In elementary school and high school, I never heard a science teacher mumble a word about evolutionary theory, much less introduce a lesson about it. The church community I grew up in would not touch this issue, except perhaps to condemn it with furrowed brows. Even in university at the time, in the late 80s, evolution was left out of my introductory biology class.
I am so grateful to have discovered evolutionary biology, mostly on my own in my early 20s. It reminded me of studying astronomy or physics or mathematics—there is an awe and wonder that comes from understanding how the universe is made, and another layer that comes from appreciating the brilliant reasoning that allowed us to understand the formation of stars, the laws of motion, and the origins of all life on Earth.
It's understandable why my church elders were silent: evolution explains the origins and diversification of life in a way that directly contradicts literal religious or mythological accounts of creation. It is certainly possible to remain religious while accepting evolution—many people do—but for some believers, evolutionary biology feels like an unacceptable affront to faith, because it replaces a story of intentional design with a story of natural processes unfolding over vast time.
There are experts in evolutionary science who can explain this far better than I can. Still, I want to set aside space for it in my own voice, because the basic logic is not hard to understand, the evidence is overwhelming, and the emotional resistance to it often has very little to do with evidence and a great deal to do with identity, belonging, and sacred narrative—topics I have already been discussing.
What follows is a tour through the core mechanism of natural selection, a few common misunderstandings, the idea of speciation, and then several side corridors that matter for this essay: cultural evolution, sexual selection, and the uncomfortable fact that even religiosity itself is shaped not only by culture, but also by temperament, inheritance, and biology.
Selection
Natural selection is the central guiding principle of evolutionary theory. The logic is profoundly simple. It requires only that we accept three basic facts:
1) Organisms vary (physically, physiologically, behaviourally).
2) Some variation is heritable (traits are influenced by DNA, even though environment matters enormously too).
3) Some traits affect reproductive success—not in a morally loaded sense of “deserving,” but in the literal sense that some variants leave more surviving offspring than others.
If a heritable trait increases the probability of leaving more surviving offspring in a particular environment, then over generations the population will contain more of that trait. If a trait reduces reproductive success, it tends to diminish. That’s it—natural selection is differential survival and reproduction acting on inherited variation, repeated over time.
You can see the basic logic everywhere, from selective breeding in crops and animals (“artificial selection”), to antibiotic resistance in microbes, to the obvious family resemblance in both physical and psychological traits among human relatives. None of this requires the belief that genes are the only cause of traits. It requires only the admission that heredity is a major contributor. A point worth emphasizing, because it is often misunderstood, is that natural selection is not about “improvement” in any moral or progressive sense. It is simply a filter that favours whatever works well enough in a local environment at a given time.
Mutation
DNA replication is highly accurate, but not perfect. Across generations there are small changes—mutations—introduced into genetic material. “Mutation” here does not mean “bad.” It simply means “change.” Most mutations are neutral, many are harmful, and a few are beneficial in a given environment. Sexual reproduction adds still more variation by shuffling existing variants into new combinations, so evolution does not work only with brand-new mutations but also with new mixes of old genetic material.
Mutations do not happen because the organism needs them. A bacterium under stress does not somehow produce the exact helpful mutation it would most like to have. At the deepest level, whether a particular copying error happens in a particular cell at a particular moment is still a fundamentally accidental event. But that does not mean every part of the genome is equally likely to change. Some kinds of DNA changes happen more often than others, and some parts of the genome have a higher probability of experiencing mutations than others. Mutation is fundamentally random in origin, but statistically biased in pattern, and those biases affect what raw material natural selection gets to work with.
When small genetic changes happen to produce a trait that improves survival or reproduction in a particular environment—say, a slightly different beak shape that lets a bird get food more efficiently—those variants will, on average, become more common. They become more common for a very simple reason: the creatures carrying the useful variant survive better and leave more offspring. Over many generations, the accumulation of such changes can produce substantial transformations, including changes in complex organs and behaviours. Darwin’s finches in the Galápagos remain a famous entry point into this idea because long-term field work and later genetic work showed how ecological pressures can shape beak traits across populations.
The Time Scale of Evolution
One reason evolution feels counterintuitive is that large organisms reproduce slowly relative to a human life. Big evolutionary changes can take thousands or millions of years, just as major geological or astronomical processes do. We do not watch a canyon form in a single afternoon, and we do not watch a star age in real time, but the evidence for those processes is still decisive. Evolution is similar: long processes are inferred from converging lines of evidence. Fossils are one line of evidence—imperfect, but immensely powerful. Fossilization is rare and biased toward certain environments and tissues, so the record will always be incomplete. Still, the overall pattern—order in time, branching diversification, and transitional forms—fits evolutionary predictions very well. Comparative anatomy, fossils, biogeography, embryology, and genetics all point to the same branching story.
Common Ancestry and Cousins
A cliché misunderstanding goes like this: “Evolution says humans descended from chimpanzees.” That is not what evolutionary biology claims. Humans and chimpanzees are not ancestor and descendant; they are cousins. And “cousin” is not just a metaphor here. It is literally the right genealogical idea: two living lineages sharing an older common ancestor. In ordinary family language, we talk about first cousins or second cousins. Chimpanzees are obviously not that kind of close cousin; if one insisted on stretching the family language into absurd distances, they would be something like our three-hundred-thousandth cousins. Current genetic evidence places the human–chimpanzee split on the order of about 6 million years ago.
The same logic generalizes outward. Every living thing on Earth is, in the broad genealogical sense, our cousin. For me, this is not depressing at all. It is a source of awe—a kind of cosmic kinship. If a reader wants a visual sense of this, it is worth looking up one of the modern phylogenetic tree charts online, such as OneZoom. The exact dates of particular branching points are still being refined, but the branching structure itself is already known very well. And the scale is staggering. Humans and mice last shared a common ancestor around 90 million years ago. Mammals and birds last shared a common ancestor on the order of 310 million years ago. Humans and fish share a common ancestor on the order of 430 to 450 million years ago. We are talking about tens to hundreds of millions of years, not a few thousand.
Speciation
Over the short term, evolution often looks like shifting trait frequencies within a species. Over the long term, divergence can accumulate until populations become reproductively isolated—meaning they can no longer interbreed successfully under natural conditions. That is speciation.
