Plant-based game theory

Sep 21 2019

Sunflowers, believe it or not, play non-zero-sum games with one another—and do so with impressive skill! At least, that’s one reading of a study published this week in the Proceedings of the Royal Society. 

A typical sunflower, not surprisingly, tends to send its roots more profusely into nutrient-rich patches of soil than into nutrient-poor patches. But two researchers—Megan Ljubotina and James Cahill—report that, when there is another sunflower in the neighborhood, this behavior gets recalibrated.

If much closer to the nutrient-rich patch than its neighbor, the sunflower sends its roots into the patch more profusely than when there’s no neighbor around—as if it were rushing to colonize land before a rival gets to it.


But if the nutrient patch is midway between the sunflower and its neighbor, it sends it roots into the patch less profusely than if there’s no neighbor around. Ljubotina and Cahill suggest that this may be a way “to avoid competition in highly contested patches.” Presumably the logic is akin to the logic of neighboring countries that behave with restraint to avoid the lose-lose outcome of mutually costly conflict. It’s an implicit non-aggression pact.

I’m sure there are other explanations. But the main point for our purposes is that the non-aggression pact explanation, whether right are wrong, isn’t crazy. Sunflowers may seem too dim-witted to evince strategic savvy, but organisms don’t have to be smart enough to understand game theory in order for natural selection to incline them to play their games well.

Same goes for us. Sure, we, unlike sunflowers, are smart enough to understand game theory. But that’s not the only thing that leads us to pursue its logic. 

Such emotions as gratitude, trust, pride, and moralistic indignation seem to have been built into our perhaps-a-bit-dim-witted ancestors as a way to get them to play social games well—to, for example, reciprocate favors and thus form lasting friendships but to rebuff or even attack people who tried to take advantage of them. 

None of this has to involve explicit understanding of why these strategies make sense—that, for example, friendship is the repeated playing of games to a win-win outcome. Chimps don’t spend time pondering game theory, and for all we know they don’t ponder much of anything—but they have trusted allies, presumably because they have the feeling of trust.     

Same goes for the psychology of tribalism—the psychology that shapes our interactions with members of our group (national, ethnic, ideological, whatever) and with other such groups: We are under its sway in ways that, and for game theoretical reasons that, we don’t automatically understand. And—to further insulate us from reality—the swaying is done not just by emotions but also by subtle cognitive biases that can warp our view of the other tribe and of members of our own tribe. 

This cluelessness would be less problematic if it weren’t for some technological developments that have taken place since natural selection designed this infrastructure of emotional and cognitive guidance. Like the invention of nuclear weapons. And for that matter the invention of rifles. And of social media. And so on. 

All of which helps explain why the psychology of tribalism is important enough to be an intermittently recurring rubric in this newsletter (complete with a colored bar that, when clicked, will take you to the “psychology of tribalism” section of our archives). Precisely because we’re not naturally aware of how and when this psychology is warping our perception, and precisely because the stakes are so high, it’s important to keep exploring that psychology and to reflect on it fairly often.   

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