What lies at the heart of every living thing is not a fire, not warm breath, not a ‘spark of life.’ It is information, words, instructions,” Richard Dawkins declared in 1986. Already one of the world’s foremost evolutionary biologists, he had caught the spirit of a new age. The cells of an organism are nodes in a richly interwoven communications network, transmitting and receiving, coding and decoding. Evolution itself embodies an ongoing exchange of information between organism and environment. “If you want to understand life,” Dawkins wrote, “don’t think about vibrant, throbbing gels and oozes, think about information technology.”

We have become surrounded by information technology; our furniture includes iPods and plasma displays, and our skills include texting and Googling. But our capacity to understand the role of information has been sorely taxed. “TMI,” we say. Stand back, however, and the past does come back into focus.

The rise of information theory aided and abetted a new view of life. The genetic code—no longer a mere metaphor—was being deciphered. Scientists spoke grandly of the biosphere: an entity composed of all the earth’s life-forms, teeming with information, replicating and evolving. And biologists, having absorbed the methods and vocabulary of communications science, went further to make their own contributions to the understanding of information itself.

Jacques Monod, the Parisian biologist who shared a Nobel Prize in 1965 for working out the role of messenger RNA in the transfer of genetic information, proposed an analogy: just as the biosphere stands above the world of nonliving matter, so an “abstract kingdom” rises above the biosphere. The denizens of this kingdom? Ideas.

“Ideas have retained some of the properties of organisms,” he wrote. “Like them, they tend to perpetuate their structure and to breed; they too can fuse, recombine, segregate their content; indeed they too can evolve, and in this evolution selection must surely play an important role.”

Ideas have “spreading power,” he noted—“infectivity, as it were”—and some more than others. An example of an infectious idea might be a religious ideology that gains sway over a large group of people. The American neurophysiologist Roger Sperry had put forward a similar notion several years earlier, arguing that ideas are “just as real” as the neurons they inhabit. Ideas have power, he said:

Ideas cause ideas and help evolve new ideas. They interact with each other and with other mental forces in the same brain, in neighboring brains, and thanks to global communication, in far distant, foreign brains. And they also interact with the external surroundings to produce in toto a burstwise advance in evolution that is far beyond anything to hit the evolutionary scene yet.

Monod added, “I shall not hazard a theory of the selection of ideas.” There was no need. Others were willing.

Dawkins made his own jump from the evolution of genes to the evolution of ideas. For him the starring role belongs to the replicator, and it scarcely matters whether replicators were made of nucleic acid. His rule is “All life evolves by the differential survival of replicating entities.” Wherever there is life, there must be replicators. Perhaps on other worlds replicators could arise in a silicon-based chemistry—or in no chemistry at all.

What would it mean for a replicator to exist without chemistry? “I think that a new kind of replicator has recently emerged on this very planet,” Dawkins proclaimed near the end of his first book, The Selfish Gene, in 1976. “It is staring us in the face. It is still in its infancy, still drifting clumsily about in its primeval soup, but already it is achieving evolutionary change at a rate that leaves the old gene panting far behind.” That “soup” is human culture; the vector of transmission is language, and the spawning ground is the brain.

For this bodiless replicator itself, Dawkins proposed a name. He called it the meme, and it became his most memorable invention, far more influential than his selfish genes or his later proselytizing against religiosity. “Memes propagate themselves in the meme pool by leaping from brain to brain via a process which, in the broad sense, can be called imitation,” he wrote. They compete with one another for limited resources: brain time or bandwidth. They compete most of all for attention. For example:

Ideas. Whether an idea arises uniquely or reappears many times, it may thrive in the meme pool or it may dwindle and vanish. The belief in God is an example Dawkins offers—an ancient idea, replicating itself not just in words but in music and art. The belief that Earth orbits the Sun is no less a meme, competing with others for survival. (Truth may be a helpful quality for a meme, but it is only one among many.)

Tunes. This tune has spread for centuries across several continents.

