If I had to pick one tribe to go back and live with permanently — and I hate doing this, it’s not a contest — it would be the people of Anuta, in the South Pacific. It’s got white beaches, blue seas, good food and gentle, friendly people who have a wonderful philosophy of sharing. And it’s warm.

Whenever you face something new, you revert to your own tribal ways. People ask me how I can live among cannibals, or tribes that practise female circumcision, and not tell them what's right or wrong. I know that's not the way to understanding. I try not to judge.

I grew up very Christian ... My family are still very Christian. I am in no way disrespecting them when I say this: it was overbearing. I believed I was touched by Jesus, and I prayed all the time. I was still very Christian when I left the Marines. I would tell everyone about Jesus — it was almost evangelical. I thought all the good things in my life were because of my faith. When I came back from expeditions, I had some experiences that made me readdress all that. I'd pretty much known all along that Christianity wasn't for me. Ever since then, I've been on my own quest to find another truth. I can't read novels, but I do read books about cosmology, about astrophysics, about genetics. I'm interested in altered states of mind, and creation myths. It's all part of the same thing — I want to know why we think what we think. Now, I'd describe myself as pan-deist, reluctantly verging on atheist.