The human genome is no more than a string of four letters -- A, T, C, and G -- repeated over and over, more than three billion times. To the untrained eye, these letters, also known as nucleotides or bases, appear meaningless. But when scientists look at our genetic code, they can see an amazing story of human history and our connectedness to other creatures on this planet. They see long strings of code that are almost identical to the code in baker's yeast. They see the differences -- sometimes no more than a single letter -- that can mean the difference between health and disease. They see genetic code that has no known function but has repeatedly copied itself and hitchhiked across the human genome. They see densely populated regions, where genes are bunched up together, and vast deserts, with no meaningful code in sight. Here, explore an actual stretch of human DNA and see what the experts see.