Speciation is not always a sharp on/off switch. In nature it often behaves more like a continuum. The Ensatina salamander example is a real case, and it is useful because it makes that idea vivid. Around California’s Central Valley, populations of these salamanders spread in a rough loop. Neighbouring populations along the loop can still interbreed with the populations beside them. But by the time the two far ends of the loop meet again in Southern California, they have changed enough that they no longer interbreed successfully with each other, or do so only rarely. A simple analogy would be a circle of people, each speaking a dialect just a little different from the dialect of the person next to them. Each person can understand the neighbours on either side, but the person across the circle sounds incomprehensible. Ring species work something like that, except the differences are genetic and reproductive rather than linguistic. That is the point: species boundaries can emerge gradually, not by magic and not all at once.
One thing I want to state explicitly, because people often get confused here: even if a behaviour or trait has evolved, that does not mean it is morally right, or that we should accept it. Evolution describes how traits spread. It does not tell us what we ought to value.
Compromise, Not Perfect Design
Evolution also does not produce perfect design. It modifies what already exists. That is why living bodies so often look less like clean engineering and more like a history of workable compromise. Humans are full of such compromises. In adult humans, the passage for food and the passage for air share anatomy in the throat, which is one reason choking is even possible. Our spines and backs also show the costs of walking upright. The human spine has an S-shape that helps us balance over our hips and walk efficiently on two legs, but it also turns a structure inherited from four-legged ancestors into a vertically loaded column. The result is chronic stress on the lower back, high rates of disc degeneration, herniated discs, sciatica, and persistent back pain. Human childbirth is unusually difficult because pelvic form, fetal growth, and the evolution of large brains create a tight compromise. It is not as though the body is simply poorly designed. The point is that evolution works with inherited materials and trade-offs, not with fresh blueprints.
The vertebrate eye is another striking example. The retina is effectively wired backward: light has to pass through layers of neural tissue before it reaches the photoreceptors. Where the optic nerve exits the eye there is a literal blind spot, because that patch contains no photoreceptors. And because light must travel through the retinal layers first, the vertebrate eye needs compensatory tricks just to reduce scattering and preserve image quality. Müller cells help act like optical fibers to guide light through this awkward arrangement. The design also forces a trade-off between a clear optical path and the blood supply the retina needs. The system works, but it is hardly what a tidy engineer would draw from scratch. It also comes with structural vulnerabilities: the retina can detach, and when it does, vision can be permanently damaged. The octopus, whose camera eye evolved independently, ended up with a more direct setup. Its retina is everted rather than inverted, so the nerve fibers are routed behind the photoreceptors and there is no comparable blind spot.
Our jaws and teeth tell a similar story. Over time, human faces and jaws have become smaller without tooth size shrinking in perfect proportion. The result is a mismatch between tooth size and available arch space. Softer and more processed diets appear to worsen the problem by reducing the chewing demands that help stimulate jaw growth. As a result, many modern humans grow jaws that are simply too small for the full dental package they still carry, leading to orthodontic problems such as crooked teeth, and impacted wisdom teeth.
The broader point for me is simple: evolved traits are not always functionally ideal. Some have to be restrained, some have to be accommodated, and some have to be counterbalanced by culture. If we want to become more humane, we need rules, norms, education, medicine, and institutions that limit certain inherited tendencies, compensate for the problems they create, and cultivate better ones.
Cultural Evolution
A parallel kind of evolutionary logic shows up in culture. Dawkins coined the term “meme” for cultural units that replicate, but the broader point matters more than the label. Ideas, phrases, rituals, fashions, and institutions can spread, vary, compete, split, and disappear.
Language evolution is a very good example. Languages branch and drift. Over time, groups can become mutually unintelligible—they become different language “species.” Linguists can reconstruct family trees and infer common ancestors in ways that are strikingly analogous to biology. Proto-Indo-European—the distant ancestor of languages as varied as English, German, Greek, Russian, Persian, and Hindi—existed about six to eight thousand years ago. English, German, and Dutch are much closer cousins inside the Germanic family, with a common ancestor a little over two thousand years ago. French, Spanish, Italian, Portuguese, and Romanian are cousin languages that began diverging from Latin roughly fifteen hundred to two thousand years ago. And the same logic extends beyond Europe. Mandarin and Cantonese are also cousins. Their shared recognizable ancestor lies in Middle Chinese, something over a thousand years in the past. What begins as a dialect can, given enough time and separation, harden into a clearly distinct language.
Language divergence does not require millennia only. Some changes become obvious in just the last few centuries. Afrikaans, for example, diverged from colonial Dutch over roughly the last three to four hundred years after Dutch settlement at the Cape in 1652. Even before a speech form is officially labelled a separate language, strong regional varieties can become difficult for outsiders to follow. There are strong accents within Canada, such as Newfoundland English, that can be difficult for other Canadians to understand. Mutual understanding can erode gradually long before people agree on where to draw the boundary.
While Mandarin and Cantonese are cousins, English and Mandarin are not. As I've been learning Mandarin these past few years, I've discovered what it's like to appreciate a language that shares no traceable ancestry with English at all. Somewhere far enough back there probably is a common ancestor—the ancestors of every non-African population left Africa in a single wave around sixty thousand years ago, and every human population has language. But we will never find it. The comparative method reaches back perhaps eight thousand years before the trail goes cold, because words are not copied like genes; they are replaced, one by one, until nothing recognizable survives. This is where the analogy to biology breaks. Life keeps its records in a molecule that copies itself faithfully for billions of years. Language has no direct record at all before the age of writing, and it evolves so quickly that it erases its own history.
Religions also behave this way. Doctrines split. Schisms occur. New denominations form. We see this clearly in Christianity: the East–West Schism of 1054 formalized the great split between Roman Catholic and Eastern Orthodox Christianity; the Reformation is conventionally dated to 1517; and those Protestant branches splintered further into Lutherans, Calvinists, Anabaptists, Anglicans, Methodists, Baptists, Pentecostals, and countless smaller groups. This fragmentation is not just ancient history. In the United Methodist Church, more than 7,600 U.S. congregations left between 2019 and the end of 2023, roughly a quarter of the denomination’s earlier U.S. total.
Buddhism diversified too. One line of early Buddhism led to Theravada, while Mahayana arose later as another major descendant branch around the beginning of the Common Era. Islam experienced its defining Sunni–Shia split in the struggles over succession after Muhammad’s death. The family-tree metaphor is not perfect, but it is illuminating: religions do not descend from heaven as finished products. They branch, drift, quarrel, and split inside history.
