Death is usually a grim topic; sometimes, it’s even taboo. Nevertheless, you manage to address it without prejudices and with admirable curiosity. What are the most important questions posed in this book?

Juan José Millás: The most important question this book begins with is why we age and why we die. These are the two fundamental issues. There’s no old age in nature; there’s plenitude or death. So, why do human beings age? Is death biologically scheduled? It’s a topic of discussion among scientists. It’s curious, because childhood, adolescence, maturity and menopause are scheduled, but some scientists think that death is not. So, if death is not scheduled, why do we die? These two big questions across the entire book.

Juan Luis Arsuaga: That’s why the book is like a pilgrimage. We go to different sites on the Iberian Peninsula looking for answers to these questions.

Some have said that you’ve created a new literary genre.

J.L.A. When we began the first book, we were aware that we had no model, and that what we wanted to do hadn’t been done before. There are formulas that have very successful, but I hadn’t read anything like this, and even less about these things. Looking at them now, this book and the previous one are hybrids. They have something of Dialogues of Plato, and also of literature’s classic partners, from Sancho Panza and Don Quixote to Sherlock Holmes and Watson, without – of course – resembling any of them, obviously. Unforeseen things happen to us in this book. There are also a lot of voices from people we talked to. We go to places where we don’t know what is going to happen to us. It’s a formula that had never been done in science. What it isn’t is a guarantee of success.

We’re living a golden age for books that are popularising science. What’s behind this sudden popularity?

J.L.A.: What’s happening is wonderful.

J.J.M.: People are curious. We can’t read science books because they’re so complex, but if it’s told a certain way – without losing rigour – it can reach a lot of people with some higher education; it’s an opportunity. Look at the success of Yuval Noah Harari’s book Sapiens. No one had ever written a history of humanity that way. We have a relatively recent case in Spain: Infinity in a Reed, by Irene Vallejo, which tells the history of books with absolute rigour. What publishing company would think that a book about the history of books could end up being a best-seller? But she tells it in such a way that you say, “Damn, that’s interesting”. She tells it in a fantastic way. There’s an association between thematic content and formal content that fits, clicks.

On the other hand, contemporary societies have become so distanced from natural life that it seems like we’ve stopped being part of nature. We go to the countryside and feel like Martians who’ve arrived on Earth. We don’t belong to that. It’s a brutal contradiction because we are nature. We’ve lost a lot of knowledge associated with nature that is fundamental. So people are curious to know who it is, where it comes from.

After writing a book on life and another on death, have you reached some important conclusion about life?

J.J.M.: Yes, of course. I’ve found out that, for instance, old age is a product of culture. I can’t sum up everything I’ve learned from the scientific and emotional perspectives, but it’s true that I didn’t come out of those books the same as when I went into them. Recently, I was in La Palma to do a report on the volcano, and I didn’t see it as I would have seen before. My perception of reality has changed a great deal.

J.L.A.: It’s said that the most impressive and innovative thing about El Quijote is that it’s a book that deals with two people who have influenced each other to the point that, at the end of the book, they’re other people. At the end, Don Quixote and Sancho Panza have been brutally transformed by the long journey they’ve made, the things that have happened to them, the conversations they’ve had. It’s life. And, differences aside, I think something happened to us along that line.

Does this adventure end here?

J.J.M.: When we finished the previous book, we had the impression that we had reached a border. But there was another country next to that border, so on the last page, we said to ourselves, “Do we explore it?” We had the impression that the corpus was not finished. Now that we’ve reached the end of this second book, we’ve noticed that there’s another door to open; the door of the mind and consciousness, and that will be the end of this corpus. We don’t know whether we do it or not, but that door remains open as a possibility.

J.L.A: But not tomorrow, okay?