The complexity and scale of global urban development over the next quarter of a century will demand radically new approaches in development towards global sustainability (Elmqvist et al. 2018). The world’s urban population has grown from about 200 million in 1900 to 3.9 billion in 2014 and will likely reach 6.4 billion people in 2050. Over the decades to come, rapid urbanization will therefore continue, particularly in Asia and Africa. In the mid-century, 65% of populations in developing countries and nearly 90% in the developed world will live in urban areas (United Nations 2014). Cities all over the world are even now experiencing multiple impacts from global environmental change, especially climate change and land degradation, and the degree to which they must cope with and adapt to these challenges will continue to increase. While traditional, narrowly focused, planned/engineered design strategies are clearly needed to avert or mitigate such impacts in certain well-defined contexts, they are unlikely to be able to meet the full social, environmental and economic goals of cities, most notably the need for healthy, sustainable urban environments (e.g. Sustainable Development Goal 11). Strong path dependency often dominates urban development, and investments in urban infrastructure designed to fulfill one function may frequently create lock-in situations that persist over decades or even centuries. We argue that a multidisciplinary, complex systems approach, inspired by evolutionary theory, can inform the strategic design of policies and interventions to deal with challenges of growing urban regions and uncertainties in various scenarios in reducing undesirable path dependencies. Such an approach would guide the design of new (and redesign of existing) urban structures, while promoting innovative integration of grey, green and blue infrastructure in service of environmental and health objectives. Moreover, it would contribute to more flexible, effective policies for urban management and the use of urban space.

In a landmark 1977 article, Nobel laureate François Jacob made note of the highly flexible, opportunistic character of evolutionary progress, which he labeled “tinkering” (Jacob 1977). Evolutionary tinkering involves the modification and molding of existing traits and forms, which occasionally results in dramatic shifts in function in the context of changing conditions. This contrast greatly with conventional engineering and design approaches that apply tailor-made materials and tools to achieve well-defined functions that are specified a priori.

Here, we explore the idea of Urban Tinkering as the application of this evolutionary approach to urban design, engineering, management and governance. We define urban tinkering as:

“a mode of operation, encompassing policy, planning and management processes, that seeks to transform the use of existing and design of new urban systems in ways that diversify their functions, anticipate new uses and enhance adaptability, to better meet the social, economic and ecological needs of cities under conditions of deep uncertainty about the future.”

We see the discourse around evolutionary tinkering as a source of inspiration on how to navigate an urban future dominated by deep uncertainty, complexity and non-linearity. The tempo and intensity of climate changes are not known, and a flexible approach to urban design must be entertained. In this sense, admitting to our ignorance of future conditions may be the most intelligent design assumption. Urban tinkering is relevant not only to the design and planning of future infrastructure, but also to management and use of existing and planned urban spaces/structures. With new understanding of the values of ecological services in cities (Elmqvist et al. 2015), there is growing interest in increasing the links among ecological structure and other layers of urban design. To achieve the latter, approaches that encourage repurposing, experimentation, and innovative usage of existing elements are key. If well designed, an urban tinkering approach may help to reduce costly lock-in situations by incorporating infrastructure with an inherent potential to change function where needed or desired (Table 1).

Table 1 Proposed differences between conventional approaches and tinkering approaches

Linkages between evolutionary theory and the built environment are far from new. Indeed, new understandings of adaptation in evolution have at times been inspired by observation of the built environment, architecture and design—the opposite of the relationship considered here. For example, in their highly influential paper “The spandrels of San Marco and the Panglossian paradigm,” Gould and Lewontin (1979) discussed how views of adaptation in evolutionary theory could be informed by insights into architecture and design, elaborating, in particular, on the ornamentation of spandrels—the tapering triangular spaces formed by the intersection of two rounded arches at right angles. Spandrels are the necessary architectural by-products of mounting a dome on rounded arches. In many buildings, such as the Cathedral of San Marco in Venice, Italy, they are occupied by exquisite paintings and illustrations, as elegantly described by Lewontin and Gould. The analogy here is that the spandrels were not designed de novo as a space for paintings and illustrations, but were a by-product with no specific function, later used to fulfill other functions. Similarly, in evolution, Lewontin and Gould argued that many organismal traits for which we try to ascribe an adaptive explanation may in fact have no adaptive value, or maybe secondarily modified (but see critical discussion in Queller 1995).

