Technological palimpsests are everywhere; it’s the normal state of things. Darfurians are being slaughtered by Janjaweed militia mounted on horses and camels, while their Sudanese-government sponsors chip in with helicopters and Antonov cargo planes retrofitted as bombers. September 11th was a technological pastiche of new and old technologies (Boeings and box cutters), as was the 2003 Iraq invasion (stealth fighters, cruise missiles, and laser-guided smart bombs for the “shock and awe,” and jury-rigged sandbags and scrap-metal armor for Army Humvees when the Pentagon failed to provide high-tech alternatives). The Iraqi insurgents have revived the use of chlorine gas as a terror agent, a technology pioneered by patriotic German chemists in the First World War, and Saddam Hussein, whose aircraft dropped modern nerve-gas bombs on the Kurdish town of Halabja, was executed by hanging, a technology of judicial killing that goes back to the ancient Persian Empire.

Edgerton calls the tendency to overrate the impact of dramatic new technologies “futurism.” Few things, it turns out, are as passé as past futures. In the mid-twentieth century, a world was promised in which nuclear power would provide electricity “too cheap to meter,” eliminating pollution, forestalling energy crises, and alleviating world poverty; hypersonic civil air travel would whip masses of us around the globe in an hour or two; permanent settlements would be established not just on the moon but on the planets; nuclear weapons would put an end to war.

And so it goes. The “paperless office” was celebrated as long ago as 1975, in Business Week, but since then we’ve had avalanches of the stuff: global consumption of paper has tripled in the past three decades, and the average American worker now goes through twelve thousand sheets of paper every year. In 1987, Ronald Reagan announced that high-temperature superconductor technology would “bring us to the threshold of a new age,” but commercializing that technology has proved much more difficult than the original hype suggested. In 2000, Bill Clinton speculated that, as a direct result of the Human Genome Project, “our children’s children will know the term ‘cancer’ only as a constellation of stars.” (That would be nice, if only because it would indicate an improved knowledge of astronomy.) Predictions like these don’t inspire great confidence in the utopian futures now being spun around stem-cell research or nanotechnology.

But neither should we have great confidence in the more dire prophesies. In the middle of the nineteenth century, it was thought that railways would whirl people about the world with such vertiginous speed that their nervous systems could collapse under the strain. Decades later, it seemed that the telephone would be a socially disruptive force, causing aural communication to take place without any of the rich cues of face-to-face interaction, breaking down the barriers between public and private space, and making it intolerably hard not to be “at home” when one was at home.

Learning how to make new technologies is one thing; learning how, as a society, to use them is another. Carolyn Marvin’s illuminating book “When Old Technologies Were New: Thinking About Electric Communication in the Late Nineteenth Century” (1988) notes that, during the early years of the telephone, there was confusion about what codes should regulate faceless and socially clueless speech. The telephone operator, typically female, often had the responsibility of waking up the master of the house, and so joined the wife as a woman who could talk to the man in bed; Marvin writes that “sweet-voiced” telephone girls at the turn of the century “were often objects of fantasy.” It was also thought that, if just anyone could use the new device, its utility would be completely undermined. Marvin notes the firm opinion of the British postmaster general in 1895 that “the telephone could not, and never would be an advantage which could be enjoyed by the large mass of the people.” He was wrong, but understandably so. The story of how we came to terms with the new technology—how we adjusted to it, adapted to it, domesticated it, altered it to suit our purposes—didn’t come with the technical spec sheet. It never does. No instruction manual can explain how a technology will evolve, in use, together with the rhythm of our lives.

Old technologies persist; they even flourish. In that sense, they’re as much a part of the present as recently invented technologies. It is said that we live in a “new economy,” yet, of the world’s top thirty companies (by revenue), only three are mainly in the business of high tech—General Electric (No. 11), Siemens (No. 22), and I.B.M. (No. 29)—and all three go back more than a century. The heights of the early-twenty-first-century corporate world are still occupied—as they have long been—by petroleum companies (Exxon Mobil, Royal Dutch Shell, and B.P., Nos. 1, 3, and 4), retailing (Wal-Mart, No. 2), automobiles (General Motors, No. 5), and finance (I.N.G. and Citigroup, Nos. 13 and 14). No Hewlett-Packard (No. 33); no Microsoft (No. 140); no Merck (No. 289).

The tendency to exaggerate the impact of technological innovation follows from an artifact of historical consciousness. When we cannot conceive what life would be like without e-mail, say, we correctly note the pervasiveness of the new technology, but we may incorrectly assume that the things we now do through e-mail could not have been done in other ways. Of course, we must know that many things now done through e-mail were once done, and to some extent are still done, by telephone, fax, snail mail, or actually stopping by to see someone. But we can never know how the technologies that existed before electronic communication would have developed had e-mail not become dominant, or what other technologies might have come along whose development was forestalled by e-mail.

In 1897, to move mail around the city, Manhattan started to equip itself with an island-wide system of underground pneumatic tubes, which soon extended from 125th Street as far as the Brooklyn General Post Office. Through the nineteenth century, the pneumatic tube had developed roughly in step with the telegraph and then the telephone. For a long time, indeed, pneumatic tubes seemed promising—perhaps they could shunt people around as well as mail—although, ultimately, it was the telegraph and the telephone that flourished, becoming the ancestors of the electronic communication systems we use today. Yet, had there been a century of continuous improvement, who knows what benefits a dense and speedy system of message tubes might have brought? A man working on Eighty-sixth Street could send a scribbled note, chocolates, and a pair of earrings to his girlfriend on Wall Street. To have left your wallet at home could be a mistake remedied in seconds. It’s a safe guess, anyway, that, while aware of a distant past containing such figures as postmen and delivery boys, we would be unable to imagine life without the pneumatic tube.

This kind of counterfactual history has a credibility handicap—we know how things did turn out but can only imagine how they might have turned out. Still, there’s no reason to assume that the technology we have is the only technology we could have had. The birth-control pill, we say, caused a sexual revolution, and perhaps that’s true. But it joined (and only partly replaced) many other methods of contraception, some of which—like the condom—have continued to improve in all sorts of ways since the advent of the pill. And it has been argued that the pill had a dampening effect on the development of other technologies, such as male hormonal contraceptives. Is the pill the best possible outcome? The answer depends on who you are, what you want to do, and the resources you command. As it turned out, the replacement of the condom as a sexual technology, so frequently announced in past decades, was premature. The emergence of AIDS caused condom sales to more than double between the early nineteen-eighties and the mid-nineties. And, for the first time, the old technology of the condom enjoyed an advantage previously monopolized by the new technology of the pill: it could be freely talked about in polite society.