Cooperation emerges when groups are small and memories are long, study finds

social network
Social network diagram. Credit: Daniel Tenerife/Wikipedia

The tragedy of the commons, a concept described by ecologist Garrett Hardin, paints a grim view of human nature. The theory goes that, if a resource is shared, individuals will act in their own self-interest, but against the interest of the group, by depleting that resource.

Yet examples of cooperation and sharing abound in nature, from down to single-celled bacteria.

In a new paper, published in the journal Scientific Reports, University of Pennsylvania researchers use game theory to demonstrate the complex set of traits that can promote the evolution of cooperation. Their analysis showed that smaller groups in which actors had longer memories of their fellow group members' actions were more likely to evolve cooperative .

The work suggests one possible advantage of the human's powerful memory capacity: it has fed our ability as a society to cooperate.

"In the past we've looked at the interactions of two to determine the most robust evolutionary strategies," said Joshua B. Plotkin, a professor in Penn's Department of Biology in the School of Arts & Sciences. "Our new analysis allows for scenarios in which players can react to the behaviors and strategies of multiple other players at once. It gives us a picture of a much richer set of social interactions, a picture that is likely more representative of the complexities of human behavior."

Plotkin collaborated with Alexander J. Stewart, then his postdoctoral researcher and now a Royal Society research fellow at University College London, on the work, which builds on years of game theory examinations by the pair.

In their earlier works, they used the Iterated Prisoner's Dilemma scenario, in which two players face off and can choose to either cooperate or not, to understand what circumstances promote the rise of generosity versus selfishness.

In the new paper, they added two levels of complexity. First, they used a different scenario, known as a public-goods game, which allows players to interact with more than one other player at a time. The set-up also enabled the researchers to vary the number of players in a given game. In the public-goods game, a player can contribute a certain amount of a personal resource to a public pool, which is then divided equally among all players. The greatest shared benefit comes when all players contribute generously, but that also puts generous players at risk of losing resources to selfish players, a tragedy of the commons scenario.

The second added level of complexity was imbuing players with the capacity for long memories. That is, players could use the actions of their opponents from multiple earlier rounds of the game to inform their strategies for subsequent rounds. If a player repeatedly encountered a player in a group that frequently behaved selfishly, for example, they may be more likely to "punish" that defector by withholding resources in future rounds.

In addition, the populations of players were permitted to "evolve," such that more successful players, those that achieve greater payoffs, are more likely to pass their strategies on to the next generation of players.

Stewart and Plotkin found that the more players in a game the less likely that cooperative strategies could win out. Instead, the majority of robust strategies in large groups favored defection.

"This makes intuitive sense," Plotkin said. "As a group size increases, the prospects for sustained cooperation go down. The temptation to defect and become a freeloader goes up."

Conversely, their findings showed that giving players a longer memory, the ability to remember and base decisions on as many as 10 previous rounds of their opponents' actions, led to a greater relative volume of robust cooperative strategies. Part of the reason for this, the researchers said, was because greater memories allowed players to develop a broader array of more nuanced strategies, including ones that could punish individuals for defecting strategies and ensure they didn't take over the population

"A stronger memory allowed players to weed out the rare defector," Plotkin said.

In a final set of experiments, Stewart and Plotkin used computer simulations that allowed the memory capacity of players to evolve alongside the strategies themselves. They found that not only were longer memories favored, but the evolution of longer memories led to an increase in cooperation.

"I think a fascinating takeaway from our study," Stewart said, "is that you can get a set of circumstances where there is a kind of runaway feedback loop. Longer memories promote more cooperation and more cooperation promotes longer memories. That kind of situation, where you go from a simpler system to one that is more complex, is a great example of what evolution does, it leads to more and more complexity."

As a next step, Stewart and Plotkin would like to use human subjects to evaluate their mathematical findings.

"We have all these results about what kinds of strategies are successful that take into account different features of players' actions," Stewart said. "We'd like to run an experiment with people to figure out what they are actually paying attention to when they're playing. Is it their payoffs? Is it their opponents' payoffs? And see how those strategies match up to those we see in our analyses."

