''WHAT I LIKE to do,'' the evolutionary biologist Robert Trivers said on a recent afternoon in his office in Harvard Square, ''and in retrospect what I'm good at, is going into a field, seeing an opportunity to do intellectual work that hasn't been done in it, do as much as I can and then move the [expletive] on, you know?''

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Trivers has been teaching himself things and then growing bored with them his whole life. In 1956, when he was 13 and living in Berlin (his father was posted there by the State Department), he taught himself all of calculus in about three months. Around the same time, and with more modest success, Trivers-a skinny child picked on by bullies-tried to learn how to box, doing push-ups and covertly reading Joe Louis's ''How to Box'' in the school library.

Trivers would go on to join the boxing team at Phillips Academy, Andover. He would also go on to drop math his freshman year at Harvard, decide to become a lawyer, suffer a nervous breakdown that kept him from getting in to any law schools, enroll in Harvard's doctoral program in biology without having taken a single biology class as an undergraduate, and-while still a grad student-write the first in a series of papers that would revolutionize the field of evolutionary biology.

Then he dropped from sight. Rebuffed in his demand for early tenure, he left Harvard in 1978 to teach at the University of California, Santa Cruz. He befriended Huey Newton and joined the Black Panthers. He all but stopped publishing. As the literary agent John Brockman put it when introducing Trivers at a recent talk, ''Over the years there were rumors about a series of breakdowns; he was in Jamaica; in jail. He fell off the map.''

His ideas, however, seemed to do just fine without him. In the 1970s, Trivers published five immensely influential papers that braided genetics into behavioral biology, using a gene's-eye view of evolution to explain behaviors from bird warning calls to cuckoldry to sibling rivalry to revenge. According to David Haig, a Harvard professor of biology and a leading genetic theorist, each paper virtually founded a research field. ''Most of my career has been based on exploring the implications of one of them,'' says Haig. ''I don't know of any comparable set of papers.''

Trivers's ideas have rippled out into anthropology, psychology, sociology, medicine, even economics. His work provided the intellectual basis for the then-emergent field of sociobiology (now better known as evolutionary psychology), which sought to challenge our conceptions of family, sex, friendship, and ethics by arguing (controversially) that everything from rape to religion is bred in the bone through the process of evolution. The linguist and Harvard psychology professor Steven Pinker calls Trivers ''one of the great thinkers in the history of Western thought.''

Now his decades-long absence-what Trivers's friends and colleagues refer to as his ''fallow period''-finally seems to be ending. In 1994 he left Santa Cruz (''the worst place in the country,'' he now calls it) for Rutgers, and this spring he's back at Harvard as a visiting professor of psychology. A major new book on genetic conflicts within individual organisms, coauthored with Austin Burt, a geneticist at Imperial College London, is due out next spring from Harvard University Press. And thanks to Brockman-agent to some of the biggest names in science-he's under contract with Viking Penguin to write a popular book on the evolutionary origins of deceit and self-deception, one that will argue that humans have evolved, in essence, to misunderstand the world around them. Trivers thinks it could be the most important topic he has yet studied.

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In a recent guest lecture for a Harvard class called ''Human Nature,'' co-taught by Pinker and law school professor Roberto Mangabeira Unger, Trivers brought down the house. He was clear, sarcastic, funny, and theatrically profane. As in his everyday conversation, he spoke slowly and deliberately, in the syncopated, slurring drawl of a narcoleptic Beat poet. Sartorially unprofessional in a vintage Chicago Bears warm-up jacket over a black T-shirt, he dropped disdainful asides about everything from the Bush administration (''the crackheads in Washington'') to the leftist critics who had painted his ideas as biological determinism 30 years ago (the accusation ''was [b.s.] back then and I doubt it has improved in the meanwhile'') to ''the social so-called sciences.''

