Source: Diego Ramos Toro, used with permission.

Leprosy or Hansen’s Disease is a mildly contagious, usually slowly developing, infectious disease that produces symptoms including skin lesions, ulcerations, and joint deformities, along with nerve and sometimes eye damage. In the Western world, it has long been associated with the family of diseases causing skin abnormalities for which the Hebrew Bible or Old Testament prescribed isolation from the community, describing the sufferer as “unclean.” The practice of isolating sufferers of the disease in “leper colonies” continued into the 20th Century. A few Americans still contract it every year, and it’s said that they can be slow to be diagnosed because U.S. doctors are so unfamiliar with the symptoms. But, most cases these days are concentrated in a few countries including India, Brazil, Indonesia, and parts of sub-Saharan Africa. The disease’s progression can now be treated effectively with a multi-drug , and the World Health Organization, which classifies it as a “neglected tropical disease,” attempts to make the drugs available free of charge.

In 1871, Colombia established a site at which to isolate lepers in a place called Agua de Dios, a bit to the west of the country’s geographic center. In the early 20th Century, the country began to strictly enforce laws whereby a medical determination that an individual was suffering from the disease led to his or her permanent restriction to such a colony. Agua de Dios became the largest and eventually the country’s only such colony, where Hansen’s sufferers lived out the rest of their lives alongside others suffering from the disease, usually by operating small farms on land granted them there. The practice of isolating leprosy sufferers began to be phased out in 1950 when non-lepers were permitted to also live in Agua de Dios and sufferers of leprosy could freely move out.

Many residents remained in Agua de Dios even after improvements in the treatment of the disease and a better understanding that it is not so highly contagious led to the end of its official status as a leper colony. Forbidden to have children until then, younger residents began establishing families, and descendants of former Hansen’s sufferers remained a large part of the town’s population. Genetic predisposition makes susceptibility to Hansen’s run in families, yet contagion levels are low enough and available treatments effective enough that essentially no past sufferers’ descendants bear signs of the disease today. A visitor to Agua de Dios today can find no outward sign of the disease to serve as a pointer towards the town’s past.

Segue to 2018. Diego Ramos Toro, a Colombian doctoral student studying economics in the United States, decides to study the effect of past isolation and social exclusion on the psychology and culture of residents of Agua de Dios. He carries out surveys and asks dozens of randomly recruited individuals to make two money allocation decisions in both Agua de Dios and in nearby communities that had no historical association with leprosy and social exclusion. Ramos Toro invites each of his subjects to sit alone in a room with only the researcher present and to make a decision out of the researcher’s view about whether to share some money presented to him or her (a sum equivalent to about 60% of an average day’s wage in Colombia) with an anonymous resident of their own community and if so how much, and also to make a parallel decision regarding the potential sharing of an equal sum of money but with an anonymous recipient living instead in a distant part of the country.

Subjects also complete a survey that includes questions about whether any parent or grandparent had lived in Agua de Dios and suffered from leprosy, whether they knew of the place’s history as a leper colony, their degree of trust in the medical profession, and their opinion about whether Colombia’s government should allocate funds to aiding refugees from the ongoing political and economic turmoil in neighboring Venezuela (a controversial policy among Colombians). To learn more about views of doctors, he also gives subjects free vouchers for a course of medicine to protect against locally prevalent parasitic conditions for which doctors recommend an annual dose, with a system for tracking which ones used and which did not use the vouchers.

Experimental economists like me call this kind of study a “lab-in-the-field experiment.” The main “decision game” studied is called (somewhat unhelpfully) the “dictator game” not because the decision-maker is assumed to have tyrannical tendencies but rather because it is solely his or her choice whether and if so how much money is shared. The game has come under considerable scrutiny due to the unnaturalness of the decision the subjects are asked to make; nevertheless, hundreds of replications into its history of use, there is extensive agreement that, with proper care taken to assure the anonymity of the decisions made, variations in the amounts sent can be informative, e. . when correlations with characteristics of individual background or of the information about the recipient are analyzed. Ramos Toro’s study provides a good example.

The amount a subject decides to share in an anonymous dictator game is widely perceived in the experimental and research community as being an indicator of or fairness preferences, although it might also be thought of as an indicator of perceived social norms to which a member of a certain community ought to . What prediction should we make about the impact on sharing behavior of descent from individuals isolated from the rest of society on account of a disease others found frightening or repulsive?

