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In addition to imitative learning, primates traffic in another, more subtle, form of information exchange: emotion. We may think of our own emotions in highly personal terms such as joy, sadness, anger, jealousy, and love. Across the primate kingdom, however, emotional expression plays another, broader social role in facilitating the transfer of memes between group members. Recent primate research also suggests that emotional expression may have something to do with our capacity for symbolic expression. “Symbol formation results from a series of stages of affective transformations,” writes psychiatrist Stanley Greenspan, suggesting that symbols arose not from the use of human spoken language but from a deeper emotional well-spring grounded in the primate limbic system (the part of the brain
that controls emotions). Greenspan has formulated an intriguing theory that suggests an evolutionary progression of symbolic language: from engagement and signaling (like reacting to a mother’s facial expressions) to simple call-and-response interactions (like sharing environmental data) to elaborate greeting rituals (like courtship or coalition building) to “co-regulated affective signaling” (like organizing hunting parties with differentiated roles).
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Greenspan believes that this progression of signaling behavior evolved in concert with a series of genetic mutations among our primate ancestors that would ultimately equip
Homo sapiens
with our uniquely developed capacity for symbolic expression.

If this startling theory of human symbolism holds true, it suggests a radical rethinking of the origin and function of symbols. Our symbols may function not just as embodiments of abstract linguistic ideas but as conveyors of much deeper, preverbal emotional truths that spring from the source of all emotions: families. As we will see in the next chapter, the structure of family relationships has exerted a profound influence on the subsequent shape and structure of human information systems. Relationships between parents and children, siblings and extended family members, form a psychological template that resurfaces over and over again in the way we seem to structure the relationships between thoughts and ideas, providing an implicit structure for the earliest taxonomic systems.

This emotional dimension of symbols may offer a partial explanation for why certain kinds of information systems prove more successful than others. Systems based on artificial ideologies, which lack a reinforcing emotional power, routinely fail to persist. For example, when communist regimes attempted to rewrite their countries’ histories in a new ideological light, those efforts eventually faltered in the face of their citizens’ own shared memories. “Because families continue to transmit to their children a more basic nonverbal presymbolic emotional ‘truth,’” Greenspan argues, “these symbolic fabrications vanish immediately upon the collapse of the dictatorships that enforce them.”
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If our capacity for symbolic abstraction really rests so deeply in our limbic system, that may well explain why our most resilient information systems—like folk tales, urban leg- ends, and religious traditions—seem to flourish by passing through the strong social bonds of personal relationships rather than relying solely on institutional power or ideologies. As we will see later in this book, oral traditions have proved particularly durable over the years, usually outlasting more elaborate written systems that come and go with the rise and fall of their institutional sponsors.

So far, we have seen how the deep biological history of networks and hierarchies has given rise to the escalating complexity of nature’s information systems. We have seen how that process has equipped other species with the ability to preserve information beyond the life span of the individual organism through social imitation and pooling, and by encoding memes onto their physical environments. And we have seen how, among primates, deep-seated emotional responses provided the semantic scaffolding for the emergence of symbolic expression—all of which bring us to the brink of human culture. Now we must stop and ask: Can the evolutionary narrative take us any farther? Or does it end 100,000 years ago, when
Homo sapiens
reached their current anatomical state? Are our information systems still “evolving”? This is no small question.

The most coherent scientific theory of how evolutionary forces shape human culture comes from Pulitzer Prize–winning biologist E. O. Wilson, the father of sociobiology. While Wilson’s theories remain controversial in some humanist circles, as they have since the sociobiology wars of the 1970s and 1980s, his basic model of the relationship between genes and culture has become widely accepted among many mainstream biologists. Based on his lifelong study of insect colonies and his pioneering theoretical work on the intersection of biology and culture, Wilson has proposed a theory to explain how the exchange of memes (or culturgens) influences the process of genetic evolution. “Culture is created by the communal mind,” he writes, “and each mind in turn is the product of the genetically structured human brain. Genes and culture are therefore inseverably linked.”
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Wilson’s theory of gene-culture coevolution hinges on the interaction of two key operators: memes and epigenetic rules, or neural processes that govern certain aspects of cognition. Epigenetic rules come in two flavors: Primary epigenetic rules govern our immediate sense perceptions, such as our universal tendency to perceive the color spectrum in four basic color groups, or our ability to distinguish the sound of human voices from other kinds of noise; secondary epigenetic rules operate at a higher level of abstraction, affecting the way we integrate our sense perceptions, such as the tendency for all human beings to classify objects into opposing pairs like black and white, life and death, heaven and earth—notions that have no physical component in the human brain, yet seem to recur across human cultures. Secondary epigenetic rules predispose us to draw certain kinds of distinctions; culture fills in the blanks. Individuals with a strong disposition to following particular epigenetic rules are more likely to survive, and therefore pass on their genes, than those with a weaker disposition to following the rules. For example, individuals who avoid snakes out of fear are more likely to pass on their genes than individuals who step boldly in front of a rattler. So people with a genetic makeup that predisposes them to fear snakes enjoy a decided evolutionary advantage. While there is probably no actual gene that tells us to fear snakes, fear of snakes has nonetheless a clear adaptive advantage that gets passed along from generation to generation. So we can hypothesize the presence of an epigenetic rule disposing us toward a fear of snakes.

