A colleague of mine used to have two stock answers when the passenger next to him on an airplane asked what he did for a living. If he was happy to talk to the person, he said he was a marine biologist, which spurred all kinds of inquiries about ocean animals and anecdotes about snorkeling vacations. If he wasn’t interested in conversation, he said he was an evolutionary biologist, which usually resulted in the person smiling tightly and returning to their electronic device.
I’m usually not quite so premeditated about my answer to that question, though I have noticed that if I say I study insects (which is true), people will ask me how to kill the pests in their garden, or maybe about beekeeping, which I know nothing about. If, on the other hand, I say that I work on animal behavior (which is also true), I get lots of stories about people’s pets and questions about the latest nature documentaries. They often want to talk about how much smarter animals are than we give them credit for, although admittedly that usually goes for animals other than insects. Either way, I like talking to people about animals, and I am always interested in hearing how they interpret the behavior of the creatures around them.
Often, the conversation turns to how much animals are like humans, though again this topic usually excludes insects. People have always wanted to draw parallels between our lives and those of animals. Author Helen Macdonald eloquently points out, “The deepest lesson that animals have taught me: how easily and unconsciously we see other lives as mirrors of our own.”1 Of course, as she goes on to say, “Animals don’t exist in order to teach us things, but that is what they have always done, and most of what they teach us is what we think we know about ourselves.”
At the same time, what we know about ourselves these days is continually infused with the latest discoveries about where our behavior comes from, and particularly about how so many of our most human characteristics are innate, and have a basis in our genes. Headlines are full of declarations like: “Our Politics Are in Our DNA,” or “To Move Is to Thrive. It’s in Our Genes.” A paper in the prestigious scientific journal Proceedings of the National Academy of Sciences was titled “Trust Is Heritable, Whereas Distrust Is Not.”2 Even dog ownership was said to have a genetic basis.
Britain’s Telegraph screamed in June 2019: “There Is No Point Sending Your Children to Eton Because Education Is in Your Genes, Says Geneticist.” The article was reporting on work by Robert Plomin, who also said that while “environmental influences are important, too . . . they are largely unsystematic, unstable and idiosyncratic.” Sarah Knapton, the newspaper’s science editor, flatly stated that Plomin, a professor of behavioral genetics at King’s College London, had shown that “academic success is written in the genes.” Not “suggested,” mind you, “shown.” Even the #MeToo movement is, at its heart, disputing the long-held notion that men are “naturally” inclined to hit on women, and whether there is anything we can really do about it. And when people talk about what’s natural, or inherent, or fixed, or instinctive, to use just a few of the synonyms that are bruited about, they mean what biology, or our genes, determines.
By contrast, others claim the environment is all powerful. Prominent “functional medicine” practitioner, Chris Kresser, writes in his blog, “At one time scientists believed our DNA held the key to preventing and reversing disease. But we now know that our environment—not our genes—is the primary driver of health and longevity.”3 He discusses the “exposome,” the lifetime sum of an individual’s environmental exposures, as critical in determining health and disease. And to many people, one can make an uncomplicated distinction; according to a website maintained by no less august a group than the American Association for the Advancement of Science (AAAS), “Some behavior, called innate, comes from your genes, but other behavior is learned, either from interacting with the world or by being taught.”4 It then presents examples of pet behavior, neatly divided into “learned” or “innate.”
