A few months ago I saw a paper which showed that small average differences across societies on a microeconomc parameter can result in massive variance in macroeconomic trends. Small differences in average trustworthiness or patience across societies (or, more precisely, small differences in the distribution of the psychological trait) can map onto to enormous between society variation in macroeconomic indices which one might adduce derive from the minor individual differences. I was struck by this because it formally and clearly elucidated a major issue I've noted across many domains of the human sciences.
In short this is simply a wider elaboration of the same problem which crops up when one is talking about genotype ⇒ phenotype mapping.
Idealized models where a gene leads to a protein product which performs a specific and precise function don't really apply to a lot of the variation that we're interested in. This is why the statistical techniques of quantitative genetics are still useful and relevant a century after they were first pioneered during the pre-Mendelian era. Nevertheless, though quantitative genetics gives use important tools to map the shape of reality, it often is scaffolded by the context and contingency implied by its assumption of "random" variables and other unaccounted for parameters. It does not offer the idealized deductive power of molecular or population genetic models which start from clear and distinct first principles. The same issues are writ large when we are talking about grand social and historical forces and how they might be altered by micro or individual level variation and change. To illustrate what I'm talking about, imagine a thought experiment. You have an island with 10 operational demes. There is some gene flow across the demes, but they map onto ethno-political units, tribes if you will. Imagine that at a time in the past there is a gene, locus 1, which is fixed for allele A. Locus 1 has pleiotropic affects, controlling a variety of molecular genetic pathways which modulate various phenotypes. We will be interested in two phenotypes, one is an immunological one and another a behavioral. Imagine that the allele A codes for resistance to an endemic disease which is extant across the island. Also, allele A results in a propensity to respond violently to perceived slights. Now, consider that at some point a new variant of the endemic disease alluded to above arises, and that a minor mutant allele, B, confers much greater resistance to the new strain. Over time B replaces A, substitutes, at locus 1. Not only does B change the immunological response of the individual, but it also results in a behavioral modification in terms of the propensity noted above. Imagine that an individual who carries B has a reduced propensity of violent response toward perceived slights. So as a result of selection for a disease there has been an average change in behavioral response within the population. What does this predict in macro terms? One could infer that across the whole island rates of violence will drop with the change in biosocial propensities. But remember when I said about that one of the problems with quantitative genetics is that it doesn't account for the parameters explicitly, the host of mediating affects, influences and variables which modulate and guide the phenotypic expression? Note that I said there are 10 demes on the island. Imagine that the drop in interpersonal violence within the demes causes a host of social changes. For example, all the demes now become much more tightly organized and hierarchical because the lower violence levels also track decreased individualism and a greater ability to accept overbearing leaders. Whereas before the demes were relatively loose social units where interpersonal tension prevented mass mobilization, now they are coalescing into tight political units characterized by greater within group cohesion. One byproduct of this may be greater between group violence, as the demes now begin to compete which each other as the leaders attempt to secure status and wealth through warfare. So in this model the reduced tendency toward interpersonal violence may actually result in a higher death rate per generation as the intensity and frequency of between group conflict increases! Of course the above was just a thought experiment, but it sketches out why I think one could be very careful about drawing straight lines between behavior genetic parameters and social and historical dynamics. But this isn't only an issue going from behavior genetics to sociology or microeconomics to macroeconomics, it is a major problem in historical research in general, or, more accurately, it is the reason that old-fashioned history has not been superseded by more explicitly scientific historical disciplines (e.g., cliometrics). But this does not mean that the lack of a positive program from micro-level disciplines means that history is not immune to the tendency to draw lines where the causal chain seem weak. Consider for example the hypothesis that a specific text, or religion scripture, has a major affect in how a society develops and shapes its values and outlook. How can we go about proving the plausibilities of arguments? The reality is on the individual level the vast majority of humans were illiterate until recently, and psychological science has of late been throwing into doubt the importance of explicit cognition and rationality in our day to day behavior. This seems to pull the legs out from the attempts of many historians to construct narratives which rely upon texts and documents as the primary causative pistons of change and cultural evolution. That being said, even if the behavioral and psychological sciences offer negative findings in relation to some of the intuitive assumptions of traditional history (I would say that much of social history is less text focused and so is less susceptible to the critiques I allude to here), they do not themselves offer up simple models which translate micro-level propensities and changes to marco-level dynamics. Ultimately I think when it comes to grand social claims we live in an era of destruction and negation. Disciplines such as cognitive psychology, which establish the nature of the atomic unit of social organizations, the mind, can offer insights into the constraints and boundaries which scaffold macro-level processes. There are a thousand positive claims made in the historical and sociological sciences, and their 'natural experiments' are often validated by the rhetorical fluidity of the proponents of any given model or theory. Though I am not a religious adherent to the Popperian tendency toward privileging falsification, I do think that as behavior genetics & econonmics and cognitive psychology advance their role will initially be as parsimonious knives cutting away the fat of narrative storytelling which so easily infests history or sociology. Perhaps at some point in the future we will be able to cross the gauntlet of intermediary variables which result in a positive social science which spans mind and society, but I doubt we're there yet.