Steven Pinker has the olive-pitter with him tonight. The shiny device, with levers that look a bit like those on a corkscrew, is something that his mother found in an antique shop in Florida. It also is a graphic example of the way Pinker and other evolutionary psychologists are currently thinking about how our minds function.

The standing-room-only crowd at the Jewish Public Library in Montreal doesn't know he has it. They've come expecting an interesting talk from a local boy who made good, someone who at the age of 43 is in the forefront of linguistic psychology, a professor in the Department of Brain and Cognitive Sciences at the Massa-chusetts Institute of Technology and the director of MIT's McDonnell-Pew Center for Cog-nitive Neuroscience. Only those who've dipped into his 600-page best seller How the Mind Works, or caught his snappy articles in the New York Times Magazine or the New Yorker know just what to expect.

Pinker makes his way up the side of the hall to the front, stopping to shake a hand, say a word, smile, laugh. He's tall, slim, and tonight he's wearing dark trousers, dark jacket, a white shirt, a chartreuse tie with a white window-pane plaid ... and cowboy boots. His curly, graying dark hair is nearly shoulder-length. His blue eyes twinkle, and he grins a lot.

A McGill graduate (BA honours in psychology 1976) with a PhD from Harvard, he was publishing articles on psycholinguistics in academic journals before he finished his doctorate, and putting out complete tomes before he was 30. At the moment he is the latest intellectual superstar, with much of the buzz on the Internet, as befits a man who uses computer analogies when talking about the brain. Do a search and you'll find websites discussing his more controversial ideas along with radio interviews from the BBC, profiles from Wired magazine and a blurb at the on-line bookstore Amazon.com calling him "fast and funny enough to host Saturday Night Live in its gold-en age." Tonight, armed with olive-pitter and camp songs, he's about to wow a home-town audience.

Evolutionary psychologists like Pinker have been called Darwinist extremists by their critics. To be sure, few today question Darwin's basic premi-ses: creatures with traits which give them an adaptive advantage leave more young than those who don't. If these traits are passed on genetically, their young will be more successful at reproduction, too. Eventually these useful traits will be found throughout the population. The survival of the fittest, the 19th century called it. "Nature red in tooth and claw," Tennyson wrote. Ah yes, evolution: how we got from swinging in trees to walking upright, the man (or woman) in the street would say.

However the phenomenon is defined, there's little argument that our opposable thumbs and upright posture have been engineered by natural selection. Creatures who had them were more successful than those who didn't. Most scientists would also include our big brains among those genetically determined adaptive advantages. The difference of opinion comes when Pinker and his colleagues apply the idea of natural selection to the mind, to, as Pinker puts it, "a special thing the brain does which makes us see, think, feel, choose and act. That special thing is information processing, or computation."

But what makes our brains different from those of other animals? Brain tissue and neurons look pretty much the same whether they're from birds, spiders, lions or chimpanzees. Don't we just have more? Pinker suggests that the organization of "the mammoth tangle of spaghetti of the brain" is the key. Books are just combinations of the same few dozen characters, he points out. The content of a book lies in the pattern of ink marks and is apparent only when the piece is read. "Similarly, the content of brain activity lies in the patterns of connections and patterns of activity among the neurons," and Pinker contends these patterns may be genetically determined. "Human thought and behaviour, no matter how subtle and flexible, could be the product of a very complicated program, and that program may have been our endowment from natural selection."

Pinker calls these patterns of neural organization "mental organs," not that they resemble other organs such as the heart or the lungs. Rather, he says, "they are coherent circuits, which may not take physically nice shapes, just as a program in a computer may be fragmented across discontinuous regions of disk or memory."

At this point, few evolutionary psychologists are researching the actual physical organization of the mental organs they postulate. It's not that "prodding brain tissue is irrelevant to understanding the mind, only that it is not enough," Pinker writes. So evolutionary psychologists study behaviour that is universal, or nearly so, in our species -- things like talking baby talk to infants, sharing food and liking flowers. Then they try to understand it in light of how the behaviour might have helped us survive during those hundreds of thousands of years we were hunters and gatherers. Pinpointing the actual circuits in the nervous system which give rise to particular behaviour is something they leave to others.

The idea that natural selection is responsible for how we act is a red flag to some scientists, however. For example, Harvard paleontologist Stephen Jay Gould thinks what Pinker and his colleagues are talking about amounts to no more than accidents of evolution. Other critics say that the attention evolutionary psychologists give to behavioural differences between men and women is sexist.

The study of relations between the sexes is indeed a very fertile field for evolutionary psychologists. Pinker wrote about them recently in "Boys Will Be Boys: An evolutionary explanation for Presidents behaving badly" in the New Yorker: "A prehistoric man who slept with 50 women could have sired 50 children, and would have been more likely to have descendants who inherited his tastes. A woman who slept with 50 men would have had no more descendants than a woman who slept with one. Thus, men should seek quantity in sexual partners; women, quality," Pinker wrote. "Indeed, in all societies known to ethnography it is the males who seduce, proposition, hire prostitutes and accumulate spouses....