Psychologically, that has an important implication: people often treat their own local, historically contingent version of a faith as if it were timeless and universal, when in reality it carries the fingerprints of geography, conflict, institutions, inheritance, and politics.
Sexual Selection
Another important evolutionary idea is sexual selection: traits can spread not because they help survival directly, but because they affect mating success. The peacock’s tail is the classic case—beautiful, costly, cumbersome, and yet selected because it becomes desirable within the mating preferences of the species. Darwin understood that biology is not only about staying alive long enough to reproduce; it is also about courtship, display, preference, and attraction. Richard Prum has argued, persuasively in my view, that sexual selection can include a genuinely esthetic component: preferences themselves can become evolutionary forces, and traits can spread because they are found attractive, not merely because they advertise some practical advantage.
None of which makes us peacocks. But human mate choice does attend to looks, voice, movement, confidence, style, humour, conversation, and perhaps aspects of intelligence itself. Some theorists—notably Geoffrey Miller—have argued that traits such as humour, creativity, artistry, music, and parts of intelligence may have been shaped at least partly by sexual selection because they function as displays: they can signal mental agility, creativity, or the ability to hold another person’s attention. The evidence is mixed and the details are debated, but the idea is serious.
Temperament, Inheritance, and Religion
Religiosity itself is not only cultural. Which particular religious group a person belongs to is largely a cultural and family-transmitted matter. But the broader tendency to be religious at all—to find religion important, compelling, consoling, or identity-defining—shows a meaningful inherited component. Twin research repeatedly suggests that adult religiosity has a moderate hereditary component, but the size depends a great deal on what exactly is being measured. Broadly speaking, estimates often land from the high 20s into the low 60s. More outward or socially enforced measures tend to sit lower, while more inward, identity-heavy, or conversion-like dimensions can sit higher. And when researchers say that some dimension of religiosity has a heritability of 60%, they do not mean that 60% of one person’s religion is “caused by genes.” They mean that, in the population being studied, about 60% of the variability between people on that trait is statistically associated with genetic variability.
What matters more here than raw ability is cognitive style. Some people are more comfortable sitting with analytical doubt and ambiguity; others are more drawn to certainty, authority, and the reassurance of a shared communal answer. Neither style is a measure of intelligence or its absence. (Meta-analyses do report a modest average negative association between intelligence-test scores and religiosity, but the effect is small, appears to have weakened over time, is substantially explained by education, and tells us nothing about any individual believer—a great many brilliant people are religious.)
A trait dimension that is relevant here is schizotypy—not a disorder, but a normal spectrum of personality involving vivid imagination, unusual perceptions, openness to magical ideas, and a strong tendency to find patterns. Most religious people sit nowhere near the high end of it. But someone who is more prone to unusual inner experiences, and to sensing hidden connections, may be more likely to interpret those experiences as messages, revelations, or signs coming from outside the self. Schizotypy itself appears to be moderately heritable, often estimated in roughly the 30% to 50% range, and higher levels of its unusual-experiences dimension are repeatedly associated with stronger paranormal belief.
Moral psychology belongs here too. As the psychologist Jonathan Haidt and his colleagues have documented, some people are more temperamentally drawn to moral themes like loyalty, authority, and purity; others prioritize harm reduction and fairness more strongly. These inclinations appear to be at least partly heritable as well, though the size of that effect is debated. Religions, especially organized and more traditional ones, tend to be associated with stronger emphasis on loyalty, authority, and purity, with less emphasis on harm reduction and fairness. That is one reason some people feel deeply at home in religious cultures while others experience them as alienating.
None of this makes religiosity a defect or a symptom. It makes it one more dimension of the ordinary variation in human temperament—as deeply rooted in our nature as personality, taste, or political disposition. That, in a sense, is the deepest point of this chapter: the religious impulse is not an alien intrusion into human life but a natural product of the same evolutionary and developmental forces that shaped everything else about us.
Conclusion
Once a person really absorbs the logic and evidence for evolution, as I did in my early 20s and beyond, it becomes difficult to look at literal creation myths in the same way again. For me, this shift does not drain the world of meaning. It opens the door to a deeper, steadier awe: reverence for reality as it actually is.
A landmark twin study, drawing on more than ten thousand twin pairs, showing that political and social attitudes carry a substantial heritable component while party identification does not. The pattern mirrors what has been found for religion: the broad disposition is partly inherited, but the particular affiliation is learned within the family. It helped launch the study of the genetics of political temperament.
Claridge, G. (Ed.). (1997). Schizotypy: Implications for illness and health. Oxford University Press.
The standard scholarly treatment of schizotypy as a normal, continuously distributed feature of personality rather than a disease category. It assembles the evidence that traits such as unusual perceptions, magical thinking, and openness to anomalous experience vary across the whole population. Some temperaments are more inclined to read inner experiences as messages from beyond the self.
Dawkins, R. (1976). The selfish gene. Oxford University Press.
The landmark popular statement of the gene-centred view of evolution, which reframes organisms as vehicles built by genes to propagate themselves. It also introduced the term "meme" for a unit of culture that replicates, varies, and competes much as a gene does.
Franze, K., Grosche, J., Skatchkov, S. N., Schinkinger, S., Foja, C., Schild, D., Uckermann, O., Travis, K., Reichenbach, A., & Guck, J. (2007). Müller cells are living optical fibers in the vertebrate retina. Proceedings of the National Academy of Sciences, 104(20), 8287–8292. https://doi.org/10.1073/pnas.0611180104
A study showing that the vertebrate retina is optically "inverted"—light must pass through layers of neural tissue before reaching the photoreceptors—and that specialized Müller glial cells act as living optical fibers guiding light through this awkward arrangement. The finding is sometimes offered as evidence that the eye is well engineered after all. But the human eye uses a compensatory workaround for a suboptimal inherited design that still leaves a blind spot and a vulnerability to retinal detachment. The octopus's independently evolved eye has neither problem.
