nthropologists have got to be the most frustrated of all scientists. Unlike botanists or zoologists, who can't even pretend to know what it's like to be a peach tree or a three-toed sloth, anthropologists study a species whose interior life they, as fellow hominids, should at least theoretically understand. And yet no matter how much evidence they gather -- how many obsidian spear points or fossilized pelvic bones or even oral creation myths -- most of the truly meaningful questions in their field remain fundamentally mysterious: Did the Olmecs feel parental love as we do? Did Neanderthals have any recognizable concept of free will? Do even modern-day nomads experience the ideas of ''home'' and ''loss'' in a way that we possession-freighted Westerners can fathom?

This sense of anthropology's teasing opacity lies at the heart of ''Parasites Like Us,'' Adam Johnson's grim romp of a first novel (after last year's story collection, ''Emporium''). The book begins with Hank Hannah, a professor of anthropology at the University of Southeastern South Dakota, addressing himself to his colleagues of the future. The culture once known as ''America,'' it seems, has summarily extinguished itself, and Hank, one of its sole survivors, wants to set posterity straight about its decline and fall. ''Professors of tomorrow,'' he writes, ''as you excavate the empire that was America, you'll find a million unusual objects to puzzle over. Don't bother. Make no theories concerning the purpose of a Slinky. . . . Waste no time attempting to understand golf carts, greeting cards, StairMasters and car alarms.'' The crucial truths about the late, great empire lie beyond such cultural detritus, and Hank's narrative is intended to fill in the gap, providing an answer to that all-important question of the future: what was life at the turn of the 21st century really like?

As an anthropologist himself, Hank is in an excellent position to answer this question, since he knows how little a lost culture's artifacts can tell us. (''The point of anthropology,'' he says, ''is not discovery, but learning to tolerate the unknown.'') His own area of study is the Clovis culture, a prehistoric people who crossed the Bering Land Bridge from Siberia to America 12,000 years ago, only to disband mysteriously 300 years later. His pet hypothesis is that the Clovis, who left behind no monuments or art except for a wealth of impressively deadly spear points, caused their own downfall through sheer waste, by hunting 35 species of large North American mammals to extinction. ''An entire people had been selfish,'' as Hank puts it to his eventual readers. ''They'd lived solely for themselves and they'd left their offspring nothing.''

If that description reminds you of another, somewhat more recent society of hominids, you're digging in the right bone pile. For when it comes to profligacy and the reckless embrace of material consumption over artistic and spiritual development, no people were more accomplished than Homo americanus, circa A.D. 2003. Like the Clovis, they were a scourge on the continent that supported them. And also like the Clovis, they proved to be too voracious to survive, scripting their own ruin by overindulging their excessive appetites.

The machinery of this second great American vanishing is set in motion when one of Hank's proteges, a graduate student named Eggers (no comment there), stumbles upon a Clovis burial site on the grounds of a local Indian reservation. Buried among the bones and spearheads are two clay spheres unlike any Clovis artifact ever encountered. Before Hank and his students get a chance to excavate the site, however, construction crews move in to start work on Phase 2 of a nearby casino complex. During a made-for-television purification ceremony to mark the groundbreaking, one of the orbs is cracked open, giving the world more of a Phase 2 than it bargained for: the orb turns out to be a latter-day Pandora's box, releasing a 12,000-year-old virus (apparently the actual cause of the Clovis disappearance) that ends up killing nearly everyone on the continent.

Johnson relates all of this with great ingenuity and bravado -- as well as a good deal of unfocused energy. His account of America in decline is a bizarre hybrid, careering from slapstick to domestic drama to disaster-movie histrionics with an abandon that readers will find either exhilarating or jarringly inconsistent. The basic atmosphere of the book is what you might call ''neo-White Noise'' -- that familiar ambience of menacing technological crisis for which Don DeLillo should be collecting residuals. But Johnson adds to that base a layer of comic absurdity beyond anything that DeLillo and his imitators have yet attempted. There's also a bit of romantic comedy thrown in, with Hank wooing a visiting professor -- Yulia Terrasova Nivitski, a paleobotanist from the University of Northwestern North Dakota -- who has an adorable Russian accent and an equally adorable young son, given to saying things like: ''My friends and I will one day be scientists. Our project could be a tool for peace or a weapon of mass destruction, depending on whether or not the world appreciates us.''

The most daring element in this heterogeneous mix, however, may well be the vein of earnest solemnity that Johnson adds to it. Unlike most satirists, he's not afraid to let the mask of irony fall occasionally, launching into flights of plaintiveness that sometimes border on the maudlin. Specifically, he has Hank spend much of the book sulking over his abandonment by various important figures in his life -- his mother, who disappeared when he was a child; his beloved stepmother, who died of an unnamed disease just six months before the novel begins; even his old mentor, who took off for Florida after retirement and hasn't been heard from since.

But are such forays into earnestness advisable in a novel like this? True, they do underline Johnson's critique of contemporary America as a culture rich in everything except the warmth of human connection. But somehow, amid all the end-of-civilization high jinks, Johnson forgets to give us much concrete detail about the shadowy relationships from Hank's past. As a result, Hank's persistent keening comes off as a bit sentimental and false, like a strained attempt to beef up this comic novel with some extra emotional weight. There's no question that ''Parasites Like Us'' is an artifact of real ambition and originality. But the book ultimately suffers from the same problem as Hank's theory about the Clovis -- it's got brilliance to burn, perhaps, but it gets a few too many things wrong.