"But only in special circumstances are sexual partners freely available....That's why homely rock stars and octogenarian oil barons can marry supermodels, and why powerful male politicians may face temptations that most of their constituents do not."

Yet to all appearances Pinker is more SNAG (Sensitive New Age Guy) than male chauvinist. "Discrimination against individuals on the basis of their race, sex or ethnicity is wrong," he says flatly in How the Mind Works. He adds, "A denial of human nature, no less than emphasis on it, can be warped to serve harmful ends. We should expose whatever ends are harmful and whatever ideas are false, and not confuse the two."

His own search for true ideas began with the way children acquire language -- any language. "I was always interested in psychology, and the study of grammar and language was just a special case," he says. "Evolution came in because I was always interested in the innate language mechanisms that made language acquisition possible, and evolution is the source of innate mechanisms."

While at McGill, Pinker says he was strongly influenced by his fellow students, who were "equally passionate about psychology and cognitive science." Among his faculty influences were Al Bregman, who when Pinker was there was "the department's only full-time cognitive psychologist," and Jock Millenson, "the department's token Skinnerian and resident bad boy." Pinker adds, "Jock was ahead of his time in using a minicomputer to control his experiments (this was 1975), and when he and his technician vanished at the beginning of the summer, it fell on me to figure out how the lab worked and I soon became the resident programmer and electrician."

Work in Dalbir Bindra's neuroscience lab programming computers and inserting electrodes into rats' brains was also important. "It quickly taught me that neuroscience was not for me -- I am a klutz, and knew that I had better stay away from any field in which success would depend on manual dexterity."

Be that as it may, in front of the audience at the Jewish Public Library, Pinker does a bit of sleight-of-hand. From somewhere he pulls out his mother's olive-pitter. He holds it up for the crowd to see.

"What is it?" he asks. "To figure it out, you've got to do a little reverse engineering. You notice the rings and the lever and you think, well, maybe it's supposed to take seeds out of something. So you try cherries but they're too small. Then you try olives, and all of a sudden you know why canned olives have a little X on the end: that's where this little blade cuts them."

Murmurs from the crowd. Obviously more than one person has wondered about those X's.

"This is what Sony engineers do when Panasonic comes out with something new, and vice versa," Pinker goes on. "They buy the device, and then they take it apart to figure out how it works. What I'm suggesting is that to understand the mind, we need to do some reverse software engineering on it."

A sweet tooth is a case in point, Pinker says, after going down a list of questions evolutionary psychologists are asking, including: Why do we like sweet things? Why is the thought of eating worms disgusting? Why do fools fall in love?

Sweet foods are high in energy but were in short supply during our hunter-gatherer days, he points out. People who ate them probably were healthier and had healthier children, so it paid, genetically, to want to eat them. Hence delight in sweet things is practically universal among humans and sweet-sensing taste buds are right there on the tips of our tongues.

When he's talking about worms, Pinker makes a face, and then, to the surprise of his audience, breaks into a rendition of "Great green gobs of greasy, grimy gopher guts." Disgust is a universal human emotion, he goes on, "signaled with its own facial expression and codified everywhere in food taboos." It arises from the "omnivore's dilemma," the fact that we can eat almost anything. But some things are toxic or might be contaminated, so we have to learn what they are. An innate capacity to be disgusted would make it easier to learn -- through kids' songs about gopher guts as well as religous laws -- what is generally not safe to eat. Dying of food poisoning at a young age is a good way to leave few descendants.

To leave any descendants at all, we have to have a relationship with somebody of the other sex. Strictly speaking, you don't need love to do that, but Pinker says that all cultures recognize the folly that is love, even those where marriages are arranged. "In some respects love is a marketplace: people try to end up with the smartest, richest, healthiest person who will have them. And if you look at couples, you'll see that usually they are pretty well matched, the Tens marry the Tens, and the Nines marry the Nines. But the amazing thing is, you can't will yourself to fall in love.

"Why? Well, if you do some reverse engineering on the idea, you see that love is the kind of commitment problem economists talk about. This person before you may be the best person you can attract now, but next year you might be able to attract someone better. In that case any rational person would find it necessary to break the agreements he or she has made.

"But when we're in love, we're not rational. Our hearts pound and we sweat and our bodies broadcast that we're under control of the in-voluntary part of our nervous system. The very irrationality of love makes it less likely that we'll make a rational decision down the line to leave our lover -- and we signal that's the case, which makes us that much more attractive a partner for the other person." That increases the chances that our genes, including those that give us the mental organization allowing us to love irrationally, get passed on. And passing on genes is what natural selection is all about.

At the end of his talk, Pinker answers questions for a half hour, and is rewarded with thunderous applause. Then he slips away for a late supper with his family -- mother, father, wife, brother and sister, as well as various aunts, uncles and cousins. A group of pleasant, intelligent people by the looks of them. Good genes, all the way around.