If there is a secret to the remarkable success of Thomas’s little book (nine weeks on the best-seller list, 260,000 copies in print), it is that she gives the imprimatur of science to something most Americans already believed but were embarrassed to admit: that their dogs are at least as interesting as the human beings they know. The 11 dogs that shared Thomas’s various homes over three decades lived lives packed with emotion, rich in intellectual pursuits and in the tapestry of family life and tradition. They didn’t just mate, they fell in love and married. They didn’t just run off, they explored their environment, mentally mapping a range that in one case extended to 130 square miles. They may appear to comprise an unruly mob, but in fact they inhabit a distinctive hierarchy, a society no less complex for the fact that it is mediated by squirts of urine. Thomas’s subject is “dog consciousness,” whose existence she takes as a given: the scientific assumption to the contrary, she writes, “is astonishing.”

The largest of the dogs is Sundog, a 10-year-old German shepherd/yellow Lab cross. He is the animal made famous in Thomas’s book for learning by observation the proper way to share an ice-cream cone with a human: one lick at a time. This is a remarkable achievement for a creature who usually feels free to gobble, although Thomas neglects to add that most people whose dogs have licked their cones probably don’t want them back anyway. At the mention Of his name, Sundog rolls over to show his belly, yawns and goes back to sleep.

Of course, Thomas is not the first writer to find her subject matter literally at her feet. Probably the only topic more thoroughly covered in literature than dogs is cats. But popular writers usually discuss dogs in their capacity as pets, while scientists studying canine behavior generally use wild or feral animals. By taking her own dogs as her subject, Thomas has achieved a remarkable level of intimacy for a work with scientific pretensions. But her careful observations and graceful, understated prose elevate her book far beyond the lachrymose standard for pet reminiscences.

Thomas has only limited training in ethology, although she wasn’t trained for a number of the things she has done in her long and fascinating career. In the early 1950s, she was a young woman still in college when her father, Laurence K. Marshall, retired as president of Raytheon Co. and determined to do something unique with his life. That turned out to be a trip with his family to a virtually unknown–to Americans–part of the Kalahari Desert of south-central Africa, an experience that shaped the rest of their lives. Marshall worked until a few years before his death in 1980 on a project to teach dry-country farming to the Kalahari Bushmen. Elizabeth’s brother, John, became a documentary filmmaker on the Kalahari Bushmen and other subjects, and her mother, Lorna, is, at 94, finishing her second book on hunter-gatherers. Elizabeth herself published a classic study of Bushmen, “The Harmless People.” She followed it with works on other tribes and on animals, including elephants, lions, wolves and circus tigers. Since 1987 she has published two novels, “Reindeer Moon” and “The Animal Wife,” beautiful and original stories set among Paleolithic huntergatherers whose lives are not that different from those of the Bushmen a generation ago.

The work that grew into “The Hidden Life of Dogs” began 30 years ago when Thomas lived in Cambridge, Mass., with her husband, Stephen–a historian and political consultant–two young children and a burgeoning menagerie of dogs. There was a pug and then another, a husky and then a second husky, the amazing Misha. Flouting leash laws, Misha would lope for hours or days through the farthest suburbs of Boston, yet always found his way back home. A seldom asked question took shape in Thomas’s mind: what do dogs want? She began following Misha on his jaunts, and although she never figured out how he negotiated the maze of streets, she came to a conclusion about why he did it: to encounter, circle and, in a brief test of strength, dominate as many other dogs as possible. This was her first evidence that dogs had emotional needs of their own unrelated to food, sex or anything with two legs.

The two younger dogs–Pearl, an Australian sheepdog, and Misty, a Belgian–grow bored with serenity and resume sniffing, primarily each other. Suddenly they bolt out the door and to the far end of the field, where they stand yapping at a tree that looks no different from any other between Maine and Pennsylvania. After a minute they turn and trot back to Thomas.

“What was that about?” the visitor asks.

“Probably an animal,” Thomas murmurs.

“But what kind of animal?”

Thomas shrugs, expressing both the irrelevance of the question and the impossibility of ever answering it. If she didn’t see what they were chasing, and they didn’t catch it, how should she know what it was? Ten seconds out the door, and already they have left the realm of human observation and knowledge. Whatever else a dog may do, he won’t answer their questions.

