The Natural Right to Punish Cheaters Among Bacteria

In our discussion of the evolution of morality at the Liberty Fund conference in Tucson, some discussants complained that Ridley's account of the spontaneous evolution of morality did not recognize the importance of reason in moral judgment.  Ridley says a lot about Adam Smith's emphasis on moral sentiments, but he ignores Smith's recognition that the moral sentiments are guided by moral reasoning.

In response to this, Ken Blanchard (a political scientist at Northern State University, Aberdeen, South Dakota) said that evolutionary morality is always rational in the sense that there is some evolutionary logic in morality, even when there is little or no conscious reasoning involved.  For example, he observed, there is an evolutionary logic of justice even among bacteria.  All dead organic material is potential food for bacteria.  But the large organic molecules must be broken down by bacteria secreting enzymes that break up proteins and peptides, so that the smaller molecules can then be absorbed through the bacterial cell membranes.  Through "quorum sensing," bacteria communicate their presence to one another by secreting signaling molecules, detecting changes in concentration of signaling molecules, and then regulating the transcription of genes in response.  Once the signaling molecules exceed a certain threshold level (the quorum), this triggers changes in gene expressions.  In this case, it triggers the secretion of enzymes for dissolving the organic material into nutrients that can be consumed by the bacteria.  But since secreting enzymes is costly for bacteria, evolution can favor the appearance of mutant bacteria that cheat by not secreting the enzymes but then consuming the nutrients generated by the work of the other bacteria that secret the enzymes: the cheaters can thus enjoy the benefits of a public good without paying their fair share of the costs for producing that public good.  To enforce cooperation, bacteria have evolved the capacity for detecting these cheaters and punishing them by secreting cyanide that kills them.  Here then is the evolutionary logic of justice among bacteria in which those who fail to cooperate for the common good are punished.

I now realize that Blanchard was reporting the research of microbiologist E. Peter Greenberg and his colleagues.  Greenberg first introduced the term "quorum sensing" in 1994 to denote the regulation of bacterial gene expression by population sensing (Fuqua, Winans, and Greenberg 1994; Davis 2004).  Thirty years ago, most microbiologists assumed that bacteria could not communicate with one another, and so they could not use communication to coordinate social cooperation.  But now Greenberg and others have shown that just as human beings communicate with words, bacteria communicate with signal molecules, which allows them to cooperate with one another.  This has become part of a new field of research--called "sociomicrobiology"--that studies the social evolution of microorganisms (Parsek and Greenberg 2005; West et al. 2006).  As with plants and animals, bacterial cooperation is subject to social cheating, and one way to suppress cheating is for bacteria to engage in policing that punishes cheaters.  The bacterium Pseudomonas aeruginosa shows this, because these are the bacteria described by Blanchard, that secrete cyanide to punish social cheaters (Wang et al. 2015).

Policing punishment to enforce social cooperation has been seen in many animals (Clutton-Brock and Parker 1995; Bekoff and Pierce 2009).  For example, among social insects--particularly, ants, bees, and wasps--each worker in the colony would benefit from rearing her own sons, rather than the queen's sons.  But other workers have evolved to prevent this because it reduces the reproductive efficiency of the colony, and the policing workers are more related to the sons of the queen than the sons of other workers.  This has favored an evolutionary selection for policing by workers, who destroy the eggs laid by other workers (Ratnieks, Foster, and Wenseleers 2006).

A different kind of policing has been observed among some primates.  Among pigtailed macaques (Macaca nemestrina), building and preserving social networks requires conflict management.  A small group of individuals who are high ranking in the power structure--alpha males--exercise third-party policing by intervening impartially to control conflicts.  When monkeys come into conflict, a high-ranking individual can intervene with a threat that pacifies the conflict (Flack, de Waal, and Krakauer 2005; Flack, Girvan, de Waal, and Krakauer 2006).

