Jerry Coyne, Why Evolution is True (2009)

Jerry A. Coyne, Why Evolution is True. Viking, Feb. 2009.

This is another of a dozen or so most significant books that I’ve read over the past decade or more that I’ve put off writing up on this blog simply because my notes were long and so it’s more of a chore than usual to boil them down to a coherent post that anyone might actually read. But I’m finally catching up on these and determined to finish in another few weeks.

This is one of two books that appeared in 2009 (the other by Richard Dawkins) that laid out the varieties of evidence that evolution has in fact occurred, and is not, as detractors claim, “just a theory” or “a theory in crisis.” (The other book by Dawkins obviously has some overlaps with this one, but each of these authors makes some distinct points, too.)

Jerry Coyne was a professor (now retired) at the University of Chicago who realized that “even many of my fellow biologists were unacquainted with the many lines of evidence for evolution” (pp xix – xx). So this book lays out those main lines of evidence, for them, and for the many lay readers who accept evolution but may need talking points to defend themselves.

Coyne (or perhaps his publishers) set up a promotional website for the book, with the same name (, where he continues to post, though mostly on social and political issues these days.

The book is about 240 pages of text, with another 50 pages of notes, references, and index.

(Note: I use abbreviations like mya to mean “millions of years ago”)


As usual I didn’t boil down my 6000 words of notes much, though I did refine them; so here is the summary reduced to numbered points:

Coyne outlines the multivarious lines of evidence for the fact of evolution. He discusses the modern theory of evolution and its six components, including the fact of biological evolution (though all the evidence), the idea of natural selection, and so on, the kinds of predictions it can make as a theory, and how evidence for 150 years has repeatedly confirmed those predictions. The lines evidence boil down to

1) the evidence of the fossil record;

2) the evidence of vestiges and atavisms in current biological features that were once useful but are now useless or even harmful;

3) how the distribution of species around the world, how there are different species on different islands and continents, in patterns that show their geographical spread;

4) how the appearance of “design” is explained by natural selection, an idea that still shocks people;

5) how sex drives evolution, the differing mating strategies of the two sexes prioritizing different kinds of health;

6) how species — populations that don’t interbreed with other groups — arise via reproductive barriers, e.g. separated by mountain ranges, continental drift, etc. ; analogous to how languages evolve; and

7) How evidence for human evolution, once only a speculation by Darwin, has been elaborated and compounded.

And finally he addresses how evolution entails notions of purpose, morality, and meaning, thus frightening conservatives; but genes aren’t destiny, and we make our own purposes through work, family, avocation, contemplating the universe.


Excellent book, for compiling at a high level (unlike so many science books that focus on relative minutia) all the lines of evidence for one of the greatest theories of all time, that explains one of the most revelatory facts of history of all time. I was familiar with much of its ideas, of course, but the idea that species arise from slow geological divisions that separate populations, was new to me.


  • Author cites a 2005 Pennsylvania lawsuit over teaching evolution and intelligent design in schools; the decision came down for evolution and against ID, but this was part of a never ending battle.
  • “For those who oppose Darwinism pure as a matter of faith, no amount of evidence will do—theirs is a belief not based on reason. But for the many who find themselves uncertain, or who accept evolution but are not sure how to argue their case, this volume gives a succinct summary of why modern science recognizes evolution as true.” P xiv.


  • The process of evolution, natural selection, is a mechanism of staggering simplicity and beauty. Darwin’s idea has been called the greatest idea that anyone ever had. His evidence that life had changed over time was accepted relatively quickly even though no mechanism was then known; genetics was unknown at the time. Those ideas were worked out in the early 20th century, and evidence has continued to mount. There is no doubt among scientists…
  • So why is a book needed? Because the idea that we’re related to other creatures, that maybe we’re not divinely special, bothers many people; it has implications in morality. This resistance stems largely from religion. Creationism always derives from religion. Despite all the evidence, many Americans simply don’t believe it. Only 40% of Americans accept evolution. European countries fare higher.
  • So this book will discuss the many lines of evidence for evolution, and why accepting it won’t lead to dire consequences of meaning, morality, or even religious belief.

Ch 1, What Is Evolution?

