Field of Science

The Evolution of Cooperation

First of all, a personal triumph: I've had my first academic paper accepted! "A New Phylogenetic Diversity Measure Generalizing the Shannon Index with Application to Phyllostomid Bats" is tentatively accepted for publication at the American Naturalist, a venerable biology journal. Whooo!

But on to our main topic: It's one of evolution's oldest riddles. If evolution is a brutal battle for survival, in which only the fittest survive, why do we see so much cooperation in nature? Why, in extreme cases, do some animals sacrifice themselves to help others of their species? In the competition between individuals, genes, and species, what kind of advantage does this altruistic behavior confer?

This question is quite deep and has generated an array of possible answers, whose implications go beyond evolutionary biology. I'll outline the history of how this question has been explored, and offer something of a synthesis to conclude.

  • Reciprocation-It pays to help someone else if that person will help you in return. This fact is incontrovertible, and helps explain many of the interactions we see in nature, like monkeys grooming each other. However, reciprocation does not explain the acts of extreme altruism sometimes seen in nature, such as cellular slime moulds that sacrifice themselves to help others find food. So it can’t be the whole story—some actions really are selfless.

  • Group selection-This is the idea that Darwinian evolution acts on groups of organisms as well as on individuals. If the members of a group cooperate well together, then the group as a whole may survive, while other less cooperative groups die off. This idea fell out of favor in the 60's as mathematical analysis showed group selection is generally a much weaker evolutionary force than individual selection. New models, however, show that group selection can be important in some circumstances.

  • Kin discrimination-This view holds that the real unit of Darwinian selection is not organisms or groups but genes. Since genes are the material that is passed on through generations, the genes that help themselves out will survive the best. So if your gene “sees” that another individual has the same gene, your gene will “want” to help that person out in order to further its own interests. Of course, genes can’t really see each other. But your genes can tell you to help out your relatives, who are likely to have the same genes as you. This is the kin discrimination theory: our genes tell us to help our immediate family members, and thereby further their own gene-centric interests. Preferential behavior toward relatives is commonly observed in animals, and one study even found closely-related plants helping each other out.

  • Repeated interactions-Axelrod’s tournaments of Prisoner’s Dilemma games show that, while it may be beneficial to act selfishly in the short run, more cooperative strategies are better if you know you’ll be interacting with someone repeatedly. The best strategies for repeated interactions are those which reward others who cooperate with you and punish those who don’t.

  • Spatial structure-Cooperators do best if they’re surrounded by other cooperators. One way this can happen is in ecosystems where offspring are born close to their parents and don’t move much. In this case, the children of cooperators stay and cooperate with their relatives, while the children of selfish bastards hang out with their selfish bastard relatives and be miserable. Thus, systems with a strong spatial structure and little movement tend to favor cooperators. The system breaks down if the selfish bastards can move fast enough to find the cooperators and exploit them. Robert Austin found that spatial separation could help "altruistic" bacteria survive coexist with their "selfish" bretheren.

  • Punishment-Evolutionary biologists have also explored the idea that punishment can help enforce cooperative behavior. Punishment can be “vigilante-style”, where any individual who sees someone else acting unethically can hurt them, or there can be some kind of agreed-upon authority whose job it is to punish misbehavers. The question of if and how punishment works in nature seems still up for debate.

Bottom line is, it doesn’t pay to be a nice guy in a world of assholes. But if you can find other nice people to interact with, and some mechanism for keeping the assholes out of your little nice-people club, then you’re on to something.

Each of the proposed mechanisms for cooperation has interesting implications for human society. I’ll highlight just one of them for now: spatial structure. When humans first evolved, long-distance travel was difficult, and so different societies could develop independently with their own norms of cooperation or selfishness. But now we can travel across the world in a day, so the spatial separation is gone. Any thoughts on the implications of this change for the stability of human cooperation?

Further reading


  1. Congrats on your publication! Do let us know when it officially appears.

  2. Good post, Ben.

    To your question: I would submit that removal of spatial distance is only one aspect. With global interconnectedness via the internet, cell phones, etc, the impetus for competition is decreasing and the ability (and need) for cooperation is increasing.

  3. congrats on your publication.

    interesting topic. it's great to see how mathematics seeps into any topic, including ecology and evolution.

    i'm currently reading _the dominant animal_ by eherlich and eherilich. def' a "layman's" book but that's fine. very interesting.

    does coevolution affect your models at all?

    do you ever blog on magic? (i found you through mtgsalvation. i'm just getting started blogging on magic).

  4. Thanks for the congrats, peeps! There's still another round of revisions to be done, followed presumably by more delay, so I'm not expecting any printing within a year. But it's good to be in.

    @rafe-I have mixed feelings on this subject. On the one hand, global interconnection is increasing cross-cultural understanding and leading to global cooperation in areas like economics (and climate, I hope?)

    On the other hand, we're getting to the point where we all sink or swim together. Our ecological problems are global rather than local, so we only get one chance from now on. This scares me.

    @james-Yeah, it took me several years of grad school to realize all the cool things you could study as a mathematician. I touched on coevolution a bit here, but it's an important topic and I should return to it.

    I have not tried blogging on Magic, though I do sometimes feel an urge to share my thoughts on the subject. Good luck with yours!

  5. I touched on coevolution a bit here, but it's an important topic and I should return to it.

    Is coevolution dual to evolution?

  6. I don't think so--not any more than "cooperation" is dual to "operation." But it would be cool if it were!

  7. I would love it if someone with a mathematical background would create a model of the cooperate v selfish selection that includes the selfish being selfish. When punishment is modelled it is always assumed that only the cooperators are punishing. Empirical studies show selfish punish as much or more as cooperators, as we should expect, but this puzzles everyone else. Cooperators are a fitness limiting resource for selfish, and simple evolutionary theory tells us that selfish will select for the ability to maximize their fitness by excluding or impeeding other selfish. I believe this is likely the key to the puzzle here.
    You might like my paper

  8. You know, introducing "selfish punishers" into the mix is a pretty good idea! I'm not convinced it would change things, but it's worth finding out. I'll work on this when I get a chance.


  9. @c_turchick

    I agree with the premise of your paper. You would probably like Jonathan Haidt's TED talk.

  10. Two years ago I wrote an artificial life simulation for my pure math thesis (quite a stretch, I know!) and since then have been wondering about how to measure the complexity of phylogenetic trees (seeing as the simulations can capture copious such data). How random and cool to stumble upon it here! Do you have a link to the PDF perchance?


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