Explore further

Game theory analysis shows how evolution favors cooperation's collapse

More information: Alexander J. Stewart et al, Small groups and long memories promote cooperation, Scientific Reports (2016). DOI: 10.1038/srep26889
Journal information: Scientific Reports

Citation: Cooperation emerges when groups are small and memories are long, study finds (2016, June 1) retrieved 21 August 2019 from
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Jun 01, 2016
so, the study says that.. big cities and political powers associated with large voting centers, all due to the humans involved and how they a steaming pile of ill informed, low empathy, low data retention/memory jackbooted fascist capitalistic oligarchical sociopath crap, which should not be allowed to decide the fate of even a dead rat?

Sounds like it to me.....perhaps I'm mis-readng the end result of what the study means, but I don't think so.....

Jun 01, 2016
Hence the development of 'Common Law', perhaps ? This was run by local stake-holders, rather than handed down from the 'Big House' by 'Grand Folk' unfamiliar with local nuances...

And, yes, a world apart from 'Roman Law'...

Jun 02, 2016
KBK, no. What it means is that given there are billions of people in the world, if we are unable to punish those who cheat, e.g. those that pollute, then cooperation is not favoured. We have enough memory. The question is whether we can use it to punish. No carbon tax, not commons.

Jun 02, 2016
A better ending sentence - no carbon tax, we crap in our own back yard until we drown in it.

Jun 02, 2016
A better ending sentence - no carbon tax, we crap in our own back yard until we drown in it.

Punishing by taxation is a poor way to control behaviour because governments that tax, spend, and taxing becomes mandatory because government spending never goes down, which means the government itself becomes addicted to coal that it can tax.

It's already the case that coal pollutes so much it costs four times than what it's worth to the public. There's no extra need to "punish cheaters", but simply to raise awareness and once people agree they can vote coal burning to be made illegal.

Jun 02, 2016
Besides, taxing carbon in general hurts everybody equally, not just those who "cheat", and so the punishment itself hurts our ability to do anything about the situation by incurring extra costs in everyday life and business.

It would be like whipping yourself for behaving badly, which is just silly drama. Self-flagellation won't help you change, although it makes you feel like you're doing something for the better because you're hurting. Medicine often tastes bitter, but not all that tastes bitter is medicine.

Instead of punishing people for using carbon - which they can't help - a more constructive alternative is to find something better to use, and that also means something cheaper to use.

Jun 02, 2016
Eikka, it should be obvious that a carbon tax can be offset by reductions in other taxes. In fact this is the usual proposal. If coal use was reduced, increases in other taxes could offset government loss - or less spending may be required.

You don't think people are aware of the warming or toxic effects of coal??? Even if we only take those that accept the science of AGW, many of these people won't do anything until it costs them something.

You're trotting out a standard "do nothing" response. Again, do nothing and we will crap in our own back yard until we drown in it.

Jun 02, 2016
I like the fact that this is the social sciences and we are making comments and having minor discussions and not laying judgement at one another's feet ---with post ratings.

Properly civilized, IMO.

Jun 02, 2016
Speaking of the unspoken issue at hand:

essentially that cutting edge science can wreak havoc with controlling oligarchy, in the given technology's emergence and development from that emergence.

so, a place to institute control and observation AND most importantly..a method of controlling and inserting the mindset and dialogue in the unfolding..WILL take place in a website like physorg.

So, go to the wildcard emergence watering hole and insert subtle control structures/methods.

Like comment weighting AND a method of making sure no one sees them (the slider, and memory of the given user's slider position), and if seen, to deride, so those comments and potentialities are neutralized and/or smeared. Then the connected shill fill.... for the necessary down voting.

In any system of oligarchy, this would be a obvious form of common sense activity.

And that is what has happened to the comment section at physorg.

Jun 06, 2016
It seems to me that you can achieve better results for offering subsidies. That way you are giving positive reinforcement, companies will want to change, and then once they change you can reduce the subsidies and they are already invested in the change they made to receive the subsidies, and there you have it.

Like "Meaningful Use" laws in the medical field. You do not have to follow them, but you get money if you do, and once you made the changes they wanted, they can stop giving you money and you still have the changes they wanted.

Its a lot cleaner than charging ever-increasing fines. And people resent fines, they will be much happier with a subsidy that fades and disappears than they would be with a Fine that just tripled.

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