Graham, J., Haidt, J., & Nosek, B. A. (2009). Liberals and conservatives rely on different sets of moral foundations. Journal of Personality and Social Psychology, 96(5), 1029–1046. https://doi.org/10.1037/a0015141
The core empirical statement of moral-foundations theory, showing that liberals and conservatives draw on partly different moral intuitions: conservatives weight loyalty, authority, and purity more heavily, while liberals emphasize harm and fairness. These "binding" foundations tend to be elevated among the more religious. Some temperaments feel at home in traditional religious cultures while others find them alienating.
Grant, P. R., & Grant, B. R. (2014). 40 years of evolution: Darwin's finches on Daphne Major Island. Princeton University Press.
A synthesis of four decades of field research on the finches of Daphne Major in the Galápagos, the modern successor to Darwin's own observations. Year-by-year measurement shows ecological pressures—drought, food supply, competition—reshaping beak size and shape across generations, evolution observed almost in real time.
Koenig, L. B., McGue, M., Krueger, R. F., & Bouchard, T. J., Jr. (2005). Genetic and environmental influences on religiousness: Findings for retrospective and current religiousness ratings. Journal of Personality, 73(2), 471–488. https://doi.org/10.1111/j.1467-6494.2005.00316.x
A twin study finding that the heritability of religiousness is moderate but strongly age-dependent: genetic influence is weak in childhood, when shared family environment dominates, and rises substantially by adulthood. The result helps explain why estimates of the heritability of religiousness vary so widely across studies. The broad tendency to be religious carries a real inherited component.
Kumar, S., Stecher, G., Suleski, M., & Hedges, S. B. (2017). TimeTree: A resource for timelines, timetrees, and divergence times. Molecular Biology and Evolution, 34(7), 1812–1819. https://doi.org/10.1093/molbev/msx116
A description of TimeTree, a public database that synthesizes thousands of molecular studies into consensus estimates of when evolutionary lineages diverged. It is the source of the divergence-time figures used in this chapter—human and chimpanzee, human and mouse, mammal and bird, human and fish. The exact dates continue to be refined, but the branching structure they describe is already well established.
Lewis Center for Church Leadership. (2024). Twenty-five percent of churches disaffiliated from the United Methodist Church. Wesley Theological Seminary. https://www.churchleadership.com/leading-ideas/twenty-five-percent-of-churches-disaffiliated-from-the-united-methodist-church/
The final tally of congregations that formally left the United Methodist Church between 2019 and the end of 2023, reporting that roughly a quarter of U.S. congregations disaffiliated. The report also compares the characteristics of departing and remaining churches.
Miller, G. F. (2000). The mating mind: How sexual choice shaped the evolution of human nature. Doubleday.
An argument that distinctively human traits—humour, art, music, creativity, and aspects of intelligence—were shaped partly by sexual selection, functioning as displays that advertise the qualities of the mind producing them. Miller treats courtship, not only survival, as a major engine of human mental evolution.
Prum, R. O. (2017). The evolution of beauty: How Darwin's forgotten theory of mate choice shapes the animal world—and us. Doubleday.
A modern revival and defense of Darwin's largely neglected "esthetic" theory of mate choice, which holds that preferences themselves can become evolutionary forces. On this view, a trait such as the peacock's tail spreads because it is found beautiful, not merely because it signals some practical advantage. Biology is not only grim survival calculus but also a matter of attraction, display, and taste.
Rosindell, J., & Harmon, L. J. (2012). OneZoom: A fractal explorer for the tree of life. PLoS Biology, 10(10), e1001406. https://doi.org/10.1371/journal.pbio.1001406
A description of OneZoom, an interactive, zoomable map of the evolutionary tree of life designed to make the scale of common ancestry vivid and explorable. It renders the whole of life as a single connected structure a reader can navigate.
Smith, K. B., Alford, J. R., Hibbing, J. R., Martin, N. G., & Hatemi, P. K. (2017). Intuitive ethics and political orientations: Testing moral foundations as a theory of political ideology. American Journal of Political Science, 61(2), 424–437. https://doi.org/10.1111/ajps.12255
A twin analysis testing whether the individual moral foundations are the stable, heritable dispositions that moral-foundations theory implies. The authors found considerable instability in moral foundations over time and only limited evidence of heritability for the separate foundations. The paper represents one side of an unsettled debate, set here against Zakharin and Bates (2023), which reaches a stronger conclusion.
Wake, D. B. (1997). Incipient species formation in salamanders of the Ensatina complex. Proceedings of the National Academy of Sciences, 94(15), 7761–7767. https://doi.org/10.1073/pnas.94.15.7761
The classic analysis of the Ensatina salamanders as a ring species: populations spread in a loop around California's Central Valley, each able to interbreed with its neighbours, until the two ends of the ring meet in the south and no longer interbreed successfully. It is one of the clearest natural demonstrations that species boundaries can form gradually rather than all at once.
Zakharin, M., & Bates, T. C. (2023). Testing heritability of moral foundations: Common pathway models support strong heritability for the five moral foundations. European Journal of Personality, 37(4), 485–497. https://doi.org/10.1177/08902070221103957
Two twin studies testing the heritability of the moral foundations with models designed to separate genuine genetic influence from measurement error. Unlike Smith and colleagues, the authors find significant heritability for both the "binding" and the "individualizing" moral domains. The paper represents the other side of the current debate over how far moral temperament is inherited.
Zuckerman, M., Silberman, J., & Hall, J. A. (2013). The relation between intelligence and religiosity: A meta-analysis and some proposed explanations. Personality and Social Psychology Review, 17(4), 325–354. https://doi.org/10.1177/1088868313497266
A meta-analysis of sixty-three studies finding a modest negative association between intelligence and religiosity—a mean correlation of about −.24 for religious belief in the main samples. The authors propose several explanations, including a tendency for more intelligent people to resist conformity and to prefer analytic over intuitive thinking. Later re-analyses report that the association has weakened over time and is substantially explained by education.
I am so grateful to have discovered evolutionary biology, mostly on my own in my early 20s. It reminded me of studying astronomy or physics or mathematics—there is an awe and wonder that comes from understanding how the universe is made, and another layer that comes from appreciating the brilliant reasoning that allowed us to understand the formation of stars, the laws of motion, and the origins of all life on Earth.
It's understandable why my church elders were silent: evolution explains the origins and diversification of life in a way that directly contradicts literal religious or mythological accounts of creation. It is certainly possible to remain religious while accepting evolution—many people do—but for some believers, evolutionary biology feels like an unacceptable affront to faith, because it replaces a story of intentional design with a story of natural processes unfolding over vast time.
