, and most creatures are not preserved in this manner. Second, he reasoned, “the chance of discovering species with transitional grades of structure in a fossil condition will always be less, from their having existed in lesser numbers, than in the case of species with fully developed structures.” Third, in Darwin’s day, much of the world remained unexplored by paleontologists.
Another objection he addresses is: How can really different creatures evolve (even slowly) into one another, like an aquatic animal into a land one? On a related note, how can we believe that complex organs, like the eye, can be formed by slow evolution? First, regarding evolution of aquatic animals into land ones, Darwin gives some examples of creatures which live on both land and water, like the “Mustela vision of North America, which has webbed feet and which resembles an otter in its fur, short legs, and form of tail; during summer this animal dives for and preys on fish, but during the long winter it leaves the frozen waters, and preys like other polecats on mice and land mammals.” There are grades of difference within this type of organism.
What is important for Darwin’s theory is that each grade of structure had been useful to its predecessor. He addresses the example of the human eye, a complex structure which creationists often cite as evidence against his theory. Darwin readily admits the difficulty, but does not see it as insurmountable: “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.”
To answer this objection, Darwin looks at the amazing gradations of structure of eyes we see in nature, from the Articulata with an optic nerve merely coated with pigment, to the slightly more complex eyes of crustaceans and fish, to mammals, etc. The recent television series Cosmos has an episode on evolution which has an amazing segment on the evolution of the eye, and how each slight successive modification provided an advantage to each species that possessed it. Scientists today now understand the human eye as an understandable product of evolution.
Darwin foresaw this truth: “Although the belief that an organ so perfect as the eye could have been formed by natural selection, is more than enough to stagger any one; yet in the case of any organ, if we know of a long series of gradations in complexity, each good for its possessor, then under changing conditions of life, there is not logical impossibility in the acquirement of any conceivable degree of perfection through natural selection.”
He concluded, “If it could be demonstrated that any complex organ existed, which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down. But I can find out no such case.”
Chapter 7: Instinct
In this chapter, Darwin continues to address objections to this theory. Indeed, at least half of his book is devoted to answering (with the knowledge he had) legitimate objections to his theory. He addresses the objection that complex behaviors/instincts in animals like the bee (making hives) could not have developed by natural selection.
The question behind this objection is: Are instincts inherited like bodily structures, and do they vary enough so that natural selection can do its work? The answer turns out to be ‘yes’. Again, we can look at the example of dogs, which are bred not just for appearance, but for behavior/instinct. A few examples: pointers, retrievers, sheep dogs—all these types of dogs are bred for behavior/instinct as much as physical appearance. He writes, “Familiarity alone prevents our seeing how universally and largely the minds of our domestic animals have been modified by domestication. It is scarcely possible to doubt that the love of man has become instinct in the dog.”
|Dogs can be bred for instinct, like herding sheep.|
Then he addresses animal instincts in nature, particularly those which are strange and complex, and explores whether they pose serious problems for his theory. For each animal/instinct, Darwin must show how it could have evolved as beneficial for survival. These are the examples he gives, and the benefit for survival that each strange instinct provides:
1.) The cuckoo lays her eggs in other birds’ nests. Why? Because she lays eggs at longer intervals, so to care for one hatchling means leaving the nest unprotected, which is bad for survival. Laying eggs in another bird’s nest takes advantage of the maternal instinct of other birds. This behavior could have been slowly naturally selected over long periods of time for the maximum survival of the cuckoo.
2.) Slave-making ants. Some species of ants make slaves of other ants, like the F. sanguinea and the F. rufescens. The benefit of this is pretty obvious—slaves do much work for the queen and colony—protecting larvae, gathering food, and thus help the survival of the community.
3.) The honeycomb-making instinct of the hive bee. The beautiful architecture of certain bee hives is often cited as an argument for design, and against natural selection. But if it can be shown that there are gradations of structure among bee hives, from simple to more complex, it is not unreasonable to suppose that this instinct, like the bodies of the bees, slowly evolves over time so as to provide maximum benefit to the community of bees and ensure its survival. And, in fact, looking at bees around the world, we do find enormous variety in the structures they make from simple humble bees (which form rudimentary structures), to the Mexican melipona domestica (which form more complex hives), to the hive bees’ amazing hexagonal creations—which are constructed so as to most efficiently preserve wax and honey for the colony.
This idea of community vs. purely individual benefit also explains why some insect colonies have workers and soldiers that are sterile. Thus, they cannot pass on their individual offspring, but they are still produced by the queen because of the service they provide to the colony as a whole, to ensure the survival of the species.
Chapter 8: Hybridism
In this chapter, Darwin continues to address puzzling problems/objections to his theory. The question he addresses in this chapter is: “How can we account for species, when crossed, being sterile and producing sterile offspring, whereas, when varieties are crossed, their fertility is unimpaired?” The larger question is how to account for sterility in species. How does this fit into Darwin’s theory? Basically, the ability to produce fertile offspring is one of the defining characteristics of a species.
