Hauser's office office is on the ninth floor of Harvard's William James Hall, the building where the arch-behaviorist B.F. Skinner shared his quarters with maze-running rats and bar-pecking pigeons until his death in 1990. Hauser himself presides over a lab population of two dozen students; six vervet monkeys, all named for jazz musicians; and seventeen cotton-topped tamarins, named for such colleagues and friends as Pinker, Tufts philosopher Daniel Dennett, and Harvard anthropologist Irven DeVore (with whom Hauser co-teaches one of the most popular courses on campus, "Human Behavioral Biology," informally known as "Sex").

Slight and boyish at forty, sporting a goatee, turtleneck, and clogs, Hauser comes off more like an earnestly enthusiastic lab jockey than a recently tenured professor who has just attempted to write the book on animal minds. He's partial to words like "fun," "neat," and "wacky," and he takes the time to respond politely to "vicious" e-mail from a dog owner enraged by an excerpt from Wild Minds that appeared in Discover magazine (the dog owner insists that his pooch can count to six; Hauser's research has revealed that animal numeracy tops out at three or four). "Talking about animals is a great way of demystifying science gently," he says. "One of the great things about the field is a lot of it is so low-tech you can almost do it with your pets."

For all his popularizing zeal, Hauser hasn't shied away from tweaking orthodoxy within his field. One of his pet projects has been to retool classic experiments in order to suggest that monkeys might be more than the dumber cousins of the great apes that they are sometimes presumed to be. Making frequent trips to Cayo Santiago, Puerto Rico, where he studies free-ranging rhesus monkeys, he is one of the few researchers to examine animals in both the lab and the field. "The real beauty," says Hauser, "is the marriage between fieldwork, where you see the true ecological and social problems that have shaped animal minds, and lab experiments, where you can get more control."

Hauser was born in 1959 in Cambridge, Massachusetts, where his father was a graduate student in physics at Harvard. A self-described jock who was mostly interested in "having fun," he majored in animal behavior at Bucknell, which was the only college in the country to offer such a program. His first course, based on E.O. Wilson's Sociobiology, introduced him to the adaptationist point of view. Soon he found himself puzzling over philosophical conundrums involving animals. There was Ludwig Wittgenstein's famous dictum, "If a lion could talk, we would not be able to understand him." Then there was the twist on that idea by the ape researcher David Premack, who postulated, "If a chicken had grammar, it wouldn't have anything interesting to say." Finally, there was the philosopher Thomas Nagel's famous 1974 essay, "What Is It Like to Be a Bat?" While it was certainly like something to be a bat, Nagel concluded, a description of the bat's inner world remained beyond reach. "It seemed to me at the time that any one of these ideas might be right," Hauser recalls.

Despite its pessimism, Nagel's essay played a crucial role in the development of cognitive ethology. Legend has it that Nagel wrote the essay after attending a lecture by the co-discoverer of echolocation, the zoologist Donald Griffin, who sometimes released bats in his lecture halls to dramatize their ability to navigate by sonar. Griffin, in turn, was inspired by Nagel to write The Question of Animal Awareness (1976), the first in a suite of books that would challenge the behaviorist line and launch the field of cognitive ethology, a phrase Griffin coined. Griffin's Animal Thinking, published in 1984, gathered together the mounting but neglected evidence that animals from baboons to bees to shrimp often act in ways that suggest planning, intent, and awareness of other minds.

Had the eminent scholar lost his mind? Reviewing Griffin's 1992 follow-up volume, Animal Minds, in The New York Times Book Review, the philosopher Helena Cronin declared that Griffin had come out as "a sentimental softie." The psychologist Hank Davis, a fierce defender of behaviorism, likened his heresies to Salman Rushdie's The Satanic Verses. Puzzling even to some of Griffin's sympathizers--Hauser included--was his insistence on seeing "consciousness" behind ordinary instances of intelligent behavior. Some have expressed particular bafflement at Griffin's suggestion that consciousness might help compensate for the limited storage and processing power of small-brained creatures.

