In the early 1940s, two Harvard sophomores named Norman Mailer and Leonard Bernstein were rejected for participation in a study. The study, known as the Grant Study, was funded by William T. Grant, owner of the nationwide chain of 25 cent stores that also bore his name. It was to become one of the foremost “longitudinal studies” of 20th century social science, tracking the physical and emotional health of a cohort of young Harvard men through the rest of their lives.

In his proposal to the university president, Arlen V. Bock, a Harvard doctor, argued that the time was ripe for such an experiment. He cited “the stress of modern pressures,” for which “the current generation of students had been left largely unprepared.” These students had been born into the aftermath of the first World War and would graduate into another; their births coincided with the advent of broadcast technology and the consumer culture it helped spawn; and they’d been raised in an era of shifting sexual mores, by parents who endured the Great Depression. As for why the study should take place at Harvard, it was thought that Harvard grads had a high likelihood of long life—a necessity for a study that sought to answer: What is health?

Between 1939 and 1946, Bock’s team selected 268 sophomores. Alas, no record explains why Mailer and Bernstein were rejected. Back then, scientists believed that physical constitution and breeding—rather than, say, “emotional intelligence,” a happy childhood, or a capacity for love—were the best predictors of a successful life. Those men with masculine body builds—muscular mesomorphs (narrow hips, broad shoulders)—were favored over skinny ectomorphs and pudgy endomorphs. Volunteers were asked about masturbation and their thoughts on premarital sex, but not about their girlfriends or friendships. They were measured for organ function, brow ridge, moles, and the hanging length of their scrotum.

Grant withdrew his funding in 1947, and the study sputtered along for the next 20 years. In 1966, George E. Vaillant, a 32 year-old psychiatrist, was put in charge of the study, and it became his lifework. Vaillant, who was 10 to 15 years younger than the Grant members, had spent his early career studying recovery from heroin addiction. He’d become interested in how men used involuntary defenses, or coping mechanisms, to evolve and adapt incrementally to life’s setbacks. His new job, then, was a good fit. Following the Grant men through marriage, parenthood, divorce, career troubles, second (and third) marriages, bouts with alcoholism and other vices, parental death, and the golden years of grandchildren and physical lessening, would allow Vaillant to, as he put it, investigate the mysteries of incremental adaptation to his heart’s content.

“Some men came to Cambridge to be interviewed, but in most cases I went to them—to Hawaii, Canada, London, New Zealand,” writes the 82 year-old Vaillant in Triumphs of Experience: The Men of the Harvard Grant Study, his final dispatch summing up nearly 50 years of work. “There were cultural differences, too. All the New Yorkers and most of the New Englanders met me in their offices, and few offered me a meal. Virtually all the Midwesterners saw me at home and invited me to dinner. The Californians were evenly divided. Several wives were openly suspicious of the whole enterprise. One spoke so stridently into the telephone that sitting across the desk from her husband I could hear her refuse to see ‘that shrink’ under any circumstances.”

Four members ran for the United States Senate and one became a governor. The Grant men also include John F. Kennedy and Ben Bradlee, the longtime editor of The Washington Post when it published the Pentagon Papers and broke Watergate. In a 2009 article about the Grant Study, The Atlantic reported that Kennedy’s Grant files had been withdrawn and sealed until 2040. For Bradlee’s part, he’s not mentioned in Triumphs of Experience. Though Vaillant did publish a profile of Bradlee in his earlier book about the study, Adaptation to Life (1977). In that book, Vaillant used Bradlee—who appears under pseudonym, as do all Grant men—as a shining example of sublimation, a “mature defense” that describes men who adapt to their anger by finding healthy ways to re-channel it as, for example, passion for their work.

In the new book, Vaillant returns bearing another three decades of data as well as his own lengthening perspective. To avid consumers of modern happiness literature, some of Vaillant’s conclusions will seem shopworn (“Happiness is love. Full stop.”), while other results of the Grant Study appear to confirm what social science has long posited—that a warm and stable childhood environment is a crucial ingredient of success; or that alcoholism is a strong predictor of divorce. But what’s unique about the Grant Study is the freedom it gives Vaillant to look past quick diagnosis, to focus on how patterns of growth can determine patterns of wellbeing.

Life is long, Vaillant seems to be saying, and lots of shit happens. What is true in one stage of a man’s life is not true in another. Previously divorced men are capable of long and loving marriages. There is a time to monitor cholesterol (before age 50) and a time to ignore it. Self-starting, as a character trait, is relatively unimportant to flourishing early in life but very important at the end of it. Socially anxious men struggle for decades in emotional isolation and then mature past it—relatively speaking.

