The dream of placing the study and planning of cities on a scientific footing has long captivated urbanists, from Patrick Geddes and the Chicago school of social ecology in the early 20th century, to Michael Batty and the Santa Fe Institute today. Most of these attempts have built on and variously adapted Darwin’s theory of biological evolution to explain and shape urban change: here is, for example, Batty,[1] ever optimistic about the prospects of what he calls not a but the new science of cities, 'blend[ing] economics with physics in a manifestly evolutionary, neo-Darwinian framework'. In fact, the history of modern urbanism could be told as a history of analogies between natural evolution and urban change centred around the notion that cities are complex, self-regulating or self-organising organisms, analogies that urbanists have used both to justify the need for rational planning and to argue against it.

One of the key figures in this tangled genealogy is the Scottish landscape architect Ian McHarg, who built on Darwin’s theory of evolution and Howard T. Odum’s systems ecology to emancipate the field from its role as a form of decorative gardening. In the 1950s he established the landscape architecture program at the University of Pennsylvania, which grew to become an influential hotspot of ecological urbanism. He was convinced that urbanisation wreaked havoc on the planet, and that architecture should foreground the value of natural ecosystems. McHarg has had many followers but few critics, and the current climate crisis has stimulated a renewed interest in his work and legacy: last year, the McHarg Center for Urbanism and Ecology was established at the UPenn, on the occasion of the 50th year anniversary of his landmark publication Designing with Nature (1969).

McHarg is an interesting case because it allows us to tease some of the assumptions that have underpinned the notion of making urbanism scientific. In my current book project, I discuss McHarg as one of the vectors through which systems thinking has been domesticated in the field of urbanism. I am focusing on his work not to endorse it but to trace the antinomies that riddle his conceptualisation of cities, nature and design. Here I want to briefly look at the role in McHarg’s theory of the concept of fitness.

Thus, in the 1970 essay 'Architecture in an ecological view of the world,' McHarg argues that we can objectively distinguish progressive (evolving) from retrogressive processes, and that this relates to what he calls environmental fitness, drawing on Darwin, Geddes and other evolutionary thinkers, such as Lawrence Henderson, the author of the influential book The Fitness of the Environment (1913). For McHarg fitness is about being adapted for survival, and architecture is 'a business of fitting'. 'There is a requirement,' he exhorts[2] architects, 'not only to find the most-fit environment but also to adapt that environment and/or yourself in order to accomplish fitting.'

I want to draw attention to the notion of adapting environment and ourselves becoming a purpose of architecture, which I think can be described as 'neo-evolutionary' so as to distinguish it from Darwin’s emphasis on evolution not being consciously directed. As is well known, in the 5th edition of On the Origin of Species, Darwin replaced 'natural selection' by the phrase 'survival of the fittest,' coined by the British proto-libertarian sociologist Herbert Spencer, acknowledging that the original term was imprecise because it implied conscious choice. McHarg turns the concept upside down so that it becomes a process of 'fitting' in order to ensure survival: fitness is something that ought to guide the work of architects and be the measure of its success (in my research I also explore Batty’s similar use[3] of the verb 'evolve' as something that urbanists do).

This is of course hardly surprising, given that McHarg sought to adapt the concept of fitness in a field that is fundamentally about shaping urban change. Rather the interesting question is, according to what criteria and using what method does a McHargian designer evaluate current or future environments as being or not being fit? McHarg’s departure from Spencer’s use of biological analogies to defend the status quo is only ostensible. Overextended from biology to urbanism, evaluating fitness is a business of cost-benefit analysis, a systematic process of comparing the costs involved in doing something to the advantage or profit that it may bring. While it seems that McHarg draws on ecological science to challenge the narrowly economistic view of the world, there is evidence[4] that the field of systems ecology which he looked up to[5] has already assimilated such view to conceptualise natural systems in terms of energy cost-benefit analysis.[6] A McHargian designer, being as she is in the business of fitting, draws on economic, environmental and other supposedly scientific analyses to provide an optimal distribution of functions within a given territorial 'ecosystem'.

The limits to environmental fitness as an urbanistic concept can be parsed by looking at the technique of map overlay method. McHarg developed the method in the 1960s when his firm, Wallace McHarg Roberts & Todd, specialised in consulting on highway and parkway route selection, resulting in two principal studies, A Comprehensive highway route selection method: Applied to I-95 between the Delaware and Raritan Rivers, New Jersey (prepared for The Delaware-Raritan Committee on I-95, 1965) and The least social cost corridor for Richmond Parkway (prepared for the New York City Department of Parks, 1968). To ensure the best fit, McHarg first identified categories to be considered: in the New Jersey study, for example, these were topography, urbanisation, land values, residential quality, historical values, agricultural values, recreational values, wildlife values, water values and susceptibility to erosion. For each category he then drew a map on a transparency, with colours or shades representing value on a scale from high (dark) to low (light). Next, these map transparencies were stacked into composite a map, focusing on values relating to ecology, property values or scenic views. The final result was a composite map of all values, with the lightest areas identifying the least-cost/maximum-benefit solution to selecting the route.

While individual maps were based on evidently arbitrary categories and assessment criteria, combined into a single overlay the evidence appears comprehensive and convincing. In the New Jersey study, as the landscape historian Margot Lystra[7] pointed out, property value data were factored in twice, weighing the outcome in favour of wealthy Princeton residents. Acknowledging that the method 'gave high social value to the wealthy and too little to the poor,' McHarg nevertheless insisted that, as he wrote in Designing with Nature, the method 'offered a large measure of success,' add 'any man, assembling the same evidence, would come to the same conclusion'. In the end, it is not just that map overlay appears more robust than data on which it is based, but that the banner of science is mobilised to normalise certain rather than other ideas about fitness, and what or who is thus construed as 'misfit' (a term that McHarg uncritically borrowed from the fellow neo-evolutionist Christopher Alexander). This is especially controversial when McHarg turned to design, such as the unrealised proposal for environmental park Pardisan at the outskirts of Tehran, in which the fitness imaginary underpinned the microcosmic representation of the world as a neo-colonial, cultural zoo.

Despite these flaws, McHarg’s legacy is broad and tenacious, extending from his role in the development of GIS, to his formative influence on the field of ecological urbanism, and the on-going revival of his ideas in the context of progressive proposals such as the Green New Deal. Scientism has been critiqued within all these strand of his legacy, but each has been marred by their own scientisms, from the politically detached field of GIS science[8], to the uncritical adoption by McHarg’s students and followers of equally controversial concepts such as resilience[9] or ecosystem services[10]. Given these conundrums, how should the link between urbanism and science be rethought? Certainly the postmodern idea of socially constructed science appears distant, especially as it has been caricatured and appropriated by the far right. Yet if now’s the time to 'listen to the scientists',[11] as Greta Thunberg urges us, how should progressive urbanists listen to the scientists while avoiding the pitfalls of McHarg’s apolitical scientism?