Griffin's observations opened rich new areas for empirical research. In the late 1970s, the primatologists Robert Seyfarth and Dorothy Cheney, a husband-and-wife team at the University of California at Los Angeles, were among the first to take up the challenge. In Kenya's Amboseli game preserve, Cheney and Seyfarth, in collaboration with ethologist Peter Marler, conducted the definitive research on one of the most astounding discoveries in animal communication--that vervets had an elaborate system of referential alarm calls that seemed to function almost like words. For example, on seeing a snake, eagle, or leopard, a vervet emits a distinct call that prompts other troupe members to take appropriate action. On hearing the "snake" alarm, troupe members stand on their hind legs and survey the surrounding grass. On hearing "eagle," they hide under a tree. "Leopard" sends them scrambling into the tree's branches.

Sometimes the monkeys even use these calls deceptively--to gain the advantage in a skirmish by suddenly scaring a rival monkey up a tree, for example. (Whether such deception is truly intentional, however, is a matter of considerable ongoing debate.) Cheney and Seyfarth also discovered that despite this vocabulary, vervets were remarkably oblivious to certain aspects of their environment. They would immediately give the "snake" alarm call on seeing a snake, but the sight of a freshly laid python track seemed not to disturb them at all.

In 1982 Hauser, then a graduate student, joined Cheney and Seyfarth in the field. His dissertation would build on their research. Focusing on vervet development, Hauser examined how the infant monkeys learned to heed the less specific alarm calls that starlings issued to one another. But even as he was pursuing this research, he was restless. He and some fellow graduate students organized a seminar around the question of whether behavioral ecology--the traditional study of animal behavior in the wild--was "dead." As he explains it, "We all started realizing that while the field was still exciting, people were really just finding more evidence for existing theories in different species, kind of dotting i's and crossing t's." Some of the students began fusing evolutionary theory with molecular biology. Others, like Hauser, dug deeper into neurobiology and the cognitive sciences.

This turn toward neuroscience brought Hauser closer to Peter Marler, his mentors' mentor and his own hero in the field since 1970. A schoolboy at the time, Hauser had been impressed by Marler's seminal Scientific American article laying out the basic principles for comparing animal communication and human speech. In 1988, Hauser began a postdoctoral fellowship with Marler at Rockefeller University. At that point, Marler and his associates were overturning some cherished notions. For example, many researchers had held that although both humans and animals had anatomic brain asymmetries, only in humans were these asymmetries functional. Not so, Marler discovered. Japanese macaques, in fact, processed auditory signals better through their right ears (connected to the left side of the brain), in much the same way that humans favor their right ears for listening.

Hauser added some interesting findings to this foundation. In 1993, working on Cayo Santiago, he found that the facial expressions of rhesus monkeys began on the left side of the face, indicating that the right hemisphere of the brain was in control. In humans, positive expressions, such as smiling, begin on the right, while negative ones, such as those indicating fear or surprise, begin on the left. Adult rhesus monkeys, oddly, only have negative expressions, Hauser argues. Even the male's copulation grimace, he says, reflects an emotion that is mixed at best, given the intensely stressful and competitive mating situation, in which high-ranking males often drive off subordinates in the middle of the act.

Such observations made their way into Hauser's 1996 book, The Evolution of Communication (MIT), a 760-page survey of signals ranging from birdsong and bat echolocation to firefly flashes and primate facial expressions. Reviewers for such journals as American Anthropologist and Evolution remarked on the book's ambition, clarity, and verve, not to mention the fifteen-hundred-item bibliography. Not all linguists, however, appreciated the comparative perspective on human language. Derek Bickerton of the University of Hawaii, writing in Nature, chided Hauser for underplaying the significance of syntax, which in his view crucially distinguishes human language from birdsong and the like. Furthermore, he argued, vervet calls are not really comparable to words and thus cannot be taken to suggest that human language evolved from animal precursors.

