Looking at how other cultures resolved those dilemmas was a way of expanding the possibilities of their own culture. The culture of Samoa was actually more complicated and contradictory than it seems in Mead’s book. But her core idea was right: In other places, there were better paths through adolescence than the tormented, repressive American one.

As you read about Mead and her lovers, you can’t help remarking on a recurrent tragicomic hopelessness about brilliant young women’s efforts to figure out sex. That’s true whether the protagonist is Mary Shelley in the 1820s, Margaret Mead in the 1920s, or a polyamorist today. You also can’t help remarking that the person at the apex of a love triangle—the position Mead found herself in again and again—is rather likely to conclude that polyamory is natural and jealousy is cultural, while the folks at the other two vertices are more likely to argue the opposite view.

More broadly, the history of feminism has seen a pendulum swing between libertine and puritan impulses. A hundred years earlier, another great feminist anthropologist working closer to home carefully studied how adolescent village girls came of age. But Jane Austen concluded that resisting male pressure and seduction was the route to empowerment, a view that may resonate more nowadays than Mead’s free love under the palm trees.

Still, the back-and-forth doesn’t mean that nothing changes, or that the project of cultural expansion is doomed. (I doubt that my granddaughter will figure out sex entirely either, but she’ll be a lot further along than Shelley or Austen—or Mead.) Neither Mead nor Benedict could fully envision the best example of 20th-century cultural transformation. They pointed out that homosexuality was accepted in other cultures and came under fire for saying it, even from other anthropologists. Edward Sapir was another famous Boas student (and another ex-lover of Mead’s), and he argued that gay sex was not just unnatural but pathological.

Benedict was the most stable and satisfying love of Margaret Mead’s early life, and another anthropologist, Rhoda Métraux, was Mead’s partner for more than 20 years. And yet the fearless, transgressive public intellectual never openly identified herself as bisexual or lesbian. Even in the 1960s, when I was reading Coming of Age, romantic love with a woman was still far outside my personal realm of possibilities—35 years passed before I discovered it.

In 2019, it’s easy to imagine Benedict and Mead settling into a happy academic marriage with a big house and kids and dogs. In 1919, it was impossible. But the anthropologists who showed how sexual patterns and expectations could vary and change helped make that kind of marriage a reality.

The very word culture, and the idea that people in one culture can learn from people in others, is taken for granted now. But King shows how revolutionary those concepts were at a time when scientists classified people as savage, barbarian, or civilized, and three-quarters of American universities offered courses in eugenics. In the 1920s, as King vividly conveys, ideas about biologically based racial, ethnic, and gender superiority were considered scientific, modern, and progressive. (In some quarters they still are.) When the Nazis looked for examples of a science that justified racial discrimination, and a government that wrote racial categories into law, they turned to the United States.