There are many patterns of collective behavior in biology that are easy to see because they occur along the familiar dimensions of space and time. Think of the murmuration of starlings. Or army ants that span gaps on the forest floor by linking their own bodies into bridges. Loose groups of shoaling fish that snap into tight schools when a predator shows up.
Then there are less obvious patterns, like those that the evolutionary biologist Jessica Flack tries to understand. In 2006, her graduate work at Emory University showed how just a few formidable-looking fighters could stabilize an entire group of macaques by intervening in scuffles between weaker monkeys, who would submit with teeth-baring grins rather than risk a fight they thought they would lose. But when Flack removed some of the police, the whole group became fractured and chaotic.
Like flocking or schooling, the policing behavior arises from individual interactions to produce a macroscopic effect on the entire ensemble. But it is subtler, perhaps harder to visualize and measure. Or, as Flack says of macaque society and many of the other systems she studies, “their metric space is a social coordinate space. It’s not Euclidean.”
Flack is now a professor at the Santa Fe Institute, where she has spent all of her postgraduate career, except for a stint at the University of Wisconsin, Madison. Her “collective computation” group, C4, which she co-runs with her collaborator, David Krakauer, probes not just macaques but neurons, slime molds, and the internet for the rules that underlie each model, as well as the general rules underlying them all.
Flack describes her work as an investigation into three interlocking questions. She wants to understand how phenomenological rules in biology, which seem to work in aggregate, emerge from microscopic ground truths. She wants to understand how groups solve problems and come to decisions. And she wants to know how complex systems stay robust in the face of shocks, like the macaques with their own police force that acts as social glue.
At its root, though, Flack’s focus is on information: specifically, on how groups of different, error-prone actors variously succeed and fail at processing information together. “When I look at biological systems, what I see is that they are collective,” she said. “They are all made up of interacting components with only partly overlapping interests, who are noisy information processors dealing with noisy signals.”
Over the phone, by Skype, and via email, Quanta Magazine caught up with Flack to ask about C4’s current projects, her own career path, and the overarching philosophy behind her work. An edited and condensed version of our conversations follows.
Joshua Sokol: How did you get into research on problem solving in nature, and how did you wind up at the Santa Fe Institute?
Jessica Flack: I’ve always been interested in how nature solves problems and where patterns come from, and why everything seems so organized despite so many potential conflicts of interest. Those sorts of questions have been with me since I was really little.
At Cornell, I was taking evolutionary biology classes, but none of the material really addressed these questions. I would spend a lot of time in Mann Library, which was where all the good biology books were. So I would sit on the floor in the dusty, dimly lit stacks with this pile of books around me. And in that way I discovered that there was a community of people working on these questions in evolutionary biology that I found more interesting.
They weren’t in the mainstream. One of the main places that turned out to be home to a lot of these people was the Santa Fe Institute. This was in the early to mid-’90s. I emailed the Santa Fe Institute and I requested something like 40 working papers. I was being a really annoying undergraduate. And someone mailed them to me! They actually snail-mailed me 40 of these papers, and I was thrilled, and I read them all.
Sokol: Now that you’ve ended up there, can you break down what your C4 research group means by “collective computation”?
Flack: Collective computation is about how adaptive systems solve problems. All systems are about extracting energy and doing work, and physical systems in particular are about that. When you move to adaptive systems, you’ve got the additional influence of information processing, which we think allows a system to extract energy more efficiently even though it has to expend a little extra energy to do the information processing. Components of adaptive systems look out at the world, and they try to discover the regularities. It’s a noisy process.
Unlike in computer science where you have a program you have written, which has to produce a desired output, in adaptive systems this is a process that is being refined over evolutionary or learning time. The system produces an output, and it might be a good output for the environment or it might not. And then over time it hopefully gets better and better.
What we are doing at C4 is taking messy, conceptually challenging problems and turning them into something rigorous. We’re very philosophically oriented, but we’re also very quantitative, particularly in thinking about how nature can overcome subjectivity in information processing through collective computation. We really think the answer to these questions requires combining insights from statistical physics, theoretical computer science, information theory, evolutionary biology and cognitive science.
Sokol: Can you walk us through an example? In a recent paper, your group looked at communication between neurons in the brains of macaques.
Flack: The human brain contains roughly 86 billion neurons, making our brains the ultimate collectives. Every decision we make can be thought of as the outcome of a neural collective computation. In the case of our study, which was led by my colleague Bryan Daniels, the data we analyzed were collected during an experiment by Bill Newsome’s group at Stanford from macaques who had to decide whether a group of dots moving across a screen was traveling left or right. Data on neural firing patterns were recorded while the monkey was performing this task. We found that as the monkey initially processes the data, a few single neurons have strong opinions about what the decision should be. But this is not enough: If we want to anticipate what the monkey will decide, we have to poll many neurons to get a good prediction of the monkey’s decision. Then, as the decision point approaches, this pattern shifts. The neurons start to agree, and eventually each one on its own is maximally predictive.
We have this principle of collective computation that seems to involve these two phases. The neurons go out and semi-independently collect information about the noisy input, and that’s like neural crowdsourcing. Then they come together and come to some consensus about what the decision should be. And this principle of information accumulation and consensus applies to some monkey societies also. The monkeys figure out sort of semi-independently who is capable of winning fights, and then they consolidate this information by exchanging special signals. The network of these signals then encodes how much consensus there is in the group about any one individual’s capacity to use force in fights.
Sokol: I noticed that another recent paper uses the same macaque data set you produced during your graduate work at the Yerkes National Primate Research Center in Lawrenceville, Georgia. What did you find when you returned to thinking about this system?
Flack: We wanted to understand how social systems or other biological systems go from state A to state B. How a group of fish goes from shoaling to schooling, or how a social system goes from having a few super-powerful animals to a setup where there is less inequality. One mechanism known to facilitate switching between different states like this is for the system to sit near what’s called a critical or tipping point. We set out to find a way to measure, in biologically meaningful terms, how far a system sits from the critical point. Could we come up with units that mechanistically make sense?
We were interested in whether we could induce the monkey society we were studying to change from its status quo of many small fights and a few large ones to having many large fights. We observed that fights in this monkey group range in size from two to 30 or so individuals, with small fights common and large fights very rare. By simulating the society using data we had collected on fight-joining decisions, we found that we could measure the number of monkeys whose propensity to join fights would have to increase to move the system closer to the critical point.
In this system, it takes about three to five individuals to push the system over the edge. We also found that individuals vary in how much their behavior influences the system. If big contributors become more likely to join fights, the system moves toward the critical point where it is very sensitive, meaning a small perturbation can knock it over into this all-fight state. And while we didn’t study this in the paper, we speculate that the all-fight state, which means the system is going to change dramatically, might be useful. It might be something you want to do, to move toward the critical point and completely reconfigure the group if the environment is changing from known to unknown.
The macaques served as the model system for asking these questions, but we hope the approach that we developed can be applied to lots of other different kinds of data.