STAROBA dot MY

That did it. By the time they got out of school, both Shipps had entirely transformed themselves, changing from boys who might have grown up to live off the family's wealth to men consumed with going out and creating their own. "At this point," says Gregg, "I consider myself to be almost maniacally ambitious."

It shows. In 1998 the brothers went into the gym trade. They spotted a modest health club doing a modest business, bought out the owner and transformed the place into a luxury facility where private trainers could reserve space for top-dollar clients. In the years since, the company has outgrown one building, then another, and the brothers are about to move a third time. Gregg, a communications major at college, manages the club's clients, while Drew, a business major, oversees the more hardheaded chore of finance and expansion. "We're not sitting still," Drew says. "Even now that we're doing twice the business we did at our old place, there's a thirst that needs to be quenched."

Why is that? Why are some people born with a fire in the belly, while others — like the Shipps — need something to get their pilot light lit? And why do others never get the flame of ambition going? Is there a family anywhere that doesn't have its overachievers and underachievers — its Jimmy Carters and Billy Carters, its Jeb Bushes and Neil Bushes — and find itself wondering how they all could have come splashing out of exactly the same gene pool?

Of all the impulses in humanity's behavioral portfolio, ambition — that need to grab an ever bigger piece of the resource pie before someone else gets it — ought to be one of the most democratically distributed. Nature is a zero-sum game, after all. Every buffalo you kill for your family is one less for somebody else's; every acre of land you occupy elbows out somebody else. Given that, the need to get ahead ought to be hard-wired into all of us equally.

And yet it's not. For every person consumed with the need to achieve, there's someone content to accept whatever life brings. For everyone who chooses the 80-hour workweek, there's someone punching out at 5. Men and women — so it's said — express ambition differently; so do Americans and Europeans, baby boomers and Gen Xers, the middle class and the well-to-do. Even among the manifestly motivated, there are degrees of ambition. Steve Wozniak co-founded Apple Computer and then left the company in 1985 as a 34-year-old multimillionaire. His partner, Steve Jobs, is still innovating at Apple and moonlighting at his second blockbuster company, Pixar Animation Studios.

Not only do we struggle to understand why some people seem to have more ambition than others, but we can't even agree on just what ambition is. "Ambition is an evolutionary product," says anthropologist Edward Lowe at Soka University of America, in Aliso Viejo, Calif. "No matter how social status is defined, there are certain people in every community who aggressively pursue it and others who aren't so aggressive."

Dean Simonton, a psychologist at the University of California, Davis, who studies genius, creativity and eccentricity, believes it's more complicated than that. "Ambition is energy and determination," he says. "But it calls for goals too. People with goals but no energy are the ones who wind up sitting on the couch saying 'One day I'm going to build a better mousetrap.' People with energy but no clear goals just dissipate themselves in one desultory project after the next."

Assuming you've got drive, dreams and skill, is all ambition equal? Is the overworked lawyer on the partner track any more ambitious than the overworked parent on the mommy track? Is the successful musician to whom melody comes naturally more driven than the unsuccessful one who sweats out every note? We may listen to Mozart, but should we applaud Salieri?

Most troubling of all, what about when enough ambition becomes way too much? Grand dreams unmoored from morals are the stuff of tyrants — or at least of Enron. The 16-hour workday filled with high stress and at-the-desk meals is the stuff of burnout and heart attacks. Even among kids, too much ambition quickly starts to do real harm. In a just completed study, anthropologist Peter Demerath of Ohio State University surveyed 600 students at a high-achieving high school where most of the kids are triple-booked with advanced-placement courses, sports and after-school jobs. About 70% of them reported that they were starting to feel stress some or all of the time. "I asked one boy how his parents react to his workload, and he answered, 'I don't really get home that often,'" says Demerath. "Then he handed me his business card from the video store where he works."

Anthropologists, psychologists and others have begun looking more closely at these issues, seeking the roots of ambition in family, culture, gender, genes and more. They have by no means thrown the curtain all the way back, but they have begun to part it. "It's fundamentally human to be prestige conscious," says Soka's Lowe. "It's not enough just to be fed and housed. People want more."