Theoretical linkages between the built environment and evolutionary theory are thus long-standing, and not only restricted to the natural sciences. Such approaches have been adopted in social sciences and engineering; for example, in accounting for technological change and the dynamics inherent in any social process (e.g. Dosi and Nelson 1994), or in understanding the patterns and processes of urban environmental change (Bai and Imura 2000). Specific applications often highlight the need for flexible policies and governance systems which facilitate bottom-up innovation (Kronenberg and Winkler 2009). Naturally, evolutionary approaches are also characteristic of analyses of social–ecological systems which explicitly assume co-evolution and mutual dependence of social and ecological components. The shift in thinking (with respect to dominant paradigms) needed to implement such approaches implies the need for a concomitant shift in the values of key actors and those of society at large.

We emphasize that the use of evolutionary insights in this paper is but a lens. We acknowledge the many obvious differences between urban development and evolving biological systems, such as the effects of human foresight and anticipation, innovation, and dissemination of ideas over large spatial scales. Such features may help to reduce the high transaction costs often observed in evolution in biological systems (i.e., high rates of extinction). This is not to suggest that tinkering emphasizes the economic efficiency central to dominant neo-liberal economic paradigms. Quite the opposite: tinkering allows for redundancy, diversity and complexity, and emphasizes precautionary repair and replacement, all of which favor the efficient functioning of a system as a whole, but not necessarily its individual processes. Indeed, the efficiency of a given social or economic process must be considered in the context of other processes necessary to its execution, and more generally, with respect to the functioning of the whole system.

The definition of urban tinkering adopted here relates closely to concepts already familiar in urban development, e.g., urban sustainability experiments and transitions, urban system innovations, adaptive management, ecosystem-based adaptation to climate change, nature-based solutions, and urban experimental labs (see e.g. Elmqvist et al. 2018; Bai et al. 2010). Urban tinkering may also be viewed as a conceptual cousin to “urban acupuncture” (Lerner 2014), “tactical urbanism” (Garcia and Lydon 2015) and similar ideas.

In our interpretation, however, tinkering includes some dimensions not captured by these other concepts; in particular, it explicitly stresses a social–ecological–technological complex systems perspective on the multi-functionality of new and existing urban structures, developed through collaborative engagement and analysis with a range of actors. Although urban tinkering in some ways resembles a combination of adaptive management and adaptive governance, it adds an important proactive dimension, anticipation, to these more reactive approaches. In addition, tinkering implies a dimension of curiosity and playfulness in experimentation and repurposing urban systems often lacking in other approaches (Table 1 and examples in “Box 1”).

Urban tinkering, architecture and design

Urban tinkering has close parallels in the creative design disciplines, among them architecture (including landscape architecture) and design. Architects and designers use well-established methods for creating solutions integrated into their unique social/physical/ecological context (Glanville 2007). Designers do not regularly communicate with ecologists, but the different training and vocabulary of these disciplines can be merged for a wider perspective to address new urban landscape needs (Palazzo and Steiner 2011). This will require a professional interplay that is atypical and can be tense (Handel 2014). Urban tinkerers can learn from such approaches, applying their strengths in other contexts while avoiding their shortcomings.

In simultaneously addressing the potentially conflicting demands of diverse stakeholders, architects develop designs through iterative feedback cycles (e.g. Kennedy-Clark 2013; Zimmerman 2010). Each cycle of design and testing provides new information for future revision towards greater synthesis (Amiel and Reeves 2008). Feedback cycles often engage a variety of stakeholders to provide more diverse perspectives on proposed design outcomes. However, the feedback cycles so critical to integrated design typically end before the project exists in the real world. In contrast, tinkering extends this feedback process indefinitely throughout the life of the project, through a process of ongoing critical reflection and revision by stakeholders. Additionally, critique in design approaches is typically based on the imagined outcomes of a design process. This means it is limited by the imagination, foresight and empathy of the designer. Urban tinkering expands this critique from theory into practice based on the lived experience of those involved.

