The highly personal nature of the information contained in DNA can be illustrated by thinking of DNA as containing an individual's "future diary."

A diary is perhaps the most personal and private document a person can create. It contains a person's innermost thoughts and perceptions, and is usually hidden and locked to assure its secrecy. Diaries describe the past. The information in one's genetic code can be thought of as a coded probabilistic future diary because it describes an important part of a unique and personal future.

First, genetic information is powerful and personal. As the genetic code is deciphered, genetic analysis of DNA will tell us more and more about a person's likely future, particularly in terms of physical and mental well-being. The search for genetic information often involves locating predictors of undesirable and stigmatizing conditions - such as cancers, and conditions that lead to mental illness and dementia.

This information is uniquely sensitive for a number of reasons. First, unlike ordinary diaries that are created by the writer, the information contained in the genetic code is largely unknown to the person in whose genetic material it is found. Therefore, if this information is obtained by someone else without the individual's permission, another person would learn intimate details of the individual's likely future life. A stranger could, in effect, read the future diary of an individual without the individual even knowing that the diary exists. There are many people, including insurers and employers, to whom information about an individual's likely health future would be useful.

Second, deciphering an individual's genetic code also provides the reader of that code with probabilistic health information about that individual's family, especially parents, siblings and children. Third, since the DNA molecule is stable, once removed from a person's body and stored, it can become the source of an increasing amount of information as more is learned about how to read the genetic code. Finally, genetic information (and misinformation) has been used by governments to viciously discriminate against those perceived as genetically unfit.

Lee M. Silver