  • The seeming “design” of plants and animals, cf. William Paley, is an illusion, an effect produced by evolution and natural selection.
  • The modern theory of evolution can be summarized thusly: “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 time, throwing off many new and diverse species; and the mechanism for most (but not all) of evolutionary change is natural selection.” P3.7
  • The statement comprises six components: evolution, gradualism, speciation, common ancestry, natural selection, and nonselective mechanisms of evolutionary change.
  • 1st, Evolution just means change over time. Species change, based on change in DNA, originating as mutations. Different species change at different rates.
  • 2nd, Gradualism means that substantial changes take thousands or millions of generations.
  • 3rd and 4th, Speciation and common ancestry are flip sides of the same coin. All species share certain traits: common biomedical ways to use energy, the DNA code—which suggest a common ancestry. But over time a species splits, leading to different species. Speciation means the evolution of groups that can’t interbreed, generally when two populations of a given species are separated somehow and then gradually evolve in different manners. You wouldn’t notice at the time. And most species, 99 percent, go extinct without leaving descendants. The history of life forms a tree, all starting from the trunk, with branch splits at common ancestors. Every pair of species shares a common ancestor in the past; closely related species have them in the more recent past. Example of vertebrates, figure 2, of the features biologists use to deduce evolutionary relationships. Actually, the relationships had been noticed starting with Linnaeus in 1635.
  • Varieties of things that didn’t evolve don’t have similar nested arrangements—e.g. matchbooks. A creationist explanation of life wouldn’t result in such a hierarchy as we see.
  • In the past 30 years the understanding has deepened with genetic analysis. This analysis results in predictions about where the fossil records we can find common ancestors, predictions which have been fulfilled.
  • 5th, natural selection, was the most revolutionary idea of Darwin’s time, because it explains the apparent design in nature in ways that don’t require creation or supernatural guidance…. example of wooly mammoth.
  • The process requires only that individuals vary genetically in their ability to survive and reproduce… given this, natural selection, and evolution, are inevitable.
  • You’d expect something different if organisms were consciously designed. Natural selection works from the materials at hand, so its results are never perfect, and often flawed (thus so many extinctions, which ID supporters can’t explain). Mutations are changes in traits that already exist; evolution never starts from scratch. This results in numerous compromises – e.g. men’s testes. Such imperfections are important evidence for evolution.
  • 6th, processes other than natural selection. Random changes can cause evolutionary change without adaptation.
  • The six parts are not necessarily interdependent. Teleological forces were once proposed as the force of evolution.
  • But is it ‘only’ a theory? Author discusses what science means by theory. A scientific theory must be testable and make verifiable predictions. Atomic theory and general relatively made predictions that were later observed. A theory becomes ‘true’ as evidence mounts without decisive counter-evidence.
  • Evolution can make predictions, e.g.
    • We should see evolutionary change in the fossil record, more primitive species in the oldest rocks.
    • We should see cases of speciation in the fossil record, and see new species forming in the wild.
    • We should be able to find species that link groups having common ancestry, like birds with reptiles (‘missing links’ or ‘transitional forms’).
    • We should find genetic variation in species.
    • We should see examples of imperfect adaptation.
    • We should see natural selection acting in the wild.
  • There are also ‘retrodictions’, facts that make sense only in light of theory of evolution. Examples are covered in chapters 3 and 4.
  • Darwin collected data for 20 years. We now have 150 more years of evidence that evolution is true.

