How do we define life? This lecture reviews the six basic criteria

for living systems described by biologists: order, reproduction, growth and

development, energy utilization, reaction to environment, and evolution

that characterize life. The last third of the lecture is an admittedly

whirlwind review of natural selection (I got off my stride and got a

little rushed for time at the end). The goal is not a complete survey

of current biological thought, but to highlight those characteristics of

"life" that may best inform us as to how to look for signs of life

elsewhere in the Universe. Recorded live on 2009 Oct 12 in Room 1005

Smith Laboratory on the Columbus campus of The Ohio State University.