Diet

It's no secret that we need calories to fuel our body's basic energy needs. Yet many of us find it difficult to take in the right amount—and the right kind—of fuel. No matter how many guidelines we're given, we still crave what we know is bad for us.

Cognition

Quite simply, cognition refers to thinking. There are the obvious applications of conscious reasoning—doing taxes, playing chess, deconstructing Macbeth—but thought takes many subtler forms, such as interpreting sensory input, guiding physical actions, and empathizing with others. The old metaphor for human cognition was the computer—a logical information-processing machine.

Sex

At least for humans, this most basic act is anything but simple. As the pioneering sex researcher Alfred Kinsey put it, the only universal in human sexuality is variability itself. Within the universe of intimacy and pleasure that sex affords, however, there's a lot of room for error. From the behavior itself to our orientations, sex never fails to be a provacative topic.