Ch2, Written in the Rocks

  • The historical evidence for evolution is the fossil record. Fossils were known in ancient times; Aristotle discussed them; they may have inspired mythical creatures like the griffin.
  • How fossils form…they endure shifts in the earth’s crust; then they must be close enough to the surface now to be found. It’s estimated only 0.1 percent of all species have been found via fossils.
  • The fossil record was first put in order by [European] geologists who were creationists, i.e. they accepted the account of life in Genesis. They put the fossils in order of the strata they were found in. a complete ordering requires correlating strata from different locations around the world. (Not all layers are found in all places.) The principle of superposition was devised by a man who later became an archbishop. The complete record was ordered by the 19th century. But that order only indicates the relative ages of rocks, not their actual ages.
  • Since 1945 we can measure actual ages or rocks using radioactivity; certain elements decay at constant rates, their ‘half-life’, since the rocks were formed. Uranium 238 is used for old rocks, with a half-life of 700 million years. Carbon 14, half life 5730 years, is used for younger rocks, or human artifacts. Correlating different measures always agree. The half-life rates don’t vary, as creationists claim. Such dating of meteorites indicates the earth and solar system are 4.3 billion years old. Another check is the biological details of coral, indicating how much shorter the day was 380 million years ago.
  • How would the fossil record provide evidence for evolution? We would see the simplest life forms in the oldest rocks; the youngest rocks would have fossils more like living species. We would see evidence of splitting of species. The fossil record in Darwin’s time was sparse, but since then, many more fossils have been discovered, fulfilling all those predictions.
  • Figure 3 p.27 shows a timeline of life’s history. (Note that ‘first appearance’ of any form is somewhat arbitrary, given transitional forms.) There were only single cells for 2 billion years beginning 3.5by ago. Patterns are similar from animals to plants. No special theory of creation can explain these patterns.
  • Plankton are convenient specimens since they die continuously and pile up in layers on the sea floor. Take core samples of the seabed shows evidence of evolution of plankton, and other microorganisms, and later trilobites. We usually can’t understand what evolutionary pressures caused such changes, because the environments themselves are not preserved.
  • The fossil record also includes occasional ‘transitional forms’, some of which were predicted in advance of discovery. E.g. the common ancestor of birds and reptiles.
  • One example is the transitional form between fish and amphibians—Tiktaalik roseae in 2004. Neil Shubin (who wrote a book about it) was part of a team that predicted such fossils in 375mya strata. After five years of looking, they found it.
  • Birds: what use is half a wing? Intermediate stages are not hard to imagine—gliding… as some creatures do. Links between birds and reptiles were known even to Darwin. Archaeopteryx was discovered in 1860. More recently discoveries in the 1990s in China, of theropod dinosaurs. … speculation about how natural selection fashioned modern birds.
  • Evolution of whales: Duane Gish makes fun of the idea that whales emerged from animals related to cows. But some animals do live both on land and in water—the hippo. As for whales, we can look at the fossil record. Whale fossils show up at 30mya; we can look for transitional forms before that—they show up 52 to 40mya. (see figure 12, p50). Whales from land animals occurred in just the past 10my.
  • These are only a couple examples out of hundreds. A few more: a transitional form between wasps and ants. And an early snake fossil indicating descent from reptiles.
  • The fossil record 1) confirms predictions of evolutionary theory; 2) shows that transitional forms occur precisely where they should be; 3) indicates that evolutionary change involved remodeling the old into the new.
  • There is no reason why a celestial designer should have made new species from old; they all could have been constructed from the ground up.