If humans are an ambitious species, it's clear we're not the only one. Many animals are known to signal their ambitious tendencies almost from birth. Even before wolf pups are weaned, they begin sorting themselves out into alphas and all the others. The alphas are quicker, more curious, greedier for space, milk, Mom — and they stay that way for life. Alpha wolves wander widely, breed annually and may live to a geriatric 10 or 11 years old. Lower-ranking wolves enjoy none of these benefits — staying close to home, breeding rarely and usually dying before they're 4.

Humans often report the same kind of temperamental determinism. Families are full of stories of the inexhaustible infant who grew up to be an entrepreneur, the phlegmatic child who never really showed much go. But if it's genes that run the show, what accounts for the Shipps, who didn't bestir themselves until the cusp of adulthood? And what, more tellingly, explains identical twins — precise genetic templates of each other who ought to be temperamentally identical but often exhibit profound differences in the octane of their ambition?

Ongoing studies of identical twins have measured achievement motivation — lab language for ambition — in identical siblings separated at birth, and found that each twin's profile overlaps 30% to 50% of the other's. In genetic terms, that's an awful lot — "a benchmark for heritability," says geneticist Dean Hamer of the National Cancer Institute. But that still leaves a great deal that can be determined by experiences in infancy, subsequent upbringing and countless other imponderables.

Some of those variables may be found by studying the function of the brain. At Washington University, researchers have been conducting brain imaging to investigate a trait they call persistence — the ability to stay focused on a task until it's completed just so — which they consider one of the critical engines driving ambition.

The researchers recruited a sample group of students and gave each a questionnaire designed to measure persistence level. Then they presented the students with a task — identifying sets of pictures as either pleasant or unpleasant and taken either indoors or outdoors — while conducting magnetic resonance imaging of their brains. The nature of the task was unimportant, but how strongly the subjects felt about performing it well — and where in the brain that feeling was processed — could say a lot. In general, the researchers found that students who scored highest in persistence had the greatest activity in the limbic region, the area of the brain related to emotions and habits. "The correlation was .8 [or 80%]," says professor of psychiatry Robert Cloninger, one of the investigators. "That's as good as you can get."

It's impossible to say whether innate differences in the brain were driving the ambitious behavior or whether learned behavior was causing the limbic to light up. But a number of researchers believe it's possible for the nonambitious to jump-start their drive, provided the right jolt comes along. "Energy level may be genetic," says psychologist Simonton, "but a lot of times it's just finding the right thing to be ambitious about." Simonton and others often cite the case of Franklin D. Roosevelt, who might not have been the same President he became — or even become President at all — had his disabling polio not taught him valuable lessons about patience and tenacity.

Is such an epiphany possible for all of us, or are some people immune to this kind of lightning? Are there individuals or whole groups for whom the amplitude of ambition is simply lower than it is for others? It's a question — sometimes a charge — that hangs at the edges of all discussions about gender and work, about whether women really have the meat-eating temperament to survive in the professional world. Both research findings and everyday experience suggest that women's ambitions express themselves differently from men's. The meaning of that difference is the hinge on which the arguments turn.

Economists Lise Vesterlund of the University of Pittsburgh and Muriel Niederle of Stanford University conducted a study in which they assembled 40 men and 40 women, gave them five minutes to add up as many two-digit numbers as they could, and paid them 50¢ for each correct answer. The subjects were not competing against one another but simply playing against the house. Later, the game was changed to a tournament in which the subjects were divided into teams of two men or two women each. Winning teams got $2 per computation; losers got nothing. Men and women performed equally in both tests, but on the third round, when asked to choose which of the two ways they wanted to play, only 35% of the women opted for the tournament format; 75% of the men did.

"Men and women just differ in their appetite for competition," says Vesterlund. "There seems to be a dislike for it among women and a preference among men."

