Obsessed with its beauty, humbled by its flaws, humans are covered by a unique ultra-thin shield that instantly defines and shapes the body living inside it. Now, National Geographic invites you on an in-depth adventure revealing not just the science but the vital cultural meanings we attach to this largest of all human organs. A trip back in time explores the evolution of human skin - and the rainbow diversity of skin color today. Cutting-edge research unveils the role skin plays in human sexual attraction. And we go beyond biology to trace the influence of skin on our perceptions of race, our skittishness about nudity and the intriguing riddle of personal identity.

Evil. Is it a spiritual force, a meaningless superstition, or does it lay in the depths of our conscience? In Science of Evil, encounter the soul of serial killer Jeffrey Dahmer through the eyes of the priest who baptized him. Travel to war-torn Democratic Republic of the Congo with a UN official charged with administering food and medical help. And join scientists as they use cutting-edge fMRI imaging techniques in an effort to isolate the brain's mechanics of moral judgment.

National Geographic gets to the science behind what makes a man manly - his Testosterone Factor. It's one of the most important and powerful hormones in a man's body, but how does it really impact the men in your life? National Geographic presents the latest insights from leading researchers in psychology, biology and anthropology to reveal testosterone's fascinating influence on strength, status, success and even commitment.

Over the last three decades, science has been advancing our understanding of stress - how it impacts our bodies and how our social standing can make us more or less susceptible. From baboon troops on the plains of Africa, to neuroscience labs at Stanford University, scientists are revealing just how lethal stress can be. Research reveals that the impact of stress can be found deep within us, shrinking our brains, adding fat to our bellies, even unraveling our chromosomes. Yet understanding how stress works can help us figure out ways to combat it and how to live a life free of the tyranny of this contemporary plague. In Stress: Portrait of a Killer, scientific discoveries in the field and in the lab prove that stress is not a state of mind, but something measurable and dangerous.

You climb into bed, turn off the light, and close your eyes, but you can't fall asleep. For most of us, it's just one annoying night, but for people with fatal familial insomnia, or FFI, it's the beginning of the end. An extremely rare genetic disease passed down through generations, FFI's primary symptom is sleeplessness, but with a fatal twist: victims are dead within months. To understand FFI, National Geographic delves into the science of sleep-the most elusive biological function we have-to find out why we need sleep and what happens to us when we don't get it. Witness the pioneering research inside the sleeping brain as well as the mind forbidden to rest for days at a time.

Science may be on the verge of producing a limitless supply of replacement parts by regenerating damaged or aging body parts grown from our own cells. Imagine the implications if we could custom make body parts genetically indistinguishable from our own. Could it eliminate the death sentence for profound birth defects, the need for prosthetics and any shortage of transplant organs? National Geographic delves into the science of tissue engineering and tracks how scientists are beginning to harness the body's natural powers to grow skin, muscle, body parts and vital organs, even hearts.