B004R9Q09U EBOK (5 page)

In this system, the long-haired tabby is a subspecies of the species
Felis catus
. While the Linnaean system may be more accurate, for most of us it doesn’t mean much. The first group of categories, while it might not pass scientific muster, nonetheless represents the kind of informal “taxonomy” that most of us rely on each day to make sense of the world around us.

For tens of thousands of years, human beings have been doing just this: giving names to things, and sorting those things into categories (“mammals,” “birds,” and “fish”). The oldest taxonomies stretch far back into our species’ past—and perhaps even farther into our pre–
Homo sapiens
lineage (although this possibility inevitably remains a matter of speculation). Indeed, our ability to classify things may be one of our species’ great evolutionary differentiators.

Throughout our species’ time on earth, we have relied for survival on collecting and disseminating accurate information about the world around us: knowing which animals we can eat, which plants are poisonous, and so forth. For humans living in hunter-gatherer or tribal societies, folk taxonomies are fundamental tools of group survival. It would stand to reason, then, that natural selection played some role in the formation of these systems. Individuals born with an aptitude for taxonomy would likely stand a higher chance of reproductive success. If you could remember which snakes were poisonous, which mushrooms you could eat, which animals you could tame, you stood a better chance of passing on your genes to the next generation. No single human being could possibly catalog the entirety of
nature’s creation from scratch; it would take too much time and a great deal of trial and error (often of the life-ending variety). Folk taxonomies took generations to build.

While conventional histories of science often credit scientific pioneers like Linnaeaus and Aristotle as the first taxonomists, in truth taxonomies have a much longer history. The earliest folk taxonomies almost certainly predate literate civilization by thousands of years. While we may never know precisely how our ancient forbears classified the natural world, we can surmise a great deal about how these systems worked from the study of modern-day tribal societies. Every human culture ever observed has created its own taxonomy of plants and animals. Many of those taxonomies are still alive and well today. “Our predisposition to classify at all is an ancient trait,” writes Berlin, “and clearly has an adaptive advantage.”
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While the details of individual classification systems vary widely, the structure of these taxonomies reveals remarkable similarities. Something in our cognitive makeup seems to drive us to categorize the natural world in hierarchical terms: perhaps the effect of epigenetic rules (see
Chapter 1
). While we can never know exactly what our ancient ancestors’ taxonomic systems may have looked like, we can make informed speculations by contrasting the taxonomies of modern tribal cultures with traditional European systems that almost certainly contain traces of earlier prehistoric systems.

What can the study of comparative taxonomies teach us about preliterate human communities? Anthropologist Cecil Brown conducted the first comprehensive study of how preliterate human social groups organize their knowledge of the animal world. Surveying a broad range of folk classifications across numerous language groups, Brown sought to determine the level of agreement between geographically disparate cultures. The parallels, he discovered, run surprisingly deep. Even the most seemingly divergent cultures seem to employ almost identical strategies for organizing information, following a pattern that Berlin dubbed “ethnobiological rank,” or the use of hierarchical categories to describe the characteristics of plants and animals. According to Berlin, every tribal community ever studied appears to share a universal tendency to divide their knowledge of plants and animals into five or six nested categories.
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Not only is a rose a rose, then, but a flower is a flower, a plant is a plant, and so on. All human cultures appear to share the habit of categorizing flora and fauna using a similar structure; they also reach surprising degrees of consensus on the substance of those categories. Among the most commonly observed biological groupings are trees,
small plants, bushes, vines, and grass. In the animal world the most common zoological classifications include bird, fish, snake, “wugs” (what we colloquially call “creepy-crawlies”: small creatures that always include insects, often spiders, and sometimes worms), and mammals. And the similarities go even deeper. Every culture also seems to agree that things have “real names”—that a rose is more a “rose” than it is a “plant.” This psychologically primary category always lands squarely in the middle of the taxonomy, suggesting that not only do all cultures share a disposition toward creating nested taxonomies but that they also seem to recognize one category as being more accurate or true than the others.

Why are taxonomies so universal? Our capacity for classification seems to spring from two basic cognitive capabilities: binary discrimination (the ability to tell one thing from another) and lateralization of the human brain (the ability to string thoughts together). Once we distinguish two objects from each other, we can hold the objects in our minds long enough to recognize a conceptual distinction between them. This is how we distinguish black and white, male and female, good and evil, us and them. These basic categories in turn give rise to higher-level distinctions. For example, we can recognize the difference between a deer and an antelope, yet we can also recognize the ways in which they are alike. This ability to contrast degrees of sameness and difference provides the conceptual foundation for hierarchical thinking. So we can recognize that a deer and an antelope are simultaneously different (belonging to separate species) and alike (belonging to a larger family of species that also includes bison but does not include, say, rabbits). Working our way up through levels of similarity between animals, we might eventually come up with something like “mammals.” Our prehistoric ancestors spent a great deal of time doing just this, creating categories to describe the living things around them.

