It is a common observation that our present society is more complex than any of the societies or cultures which preceded it. This entails that the problems this society, and the individuals who are part of it, must confront are more complex than they ever were. Understanding complexity seems to be the only possibility for escaping this evolution in which everything seems to become more uncertain, more complicated and more changeful.
It is argued that in order to solve complex problems we need a new approach, which is neither reductionistic nor holistic but based on the entanglement of distinction and connection, of disorder and order, thus defining a science of complexity. A model of complex evolution is proposed, based on distributed variation through recombination and mutation, and selective retention of internally stable systems. Internal stability is then analyzed through a generalized mathematical closure property. Examples of closure in self-organizing and cognitive systems are discussed.