Epigenetic rules may also explain the prevalence of certain narrative archetypes that recur across human cultures: the creation myth, the hero’s descent, trickster gods, scary monsters, and visions of the apocalypse.
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The sheer prevalence of these stories across every known culture suggests the strong likelihood that human beings share some kind of inborn disposition toward particular cultural patterns. To return to the snake example: Serpents recur as symbols throughout human cultures, often taking on mythic forms. “Owing to the power of fear and fascination given them by the epigenetic rule,” Wilson writes, “[snakes] easily acquire additional mythic meaning; they serve in different cultures variously as healers, messengers, demons, and
gods.”
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It is no coincidence that snakes have been a leading cause of human mortality throughout our species’ history, so it should come as no surprise that the occurrence of serpent imagery tracks closely to the prevalence of poisonous snakes in particular regions. That rule in turn influences the course of the larger cultural system. The social group accrues an adaptive advantage by cultivating a mythology to ensure the persistence of valuable information across generations: namely, that it’s a good idea to be afraid of snakes. In other words, Eve’s hateful old serpent may boast a very old pedigree indeed: the epigenesis of Genesis?

The similarities in human behavior among otherwise disparate cultures suggest the strong possibility of epigenetic rules at work. But where exactly do these rules exist? They are not hardwired into our DNA; there is no physical mechanism to decode. Rather, they are invisible dispositions that arise from a complex combination of factors, including genetics. But we cannot see epigenetic rules any more than we can see gravity. The only path to discovering these rules lies in a process of reverse engineering, by looking for the presence of universal human behaviors that manifest across cultures.

Anthropologist Donald Brown has devoted his career to compiling what many social scientists now consider the authoritative list of “human universals,” a catalog of 200 behaviors that appear to recur in every known human culture. The list stretches from the sublime—beliefs about death, rituals, and symbolism—to the ridiculous—toys, tickling, and jokes. The list also includes no fewer than 12 types of classification: age, behavioral propensities, body parts, colors, fauna, flora, inner states, kin, sex, space, tools, and weather conditions.
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All of these behaviors are likely influenced by the presence of epigenetic rules.

If Wilson’s theory of epigenetic rules is correct, then it may well answer the question of whether information systems literally “evolve.” To continue probing that question, the next chapter will look for evidence of epigenetic rules at work in one of our species’ most ancient information systems.

Walking through the Peruvian rain forest with a guide from the local Aguaruna tribe, anthropologist Brent Berlin listened intently as his companion reeled off the names of all the plants and the animals they encountered. Berlin was impressed not only with the tribesman’s encyclopedic knowledge of the forest, but with the elaborate taxonomy he seemed to be using: categorizing plants and animals into species, genus, and family—echoing the familiar Linnaean taxonomy that most modern biologists rely on today. “To find ‘simple savages’ controlling an extensive body of knowledge akin to the scientific fields of botany and zoology,” Berlin later wrote, “is truly remarkable.”
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Even more remarkable, Berlin has since discovered, is the complexity of so-called folk taxonomies in other tribal cultures around the world. From the outback of Australia to the islands of Papua New Guinea to the depths of the Amazon, indigenous peoples not only create highly developed classification systems, but they do so in strikingly similar ways: with plant or animal “families” divided into nested hierarchies, often using exactly the same categories. For cultures that developed in geographical isolation over tens of thousands of years,
what could possibly explain such close parallels? Are taxonomies somehow wired into our genetic makeup?

For many of us the word “taxonomy” probably conjures images of academic drudgery: obscure Latin names, plodding textbooks and pallid grad students discussing the finer points of flora and fauna. Few nonbiologists ever give the subject much thought, and even among many biologists taxonomy has fallen into disrepute as a backwater of the life sciences. But for the greater part of the past 100,000 years, the practice of biological classification ranked as one of humanity’s most essential cultural pursuits. “Some people dismiss taxonomies and their revisions as mere exercises in abstract ordering,” writes Stephen Jay Gould, “a kind of glorified stamp collecting of no scientific merit and fit only for small minds that need to categorize their results. No view could be more false and more inappropriately arrogant. Taxonomies are reflections of human thought; they express our most fundamental concepts about the objects of our universe.”
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What exactly is a taxonomy? A taxonomy, in its simplest form, is a system of categories that people use to organize their understanding of a particular body of knowledge. The oldest and most familiar taxonomies involve plants and animals. And while most of us may spend little time thinking about taxonomies, we use them every day. For example, take a common animal like a tabby cat. Most of us would agree that a tabby is a kind of cat, that cats are mammals, and that mammals belong to the larger category of animals. So, the taxonomy of, say, a brown long-haired tabby cat might look something like this:

Now a biologist would consider this particular taxonomy woefully inadequate. The formal Linnaean taxonomy that most of us studied in some long-ago biology class uses a more detailed system
that allows for up to nine levels of categorization, each accompanied by a signature Latin name. So, using the example above, the equivalent Linnaean taxonomy would look like this: