Jerry Coyne. Why Evolution Is True. Penguin, 2009. (282 pages)
…while the Dover trial is an American story, creationism isn’t a uniquely American problem. Creationists — who aren’t necessarily Christians — are establishing footholds in other parts of the world, especially the United Kingdom, Australia, and Turkey. The battle for evolution seems never-ending. And the battle is part of a wider war, a war between rationality and superstition. (xiii)
But evolution is far more than a “theory,” let alone a theory in crisis. Evolution is a fact. (xiii)
Darwin matters because evolution matters. Evolution matters because science matters. Science matters because it is the preeminent story of our age, an epic saga about who we are, where we came from, and where we are going. – Michael Shermer
To many, evolution gnaws at their sense of self. (xvii)
You can find religions without creationism, but you never find creationism without religion. (xvii)
Why teach a discredited, religiously based theory, even one widely believed, alongside a theory so obviously true? It’s like asking that shamanism be taught in medical school alongside Western medicine, or astrology be presented in psychology class as an alternative theory of human behavior. (xix)
Accepting evolution needn’t turn you into a despairing nihilist or rob your life of purpose and meaning. It won’t make you immoral, or give you the sentiments of a Stalin or Hitler. Nor need it promote atheism, for enlightened religion has always found a way to accommodate the advances of science. In fact, understanding evolution should surely deepen and enrich our appreciation of the living world and our place in it. (xx)
1. What Is Evolution?
A curious aspect of the theory of evolution is that everybody thinks he understands it. – Jacques Monod
In essence, the modern theory of evolution is easy to grasp. it can be summarized in a single (albeit slightly long) sentence: Life on earth evolved gradually beginning with one primitive species — perhaps a self-replicating molecule — that lived more than 3.5 billion years ago; it then branched out over tie, throwing off many new and diverse species; and the mechanism for most (but not all) of evolutionary change is natural selection. | When you break that statement down, you find that it really consists of six components: evolution, gradualism, speciation, common ancestry, natural selection, and nonselective mechanisms of evolutionary change. (3)
The first is the idea of evolution itself. This simply means that a species undergoes genetic change over time. That is, over many generations a species can evolve into something quite different, and those differences are based on changes in the DNA, which originate as mutations. (3)
The second part of evolutionary theory is the idea of gradualism. It takes many generations to produce a substantial evolutionary change, such as the evolution of birds from reptiles. (4)
The next two tenets are flip sides of the same coin. It is a remarkable fact that while there are many living species, all of us — you, me, the elephant, and the potted cactus — share fundamental traits. Among these are the biochemical pathways that we use to produce energy, our standard four-letter DNA code, and how that code is read and translated into proteins. This tells us that every species goes back to a single common ancestor, an ancestor who had those common traits and passed them on to its descendants. But if evolution meant only gradual genetic change within a species, we’d have only one species today — a single highly evolved descendant of the first species. Yet we have many: well over ten million species inhabit our planet today, and we know of a further quarter million as fossils. Life is diverse. How does this diversity arise from one ancestral form? This requires the third idea of evolution: that of splitting, or, more accurately, speciation. (4-5)
…speciation simply means the evolution of different groups that can’t interbreed — that is, groups that can’t exchange genes. (6)
…species don’t have to split. Whether they do depends, as we’ll see, on whether circumstances allow populations to evolve enough differences that they are no longer able to interbreed. The vast majority of species — more than 99 percent of them — go extinct without leaving any descendants. (7)
…the idea of common ancestry — the fourth tenet of Darwinism — is the flip side of speciation. It simply means that we can always look back in time, using either DNA sequences or fossils, and find descendants joining at their ancestors. (8)
By sequencing the DNA of various species and measuring how similar these sequences are, we can reconstruct their evolutionary relationships. (10)
The fifth part of evolutionary theory is what Darwin clearly saw as his greatest intellectual achievement: the idea of natural selection. …Selection is both revolutionary and disturbing for the same reason: it explains apparent design in nature by a purely materialistic process that doesn’t require creation or guidance by supernatural forces. (10-11)
Over time, the population will gradually become more and more suited to its environment as helpful mutations arise and spread through the population, while deleterious ones are weeded out. …It requires only that individuals of a species vary genetically in their ability to survive and reproduce in their environment. (11)
Natural selection is not a master engineer, but a tinkerer. It doesn’t produce the absolute perfection achievable by a designer starting from scratch, but merely the best it can do with what it has to work with. (12)
Evolution is like an architect who cannot design a building from scratch, but must build every new structure by adapting a preexisting building, keeping the structure habitable all the while. (13)
So natural selection does not yield perfection — only improvements over what came before. It produces fitter, not the fittest. (13)
This brings us to the last of evolutionary theory’s six points: processes other than natural selection can cause evolutionary change. (13)
According to the Oxford English Dictionary, a scientific theory is
a statement of what are held to be the general laws, principles, or causes of something known or observed.
There are two points I want to emphasize here. First, in science, a theory is much more than just a speculation about how things are: it is a well-thought-out group of propositions meant to explain facts about the real world. …For a theory to be considered scientific, it must be testable and make verifiable predictions. (15)
Because a theory is accepted as “true” only when its assertions and predictions are tested over and over again, and confirmed repeatedly, there is no one moment when a scientific theory suddenly becomes a scientific fact. A theory becomes a fact (or a “truth”) when so much evidence has accumulated in its favor — and there is no decisive evidence against it — that virtually all reasonable people will accept it. This does not mean that a “true” theory will never be falsified. All scientific truth is provisional, subject to modification in light of new evidence. (16)
In the process of becoming truths, or facts, scientific theories are usually tested against alternative theories. (16)
So how do we test evolutionary theory against the still popular alternative view that life was created and remained unchanged thereafter? There are actually two kinds of evidence. The first comes form using the six tenets of Darwinism to make testable predictions. By predictions, I don’t mean that Darwinism can predict how things will evolve in the future. Rather, it predicts what we should find in living or ancient species when we study them. (17)
- Since there are fossil remains of ancient life, we should be able to find some evidence for evolutionary change in the fossil record. The deepest (and oldest) layers of rock would contina the fossils of more primitive species, and some fossils should become more complex as the layers of rock become younger, with organisms resembling present-day species found in the most recent layers. And we should be able to see some species changing over time, forming lineages showing “descent with modification” (adaptation)
- We should be able to find some cases of speciation in the fossil record, with one line of descent dividing into two or more. And we should be able to find new species forming in the wild.