The Greek Not-So-Blank Slate
All of this brouhaha about what’s learned and what’s cultural is, of course, the old nature-nurture debate. Questions about what we learn and what we inherit have long dominated our public conversations about equality, about why our talents and predilections vary among us and where they come from. Are we blank slates, or are our lives and actions determined long before we are born, by our genes and their effects on our bodies and brains? People have been trying to answer this question for centuries if not longer, and the question has existed in some form even before we knew there was such a thing as a gene. Scholars have long argued about the nature of “innateness,” a concept that, as British philosopher Richard Samuels says, “has led a busy life.” Philosopher Paul Griffiths, whose work I will return to in chapter 10, suggests that we have a folk concept of innateness that we use when we think about what living things are like. Both scientists and the public want to weigh in and take sides, and they will often reach to unlikely sources for support. As columnist George Will wrote in 2019, “In the argument about which is primary, nature or nurture, the former receives an emphatic affirmation from the Founding Fathers’ philosophy. Beneath the myriad patinas of culture, there is a fixed human nature that neither improves nor regresses.”5
Even Aristotle and Plato have roles here, though the question at hand was not where our behavior comes from, but the closely related issue of how knowledge itself came to be. According to Aristotle, we use our senses to comprehend the world, which means that learning, or the environment, was sufficient to explain how we operate. Plato disagreed, claiming that we do not acquire information about the world but instead are endowed, or born, with it. Prominent philosophers have weighed in on one side or the other over the ensuing centuries, but one thing remains clear: we haven’t got this question sorted out by a long shot.
The ancient Greeks had no notion of genes, of course, though they obviously knew that parents passed on characteristics to their offspring. And indeed, the argument doesn’t depend on genes. Psychologists, particularly those interested in child development, have essentially renamed the conflict as the nativist-empiricist debate, which as far as I can tell is the same old genetic versus environmental wine in new bottles, though the focus isn’t on DNA so much as on how human development uses information from different sources. The argument is also related to the idea of essentialism, which I will discuss in more detail in later chapters. Briefly, from the essentialist viewpoint every being has an essence that it carries with it and that transcends its experiences and other changes, such as growth and development. Worms are thus always wormy, and nothing that happens can make them less so. Squaring this idea with the evolution of everything from fish to badgers to people from worm-like ancestors, if not actual worms, seems a bit difficult, but the nativists suggest that evolution confers people with “primitives” or core abilities in things like language and social interactions.
Those click-baiting headlines and our fascination with the notion that something like owning a dog could be related to one’s DNA make it clear that this is much more than an academic squabble. The debate matters for many reasons. If, for instance we assume that intelligence is predetermined, we are less likely to think interventions, say in the form of social programs to improve learning in children, will be effective. On the other hand, if we assume everything can be altered by our actions, we may blame the victim, as is sometimes seen in the suggestion that those with cancer or other serious diseases could have avoided their plight by diet or exercise, or that people can just think their way out of depression. This doesn’t mean we need to find the “correct” answer—as I will show throughout this book, such an answer doesn’t exist—but that we need to be careful in how we think about the controversy.
Perhaps, ironically, we keep thinking we’ve resolved the debate, because we know—or at least we think we do—that traits as complex as intelligence or gender identity have to be affected by both genes and the environment. And yet, despite all the discoveries that show how interwoven learning is with what we call instinct, we keep either resurrecting the debate or optimistically declaring victory. Over thirty years ago, Daniel Koshland editorialized in the prestigious journal Science that “the debate on nature and nurture in regard to behavior is basically over. Both are involved.”6 Since AAAS publishes Science, someone clearly didn’t get this memo when they wrote about the innate and learned behaviors of pets, but so be it. It is abundantly clear that this pronouncement was more than a little premature.
Psychologist David Lewkowicz, in his 2010 presidential address to the International Conference on Infant Studies, refers to the “biological implausibility of the nature-nurture dichotomy.” A 2009 article by child development experts at the University of Iowa proclaimed, “Why We Should No Longer Abide the Nativist-Empiricist Debate.” One of the many respondents to the article said that it isn’t a debate, it’s a dialogue, and a necessary one, which struck me as the kind of proposed middle ground that leaves no one happy. And yet Robert Plomin, whom I mentioned previously, will have none of that, and says instead, “In the Nature-Nurture War, Nature Wins.”7
I could go on. But the truth is that the nature-nurture controversy has become what scientists call a zombie idea, one that, no matter how many times we think we have disproved it in the past, or reframed it, or even declared a victor, it springs back to life. In his blog Dynamic Ecology, Jeremy Fox calls these “ideas that should be dead, but aren’t. Zombie ideas are the most important failures of science’s self-correction mechanisms: they’re big, widespread errors or misconceptions that aren’t recognized as such.”8 His examples from the field of ecology are pretty much inside baseball for specialists, including things like whether species have more interactions in the tropics than in more temperate regions, but they underscore our inability to stop using an idea when its usefulness is long past its use-by date. Even if we believe that both nature and nurture are involved, which many of the people weighing in on the matter say, we then want to know which predominates, which one wins. Is it 50:50, 90:10? No one likes a tied game, it seems, much less one where you can’t even tell who’s playing for which team.