In a way, Trivers's rhetoric of maximum affront reflects his view of the natural world as a battlefield where unending struggles of varying intensity and subtlety play themselves out. Alliances and altruism can make evolutionary sense, he argues, but many relationships previously understood to be essentially cooperative-between mother and father, parents and offspring, brothers and sisters, even among the genes within a single organism-are instead rife with conflict. And only as conflicts can they be fully understood.

Trivers's work grew out of an insight made by the Oxford biologist William D. Hamilton, who died in 2000. In a 1964 paper, Hamilton proposed an elegant solution to a problem that had rankled evolutionary theorists for some time. In a battle of the fittest, why did organisms occasionally do things that benefited others at a cost to themselves? The answer, Hamilton wrote, emerged when one took evolution down to the level of the gene. Individuals were merely vessels for genes, which survived from generation to generation, and it made no difference to the gene which organism it survived in.

According to this logic, the degree to which an organism was likely to sacrifice for another should vary in direct proportion to the degree of relatedness: Humans, for example, would be more likely to share food with a son than a second cousin, and more likely to share with a second cousin than someone wholly unrelated. Hamilton called the concept ''inclusive fitness.''

In 1976, the Oxford zoologist Richard Dawkins would popularize Hamilton's ideas in his book ''The Selfish Gene.'' But more than anyone else, it was Trivers, then a graduate student, who grasped the profound implications of Hamilton's work. In a way, Trivers's legendary papers of the early 1970s were simply a series of startling applications of its logic.

In the most frequently cited of them, ''Parental Investment and Sexual Selection'' (1972), Trivers started from the basic observation that in most species females invest more time and energy in their offspring than males. If Hamilton was right, Trivers reasoned, this meant that females, who had more at stake in each of their offspring, would be more choosy about their mates, and that males, who had less, would compete with each other for the chance to inseminate as many females as possible. This simple idea, he argued, explained a raft of phenomena throughout the animal world, from cuckoldry to infanticide to differences in size and life span between males and females. (See sidebar.)

Two years later, in his paper ''Parent-offspring Conflict,'' Trivers explored the ways the interests of children almost inevitably come into conflict with those of their parents. Parents, equally related to all of their offspring, are equally interested in all of their survival. Their offspring, however, would have an interest in hoarding as much parental investment as possible for themselves, at least up to the point where the resulting damage to their siblings began to decrease their own inclusive fitness.

Thus offspring could be expected to evolve a range of tactics to prize more food and attention out of the parent. This, Trivers argued, is why human babies cry even when nothing is wrong with them and why some infant monkeys attack their mothers when they withhold breast milk. ''Once one imagines offspring as actors'' in their interactions with their parents, Trivers wrote, ''then conflict must be assumed to lie at the heart of sexual reproduction itself.''

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Trivers's papers tend to be short, declarative, and frankly speculative-''logic plus fractions,'' as he has described his method. But they engendered huge new areas of research. For example, according to Irven DeVore, the eminent Harvard primatologist and a long-time friend and mentor to Trivers, Trivers's work opened up ''a spectacular new paradigm in primate studies.'' ''None of us had been collecting data on kinship because no one thought it was critical,'' DeVore says. ''A lot of people had to deep-six their notes and start over, because they hadn't collected the critical thing, which was kinship data.''

At the same time, DeVore says, ''One of the brilliant things about Trivers is that he predicted so many things, he gave researchers a brief to go out and check.'' Testing his theories, after all, could be as simple as measuring sex ratios in an ant colony or comparing the size of male lizards with their frequency of copulation or observing when weaning conflict is at its most intense. And in the intervening decades, as James Thomas Costa, a biologist and social insect specialist at Western Carolina University (and currently a fellow at the Radcliffe Institute), puts it, Trivers's major ideas ''have been tweaked, but they have been borne out.''

But Trivers has not limited his ideas to animals. The second half of his first major paper, ''The Evolution of Reciprocal Altruism'' (1971), was dedicated to hypothesizing that a large proportion of human emotion and experience-gratitude, sympathy, guilt, trust, friendship, and moral outrage among them-grew out of the same sort of simple tit-for-tat logic that governed the interactions between, say, certain fish and the species of shrimp that cleaned their gills. And in his work on parent-offspring conflict, Trivers suggested that disputes between children and their parents over everything from bedtimes to marriage partners might simply be a matter of competing calculations of inclusive fitness.