There are experts in evolutionary science who can explain this far better than I can. Still, I want to set aside space for it in my own voice, because the basic logic is not hard to understand, the evidence is overwhelming, and the emotional resistance to it often has very little to do with evidence and a great deal to do with identity, belonging, and sacred narrative—topics I have already been discussing.
What follows is a tour through the core mechanism of natural selection, a few common misunderstandings, the idea of speciation, and then several side corridors that matter for this essay: cultural evolution, sexual selection, and the uncomfortable fact that even religiosity itself is shaped not only by culture, but also by temperament, inheritance, and biology.
Selection
Natural selection is the central guiding principle of evolutionary theory. The logic is profoundly simple. It requires only that we accept three basic facts:
1) Organisms vary (physically, physiologically, behaviourally).
2) Some variation is heritable (traits are influenced by DNA, even though environment matters enormously too).
3) Some traits affect reproductive success—not in a morally loaded sense of “deserving,” but in the literal sense that some variants leave more surviving offspring than others.
If a heritable trait increases the probability of leaving more surviving offspring in a particular environment, then over generations the population will contain more of that trait. If a trait reduces reproductive success, it tends to diminish. That’s it—natural selection is differential survival and reproduction acting on inherited variation, repeated over time.
You can see the basic logic everywhere, from selective breeding in crops and animals (“artificial selection”), to antibiotic resistance in microbes, to the obvious family resemblance in both physical and psychological traits among human relatives. None of this requires the belief that genes are the only cause of traits. It requires only the admission that heredity is a major contributor. A point worth emphasizing, because it is often misunderstood, is that natural selection is not about “improvement” in any moral or progressive sense. It is simply a filter that favours whatever works well enough in a local environment at a given time.
Mutation
DNA replication is highly accurate, but not perfect. Across generations there are small changes—mutations—introduced into genetic material. “Mutation” here does not mean “bad.” It simply means “change.” Most mutations are neutral, many are harmful, and a few are beneficial in a given environment. Sexual reproduction adds still more variation by shuffling existing variants into new combinations, so evolution does not work only with brand-new mutations but also with new mixes of old genetic material.
Mutations do not happen because the organism needs them. A bacterium under stress does not somehow produce the exact helpful mutation it would most like to have. At the deepest level, whether a particular copying error happens in a particular cell at a particular moment is still a fundamentally accidental event. But that does not mean every part of the genome is equally likely to change. Some kinds of DNA changes happen more often than others, and some parts of the genome have a higher probability of experiencing mutations than others. Mutation is fundamentally random in origin, but statistically biased in pattern, and those biases affect what raw material natural selection gets to work with.
When small genetic changes happen to produce a trait that improves survival or reproduction in a particular environment—say, a slightly different beak shape that lets a bird get food more efficiently—those variants will, on average, become more common. They become more common for a very simple reason: the creatures carrying the useful variant survive better and leave more offspring. Over many generations, the accumulation of such changes can produce substantial transformations, including changes in complex organs and behaviours. Darwin’s finches in the Galápagos remain a famous entry point into this idea because long-term field work and later genetic work showed how ecological pressures can shape beak traits across populations.
The Time Scale of Evolution
One reason evolution feels counterintuitive is that large organisms reproduce slowly relative to a human life. Big evolutionary changes can take thousands or millions of years, just as major geological or astronomical processes do. We do not watch a canyon form in a single afternoon, and we do not watch a star age in real time, but the evidence for those processes is still decisive. Evolution is similar: long processes are inferred from converging lines of evidence. Fossils are one line of evidence—imperfect, but immensely powerful. Fossilization is rare and biased toward certain environments and tissues, so the record will always be incomplete. Still, the overall pattern—order in time, branching diversification, and transitional forms—fits evolutionary predictions very well. Comparative anatomy, fossils, biogeography, embryology, and genetics all point to the same branching story.
Common Ancestry and Cousins
A cliché misunderstanding goes like this: “Evolution says humans descended from chimpanzees.” That is not what evolutionary biology claims. Humans and chimpanzees are not ancestor and descendant; they are cousins. And “cousin” is not just a metaphor here. It is literally the right genealogical idea: two living lineages sharing an older common ancestor. In ordinary family language, we talk about first cousins or second cousins. Chimpanzees are obviously not that kind of close cousin; if one insisted on stretching the family language into absurd distances, they would be something like our three-hundred-thousandth cousins. Current genetic evidence places the human–chimpanzee split on the order of about 6 million years ago.
The same logic generalizes outward. Every living thing on Earth is, in the broad genealogical sense, our cousin. For me, this is not depressing at all. It is a source of awe—a kind of cosmic kinship. If a reader wants a visual sense of this, it is worth looking up one of the modern phylogenetic tree charts online, such as OneZoom. The exact dates of particular branching points are still being refined, but the branching structure itself is already known very well. And the scale is staggering. Humans and mice last shared a common ancestor around 90 million years ago. Mammals and birds last shared a common ancestor on the order of 310 million years ago. Humans and fish share a common ancestor on the order of 430 to 450 million years ago. We are talking about tens to hundreds of millions of years, not a few thousand.
Speciation
Over the short term, evolution often looks like shifting trait frequencies within a species. Over the long term, divergence can accumulate until populations become reproductively isolated—meaning they can no longer interbreed successfully under natural conditions. That is speciation.
Speciation is not always a sharp on/off switch. In nature it often behaves more like a continuum. The Ensatina salamander example is a real case, and it is useful because it makes that idea vivid. Around California’s Central Valley, populations of these salamanders spread in a rough loop. Neighbouring populations along the loop can still interbreed with the populations beside them. But by the time the two far ends of the loop meet again in Southern California, they have changed enough that they no longer interbreed successfully with each other, or do so only rarely. A simple analogy would be a circle of people, each speaking a dialect just a little different from the dialect of the person next to them. Each person can understand the neighbours on either side, but the person across the circle sounds incomprehensible. Ring species work something like that, except the differences are genetic and reproductive rather than linguistic. That is the point: species boundaries can emerge gradually, not by magic and not all at once.
One thing I want to state explicitly, because people often get confused here: even if a behaviour or trait has evolved, that does not mean it is morally right, or that we should accept it. Evolution describes how traits spread. It does not tell us what we ought to value.