- We should be able to find examples of species that link together major groups suspected to have common ancestry, like birds with reptiles and fish with amphibians. Moreover, these “missing links” (more aptly called “transitional forms”) should occur in layers of rock that date to the time when the groups are supposed to have diverged.
- We should expect that species show genetic variation for many traits (otherwise there would be no possibility of evolution happening).
- Imperfection is the mark of evolution, not of conscious design. We should then be able to find cases of imperfect adaptation, in which evolution has not been able to achieve the same degree of optimality as would a creator.
- We should be able to see natural selection acting in the wild.
In addition to these predictions, Darwinism can also be supported by what I call retrodictions: facts and data that aren’t necessarily predicted by the theory of evolution but make sense only in light of the theory of evolution. (18)
As we’ll see, all the evidence — both old and new — leads ineluctably to the conclusion that evolution is true. (19)
2. Written in the Rocks
The crust of the earth is a vast museum; but the natural collections have been made only at intervals of time immensely remote. – Charles Darwin, On the Origin of Species
The formation of fossils is straightforward, but requires a very specific set of circumstances. First, the remains of an animal or plant must find their way into water, sink to the bottom, and get quickly covered by sediment so that they don’t decay or get scattered by scavengers. (21)
Taking into account all of these requirements, it’s clear that the fossil record must be incomplete. How incomplete? The total number of species that ever lived on earth has been estimated to range between 17 million (probably a drastic underestimate given that at least 10 million species are alive today) and 4 billion. Since we have discovered around 250,000 different fossil species, we can estimate that we have fossil evidence of only 0.1 percent to 1 percent of all species — hardly a good sample of the history of life! …Nevertheless, we have enough fossils to give us a good idea of how evolution proceeded, and to discern how major groups split off form one another. (22)
…the fossil record gives no evidence for the creationist prediction that all species appear suddenly and then remain unchanged. Instead, forms of life appear in the record in evolutionary sequence, and then evolve and split. (32)
What really excites people — biologists and paleontologists among them — are transitional forms: those fossils that span the gap between two very different kinds of living organisms. (32)
Showing common ancestry of two groups, then, does not require that we produce fossils of the precise single species that was their common ancestor, or even species on the direct line of descent from an ancestor to descendant. Rather, we need only produce fossils having the types of traits that link two groups together, and, importantly, we must also have the dating evidence showing that those fossils occur at the right time in the geological record. A “transitional species” is not equivalent to “an ancestral species”; it is simply a species showing a mixture of traits from organisms that lived both before and after it. 935)
One of the greatest fulfilled predictions of evolutionary biology is the discovery, in 2004, of a transitional form between fish and amphibians. This is the fossils species Tiktaalik roseae, which tells us a lot about how vertebrates came to live on the land. (35) [VIA: see NOVA video, and Your Inner Fish]
Tiktaalik shows that our ancestors were flat-headed predatory fish who lurked in the shallow waters of streams. It is a fossil that marvelously connects fish with amphibians. And equally marvelous is that its discovery was not only anticipated, but predicted to occur in rocks of a certain age and in a certain place. (38)
The first link between birds and reptiles was actually known to Darwin, who, curiously, mentioned it only briefly in later editions of The Origin, and then only as an oddity. It is perhaps the most famous of all transitional forms: the crow-sized Archaeopteryx lithographica, discovered in a limestone quarry in Germany in 1860. (The name Archaeopteryx means “ancient wing,” and “lithographica” comes from the Solnhofen limestone, fine-grained enough to make lithographic plates and preserve the impressions of soft feathers.) (39-40)
As these fossils get younger, we see the reptilian tail shrinking, the teeth disappearing, the claws fusing together, and the appearance of a large breastbone to anchor the flight muscles. (44)
While we may speculate about the details, the existence of transitional fossils — and the evolution of birds from reptiles — is fact. Fossils like Archaeopteryx and its later relatives show a mixture of birdlike and early reptilian traits, and they occur at the right time in the fossil record. Scientists predicated that birds evolved from theropod dinosaurs, and, sure enough, we find theropod dinosaurs with feathers. We see a progression in time from early theropods having thin, filamentous body coverings to later ones with distinct feathers, probably adept gliders. What we see in bird evolution is the refashioning of old features (forelimbs with fingers and thin filaments on the skin) into new ones (fingerless wings and feathers) — just as evolutionary theory predicts. (47)
Can we find any mammals that live on both land and water, the kind of creature that supposedly could not have evolved? | Easily. A good candidate is the hippopotamus, which, although closely related to terrestrial mammals, is about as aquatic as a land mammal can get. (48)
Similarly, snakes have long been supposed to have evolved from lizard-like reptiles that lost their legs, since reptiles with legs appear int he fossil record well before snakes. (53) [VIA: See "Evolution in Genesis"]
The fossil record teaches us three things. First, it speaks loudly and eloquently of evolution. The record in the rocks confirms several predictions of evolutionary theory: gradual change within lineages, splitting of lineages, and the existence of transitional forms between very different kinds of organisms. …Second, when we find transitional forms, they occur in the fossil record precisely where they should …Finally, evolutionary change, even of a major sort, nearly always involves remodeling the old into the new. (53)
There is no reason why a celestial designer, fashioning organisms from scratch like an architect designs buildings, should make new species by remodeling the features of existing ones. Each species could be constructed from the ground up. But natural selection can act only by changing what already exists. It can’t produce new traits out of thin air. Darwinism predicts, then, that new species will be modified versions of older ones. The fossil record amply confirms this prediction. (54)
3. Remnants: Vestiges, Embryos, and Bad Design
Nothing in biology makes sense except in the light of evolution. – Theodosius Dobzhansky
In medieval Europe, before there was paper, manuscripts were made by writing on parchment and vellum, thin sheets of dried animal skins. Because these were hard to produce, many medieval writers simply reused earlier texts by scraping off the old words and writing on the newly cleaned pages. These recycled manuscripts are called palimpsests, from the Greek palimpsestos, meaning “scraped again.” (55)
Like these ancient texts, organisms are palimpsests of history — evolutionary history. (56)
