I think from an evolutionary point of view, it's one of the great gifts to our species to be able to get enjoyment from responding to challenge. I think that's why we have grown constantly in terms of knowledge and technology and art and everything, because we get enjoyment from it. For instance, we have all kinds of dogs at home and they also love challenge, but their challenge is very simple. They wait until we throw a tennis ball and then they run after it because they're programmed to chase, and that's the challenge they recognize. We have consciousness which makes us able to find challenges, not just what's programmed into us like the dog would answer to the tennis ball. But we see, for instance we look at the stars and say, "Gee, I wonder how they work," or, "Can I get a better grapefruit by mixing two different kinds together?" or whatever. How to cook the chicken better, a new recipe, how to develop a faster car. All of these things help us to move ahead and in the process, they make life enjoyable. Without challenge, life would be, what would it be? In fact, imagine a life in which nothing is challenge. We would become immediately a couch potato, right? That's it. So it's an interesting issue but we don't have the vast knowledge on it but we can imagine that this was evolved as a way of getting our species to move out of the trees and the savannah, build houses, all those things. And not just because it's more comfortable, but because it's challenging and we enjoy challenge.