Such ‘live editing’ approaches should not be seen as a substitute for foresight. While testing urban infrastructure amid real-life complexity is far more rigorous than imaginative/hypothetical testing alone, it also requires large investments of time and resources. Where foresight is possible, it is far more efficient to test proposals ‘on paper’ before committing resources to build infrastructure—it is easier to move a line than a wall. Architects routinely develop a design through many hundreds of iterations using sketches and models. This is where informed human foresight and anticipation is an important addition to the evolutionary process. Many existing professional methods for envisioning and shaping future outcomes will remain important for urban tinkering, including critical reflection, scenario modeling and stakeholder critique.

In our vision, tinkering is not confined to the very local scale of, e.g., houses and neighborhoods, but could well include larger spatial scales as whole cities or regions (see “Box 1”). Some critical urban functions (e.g., mobility and water management) are best addressed at larger scales, and cumulative adjustments of smaller-scale components can serve as the basis for systemic transformation. A tinkering approach could, for example, shift transportation networks or storm water systems into more modular structures where sub-components have higher autonomy and thus lend themselves more easily to experimentation. So many urban areas are coastal; with rapid sea level rise effecting regional centers, solutions for only local landscapes will be overwhelmed by impacts on adjacent areas. Only a wide-scale solution can be effective. There is also a large untapped potential for combining subsystems (e.g. transport, information, or green infrastructure) of the larger social–ecological–technological system such that, under changing conditions, they carry out old roles in new ways or take on new ones.

At larger scales, of course, the potential complexity of tinkering approaches increases, and coordination becomes more necessary. Larger-scale tinkering with systems like interstate rail and integrated power grids requires support from large-scale actors like regional and state governments. To serve as a comprehensive approach for whole city-regions, urban tinkering must combine agile, user-driven, bottom-up approaches with far-sighted, expert-driven, top-down approaches (see Table 1).

Principles of urban tinkering

Tinkering approaches can generate inspiration and new ways of thinking in a fragmented urban world characterized by deep uncertainty, complexity and non-linearity, contrasting with many current more linear views (Fig. 2).

Fig. 2
figure 2

A linear traditional approach compared to the multifacets of tinkering approaches

The authors of this text span a diverse disciplinary background, including professional engineering, design, architecture, political science, evolutionary ecology, health and urban practice. Based on our collective experience, we propose six cross-cutting principles for successful tinkering.

Diversity of approaches

To generate improved outcomes, tinkering should embrace experimentation; i.e., it must generate a diversity of approaches to existing challenges (Fig. 2). This can be accomplished via permissive policy or regulation for the use of space or existing elements of the built environment or through the a priori design of infrastructure adaptable to multiple functions (see example in “Box 2”). Most experiments will fail or achieve less-than-optimal outcomes (just as with evolution itself), yet the aggregate result of experimentation is the progressive discovery of improved function. The tinkering approach also constitutes a strong argument for equity, as the inclusive participation of diverse stakeholders—including those that are marginalized from mainstream debates—will contribute to the requisite diversity in approaches. To draw further parallels with the living world, it seems likely that cities, the sites of relentless small-scale experimentation, will mirror ecological systems in progressing along characteristic pathways of maturity in development—i.e., ecological succession. Increased attention to the feedback loops involved in this process, and a focus on understanding collective, emergent changes in the structures of urban components over time and the underlying systemic features that favor one over another may help inform the type, location or scale of desirable tinkering approaches.

