Mehaffy and Salingaros draw a number of lessons from biological systems and use them to draw conclusions about how resilient human systems must be designed. Here’s what they suggest resilient cities must be like:
1) They have inter-connected networks of pathways and relationships. They are not segregated into neat categories of use, type, or pathway, which would make them vulnerable to failure.
2) They have diversity and redundancy of activities, types, objectives, and populations. There are many different kinds of people doing many different kinds of things, any one of which might provide the key to surviving a shock to the system (precisely which can never be known in advance).
3) They have a wide distribution of scales of structure, from the largest regional planning patterns to the most fine-grained details. Combining with (1) and (2) above, these structures are diverse, inter-connected, and can be changed relatively easily and locally (in response to changing needs). They are like the small bricks of a building, easily repaired when damaged. (The opposite would be large expensive pre-formed panels that have to be replaced in whole.)
4) Following from (3), they (and their parts) can adapt and organize in response to changing needs on different spatial and temporal scales, and in response to each other. That is, they can “self-organize.” This process can accelerate through the evolutionary exchange and transformation of traditional knowledge and concepts about what works to meet the needs of humans, and the natural environments on which they depend.By contrast, as the authors detail, our existing cities are for the most part non-resilient.