Compromise, Not Perfect Design
Evolution also does not produce perfect design. It modifies what already exists. That is why living bodies so often look less like clean engineering and more like a history of workable compromise. Humans are full of such compromises. In adult humans, the passage for food and the passage for air share anatomy in the throat, which is one reason choking is even possible. Our spines and backs also show the costs of walking upright. The human spine has an S-shape that helps us balance over our hips and walk efficiently on two legs, but it also turns a structure inherited from four-legged ancestors into a vertically loaded column. The result is chronic stress on the lower back, high rates of disc degeneration, herniated discs, sciatica, and persistent back pain. Human childbirth is unusually difficult because pelvic form, fetal growth, and the evolution of large brains create a tight compromise. It is not as though the body is simply poorly designed. The point is that evolution works with inherited materials and trade-offs, not with fresh blueprints.
The vertebrate eye is another striking example. The retina is effectively wired backward: light has to pass through layers of neural tissue before it reaches the photoreceptors. Where the optic nerve exits the eye there is a literal blind spot, because that patch contains no photoreceptors. And because light must travel through the retinal layers first, the vertebrate eye needs compensatory tricks just to reduce scattering and preserve image quality. Müller cells help act like optical fibers to guide light through this awkward arrangement. The design also forces a trade-off between a clear optical path and the blood supply the retina needs. The system works, but it is hardly what a tidy engineer would draw from scratch. It also comes with structural vulnerabilities: the retina can detach, and when it does, vision can be permanently damaged. The octopus, whose camera eye evolved independently, ended up with a more direct setup. Its retina is everted rather than inverted, so the nerve fibers are routed behind the photoreceptors and there is no comparable blind spot.
Our jaws and teeth tell a similar story. Over time, human faces and jaws have become smaller without tooth size shrinking in perfect proportion. The result is a mismatch between tooth size and available arch space. Softer and more processed diets appear to worsen the problem by reducing the chewing demands that help stimulate jaw growth. As a result, many modern humans grow jaws that are simply too small for the full dental package they still carry, leading to orthodontic problems such as crooked teeth, and impacted wisdom teeth.
The broader point for me is simple: evolved traits are not always functionally ideal. Some have to be restrained, some have to be accommodated, and some have to be counterbalanced by culture. If we want to become more humane, we need rules, norms, education, medicine, and institutions that limit certain inherited tendencies, compensate for the problems they create, and cultivate better ones.
Cultural Evolution
A parallel kind of evolutionary logic shows up in culture. Dawkins coined the term “meme” for cultural units that replicate, but the broader point matters more than the label. Ideas, phrases, rituals, fashions, and institutions can spread, vary, compete, split, and disappear.
Language evolution is a very good example. Languages branch and drift. Over time, groups can become mutually unintelligible—they become different language “species.” Linguists can reconstruct family trees and infer common ancestors in ways that are strikingly analogous to biology. Proto-Indo-European—the distant ancestor of languages as varied as English, German, Greek, Russian, Persian, and Hindi—existed about six to eight thousand years ago. English, German, and Dutch are much closer cousins inside the Germanic family, with a common ancestor a little over two thousand years ago. French, Spanish, Italian, Portuguese, and Romanian are cousin languages that began diverging from Latin roughly fifteen hundred to two thousand years ago. And the same logic extends beyond Europe. Mandarin and Cantonese are also cousins. Their shared recognizable ancestor lies in Middle Chinese, something over a thousand years in the past. What begins as a dialect can, given enough time and separation, harden into a clearly distinct language.
Language divergence does not require millennia only. Some changes become obvious in just the last few centuries. Afrikaans, for example, diverged from colonial Dutch over roughly the last three to four hundred years after Dutch settlement at the Cape in 1652. Even before a speech form is officially labelled a separate language, strong regional varieties can become difficult for outsiders to follow. There are strong accents within Canada, such as Newfoundland English, that can be difficult for other Canadians to understand. Mutual understanding can erode gradually long before people agree on where to draw the boundary.
While Mandarin and Cantonese are cousins, English and Mandarin are not. As I've been learning Mandarin these past few years, I've discovered what it's like to appreciate a language that shares no traceable ancestry with English at all. Somewhere far enough back there probably is a common ancestor—the ancestors of every non-African population left Africa in a single wave around sixty thousand years ago, and every human population has language. But we will never find it. The comparative method reaches back perhaps eight thousand years before the trail goes cold, because words are not copied like genes; they are replaced, one by one, until nothing recognizable survives. This is where the analogy to biology breaks. Life keeps its records in a molecule that copies itself faithfully for billions of years. Language has no direct record at all before the age of writing, and it evolves so quickly that it erases its own history.
Religions also behave this way. Doctrines split. Schisms occur. New denominations form. We see this clearly in Christianity: the East–West Schism of 1054 formalized the great split between Roman Catholic and Eastern Orthodox Christianity; the Reformation is conventionally dated to 1517; and those Protestant branches splintered further into Lutherans, Calvinists, Anabaptists, Anglicans, Methodists, Baptists, Pentecostals, and countless smaller groups. This fragmentation is not just ancient history. In the United Methodist Church, more than 7,600 U.S. congregations left between 2019 and the end of 2023, roughly a quarter of the denomination’s earlier U.S. total.
Buddhism diversified too. One line of early Buddhism led to Theravada, while Mahayana arose later as another major descendant branch around the beginning of the Common Era. Islam experienced its defining Sunni–Shia split in the struggles over succession after Muhammad’s death. The family-tree metaphor is not perfect, but it is illuminating: religions do not descend from heaven as finished products. They branch, drift, quarrel, and split inside history.
Psychologically, that has an important implication: people often treat their own local, historically contingent version of a faith as if it were timeless and universal, when in reality it carries the fingerprints of geography, conflict, institutions, inheritance, and politics.
Sexual Selection
Another important evolutionary idea is sexual selection: traits can spread not because they help survival directly, but because they affect mating success. The peacock’s tail is the classic case—beautiful, costly, cumbersome, and yet selected because it becomes desirable within the mating preferences of the species. Darwin understood that biology is not only about staying alive long enough to reproduce; it is also about courtship, display, preference, and attraction. Richard Prum has argued, persuasively in my view, that sexual selection can include a genuinely esthetic component: preferences themselves can become evolutionary forces, and traits can spread because they are found attractive, not merely because they advertise some practical advantage.
