To limit complexity in complex systems design, you need to be able to create agents which perform simple functions based on well-defined inputs. You can have a

To limit complexity in complex systems design, you need to be able to create agents which perform simple functions based on well-defined inputs. You can have a few different types of those agents interacting, and each should be discrete and be able to "survive" in an adequate "environment". Then the system, if designed correctly, can become much greater than the sum of its parts but you retain the relative simplicity to monkey around with the internals of the agents as well as the reservoirs to which they're attached, etc. Nature has seemed to become a system where iterative improvement is performed by virtue of the finite life cycle and sexual reproduction (including all the ways that DNA shuttles around the necessary source code).