To old-line employers of the old-boy school, this sounds like just one more reason to keep the glass ceiling polished. But other behavioral experts think Vesterlund's conclusions go too far. They say it's not that women aren't ambitious enough to compete for what they want; it's that they're more selective about when they engage in competition; they're willing to get ahead at high cost but not at any cost. "Primate-wide, males are more directly competitive than females, and that makes sense," says Sarah Blaffer Hrdy, emeritus professor of anthropology at the University of California, Davis. "But that's not the same as saying women aren't innately competitive too."

As with so much viewed through the lens of anthropology, the roots of these differences lie in animal and human mating strategies. Males are built to go for quick, competitive reproductive hits and move on. Women are built for the it-takes-a-village life, in which they provide long-term care to a very few young and must sail them safely into an often hostile world. Among some of our evolutionary kin — baboons, macaques and other old-world monkeys — this can be especially tricky since young females inherit their mother's social rank. The mothers must thus operate the levers of society deftly so as to raise both their own position and, eventually, their daughters'. If you think that kind of ambition-by-proxy doesn't translate to humans, Hrdy argues, think again. "Just read an Edith Wharton novel about women in old New York competing for marriage potential for their daughters," she says.

Import such tendencies into the 21st century workplace, and you get women who are plenty able to compete ferociously but are inclined to do it in teams and to split the difference if they don't get everything they want. And mothers who appear to be unwilling to strive and quit the workplace altogether to go raise their kids? Hrdy believes they're competing for the most enduring stakes of all, putting aside their near-term goals to ensure the long-term success of their line. Robin Parker, 46, a campaign organizer who in 1980 was already on the presidential stump with Senator Edward Kennedy, was precisely the kind of lifetime pol who one day finds herself in the West Wing. But in 1992, at the very moment a President of her party was returning to the White House and she might have snagged a plum Washington job, she decamped from the capital, moved to Boston with her family and became a full-time mom to her two sons.

"Being out in the world became a lot less important to me," she says. "I used to worry about getting Presidents elected, and I'm still an incredibly ambitious person. But what I want to succeed at now is managing my family, raising my boys, helping my husband and the community. In 10 years, when the boys are launched, who knows what I'll be doing? But for now, I have my world."

But even if something as primal as the reproductive impulse wires you one way, it's possible for other things to rewire you completely. Two of the biggest influences on your level of ambition are the family that produced you and the culture that produced your family.

There are no hard rules for the kinds of families that turn out the highest achievers. Most psychologists agree that parents who set tough but realistic challenges, applaud successes and go easy on failures produce kids with the greatest self-confidence.

What's harder for parents to control but has perhaps as great an effect is the level of privilege into which their kids are born. Just how wealth or poverty influences drive is difficult to predict. Grow up in a rich family, and you can inherit either the tools to achieve (think both Presidents Bush) or the indolence of the aristocrat. Grow up poor, and you can come away with either the motivation to strive (think Bill Clinton) or the inertia of the hopeless. On the whole, studies suggest it's the upper middle class that produces the greatest proportion of ambitious people — mostly because it also produces the greatest proportion of anxious people.

When measuring ambition, anthropologists divide families into four categories: poor, struggling but getting by, upper middle class, and rich. For members of the first two groups, who are fighting just to keep the electricity on and the phone bill paid, ambition is often a luxury. For the rich, it's often unnecessary. It's members of the upper middle class, reasonably safe economically but not so safe that a bad break couldn't spell catastrophe, who are most driven to improve their lot. "It's called status anxiety," says anthropologist Lowe, "and whether you're born to be concerned about it or not, you do develop it."

But some societies make you more anxious than others. The U.S. has always been a me-first culture, as befits a nation that grew from a scattering of people on a fat saddle of continent where land was often given away. That have-it-all ethos persists today, even though the resource freebies are long since gone. Other countries — where the acreage is smaller and the pickings are slimmer — came of age differently, with the need to cooperate getting etched into the cultural DNA. The American model has produced wealth, but it has come at a price — with ambition sometimes turning back on the ambitious and consuming them whole.