Vestiges. …a feature of a species that was an adaptation in its ancestors, but that has either lost its usefulness completely or, as in the ostrich, has been co-opted for new uses. (57) It is vestigial not because it’s functionless, but because it no longer performs the function for which it evolved. (58)
The long and short of it is this: flight is metabolically expensive, using up a lot of energy that could otherwise be diverted to reproduction. (59)
In other words, our appendix is simply the remnant of an organ that was critically important to our leaf-eating ancestors, but of no real value to us. (61)
We have a vestigial tail: the coccyx… (62)
…vestigial traits make sense only in the light of evolution. (64)
Atavisms. Occasionally an individual crops up with an anomaly that looks like the reappearance of an ancestral trait. A horse can be born with extra toes, a human baby with a tail. These sporadically expressed remnants of ancestral features are called atavisms, from the Latin atavus, or “ancestor.” They differ from vestigial traits because they occur only occasionally rather than in every individual. (64)
The most striking atavism in our own species is called the “coccygeal projection,” better known as the human tail. (65)
Dead Genes. We expect to find, in the genomes of many species, silenced, or “dead,” genes: genes that once were useful but are no longer intact or expressed. In other words, there should be vestigial genes. (67) Out of about thirty thousand genes, for example, we humans carry more than two thousand pseudogenes. (67)
A dead gene in one species that is active in its relatives is evidence for evolution, but there’s more. When you look at ψGLO in living primates, you find out that its sequence is more similar between close relatives than between more distant ones. (68)
Why doesn’t natural selection eliminate the “fish embryo” stage of human development, since a combination of a tail, fishlike gill arches, and a fishlike circulatory system doesn’t seem necessary for a human embryo? | …The probable answer — and it’s a good one — involves recognizing that as one species evolves into another, the descendant inherits the developmental program of its ancestor: that is all the genes that form ancestral structures. (77-78)
This “adding new stuff onto old” principle also explains why the sequence of developmental changes mirrors the evolutionary sequence of organisms. As one group evolves from another, it often adds its development program on top of the old one. | Noting this principle, Ernst Haeckel, a German evolutionist and Darwin’s contemporary, formulated a “biogentic law” in 1866, famously summarized as “Ontogeny recapitulates phylogeny.” This means that the development of an organism simply replays its evolutionary history. But this notion is true in only a limited sense. …Haecke’s law has fallen into disrepute not only because it wasn’t strictly true, but also because Haeckel was accused, largely unjustly, of fudging some drawings of early embryos to make them look more similar than they really are. Yet we shouldn’t throw out the baby with the bathwater. Embryos still show a form of recapitulation: features that arose earlier in evolution often appear earlier in development. And this makes sense only if species have an evolutionary history. (78)
Bad Design. Although organisms appear designed to fit their natural environments, the idea of perfect design is an illusion. (81)
What I mean by “bad design” is the notion that if organisms were built from scratch by a designer — one who used the biological building blocks of nerves, muscles, bone, and so on — they would not have such imperfections. Perfect design would truly be the sign of a skilled and intelligent designer. Imperfect design is the mark of evolution; in fact, it’s precisely what we expect from evolution. (81)
One of nature’s worst designs is shown by the recurrent laryngeal nerve of mammals. (82)
Courtesy of evolution, human reproduction is also full of jerry-rigged features. We’ve already learned that the descent of male testes, a result of their evolution from fish gonads, creates weak spots in the abdominal cavity that can cause hernias. Males are further disadvantaged because o the poor design of the urethra, which happens to run right through the middle of the prostate gland that produces some of our seminal fluid. To paraphrase Robin Williams, it’s a sewage pipe running directly through a recreation area. A large fraction of males develop enlarged prostates later in life, which squeeze the urethra a make urination difficult and painful … | Women don’t fare much better. They give birth through the pelvis, a painful and inefficient process that, before modern medicine, killed appreciable numbers of mothers and babies. (84-85)
Yes, a designer may have motives that are unfathomable. But the particular bad designs that we see make sense only if they evolved from features of earlier ancestors. If a designer did have discernible motives when creating species, one of them must surely have been to fool biologists by making organisms look as though they evolved. (85)
4. The Geography of Life
When on board H.M.S. “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. – Charles Darwin, On the Origin of Species
…evolution was necessary to explain not just the origins and forms of plants and animals but also their distributions across the globe. (88)
The biogeographic evidence for evolution is now so powerful that I have never seen a creationist book, article, or lecture that has tried to refute it. Creationists simply pretend that the evidence doesn’t exist. (88)
We now have many of the answers that once eluded Darwin, thanks to two developments that he could not have imagined: continental drift and molecular taxonomy. (90)
No creationist, whether of the Noah’s Ark variety or otherwise, has offered a credible explanation for why different types of animals have similar forms in different places. All they can do is invoke the inscrutable whims of the creator. But evolution does explain the pattern by invoking a well-known process called convergent evolution. It’s really quite simple. Species that live in similar habitats will experience similar selection pressures form their environment, so they may evolve similar adaptations, or converge, coming to look and behave very much alike even though they are unrelated. (94)
Convergent evolution demonstrates three parts of evolutionary theory working together: common ancestry, speciation, and natural selection. (94)
If evolution happened, species living in one area should be the descendants of earlier species that lived int he same place. So if we dig into shallow layers of rocks in a given area, we should find fossils that resemble the organisms treading that ground today. | And this is also the case. (96)
Creationism is hard-pressed to explain these patterns: to do so, it would have to propose that there were an endless number of successive extinctions and creations all over the world, and that each set of newly created species were made to resemble older ones that lived in the same place. We’ve come a long way from Noah’s Ark. (96)
He who admits the doctrine of creation of each separate species, will have to admit, that a sufficient number of the best adapted plants and animals have not been created on oceanic islands. – Darwin (101)
…with a few exceptions, the animals and plants on oceanic islands are most similar to species found on the nearest mainland. (106)
Envoi. The main lesson of biogeography is that only evolution can explain the diversity of life on continents and islands. But there is another lesson as well: the distribution of life on earth reflects a blend of chance and lawfulness. (109)
5. The Engine of Evolution
What but the wolf’s tooth whittled so fine
The fleet limbs of the antelope?
