Suppose that, in 1899, someone had published a book predicting that in a hundred years we would be living, on average, into our mid seventies; communicating instantaneously around the world; hurtling through the air in metal birds; watching theatre on little boxes; visiting other planets; and creating new lifeforms in our laboratories. Practical, no-nonsense readers of such a book would doubtless have concluded that the author was a lunatic. Yet here we are. Given the viral nature of memes; the creative cross-fertilization that occurs when people are connected; and the exponential growth of technology in general and of connectedness in particular, it is reasonable to conclude that we ain't seen nothin yet. Take a glimpse at Ray Kurzweil's vision of our future, and you'll be inclined to agree.

There will be people who think that Kurzweil has written a crazy book, but from the perspective of our descendants a hundred years from now, the book might not seem crazy enough. Kurzweil has the insight to recognize that we are creating technologies that will change everything, utterly. Imagine a world in which you can plug in extra processing power or memory, in which you can download to your mind many lifetimes of knowledge and experience, in which consciousness can be shared, in which you can experience what it is like to be your spouse or what it is like to be a bat. Imagine a world in which you will not have to die. The imaginations of science fiction writers pale in comparison to what real science has in store for us, and Kurzweil has given us a sneak peek at some of the most profound possibilities.

On two fronts-computer science and genetics-we are taking charge of our own evolution. Kurzweil deals skillfully (and entertainingly) with the former. To my knowledge, the definitive popular exposition of the latter has yet to be written.

Computer science and recombinant DNA technology will soon give us the power to make our evolution depend on memes (our cultural creations, our ideas and artifacts) rather than on genes. Memes evolve exponentially because, unlike genes, they do encode acquired characteristics, so in the very near future, it is likely that our descendants will be as far removed from us as we are from sponges, much less Australopithecus afarensis. The inevitable merging of our minds with those of the machines that we create will change our basic ontological situation-what it is like to be us and what experiences are possible. This is Kurzweil's theme. I know of no other writer who has seen more clearly that with the emergence of these technologies for controling its own evolution, life on earth is entering an entirely new phase.

Kurzweil's timetables might be a little off, but it is hard for me to imagine that the bizarre futures that he foresees will not come to pass. The Age of Spiritual Machines is one of those books (like Herb Simon's The Sciences of the Artificial or Marvin Minsky's The Society of Mind) that no thinking person should miss. It is more than simply a masterful synthesis and projection of current technological trends. It is a brave, bold work that cannot fail to shake you up. I hope that this book will be the beginning of a public dialogue about what we want to be and to become.