Such reactions did not surprise Hauser. In the early 1990s, he recalls, he had the "disturbing realization" that people working on human language and cognition were not interested in comparable behavior in animals. "I remember giving these talks to people who worked on humans," Hauser says. "You could tell they enjoyed hearing about animals, but it didn't really have any impact on their thinking. Although these findings on vervet communication were absolutely fundamental, linguists would write them off as not relevant to human language evolution, and cognitive scientists would see the experiment as irrelevant because it was done in the wild, using different methods."

Was it even possible, Hauser wondered, to interest researchers in a collaboration across the species divide? The key, he came to believe, lay in studying animals and human infants with the same techniques. At a 1992 comparative cognition conference at Cornell, Hauser attended a talk by the developmental psychologist Renée Baillargeon, a pioneer of the so-called looking-time technique. Researchers using this method would stage a sort of magic show, observing infants to see how long they looked at phenomena that were consistent with the logical properties of the world versus those that were inconsistent. Using this technique, researchers were busy dismantling the Swiss psychologist Jean Piaget's ideas about the ages at which infants grasped such concepts as object permanence. The technique, however, had yet to cross over into the animal kingdom. "The logic was so simple and elegant," Hauser says, "I thought, I can use this on any animal."

Hauser applied looking-time technique in his investigation of animal numeracy. The developmental psychologist Karen Wynn had already shown that five-month-olds understand such simple arithmetic problems as 1+1=2. On Cayo Santiago, Hauser staged a version of her experiment in which he showed his monkeys two bright-purple eggplants, then covered the eggplants momentarily with a screen. Once the screen was removed, the monkeys looked longer when one eggplant had mysteriously disappeared than when both remained. In another experiment, Hauser allowed the monkeys to choose between two boxes containing different quantities of fruit. Up to four versus three, they consistently went for the bigger snack--but they were unable to distinguish between larger quantities.

"What's beautiful about this," Hauser says, "is that it matches precisely what's found for human infants up to a year and it matches precisely what's encoded in all natural human languages. All languages have words for one, two, and three, but often after that it's just ëmore.'" The basic sense of number, he argues, got wired into the brain before humans diverged from other mammals. (In one of the few tossed-off speculations in Wild Minds, Hauser suggests that trade among humans produced the selective pressure in favor of our more precise counting systems.)

Nonetheless, Hauser and his students remain pretty much alone in applying looking-time technique to animal studies. Some critics ask how one can tell what animals are looking at in the field, especially since, in order to avoid any chance of learning, the experiments are limited to one trial per animal. "Yes, it's an uncontrolled situation," Hauser says. "There are a thousand monkeys on the island, there are animals fighting or playing. But we run huge samples--it's not just the study of Alex the parrot or Kanzi the bonobo. If the effect is robust, the variations are going to wash out. If it's vulnerable, we get nothing. But we get really consistent results. When we get an effect, it's huge."

Hauser is so confident of his numeracy results that he includes a basic sense of number in the innate universal tool kit he proposes in Wild Minds. Also in the tool kit are an understanding of the characteristics of animate versus inanimate objects and, more spectacularly, the ability to navigate through space. Many animals can find their way by means of "dead reckoning"--as when homing pigeons fly hundreds of miles over unfamiliar territory by the constantly shifting stars. Some animals, Hauser argues, also have the benefit of "cognitive maps," mental representations of their territory based on its basic geometry and landmarks. Some researchers have conducted studies suggesting that birds may understand such abstract, relative concepts as above, below, and middle--notions that some scholars have argued are dependent on language. Hauser has preliminary results indicating that tamarins may also possess these concepts.

When it comes to the question of language, Hauser is cautious in making strong claims for animals. He notes that Sue Savage-Rumbaugh's controversial results with the bonobo Kanzi suggest that apes may be capable of acquiring a sort of proto grammar. He also acknowledges that we haven't gotten very far in decoding the signals that primates other than vervets use in the wild. Indeed, Hauser and the Harvard anthropologist Richard Wrangham are currently researching chimp vocalizations. At the same time, Hauser says, whatever the complexity of the chimp mind, there aren't enough "bits" of data in these grunt-exchanges to suggest that the animals are having full-blown conversations--say, about the peculiar behavior of the primatologists crouching by the bushes. "I feel pretty confident saying that the level of information exchanged is nowhere near the richness of the animals' social relationships or their representations of objects in the world," he says. "There's just no way."

