Medical writer Robin Marantz Henig is a frequent contributor to The New York Times Magazine, the Washington Post, Mirabella, and Vogue. Her new book, "A Dancing Matrix" is about the work being done to understand viruses. The field has taken on new urgency since the spread of the AIDS virus. Hening says scientists have realized that emergence of a new virus is not as rare as previously though, and that it's caused mostly by human error rather than genetic mutation. They add that stresses on the ecological system can alter the balance between people and microbes, and can lead to an outbreak.