Randolph Nesse is the co-author of "Why We Get Sick: The New Science of Darwinian Medicine" (along with George C. Williams). This is the uncut version of an interview with Richard Dawkins. Thanks to RichardDawkins.net for posting the video.
The subject is evolutionary medicine.
It's interesting how one's perspective can be distorted by only thinking about animals. Nesse wonders how large multicellular species can survive when bacterial pathogens can evolve so rapidly. Part of his answer is the immune system but he also talks about pain and vomiting as adaptive responses to disease.
If you think about trees and tulips, you might come up with very different answers to the same questions. Plants survive very well without an immune system or pain. It makes you realize that there are different ways of solving a problem.