Darwin goes pretty deep into examples of plants that may be crossed, grafted, and produce hybrid plants, some of which are sterile, and some fertile. To me, this chapter is interesting from a horticultural standpoint, but not terribly important to his overall theory. This chapter may be skipped, unless you are a plant nerd.
|Plant nerds might enjoy this book.|
Chapter 9: On the Imperfection of the Geological Record
In this chapter, Darwin goes deeper into the objection he raised in chapter 6, namely that geology does not seem to support his theory: “Why then is not every geological formation and every stratum full of such intermediate links? Geology assuredly does not reveal any such finely graduated organic chain; and this, perhaps, is the most obvious and gravest objection which can be urged against my theory.” The explanation lies, Darwin believes, in the extreme imperfection of the geological record.
He gives some explanations as to why the geological record is so imperfect. First, conditions for the fossilization of any species are pretty unique. Generally, the animal needs hard parts, like bones or a shell. Also, the changing geography of the earth makes good preservation difficult: “I suspect that but few of the very many animals which live on the beach between nigh and low watermark are preserved.” The rising and falling ocean levels, degradations of rock formations—lots of factors affect fossilization.
|This is a fossil.|
Also, when we are looking for transitional forms, especially very distinct forms, like the horse and the tapir for example, “we have no reason to suppose that links ever existed directly intermediate between them, but between each and an unknown common parent.” Evolution does not posit that any creature can miraculously transform into any other creature—merely that, given enough time, different animals can evolve from common ancestors.
He also addresses the objection that not enough time has elapsed in the history of the world for his theory to be true. He refers to geologist Charles Lyell’s work Principles of Geology, where he demonstrates that the earth is at least 300 million years old, and probably much older. Now we know that the earth is over 4 billion years old, which gives plenty of time for the evolution of all life, in all its diverse forms.
Darwin compares the imperfect geological record of his day with a very ancient book: “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 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. Each word of the slowly-changing language, in which the history is supposed to be written, being more or less different in the interrupted succession of chapters, may represent the apparently abruptly changed forms of life, entombed in our consecutive, but widely separated formations. On this view, the difficulties above discussed are greatly diminished, or even disappear.”
Chapter 10: On the Geological Succession of Organic Beings
Because he was trained as both a geologist and a biologist, Darwin was somewhat obsessed with the geological record, because he devotes yet another chapter to it. He gives a few discoveries of his day which show development over time, like the observations of a Mr. Philippi in Sicily, who discovered that the successive changes in the marine inhabitants of that island have been many and gradual. A Mr. Falconer also discovered an existing crocodile “associated with many strange and lost mammals and reptiles in the sub-Himalayan deposits.” In short, some transitional forms exist, and most remained to be found in Darwin’s day.
Chapter 11: Geographical Distribution
In this chapter, Darwin focuses on possible reasons for the diversity (and similarity) of organisms throughout the world, aka the geographical distribution of organisms. Why do different (and sometimes similar) organisms inhabit different parts of the world?
One reason is that “barriers of any kind, or obstacles to free migration, are related in a close and important manner to the differences between the productions of various regions.” Also, similarity and dissimilarity of animals in different regions may be explained by the influence of different (or similar) environments, migration, and the presence of barriers (water or land) between regions. These barriers change with geologic time. Some means of dispersal of organisms include:
1.) Climate change.
2.) Changes in level of the land/sea
3.) Formation of barriers.
4.) Migration. For example, plant seeds can survive in water, on birds, driftwood, even glaciers and can thus travel very far distances, even across oceans. Darwin does experiments by soaking different plant seeds in sea water, to see how long they can float and remain fertile. Some survived immersion of 137 days!
Darwin discusses the dispersal of animals during the last Glacial period, which was understood even in the 19th century. Within a very recent geological period, central Europe and North America suffered under an arctic climate…(as evidenced by the presence “throughout a large part of the United States, erratic boulders, and rocks scored by drifted icebergs and coast-ice, plainly revealing a former cold period.”)
|The last ice age had a profound effect on the evolution of plants and animals.|
Darwin explains, “as the cold came on, and as each more southern zone became fitted for arctic beings and ill-fitted for their former more temperate inhabitants, the latter would be supplanted and arctic productions would take their place…As the warmth returned, the arctic forms would retreat northward, closely followed up in their retreat by the productions of the more temperate regions. And as the snow melted from the bases of the mountains, the arctic forms would seize on the cleared and thawed ground, always ascending higher and higher, as the warmth increased, whilst their brethren were pursuing their northern journey.”
The former presence of land bridges explains similarities between European and American species (though they are different), like the the bridge connecting Russia with Alaska, now no longer a bridge, but a barrier. This explains the fact that the species of each continent are similar, but not the same. They have been allowed to evolve independently after their migration and separation.
