Today we explore a different way of looking at evolution and what it may mean for the course of science.

First, when a female animal is checking out her prospects, natural selection would dictate that she pay attention to how healthy, or strong, or fit he is. But when it comes to finding a mate, some animals seem to be engaged in a very different game. What if a female were looking for something else - something that has nothing to do with fitness? Something ... beautiful? 

Then, a tree full of blood-sucking bats lends a startling twist to our understanding of altruism and natural selection. How can goodness and self-sacrifice thrive in a world that Darwin tells us ought to favor selfishness? We follow up on that idea with Jerry Wilkinson, chair of biology at the University of Maryland-College Park, who describes an amazing discovery he made in 1977 that revealed an entirely new way of explaining selflessness.