Over the years, there has been tremendous resistance to applying these ideas to our own species. Measuring the relative size of female and male lizards was one thing, but understanding the vagaries of human social rituals seemed quite another. According to Arthur Kleinman, chair of Harvard's social anthropology program, this sort of thinking ''made extraordinary leaps from scientific fact to generalizations about the relationship between behavior and evolution, and there was in fact very little data to support it.''

Trivers-for all his taste for combat-has largely been on the sidelines in the long war over sociobiology. While he insists he's perfectly happy to let others take the heat, there are traces of bitterness. In his lecture to Pinker and Unger's ''Human Nature'' class, he claimed that the contribution of E. O. Wilson, author of the popular 1975 book ''Sociobiology,'' to evolutionary theory was largely semantic: In inventing the term sociobiology, Trivers said, Wilson made himself into ''the father of the discipline, when he's really the father of the name of the discipline.'' And he still nurses a grudge at the removal, in later editions, of his foreword for the first edition of ''The Selfish Gene.'' By removing it, Trivers charges, Dawkins ''rewrote intellectual history.'' (In an email, Dawkins calls the deletion ''an unfortunate error of judgment,'' and adds that there are plans to include the original foreword in a forthcoming edition of the book.)

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For Trivers, conflict is more than just an evolutionary principle-it's a kind of personal credo. As a young man, he freely recalls, he fought bitterly with his father. In Jamaica, where he is carrying out a long-running research project on the link between childhood growth patterns and personality, he has been charged and acquitted for assault over a fistfight in a bar, and he spent 10 days in jail after an angry dispute over a hotel bill. He has practiced arnis, a Filipino martial art involving a machete, since a Jamaican man threatened to kill him, in what he describes as an extortion attempt. And his politics tend toward a sort of revolutionary vigilantism, in part a reflection of his brief membership in the Black Panthers and his close friendship with Huey Newton, who was godfather to one of Trivers's daughters.

As Trivers put it to me, ''I think organisms require direct physical feedback sometimes.''

Trivers seems unable not to be forthcoming, yet he is leery of letting the more sensational aspects of his biography and personality overshadow his work. The morning after one of our last conversations, he left a message on my voicemail. He was at the airport on the way to Jamaica.

''I really hope you don't do the usual journalistic thing,'' he said, ''which is to try to dress up my life so that it's just some sort of freak show, or just some kind of 'Oh, he's brilliant and he also does these weird funny things.' I really hope you don't go that route. The most important thing in my life, and it has been for a few years, is that I'm extremely productive again, roughly back to the stage when I was doing my great work back at Harvard.''

He's certainly returning to the ideas generated by that work. The book on deceit and self-deception that he's now starting grows out of a brief but widely cited passage from his introduction to Dawkins's ''The Selfish Gene.'' If deceit, he wrote, ''is fundamental to animal communication, then there must be strong selection to spot deception and this ought, in turn, to select for a degree of self-deception, rendering some facts and motives unconscious so as not to betray-by the subtle signs of self-knowledge-the deception being practiced.'' Thus, the idea that the brain evolved to produce ''ever more accurate images of the world must be a very naive view of mental evolution.'' We've evolved, in other words, to delude ourselves so as better to fool others-all in the service of the great game of propagating our genes.

For Trivers, this isn't a mere technical question but the key to unlocking all sorts of deep human mysteries.

''I'm trying to take it every [expletive] place I can,'' Trivers told me. ''It's a critical topic. How many pretenders to the throne have there been? Marx had a theory of self-deception, Freud thought he had the topic knocked. So there've been a lot of major-domos in there. None of that [expletive] survived the test of time, so it's a huge opportunity.''

Drake Bennett is the staff writer for Ideas. Email drbennett@globe.com.