Ch3, Remnants: Vestiges, Embryos, and Bad Design

  • Manuscripts on parchment that were overwritten, recycled, called ‘palimpsests’. Traces of the earlier writings can often be detected; thus three treatises by Archimedes were discovered.
  • Organisms are palimpsest of evolutionary history. Vestigial organs make sense only as remnants of traits that were once useful in an ancestor.
  • Vestiges
  • Anecdote about trying to photograph an ostrich running. Its wings are a vestigial trait. Fossils show ostriches are descended from birds that flew; now, the wings are used for other things—for maintain balance, and to threaten its enemies. There are dozens of other species of flightless birds around the world. They all have wings. The penguin’s became flippers.
  • We have good guesses about why such species lost the ability to fly. Many are on islands; many islands lack mammals and reptiles. Flight is metabolically expensive; when not needed, selection would favor mutations that would result in reduced wings.
  • Vestigial eyes are common in burrowers and cave dwellers.
  • Whales have vestigial pelvis and leg bones—not even connected to the rest of the skeleton.
  • Humans have the appendix, once an organ that was used to digest cellulose. At one time, more than 1 person in 100 died of appendicitis. Surgery has now eliminated the natural selection against it.
  • We also have a vestigial tail; tiny muscles that give us goose bumps (once used to raise fur as insulation or defense); and the muscles that allow some people to wiggle their ears.
  • Atavisms
  • These are anomalies that look like the reappearance of an ancestral trait – a horse with an extra toe, or a human baby with a tail. These occur only occasionally. Some whales are even born with a fully formed rear leg. These result from dormant genes that were reawakened in some way. Horses sometimes reveal extra toes—they were regarded as supernatural wonders by Julius Caesar and Alexander the Great.
  • In humans, the most striking one is the human tail. …when they occur, they’re removed by surgeons.
  • Hen’s teeth can be brought about by grafting tissues of a chicken embryo with that of a developing mouse… a protein from the mouse enables dormant genes for teeth to form.
  • Dead Genes—
  • From the previous examples, we can predict that many genomes will contain silenced or ‘dead’ genes that are no longer expressed. Vestigial genes. We can read DNA code now and test such predictions. And these predictions have been fulfilled—virtually every species has such pseudogenes, some still active in relative species. Out of 30,000 human genes, there are about 2000 pseudogenes. The most famous is one that, in other species, is used to make vitamin C (which is why humans have to get it in food). Furthermore, this pseudogene is more similar between close relatives than between distant ones. These facts make no sense if these species were specially created.
  • We also harbor dead genes from other species—retroviruses, like HIV, that insert themselves into the DNA of host species, and some examples of common locations in related species point to common ancestry. Another example: the genes that give mice a strong sense of smell, but a poor one in humans. In humans these genes became inactivated, since we depend more on vision. Dolphins have even more of these genes deactivated.
  • Palimpsest in Embryos
  • Comparative anatomy in the days before Darwin found things that didn’t make sense, like the similarity of vertebrate embryos (which look like fish at one point), but which make sense given evolution. Embryonic features called branchial arches develop into different structure in different animals. The development of blood vessels shows similar developmental patterns. These developments recapitulate the evolutionary sequence…because evolution adds new stuff onto the old stuff, a sequence that’s mirrored… ontogeny recapitulates phylogeny. This is true only to the extent that embryonic stages resemble the embryonic forms of ancestors.
  • Darwin considered embryology his strongest evidence for evolution. Other examples have been found since. One is the period as embryos that humans are covered with a coat of hair called ‘lanugo’. The grasping reflex of infants may be another.
  • Bad Design
  • Every species is imperfect in many ways… e.g. our appendix. If organisms were built by a designer, there should be no such imperfections. Whereas imperfections are what we would expect from evolution. New parts are built on top of old ones, so compromises are necessary.
  • Flounder (Dover sole – it’s flat and so easy to bone) is a species of flatfish; they’re born upright, then a month later both eyes migrate to one side so the fish can swim flat along the bottom. Poor design, compared to fish that are born that way.
  • Another example is the laryngeal nerve of mammals, which loops around the aorta, much longer than it needs to be. It makes sense only knowing the evolutionary history of fishlike ancestors.
  • Also: the descent of male testes, which involves risk of hernias; the urethra running through the prostate gland, an organ prone to infection. Another famous example: the size of women’s pelvises vs. the large size of infant heads.
  • Michael Behe (an ID proponent) argues that a designer might have had some other reason for designing these features. Author: “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.”