Ultimately, he speculates that animals are something akin to Gregor Samsa in Franz Kafka's "The Metamorphosis": "severely handicapped" in their ability to say what's on their minds. "These animals are whipping along with all these concepts and no vehicle to express them with," he explains. "Once that language capacity evolved in humans, what a revolution that must have been. Suddenly, all this stuff that's inside can be put outside."

Whether or not animals can be said to possess language, one can still ask: Do animals have self-awareness? Do they have beliefs? What do they understand about other animals' minds? Are they moral? Wild Minds gives these issues ample consideration, but Hauser is clearly peeved that fixation on such higher-order investigations lets chimps hog the limelight. "First, there's this idea that humans are special and animals are not. In primatology, there's the idea that chimps are special and all other apes and monkeys are not. It's true, on some of the big questions, the most interesting research has been done on chimps." But in a chimpocentric world, he says, work on monkeys often gets "sideswiped."

Even on the big questions, Hauser has been trying to get his colleagues to give monkeys a closer look. In 1994 he reran Gordon Gallup's classic 1970 experiment showing that chimpanzees are able to recognize themselves in mirrors. When their heads were marked with a red dot, most of the chimps that looked in the mirror would immediately touch the mark on their heads, sometimes then sniffing their fingers. Since then, researchers have found that orangutans and bonobos--but never monkeys--are similarly able to recognize their reflections. (Curiously, only one gorilla--Koko, the celebrity signing ape--has ever passed the test.)

The experiments, Hauser argued, failed to account for certain of the monkeys' species-specific attributes. Tamarins, for example, which diverged from the human and ape evolutionary line some fifty million years ago, have virtually no facial expressions and do not attend to the face as much as apes do. Therefore, he reasoned, relatively subtle markings like a small dot on their dark skin are unlikely to interest them. So Hauser used a much stronger mark, coloring his cotton-topped tamarins' spectacular tuft of white hair with flamingo-pink Manic Panic dye. Before the dye was applied, tamarins paid only brief attention to their mirrored selves. But on this extreme bad hair day, they gazed into the mirror at length, most of them touching their hair at least once.

Hauser's findings set off a testy exchange with Gallup, who criticized his experimental design and rickety data. In Wild Minds, Hauser admits that when he reran the tests adjusting for various criticisms, the monkeys exhibited a "general failure." Still, he insists, "this should not be interpreted as evidence that tamarins lack self-recognition." Besides, Hauser says, his point was not just to stick up for monkeys but to argue that the mirror test is "the wrong test" of self-awareness. He cites the perplexing case of people with prosopagnosia, a rare condition that leaves a person unable to recognize her own face in a mirror. There is no evidence, he argues, that such people lack self-awareness. Mirror self-recognition, therefore, does not tell us anything about animals' "sense of self"--much less whether they are conscious, or have an awareness of death, as some have gone so far as to suggest.

Still, Hauser is willing to indulge in some admittedly whimsical speculation on the question. In 1997 he observed rhesus monkeys on Cayo Santiago staring with fascination at pieces of a broken mirror. On his Web site, he suggests that the mobility of these mirrors may have enabled the monkeys to recognize themselves. "The logic might run like this: I am holding a mirror in my hand. There is another monkey's face. It can't be another monkey because I am not carrying one. It must be me."

If we can't be sure whether animals are aware of themselves, it might seem even more difficult to determine whether they are aware of each other. Might primates be said to have a "theory of mind"? The term, coined by the ape researcher David Premack in 1978, generally refers to the recognition that others have beliefs and that these beliefs can differ from one's own.

