OK, I’m paraphrashing. But a brief exchange with an audience member during the question-and-answer session was a highlight of last night’s Jared Diamond lecture at Carnegie Music Hall.

Diamond, Pulitzer-winning author of Guns, Germs and Steel, spoke to a full house about what we can learn from traditional societies, which is the theme of his new book, The World Until Yesterday. Afterward, an audience member asked him about two aspects of traditional (essentially, tribal) societies that Diamond hadn’t touched on: attitudes toward homosexuality and the prevalence of guilt and shame.

As usual, Diamond — 75 and sporting a gold National Geographic Society lapel pin — prefaced his answer by noting that traditional societies are notably diverse in almost everything they do. They are far more diverse, in fact, than are modern societies.

On homosexuality, his example was a tribe in New Guinea that practices “institutionalized male homosexuality.” That is, boys all live together, segregated from girls, until it is time to marry. Then the boys are told to mate with females, who up till that point they’d been taught were “unclean.”

“And it works,” Diamond concluded, illustrating a larger point about how cultures have developed different means to cope with universal issues.

Diamond didn’t actually mention the military. But a chapter of The World Until Yesterday is devoted to chronic warfare in tribal societies. He focuses on New Guineans, among whom he’s lived and worked on-and-off for five decades. And all the men in such societies are expected to be warriors.

Most of the formal Monday Night Lectures talk actually focused on a different chapter of the book, about how traditional societies treat their elders: In many ways, he argued, it’s better than how Westerners treat the elderly, whom we force into retirement, warehouse and disconnect from meaningful contributions to society.

The World Until Yesterday is a fascinating, provocative work. Here’s my preview of last night’s talk based on a phone interview with Diamond.