What but fear winged the birds, and hunger
Jewelled with such eyes the great goshawk’s head?
- Robinson Jeffers, “The Bloody Sire”
One of the marvels of evolution is the Asian giant hornet…
[VIA: Stinkin' awesome!]
Selection is not a mechanism imposed on a population from outside. Rather, it is a process, a description of how genes that produce better adaptations become more frequent over time. When biologists say that selection is acting “on” a trait they’re merely using shorthand to say that the trait is undergoing the process. In the same sense, species don’t try to adapt to their environment. There is no will involved, no conscious striving. Adaptation to the environment is inevitable if a species has the right kind of genetic variation. (117)
Three things are involved in creating an adaptation by natural selection. First, the starting population has to be variable: mice within a population have to show some difference in their coat colors. … | Second, some proportion of that variation has to come from changes in the forms of genes, that is, the variation has to have some genetic basis (called heritability). (117)
The term “random” here has a specific meaning that is often misunderstood, even by biologists. What this means is that mutations occur regardless of whether they would be useful to the individual. Mutations are simply errors in DNA replication. (118)
The third and last aspect of natural selection is that the genetic variation must affect an individual’s probability of leaving offspring. (118)
Evolution by selection, then, is a combination of randomness and lawfulness. There is first a “random” (or “indifferent”) process — the occurrence of mutations that generate an array of genetic variants, both good and bad (in the mouse example, a variety of new coats colors); and then a “lawful” process — natural selection — that orders this variation, keeping the good and winnowing the bad (on the dunes, light-color genes increase at the expense of dark-color ones). (118)
…the idea that, in evolution, “everything happens by chance” (also stated as “everything happens by accident”) …is flatly wrong. No evolutionist — and certainly not Darwin — ever argued that natural selection is based on chance. Quite the opposite. (119)
True, the raw materials for evolution — the variations between individuals — are indeed produced by chance mutations. …But it is the filtering of that variation by natural selection that produces adaptations, and natural selection is manifestly not random. It is a powerful molding force, accumulating genes that have a greater chance of being passed on than others, and in so doing making individuals ever better able to cope with their environment. It is, then, the unique combination of mutation and selection — chance and lawfulness — that tells us how organisms become adapted. Richard Dawkins provided the most concise definition of natural selection: it is”the non-random survival of random variants.”(119)
The theory of natural selection has a big job — the biggest in biology. Its task is to explain how every adaptation evolved, step by step, from traits that preceded it. (119)
And each step of the process, each elaboration of an adaptation, must confer a reproductive benefit on individuals possessing it. …There is no “going downhill” in the evolution of an adaptation, for selection by its very nature cannot create a step that doesn’t benefit its possessor. (120)
First, in principle we should be able to imagine a plausible step-by-step scenario for the evolution of that trait, with each step raising the fitness 9that is, the average number of offspring) of its possessor. …It is telling, however, that biologists haven’t found a single adaptation whose evolution absolutely requires an intermediate step that reduces the fitness of individuals. (120)
Here’s another requirement. An adaptation must evolve by increasing the reproductive output of its possessor. (120)
And adaptations always increase the fitness of the individual, not necessarily of the group or the species. (121)
As evolution predicts, we never see adaptations that benefit the species at the expense of the individual — something that we might have expected if organisms were designed by a beneficent creator. (122)
Evolution Without Selection. Most biologists define evolution as a change in the proportion of alleles (different forms of a genes) in a population. (122) …And so, especially in small populations, the proportion of different alleles can change over time entirely by chance. And new mutations may enter the fray and themselves rise or fall in frequency due to this random sampling. Eventually the resulting “random walk” can even cause genes to become fixed in the population (that is, rise to 100 percent frequency) or, alternatively, get completely lost. | Such random change in the frequency of genes over time is called genetic drift. (123)
Animal and Plant Breeding. The success of dog breeding validates two of the three requirements for evolution by selection. …If artificial selection can produce such canine diversity so quickly, it becomes easier to accept that the lesser diversity of wild dogs arose by natural selection acting over a period a thousand times longer. (126)
There’s really only one difference between artificial and natural selection. In artificial selection it is the breeder rather than nature who sorts out which variants are “good” and “bad.” In other words, the criterion of reproductive success is human desire rather than adaptation to a natural environment. …Cows, sheep, pigs, flowers, vegetables, and so on — all came from humans choosing variants present in wild ancestors, or variants that arose by mutation during domestication. (127)
Evolution in the Test Tube. First, natural selection can promote the evolution of complex, interconnected biochemical systems in which all the parts are codependent, despite the claims of creationists that this is impossible. Second, as we’ve seen repeatedly, selection does not create new traits out of thin air: it produces “new” adaptations by modifying preexisting features. (129)
Resistance to Drugs and Poisons. It is a widespread belief that drug resistance occurs because somehow the patients themselves change in a way that makes the drug less effective. But this is wrong: resistance comes from evolution of the microbe, not habituation of patients to the drug. (131) …when a population encounters a stress that doesn’t come from humans, such as a change in salinity, temperature, or rainfall, natural selection will often produce an adaptive response. (132)
Selection in the Wild. …we shouldn’t expect to see more than small changes in one or a few features of a species — what is known as microevolutionary change. Given the gradual pace of evolution, it’s unreasonable to expect to see selection transforming one “type” of plant or animal into another — so-called macroevolution — within a human lifetime. Though macroevolution is occurring today, we simply wont be around long enough to see it. Remember that the issue is not whether macroevolutionary change happens — we already know from the fossil record that it does — but whether it was caused by natural selection, and whether natural selection can build complex features and organisms. | Another factor making it hard to see real-time selection is that a very common type of natural selection doesn’t cause species to change. (133)
If we want to see selection in action, then, we should look in species that have short generation times and are adapting to a new environment. (133)
Can Selection Build Complexity? …”God of the gaps” argument, and it is an argument from ignorance. What it really says is that if we don’t understand everything about how natural selection built a trait, that lack of understanding itself is evidence for supernatural creation. …Since ID itself makes no testable scientific claims, but offers only half-baked criticisms of Darwinism, its credibility slowly melts away with each advance in our understanding. Further, ID’s own explanation for complex features — the whim of a supernatural designer — can explain any conceivable observation about nature. (137)
But if you can’t think of an observation that could disprove a theory, that theory simply isn’t scientific. (138)
If the history of science teaches us anything, it is that what conquers our ignorance is research, not giving up and attributing our ignorance to the miraculous work of a creator.