Shift in function

Often, tinkering approaches will lead to reimagined uses for existing urban elements (Fig. 2). To some extent, this is possible even with highly specialized elements (see example in “Box 3”). However, there will also be benefits to incorporating relatively unspecialized elements in urban design, to explicitly allow for multiple or shifting uses. For example, accessible public spaces are widely recognized as a critical feature of healthy cities, in part because they can be used by a wide variety of stakeholders to provide a diversity of social, economic, cultural and environmental services (see “Box 2”). There may be a role, too, for modular mobile structures that can be adapted to different uses or easily removed, replaced or combined according to need. Based on the principle that nothing is useless, old shipping containers, for example, have been used for everything from living spaces to restaurants to hotels to sanitation facilities to hospitals. For such outcomes to be successful, as with many of the tinkering approaches, participation among diverse stakeholders is key: one must draw from many points of view to give birth to novel ideas, escaping the constraints of tradition or common use. Playful imaginative experimentation, in a tinkering approach, can be useful in identifying valuable shifts in function.

A universal opportunity for urban tinkering can be on sanitary landfills which are infrastructure features worldwide. These sites are defined as engineering solutions to solid waste but have the potential to add value to many urban needs. The vast landforms can be sites of ecological structure, social amenity spaces (sports, family gatherings, urban agriculture) if the planning perspective can be changed. Each landfill site has a different potential, constraints by soil quality, adjacent land-uses, and economic needs, but “engineering” as the typology may be discounting the land’s highest value. Experimentation with different, new end-uses can bring new values to land parcels often considered derelict (Handel 2013).

Sense of place

Solutions obtained through urban tinkering are highly local, reinforcing the importance of place-based methods and the participation of local stakeholders (Table 1, Fig. 2). Often, a new function will arise out of the novel juxtaposition of otherwise familiar elements—by definition a local phenomenon (see example in “Box 4”). Juxtaposition need not be merely physical, but can involve linkages which produce its equivalent in social space. Opening urban spaces to tinkering approaches depends on a deep understanding of the relationships of people to places. Thus, for example, work emerging around the use and enjoyment of urban nature hints at the need or desire for a ‘facilitated’ nature experience (Brill 2017; Baigrie 2014). There is evidence to suggest that, in an urban setting, small signifiers that demonstrate the validity of multiple functions are extremely useful both in rendering hard infrastructure more accessible (for example a ladder into a dam to allow for swimming) and in making ‘wilderness’ more accessible (for example a toilet at a picnic site, or a bench). Small interventions, ‘signifiers’, small acts of ‘tinkering’, can serve to make urban features more accessible and potentially more equitable (and just). Indeed, such acts can expand the sense of ownership and belonging and allow for the kind of civic partnerships that can be useful in managing cities, particularly those that face fiscal constraints.

Remnants of past ecological structure and function exist in many urban centers, often in interstitial areas surrounded by large commercial or residential zones. These can be celebrated as mementos of preexisting ecologically functioning landscapes, and serve as reminders, not just of nature lost, but of the potential to restore lost landscape functions for a healthier future. People respond to the experience of urban nature as a guidepost to a most useful landscape (Lerner 2018).

Coordination—adaptive management, adaptive governance—anticipation

There is room for both top-down (e.g., policy/regulation, large-project repurposing, structured experimentation) and bottom-up (e.g., local innovation, unstructured playful experimentation) approaches in urban tinkering, as well as for the combination of adaptive management, adaptive governance and anticipation. Critically, top-down approaches involving regulatory or policy action can fully complement bottom-up tinkering approaches, providing space, resources, opportunity and encouragement for local innovation (see example in “Box 5”).

Extended time horizon

In biological systems subject to natural selection, the criterion for success is simple and obvious: survive and reproduce. In the context of a tinkering approach to urban development, success may be much less obvious, and will require new metrics.

For example, the success of a tinkering approach should be measured in the aggregate, rather than in individual projects, since new challenges and opportunities are identified throughout the life of a project. The necessary temporal scale may also vary significantly. On the one hand, a particular tinkering effort may be ephemeral but of great value, opening opportunities for further important downstream actions. On the other hand, quite a long interval may be needed to assess the value and efficacy of a tinkering paradigm.