Ch4, The Geography of Life

  • Isolated islands between south America and Africa. A real-life predecessor to Robinson Crusoe. These islands have many ‘endemic’ species found nowhere else in the world, and also no native species of amphibian, reptile, or mammal. Such patterns on many islands are striking evidence for evolution. As Darwin realized; his two chapters on ‘biogeography’ have been refined and supported by later studies. Creationists just pretend this evidence doesn’t exist.
  • Some theologians tried to reconcile these patterns with the Noah’s Ark story. Not plausible; so they retreated to a theory of multiple creations. Problems there too. Then came Darwin, though he didn’t figure everything out. Now we understand about continental drift, which explains certain patterns. And from DNA taxonomy we can see the times since different species diverged. All these evidence are consistent and support evolution.
  • Continents
  • Different areas with similar climates and terrain nevertheless have different types of life. No cacti in old world deserts, for instance. Marsupials in Australia, and placental mammals, in the rest of the world, fill similar roles.
  • If these animals and plants were specially created, why wouldn’t similar environments have similar lifeforms? Evolution explains this by a process called convergent evolution, demonstrating common ancestry, speciation, and natural selection. Predictions can be made, e.g. fossil marsupials on Antarctica—that were found. Similar predictions can be made about fossil ancestors of existing species. This led to Darwin’s hypothesis that humans evolved in Africa—before fossils of early humans were discovered there, beginning in 1924.
  • And continental drift explains patterns of glacial scratching in south America and Africa… during the Permian.
  • Islands
  • There are two types: continental islands, that were once connected to continents; and oceanic islands, which were not. The latter are missing many native species we see on continents and continental islands, and usually the same missing groups. No mammals, amphibians, or fresh-water fish. Yet these species do quite fine on these islands when humans introduce them there; in fact they often destroy native forms.
  • The kinds of species that are on oceanic islands are present in many similar species, e.g. the Galapagos finches. Honeycreepers in Hawaii. Other examples. The species that are common on oceanic islands are those that can disperse, by floating or flying. Even some aerial mammals, an aquatic mammals.
  • Dispersal events can be rare and still happen over enough time—see example p106m.
  • Finally, the species on oceanic islands are most similar to species found on the nearest mainland.
  • Continental islands, of course, have species similar to the continents, since they were populated before splitting away. And very old continental islands have evolutionary patterns between those of oceanic island, and young continental islands.
  • Only evolution can explain these patterns (unless the creator intended to make species *look* as they evolved that way). These patterns combine chance and lawfulness. And explain why island ecologies are relatively fragile.

Ch5, The Engine of Evolution

  • About the Asian giant hornet. They attack introduced European honeybees and destroy their nests. But the honeybees native to Japan can fight the hornets off—they swarm on the invader and cook it to death. The European honeybees will either die-off, or survive via some (other) adaptation to fight the hornets.
  • Other adaptations: a roundworm that infects ants. Parasites. Animals that look like plants and vice versa. The woodpecker’s skull.
  • These are *seem* designed, but Darwin explained how natural selection works. “It is hard to overestimate the effect that this insight had not only on biology, but on people’s worldview. Many have not yet recovered from the shock, and the idea of natural selection still arouses fierce and irrational opposition.” P115b
  • Since Darwin we’ve accumulated lots of evidence that it works.
  • It’s the most misunderstood part of Darwinisn. Example of white mice…. natural selection is a process; there’s no conscious striving.
  • It requires that a population has variation; the variation has to be at least partly genetic; and that the genetic variation must affect an individual’s probability of reproducing. Note that ‘random’ variation of mutations just means that mutations occur regardless of whether they would be useful to the individual (p118m); you could just as well call then ‘indifferent’ mutations.
  • It’s a misunderstanding that in evolution “everything happens by chance”. The mutations are chance, but the process of natural selection is not.
  • Natural selection has to explain everything about the nature of species, and create new features based on earlier features.
  • We can make predictions: that we can imagine plausible scenarios for the evolution of any trait; that each adaptation must increase the reproductive output of its possessor. You won’t see adaption in one species that only benefit other species. And adaptations increase the fitness of individuals, not the species or group.
  • Note that natural selection isn’t the *only* process of evolutionary change. In small populations, proportions of alleles can change by chance. This is called genetic drift. Examples are frequencies of blood types in different groups. In small populations genetic drift can overwhelm selection.
  • Animal and plant breeding is obvious evidence that selection works. Domestic dogs came from a single gray wolf species about 10,000 years ago. Wild crop plants, in the last 12,000 years.
  • We can also demonstrate selection in the test tube, and see thousands of generations in real time. … examples p128f.
  • Other examples: resistance to drugs and poisons. Antibiotics. Best example we have of natural selection in action. Staph strains become resistant to penicillin. Drugs against viruses. An arms race. Requiring the pharmaceutical companies to keep making new drugs as the old ones become ineffective.
  • Can we see selection in the wild, without human intervention? Examples in ‘higher’ plants and animals are necessarily rare, and slow. Best cases are whether species are adapting to a new environment. Famous examples include the finches of the Galapagos Islands. Soapberry bugs that live on new varieties of plants. Flowers that bloom earlier during droughts.
  • But can selection build complexity? Of course, there is no alternative theory, aside from supernatural ones. IDers give examples of complex traits they think couldn’t have evolved. God of the gaps. As more is understood, ID is forced to retreat. And ID can explain *anything*; it makes no predictions, has no possible observations that would disprove it.
  • And we can imagine plausible pathways for these many traits, even blood-clotting mechanisms eg. We can also compare time-rates of observed evolution and conclude that there was plenty of time for the fossil record to develop as it did. “don’t appreciate the immense spans of time…” p141m. And Darwin himself rebutted the argument about the complexity of the eye. … details.