Triumphs of Experience is not only a history of how the Grant men adapted (or not) to life over 70-plus years, but of how author and science grew up alongside them. Yet what unifies Triumphs is the same question posed originally by Bock, the study’s founder: What factors meaningfully and reliably predict the good life? Vaillant’s mission is to uncover the “antecedents of flourishing.”

To this end Vaillant establishes a “Decathlon of Flourishing,” a sort of Happiness Olympics in which each Grant member’s life competes. The “events” include: good subjective and objective physical and mental health at age 80; close to kids between ages 60 and 75; availability of social supports other than wife and kids between ages 60 and 75; in a good marriage between ages 60 and 85; and earned income in study’s top quartile.

Starting at the beginning, Vaillant ranks each man’s childhood along a spectrum from “Cherished” to “Loveless.” Representing “Loveless” is a Grant member whom Vaillant refers to as “Sam Lovelace.” Lovelace grew up distant from both parents—a “moody” mother and a “remote, anxious, tired” father. They left the young Lovelace with “a profound lack of trust in them or anyone else, including himself.” Lovelace got all A’s in school but lacked stimulation. As an adult he visited his parents often, but only because he feared they would soon die. At 50, Lovelace, an architect, felt bullied at work. He and his alcoholic wife had no guests to the house. “During the interview,” writes Vaillant, “he smoked incessantly and gazed out the window, making no eye contact…I asked him who his oldest friend was, but he told me instead about a man whom he greatly envied.”

Vaillant interviews Lovelace again, at age 53, following the death of his wife. “With the burden of his agonizing marriage relieved, his life was one important degree less dangerous, and he was no longer the cadaverous, worried man I had met three years before.” Lovelace has now become president of a retirement home, and his social life has improved, if marginally. He will marry again in his 60s.

When Vaillant returns a third time, Lovelace is 79 and looks younger than he had 25 years earlier. Compared to the marriages of other men in the study, Lovelace’s second ranks in the “unhappy” category. Yet Lovelace claims that his wife is the best thing that ever happened to him. “Like many of the Loveless men, it was hard for him to let love in,” writes Vaillant. “Even this ambiguous marriage was an improvement over anything he had ever had before, and he could appreciate and rejoice in that.”

Vaillant concludes that a loving childhood is one of the best predictors of mid and late-life riches: “We found that contentment in the late seventies was not even suggestively associated with parental social class or even the man’s own income. What it was significantly associated with was warmth of childhood environment, and it was very significantly associated with a man’s closeness to his father.”

Another Grant member, “Dylan Bright,” spent his adult life rebounding from an absent father and a mother who made him wear mittens to bed because of his “perfectly revolting” (her words) habit of masturbating when he was two. Childhood saddled Bright with barely tamed aggression. He learned the coping style of what Vaillant calls reaction formation, “containing emotional impulses by doing their opposite,” such as a program of rigid self-denial that included periods of sexual abstinence. “Bright’s adaptive responses were ingenious,” writes Vaillant. He played football, wrestled, learned to laugh a lot, and poured himself into a career teaching poetry. Bright’s exuberance for life helped “anesthetize” his grief. He made a successful second marriage before alcohol and cigarettes killed him at sixty-two.

“Lives change and things can get better,” writes Vaillant. “But the people who don’t learn to love early pay a high price.” Dylan Bright died too young to compete in the Decathlon of Flourishing. Sam Lovelace scored zero.

Given the Grant Study’s focus on how men evolve and adapt, the centerpiece of Triumphs of Experience is the chapter on maturation, in which Vaillant sets out to explore an enormous and fascinating question: What should a person be at the end of his life that he was not at the beginning?

Vaillant began with the old Eriksonian model, in which maturation is equated with a deepening capacity for love and work. But the model didn’t hold. Over time, writes Vaillant, the men’s standing in these two realms was “as changeable as the weather…Periods of success at work and love came and went unsystematically and according to circumstance.”

In abridged form, Erik Erikson’s stage theory of psychosocial development envisioned life as ladder of progressions, or emotional achievements: One begins at the bottom of the ladder, with the adolescent task of Identity (separating from social, economic, and ideological dependence upon one’s parents), then climbs to Intimacy (the capacity to live with another person in an interdependent, committed relationship), then Generativity (the assumption of responsibility for the growth of others), and finally rings the bell at Integrity (the ability to come to terms with the past and future in the face of dwindling days).

Seeking a more complete model of how men “grow up,” Vaillant builds off Erikson, adding two more rungs: Between Intimacy and Generativity—i.e. between relationships and breeding—Vaillant adds Career Consolidation, defined as commitment to a career, compensation, contentment, and competence. Between Generativity and Integrity, Vaillant adds Guardianship, or caretaking, which manifests as charitable work, volunteering, or the curating of cultural riches for future generations.