Why do people around the world seem to reach such similar conclusions about the natural world? Surely there is nothing inherent in the plants or animals themselves. As Darwin later proved, Aristotle’s notion of idealized forms was classical wishful thinking. We can only assume that our innate disposition toward the animal kingdom reflects a kind of evolutionary consensus. How can we explain the re
markable consistency of these information systems across far-flung cultures? There is no gene, as far as we know, that dictates the structure of taxonomies, yet all human beings seem to share a certain disposition toward categorizing and naming things in structurally similar ways. Such a cultural universal tendency seems to point to the strong likelihood of an epigenetic rule at work. Just as we perceive similar degrees of the color spectrum or a need to tell stories to each other, we seem to have a deep inborn urge to categorize the world around us.

The evolutionary advantage of taxonomic consensus seems self-evident. Perhaps we can imagine our distant ancestors huddled around a fire planning the next day’s hunt; surely it would benefit the group as a whole if everyone could agree on a goal of hunting “bison” as opposed to, say, “mammals.” Similarly, reproductive advantage would accrue to those people who knew to tread carefully around “snakes,” rather than worrying about “reptiles” in general, or making fine-tooth distinctions between green snakes and rattlers. The psychological primacy of the genus seems to make eminent evolutionary sense.

The remarkable similarities between folk taxonomies suggest that categorical thinking cannot be the product of human cultural idiosyncrasy. The parallels simply run too deep; there must be an evolutionary basis. Just as all human beings are born with a disposition toward spoken language, so we are also born with a tendency toward hierarchical categories. Wilson’s theory of gene-culture coevolution seems to offer the most plausible explanation: epigenetic rules that dispose us toward a certain kind of categorical thinking.

If epigenetic rules do indeed equip us with a disposition toward recognizing things as having “real names” at a certain level in a taxonomic hierarchy, then it stands to reason that such a disposition might continue to reverberate even after human beings moved on from thinking about plants and animals to consider larger bodies of subject matter. The structure of folk taxonomies seems to have shaped the way human beings create all kinds of categorical meaning. In his
classic 1958 essay “How Shall a Thing Be Called?” philosopher Roger Brown observed that “the dime in my pocket is not only a dime. It is also money, a metal object, a thing, and, moving to subordinates, it is a 1952 dime, in fact, a particular 1952 dime.”
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Yet somehow most of us would likely call a dime a “dime.”

Brown’s intuition meshes exactly with Berlin’s model of ethnobiological rank, suggesting that our ancient taxonomic tendencies influence our perceptions of other kinds of categories as well. According to Brown, the dime is the thing’s “real name,” reflecting the same notion of psychological primacy that Berlin identifies with the generic level of categorization. Linnaeus too seems to have recognized the primacy of the genus, placing it at the heart of his own classification system. Berlin’s research into folk classification reveals the same result: that the genus occupies a central position as the “real” name of any given organism. The genus represents a kind of focal point in our orientation to the world, from which all the other categories derive.

We could also speculate as to an epigenetic basis for the final level of categorization, the cross-reference; for example, “edible plants” or “dangerous animals.” It is surely no great stretch to suppose that our facility for cross-referencing, for creating “meta” categories, stems from this capacity to pull otherwise unrelated things into a category of the mind.

In this universal human tendency to organize information into categories, we can also recognize the familiar contours of networks and hierarchies. A folk taxonomy is a classic hierarchical system, but it depends for stability on the reinforcing presence of a network. Categorical hierarchy provides a framework capable of scaling to encompass the phenomenal world, while the underlying social network cements its role in the culture and ensures its longevity from generation to generation. This archetypal pattern of hierarchical taxonomy reinforced by social networks echoes repeatedly throughout the history of humanity’s subsequent information systems.

Recent research into human–computer interaction seems to back up the claim. In 1996 IBM researchers discovered that, when Web users tried to navigate their way around the IBM Web site, they become lost once they traveled beyond five or six levels deep in the menu structure, even though the site comprised a series of menus
extending 14 or 15 levels down. Perhaps at some unconscious level, our experience of navigating the Web owes something to our evolutionary disposition toward understanding the world in terms of taxonomies.

While we may never be able to model the epigenetic rules governing taxonomic systems precisely, the presence of such rules would suggest that the structure of our modern classification systems—with their hierarchical categories, binomial naming schemes, and cross-referencing—are not the product of individual human genius (which is not to denigrate the contributions of great taxonomists like Aristotle and Linnaeus), but that these systems emerged over a much longer period stretching deep into our genetic past. If taxonomy is rooted in our evolution as a species, the structure of these systems should also have a corresponding cognitive basis in the human mind. And indeed, the human mind appears to be particularly well suited to think in terms of hierarchical categories. Here we must refer briefly to the work of prototype theorists, who have pioneered a new understanding of how the mind creates categories.