Catchphrases. One text snippet, “What hath God wrought?” appeared early and spread rapidly in more than one medium. Another, “Read my lips,” charted a peculiar path through late 20th-century America. “Survival of the fittest” is a meme that, like other memes, mutates wildly (“survival of the fattest”; “survival of the sickest”; “survival of the fakest”; “survival of the twittest”).

Images. In Isaac Newton’s lifetime, no more than a few thousand people had any idea what he looked like, even though he was one of England’s most famous men. Yet now millions of people have quite a clear idea—based on replicas of copies of rather poorly painted portraits. Even more pervasive and indelible are the smile of Mona Lisa, The Scream of Edvard Munch and the silhouettes of various fictional extraterrestrials. These are memes, living a life of their own, independent of any physical reality. “This may not be what George Washington looked like then,” a tour guide was overheard saying of the Gilbert Stuart portrait at the Metropolitan Museum of Art, “but this is what he looks like now.” Exactly.

Memes emerge in brains and travel outward, establishing beachheads on paper and celluloid and silicon and anywhere else information can go. They are not to be thought of as elementary particles but as organisms. The number three is not a meme; nor is the color blue, nor any simple thought, any more than a single nucleotide can be a gene. Memes are complex units, distinct and memorable—units with staying power.

Also, an object is not a meme. The hula hoop is not a meme; it is made of plastic, not of bits. When this species of toy spread worldwide in a mad epidemic in 1958, it was the product, the physical manifestation, of a meme, or memes: the craving for hula hoops; the swaying, swinging, twirling skill set of hula-hooping. The hula hoop itself is a meme vehicle. So, for that matter, is each human hula hooper—a strikingly effective meme vehicle, in the sense neatly explained by the philosopher Daniel Dennett: “A wagon with spoked wheels carries not only grain or freight from place to place; it carries the brilliant idea of a wagon with spoked wheels from mind to mind.” Hula hoopers did that for the hula hoop’s memes—and in 1958 they found a new transmission vector, broadcast television, sending its messages immeasurably faster and farther than any wagon. The moving image of the hula hooper seduced new minds by hundreds, and then by thousands, and then by millions. The meme is not the dancer but the dance.

For most of our biological history memes existed fleetingly; their main mode of transmission was the one called “word of mouth.” Lately, however, they have managed to adhere in solid substance: clay tablets, cave walls, paper sheets. They achieve longevity through our pens and printing presses, magnetic tapes and optical disks. They spread via broadcast towers and digital networks. Memes may be stories, recipes, skills, legends or fashions. We copy them, one person at a time. Alternatively, in Dawkins’ meme-centered perspective, they copy themselves.

“I believe that, given the right conditions, replicators automatically band together to create systems, or machines, that carry them around and work to favor their continued replication,” he wrote. This was not to suggest that memes are conscious actors; only that they are entities with interests that can be furthered by natural selection. Their interests are not our interests. “A meme,” Dennett says, “is an information-packet with attitude.” When we speak of fighting for a principle or dying for an idea, we may be more literal than we know.

Tinker, tailor, soldier, sailor....Rhyme and rhythm help people remember bits of text. Or: rhyme and rhythm help bits of text get remembered. Rhyme and rhythm are qualities that aid a meme’s survival, just as strength and speed aid an animal’s. Patterned language has an evolutionary advantage. Rhyme, rhythm and reason—for reason, too, is a form of pattern. I was promised on a time to have reason for my rhyme; from that time unto this season, I received nor rhyme nor reason.

Like genes, memes have effects on the wide world beyond themselves. In some cases (the meme for making fire; for wearing clothes; for the resurrection of Jesus) the effects can be powerful indeed. As they broadcast their influence on the world, memes thus influence the conditions affecting their own chances of survival. The meme or memes comprising Morse code had strong positive feedback effects. Some memes have evident benefits for their human hosts (“Look before you leap,” knowledge of CPR, belief in hand washing before cooking), but memetic success and genetic success are not the same. Memes can replicate with impressive virulence while leaving swaths of collateral damage—patent medicines and psychic surgery, astrology and satanism, racist myths, superstitions and (a special case) computer viruses. In a way, these are the most interesting—the memes that thrive to their hosts’ detriment, such as the idea that suicide bombers will find their reward in heaven.