Why does this matter? Can’t we just let the zombie wander the landscape, shedding DNA like rotten body parts and moaning about inheritance? (Jeremy Fox mused in 2012 that perhaps having the zombie apocalypse come to pass wouldn’t necessarily be such a bad thing, at least from the perspective of the zombies.) But I am afraid we can’t do that. We need to stop these fruitless debates about the inherent nature of sexism, or of genius, or of any one of a number of other topics that are central to our lives. A 2017 New York Times article titled “The Unexamined Brutality of the Male Libido”9 argued that we are simply stuck with brutish men who can’t or won’t examine their destructive sexuality. Sorry, ladies, complain all you want—it’s just immutable male nature. Like so many articles of this kind, it struck a nerve, with over 1,200 comments within hours of publication, some with furious condemnation, others expressing passionate agreement. Here’s the problem: if people genuinely believe that men will always grow up with violent or dominating tendencies, then even if they see men behave otherwise, they will discount it, or at least they won’t trust its permanence.
We also need to resolve our thinking about what is nature and what is nurture because we use our notions about what “comes naturally”—in other words, what is instinctive—in contradictory ways. For example, so-called women’s work, whether it’s done in the home or in “pink collar” jobs like nursing or teaching, can be seen as women just doing what comes naturally, using their maternal instincts or their innate ability to empathize to take care of other people’s needs. If one then assumes that “coming naturally” means effortless, requiring no conscious thought or special skill, such a skill is not seen as “real” work—or in some cases, seen at all. But that’s just as silly as suggesting that learned skills, like mountain climbing or solving crossword puzzles, are somehow more important or more difficult than ones that seem to arise from our genetic makeup. In the chapters that follow, I will show how it’s the interplay between genes and environment that’s important, and not one contributor or the other. We don’t need to be either a blank slate proponent or a genetic determinist, and in fact those sides don’t accurately represent the biology.
It’s also important to point out that our obsession with changeable versus immutable is nowhere more obvious than when it comes to behavior. Sure, we wonder about how all of our characteristics got to be the way they are, but the knives are drawn when we discuss our aggression, our xenophobia, or our love of cats (or dogs). The headlines never blare, “Genetic Basis for Blood Cell Shape Revealed!” because we already assume that such characteristics depend on our genes; it’s not as though we can will ourselves to have rounder lymphocytes. And yet all attributes, behavior or not, have contributions from both genes and the environment, in a complex way that defies a simple apportionment into percentages of each. Behavior seems so flexible, so ephemeral, that we can notice the way it seems to be inherited, as when twins share the same hobbies, but be perplexed that such fleeting attributes are passed on in the genes.
A Tangle of Blueprints
So if it’s not nurture alone, and it’s not nature alone, and it’s also not some combined percentage of the two, where do our characteristics come from? The word that scientists use to describe how genes and environment work together to produce a trait (including a behavior) is interaction, which of course is used in common parlance as well. In biology, we use this word to mean that the effect of an organism’s genes depends on the organism’s environment, and the effect of an organism’s environment depends on its genes. The philosopher of science Evelyn Fox Keller calls this the entanglement of genotype and environment, which also conveys the inextricable nature of the relationship between the two.10
We can illustrate the tangle if we review a seemingly simple case that is often considered the epitome of a single-gene defect in humans, phenylketonuria (PKU). PKU was the first condition widely used in screening infants, using the heel-prick blood samples taken from newborn babies. PKU is a simple disorder with devastating effects: babies with two copies of a defective gene cannot properly metabolize the amino acid phenylalanine, which builds up in their bloodstream and eventually leads to severe intellectual disabilities.