Ignorance more frequently begets confidence than does knowledge: it is those who know little, and not those who know much, who so positively assert that this or that problem will never be solved by science. – Darwin
The lesson, then, is that selection is perfectly adequate to explain changes that we see in the fossil record. One reason why people raise this question is because they don’t (or can’t) appreciate the immense spans of time that selection has had to work. (141)
The obvious conclusion: we can provisionally assume that natural selection is the cause of all adaptive evolution — though not of every feature of evolution, since genetic drift can also play a role. …To really see the power of selection, we must extrapolate the small changes that selection creates in our lifetime over the millions of years that it has really had to work in nature. (143)
6. How Sex Drives Evolution
It cannot be supposed, for instance, that male birds of paradise or peacocks should take such pains in erecting, spreading, and vibrating their beautiful plumes before the females for no purpose. – Charles Darwin
Traits that differ between males and females of a species — such as tails, color, and songs — are called sexual dimorphisms, from the Greek for “two forms.” (146)
The Solutions. Remember that the currency of selection is not really survival, but successful reproduction. (148)
Sexual selection comes in two forms. One, exemplified by the Irish elk’s huge antlers, is direct competition between males for access to females. The other, the one that produces the widowbird’s long tail, is female choosiness among possible mates. (148)
In both types of sexual selection, males compete for females. Why isn’t it the other way around? We’ll learn shortly that it all rests on the difference in size between two tiny cells: the sperm and the egg. (149)
There is simply no doubt that female choice has driven the evolution of many sexual dimorphisms. Darwin was right after all. | So far we’ve neglected two important questions: Why do females get to do the choosing while males must woo or fight for them? And why do females choose at all? (154)
Why Sex? Why sex evolved is in fact one of evolution’s greatest mysteries. (155) First, why are there just two (rather than three or more) sexes… second, why do these two sexes have different numbers and sizes of gametes (males produce a lot of small sperm, females fewer but larger eggs)? (156) Theoreticians have shown rather convincingly that natural selection will favor changing this ancestral state into a state in which one sex (the one we call “male”) makes a lot of small gametes — sperm or pollen — and the other (“female”) makes fewer but larger gametes known as eggs. | It’s this asymmetry in the size of gametes that sets the stage for all of sexual selection, for it causes the two sexes to evolve different mating strategies. (156)
The evolutionary difference between males and females is a matter of differential investment — investment in expensive eggs versus cheap sperm, investment in pregnancy (when females retain and nourish the fertilized eggs), and investment in parental care in the many species in which females alone raise the young. (157)
What this adds up to is that, in general, males must compete for females. Males should be promiscuous, females coy. (158)
…the good-genes model remains the favored explanation of sexual selection. This belief, in the face of relatively sparse evidence, may partly reflect a preference of evolutionists for strict Darwinian explanations — a belief that females must somehow be able to discriminate among the genes of males. | There is, however, a third explanation for sexual dimorphisms, and it’s the simplest of all. It is based on what are called sensory-bias models. These models assume that the evolution of sexual dimorphisms is driven simply by preexisting biases in a female’s nervous system. And those biases could be a by-product of natural selection for some function other than finding mates, like finding food. (166-167)
…natural selection may often create preexisting preferences that help animals survive and reproduce, and these preferences can be co-opted by sexual selection to create new male traits. (167)
7. The Origin of Species
Each species is a masterpiece of evolution that humanity could not possibly duplicate even if we somehow accomplish the creation of new organisms by genetic engineering – E.O. Wilson
In other words, both locals and scientists had distinguished the very same species of birds living in the wild. This concordance between two cultural groups with very different backgrounds convinced Mayr, as it should convince us, that the discontinuities of nature are not arbitrary, but an objective fact. (169) [c.f. Animal Species and Evolution]
We see clusters in all organisms that reproduce sexually. | These discrete clusters are known as species. (169)
A better title for The Origin of Species, then, would have been The Origin of Adaptations: while Darwin did figure out how and why a single species changes over time (largely by natural selection), he never explained how one species splits in two. …If we want to explain biodiversity, then, we have to do more than explain how new traits arise — we must also explain how new species arise. for if speciation didn’t occur, there would be no biodiversity at all — only a single, long-evolved descendant of that very first species. (170)
One obvious answer is based on how we recognize species: as a group of individuals that resemble one another more than they resemble members of other groups. According to this definition, known as the morphological species concept, the category “tiger” would be defined something like “that group including all Asian cats whose adults are more than five feet long and have vertical black stripes on an orange body, with white patches around the eyes and mouth.” (170)
At what point are differences between populations large enough to make us call them different species? This concept makes the designation of species an arbitrary exercise, yet we know that species have an objective reality and are not simply arbitrary human constructs. (171)
When you ponder cryptic species, and variation within humans, you arrive at the notion that species are distinct not merely because they look different, but because there are barriers between them that prevent interbreeding. (172)
Mayr defined a species as a group of interbreeding natural populations that are reproductively isolated from other such groups. (172)
And this means that a species is also an evolutionary community. …The biological species, then, is the unit of evolution — it is, to a large extent, the thing that evolves. …if you can explain how reproductive barriers evolve, you’ve explained the origin of species. (174)
How do you get one species to divide into two, separated by reproductive barriers? Mayr argued that these barriers were merely the by-products of natural or sexual selection that caused geographically isolated populations to evolve in different directions. (175)
It’s important to realize that species don’t arise, as Darwin thought, for the purpose of filling up empty niches in nature. …The study of speciation tells us that species are evolutionary accidents. The “clusters” so important for biodiversity don’t evolve because they increase that diversity, nor do they evolve to provide balanced ecosystems. They are simply the inevitable result of genetic barriers that arise when spatially isolated populations evolve in different directions. | In many ways biological speciation resembles the “speciation” of two closely related languages from a common ancestor (an example is German and English, two “sister tongues”). (176-177)
Languages are like biological species in that they occur in discrete groups rather than as a continuum: the speech of any given person can usually be placed unambiguously in one of the several thousand human languages. | The parallel goes even further. The evolution of languages can be traced back to the distant past, and a family tree drawn up, by cataloging the similarities of words and grammar. …This is precisely the way biologists predict what missing links or ancestral genes should look like. (177)
The first prediction is that if speciation depends largely on geographical isolation, there must have been lots of opportunities during the history of life for populations to experience that isolation. After all, there are millions of species on earth today. (178-179)
The way we discovered how species arise resembles the way astronomers discovered how stars “evolve” over time. (182)
Historical reconstruction of a process is a perfectly valid way to study that process, and can produce testable predictions. We can predict that the sun will begin to burn out in about five billion years, just as we can predict that laboratory populations artificially selected in different directions will become genetically isolated. (183)
