He told me that few people realize that he listened to those students for more than two hours, and that they hadn’t intercepted and surprised him: He went out to meet them, knowing how angry they were. “I felt that I had to model the principles that I believed — which is that I am committed to free and open expression,” he said. “I hardly could cower in my house .”

Although he stayed calm — which he attributes to years of training in karate and its premium on self-control — he was rattled, deeply, by the encounter. He soon took his first sabbatical ever. He read books about equanimity in the face of injustice. “I did not want to become a different person,” he said. “I certainly did not want to become embittered.”

His work on “Blueprint” was already long underway, and he lost himself in it, devoting “my heart and soul and all my learning.” It shows. The book is a hefty, dazzlingly erudite synthesis of history, philosophy, anthropology, genetics, sociology, economics, epidemiology, statistics and more. It uses everything from shipwrecks to the primatologist Jane Goodall to make its pro-kindness case, and it inadvertently shames you into realizing that while most of us, standing at the buffet of knowledge, content ourselves with a pork chop and rice pudding, Christakis pillages the carving station and the omelet station and the soup array and the make-your-own-sundae bar.

“Blueprint” — and its theory about the evolutionary origins of virtue — became his balm. That’s clear in the book itself, which makes unmistakable allusions to the Yale ugliness. “I have seen the effects of overidentifying with one’s group and witnessed mass delusions up close,” he writes. He rues America’s intense polarization, which perhaps makes this “an odd time for me to advance the view that there is more that unites us than divides us.” But advance that view he does.

His reasoning, oversimplified, is this: Complex societies are possible and durable only when people are emotionally invested in, and help, one another; we’d be living in smaller units and more solitary fashions if we weren’t equipped for such collaboration; and human thriving within these societies guarantees future generations suited to them.

Yes, there are hideous wars and horrid leaders. But if that were the sum of us, how to explain all the peace and progress? Christakis urges a wide angle and the long view.

“To accept this belief that human beings are evil or violent or selfish or overly tribal is a kind of moral and intellectual laziness,” he told me. It also excuses that destructiveness. “The way to repair our torn social fabric is to say: Wait a minute, that’s not quite right.”