Ch6, How Sex Drives Evolution

  • The colorful tails of peacocks seem to violate Darwinism; they are maladaptive. And why aren’t females equally colorful? Other species pose similar problems: huge antlers; strange behaviors in bower birds; bright colors, which attract more predators.
  • These are called ‘sexual dimorphisms’. Darwin realized they are nearly always restricted to males. The key is that selection is not keyed to survival—but to reproduction. Darwin called it ‘sexual selection’, selection that increases an individual’s chance of getting a mate.
  • Two forms. One is about direct competition between males; the other is female choosiness among possible mates. Plenty of evidence: elephant seals who battle for harems; birdsongs that are threats. Some competition goes on even after the sex act, to protect against other males impregnating the female. Some species have offensive weapons to remove the sperm from previous males. Darwin and Wallace split on aspects of sexual selection. Experiments have been done to validate female choice.
  • Why is it males compete for females? Because the differences between sperm and egg. Why does sex exist at all? It’s still something of a mystery. An individual sacrifices 50% of his genes. Under natural selection, a gene for parthenogenesis would spread quickly. But it hasn’t happened. One reason may be the shuffling of genes enables faster evolution to counter changing environments.
  • But why two sexes, and why the different sizes of sperm and eggs? Theoretical models have shown these situations are the most stable. That leads to different mating strategies of sexual selection. Males can produce many more children in a life than females. The strategies reflect differential investment. For males, mating is cheap; for females it’s expensive. Thus conflicting interests in choosing mates. Males can be promiscuous; females are choosy. The variance in the range of mating success is higher among males. Few species are monogamous. Some ‘socially monogamous’ species display sexual dimorphisms… because they are not *actually* monogamous. Wrens among whom adultery is rife. Many bird species display similar behaviors. Occasional species, like seahorses, display reverse patterns, in which males invest more time in raising young than the females. Again, evolutionary theory explains all these patterns, which creationism cannot.
  • What do females look for in a mate? Darwin proposed that females made purely aesthetic choices. He wasn’t quite right. Evidence has revealed two answers: females can benefit directly by choosing males to provide child care; or indirectly, by choosing males who have better genes than others. … signs like bright colors or huge tails are signs of overall health. Only two studies have shown this: with gray tree frogs, and peacocks.
  • A third explanation is ‘sensory-bias’—the biases in the female’s nervous system that reflect survival strategies. Several studies have shown that females respond strongly to unfamiliar traits.