None of which makes us peacocks. But human mate choice does attend to looks, voice, movement, confidence, style, humour, conversation, and perhaps aspects of intelligence itself. Some theorists—notably Geoffrey Miller—have argued that traits such as humour, creativity, artistry, music, and parts of intelligence may have been shaped at least partly by sexual selection because they function as displays: they can signal mental agility, creativity, or the ability to hold another person’s attention. The evidence is mixed and the details are debated, but the idea is serious.
Temperament, Inheritance, and Religion
Religiosity itself is not only cultural. Which particular religious group a person belongs to is largely a cultural and family-transmitted matter. But the broader tendency to be religious at all—to find religion important, compelling, consoling, or identity-defining—shows a meaningful inherited component. Twin research repeatedly suggests that adult religiosity has a moderate hereditary component, but the size depends a great deal on what exactly is being measured. Broadly speaking, estimates often land from the high 20s into the low 60s. More outward or socially enforced measures tend to sit lower, while more inward, identity-heavy, or conversion-like dimensions can sit higher. And when researchers say that some dimension of religiosity has a heritability of 60%, they do not mean that 60% of one person’s religion is “caused by genes.” They mean that, in the population being studied, about 60% of the variability between people on that trait is statistically associated with genetic variability.
What matters more here than raw ability is cognitive style. Some people are more comfortable sitting with analytical doubt and ambiguity; others are more drawn to certainty, authority, and the reassurance of a shared communal answer. Neither style is a measure of intelligence or its absence. (Meta-analyses do report a modest average negative association between intelligence-test scores and religiosity, but the effect is small, appears to have weakened over time, is substantially explained by education, and tells us nothing about any individual believer—a great many brilliant people are religious.)
A trait dimension that is relevant here is schizotypy—not a disorder, but a normal spectrum of personality involving vivid imagination, unusual perceptions, openness to magical ideas, and a strong tendency to find patterns. Most religious people sit nowhere near the high end of it. But someone who is more prone to unusual inner experiences, and to sensing hidden connections, may be more likely to interpret those experiences as messages, revelations, or signs coming from outside the self. Schizotypy itself appears to be moderately heritable, often estimated in roughly the 30% to 50% range, and higher levels of its unusual-experiences dimension are repeatedly associated with stronger paranormal belief.
Moral psychology belongs here too. As the psychologist Jonathan Haidt and his colleagues have documented, some people are more temperamentally drawn to moral themes like loyalty, authority, and purity; others prioritize harm reduction and fairness more strongly. These inclinations appear to be at least partly heritable as well, though the size of that effect is debated. Religions, especially organized and more traditional ones, tend to be associated with stronger emphasis on loyalty, authority, and purity, with less emphasis on harm reduction and fairness. That is one reason some people feel deeply at home in religious cultures while others experience them as alienating.
None of this makes religiosity a defect or a symptom. It makes it one more dimension of the ordinary variation in human temperament—as deeply rooted in our nature as personality, taste, or political disposition. That, in a sense, is the deepest point of this chapter: the religious impulse is not an alien intrusion into human life but a natural product of the same evolutionary and developmental forces that shaped everything else about us.
Conclusion
Once a person really absorbs the logic and evidence for evolution, as I did in my early 20s and beyond, it becomes difficult to look at literal creation myths in the same way again. For me, this shift does not drain the world of meaning. It opens the door to a deeper, steadier awe: reverence for reality as it actually is.
References
Alford, J. R., Funk, C. L., & Hibbing, J. R. (2005). Are political orientations genetically transmitted? American Political Science Review, 99(2), 153–167. https://doi.org/10.1017/S0003055405051579
A landmark twin study, drawing on more than ten thousand twin pairs, showing that political and social attitudes carry a substantial heritable component while party identification does not. The pattern mirrors what has been found for religion: the broad disposition is partly inherited, but the particular affiliation is learned within the family. It helped launch the study of the genetics of political temperament.
Claridge, G. (Ed.). (1997). Schizotypy: Implications for illness and health. Oxford University Press.
The standard scholarly treatment of schizotypy as a normal, continuously distributed feature of personality rather than a disease category. It assembles the evidence that traits such as unusual perceptions, magical thinking, and openness to anomalous experience vary across the whole population. Some temperaments are more inclined to read inner experiences as messages from beyond the self.
Dagnall, N., Denovan, A., Drinkwater, K., Parker, A., & Clough, P. (2016). Toward a better understanding of the relationship between belief in the paranormal and statistical bias: The potential role of schizotypy. Frontiers in Psychology, 7, 1045. https://doi.org/10.3389/fpsyg.2016.01045
A study of 254 volunteers testing which dimension of schizotypy best predicts paranormal belief, using the Oxford–Liverpool Inventory alongside the Revised Paranormal Belief Scale. Of the four schizotypy factors, Unusual Experiences—perceptual aberrations and magical thinking—showed the strongest association with paranormal belief, while the negative dimension showed none at all. The authors also found that paranormal belief mediated the relationship between unusual experiences and errors in judging randomness, and they caution that self-selection by people already interested in the paranormal may inflate the association.
Dawkins, R. (1976). The selfish gene. Oxford University Press.
The landmark popular statement of the gene-centred view of evolution, which reframes organisms as vehicles built by genes to propagate themselves. It also introduced the term "meme" for a unit of culture that replicates, varies, and competes much as a gene does.
Franze, K., Grosche, J., Skatchkov, S. N., Schinkinger, S., Foja, C., Schild, D., Uckermann, O., Travis, K., Reichenbach, A., & Guck, J. (2007). Müller cells are living optical fibers in the vertebrate retina. Proceedings of the National Academy of Sciences, 104(20), 8287–8292. https://doi.org/10.1073/pnas.0611180104
A study showing that the vertebrate retina is optically "inverted"—light must pass through layers of neural tissue before reaching the photoreceptors—and that specialized Müller glial cells act as living optical fibers guiding light through this awkward arrangement. The finding is sometimes offered as evidence that the eye is well engineered after all. But the human eye uses a compensatory workaround for a suboptimal inherited design that still leaves a blind spot and a vulnerability to retinal detachment. The octopus's independently evolved eye has neither problem.