Ramos Toro chose this particular decision task because he had heard that members of this community seemed exceptionally kind towards one another, and he read about a history of social at Agua de Dios over such activities as a local theatre, an orchestra, and the like. He also conjectured that members of the community might have felt greater for one another than for outsiders due to having in the past been shunned and isolated, hence his decision to have subjects make two sharing choices, one with an anonymous community member, another with an anonymous fellow countryman at a far-removed location.

Results bear out these conjectures as follows. First, residents of Agua de Dios shared more on average in both dictator games than did residents of nearby towns without its special history, suggesting greater overall empathy or altruism on average. Second, the difference between the amount sent to a local versus that sent to a distant outsider was larger in Agua de Dios than at the other sites, implying more “insider favoritism.” Despite this, the Agua de Dios residents actually sent slightly more to outsiders than did the residents of the other nearby towns, thus showing greater empathy, altruism or fairness with respect to strangers.

Agua de Dios residents having a historical connection to its leper colony history also expressed significantly greater support for Colombian government assistance to Venezuelan refugees than did other residents of Agua de Dios and residents of the other communities. Thus, the larger differential of sharing with insiders versus outsiders is not due to lack of empathy for outsiders, but to stronger favoritism towards insiders relative to a somewhat higher base level of altruism or empathy towards strangers. (In the other communities, there was also significant favoritism shown towards insiders—just not as much as at Agua de Dios.)

As for the elements of the study relating to medicine, Ramos Toro’s interest lay in the possibility that a past history of being sentenced to lifelong social exclusion by a doctor, plus some history of degrading or dangerous medical interventions (including some medical experiments unlikely to meet today’s ethical review board standards), may have created a lack of trust in the medical profession which might persist to the present day and might even interfere in the seeking out of appropriate medical care (a problem well known in today’s developing world). In the event, the study found support for these conjectures in at least two respects: those Agua de Dios residents descended from leprosy sufferers expressed significantly more negative views about doctors, and they also made significantly less use of the medicinal vouchers given freely to all participants.

A crucial fact to keep in mind is that no subject in the 2018 research had been consigned to Agua de Dios when it was a leper colony. Rather, a substantial proportion of the subjects at Agua de Dios had one or more grandparents who had been so consigned. We’re accordingly looking at the effects of a community’s past experience that seem to affect its culture into the third generation. Yet the average resident of Agua de Dios who did not have an ancestor with such direct connection to that past made choices statistically indistinguishable from those in the other communities of the region, and also from other communities in Colombia looked at in a 2019 follow-up. The follow-up study further demonstrated that freshly recruited subjects in Agua de Dios behaved still more differently from other subjects if the experimenter mentioned the place’s history as a leper colony, but this applied only to those descended from at least one leprosy sufferer.

The fact that Agua de Dios residents without the historical connection seemed no different from other Colombians doesn’t prove that there wasn’t some impact of a local “culture of empathy” within Agua de Dios on new residents in, say, the 1950s and 1960s when non-lepers first began to live in the community. But unfortunately, there’s no study available to show whether that sort of cultural impact did or didn’t exist at the time. What the results do suggest is that any such impact on residents without such family ties had worn off by 2018.

The study has urgent policy implications with respect to the importance of trust between medical practitioners and prospective patients. But I also find deeply compelling its suggestions with regard to the nature of human empathy. I avoided adding here photos of the effects of leprosy lest it turns away readers since evolutionary psychologists write extensively of what they consider a natural human inclination to shun people bearing visible “deformities,” an idea which seems intuitively plausible and consistent with folk practices in traditional societies.

I shared Ramos Toro’s suspicion that the inhabitants of a leper colony are likely to have formed unusually caring bonds with one another for this reason: sharing the knowledge that each has experienced the same suffering in the form of seeing the visible repulsion that the very sight of oneself causes in strangers, a typical resident might naturally have felt empathy towards fellow sufferers and perhaps some in being comfortable with and accepting of one another. The data ably collected by Ramos Toro and local assistants might be explained by such feelings, and the evidence of their persistence over the generations is an exciting dividend of the still-evolving method of experimental and behavioral economic analysis.