8. What About Us?
Darwinian Man, though well behaved, At best is only a monkey shaved. – William S. Gilbert and Arthur Sullivan, Princess Ida
Australopithecus africanus (“Southern ape-man”).
Since Dart’s time, paeloanthropologists, geneticists, and molecular biologists have used fossils and DNA sequences to establish our place in the tree of evolution. We are apes descended from other apes, and our closest cousin is the chimpanzee, whose ancestors diverged from our own several million years ago in Africa. These are indisputable facts. (192)
Pithecanthropus erectus (now called Homo erectus)
…we can’t expect to find the single particular species that represents the “missing link” between humans and other apes. We can hope only to find its evolutionary cousins. (195)
One could not ask for a better transitional form between humans and ancient apes than Lucy. Australopithecus afarensis.
Homo habilis means “handy man, the first unequivocally tool-using human.
Looking at the whole array of bones, then, what do we have? [The above list is not the complete list from Coyne's book, but a selection of the major ones listed] Clearly, indisputable evidence for human evolution from apelike ancestors. …It’s a fact that our divergence from the ancestor of chimps occurred in East or Central Africa about seven million years ago, and that bipedal walking evolved well before the evolution of large brains. (207)
Nothing shows the intermediacy of these fossils better than the inability of creationists to classify them consistently. | What, then, propelled the evolution of humans? It’s always easier to document evolutionary change than to understand the forces behind it. …the most profound environmental change in East and Central Africa was drought. (208)
Many biologists feel that these changes in climate and environment had something to do with the first significant hominin trait to evolve: bipedality. (209)
These mysteries about how we evolved should not distract us from the indisputable fact that we did evolve.
Our Genetic Heritage. …humans and chimps differ not only in the sequence of genes, but also in the presence of genes.
Putting this together, we see that the genetic divergence between ourselves and chimpanzees comes in several forms — changes not only in the proteins produced by genes, but also in the presence or absence of genes, the number of gene copies, and when and where genes are expressed during development. We can no longer claim that “humanness” rests on only one type of mutation, or changes in only a few key genes. But this is not really surprising if you think about the many traits that distinguish us from our closest relatives. There are differences not only in anatomy, but also in physiology (we are the sweatiest of apes, and the only ape whose females have concealed ovulation), behavior (humans pair-bond and other apes do not), language, and brain size and configuration (surely there must be many differences in how the neurons in our brains are hooked up). Despite our general resemblance to our primate cousins, then, evolving a human from an apelike ancestor probably required substantial genetic change. (211)
The Sticky Question of Race Most biologists stay as far away from it as they can. A look at the history of science tells us why. From the beginning of modern biology, racial classification has gone hand in hand with racial prejudice. (212)
As we would expect from evolution, human physical variation occurs in nested groups, and in spite of valiant efforts by some to create formal divisions of races, exactly where one draws the line to demarcate a particular race is completely arbitrary. There are no sharp boundaries: the number of races recognized by anthropologists has ranged from three to more than thirty. | …Direct genetic evidence, accumulated over the last three decades, shows that only about 10 to 15 percent of all genetic variation in humans is represented by difference between “races” that are recognized by differences in physical appearance. The remainder of the genetic variation, 85 to 90 percent, occurs among individuals within races. (213)
For some biologists, the existence of greater variation between races in genes that affect physical appearance, something easily assessed by potential mates, points to one thing: sexual selection. …A group of humans can change their culture much faster than they can evolve genetically. but the cultural change can also produce genetic change. (215)
…most controversy about race centers not on physical differences between populations, but behavioral ones. Has evolution caused certain races to become smarter, more athletic, or cannier than others? We have to be especially careful here, because unsubstantiated claims in this area can give racism a scientific cachet. So what do the scientific data say? Almost nothing. Although different populations may have different behaviors, different IQs, and different abilities, it’s hard to rule out the possibility that these differences are a nongenetic product of environmental or cultural differences. If we want to determine whether certain differences between races are based on genes, we must rule out these influences. Such studies require controlled experiments: removing infants of different ethnicity from their parents and bringing them up in identical (or randomized) environments. What behavioral differences remain would be genetic. Because these experiments are unethical, they haven’t been done systematically, but cross-cultural adoptions anecdotally show that cultural influences on behavior are strong. (215-216)
The DNA data shows that, overall, genetic differences among human populations are minor. (216)
The lesson from the human fossil record, then, combined with more recent discoveries in human genetics, confirms that we are evolved mammals — proud and accomplished ones, to be sure, but mammals built by the same processes that transformed very form of life over the past few billion years. (220)
9. Evolution Redux
After sleeping through hundred million centuries we have finally opened our eyes on a sumptuous planet, sparkling with color, bountiful with life. Within decades we must close our eyes again. Isn’t it a noble, an enlightened way of spending our brief time in the sun, to work at understanding the universe and how we have come to wake up in it? This is how I answer when I am asked — as I am surprisingly often — why I bother to get up in the mornings. – Richard Dawkins
After [a] talk, a member of the audience approached me and said,
I found your evidence for evolution very convincing — but I still don’t believe it.