Just as it is with bacteria and other animals, human beings have a naturally evolved propensity to punish cheaters who violate the social contract that supports social cooperation.  Lucretius recognizes this when he speaks of how justice originated when our early human ancestors formed "common pacts of peace" neither to harm nor be harmed, and here he follows Epicurus who taught that natural justice is "a pledge of reciprocal usefulness, neither to harm one another nor be harmed," which is enforced by the fear of punishment of those who violate this social contract (5.1012-1025).  This is the evolutionary Epicurean morality that Nietzsche promoted in Human, All Too Human.  This also corresponds to Locke's teaching about the "executive power of the law of nature"--the natural right to punish cheaters who violate the law of nature.

Extensive cross-cultural experimental research by evolutionary psychologists has shown that human beings are very good at detecting cheaters in a social exchange.  This has led them to conclude that one of the evolved mechanisms of the human brain is a cheater detection module (Cosmides & Tooby 1992, 2016; Van Lier, Revlin, De Neys 2013).  As I have indicated in some previous posts, Judge Morris Hoffman (2014) has surveyed the evidence for concluding that evolution built the human brain to punish cheaters, and that this explains how the legal system for punishment can be rooted in our evolved human nature.

This suggests that Darwinian natural right as enforced by the natural right to punish cheaters could have appeared in some form very early in the evolutionary history of life--perhaps with the first bacteria.

Some of these points have been developed in other posts--on bacterial morality (here), on the Lockean right to punish cheaters (here, here, and here), and on Nietzsche's evolutionary morality (here and here).


REFERENCES

Bekoff, Marc, and Jessica Pierce. 2009. Wild Justice: The Moral Lives of Animals. Chicago: University of Chicago Press.

Clutton-Brock, T. H., and G. A. Parker. 1995. "Punishment in Animal Societies."  Nature 373: 209.

Cosmides, Leda, and John Tooby. 1992. "Cognitive Adaptations for Social Exchange." In J. H. Barkow, Leda Cosmides, and John Tooby, eds., The Adapted Mind: Evolutionary Psychology and the Generation of Culture, 163-228.  Oxford: Oxford University Press.

Cosmides, Leda, and John Tooby. 2016. "Adaptations for Reasoning About Social Exchange." In David M. Buss, ed., The Hundbook of Evolutionary Psychology, 2nd ed., 2 vols., 2:625-68. Hoboken, N.J.: John Wiley.

Davis, Tinsley H. 2004. "Biography of E. P. Greenberg."  Proceedings of the National Academy of Sciences 101: 15830-15832.

Flack, Jessica C., Frans de Waal, and David C. Krakauer. 2005. "Social Structure, Robustness, and Policing Cost in a Cognitively Sophisticated Species." The American Naturalist 165: E126-E139.

Flack, Jessica C., Michelle Girvan, Frans de Waal, and David C. Krakauer. 2006. "Policing Stabilizes Construction of Social Niches in Primates."  Nature 439: 426-29.

Fuqua, W. Claiborne, Stephen C. Winans, and E. Peter Greenberg. 1994. "Quorum Sensing in Bacteria: the LuxR-LuxI Family of Cell Density-Responsive Transcriptional Regulators." Journal of Bacteriology 176: 269-75.

Hoffman, Morris. 2014. The Punishing Brain: The Evolution of Judge and Jury. Cambridge: Cambridge University Press.

Parsek, Matthew R., and E. P. Greenberg. 2005. "Sociomicrobiology: The Connections Between Quorum Sensing and Biofilms." TRENDS in Microbiology 13:27-33.

Ratnieks, F. L. W., K. R. Foster, and T. Wenseleers. 2006. "Conflict Resolution in Insect Societies." Annual Review of Entomology 51: 581-608.

Van Lier, Jens, Russell Revlin, and Wim De Neys. 2013. "Detecting Cheaters Without Thinking: Testing the Automaticity of the Cheater Detection Module." PLoS ONE 8 (1): e53827.

Wang, Meizhen, Amy L. Schaefer, Ajai A. Dandekar, and E. Peter Greenberg. 2015. "Quorum Sensing and Policing of Pseudomonas aeruginosa Social Cheaters." Proceedings of the National Academy of Sciences 112: 2187-2191.

West, Stuart, Ashleigh S. Griffin, Andy Gardner, and Stephen P. Diggle. 2006. "Social Evolution Theory for Microorganisms." Nature Reviews Microbiology 4: 597-607.