As on the land, so in the waters of the sea, slow migrations in response to geologic and climatic changes produce new organisms. “Thus, as I believe,” Darwin writes, “a considerable number of plants, a few terrestrial animals, and some marine productions, migrated during the Glacial period form the northern and southern temperate zones into the inter tropical regions, and some even crossed the equator. As the warmth returned, these temperate forms would naturally ascend the higher mountains, being exterminated on the lowlands; those which had not reached the equator, would re-migrate northward or southward towards their former homes…Thus many of these wanderers, though still plainly related by inheritance to their brethren of the northern or southern hemispheres, now exist in their new homes as well-marked varieties or as distinct species.”
Thus, the distribution of organisms throughout the world is explained by complex geologic, climate, and other factors.
Chapter 12: Geographical Distribution (Part 2)
In this chapter, Darwin continues his discussion of possible reasons for the geographical distribution of organisms throughout the world, focusing specifically on the inhabitants of oceanic islands. Darwin famously spent a good deal of time studying the plants and animals of the Galapagos Islands (off the coast of South America), while serving as a scientist on a voyage of a ship called The Beagle.
|The Galapagos Islands.|
He discovered that, although on oceanic islands the number of kinds of inhabitants is limited, the proportion of endemic species (i.e. those found nowhere else in the world) is often extremely large: “Thus in the Galapagos Islands nearly every land-bird, but only two out of the eleven marine birds, are peculiar.”
The inhabitants of oceanic islands are, in part, determined by their proximity to continents, and the ability of organisms to migrate. Thus, there are fewer mammals on oceanic islands. Once the colonist animals from nearby continents arrive, “such colonists would be liable to modifications—the principle of inheritance still betraying their original birthplace.” Darwin, for example, believed that the various species of finches on the Galapagos islands (each adapted to their environment) all descended from a single finch which first migrated from South America. For more on Darwin’s finches, check out his memoir The Voyage of the Beagle.
Chapter 13: Mutual Affinities of Organic Beings: Morphology: Embryology: Rudimentary Organs
In this chapter, Darwin discusses the impact his theory might have on systems of classification of species. Rather than basing this system on external similarities, Darwin believes that species should be classed based on common descent. He writes, “All true classification is genealogical; that community of descent is the hidden bond which naturalists have been unconsciously seeking, and not some unknown plan of creation.”
Thus, scientists, must be careful in comparing superficial similarities: “For animals, belonging to two most distinct lines of descent, may readily become adapted to similar conditions, and thus assume a close external resemblance; but such resemblances will not reveal—will rather tend to conceal their blood-relationship to their proper lines of descent.”
The structure of a hand-like feature presents a problem to the systematist, but not under Darwin’s theory of descent. On his theory, we should expect similar structures in widely different creatures: “What can be more curious that that the hand of a man, formed for grasping, that of a mole for digging, the leg of the horse, the paddle of the porpoise, and the wing of the bat, should all be constructed on the same pattern, and should include the same bones, in the same relative positions?”
He also states that embryos provide clues to similar lines of descent, for embryos tend to retain their ancient structures (for a while): “Community in embryonic structure reveals community of descent.
Lastly, Darwin discusses how we might understand “useless” or “rudimentary” organs (like teeth in whale embryos, which are discarded when born) under natural selection (or creation). His answer is that these characteristics demonstrate lines of descent. An ancient ancestor of the whale probably needed teeth. Evolution works with what it has…it cannot make something from scratch. Darwin, fond of similes, explains that “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.”
Darwin concludes his book by summing up the main points of his book, which I shall attempt to do in as simple and straightforward a way as I can manage, with a few concluding points. The argument goes something like this:
-Domesticated plants and animals show a great potential for variation.
-This variation also exists in nature.
-There is a struggle for existence.
-Thus, those animals which produce, through variation, traits which aid in survival will be “naturally selected” to survive.
-Over millions of years and constantly-changing geological and climate conditions, natural selection will produce nearly limitless forms of life through slow, successive modifications, filling all the various niches in nature.
-Objections, like the seemingly “irreducible complexity” of the eye, have been explained by modern biology to be the product of evolution.
-Other objections, like the apparent lack of transitional forms and fossils, have been, and are being, addressed by thousands of fossils which have been found since Darwin’s day.
-Essentially, evolution is the great unifying theory of modern biology. Like the theory of gravity, it best explains all the facts we have.
The theory of evolution is quite staggering in its implications, especially for people with a religious worldview (which is the vast majority of people in the world). The notion that the incredible diversity of life can be understood through natural, not supernatural, explanations can be quite unsettling. The idea that human beings were not specially created, but are just one tiny twig on the great and ever-branching tree of life, is quite humbling.
But given human beings’ tendency to exploit nature, maybe a little humility is what we need right now. Understanding the amazingly complex interconnectedness of life, and the fact that we are just as much a part of nature as trees and insects and fish, should give us pause as we consider our destructive impact on this planet we all share. Arrogantly seeing ourselves as somehow “above” nature is perhaps an unhealthy, and certainly an unnatural view—one which I am pleased to discard.