This statement encapsulates a deep and widespread ambiguity that many feel about evolutionary biology. The evidence is convincing, but they’re not convinced. How can that be? (221)
What’s not a problem is the lack of evidence. …the fossil record, biogeography, embryology, vestigial structures, suboptimal design, and so on …And it’s not just small “microevolutionary”changes, either: we’ve seen new species form, both in real time and in the fossil record, and we’ve found transitional forms between major groups, such as whales and land animals. (222)
Every day, hundreds of observations and experiments pour into the hopper of the scientific literature. …And every fact that has something to do with evolution confirms its truth. Every fossil that we find, every DNA molecule that we sequence, every organ system that we dissect supports the idea that species evolved from common ancestors. Despite innumerable possible observations that could prove evolution untrue, we don’t have a single one. (222-223)
Now, when we say that “evolution is true,” what we man is that the major tenets of Darwinism have been verified. (223)
There is no dissent among serious biologists about he major claims of evolutionary theory — only about the details of how evolution occurred, and about the relative roles of various evolutionary mechanisms. Far from discrediting evolution, the “controversies” are in fact the sign of a vibrant, thriving field. What moves science forward is ignorance, debate, and the testing of alternative theories with observations and experiments. A science without controversy is a science without progress. (223)
…like the business man I encountered after my lecture, many people require more than just evidence before they’ll accept evolution. To these folks, evolution raises such profound questions of purpose, morality, and meaning that they just can’t accept it no matter how much evidence they see. It’s not that we evolved from apes that bothers them so much; it’s the emotional consequences of facing that fact. And unless we address those concerns, we won’t progress in making evolution a universally acknowledge truth.
Nobody lies awake worrying about gaps in the fossil record. many people lie awake worrying about abortion and drugs and the decline of the family and gay marriage and all of the other things that are opposed to so-called ‘moral values.’ – Michael Ruse
Nancey Pearcey argues (and many American creationists agree) that all the perceived evils of evolution come from two worldviews that are part of science: naturalism and materialism. Naturalism is the view that the only way to understand our universe is through the scientific method. Materialism is the idea that the only reality is the physical matter of the universe, and that everything else, including thoughts, will, and emotions, comes from physical laws acting on that matter. (224)
But Pearcy’s notion that these lessons of evolution will inevitably spill over into the study of ethics, history, and “family life” is unnecessarily alarmist. …Evolution is simply a theory about the process and patterns of life’s diversification, not a grand philosophical scheme about the meaning of life. it can’t tell us what to do, or how we should behave. And this is the big problem for many believers, who want to find in the story of our origins a reason for our existence, and a sense of how to behave. (225)
…there is also huge scientific literature on how evolution can favor genes that lead to cooperation, altruism, and even morality. Our forebears may not have been entirely beastly after all, and in any case, the jungle, with its variety of animals, many of which live in quite complex and cooperative societies, is not as lawless as the saying implies. (226)
My own view is that conclusions about the evolution of human behavior should be based on research at least as rigorous as that used in studying nonhuman animals. (230)
…genes aren’t destiny. …”genetic” does not mean “unchangeable.” All sorts of environmental factors can affect the expression of genes. (230)
It is clear, then, that whatever genetic heritage we have, it is not a straightjacket that traps us forever in the “beastly” ways of our forebears. Evolution tells us where we came from, not where we can go. (231)
The fairest thing we can experience is the mysterious. it is the fundamental emotion which stands at the cradle of true art and true science. He who knows it not and can no longer wonder, no longer feel amazement, is as good as dead, a snuffed-out candle. it was the experience of mystery — even if mixed with fear — that engendered religion. A knowledge of the existence of something we cannot penetrate, of the manifestations of the profoundest reason and the most radiant beauty, which are only accessible to our reason in their most elementary forms — it is this knowledge and this emotion that constitute the truly religious attitude; in this sense, and in this alone, I am a deeply religious man … Enough for me the mystery of the eternity of life, and the inkling of the marvelous structure of reality, together with the single-hearted endeavour to comprehend a portion, be it ever so tiny, of the reason that manifests itself in nature. – Albert Einstein
I don’t have to know an answer. I don’t feel frightened by not knowing things, by being lost in a mysterious universe without any purpose, which is the way it really is as far as I can tell, possibly. it doesn’t frighten me. – Richard Feynman
Only relatively few people can find abiding consolation and sustenance in the wonders of nature; even fewer are granted the privilege of adding to those wonders through their own research. (232)
Evolution is neither moral nor immoral. It just is, and we make of it what we will. I have tried to show that two things we can make of it are that it’s simple and it’s marvelous. (233)
But there is something even more wondrous. We are the one creature to whom natural selection has bequeathed a brain complex enough to comprehend the laws that govern the universe. And we should be proud that we are the only species that has figured out how we came to be. (233)
— VIA —
This book is a “must read” for anyone involved in the popular conversation. Ask any random religious person who disregards evolution, “How many books on evolution have you read?” and you will soon find out that those who reject evolution actually know very little about it. This makes their dismissal whimsical, dogmatic, ignorant, and arrogantly dismissive. Attitudes aside, ignorance is the problem, a grotesque problem that Coyne’s book remedies, at least, partially; people still need to pick it up and read it.
Coyne’s Preface and Introduction present very well the “state” of the matter (creationism/evolution and the popular dialogue), and I appreciate his candor and tone of respect (although it appears that his tone and rhetoric has become more militant and vitriolic through his blog and articles). Regardless, it behooves anyone, especially any non-scientist types, to trust the work of people in their area of expertise, and this trust I readily commend to Coyne which is earned by his substantive presentation of “the goods” of evolution. While at times technical, for the most part the concepts are readily accessible, understandable, and at times, entertaining (like the Asian bees!)
However, there are a few areas of contention that need to be discussed and debated. They are presented here with all due respect to the author and the conversation, and with the hope of further insight from the global internet community.
