From Ward's new book, Life as We Do Not Know It
"Extraterrestrial life, in Ward’s view, may be so simple that scientists will have difficulty recognizing it as life. In fact, he argues, the scientific community has defined life on Earth too narrowly. He suggests the tree of life be modified to include viruses (currently seen as nonliving because they cannot replicate without a host) and maybe the disease-causing proteins known as prions. Some viruses contain RNA rather than DNA, prompting Ward to speculate that our own planet may harbor yet-unknown RNA life."
http://www.tcsdaily.com/article.aspx?id=012206B