When I was taught history, the treatment was chronological and highly Eurocentric (I went to school in England). The working assumption was that Africa, China, and India did not exist, or at least had no history. We "did" in class, rapidly and in order, Egypt, Babylon, Greece, Rome, the Dark Ages, the Middle Ages, the Renaissance, and finally the discovery of the New World. The assumption was that the Americas before Columbus were completely empty -- no Incas, no Mayans, no Aztecs, no North American tribes. Before 1492, this hemisphere was presumed to contain nothing of much interest.

And not much more after 1492, until the first significant American, Benjamin Franklin, arrived in Britain bringing with him electricity. This coincided with the beginning of the Industrial Revolution and technology. Before that, technology either didn't exist or did not amount to much.

So much for my summary of history as I was taught it. In fact, I now believe that the Industrial Revolution merely marked the apparent dominance of one type of technology over another. And I will argue that it is at most a temporary dominance, likely to end before the middle of this century. The two types of technology I will term "gray technology" and "green technology." I do not know who coined these terms, but I first met them in the address given by Freeman Dyson, distinguished physicist and educator, on accepting the Templeton Prize for 2000.

The names should make the meanings clear enough. "Green" technology is agriculture, grains and fruit and root crops and vineyards and orchards and cotton and flax, as well as animal husbandry and all its products, meat, milk, cheese, eggs, wool, honey, silk, and leather. The benefits of green technology have been with us as long as civilization, ten thousand years and maybe more. "Gray" technology is bronze and iron and steel, coal and oil and electricity, steam engines and trains and cars and planes and spacecraft, plastics and computers and telephones and television.

We probably think of gray technology as more recent, rising to prominence only about 3,000 years ago with the mining of metals, and to dominance later with the production of machines. But this is largely a matter of definition. A spear tipped with sharp flint is gray technology. However, I think my teachers were right in one sense: most of us accept that it is predominantly the products of gray technology that have over the past 300 years given to the developed world its characteristic shape and functions.

Part of the reason for this is simple visibility. Gray technology products are often huge, like skyscrapers and bridges and superhighways, or very loud, like demolition work and rocket launches and teenagers' car radios. We may not notice the green technology products, like the hybrid wheats whose shorter growing season allows them to flourish closer to the poles, or rice with triple the yield of older strains.

We tend to have another instinctive reaction, based perhaps on our own long unremembered history as children of Nature: "Gray technology is bad; green technology is good." We blame gray technology for weapons of mass destruction, for environmental pollution, for land devastated by strip mining or made poisonous by toxic residues. Green technology suggests trees and flowers and honeybees. On the other hand, green technology also has its darker side. Anthrax is much on our minds today, and more lethal varieties of this and other diseases result from a perverted form of green technology. At their best, gray and green make life longer, more comfortable, and less hazardous. At worst, both kill.

The contest between the technologies still goes on, but more and more the duel is down at the microscopic level. Gray technology, after centuries of exploring the limits of bigness, now concentrates equally on the limits of smallness. Driven by the physical limitation imposed on signal travel times by the speed of light, we ask how many integrated circuits can fit on a pinhead, or if a transistor can be made from a single molecule (today's answer: probably), or how we can build a structure by placing the atoms that compose it into position one by one. At the same time, the focus in green technology has moved from biology to microbiology. If we want to understand the behavior of whole organisms and of single cells, the keys to that understanding often require an understanding of the structure and function of individual molecules. Much of today's green technology is conceptually similar to modern gray technology: analyzing, moving, and placing into precise position single molecules.

When I stated earlier that I thought the apparent dominance of gray technology would end in less than 50 years, I did not speculate as to what would replace it. One common view is that this century will see the triumph of biological science, as the twentieth century seemed like a triumph of physical science. I argue for a rather different future, one in which gray and green technologies more and more become complementary. The tools we are developing for molecular manipulation and placement will certainly be used to build microscopic machines and components. Just as surely, they will be applied to create specialized biological units, everything from "bespoke" viruses to tailor-made molecules that combat a specific disease in a unique individual.

Equally certainly - though we still have no idea how to do this - new tools will permit syntheses of biological and non-biological components. We will mix and match, molecule by molecule, the gray and the green. To do what? Let's just list a few obvious products of medical interest: biological/non-biological neural connectors, bridging gaps in nerve tissue to cure paraplegia; artificial eye lenses, able to change focus in response to the action of eye muscles exactly as natural lenses do (today's artificial lenses, wondrous as they are, have a fixed focal length); and artificial cochleas, restoring hearing by replacing inner ears damaged by age or excessive sound levels (teenagers' car radios again).

That's the "near future" prospect. A century from now, we should be seeing not just repair and rehabilitation, but improvement beyond natural performance. The road ahead for gray technology and green technology does not lie in the predominance of one over the other. It lies in their fusion, to produce miraculous results that neither can possibly achieve alone.

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