Nowadays we think of homesickness as something kids have on sleepovers. It certainly hasn’t appeared on a death certificate for 100 years. The last person who was diagnosed with nostalgia as a cause of death died in 1918.

Lofthouse: How did it beome so much less serious, then? Why has the idea of homesickness changed so much?

Smith: With modernity came a different set of values. It’s not just that it got easier to travel and go back home and communicate through telephones and the Internet and so on. It’s about frontier spirit—in [the current] cultural atmosphere, longing for something that’s comforting and reassuring might seem unambitious. If I feel homesick today, I might think I should grow out of it and enjoy the adventure.

We used to have these words for the feeling of wanting to be home, the feeling of wanting to be in one place for a very long time, which have now disappeared. There’s a wonderful word: “homefulness,” which is the feeling you get when you turn the corner of your road or your airplane lands and you know you're near home. It’s a lovely combination of relief and belonging.

Lofthouse: Are there any emotions our culture takes more seriously than it used to?

Smith: We give happiness a lot of space in our discussions. But it’s a relatively recent phenomenon that happiness is something you’d want to aim for. If you look back to 16th-century Renaissance Europe, there's a fascination with sadness that’s almost the equivalent of today’s fascination with happiness. You start seeing a lot of authors writing about how to be sad better, and what the appropriate sort of sadness is. It’s seen as valuable because it brings you closer to God. It makes you more humble and more serious. In some cases, a more severe form of sadness, melancholia, was aligned with genius. I think the way we valorize happiness today is problematic. It creates pressure to feel upbeat and cheerful all the time.

Lofthouse: Are you saying we could be happier if we didn't obsess about happiness so much?

Smith: I definitely think so. I’ve read self-help books about happiness that make the case that if something’s important, you need to measure it and you need to figure out how to have more of it. I think that’s a mistake. There’s been some interesting research on the concept of emodiversity recently. The cause-and-effect relationship isn’t completely clear, but stronger physical and mental health is correlated with experiencing a range of emotions instead of just being happy or content all the time. It means allowing yourself to feel sad, angry, irritable, bored, and frustrated. All the things we’re told we ought not to feel.

Lofthouse: You talk about this sort of double life of emotions as an experience that’s both private and shared. Can you talk about that?

Smith: In the biological sense, our emotions are collective. They’re shared. Our bodily responses belong to people and animals who were having emotions millions and millions of years ago.