Memes could travel wordlessly even before language was born. Plain mimicry is enough to replicate knowledge—how to chip an arrowhead or start a fire. Among animals, chimpanzees and gorillas are known to acquire behaviors by imitation. Some species of songbirds learn their songs, or at least song variants, after hearing them from neighboring birds (or, more recently, from ornithologists with audio players). Birds develop song repertoires and song dialects—in short, they exhibit a birdsong culture that predates human culture by eons. These special cases notwithstanding, for most of human history memes and language have gone hand in glove. (Clichés are memes.) Language serves as culture’s first catalyst. It supersedes mere imitation, spreading knowledge by abstraction and encoding.

Perhaps the analogy with disease was inevitable. Before anyone understood anything of epidemiology, its language was applied to species of information. An emotion can be infectious, a tune catchy, a habit contagious. “From look to look, contagious through the crowd / The panic runs,” wrote the poet James Thomson in 1730. Lust, likewise, according to Milton: “Eve, whose eye darted contagious fire.” But only in the new millennium, in the time of global electronic transmission, has the identification become second nature. Ours is the age of virality: viral education, viral marketing, viral e-mail and video and networking. Researchers studying the Internet itself as a medium—crowdsourcing, collective attention, social networking and resource allocation—employ not only the language but also the mathematical principles of epidemiology.

One of the first to use the terms “viral text” and “viral sentences” seems to have been a reader of Dawkins named Stephen Walton of New York City, corresponding in 1981 with the cognitive scientist Douglas Hofstadter. Thinking logically—perhaps in the mode of a computer—Walton proposed simple self-replicating sentences along the lines of “Say me!” “Copy me!” and “If you copy me, I’ll grant you three wishes!” Hofstadter, then a columnist for Scientific American, found the term “viral text” itself to be even catchier.

Well, now, Walton’s own viral text, as you can see here before your eyes, has managed to commandeer the facilities of a very powerful host—an entire magazine and printing press and distribution service. It has leapt aboard and is now—even as you read this viral sentence—propagating itself madly throughout the ideosphere!

Hofstadter gaily declared himself infected by the meme meme.

One source of resistance—or at least unease—was the shoving of us humans toward the wings. It was bad enough to say that a person is merely a gene’s way of making more genes. Now humans are to be considered as vehicles for the propagation of memes, too. No one likes to be called a puppet. Dennett summed up the problem this way: “I don’t know about you, but I am not initially attracted by the idea of my brain as a sort of dung heap in which the larvae of other people’s ideas renew themselves, before sending out copies of themselves in an informational diaspora.... Who’s in charge, according to this vision—we or our memes?”

He answered his own question by reminding us that, like it or not, we are seldom “in charge” of our own minds. He might have quoted Freud; instead he quoted Mozart (or so he thought): “In the night when I cannot sleep, thoughts crowd into my mind.... Whence and how do they come? I do not know and I have nothing to do with it.”

Later Dennett was informed that this well-known quotation was not Mozart’s after all. It had taken on a life of its own; it was a fairly successful meme.

For anyone taken with the idea of memes, the landscape was changing faster than Dawkins had imagined possible in 1976, when he wrote, “The computers in which memes live are human brains.” By 1989, the time of the second edition of The Selfish Gene, having become an adept programmer himself, he had to amend that: “It was obviously predictable that manufactured electronic computers, too, would eventually play host to self-replicating patterns of information.” Information was passing from one computer to another “when their owners pass floppy discs around,” and he could see another phenomenon on the near horizon: computers connected in networks. “Many of them,” he wrote, “are literally wired up together in electronic mail exchange.... It is a perfect milieu for self-replicating programs to flourish.” Indeed, the Internet was in its birth throes. Not only did it provide memes with a nutrient-rich culture medium, it also gave wings to the idea of memes. Meme itself quickly became an Internet buzzword. Awareness of memes fostered their spread.