Although Premack's notion initially didn't spark much additional work with apes, developmental psychologists took it up with alacrity. In a classic test, a child watches while one puppet, named Sally, places a ball in a basket in the presence of another puppet, Anne. At that point, Sally leaves the room, and the child sees Anne move the ball to a box. When Sally returns, the child is asked where Sally will look for the ball. Four-year-olds will correctly indicate the basket, the original hiding place. They understand that Sally has no way of knowing that the ball has been moved. Younger children, however, think Sally will look in the box. It seems they cannot distinguish between what they know about the situation and what Sally knows. That is, they have no theory of mind.

Primate research into such questions picked up in the late 1980s. Some writers, surveying the literature, conclude that the great apes, like four-year-olds, have a theory of mind: They can grasp that others may have false beliefs. But in Wild Minds Hauser is much more skeptical. He cites, for example, one of a suite of experiments by Daniel Povinelli in which chimpanzees gestured for food just as often from trainers wearing bags over their heads or blindfolds over their eyes as from those with bags just to the side of their heads or blindfolds over their mouths. They don't seem to grasp the connection between seeing and knowing--in other words, that someone who can't see them begging doesn't know they are there.

As badly as Povinelli's chimps tested, a control group of rhesus monkeys did even worse. But as Hauser points out, the ordinary monkeys were competing against an ape "dream team"--animals that had been "enculturated" through language training and intense exposure to human artifacts and situations. At the same time, he acknowledges, monkeys may not have much need for a theory of mind. Since their family groups tend not to break into smaller units, as chimps' do, and they are almost never alone, individuals rarely differ substantially in what they know.

Despite his general doubts as to whether primates have a theory of mind, Hauser nonetheless offers some tentative evidence that tamarins may nominally understand that other minds can hold false beliefs. In designing a nonverbal version of the Sally-Anne test for tamarins, Hauser took a cue from the developmental psychologists Wendy Clements and Josef Perner of the University of Sussex. This duo had observed that in the classic test with human infants, before the three-year-olds answered, incorrectly, that Sally would look in the second hiding place, they would spend a moment looking at the first hiding place (where the returning Sally ought to think the ball remained). Perhaps the younger children implicitly understood that Sally held a false belief, Hauser speculated, even if they couldn't express their understanding explicitly, in words. (As the cognitive scientist in Hauser puts it, "Somewhere along the path from looking to speaking, there is a computational error.")

In Hauser's test, which he carried out with his graduate student Laurie Santos, a tamarin watches as Joe enters a room. Joe eats part of an apple, hands the tamarin a piece, and then puts the rest in one of two opaque boxes. When Joe leaves, the experimenter moves the apple into the second box. Joe returns and looks for the apple. The tamarins stared longer when Joe, against logic, looked in the second box, even though he hadn't seen the apple being moved.

The paper has yet to be published in a scientific journal. One critic has expressed doubts about the validity of the looking-time method for infants, let alone primates. Another asked, since we know apes don't have a theory of mind, why should we think monkeys do? Hauser calls this a "really weird" phylogenetic claim. "You wouldn't say, ëHumans don't have echolocation, so why should bats?' We know evolution works in weird ways."

Curiously, Hauser makes no mention of his theory-of-mind results with tamarins in Wild Minds. "I didn't want to give the impression that all it required was this one intelligent experiment by Hauser to show that the field was all wrong," he says. "I tried really hard not to promote things I didn't think were really solid." He mentions the best-selling books of his close friend Steven Pinker. "Steve is a very forceful writer. If you read The Language Instinct, you think, ëOh we've got the problem of language acquisition solved.' But in fact we don't. And reading How the Mind Works, you might think evolutionary psychology has all the answers, but there's so much controversy in that field it's outrageous." For example, Pinker makes a powerful case for the "cheater detector," or the idea that humans have a built-in module for sniffing out deceivers. However, Hauser protests, "there's also so much counterevidence" that isn't discussed.

