A MINGLED YARN

The behavior of nonliving and living systems is generally viewed as be ing qualitatively different. The key difference is often summarized by saying that whereas living systems are complex, nonliving ones are si mple. This distinction is often the basis for claiming essential diffe rences in conceptual stances, methods, and theories between scientific fields. I argue first that nonliving systems can display the unpredic table, irreducible, irreversible, and emergent-in sum, complex-propert ies of living systems. Then I discuss an emerging field called complex ity theory, the principles of which offer the promise of bringing quan titative unity to an enormous range of phenomena, living or dead.