Graham, J., Haidt, J., & Nosek, B. A. (2009). Liberals and conservatives rely on different sets of moral foundations. Journal of Personality and Social Psychology, 96(5), 1029–1046. https://doi.org/10.1037/a0015141
The core empirical statement of moral-foundations theory, showing that liberals and conservatives draw on partly different moral intuitions: conservatives weight loyalty, authority, and purity more heavily, while liberals emphasize harm and fairness. These "binding" foundations tend to be elevated among the more religious. Some temperaments feel at home in traditional religious cultures while others find them alienating.
Grant, P. R., & Grant, B. R. (2014). 40 years of evolution: Darwin's finches on Daphne Major Island. Princeton University Press.
A synthesis of four decades of field research on the finches of Daphne Major in the Galápagos, the modern successor to Darwin's own observations. Year-by-year measurement shows ecological pressures—drought, food supply, competition—reshaping beak size and shape across generations, evolution observed almost in real time.
Koenig, L. B., McGue, M., Krueger, R. F., & Bouchard, T. J., Jr. (2005). Genetic and environmental influences on religiousness: Findings for retrospective and current religiousness ratings. Journal of Personality, 73(2), 471–488. https://doi.org/10.1111/j.1467-6494.2005.00316.x
A twin study finding that the heritability of religiousness is moderate but strongly age-dependent: genetic influence is weak in childhood, when shared family environment dominates, and rises substantially by adulthood. The result helps explain why estimates of the heritability of religiousness vary so widely across studies. The broad tendency to be religious carries a real inherited component.
Kumar, S., Stecher, G., Suleski, M., & Hedges, S. B. (2017). TimeTree: A resource for timelines, timetrees, and divergence times. Molecular Biology and Evolution, 34(7), 1812–1819. https://doi.org/10.1093/molbev/msx116
A description of TimeTree, a public database that synthesizes thousands of molecular studies into consensus estimates of when evolutionary lineages diverged. It is the source of the divergence-time figures used in this chapter—human and chimpanzee, human and mouse, mammal and bird, human and fish. The exact dates continue to be refined, but the branching structure they describe is already well established.
Lewis Center for Church Leadership. (2024). Twenty-five percent of churches disaffiliated from the United Methodist Church. Wesley Theological Seminary. https://www.churchleadership.com/leading-ideas/twenty-five-percent-of-churches-disaffiliated-from-the-united-methodist-church/
The final tally of congregations that formally left the United Methodist Church between 2019 and the end of 2023, reporting that roughly a quarter of U.S. congregations disaffiliated. The report also compares the characteristics of departing and remaining churches.
Linney, Y. M., Murray, R. M., Peters, E. R., MacDonald, A. M., Rijsdijk, F., & Sham, P. C. (2003). A quantitative genetic analysis of schizotypal personality traits. Psychological Medicine, 33(5), 803–816. https://doi.org/10.1017/S0033291703007906
A twin study of 733 female twin pairs using the Oxford–Liverpool Inventory of Feelings and Experiences, the standard instrument for measuring schizotypy across the general population. Heritability was estimated at roughly 50% for most dimensions and lower—about 37%—for delusional ideation, with the best-fitting models attributing the remainder to individual rather than shared family environment. The positive and negative components of schizotypy proved relatively independent genetically, which suggests the trait is not a single inherited quantity but a cluster of partly separate ones.
Miller, G. F. (2000). The mating mind: How sexual choice shaped the evolution of human nature. Doubleday.
An argument that distinctively human traits—humour, art, music, creativity, and aspects of intelligence—were shaped partly by sexual selection, functioning as displays that advertise the qualities of the mind producing them. Miller treats courtship, not only survival, as a major engine of human mental evolution.
Prum, R. O. (2017). The evolution of beauty: How Darwin's forgotten theory of mate choice shapes the animal world—and us. Doubleday.
A modern revival and defense of Darwin's largely neglected "esthetic" theory of mate choice, which holds that preferences themselves can become evolutionary forces. On this view, a trait such as the peacock's tail spreads because it is found beautiful, not merely because it signals some practical advantage. Biology is not only grim survival calculus but also a matter of attraction, display, and taste.
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A description of OneZoom, an interactive, zoomable map of the evolutionary tree of life designed to make the scale of common ancestry vivid and explorable. It renders the whole of life as a single connected structure a reader can navigate.
Smith, K. B., Alford, J. R., Hibbing, J. R., Martin, N. G., & Hatemi, P. K. (2017). Intuitive ethics and political orientations: Testing moral foundations as a theory of political ideology. American Journal of Political Science, 61(2), 424–437. https://doi.org/10.1111/ajps.12255
A twin analysis testing whether the individual moral foundations are the stable, heritable dispositions that moral-foundations theory implies. The authors found considerable instability in moral foundations over time and only limited evidence of heritability for the separate foundations. The paper represents one side of an unsettled debate, set here against Zakharin and Bates (2023), which reaches a stronger conclusion.
Wake, D. B. (1997). Incipient species formation in salamanders of the Ensatina complex. Proceedings of the National Academy of Sciences, 94(15), 7761–7767. https://doi.org/10.1073/pnas.94.15.7761
The classic analysis of the Ensatina salamanders as a ring species: populations spread in a loop around California's Central Valley, each able to interbreed with its neighbours, until the two ends of the ring meet in the south and no longer interbreed successfully. It is one of the clearest natural demonstrations that species boundaries can form gradually rather than all at once.
Zakharin, M., & Bates, T. C. (2023). Testing heritability of moral foundations: Common pathway models support strong heritability for the five moral foundations. European Journal of Personality, 37(4), 485–497. https://doi.org/10.1177/08902070221103957
Two twin studies testing the heritability of the moral foundations with models designed to separate genuine genetic influence from measurement error. Unlike Smith and colleagues, the authors find significant heritability for both the "binding" and the "individualizing" moral domains. The paper represents the other side of the current debate over how far moral temperament is inherited.
Zuckerman, M., Silberman, J., & Hall, J. A. (2013). The relation between intelligence and religiosity: A meta-analysis and some proposed explanations. Personality and Social Psychology Review, 17(4), 325–354. https://doi.org/10.1177/1088868313497266
A meta-analysis of sixty-three studies finding a modest negative association between intelligence and religiosity—a mean correlation of about −.24 for religious belief in the main samples. The authors propose several explanations, including a tendency for more intelligent people to resist conformity and to prefer analytic over intuitive thinking. Later re-analyses report that the association has weakened over time and is substantially explained by education.
