So much guilt, myth, and historical misinformation has accumulated around the saga of the American Indian that it is a wonder that anything new can possibly be said. Yet in fact we understand comparatively little about North America before the arrival of the Europeans. The difficult task is made more so by the many layers of politically correct ideology and old habits of thinking which threaten any new interpretation of the Indian past.

A great many people, not only American Indians, have a huge ideological and political stake in how this story plays out. But, in “1491” (Alfred A. Knopf, 480 pages, $30) Charles Mann has done his homework and navigates these minefields with aplomb. He has not only absorbed the substance of a vast range of new research that has emerged during the past 10 years but has personally visited many of the important sites in the company of key archaeologists and scholars. What he has to tell us is indeed a revelation.

In bringing us up to date, Mr. Mann has focused on three aspects of his investigation. The first is the question of demography. How many Indians lived here before Contact? How big were the villages and the cities? How densely settled? How did the Indian population rise and fall?

The second question deals with origins. When did the Paleo-Indians arrive, and how did they get here? Was there one migration, or several? What is the earliest date of Indian presence in the New World?

His final point of interest is a total reassessment of Indian ecology. How did Indians throughout the hemisphere relate to their environment? How did they live on the land, and how did the land affect the way they lived? We thought we knew the answers to most of these questions, but we were very much mistaken.

Why, one may ask, are these issues so important? Besides the fact that this is our hemisphere, we are fascinated with these peoples because they represent the only other totally separate human experiment (except for minor pockets) on the planet. Cut off from any influence from the Eurasian landmass, they were free to develop on their own, in their own way, just as if they had been living on Mars.

In many ways, this situation is an ethnographic equivalent to twin studies, which analyze the development of identical twins separated at birth. In this case, the Indians were separated from the rest of humanity approximately 15,000 years ago. Indian civilization thus constitutes an independent expression of man’s genetic inheritance, uninflected by any other cultural templates. No Egypt, no Mesopotamian civilizations, no Chinese influence; just indigenous peoples living on an isolated continent. One recent study suggests that all American Indians are descended from a tribe numbering only 200-300 individuals!

The resulting societies were, at the same time, both very familiar (we are all human) as well as incomprehensibly alien. It was this confusing mix that made it so difficult for the arriving Europeans to make any sense of what they saw. The resulting errors and misunderstandings have continued to the present day.

To begin with, there were a whole lot more of these people than we thought. Some current estimates put the population of the central Mexican plateau alone at around 25.2 million in 1491. Compare that to fewer than 10 million for Spain and Portugal together. According to Mr. Mann’s sources, central Mexico was then the most densely populated place on earth, with more than twice as many people per square mile as China or India.

Other estimates put the total Indian population in the hemisphere somewhere between 90 million and 112 million people. Certain vast cities (Teotihuacan, for example) were significantly larger than any city in Europe at the time. These high population counts were not confined just to the large urban areas. As key domesticated crops (maize, beans, and squash) were slowly adapted by the northern tribes, their populations also expanded exponentially.

Then came the diseases – the “germs” part of Jared Diamond’s “Guns, Germs, and Steel.” Sweeping inland from early contacts in the Caribbean, European contagions hit North America even before the Spaniards did. In one instance, the population of the Caddo (a large tribe near Texas) plummeted from around 200,000 to 8,500 – a drop of nearly 96%. Catastrophic losses almost as severe occurred throughout both continents.

The causes of these pandemics have been much discussed, with emphasis on the Indians’ lack of immunity when exposed to European pathogens. There was, however, another important genetic factor. Because the original in-migrating tribes were so small, there was a genetic constriction that severely limited the Indians’ genomic flexibility.

One consequence of this population calamity the a grave miscalculation made by the Europeans about the essential nature of Indian society. “That’s one reason whites think of Indians as nomadic hunters,” the anthropologist Russell Thornton explained to the author. “Everything else – all the heavily populated urbanized societies – were wiped out.”

This is what is known as the “illusion of permanence” fallacy: We assume that what we experience personally, in our lifetime, is the way things really are and always have been. Europeans thought the Indians they saw were always thus. Only now are we beginning to understand how wrong they, and we, have been.

In the most gripping part of this marvelous book, the section dealing with Indian ecology, Mr. Mann shows in great detail how this fallacy has worked for hundreds of years to obscure and distort the truth of the Indian experience. One of the most persistent myths is that these peoples “lived lightly on the land.” This is the central message projected by the new National Museum of the American Indian in Washington, D.C., and put forth in mountains of books with titles like “Sacred Ecology,” “Guardians of the Earth,” “Mother Earth Spirituality,” and so on.

According to Mr. Mann, a publication called “The Native Cultures Authenticity Guideline” assesses the portrayal of the “Five Great Values” shared by all the major Native cultures. “Getting Along with Nature – respecting the sacred natural harmony of and with Nature,” is one. This was the view first promulgated by the early European settlers, and it has prevailed ever since. This is, in fact, a delusion.

It turns out that what the Indians actually did “on the earth” was to mold it, modify it, cultivate it, burn out the underbrush, clear it, change the composition of the plant material and the soil to suit their needs, and generally dominate the landscape, both flora and fauna, to an unimaginable degree. When the Mayflower people wandered into the woods of New England, they assumed these were natural growths. In fact, the open forest of mostly nut bearing trees was a product of careful Indian husbandry.

And so it was throughout the land, in both woods and prairie. Practically the entire state of California was a carefully cultivated, totally artificial landscape designed for the production of acorns, the staple crop for the Indian tribes of that region. Incredibly, this same pattern of careful development is found even in remote parts of the Amazon – the ultimate “forest primeval”: Vast tracts of specially altered soils had supported major populations there for thousands of years.

Mr. Mann’s point is this: In the Western Hemisphere, after the arrival of the Indians, there was no such thing as “wilderness.” There is no “wilderness” now, and there was none before. It is a mistaken concept created by romanticizing Westerners infatuated with the pseudo-sublime of Rousseau and his deluded brethren. What the Hudson River painters swooned over, in their idealized renderings of wilderness landscapes, was actually nothing more than the degraded state of forests formerly managed by the Indians of the region.

With apologies to Thomas Cole and his colleagues, and with thanks to Charles Mann, our concept of pure wilderness untouched by grubby human hands must now be jettisoned. The real relationship between Man and Nature is this: that they are one and the same. Man has always controlled Nature, and always will.

So, we can forget about the “natural” method of forest management (leaving it completely alone) and start clearing out the brush and doing selective cutting and burning just as the Indians had been doing for 10,000 years. We can create whatever landscape we want, just as the Indians did. Of course, we’ll also have to think up a new name for the Wilderness Society. How about just folding it into the Garden Conservancy?

Mr. Pettus last wrote in these pages on evolution.