What could be a clearer example of a genetic cause? (Indeed, even genetics textbooks sometimes describe it as such, and historian of science Diane Paul has written extensively about the adoption of PKU as the poster child for genetic diseases.)11 And yet this characterization is incorrect. It turns out that if these babies are given a special diet that makes up for the phenylalanine they cannot digest, they develop quite normally. Thus one could equally argue that the disease is completely environmental: it all depends on what they eat (or are given). Note that it is not just that both genes and the environment matter; their interaction is what matters. The outcome, whether the child grows up intellectually disabled or not, depends on which diet they receive only if they have the defective genes, or, equally, it depends on which genes they have, but only if they have an unrestricted diet. Even in this simple case, we cannot ascribe a greater cause to genes or environment.
You might object that, in the usual environment (an unrestricted diet), PKU is indeed an example of a genetic characteristic. But this objection actually proves my point: whether or not a trait can be considered “genetic” (nature) or “environmental” (nurture)—a very rare occurrence in any event—depends on the environment and the genetics, respectively. Of course, most characteristics, especially behavioral ones, are more complex in their genetics and the environmental variation less so, than in PKU.
Part of the problem may be that English doesn’t have a good word for how the interaction—or entanglement—functions. We sometimes say that genes “underlie” or “underpin” behavior, as a way to distinguish their action from “determining” behavior, but these words still suggest that the genes are somehow fundamental, with the environment varying around them, which isn’t the case either.
And speaking of terminology, the language used to discuss genes and how DNA is related to the way we are, whether that is physical or behavioral, is often fraught with confusion. The genome is sometimes said to provide a “blueprint,” suggesting that all one needs to do to make a living creature is to follow the instructions. Even the website of the National Institutes of Health in the United States claims that “each genome contains all the information needed to build and maintain that organism.”12 Both ideas imply that the environment is secondary and the genes contain what’s important, which is not true. Even Wikipedia lists the blueprint metaphor as one of the biggest misconceptions about genetics.
So what’s wrong with saying the genome has instructions? For one thing, as Eric Turkheimer, a renowned behavioral geneticist who has studied human behavior for many years, says, “The relationship between blueprints and buildings is nothing like the relationship between genotypes and organisms. A blueprint of a house has a roof and walls and windows and a floor that have a direct one-to-one correspondence with the roof, walls, windows and floor in the house. There is nothing like this in DNA: there aren’t head genes and feet genes, much less extraversion genes and divorce genes.”13 Another way to look at it is that one could reverse engineer a blueprint from a house—by looking at the way it is structured, one could reproduce, more or less, the drawings that directed its construction. But no one could look at an animal and say with any confidence what its genome is. Similar objections could be made to other common metaphors, like genes “coding for” characteristics, or behavior being “hardwired.” The entanglement makes it impossible for such one-way processes to occur.
The Unhuman Solution
A way out of the conundrum is to think about human behavior in the context of other animals. Plato and Aristotle disagreed about where human knowledge comes from, but they did not think to question how a bird knows to build a nest, or how bees know to summon their colony to a rich source of nectar miles away. They probably thought the answer was obvious: animals operate by blind instinct, such as Plato’s suggestion that humans are born with innate sources of understanding. Surely their senses are sufficient.
But this kind of human exceptionalism won’t pass muster, particularly now that we understand that humans and other creatures all evolved from common ancestors. How could people need a special form of knowledge acquisition when all other animals happily go about their days without agonizing over the balance between nature and nurture? Only the most ardent human exceptionalist would cling to the notion that people—not chimpanzees, not dolphins, not even dogs—are the only species in which behavior springs from upbringing and upbringing alone, or the only species in which we need to consider the balance of upbringing and our biology. That doesn’t mean that the alternative is a genetic determinism of the sort bemoaned by the New York Times writer regarding brutish men, that shrug of “what are you going to do, it’s human nature.” It means that the notion that genes “code for” or are a “blueprint for” behavior is simply wrong, whether you are talking about apes or people. I don’t want to be disingenuous and claim that humans have no unique qualities, but it simply isn’t reasonable for the nature-nurture controversy to apply only to humans, and to only human behavior at that.
