The Necessity of Complexity
Cities — crucibles of innovation and economic development, befitting the well-being and prosperity of inhabitants — possess what is arguably humanity’s greatest invention: the manifold exchange of diverse assortments of ideas. Social, economic, or otherwise, this dynamic is catalysed by propinquity; the aspect of ‘nearness’ engendering the recombinant mutation of information as it courses through cities. In economic terms, these processes are described as knowledge externalities or spillovers, which provide a mechanism describing how the diffusion and accretion of human capital can be both the cause and the consequence of human agglomeration1|2|3. The same processes and their requisite connectivity and diversity are of necessity mirrored in the urban structures of historical cities; ultimately, a manifestation of the deeper nature of complex systems.
A prescient synthesis of these ideas is provided by Jane Jacobs, whose vociferous attacks on the urban planning establishment4 and unorthodox forays into urban economics5 argued, at heart, that it is specifically diversity and its requisite complexity that provides the energising force sustaining vibrant economies and healthy neighbourhoods. From an economic point of view, the hallmark of Jacobs’ hypothesis is that this dynamic flourishes due to spillovers between diverse entities within competitive environments: Jacobs Externalities, as it is now known, has provided inspiration for formal economic models describing the role of the external effects of human capital as an explanation for economic growth6|(Desrochers2007), a view which has gained acceptance in economic research7|8|9 showing that increases to economic diversity are “strongly associated with increased output, productivity, and growth” (Quigley, 1998. pg. 136)10. A similar dynamic is observed for social heterogeneity and creative capital2. Importantly, these processes often cannot be observed at overly coarse or aggregate scales11. Ongoing developments in high-resolution geospatial analysis methods combined with improved granularity of data make it increasingly feasible to zero-in on the level at which this dynamic operates.
A common thread binds Jacobs’ ideas on economic development with her thoughts on planning, and arrives at the essence of her argument: misplaced emphasis on efficiency — at the expense of diversity — has resulted in forms of urban planning (and / or economic policy) that sever the necessarily complex webs of social and economic processes. She describes such approaches as ‘preformationist’, meaning that growth is erroneously assumed to be the result of the simple quantitative expansion of pre-existing and static arrangements, therefore leading to the mistaken impression that city processes are simplistic and should be engineered and optimised. The familiar mantras espoused by modernist architects: buildings are machines for living in; form follows function; less is more, even if legitimate and necessary criticisms of the state of architecture at the time, became debilitating once applied at the larger scale of neighbourhoods and cities12. Planners “declared themselves enemies of diversity, fearing chaos and complexity because they saw it as disorganized, ugly, and hopelessly irrational” (Harvey, 1989. pg. 74)13, masterplans consequently imposed idealised abstractions of social and functional order reinterpreted in the name of efficiency. Heavy-handed slum clearances and large-scale infrastructure projects subsequently dismembered the urban fabric, in some cases decimating entire neighbourhoods13|14|15. A more recent manifestation of the efficiency paradigm has emerged within Smart Cities and Digital Twins hype, positing that connected citizens and the ubiquity of urban sensors could streamline all manner of city services ranging from garbage collection to utility provision to citizen e-services. However, these notions are often accompanied by dark undercurrents: in spite of increasingly decentralised access to technology, systems are conceived and managed using centralised and top-down archetypes that are brittle and biased. Private interests may supersede public interests; lesser represented or underprivileged citizens may be bypassed by infrastructure networks; and large-scale idealised urban development schemes — sometimes with eerie resemblance to modernist masterplans — prove unable to support the complexities required by local economies or in support of vibrant streets16|17|18|19|20.
Jacobs emphasises that she “does not mean that cities are economically valuable in spite of their inefficiency and impracticality but rather because they are inefficient and impractical” (Jacobs, 1969. pg. 228)5, meaning that the very mechanisms underlying these perceived inefficiencies are a necessary dynamic for the development of cities and the reason for the agglomeration of people in the first place. She describes this as an ‘epigenetic’ view of growth, wherein processes of development arise as an accretive co-evolutionary process from overlapping ‘webs of interdependent co-developments’ (Jacobs, 2000. pg. 19)21. This entanglement of accidental and unstable combinatorial possibilities allows information to be combined in myriad unexpected and innovative configurations: it is these processes that lead to longer-term discovery and resilience, and it is also these processes that are incapacitated by the brittleness introduced by the efficiency paradigm. Jacobs’ thinking bears resemblance to Stuart Kauffman’s notion of supracriticality: The point at which a critical mass of inter-relationships may trigger explosions in the diversity of molecular species (Kauffman, 1995. pg. 116)22 and bouts of co-evolutionary development on coupled fitness landscapes to an edge of chaos23. Kaufman, in turn, explicitly connects these concepts back to Jacobs’ economic theories wherein ‘the web structure of an economic system is itself an essential ingredient in how that economic system grows and transforms and “diversity begets diversity, driving the growth of complexity”22 (pg.295–296). Thus, in complex systems terms, cities can be framed as The Visible Expression of Co-evolving Complexity24, or as dissipative structures harnessing flows of energy — in the form of ideas, relationships, and resources — constantly adapting in order to seek-out and maximise the beneficial use of these flows25. More intuitively, inspired by Darwin’s tangled bank analogy (Darwin, 1859. pg. 489)26, Jacobs likens these processes to high-biomass rainforests interleaving innumerably diverse assortments of species into complex cascades of interdependencies capable of extracting maximal benefit from the sun’s energy27. “Sunlight is captured in the conduit, it’s not only converted but repeatedly reconverted, combined and recombined, cycled and recycled…”21 (pg.46). Critically, Jacobs’ insight is that it is not simply the quantity of sun at an ecosystem’s disposal, but the complexity and richness in which the sun’s tendrils can be folded and interwoven to extract seemingly magical multiplicative gains, ergo the importance of complexity for the growth of economies and the adaptive resilience of neighbourhoods. These dynamics are necessarily complex, fluid, and unpredictable, and resonate strongly with contemporary complex systems interpretations of diversity and its rich history of ecological interpretations and methods14|28.
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