Arbus at the “New Documents” show at the Museum of Modern Art, in 1967. Photograph by Dan Budnik

In 1969, the Metropolitan Museum of Art agreed to buy three photographs by Diane Arbus, for seventy-five dollars each. Wiser counsels prevailed, however, and a few months later the museum decided to take only two. Why splurge? The Museum of Modern Art was more daring; in 1964, it had acquired seven Arbus photos, including “Child with a toy hand grenade in Central Park, N.Y.C.” Not until the aftermath of Arbus’s death, however, in 1971, and the retrospective of her work at moma the following year, did public fascination start to seethe, swelling far beyond the bounds of her profession. The swell has never slowed, and prices have followed suit. At Christie’s, in 2007, “Child with a toy hand grenade” sold for two hundred and twenty-nine thousand dollars. Last year, another print of it, this one signed by the artist, fetched seven hundred and eighty-five thousand dollars. That’s quite a hike.

Who is this kid, and what is he doing with a weapon, even a fake one, in Central Park? Well, his name is Colin Wood, and Arbus met him there in early 1962, when he was seven. We have a contact sheet of the pictures that she took that day. (It is reprinted in “Revelations,” a hefty and absorbing volume published in 2003 to accompany an Arbus retrospective.) Colin is dressed in shorts and suspenders which lend him a Teutonic air, and he is happy to strike a pose. There are eleven images, and in six of them he stands with hands on hips. Most of the time, he looks jaunty and self-possessed, and you can count the missing teeth in his grin. So why did Arbus pick the shot in which he tightens his mouth into a stretched-out grimace, cupping one hand into an upturned claw while the other grips a grenade? Isn’t he just making sport, or doing an impersonation of someone—an actor in a monster movie, say—consumed by sudden dread? Might Arbus, in short, be guilty of rigging the evidence to fit a mood, making fear out of fun?

That was what I had always suspected, until I read “Diane Arbus: Portrait of a Photographer,” by Arthur Lubow (Ecco). One coup, in this new biography, is an interview with Colin Wood, conducted by Lubow in 2012. We learn that Wood was a Park Avenue kid, stranded at the time with nannies while his parents were busy divorcing, and “living primarily on powdered Junket straight from the box.” He brought his toy guns to school. Wood says of Arbus, “She saw in me the frustration, the anger at my surroundings, the kid wanting to explode but can’t because he’s constrained by his background.” If she did see all that, it was by instinct, with a touch of fellow-feeling; she had started out much like Colin, and continued that way. Now she found a boy preparing to pull the pin, and snapped. “Giving a camera to Diane,” Norman Mailer said, after sitting for her, “is like putting a live grenade in the hands of a child.”

Arbus was born into wealth, and you could, if inclined, construe the life that followed as one long struggle to get away from wealth—to crawl free of it, like someone seeking the exit from a treasure-stacked cave. “The outside world was so far from us,” Arbus said. She was a Russek, which to anyone who suddenly needed a mink stole, in the depths of the Great Depression, was a name to reach for. Russeks, founded by her maternal grandfather, was originally a furrier’s; by 1924, it was a department store on Fifth Avenue, selling not only furs but also gowns, coats, and, as an advertisement put it that year, “smart accessories for the correctly dressed woman.” In 1919, Diane’s mother, Gertrude, married a young window dresser at the store named David Nemerov. Their son, Howard, who grew up to become poet laureate, was born twenty-one weeks after the wedding. Diane was born in 1923, and her sister, Renee, in 1928.

No woman was more correctly dressed than Gertrude. She sailed to Paris with her husband whenever he went to survey the new couture collections. Her pleasure was to be chauffeured to Russeks and to parade through its rooms, past bowing and smiling staff, accompanied by her older daughter, who, in white gloves and patent-leather slippers, saw herself as “a princess in some loathsome movie.” One thing Arbus claimed to have suffered from, as a child, was that “I never felt adversity.”

There are two responses to this. One is: Give me some of that suffering. If you had asked any of the Dust Bowl farmers photographed in their thin clothes by Dorothea Lange whether they would mind getting dressed up, after a fancy breakfast, and going to a workplace where everyone was nice to them, they would have said that, all things considered, they could handle it. Was there, in Arbus, a lingering whiff of the poor little rich girl? To say that she slummed would be unfair, but she revelled in settings that money couldn’t touch, or in surfaces where it had left its scratch marks: Brenda Frazier, pictured in 1966, twenty-eight years after she had been crowned “débutante of the year,” appears to be held together by powder, paint, and pearls.

Regular politics, and the calls of social responsibility, certainly meant little to Arbus. She stepped aside from the notion that a photograph might, in addition to its aesthetic shape and shock, harbor some documentary worth, especially in an era of deprivation or unrest. Not many Jews would go, willingly and uncritically, to listen to Nazis in Yorkville. If she was a pilgrim on the fringes of society, it was fascination rather than compassion that drove her there, and many of the outcasts she discovered, far from being ground down, had elected to cast themselves out. The balding and shirtless figure who glares at us in “Tattooed man at a carnival, Md.” (1970) requests not an atom of our pity. Indeed, he puts our undistinguished bodies to scorn, brandishing the art work of his torso as though to holler, “Get a load of me.”

On the other hand, we may choose to take Arbus at her word. If all that privilege brought her a world of pain, so be it. And it’s hard to think of a more frangible instance of motherhood than Gertrude, who, according to Lubow, “typically stayed in bed in the morning past eleven o’clock, smoking cigarettes, talking on the telephone, and applying cold cream and cosmetics to her face.” At one point, she fell into a ravine of depression and got stuck, sitting wordlessly at the family dinner table. “I stopped functioning. I was like a zombie,” she recalled later. Her husband, meanwhile, presented an alternative—and no less daunting—role model. Though Gertrude’s parents had believed that she was marrying down, David, smooth and frictionless, rose through the ranks of Russeks as if stepping into the elevator. By 1947, he had arrived at the position of president.

Arbus inherited both strains: the urge to follow your star, plus the rage to cut yourself off and plunge into personal lockdown. One further twist in her upbringing was that she did not endure it alone, for her brother, Howard, was close to her, although whether that closeness offered aggravation or relief is open to debate. Both were precocious students, and they shared other talents, too. Diane masturbated in the bathroom with the blinds up, to insure that people across the street could watch her, and as an adult she sat next to the patrons of porno cinemas, in the dark, and gave them a helping hand. (This charitable deed was observed by a friend, Buck Henry, the screenwriter of “The Graduate.”) Not to be outdone in these vigorous stakes was her brother, who later, in a book called “Journal of the Fictive Life,” defined his self-abuse as “worship.” He added, “My father once caught me at it, and said he would kill me if it ever happened again.” A friend of Gertrude’s once told Howard that reading Freud would make you sick. On the contrary, it would be like a day in the life of the Nemerovs.