This is not to say that we aren’t fascinated by the similarities and differences between what animals learn (or don’t) and what we learn. A 2021 article in New Scientist titled “Human-Like Intelligence in Animals Is Far More Common than We Thought” goes on to say, “Tests reveal that they don’t merely act on instinct but can think flexibly, like us.” Alternatively, coverage of a paper in Nature, one of the premier science journals, was headlined “Puppies Are Hardwired to Understand Us” and reported on a study that examined how well eight-week-old Labrador and golden retrievers responded to human cues like pointing. The title might be somewhat undermined by the statement: “Some puppies were more successful than others, but the researchers found that approximately 43% of that variation in performance was due to genetics,” which suggests that the hardwiring has its limits. Commentary on the same paper in Science, Nature’s peer journal, stated, “If social intelligence is genetic, dogs should display it at a very young age. And there shouldn’t be any learning required.”14
But of course social intelligence, and everything else we (or puppies) do, requires input from both the genes and the environment (or learning). Behavior isn’t genetic, whatever that means. It’s that entanglement again, whether in dogs, humans, hippos, or hamsters. The question of whether nature or nurture is more important is impossible to answer. But we can ask a much more interesting question: How does behavior evolve? How do the characteristics of everyone, human and animal, come to be? This book explores that question, by examining how genes and the environment act in concert to produce behaviors as different as fetching in dogs and chirping in crickets.
Recall the example of brutish men, but cast it in a new light. Men are not genetically programmed to cheat on their mates or sexually harass their coworkers, but neither are they programmed to be caring and cooperative. Genes don’t work that way. By the same token, the social milieu or the patriarchy are not the only factors that affect their cheating (or caring). The effect of genes on behavior depends on the organism’s environment and vice versa. It’s not just that nature and nurture both contribute, it’s that you can’t meaningfully consider the action of one without the other.
In the chapters that follow, I look at how behaviors in a wide range of animals evolve, and how we think about the role of genes and the environment when it comes to both animal and human behavior. Chapter 1 lays the groundwork by asking a question that turns out to be much more difficult to answer than it might first appear: What is behavior? This question has a companion: Is behavior special? In other words, is behavior somehow different from physical characteristics like the shape of a nose or how much fur your cat has? Chapter 2 examines what we know about the way behavior evolves, making use of Iranian snakes and skydancing hummingbirds. It also takes a good hard look at the idea that humans, or any other mammals, have a “lizard brain” underlying our more sophisticated actions. Chapter 3 details how much genes can tell us about behavior, starting with some work on fruit fly courtship by one of the rare early women evolutionary biologists and showing what it really means for a behavior to be heritable.
In chapter 4, I use the domestication of our most familiar animal companion, the dog, to see just how much behavior can change with a few thousand years of cooperation, and cast some doubt on the notion of a domestication syndrome. Chapter 5 continues the domestication theme with cats but also including some other species, like guinea pigs, which turn out to have attained their iconic status as experimental subjects because of the anti-vivisectionist stance of George Bernard Shaw. Chapter 6 takes a look at mental disorders in animals, with crayfish that are anxious and dogs with a form of obsessive-compulsive disorder. Chapters 7 and 8 survey both animals that we think are clever, like ravens, and those we have often dismissed as being mere automatons, like bees and crabs, asking just what we mean by birdbrained and whether intelligence is all about the brain. Oh, and we’ll also consider the assfish, and no, I am not making that name up. In chapter 9, I will explore the evolution of language, or what seems like it, in animals, trying to determine whether the Rubicon of human speech is as uncrossable as some would have you believe. Chapter 10 visits the thorny topic of sex and gender, with another look at whether men, or male animals in general, are all that inherently brutal. And finally, because the COVID-19 pandemic made us think about disease in our lives in a wholly new way, chapter 11 is about how behavior that fights disease—from birds fumigating their nests with cigarette butts to ants performing battlefield triage to chimps chewing leaves that rid their guts of worms—can evolve. In the end, I hope that understanding how behavior evolves helps us see both other animals and ourselves better, and that the battle between nature and nurture is not worth fighting.