A notorious example of a meme that could not have emerged in pre-Internet culture was the phrase “jumped the shark.” Loopy self-reference characterized every phase of its existence. To jump the shark means to pass a peak of quality or popularity and begin an irreversible decline. The phrase was thought to have been used first in 1985 by a college student named Sean J. Connolly, in reference to an episode of the television series “Happy Days” in which the character Fonzie (Henry Winkler), on water skies, jumps over a shark. The origin of the phrase requires a certain amount of explanation without which it could not have been initially understood. Perhaps for that reason, there is no recorded usage until 1997, when Connolly’s roommate, Jon Hein, registered the domain name jumptheshark.com and created a web site devoted to its promotion. The web site soon featured a list of frequently asked questions:

Q. Did “jump the shark” originate from this web site, or did you create the site to capitalize on the phrase?

A. This site went up December 24, 1997, and gave birth to the phrase “jump the shark.” As the site continues to grow in popularity, the term has become more commonplace. The site is the chicken, the egg and now a Catch-22.

It spread to more traditional media in the next year; Maureen Dowd devoted a column to explaining it in the New York Times in 2001; in 2002 the same newspaper’s “On Language” columnist, William Safire, called it “the popular culture’s phrase of the year”; soon after that, people were using the phrase in speech and in print without self-consciousness—no quotation marks or explanation—and eventually, inevitably, various cultural observers asked, “Has ‘jump the shark’ jumped the shark?” Like any good meme, it spawned mutations. The “jumping the shark” entry in Wikipedia advised in 2009, “See also: jumping the couch; nuking the fridge.”

Is this science? In his 1983 column, Hofstadter proposed the obvious memetic label for such a discipline: memetics. The study of memes has attracted researchers from fields as far apart as computer science and microbiology. In bioinformatics, chain letters are an object of study. They are memes; they have evolutionary histories. The very purpose of a chain letter is replication; whatever else a chain letter may say, it embodies one message: Copy me. One student of chain-letter evolution, Daniel W. VanArsdale, listed many variants, in chain letters and even earlier texts: “Make seven copies of it exactly as it is written” (1902); “Copy this in full and send to nine friends” (1923); “And if any man shall take away from the words of the book of this prophecy, God shall take away his part out of the book of life” (Revelation 22:19). Chain letters flourished with the help of a new 19th-century technology: “carbonic paper,” sandwiched between sheets of writing paper in stacks. Then carbon paper made a symbiotic partnership with another technology, the typewriter. Viral outbreaks of chain letters occurred all through the early 20th century. Two subsequent technologies, when their use became widespread, provided orders-of-magnitude boosts in chain-letter fecundity: photocopying (c. 1950) and e-mail (c. 1995).

Inspired by a chance conversation on a hike in the Hong Kong mountains, information scientists Charles H. Bennett from IBM in New York and Ming Li and Bin Ma from Ontario, Canada, began an analysis of a set of chain letters collected during the photocopier era. They had 33, all variants of a single letter, with mutations in the form of misspellings, omissions and transposed words and phrases. “These letters have passed from host to host, mutating and evolving,” they reported in 2003.

Like a gene, their average length is about 2,000 characters. Like a potent virus, the letter threatens to kill you and induces you to pass it on to your “friends and associates”—some variation of this letter has probably reached millions of people. Like an inheritable trait, it promises benefits for you and the people you pass it on to. Like genomes, chain letters undergo natural selection and sometimes parts even get transferred between coexisting “species.”

Reaching beyond these appealing metaphors, the three researchers set out to use the letters as a “test bed” for algorithms used in evolutionary biology. The algorithms were designed to take the genomes of various modern creatures and work backward, by inference and deduction, to reconstruct their phylogeny—their evolutionary trees. If these mathematical methods worked with genes, the scientists suggested, they should work with chain letters, too. In both cases the researchers were able to verify mutation rates and relatedness measures.

Still, most of the elements of culture change and blur too easily to qualify as stable replicators. They are rarely as neatly fixed as a sequence of DNA. Dawkins himself emphasized that he had never imagined founding anything like a new science of memetics. A peer-reviewed Journal of Memetics came to life in 1997—published online, naturally—and then faded away after eight years partly spent in self-conscious debate over status, mission and terminology. Even compared with genes, memes are hard to mathematize or even to define rigorously. So the gene-meme analogy causes uneasiness and the genetics-memetics analogy even more.

