The ultimate hook for me is this: you're not going to convince anybody to dedicate their really hard, preciously earned time to deep-dive a topic as obscure as sleep evolution unless you convince them there's a why there. So if you've ever had a poor night's sleep, the reason it occurred is evolutionary. We are the products of 1.5, 1.8 billion years of evolution, and it turns out the answer is not even sleep. It's something much, much, much deeper, because sleep evolved relatively recently in the grand scheme of things. It evolved for complex neural nets. You have to have a big brain for sleep to really matter. Circadian rhythms, though — the first eukaryotes and prokaryotic life on the planet — had to time their behaviors adaptively. So the framing of the book is: why do we do what we do? Why do we experience the kinds of symptoms we do in the modern world? And the answer is a 1.5-billion-year-old answer. It goes back to the first life on this planet. If you're somebody who likes probing the why, you'll like this book.

You're going up these trees, you're spending hours to climb, and it actually takes a lot of energy to get all the gear out there. I remember distinctly the very first time I went out to the field. It was my pilot season, my doctoral supervisor's there, I have two Ugandan rangers next to me, and they're watching me do this for the first time.

To describe it: you have a throw line and an 8-ounce weight on the line, and you've got to throw it up above a crotch in the tree that's about 10 meters higher than the actual nest itself. Sometimes my highest throw was something like 120 feet, because my highest climb was 22 meters. That's the absolute max range I could get. You've got to shoot it through branches. It was crazy.

I had bought three of these weights. I get out there and I'd say within five throws, I got all three weights stuck in the tree. I thought, well, that's it. My dissertation is ruined. I've flown halfway across the world for absolutely no reason, I brought all this junk out here. Kevin's looking at me, like, oh god, I don't know what we're going to do. Then Felix, the ranger, throws off his gumboots, scales the tree beautifully, climbing like the locals climb. He just picks up the weights, laughs, throws them down. And I'm like, okay, I need to learn to climb like a local.

So I perfected this art. For anything under 10 meters, I was climbing like a local. I wouldn't even go up with any gear. It was stupid, but I was 23, 24 years old. I wanted to get a PhD. Now I look back, and the closest hospital was an 8-hour drive through the Rwenzori Mountains. Like, what was I thinking? If my son did that, I'd be like, that's so stupid. But you have to take your calculated risks, I guess. You don't think about it when you're a 22, 23-year-old boy.