Ch7, The Origin of Species

  • Ernst Mayr gathering birds in New Guinea. It was later realized that the locals and western taxonomists classified different birds in virtually the same way—i.e. the existence of distinct groups, species, is an objective fact. How do species arise? Darwin actually didn’t do a very good job of explaining them; he focused mostly on adaptations.
  • It wasn’t until the 1930s that the problem was addressed. Now we have fairly complete ideas, and evidence.
  • What are species? One idea is simply by morphological resemblance. One problem is there are differences between males and females; between groups in difference places [humans]. And some species look virtually identical [but don’t interbreed]. Mayr and others recognized this and in 1942 proposed the definition of species that stands: an interbreeding population that doesn’t interbreed with other groups. (p172)
  • Why don’t related species interbreed? Their mating seasons don’t overlap; different pheromones or mating displays and thus don’t find one another attractive. Among animals, a fetus might die before birth, or be sterile.
  • Such groups are also evolutionary communities—changes can spread throughout that community but not farther. A unit of evolution. How do reproductive barriers evolve? Similar species are often separated by geological barriers. Mountain ranges, continental drift, glaciers, deserts, drought… which might later disappear. Isthmus; rivers. Isolation by travel to oceanic islands.
  • Species don’t arise because there are empty niches in nature; they are evolutionary accidents resulting from spatially isolated populations. Similar to languages (p177…) Which can be traced into the past by examining similarities of words and grammar, much like reconstructing evolution via DNA analysis. (OTOH languages can cross-fertilize by exchanging words and phrases. (See Pinker, The Language Instinct, for further discussion.)
  • Evidence? The pace is so slow we can’t witness it. But we can make predictions and calculations. Given one species 3.5 billion years ago, it could have become 100 million by now even if each ancestral split happened only once every 200 million years (!). [[ good example of how time scales allow much to happen that would seem to human intuition impossible; it’s like that chessboard example in which the amount of money doubles from one square to the next ]]
  • Scientists can isolate different populations in labs and see what happens, e.g. with fruit flies. Genetic barriers have occurred in a year p180. We can also study sister species to see how long ago they split, relative to whatever geological barrier separated them. E.g. species on either side of the Isthmus of Panama, formed 3mya. We also see isolated populations of single species beginning to isolate. And we see that reproductive isolate increases slowly with time.
  • The way we discover how species arise is similar to how astronomers discover how stars ‘evolve’ over time.
  • So geographic speciation is the most common; ‘sympatric’ speciation is also possible, but uncommon. We’ve seen a few examples (cichlids in lakes in Cameroon). Polyploidy speciation… especially in plants, where sterile hybrids have been bred for human consumption (bananas)…. resulting from changes in chromosome number; it can happen relatively very fast. We’ve seen at least five new plant species that arose this way; hybrids between native species and an introduced one.

Ch8, What About Us?

  • 1924, Raymond Dart acquired a box of fossils and quickly realized he had something remarkable. Darwin had speculated that our species originated in Africa because our closest apparent relatives live there, but he had no evidence. Dart found the first evidence, a skeleton of what came to be called Australopithecus africanus. It was the first of many fossils that showed humanity’s descent from other apes, that our closest cousin is the chimpanzee, and they we diverged from a common ancestor several million years ago.
  • It’s significant that resistance to evolution focuses on the claim that *humans* evolved—this was the issue in the Scopes ‘Monkey Trial’. [[ People don’t care whether *other* animals evolved. ]]
  • Later discoveries included those in the Olduvai Gorge in the 1930s, and “Lucy” in 1974. These show our place in a tree of evolution that includes other primates, a relationship confirmed by molecular data derived from DNA and protein sequencing. The divergence was about 7 million years ago. We can imagine what our common ancestral species was like, though keep in mind that the fossils we find are as often specimens of various species, many of which went extinct and haven’t survived to the present. But we see a trend from smaller brains and larger teeth, and toward great bipedalism, in species, over time. (figures 24 and 25)
  • Most specimens go back only 4my, though several from about 6my have been recently discovered. One discovery is that bipedalism came *before* brain sized increased. Tool-use appears about 2.5my in Homo habilis. Homo erectus was the first to leave Africa; it lasted from 1 ½ mya to about 300,000 ya, though one of its descendants may have been Neanderthal man, which showed up about 230,000ya, then abruptly disappeared 28,000 years ago. The prevailing theory seems to be that Homo sapiens spread out of Africa (beginning about 60,000ya) and replaced both H. erectus and the Neanderthals… Meantime other offshoots, like the so-called ‘hobbit’ specimen discovered in 2003, may have survived until must later (18,000) by being isolated.
  • (Tellingly, creationists can’t even agree on which fossils are human and which are apes.)
  • What drove this evolution? Possibly climate; Africa was in drought from 10 to 3 three million years ago. Bipedality enabled efficient travel, a posture above the surface, or a greater ability to use tools to gather new kinds of food.
  • Another question is exactly which genes distinguish humans from other species. An initial finding was that our genes are only about 1.5% different from chimp genes. However this is misleading: 1.5% variation in a protein sequence leads to many more differences in actual proteins.
  • Such analysis brings up the question of race, i.e. populations of a single species that are geographically separated and that differ genetically. Evidence suggests that average variation between races is far smaller than typical variation among individuals. Some variation may be response to environment: the sickle-cell anemia trait confers resistance to malaria. The obvious skin and hair differences are likely the result of sexual selection among isolated groups; such selection driven by cultural change can produce changes relatively quickly.
  • Some changes are the relatively recent effects of selection on different populations: the endurance of lactose tolerance tied to populations that did or did not begin domesticating cows 7-9,000 years ago,
  • Are we still evolving? Possibility, maybe even in a negative way: improvements in nutrition and medical care keep many people alive, and reproducing, today, who would have died on the African Savannah. OTOH some genes that were useful then have meretricious effects now: the craving for sweetness, from things that were rare but nutritious on the savannah, now results in obesity and heart problems because these things are now plentiful. The effects depend on whether they affect people before or after they stop having offspring…
  • But are we getting stronger, smarter..? We don’t know. Unless we start deliberate genetic manipulation…

