Corey L. Fincher, Randy Thornhill, Damian R. Murray, and Mark Schaller
Pathogenic diseases impose selection pressures on the social behaviour of host populations. In humans (Homo sapiens), many psychological phenomena appear to serve an antipathogen defence function. One broad implication is the existence of cross-cultural differences in human cognition and behavior contingent upon the relative presence of pathogens in the local ecology. We focus specifically on one fundamental cultural variable: differences in individualistic versus collectivist values. We suggest that specific behavioural manifestations of collectivism (e.g. ethnocentrism, conformity) can inhibit the transmission of pathogens; and so we hypothesize that collectivism (compared with individualism) will more often characterize cultures in regions that have historically had higher prevalence of pathogens. Drawing on epidemiological data and the findings of worldwide cross-national surveys of individualism/ collectivism, our results support this hypothesis: the regional prevalence of pathogens has a strong positive correlation with cultural indicators of collectivism and a strong negative correlation with individualism. The correlations remain significant even when controlling for potential confounding variables. These results help to explain the origin of a paradigmatic cross-cultural difference, and reveal previously undocumented consequences of pathogenic diseases on the variable nature of human societies.
Part of their argument is one that I've been half-jokingly suggesting about the ferociously xenophobic pygmy negritos of North Sentinel Island in the Andamans, off the coast of Indonesia. As I wrote in 2006:
A long time theme here at iSteve.com is defending human biodiversity. Although defending plant and animal biodiversity is extremely fashionable, nobody else speaks up for human biodiversity. Of particular concern to me has been the survival of the pygmy negrito Andamanese of North Sentinel Island in the Indian Ocean (located roughly where Skull Island in "King Kong" would be), one of the last tribes out of contact with the rest of the world. If they ever come into contact with us, most of them will die from diseases for which they have no defenses.
Fortunately, the Sentinelese have no intention of going down without a fight. The Daily Telegraph reports:
Stone Age tribe kills fishermen who strayed on to island
But, it's not at all clear that this evolutionary mechanism, if it exists, could play a sizable role in explaining why, say, the Japanese are more collectively minded.
Certainly, infectious diseases have played a hugely important r0le in the development of cultural and biological differences among humans, but this paper has some major problems. Let's leave aside for now the individualism / collectivism dimension, which clearly is difficult to define, much less measure accurately.
Let's look at their measure of disease. To measure the pathogen burden in about 100 different locations, they look at incidence rates for nine infectious diseases, eight of them from the early or mid-20th Century:
To create our primary measure of pathogen prevalence, we were able to estimate the prevalence of nine pathogens detrimental to human reproductive fitness (leishmanias, trypanosomes, malaria, schistosomes, filariae, leprosy, dengue, typhus and tuberculosis) within each of the 93 geopolitical regions worldwide. By necessity, a contemporary source was used to estimate the prevalence of tuberculosis (National Geographic Society 2005), but the prevalence of the remaining eight pathogens was estimated on the basis of old atlases of infectious diseases and other historical epidemiological information (Simmons et al. 1944; Rodenwaldt & Jusatz
But, the key point in the war between germs and people is that it's a constant struggle that goes on and on. All this correlation tells us is that during the first six decades or so of the 20th Century, northern Europeans and their offspring tended to be richer, more scientific, and thus had better public health systems than everybody else. Not surprisingly, their traditional high individualism correlates with low levels of infectious disease at that time.
Although European individualism appears to be deeply rooted many centuries into the past, European health and cleanliness most definitely is not. The cultures that emerged from the barbarian invasions of the Roman Empire were among the dirtiest ever.
When Germanic barbarians took over the Roman Empire and couldn't figure out how to keep the supply of clean water flowing to the cities, the population dropped and the survivors dispersed. The English, for example, developed a culture where their upper classes lived in splendid isolation in the healthy countryside, and congregated in London only in summer, when the risk of epidemic was lowest in that northern region.
When 19th Century Europeans finally developed sanitary habits, supported by the wealth of the Industrial Revolution, the populations of their cities finally exploded.
Today, the four countries with the longest life expectancies (a reasonably proxy for low levels of infectious diseases) are cool Andorra (in the Pyrenees), Macau (across from subtropical Hong Kong), temperate Japan, and tropical Singapore). So, psychologically collectivist East Asians are rapidly overtaking Europeans in freedom from infectious disease, and its not clear that Europeans were better off before the 19th Century either. Marco Polo, for example, was impressed by the cleanliness of China, and so were Christian missionaries in 16th Century Japan.
Both Europe and East Asia, having trade contact with each other for millennia, were within the Old World disease complex, unlike the resistance-weak New World.
Pathogen burden is a function of a lot of different factors: climate (warm is typically worse, but cold is worse for some respiratory diseases); density of population; public health measures such as drinking water, sewer systems, mosquito-spraying, and vaccinations; exposure to domestic animals; isolation; and experience with the diseases in generations past leading to selection for resistance or in childhood leading to individual immunity. It's an extremely dynamic feedback system, with only climate being close to a constant over evolutionary time.