Intense feelings in early romantic relationships are a combination of pheromones and dopamine, and their persistence would suffer productivity and civilization.

“I think it's a combination of pheromones, and it's a combination of dopamine and look like I get it, I get it, I get it, but why do we have to look at it like those early days of a relationship where you, look, we've both been in love. We've both been in a romantic relationship where just the person brushes up next to you or the scent of them hits you, and it's like an electric shock through you. ... But if that stayed forever, you would never get anything done. Like civilization would perish.”