Emergent Spatial Structures in Flocking Models: A Dynamical System Insight

Jean-Baptiste Caussin, Alexandre Solon, Anton Peshkov, Hugues Chaté, Thierry Dauxois, Julien Tailleur, Vincenzo Vitelli, and Denis Bartolo

Published April  8, 2014

How do individual animals form swarms, schools, and flocks? In the 1990s, physicists modeled collections of self-propelled particles (so-called “active matter”) and could simulate the ordering that occurs in animal flocks.  Theoretical models have reproduced many aspects of this collective behavior, but a number of questions have persisted. One concerns the observation that in polar, active matter—think of a collection of small, mutually interacting swimming arrows—the particles organize themselves into three possible pattern classes: density waves, solitary waves (solitons), and traveling “droplets.”

No single theory has been able to explain the formation and diversity of these patterns. However, in a paper in Physical Review Letters, Jean-Baptiste Caussin and collaborators from institutes in France, Germany, and the Netherlands, have solved a hydrodynamic model of polar active particles and have accounted for the origin and variety of these propagating swarm structures.  

Synopsis Image                

Figure: J.-B. Caussin et al., Phys. Rev. Lett. (2014)

The authors described a polar fluid’s motion governed by a density field (capturing the distribution of particles) and a polarization field (capturing the polar interactions determined by the direction in which each particle is pointing).   By including an effective mean-field potential and frictional forces, the model could reproduce all of the commonly observed patterns. The authors suggest their model provides a “unified theory” of flock patterns—one that allows patterns to emerge as a general feature of the dynamics of polar active fluids, independently of specific model details (e.g., the functional form of the hydrodynamic coefficients). – David Voss

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Domesticated Agriculture in Southwest Asia 11,000 Years Ago

Perspective: The Roots of Cultivation in Southwestern Asia

George Willcox,
Archeorient, CNRS-Universite Lumiere Lyon 2, 1 Rue Raulin, Lyon F-69365, France.

The origins of agriculture have been the source of much speculation, but recent discoveries are enabling archaeologists to piece together a more accurate picture. Fifty years ago, the earliest known farming village was Jericho in the southern Levant, dated to about 11,000 years ago (1). Since then, a series of sites dated hundreds of years earlier has been found in an arc extending to northern Iraq. Discoveries in Iran at Chogha Golan and Sheikh-e Abad (2), dated to 11,700 years ago... read more.

Science 5 July 2013:
Vol. 341 no. 6141 pp. 39-40
DOI: 10.1126/science.1240496

Controlling Self-Organizing Dynamics on Networks Using Models that Self-Organize


Pierre-Andre' Noel, Charles D. Brummitt, and Raissa M. D’Souza

University of California, Davis, California 95616, USA


Controlling self-organizing systems is challenging because the system responds to the controller. Here, we develop a model that captures the essential self-organizing mechanisms of Bak-Tang-Wiesenfeld (BTW) sandpiles on networks, a self-organized critical (SOC) system. This model enables studying a simple control scheme that determines the frequency of cascades and that shapes systemic risk. We show that optimal strategies exist for generic cost functions and that controlling a subcritical system may drive it to criticality. This approach could enable controlling other self-organizing systems. Read More.


PACS numbers: 89.75.Hc, 02.30.Yy, 05.65.+b, 45.70.Ht

The Diffusion of Microfinance 

Abhijit Banerjee, Arun G. Chandrasekhar, Esther Duflo, and Matthew O. Jackson

Science 26 July 2013: Vol. 341 no. 6144 DOI: 10.1126/science.1236498

How do the network positions of the first individuals in a society to receive information about a new product affect its eventual diffusion? To answer  this question, we develop a model of information diffusion through a social network that discriminates between information passing (individuals must be aware of the product before they can adopt it, and they can learn from their friends) and endorsement (the decisions of informed individuals to adopt the product might be influenced by their friends’ decisions). We apply it to the diffusion of microfinance loans ... read more.

