Through self-organization, a system becomes ordered in space
and/or time, often leading to emergent properties that
qualitatively differ from those of its individual units. The
reductionist approach — systematically dismantling complex
systems to examine individual components — has been successful
for the sciences over the past few centuries, from the isolation
of the elements in chemistry, the discovery of atomic and
subatomic particles in physics, to the purification and study of
proteins, DNA and RNA in biology. Although this reductionist
approach in biology will continue, there is increasing interest
in determining the properties of systems of interacting
biomolecules. How do networks of proteins and genes integrate
and respond to signals? How do dynamic organelle structures,
such as the mitotic spindle, form? What controls growth and
division? How does the genome create an organism? Self-
organization is central in these processes1, at various sizes
(Fig. 2). Self-organized systems differ from self-assemb