“Radical Evolution: The Promise and Peril of Enhancing Our Minds, Our Bodies – and What It Means To Be Human” (Doubleday, 400 pages, $26) opens with a New Yorker cartoon depicting Modern Man standing on an infinite staircase gazing up at it with a puzzled expression on his face. Below him stands a less-evolved caveman who comments, “I was wondering when you’d notice there’s lots more steps.” As Joel Garreau explains in this fascinating and disturbing book, not only is human evolution continuing, it is picking up speed at a fearful rate, dragging us all into a terrifying and uncharted landscape unlike anything we have seen before.

In the past, our technologies have been designed to control the outside world; now they are directed inward, toward ourselves. A threshold has been crossed, and an imminent and cataclysmic upheaval in human affairs is under way. We need to understand what is happening if we are going to have any chance of controlling our future, and, in “Radical Evolution,” Mr. Garreau volunteers to be our guide.

There are four interrelated technologies that have the potential to modify human nature itself. The parent of them all is the information revolution. The other key areas include genetic technologies, the development of advanced robots, and the incredible explosion of nanotechnologies. Most of us have picked up some vague vibrations of this emerging technology, but we don’t really understand it and we don’t know where it is taking us. It is mostly something we feel, like the ominous rumbling of the R train inside Zankel Hall.

The first thing to grasp is the rate of acceleration of the revolution itself. It took us 1,800 years to get from the Roman Empire to the Industrial Revolution; 169 years to get to the moon; and then a mere 20 years to the Information Age. Mr. Garreau quotes a professor of innovation: “My son today wakes up in the morning certain of one thing. And that’s that the world will be different by nightfall. He expects it. Humans didn’t use to live that way.” The world has already moved too fast for most of us to catch up.

Did you know that the Defense Advanced Research Projects Agency is working on techniques that would enable men to fight for weeks, night and day, without eating or sleeping? That’s just the beginning. We are already aware of stem-cell research and steroid use, but now comes a vast array of human-enhancement techniques (to banish aging, increase our kids’ SAT scores by 200 points, defeat diseases) that could, in effect, lead to the rapid evolution of an altogether new man.

As Mr. Garreau leads us through this world of innovation and creativity, we get to know many of the key players, visionaries, and Cassandras – Ray Kurzweil, Bill Joy, and Francis Fukuyama among them – as well as groundbreaking laboratories that are creating the future. But is this something that we want to do? Do we have any choice in the matter? Are we headed for heaven or for hell?

It’s going to be heaven for sure, says Mr. Kurzweil and many other experts including Gregory Stock, who has written books with titles like “Redesigning Humans: Our Inevitable Genetic Future.” A federal document called “Converging Technologies for Improving Human Performance” concluded with this encouraging prediction: “The twenty-first century could end in world peace, universal prosperity, and evolution to a higher level of compassion and accomplishment.”

Not only are we going to make ourselves more intelligent and live very long and productive lives; this is what we were meant to do. “We will be part of this very rapid explosion of intelligence, and beauty, and a very rapid acceleration of this evolutionary process. And that, to me, is what God is.” Thus Mr. Kurzweil and others, filled with hope, anticipate the “Heaven Scenario.”

But it’s not how Mr. Joy (“The Edison of the Internet”) sees it. “I think it is no exaggeration to say we are on the cusp of the further perfection of extreme evil,” he predicts. He and others are appalled by the threats posed by this new technology. All it will take is one false step, and we are finished. Engineered evolution will produce separate, and warring, species of humans. Self-replicating “nanobots,” more intelligent than humans, could take over and “suck everything vital out of all living things.” A simple laboratory accident and “gray goo” will eat us all. Oops.

The “Hell Scenarios” are many and they are very convincing. There is, however, a third possibility: what Mr. Garreau calls the “Prevail Scenario.” Perhaps humanity is not playing a finite game, but an infinite one, in which the goalposts are always shifting. This game is filled with doubts and uncertainties, but rooted in the essential human desire to transcend limits. Thus this sudden acceleration of human creativity and invention is more an outgrowth of our essential nature than a Frankenstein aberration based on overweening hubris. Mankind will prevail in this crisis because we have an uncanny history of muddling through in defiance of historical forces that seem certain and inevitable.

I think Mr. Garreau is right, and I see a parallel here with democracy itself. The aggregate of voters often reaches levels of electoral wisdom hard to predict. So here, despite the undeniable threats looming, humans on earth with their increasing interconnectivity and commonality might just deal with this evolutionary crisis in surprisingly creative ways. It’s that or the gray goo.

Mr. Pettus last wrote for these pages on genetically modified food.