Original Article
Universal cognitive mechanisms explain the cultural success of bloodletting

https://doi.org/10.1016/j.evolhumbehav.2015.01.003Get rights and content

Abstract

Bloodletting—the practice of letting blood out to cure a patient—was for centuries one of the main therapies in the west. We lay out three potential explanations for bloodletting's cultural success: that it was efficient, that it was defended by prestigious sources—in particular ancient physicians—, and that cognitive mechanisms made it a particularly attractive practice. To test these explanations, we first review the anthropological data available in eHRAF. These data reveal that bloodletting is practiced by many unrelated cultures worldwide, where it is performed for different indications and in different ways. This suggests that the success of bloodletting cannot only be explained by its medical efficiency or by the prestige of western physicians. Instead, some universal cognitive mechanisms likely make bloodletting an attractive form of therapy. We further test this hypothesis using the technique of transmission chains. Three experiments are conducted in the U.S., a culture that does not practice bloodletting. Studies 1 and 2 reveal that stories involving bloodletting survive longer than some other common therapies, and that the most successful variants in the experiments are also the most successful variants worldwide. Study 3 shows how a story about a mundane event—an accidental cut—can turn into a story about bloodletting. This research demonstrates the potential of combining different methodologies—review of anthropological data, experiments, and modeling—to investigate cultural phenomena.

Section snippets

Anthropological data

We performed a search in the Human Relations Area Files anthropological database (eHRAF: World Cultures database) for the words ‘bloodletting,’ ‘bleeding,’ ‘phlebotomy,’ ‘venesection,’ and ‘cupping.’ This yielded 154 references (see ESM for the full list of references, available on the journal's Website at www.ehbonline.org). The first coding aimed at eliminating the instances of cupping that did not involve bloodletting. All instances of cupping that did not involve a cutting tool, incisions,

Experimental data

To further evaluate the role of universal cognitive mechanisms in the attractiveness of bloodletting, we conducted a series of experiments with U.S. participants. As mentioned above, phlebotomy is a rare practice in modern western medicine, and bloodletting is not common as an alternative form of therapy either, so that these participants belong to a population that can be considered not to practice bloodletting. In order to limit the impact of participants' explicit beliefs about the efficacy

Modeling

Experiments have constraints on the number of participants as well as the number of generations. As a result, some of the effects observed might seem too weak to have a significant effect on cultural evolution. However, even very small tendencies can be magnified over multiple transmission episodes and have large effects on cultural evolution (e.g. Kalish, Griffiths, & Lewandowsky, 2007). Modeling bypasses experimental limitations and provides a more accurate representation of the consequences

Conclusion

Three explanations were put forward for the cultural success of bloodletting: medical efficiency, prestige and conformity bias, and attraction based on universal cognitive mechanisms. Regarding medical efficiency, the present data offer no support. Contrary to what one might expect if bloodletting was efficient to treat specific indications, we found it to be applied to a wide variety of indications. Moreover, there was no sign that bloodletting was most often practiced on the population that

Supplementary materials

The following are the supplementary data to this article.

Supplementary material 1. Coding of HRAF files, description of the distraction task for all studies and of the disgust control task for study 1, and simulation results.

Supplementary material 2. Maps representing patterns in the practice of bloodletting worldwide.

Supplementary material 3. Anthropological data.

Acknowledgments

We thank the Swiss National Fund for an Ambizione grant to H. Mercier, and the Center for the Study of Mind in Nature (Olso) for its support. N. Claidière gratefully acknowledges funding from the ASCE and LICORNES programs of the French Agence Nationale de la Recherche funding agency. We also thank Dan Sperber, Hugo Viciana, Alex Mesoudi, and two anonymous reviewers for their very useful comments.

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