Cities and their complexities are part of a biological system, where human developments are influenced by successful past achievements. Cities are manipulated by and created from their particular set of conditions; the components may be advanced through the collaboration of every citizen's interaction with the whole, which may not be completely predictable and fulfills no calculated "optimal future form1." It is the interaction of people with their environments, both natural and technical, over time that creates an evolution of the city: Geddes' Work-Place-Folk triad. I believe this concept of co-evolution can be related to Kiesler's theories on Correalism which he defines as "the dynamics of continual interaction between man and his natural and technical environments" 2
Darwin's theory of evolution is the result of natural selection, where future development is random and follows only one rule: the survival of the fittest. Geddes' theory of evolution differs; he believed Darwin gave too much emphasis on natural selection and the struggle for existence. Furthermore he believed that humans have control over our evolutionary nature and our morals of idealism have led us to an evolution based on synergy and co-operation, where he saw evolution happening despite natural selection. Geddes believed that the ideals, perceptions, and activities of the individual are all accounted for in the makeup of the whole. This repetitive feedback loop pushes societies to evolve further. For example when a high percentage of the population chooses to buy their groceries online and have them delivered to their doorsteps, the size and number of brick-and-mortar grocery stores decreases. This can be related to the "actant effect" as described by Jane Bennett in Vibrant Matter3. Cities can be viewed as environments themselves, where they influence the behaviors of its inhabitants and the actions of the inhabitants affect the city-thus creating a constant feedback loop for potentially positive evolution where all aspects of society affect change. Changes that co-evolve and fit into standardization transform into higher, more sophisticated standards, whereas when things deviate from a standard they decline and ultimately die.
An urban planner must propose schemes for urban development adaptively, amid the intricate dynamic that relates all of the city's elements. Planners must also use an approach which combines successful traditional models as well as technologically advanced innovative city forms.4 In terms of intentional modification, Geddes believed gradual changes happened naturally over time, so modifications to the city should be minor-conservative but continuous in order to give the city freedom to change for the better. Geddes applied his conservative surgery methods in the slums of Edinburgh, Scotland; and while working in India in Tanjore for the Madras Presidency, where he enlarged existing lanes rather than enacting mass demolition of existing structures. He removed only the most dilapidated and unsanitary structures so as to allow every house to have access to light and ventilation.5
Historically cities have been parasitic, where they draw upon the weaker countryside for resources ranging from soil for growing food, to a labor force, and even the fresh genetic variance of new migrants. When a city runs out of resources, it reaches out to colonize new territories to engage new supply lines. These conglomerations of cities, towns and regions form an agglomeration Geddes refers to as a conurbation. This linking of different people and places that live in coisolation can be related to Peter Sloterdijk's conception of foam. Where urban interaction affects relationships and interconnectivity when a city becomes larger the density of the foam increases small egospheres collect in a larger network of evolving organisms.
According to Marshall and Batty, recent developments in urban theory-including theories of self-organization and nonlinearity-have called the predictability of historical sciences into question. They conclude that "cities are emergent and adaptive, and that we cannot expect them to stay in a state of equilibrium, as they are intrinsically unstable and always in flux." Therefore cities do not reach an ideal form but rather move from one semi-stable form to another. DeLanda states in The Nonlinear Development of Cities that cities contain two contrasting systems at play: The first is command hierarchies where homogeneous structures prevail and alien (heterogeneous) elements are weeded out; everything is arranged in a hierarchy. The second form is self-organizing where a more heterogeneous mix and an articulation of diversity prevails. Cities exist as a mix of command hierarchies and self-organizing systems where the marketplace is self-organizing and the state bureaucracy holds the position of command hierarchy. "No one entity determined the flow of goods and a global order emerged spontaneously out of the interaction of many different agents; commercial towns tend to be highly heterogeneous with an articulation of diverse elements whereas state towns tend toward formations of homogeneity of ideas and values."
Some implications of Geddes theory on town planning are that a planner will always start with a civic survey from which they can create a diagnosis. From there it is possible to design a plan-one cannot predict the future needs of a city without knowing its past, and one cannot build houses without studying where people want to work.4