OUR POSTHUMAN FUTURE: Consequences of the Biotechnology Revolution, by Francis Fukuyama. Farrar, Straus & Giroux, 256 pp.

REDESIGNING HUMANS: Our Inevitable Genetic Future, by Gregory Stock. Houghton Mifflin, 277 pp.

For the past few weeks, my wife and I have been discussing the idea of having the cats cloned. Not, mind you, in practical tones: Our vet is excellent, but not quite ready to offer that service. One day, though, he might. If so, would we want to make auxiliary backup kittens? And if not, why not? My wife usually takes an anti-cloning position, on grounds of moral sentiment -- though other kinds of sentiment might win the day if the technology were actually available and not too expensive. My own arguments, pro and con, tend to be influenced by whether or not the cats let me sleep the night before.

It is, in its modest way, a philosophical discussion: half-joking, but also half-serious. Those old enough to remember when computers were big, rare and expensive probably have developed the habit of bracing themselves at each announced breakthrough in biotechnology. The scenario mooted in our living rooms today could be a market option later in the decade. Hypothetical questions serve as a way to clarify one's ethical principles. (Mine being, it seems, utilitarian: Deciding for or against feline cloning would involve calculations of how much pleasure and pain it would create, especially for me.) But given the prospect of "the biotech revolution" eventually accelerating as fast as "the information revolution" (which has now consolidated its regime), there really are no hypothetical questions - only choices we haven't had to make yet.

For Gregory Stock -- the author of Redesigning Humans and director of the Program of Medicine, Technology and Society at the University of California at Los Angeles -- ethical debates over cloning are, ultimately, rather trivial. For one thing, the ability to make carbon copies of living creatures (even, potentially, of humans) is the tip of the biotechnological iceberg. In mapping the genome, we have gone well beyond the capacity to screen for birth defects; future advances will involve "germline" technology, in which adjustments made to the genetic makeup of embryonic cells will permit "enhancement" of organisms -- for instance, overriding the biological mechanisms of aging. Parents who can afford it may be able to give their children the additional inheritance of chromosomes designed to maximize intelligence, athletic ability, resistance to disease and the high serotonin levels making for a good mood.

Evolutionary processes shaped humanity over the last few million years. Now the tables have turned. The author solemnly informs us that the cyberpunk vision of the movie Johnny Mnemonic -- in which the future of humanity includes Keanu Reeves' having a computer built into his head -- is probably unrealistic. This is comforting, somehow. But the limits (much less the risks) of biological engineering are by no means Stock's primary concern. His explanations of the emerging technology, and his projections of its foreseeable development, have the quality of a plausible and well- made infomercial.

For Stock, biotechnology poses no moral dilemmas, only technical problems - which qualified scientists are going to solve, so everyone else should just shut up. Every so often, the author refers to the "angst" of those worried that bio-engineering "will tear the fabric of our society," or the "inchoate concerns about human genetic design," such as the fear that the genomically upgraded bodies of the future "will fail at some point, like flawed mutants in a horror movie." Or, perhaps, like a straw man, soundly thrashed.

As Stock puts it in a sentence as ineffable as it is inarguable, "People's worldviews in this sensitive area hold an inordinate sway on their thinking." But their concerns are, finally, irrelevant. The research is too interesting, and the possible benefits too alluring. (Think "built-in Viagra dispenser.") "We have spent billions to unravel our biology, not out of idle curiosity, but in the hope of bettering our lives," Stock writes. "We are not about to turn away from this." Whatever else you can say about his informative yet somehow mindless book, the author of Redesigning Humans certainly does put his money on the table.

Our Posthuman Future, by Francis Fukuyama, is chock-full of what Stock would call "vague philosophical apprehension." Indeed, about halfway through the book, Fukuyama undertakes a critical review of modern ethical theory from David Hume through John Rawls,  whose arguments, while conceptually precise, are the products of a world that predates genomic mapping and germline renovation. For Stock, there is no point in worrying about what his subtitle advertises as "our inevitable genetic future." But for Fukuyama, it is precisely that sense of an imminent, irreversible transformation -- in which the species will redraw the line between nature and humanity -- that obliges our worries to become, in the strictest sense, philosophical.

Drawing on a set of arguments that will be familiar to readers of his book The End of History and the Last Man (1992) and utterly bewildering to everyone else, Fukuyama returns to Plato's notion that the soul is divided into three parts: reason, desire and something called thymos, which Fukuyama glosses as "the prideful side ... that demands that other people recognize one's worth or dignity." For Hegel, too, the demand of the self for honor from the Other is a distinctly human need -- giving rise to struggles (since the Other makes the same demand for recognition) that shape civilization. A young enthusiast of Hegelian philosophy named Marx derived from it the theory that all previous history-making conflicts would culminate in the perfect harmony of Communism. Not so, according to Fukuyama, who argues that liberal capitalism permits the fullest possible satisfaction of the constitutively human demands for rationality, pleasure and recognition. The global market is, basically, as good as it gets.

But what happens to this neat accord between human nature and the social order once science allows us to (1) adjust brain chemistry to get thymotic self-esteem with a prescription and (2) engineer our offspring to be smart and strong and worthy of honor, whether they have struggled to accomplish anything or not? Not to mention (3) earn lots of money doing so (which makes the whole biotech enterprise self-funding). Where do we draw the line? Who draws it? And on what grounds?

Fukuyama wants to find grounds for regulating biotechnology, including an outright ban on attempts to clone human beings. His book represents a laborious and (I think) finally circular argument that the defense of human dignity involves placing limitations on how much we tamper with human nature. "What is it that we want to protect from any future advances in biotechnology?" he writes. "The answer is, we want to protect the full range of our complex, evolved natures against attempts at self-modification."

Well, okay. But isn't "self-modification" pretty much the definitive commodity offered by the market in goods and services? Isn't it part of "our complex, evolved natures"? There is little evidence of Faustian striving among, for example, house cats. If it is part of our human nature, what is there in human nature that makes us recoil at tampering with it? (Some of us, anyway; and even then, not without fascination at the prospect.)

Of course, Stock would consider all such questions a waste of time -- an evasion of the inevitable. And he is probably right, in a kind of self-fulfilling way. Will the genetically enhanced clone children of 50 years from now be able to make any sense of our misgivings? I don't know, but I somehow imagine them being as smart as Fukuyama, and as disinclined to ask hard questions as in Redesigning Humans.