According to the results of the Grant Study, these maturational markers are not academic, they’re tied to health and longevity: In 2011, only four of the 31 Grant men who failed, in Vaillant’s estimation, to mature past Intimacy were still alive; fifty of the 128 men who reached Generativity were still alive; and the Generative died on average eight years later than those who never achieved Career Consolidation. The men who did not cultivate gratifying careers shared a lifelong inability to deal with anger.

But as Vaillant aged with the men, he discovered that even his modified model of maturation needed modification. In his younger days, Vaillant had never thought of “Wisdom” as a model of maturity. Nor had he been able to conceive of Career Consolidation in terms other than “black-and-white, good-or-bad.” One either committed to a calling, built a career, or didn’t. In retrospect, this flaw in the Grant Study seems obvious: How can a 45 year-old researcher assess the maturity of 60 year-olds?

After all, Vaillant’s own life, as The Atlantic reported in 2009, has not always been a model of adaptive health. His mother’s father was a prominent banker, while Vaillant’s own father, an archeologist, became a curator at the American Museum of Natural History. But at 44, when Vaillant was 10, his father committed suicide in their backyard in Pennsylvania. His mother swept the loss under the rug and moved the family to Arizona. Vaillant attended Harvard and Harvard Medical School. After 15 years of marriage and four children, he divorced his first wife in 1970, when he was in his mid-30s. He married again, had another child, and left that wife in the early 1990s for a colleague at the Grant Study. Five years later he divorced the third wife and returned to the second. Four of Vaillant’s children have gone long periods without speaking to him. Vaillant compared his family to King Lear’s and called himself “a disconnected, narcissistic father.”

If Vaillant’s ambition created strife at home, halting his own progress through Intimacy and Generativity, it also informed his stewardship of the Grant Study. Vaillant’s emphasis on achievement—i.e. his belief that men could not give themselves away until they’d carried out the essentially “selfish” task of committing to a career—nearly led him to overlook one of the study’s most important members, a man he dubbed Charles Boatwright.

Boatwright had enjoyed a loving childhood with his father, mother, and sister. After Harvard, however, he was rejected from the military because of poor eyesight. There ensued a lifetime of bouncing around. Boatwright found work equipping navy ships with radar equipment. Then he moved to Vermont to manage a tree farm. In Vermont he helped build a lumber cooperative, an egg cooperative, and a high school. He worked as a journalist, a milk deliverer, a carpenter, a painter, an accountant for a gas station, and an artificial inseminator of cattle. In the 1950s, an interviewer for the Grant Study noted that Boatwright had “persistent difficulty in establishing a career,” and yet Boatwright also struck the interviewer as one of the most stable men in the study—a paradox that took Vaillant a lifetime to unravel.

“I thought back to those early years,” writes Vaillant in Triumphs of Experience. “I’d found Boatwright’s file tedious going. His lack of career commitment was one of the reasons I’d scored him as a potential ‘bad outcome’… It was easy to marshal other evidence of failure, too: a divorce, an estrangement from his daughter, a drifting son.” When in 1974, Boatwright, then 49, filed a glowing report on his life—“I have learned to be more kind, and have more empathy. I have learned to be tolerant.”—the young Vaillant rolled his eyes: “I thought I recognized the kind of premature selflessness that cloaks a lack of clear identity—a series of early efforts to deny his own needs and project them onto others.”

When Vaillant began working on the Grant Study, in his early 30s, he remembers: “I was too deep into the ‘selfish’ phase of my own career consolidation to understand what Charles Boatwright was about…as he moved from one job to another, it was hard to tell where his commitment or his competence lay…It took me a long time to understand that the career that Boatwright consolidated was looking after others more needy than himself.”

In his 50s, Boatwright borrowed money to pursue his dream of buying a boatyard. He later married the widow of his deceased business partner, and became stepfather to her three children. “No one has ever healed me with such love,” Boatwright wrote of the second marriage. “And in return I have come to love her completely…Being a stepfather has an enormous number of problems, but I seemed to have coped well.”

In late life, Boatwright donated more money than he could afford to land conservation; volunteered in Vermont, where they had a vacation home; and at 83 he still worked 28 hours a week. In the Decathlon of Flourishing, Boatwright scored 7 out of 10. Only 3% of Grant members scored higher.

“With age you acquire more understanding,” Boatwright explained when he was 79. “The things you felt so passionate about when you are young, you learn to let go of. You realize that all those things you thought you were going to be, you ain’t. As I have often said, at this stage in life it’s not what you’ve accomplished in a day, but how the day felt.”