In This Issue
Winter Issue of The Bridge on Complex Unifiable Systems
December 15, 2020 Volume 50 Issue 4
The articles in this issue are a first step toward exploring the notion of unifiability, not merely as an engineering ethos but also as a broader cultural responsibility.

Evolving an Ecological Perspective

Thursday, December 17, 2020

Author: Simon A. Levin

François Jacob (1977), in his essay “Evolution and Tinkering,” brilliantly made the case that the world has self-assembled, constrained by history: Organisms have not been designed from scratch as the best solutions to the puzzles of survival and reproduction s, but are the products of a sequence of modifications to address strings of abiotic and biotic challenges. In fact, -Stephen Jay Gould (1989, pp. 45ff) proposed the thought experiment of “replaying the tape of life” and concluded that doing so would produce a different outcome.

Evolution and Interdependence

Ecosystems are complex, with interdependencies and, in the words of Charles Darwin, a “tangled bank” that is not the work of a master craftsman but, in Jacob’s metaphor, a tinkerer. The complex processes by which species come to exploit one another, compete for common resources, or depend on one another directly or indirectly have arisen by evolutionary self-organization.

Over time, to some extent the biosphere has become more and more interconnected, and the interdependencies in general confer a robustness through selection processes that distinguish them from what a randomly assembled system would look like. Ecosystems and the biosphere are, like physical and social systems, complex adaptive systems, made up of individual agents that adapt behaviorally, physiologically, or through genetic modification. Those changes produce emergent properties at higher levels of organization that feed back to influence dynamics at the level of the agents.

The word adaptive here refers to processes at the level of the individual agents, and there is no guarantee that what is myopically good for those agents will improve the long-term success of the system. The existence of patterns and processes on multiple organizational scales leads to conflicts both between the agents and the groups to which they belong and between the groups and the interests of the whole ecosystem or biosphere. People and the planet are suffering from conflicts today as selfish interests lead to activities that degrade the world and its resources. Garrett Hardin (1968), building on the ideas of William Forster Lloyd, described this as the “tragedy of the commons.”

Evolution and Robustness

In addressing the challenges facing humanity, much can be learned from the evolution of ecological systems. Natural selection has led to mechanisms that confer robustness, or else organisms would not survive to reproduce. At the system level, tight interdependencies have similarly been selected; but the process of transformational evolution, as elucidated by Richard Lewontin (1977), or what Tim Lenton and collaborators (2018) have termed sequential selection, can serve as a filter that ultimately produces more robust systems.

The features that lead to success through this transformational process are those that lead to better integration of lower-level mechanisms, akin to Elinor Ostrom’s (2009) notions of polycentricity. Local feedback loops, including direct and indirect mutualisms such as syntrophy, can create coherent units that are key to the robustness of the larger system. Such hierarchical arrangements, built on modular units, can be seen in genomes as well as in higher-order ecological assem-blages. They provide the basis for system integration and suggest the adaptive value of modular organization in systems more generally.

This raises questions about what features make systems robust or resilient, and even whether robustness is a good thing. The answer depends to a large extent on the scale. In general, robustness at the system level is crucially dependent on the lack of robustness at lower levels—that is, the ability of the system to reconfigure or replace components to adapt to change. Influenza A, for example, remains a scourge for humanity because individual strains are rapidly replaced by others that allow the virus to escape the population’s herd immunity. Robustness does not mean stasis; variation and exploration are common features that are essential to adaptation in the face of changing environments.

Identifying System Features of Robustness

To what extent has natural selection and transformational or sequential evolution led to increasing robustness over time, and how is that robustness manifest at different scales? What are the generic features of systems that confer robustness?

All of life involves the interplay between processes that generate variation and those that winnow or restrain it; indeed, recognition of this essential coupling is reflected in the basic law of evolutionary change, the fundamental theorem of natural selection (Fisher 1930). The physiology of organisms depends on -processes that drive dynamics and those that regulate it; when these get out of balance, pathologies result. In this way, financial systems, for example, are no different, in that high-speed trading and other innovations can outrun system regulation and lead to market crashes.

One of my favorite metaphors for designing for robustness is the vertebrate immune system, which has evolved to deal with both the predictability of assault by pathogens and the unpredictability of the nature of those pathogens and the timing of their emergence in populations. The immune system therefore involves the hierarchical and temporal deployment of generalized mechanisms, such as barriers and macrophages, and specific antibody responses that take time to develop.

General resilience is an important feature of any effective response system (Carpenter et al. 2012). Structural features that can confer such resilience include redundancy, variation, and modularity. Modularity is an essential component of both ecosystems and genomes, restraining systemic contagion and providing building blocks for reorganization.

Questions for Research

Efforts to understand the complexity of ecosystems, or indeed of any systems, raise a plethora of challenges that suggest an agenda for research. How do we scale from the microscopic to the macroscopic and characterize the emergence of pattern? What is the potential for major regime shifts, and are there early warning indicators? How and to what degree are the conflicts between levels of organization resolved over evolutionary time, and what can we learn from this as we endeavor to preserve the biosphere?

These questions reflect management challenges concerning optimal paths forward for biological and socioeconomic systems alike, and they fall clearly within the domain of systems engineering. The challenges certainly will keep scientists and engineers occupied for decades to come.


Carpenter SR, Arrow KJ, Barrett S, Biggs R, Brock WA, Crépin A-S, Engström G, Folke C, Hughes TP, Kautsky N, and 12 others. 2012. General resilience to cope with extreme events. Sustainability 4(12):3248–59.

Fisher RA. 1930. The Genetical Theory of Natural Selection. Oxford: Clarendon Press.

Gould SJ. 1989. Wonderful Life: The Burgess Shale and the Nature of History. New York: Norton.

Hardin G. 1968. The tragedy of the commons. Science 162(3859):1243–48.

Jacob F. 1977. Evolution and tinkering. Science 196(4295):1161–66.

Lenton TM, Daines SJ, Dyke JG, Nicholson AE, Wilkinson DM, Williams HTP. 2018. Selection for Gaia across multiple scales. Trends in Ecology & Evolution 33(8):633–45.

Lewontin RC. 1977. Adaptation. Enciclopedia Einaudi Turin 1:198–214.

Ostrom E. 2009. A Polycentric Approach for Coping with Climate Change. Policy Research Working Paper 5095. Washington: World Bank.

About the Author:Simon Levin (NAS) is the James S. McDonnell Distinguished University Professor in Ecology and Evolutionary Biology at Princeton University.