Nonetheless, Hauser's notion of the mind as a collection of tools puts him squarely on Pinker's side of the fence. Not all researchers in primate--let alone human--cognition embrace this view. In his new book, The Cultural Origins of Human Cognition, Michael Tomasello of the Max Planck Institute for Evolutionary Anthropology argues that language and other specialized skills don't reflect specialized modules. Rather, they spring from one simple, "uniquely human biological adaptation." What's important is not the full-blown understanding of false beliefs that emerges at around three and a half but what he calls "the nine-month revolution"--the understanding that others are intentional agents "like me" that emerges toward the end of the first year. It is this understanding that allows us to share "joint attention" with another person and to learn what they know.

One of the most surprising differences between humans and other animals--one Hauser also emphasizes--is that only humans seem capable of true imitation. That is, imitation not just of another's actions but of his or her underlying intentions. Apes don't truly ape, and the monkey that sees doesn't necessarily do. In Tomasello's opinion, this unique human ability to understand the intentions of others is what made science possible. Understanding of invisible causal forces like "intentions" and "thoughts" evolved first to explain and predict the behavior of other people. It was then "transported" to explain the behavior of inanimate objects influenced by forces such as gravity. Strangely, our knowledge of physics and chemistry may flow from our innate grasp of psychology.

Perhaps even more surprisingly, experiments with physics may help elucidate some of the more mysterious aspects of animal psychology, including the vexed question of where in the branching tree of evolution morality begins. Ever the empiricist, Hauser offers an arresting line of argument based on two very simple concepts. In one experiment, two-year-old children or adult tamarins watched a researcher drop an object down an S-shaped pipe running diagonally toward a box. Both the kids and the monkeys looked for the object directly below the point where the object was released--and not in the box, where the tube ended. They did this not just once but twenty or thirty times in a row.

Children and tamarins are vulnerable to what Hauser calls "Kuhnian perseverance," or repeating an action because their theoretical framework--in this case, a "gravity bias"--drives them to do so. They are also constrained by what he calls "Cartesian perseverance." According to Descartes, rationality requires control over passionate impulses--and animals are incapable of exercising such control. As a result, animals will sometimes make the same passion-based blunders over and over again. Hauser cites experiments in which chimps and macaques, faced with a hand or box holding four treats and one holding a single treat, always picked the four treats, even when the rule of the game was that they would get whatever serving they didn't pick.

Morality would seem to have little to do with pellets of food dropping down a tube. But such experiments, Hauser argues, show why animals, like children, have no role in shaping rules of conduct. "To make an ethical decision," he writes, "...we must choose between two or more alternative possibilities. Sometimes the most tempting possibility is the wrong thing to do."

Although Hauser believes animals have rich emotional lives, his skepticism that animals have a true sense of self leads him to reject the notion that animals experience empathy--that is, that they not only know what other animals feel but also share in those feelings. Indeed, while there are some reports of primates appearing to grieve for the dead, there are virtually none of primates acting to comfort those in grief. But given Hauser's tendency to find evidence among his monkeys for things he's not sure he believes in more generally, perhaps it's not surprising that he's devising an experiment for empathy.

The experiment will be an "ethical" version of those, conducted in the 1940s and 1950s, that examined rats' willingness to give each other nasty shocks if it meant gaining access to food. In his primate version, Hauser will play recordings of a monkey in serious distress to other monkeys. If a listening monkey exhibits neurobiological signs of distress along with an appropriate behavioral response, Hauser will consider calling it empathy.

In a way, empathy is where Hauser departs most clearly from Jeffrey Masson and Elizabeth Marshall Thomas. The moral goodness of animals is precisely what books like When Elephants Weep and The Hidden Life of Dogs insist on, often with great eloquence. Some psychologists have pointed out that it is humans' own considerable ability to empathize that leads us to anthropomorphize animals--not to mention cranky computers, stalled car engines, and forces of nature. Can Hauser's book help spark a Kuhnian paradigm shift in the way the common reader conceives of animal minds? Perhaps. After all, his work gives ample reason to respect animal minds without presuming they are exactly like ours.