Sharon Begley in Newsweek reports on a hypothesis about "collectivism" and pathogens:
The West epitomizes individualistic, do-your-own thing cultures, ones where the rights of the individual equal and often trump those of the group and where differences are valued. East Asian societies exalt the larger society: behavior is constrained by social roles, conformity is prized, outsiders shunned. "The individualist-collectivist split is one of the most powerful differences among cultures," says Nisbett. But the reason a society falls where it does on the individualism-collectivism spectrum has been pretty much a mystery. Now a team of researchers has come up with a surprising explanation: disease-causing microbes. Societies that evolved in places with an abundance of pathogens, they argue, had to adopt behaviors that add up to collectivism, for reasons of sheer preservation. Societies that arose in places with fewer pathogens had the luxury of individualism, which is less effective at limiting the spread of disease but brings with it other social benefits, such as innovation.
There have been a lot of papers lately trying to match clines (that is, gradients) of phenotypes or genes with current ecological conditions. Climate is the most frequent (often, measured in terms of temperature or rainfall). Pathogens sort of follow the climate gradient, with some exceptions -- sometimes but not always allowing for the fact that malaria is the largest.
But in some cases, much more important will be the historical dimension. Many, (but not all) people who live in high-pathogen areas today had ancestors who adopted agriculture relatively early, began living in denser concentrations and larger groups, and who therefore experienced in common a range of selective pressures that have nothing to do with pathogens.
Would it be surprising that early agriculturalists living in emerging villages and cities might have been subject to pressures that enhanced collectivism? Such changes may have been facilitated by genetic changes, but would have also included cultural adaptations. Yet a correlation with pathogens would emerge as a side-effect of the history of agriculturalism, not as a direct cause.
To my mind, these kinds of historical correlations rooted in ecological change will be a central problem of anthropological genomics. Recent human evolution has been dominated by a few very large changes -- like boulders thrown into a pond that have spread massive ripples through many elements of human genetics, anatomy, and behavior. These changes are not yet complete -- the ripples have not settled down nor reached the shore. For this reason, there will be many correlations that have been induced by the large ecological changes, making bivariate spatial comparisons a poor test of cause.
I would say that historical correlation is a problem with a number of recent studies of cranial variation. Lately, it has been fashionable to test the hypothesis that cranial variation is adaptive to climate, by looking for spatial correlations between cranial measurements and climatic variables. But this test assumes that the correlations have not emerged as a result of some other cause. That might not be such a bad assumption, if humans had been static within their current geographic range for a long, long time. But humans have been anything but static -- in fact, their dynamism over the last 40,000 years has been the cause of profound changes in human biology. Naturally, things will be correlated with climate, because climate has been correlated with human subsistence and population size changes.
A better test of adaptation on cranial variables would propose concrete mechanical (or developmental) reasons why a cranial trait helps someone to better survive under a given climatic regime. Finding a correlation in space is not enough. This is why Bergmann's and Allen's rules are more compelling than the more nebulous idea that "facial form" adapts people to their climate.
Likewise in the case of pathogens -- a correlation between current pathogen load and current behavioral "collectivism" does not suggest a causal relationship between the two. Instead, we would want some kind of functional hypothesis to account for pathogens causing people to change in their attitudes toward cooperating. Concepts like the "luxury of individualism" make little sense. Of course, some people will prefer to behave with individual autonomy. But how would a recurrent epidemic disease stop them?