Ch9, Evolution Redux

  • Still, people can see the evidence and remain unconvinced. There’s plenty of evidence. Predictions have been fulfilled. Hundreds of new experiments and observations every day confirm the truth of evolution. We don’t see observations that disprove it. The major tenants have been verified. That doesn’t mean there aren’t details that haven’t been worked out. These issues don’t discredit the basic principles; they’re how they are understood and developed.
  • The problem seems to be the implications of evolution about purpose, morality, and meaning. [[ of course this is why critics of evolution of life don’t worry about the evolution of stars. ]] Evolution presupposes a worldview of naturalistic materialism. Supernatural explanations are not needed. Yet people do need a sense of what to do, how to behave, what it all means. Evolution cannot provide that.
  • A common fear is that if we recognize we are evolved animals, morality goes out the window, a common criticism from right-wing pundits (DeLay, Coulter). ‘Selfish’ gene (Dawkins’ term) does not mean selfish in the orindary sense. In recent years evolutionary psychology has explored how human behavior can be understood as natural selection operation on our ancestors. All human societies share a number of human ‘universals’ –language, male dominance, religious belief, art, dance and music…. Which we can understand as having arisen in the 300,000 generations humanity lived as hunter-gatherers. Still, evolutionary explanations can be too easy, a sort of ‘just-so’ story. But surely some behaviors are adaptive: eating, sleeping, a sex drive, parental care, favoring relatives over nonrelatives. (These do not have to be ‘learned’ culturally.) Also perhaps likely: sexual behavior in males vs females. And other behaviors sometimes seen as adaptation, but for which we have no evolutionary understanding: religion, morals, music. [[ But evolutionary bases for these have certainly been proposed. ]]
  • And in any case, genes aren’t destiny; there are plenty of ways we can overcome effects or tendencies provided by our genes. And social standards change: slavery, human sacrifice are no longer considered permissible; equality of sexes is increasingly the norm. [[ A major theme of Steven Pinker. ]]
  • Evolution is purposeless, but we make our own purposes through religious or secular thought. Work, family, avocations, contemplating the universe. Einstein quote. Science means accepting a sense of humility and knowing we’ll never have all the answers. Accepting evolution won’t sunder society; we know that from the many European countries that have done so and still thrive. On the contrary…

The study of evolution can liberate our minds. Human beings may be only one small twig on the vast branching tree of evolution, but we’re a very special animal. As natural selection forged our brains, it opened up for us whole new worlds. We have learned how to improve our lives immeasurably over those of our ancestors, who were plagued with disease, discomfort, and a constant search for food. We can fly above the tallest mountains, dive deep below the sea, and even travel to other planets. We make symphonies, poems, and books to fulfill our aesthetic passions and emotional needs. No other species has accomplished anything remotely similar.

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.


Personal comments: I’ve always thought the resistance among the religious to evolution is psychological or at least ideological; they do not or cannot admit the evidence and draw rational conclusions.

Rather, they are driven by human vanity. They can’t bear the thought that, in a deep sense, humans are animals, even though, physiologically, the resemblances are obvious. Perhaps an alternative explanation for the resistance is the inability of humans to appreciate the incredibly large spans of time in which, bit by bit, evolutionary changes occur and new species evolve. Or perhaps simply the unwillingness to admit that things do change — the bane of conservatives.

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