Genes at least have a grounding in physical substance. Memes are abstract, intangible and unmeasurable. Genes replicate with near-perfect fidelity, and evolution depends on that: some variation is essential, but mutations need to be rare. Memes are seldom copied exactly; their boundaries are always fuzzy, and they mutate with a wild flexibility that would be fatal in biology. The term “meme” could be applied to a suspicious cornucopia of entities, from small to large. For Dennett, the first four notes of Beethoven’s Fifth Symphony (quoted above) were “clearly” a meme, along with Homer’s Odyssey (or at least the idea of the Odyssey), the wheel, anti-Semitism and writing. “Memes have not yet found their Watson and Crick,” said Dawkins; “they even lack their Mendel.”

Yet here they are. As the arc of information flow bends toward ever greater connectivity, memes evolve faster and spread farther. Their presence is felt if not seen in herd behavior, bank runs, informational cascades and financial bubbles. Diets rise and fall in popularity, their very names becoming catchphrases—the South Beach Diet and the Atkins Diet, the Scarsdale Diet, the Cookie Diet and the Drinking Man’s Diet all replicating according to a dynamic about which the science of nutrition has nothing to say. Medical practice, too, experiences “surgical fads” and “iatro-epidemics”—epidemics caused by fashions in treatment—like the iatro-epidemic of children’s tonsillectomies that swept the United States and parts of Europe in the mid-20th century. Some false memes spread with disingenuous assistance, like the apparently unkillable notion that Barack Obama was not born in Hawaii. And in cyberspace every new social network becomes a new incubator of memes. Making the rounds of Facebook in the summer and fall of 2010 was a classic in new garb:

Sometimes I Just Want to Copy Someone Else's Status, Word for Word, and See If They Notice.

Then it mutated again, and in January 2011 Twitter saw an outbreak of:

One day I want to copy someone's Tweet word for word and see if they notice.

By then one of the most popular of all Twitter hashtags (the “hashtag” being a genetic—or, rather, memetic—marker) was simply the word “#Viral.”

In the competition for space in our brains and in the culture, the effective combatants are the messages. The new, oblique, looping views of genes and memes have enriched us. They give us paradoxes to write on Möbius strips. “The human world is made of stories, not people,” writes the novelist David Mitchell. “The people the stories use to tell themselves are not to be blamed.” Margaret Atwood writes: “As with all knowledge, once you knew it, you couldn’t imagine how it was that you hadn’t known it before. Like stage magic, knowledge before you knew it took place before your very eyes, but you were looking elsewhere.” Nearing death, John Updike reflected on

A life poured into words—apparent waste intended to preserve the thing consumed.

Fred Dretske, a philosopher of mind and knowledge, wrote in 1981: “In the beginning there was information. The word came later.” He added this explanation: “The transition was achieved by the development of organisms with the capacity for selectively exploiting this information in order to survive and perpetuate their kind.” Now we might add, thanks to Dawkins, that the transition was achieved by the information itself, surviving and perpetuating its kind and selectively exploiting organisms.

Most of the biosphere cannot see the infosphere; it is invisible, a parallel universe humming with ghostly inhabitants. But they are not ghosts to us—not anymore. We humans, alone among the earth’s organic creatures, live in both worlds at once. It is as though, having long coexisted with the unseen, we have begun to develop the needed extrasensory perception. We are aware of the many species of information. We name their types sardonically, as though to reassure ourselves that we understand: urban myths and zombie lies. We keep them alive in air-conditioned server farms. But we cannot own them. When a jingle lingers in our ears, or a fad turns fashion upside down, or a hoax dominates the global chatter for months and vanishes as swiftly as it came, who is master and who is slave?

Adapted from The Information: A History, A Theory, A Flood, by James Gleick. Copyright © 2011 by James Gleick. Reprinted with the permission of the author.

James Gleick is the author of Chaos: Making a New Science, among other books. Illustrator Stuart Bradford lives in San Rafael, California.