This may be illustrated in the many urban areas near oceans, where the continuing sea level rise challenges infrastructure, residences, and coastal habitats. The large-scale urbanization near coastal zones creates a landform constraint where habitats (important for marine and well as upland ecological functioning) cannot migrate to higher ground when current sea–land edges are inundated. This is “coastal squeeze” where habitats are trapped and lost. However, without a reliable prediction of the degree and timing of sea level rise, tinkering with a variety of landform modifications may be necessary for ecological and economic sustainability (see “Box 6”).

Design of new landscape architecture projects must also recognize the rapid shift of vegetation zones that is now occurring (Grimm et al. 2013). Designs based only on current conditions denies the dynamic conditions facing today’s habitats. Stasis is not possible, and new approaches to tinkering with landscape design may be broadly necessary. Landscape elements, woodlands, meadows, shrublands, will shift in response to local climate and soil conditions if dispersal rates keep pace with climate shifts. A mosaic of habitats selected to reflect many possible future habitat placements can allow movement of species. In this sense stasis of a living landscape design is replaced by a suite of tinkering gestures, acknowledging that the habitats will reposition, in a currently unknown way. Again, admitting ignorance of the future advances the urgency of tinkering for resilient landscape structure.

Multi-systems approach

Conceptually, tinkering shares much with systems approaches, the two critical elements of which are analytic modes that can capture complex feedbacks, especially across sectors, and broad processes of engagement across stakeholder domains (e.g., public, private and civil sectors). Tinkering is a local manifestation of such approaches wherein actors from across society create joint experiments to achieve common goals. While the analytic component may be implicit in tinkering approaches, tinkering necessarily avails itself of feedback processes and draws upon cross-sectoral engagement.

A critical component to tinkering is social opportunity. Space (social, policy and physical) needs to be created for opportunities that allow for interventions or tinkering—opportunities to design in unconventional ways, to make innovative suggestions, to approach things differently. Significantly, these spaces, or gaps, can allow for champions (i.e., tinkers, in this reimagining) to emerge. People must feel empowered and unfettered to act, to try, to fail, to try again (“Box 7”). The literature suggests that champions emerge as a result of a particular set of personal characteristics (Howell 2005), but there need to be openings for these characters to emerge. The importance of individual citizens contributing to innovation, diversification and experimentation in, e.g., urban green space governance is often noted (Buijs et al. 2016; Mattijssen et al. 2017). Authorities need to allow flexibility with regard to mechanisms for bottom-up problem-solving, hence some system of flexible governance is required, as with urban commons (Colding and Barthel 2013) or so-called mosaic governance, which allows for context-sensitive planning, enhancing relationships between the diversity of landscapes and communities across cities (Buijs et al. 2016). The kind of social space that allows for this is often shunned as unconventional, time-wasting, or unproductive in the traditional economic sense. Inversely, the danger or blockage to useful redesign or rethinking around infrastructure and practice is restricted access. The sense of ‘license to act’—to engage, to fiddle with things—is critical to the process of tinkering.

Caveats and challenges to global sustainability

Finally, achieving the critical, but extremely challenging task of transforming social, economic, ecological, and technical infrastructure systems toward global sustainability in the long-term will require more than adding up combined tinkering efforts of cities. Although in our view, urban tinkering may have a tremendous potential to bring together fragmented dimensions of urban development, it is not a panacea. It is unlikely to, by itself, effectively address all the urban challenges we face, nor to deliver the kind of transformative change and at the scales and magnitude required to meet the sustainable development goals. It is also unlikely to completely displace conventional engineering from large-scale planned infrastructure.

Furthermore, no matter how transformative urban tinkering efforts are, we cannot assume that global sustainability and the successful implementation of SDG11 and the New Urban Agenda will be a granted as an end result. In fact, there are likely to be significant trade-offs, contestations, conflicts and unforeseen side effects and consequences of urban sustainability initiatives at all scales. To address these challenges, local and regional tinkering initiatives may need to be combined with a new globalization taking on a new face with a multipolar world developing, with thriving local and regional social, cultural and ecological diversity and governance, and where a new urban–rural regional integration is possible. Moving forwards requires flexibility, understanding of what determines learning, visions and imagination, and open-mindedness to deal with the unexpected, challenges and opportunities and deep uncertainties.