What lives Thomas’s dogs seem to have led, so full of love, jealousy passion and fear! Bingo, the senior pug, bore an unrequited love for the beautiful husky Maria. Yet when he saw Maria running excitedly around a cage holding pet mice and birds, he knocked her down. To Thomas this demonstrates “moral fiber,” because Bingo risked Maria’s displeasure over a matter of principle. The principle, in all likelihood. was no grander than Bingo’s sense that it was annoying and undignified to have an adult dog carrying on in the kitchen like an excited puppy. But Thomas leaves just enough ambiguity in her account so that readers may choose to believe that Bingo was protesting the injustice of a big animal chasing a small one. If true, that would be a feat of canine empathy even more astonishing than knowing how to share an icecream cone.

Even when their behavior was at its most doglike, Themas’s pets seem to have internalized many of the subtlest human emotions. Koki, a high-status female, happened to give birth at the same time as the low-ranking Viva. By the iron law of the pack, handed down intact from their wolf forebears, only one litter could survive. Koki enforced this by killing Viva’s puppies. “Koki did what she had to do, and the other dogs knew it,” writes Thomas. Even Viva seemed to understand “that her pups had no right to be born.” Yet at the same time Koki felt bad about it, skulking around anxiously and gratefully relinquishing the lone survivor to Thomas, as if glad to be relieved of the awful burden of instinct.

It is impossible to read this passage without being moved by its beauty and eloquence. But this is not the same as accepting its accuracy. Daniel C. Dennett, director of the Center for Cognitive Studies at Tufts University admires Thomas’s book and believes that “a great deal of it” will be confirmed by experimental investigation. On the other hand, he considers her analysis of Koki’s motives in this passage “baloney” “We don’t automatically understand our own instincts,” he says. “Why should dogs? Thomas has lots of intuition and imagination, but she is not trying to do science.” The well-known animal expert Michael W. Fox is also baffled by Thomas’s view of the infanticide, since her dogs had adequate food and shelter to raise two litters. His assessment of the book is that it’s “a pretty good attempt by an anthropologist to be an ethologist.”

For her part, Thomas refuses to be relegated to the swamps of science where “intuition” and “imagination” grow wild. “The assumption is, if you’re not darting and banding and collaring them you’re not being scientific. That’s horsefeathers. Observing is a perfectly valid scientific technique.” Thomas is loud in her scorn of the discredited behaviorist view of dogs-impersonal tail-wagging machines, processing stimuli into responses as indifferently as they convert biscuits into droppings. Not all scientists think this way any longer (page 63). Yet the truth is, dogs actually seem like that a lot of the time; So, of course, do people. Thomas describes a poignant moment when she believed she could actually enter her dogs’ world, to see through their eyes and think their thoughts. Somewhat disappointingly, though, this epiphany came to her as she and her dogs lay together on the ground one sunny afternoon, practicing “pure, flat immobility.” What primates experience as boredom. she concludes, dogs feel as peace. And the answer to her motivating question–“What do dogs want?”–turns out to be that they want the company of other dogs, which seems not much of a revelation. Perhaps something more provocative will emerge from her next book, “The Tribe of Tiger: Cats and Their Culture.” “Human brains and dog brains have some striking similarities,” Thomas says: “Cat brains are wired very differently.” In answer to the question “What do cats want?” Thomas says simply: “Mice.”

Yet Thomas has surely done something unique and wonderful in her book. To the nation’s army of dog lovers she is a hero–even if a few of them, according to animal trainer and author Vicki Hearne, appear to have misunderstood the point of the story about Misha and are letting their dogs loose in the streets, where they’re getting creamed by taxis. (Thomas, whose initial reaction was that no dog owner could be that dumb, says she’ll add a warning to future editions.) They descend on Thomas when she signs books, often with the same two questions “Do you really let your dogs sleep in your bed?” and–“Do dogs have souls?” The answer to the first is “Where do your dogs like to sleep?” and to the second, “If we have souls, then dogs have souls, and if we go to heaven, so do they.”

“How do you know?”

“Because if dogs are not there,” she says, smiling, “it is not heaven.”