The study of high-achieving high school students conducted by Ohio State's Demerath was noteworthy for more than the stress he found the students were suffering. It also revealed the lengths to which the kids and their parents were willing to go to gain an advantage over other suffering students. Cheating was common, and most students shrugged it off as only a minor problem. A number of parents — some of whose children carried a 4.0 average — sought to have their kids classified as special-education students, which would entitle them to extra time on standardized tests. "Kids develop their own moral code," says Demerath. "They have a keen sense of competing with others and are developing identities geared to that."

Demerath got very different results when he conducted research in a very different place — Papua, New Guinea. In the mid-1990s, he spent a year in a small village there, observing how the children learned. Usually, he found, they saw school as a noncompetitive place where it was important to succeed collectively and then move on. Succeeding at the expense of others was seen as a form of vanity that the New Guineans call "acting extra." Says Demerath: "This is an odd thing for them."

That makes tactical sense. In a country based on farming and fishing, you need to know that if you get sick and can't work your field or cast your net, someone else will do it for you. Putting on airs in the classroom is not the way to ensure that will happen.

Of course, once a collectivist not always a collectivist. Marcelo Suárez-Orozco, a professor of globalization and education at New York University, has been following 400 families that immigrated to the U.S. from Asia, Latin America and the Caribbean. Many hailed from villages where the American culture of competition is alien, but once they got here, they changed fast.

As a group, the immigrant children in his study are outperforming their U.S.-born peers. What's more, the adults are dramatically outperforming the immigrant families that came before them. "One hundred years ago, it took people two to three generations to achieve a middle-class standard of living," says Suárez-Orozco. "Today they're getting there within a generation."

So this is a good thing, right? Striving people come here to succeed — and do. While there are plenty of benefits that undeniably come with learning the ways of ambition, there are plenty of perils too — many a lot uglier than high school students cheating on the trig final.

Human history has always been writ in the blood of broken alliances, palace purges and strong people or nations beating up on weak ones — all in the service of someone's hunger for power or resources. "There's a point at which you find an interesting kind of nerve circuitry between optimism and hubris," says Warren Bennis, a professor of business administration at the University of Southern California and the author of three books on leadership. "It becomes an arrogance or conceit, an inability to live without power."

While most ambitious people keep their secret Caesar tucked safely away, it can emerge surprisingly, even suddenly. Says Frans de Waal, a primatologist at the Yerkes Primate Center in Atlanta and the author of a new book, Our Inner Ape: "You can have a male chimp that is the most laid-back character, but one day he sees the chance to overthrow the leader and becomes a totally different male. I would say 90% of people would behave this way too. On an island with three people, they might become a little dictator."

But a yearning for supremacy can create its own set of problems. Heart attacks, ulcers and other stress-related ills are more common among high achievers — and that includes nonhuman achievers. The blood of alpha wolves routinely shows elevated levels of cortisol, the same stress hormone that is found in anxious humans. Alpha chimps even suffer ulcers and occasional heart attacks.

For these reasons, people and animals who have an appetite for becoming an alpha often settle contentedly into life as a beta. "The desire to be in a high position is universal," says de Waal. "But that trait has co-evolved with another skill — the skill to make the best of lower positions."

Humans not only make peace with their beta roles but they also make money from them. Among corporations, an increasingly well-rewarded portion of the workforce is made up of B players, managers and professionals somewhere below the top tier. They don't do the power lunching and ribbon cutting but instead perform the highly skilled, everyday work of making the company run. As skeptical shareholders look ever more askance at overpaid corporate A-listers, the B players are becoming more highly valued. It's an adaptation that serves the needs of both the corporation and the culture around it. "Everyone has ambition," says Lowe. "Societies have to provide alternative ways for people to achieve."

Ultimately, it's that very flexibility — that multiplicity of possible rewards — that makes dreaming big dreams and pursuing big goals worth all the bother. Ambition is an expensive impulse, one that requires an enormous investment of emotional capital. Like any investment, it can pay off in countless different kinds of coin. The trick, as any good speculator will tell you, is recognizing the riches when they come your way.

TIME