"The last 20 years have been marked by an astonishing growth in our knowledge about the molecules that make up living things. And among those molecules, none has attracted more attention than DNA. The DNA code of hundreds of life forms has been sequenced, and this code contains not only information needed to assemble all proteins; a myriad of bit and pieces of DNA are also involved in controlling when proteins are built and destroyed. It is thus not surprising that DNA has been called the software of life, but the metaphor breaks down when we look more closely. Contrary to any reputable software, small, random "errors" are introduced in the code each time DNA is copied in order to be transmitted to the next generation. Most often, these changes have no effect whatsoever. Almost all the remaining changes are deleterious and are most likely the cause of the many diseases that affect many human beings at some point in their lives. But a small portion of these random "errors" allow those who carry them to better adapt to the environment in which they live. And the fast and slow accumulation of those favorable "errors" is what ultimately gave rise to the immensely successful history of life in the planet. Two indispensable conclusions arise: first, disease is often caused by the same mechanism, random mutation, that allowed us to become conscious beings and, therefore, those of us who are healthy and can pursue happiness have a basic biological and ethical debt towards those who are not; second, the massive changes that we are introducing into the environment are making many of us sick simply because our ancestors never saw them and thus, never "adopted the right genes" for them. Contrary to all other species that ever existed, therefore, we are increasingly putting our future as a species in our own hands". - University of Arizona College of Science