EQUAL CONJECTURE. While it is important to take creationism (emphasis on the ism) to task in light of the evidence, assertions on what a creator would or would not do is, (a) irrelevant, in that this ought to be a conversation for theological discussion — a discipline that ought not be blurred with science — a point that Coyne himself would perhaps agree with and is substantiated throughout his thesis, and, (b) comparable to the very argumentation that Coyne is in opposition to, namely, that creationists assert that a creator would do “such-and-such.” He writes, “There is no reason why a celestial designer, fashioning organisms from scratch like an architect designs buildings, should make new species by remodeling the features of existing ones. Each species could be constructed from the ground up.” (54) While contrasting this with natural selection makes a valid point about natural selection, this editorialized statement (a) presupposes what kind of creator this “creator” must be, and, (b) is outside the realm of commentary by the very nature of the disciplines — science and theology. Using scientific logic, Coyne compares what natural selection does with what a creator ought to have done. This is neither warranted, nor helpful in the conversation, and the kind of nonsensical statement that Coyne himself suggests ought not be a part of the discussion. Again, creationism ought to be taken to task. But impositions upon what the creator is/ought/should be like is a kind of conjecture that need not be invoked.
INTELLIGENTLY DESIGNED, NOT INTELLIGENT DESIGN. The discussion on natural breeding by owners in comparison to natural design without human direction seems to be a slippery comparison. This parallelism — from Darwin himself, of course — seems to indicate that the “natural” selection process is itself quite intelligent, breeding by “human” intelligence, and natural selection by “natural” intelligence. The terms here are difficult as the ID proponents have hijacked the terms “intelligent” and “design” and are holding them hostage. However, from a purely denotative sense, it seems fully appropriate to regard the “design” (purpose, planning, or intention that exists or is thought to exist behind an action, fact, or material object ) of the natural world as “intelligent” (able to vary its state or action in response to varying situations, varying requirements, and past experience). Could it be possible to use these words without necessarily invoking “theism?” And if so, could that mean the conversations might possibly have more commonality/mutuality than animosity? And is this perspective viable enough to move “naturalists/materialists” to accept “intelligence” as part of the cosmos?
SCIENCE AS DISPROVABLE MEANS METAPHYSICS IS ALSO DISPROVABLE. Coyne writes, “…but if you can’t think of an observation that could disprove a theory, that theory simply isn’t scientific.” (138) The importance of this statement cannot be overstated. There are boundaries and guidelines as to what qualifies as science. However, this truth is double-edged, namely, if a theory that which cannot be disproved is not categorically scientific, then scientific proofs/validations, etc., cannot therefore disprove the truth of the assertion. In other words, Coyne, by his own admission here, and the truth of the statement of disprovability is fundamentally incapable of making any statements of validation on anything supernatural or transcendent. This goes straight to the heart of “materialism” or “naturalism” that are elucidated in the last chapter of this book. Yes, evolution is true. And, any transcendent or metaphysical explanation that imposes itself upon the scientific and natural world are de facto discounted as irrelevant and absurd. However, conversely, transcendence and metaphysics are thus free from the imposition of scientific inquiry and invalidation.
THE CONNECTION OF RACE, EVOLUTION, AND PURPOSE. In chapter 8, Coyne carefully (and excellently) deals with the issue of race, a very difficult topic indeed. The connections he makes there are addressed with an almost empathic caution that validates the concerns and realities, and exhorts scientists to be careful when approaching this crossroad. It should be appreciated that Coyne does the same thing in chapter 9 with the whole of the evolution/religious themes and the philosophies of Christians especially. He is to be commended on the carefulness with which he deals with that topic, and he illuminates well the heart of the issue. However, it appears that Coyne draws direct scientific lines between genetics and race that bolsters the incoherence of those connections (citing the differences in genetic information and the construct of race), but when it comes to providing that same connection between evolution and social behavior as a whole, the relationship seems more blurry. The leap to social implications seems to be a wider chasm, which may need to be illuminated in order to understand more clearly the vehement resistance that people have to evolution.
SUPERNATURAL EXPLANATIONS DO NOT MEAN THE END OF INQUIRY. Coyne writes, “supernatural explanations always mean the end of inquiry: that’s the way God wants it, end of story. Science on the other hand, is never satisfied: our studies of the universe will continue until humans go extinct.” While it must be understood that Coyne is observing and addressing correctly the assertions and implications of this theologically dogmatic proposition, this is, fundamentally, fallacious logic, whether it is held by a religious person or someone criticizing a person’s religious beliefs. The more theologically astute position would embrace the mystery, discovery, and inquiry of the means and processes of God, even if one held a conviction of the desires of God. In addition, a “creation conviction” (that God created everything) would necessarily include “scientific curiosity and inquiry.” That is, a sophisticated theology embraces science as part of that creation, and would never bifurcate or falsely dichotomize the two in conflict. Again, Coyne is rightly addressing the assertions of many who claim otherwise, so this comment is not so much against Coyne, but the proposition itself.
FREE WILL? Coyne says, “The world still teems with selfishness, immorality, and injustice. But look elsewhere and you’ll also find innumerable acts of kindness and altruism. There may be elements of both behaviors that come from our evolutionary heritage, but these acts are largely matters of choice, not of genes.” (230) Coyne writes later, “In many countries, the equality of men and women is now taken for granted. Richer nations are becoming aware of their obligations to help, rather than exploit, poorer ones.” (231) There is far too much philosophy to elucidate here regarding these quite loaded statements. One could argue with the premises, of course, or question the validity of morality and naturalistic evolution, but this is a biology book, not a philosophy book. However, that’s the point. Without delving deep, suffice to say, it seems here is the crux of the issue, or at least an example or illumination of the very problem that was stated in the beginning of the book, and is platformed in thousands of contemporary conversations. It is this invocation of the possibility of free will, the issue of morality, and the global consciousness, that highlights the deeply intertwined social and philosophical implications which are naturally (pun intended) and deeply connected to evolutionary theory and constructs. It appears that even Coyne himself cannot ignore nor fully explain (not talking about evidence) this relationship even though he states that, “Evolution is neither moral nor immoral. It just is, and we make of it what we will. I have tried to show that two things we can make of it are that it’s simple and it’s marvelous.” (233) The problem, of course, is that we have made much of it. The religious and the naturalists, the faithful and the secular. While marvelous, it is not simple.
THANK YOU. Sentimentally and humanistically, thank you. The conversation can hopefully be more intelligent, informed, respectful, and fruitful because of Coyne’s contribution in explaining Why Evolution is True.