So, should we give in to hope? I think that Robert Sapolsky, a Stanford professor, neuroscientist, author of many books and giver of many talks, has the answer.

He’s a public science star of sorts. He may not be as well-known as Neil deGrasse Tyson, but he’s doing pretty well for a (self-described) strident atheist who points out in his recent book, “Behave: The Biology of Humans at Our Best and Worst,” that free will, the way we usually imagine it, is an illusion.

He’s not a Pollyanna, is my point. No sugarcoating from Dr. Sapolsky.

But, surprisingly, he is an eloquent admirer of certain forms of irrationality. He gave a funny, rich and convincing talk in 2009 to Stanford seniors on what separates humans from animals. I know it’s not brand new, but I still turn to it occasionally because it’s so clear and persuasive. It has more than 400,000 views online.

After describing many differences between humans and animals, even our close relatives, like the mountain gorillas, Dr. Sapolsky presents what he sees as one of the most remarkable human qualities: the ability to hold on to two contradictory ideas at once and find a way forward.

His main example is Sister Helen Prejean, who wrote the book “Dead Man Walking,” based on her work ministering to death row inmates. She said that the more unforgivable the sin, the more it must be forgiven, and the more unlovable the person, the more important it is to love him or her.

That is not, Dr. Sapolsky argues, a conclusion any animal could come to. But a human can spend her life acting on that conviction. And that ability, he said, is the “most irrational, magnificent thing that we are capable of as a species.”