Theoretical Biology and Complexity: Three Essays on the Natural Philosophy of Complex Systems is made up of three short essays-each separately conceived and written, each with distinct thrusts and emphases, but nevertheless closely related in substance and spirit. All three spring from a common concern: to grasp and comprehend the material basis of living systems. The first essay is about the interaction between particles and the consequent observable manifestations. It casts the analysis of the measurement process into an elegant dualism relating modes of description, and explores the conseq