Anticipating Critical Transitions

October 19, 2012

New article by: Scheffer et al. (2012)


Tipping points in complex systems may imply risks of unwanted collapse, but also opportunities for positive change. Our capacity to navigate such risks and opportunities can be boosted by combining emerging insights from two unconnected fields of research. One line of work is revealing fundamental architectural features that may cause ecological networks, financial markets, and other complex systems to have tipping points. Another field of research is uncovering generic empirical indicators of the proximity to such critical thresholds. Although sudden shifts in complex systems will inevitably continue to surprise us, work at the crossroads of these emerging fields offers new approaches for anticipating critical transitions.


Scheffer et al. (2012). Anticipating Critical Transitions. Science 338, 344-348.

Also, see related IRCS Interpretive Brief


Leads on Predicting Institutional Collapse

James K. Hazy, July 3, 2012

A recent study uses catastrophe models, an approach that has been proven across multiple disciplines from physics to ecology, to describe tipping-point events in dynamical systems. These are points, or values of a parameter--describing environmental conditions, the "container," wherein the system functions--that once crossed, can lead to sudden collapse in population density. If similar models can be applied to human organizing, then lessons from these systems may also apply to potential catastrophic collapse of social, political, and economic systems.

The study was conducted using yeast cultures, and therefore is not directly applicable in the human case. But it does provide possible leads for human systems researchers... read more.

Leads on The Mechanisms of Communications

James K Hazy, June 8, 2012

Recent research combines information theory with Bayesian logic to provide insights into effective communications among human beings. The two studies described (Frank & Goodman, 2012; Kemp & Regier, 2012) offer distinct yet complementary insights about some possible general principles of language.

Frank and Goodman (2012) implicitly consider this question by describing a “language game”  ...read more


Frank, M. C. & Goodman, N. D. (2012). Predicting Pragmatic Reasoning in Language Games. Science, 336, 998.
Kemp, C. & Regier, T. (2012). Kinship Categories Across Languages Reflect General Communications Principles. Science 336, 1049-1054.

The Social Conquest of Earth

a book by E. O. Wilson, May 13, 2012

The evolutionary basis for pro social behavior in humans remains a controversial topic. In particular, the question of how large-scale human cooperative activities like social, cultural, political and economic systems might have evolved through natural selection processes is a fundamental one. Of particular ontological and epistemological interest is the appropriate unit of selection for individual and collective altruistic and pro-social behavior because these behaviors enable the requisite complex organizing that under girds human systems.

Interestingly, this question is also at the center of a theoretical dispute in evolutionary biology that erupted as a consequence of the cover article in the journal Nature written by a group that included the prominent evolutionary biologist Edward O. Wilson. The dialogue continues with Wilson's new book: The Social Conquest of Earth. ... Read more.


Decision-Making in Kind and Wicked Environments

James K. Hazy, April 26, 2012

Deciding which expert to believe when one is decidedly more confident that others is both a common practical problem and an important conundrum in the theory of human interaction dynamics (HID). As shown in a recent study (Koriat,2012), it turns out that the best choice depends upon how well consensus opinion correlates with conditions in the environment ... read more.



Evidence that Dynamic Foraging Behaviors Are Innate in Multiple Species including Human Beings

James K. Hazy, April 18, 2012


Dynamic foraging behaviors are defined in human interaction dynamics (HID) as those behaviors that occur as individuals contemplate whether to engage static foraging among the known options in the local environment, or to delay gratification and begin to search for new ones that might be fruitful at a later time. The biological mechanisms that enable this process are being uncovered in human neural processes.

In one recent study, dynamic foraging was shown to involve different areas of the human brain depending upon ... read more



Location and Neighborhood Factors are Powerful Attractors Driving Social Functioning

Washington, DC, April 16, 2012

Over the course of 40 years, Robert J. Sampson has been gathering massive amounts of sociological data about the USA's city of Chicago's neighborhoods. His study, published in his recent book, Great American City: Chicago and the Enduring Neighborhood Effect, challenges current orthodoxy and offers strong support for complex systems methods. Among other things he found that two coarse-grained social system properties drove neighborhood outcomes ...read more 


Mark your calendars...

The Institute is proud to be sponsoring several upcoming events that are intended to further research in Human Interaction Dynamics( HID). For example, in Orlando in August there will be several events ... read more 


The Institute

The Institute for Research in Complexity and Society applies findings and insights from the scientific and mathematical study of complex systems to the challenges and opportunities facing today's world community ... read more