Kaati G., Bygren L. O., and Edvinsson S. (2002), “Cardiovascular and diabetes mortality determined by nutrition during parents’ and grandparents’ slow growth period”, European Journal of Human Genetics, 10, 682-688.
It has been shown that low food availability during childhood or adolescence predisposes to cardiovascular diseases (p.682). Similarly, one’s risk to die of a stroke is affected by his mother’s food intake during pregnancy. But what if there were even more distant causes to cardiovascular issues?
To test for this hypothesis, the authors used the data provided by the parish of Överkalix in Northern Sweden (well known to all geneticists). They used 239 probands, individuals born in 1890, 1905 and 1920 as material. Cause of death for all these individuals are known
This region of Sweden is particularly isolated and in case of hardship little help is to be expected from the outer world. Thus a failed harvest would strongly affect the population. On the other hand, there was little chance to export the agricultural surpluses, as a result a plentiful harvest would be followed by serious overfeeding. The authors’ attention turned to the slow growth period (SGP, i.e. 8-10 years old girls and 9-12 years old boys) of the probands’ parents and grandparents, which turned out to be particularly instructive (p.683). Based on wheat price series, the authors identified 18 years of crop failure and 20 years of plenty from 1799 to 1890. The other ones were considered to have had neither poor nor abundant harvests.
The most significant conclusion reached by the researchers was that a proband’s paternal grandfather exposure to food availability was strongly correlated with the probands’ survival in the 1890 and 1905 cohorts. The probands whose paternal grandfather had been exposed to crop failure during his SGP were protected from cardiovascular-related causes of death (p.684). On the other hand “if the paternal grandfathers had access to a surfeit of food during SGP, the probands (their grandchildren) had a fourfold over-risk for death of diabetes mellitus”. The article lists other effects of over- and under-feeding of one’s ascendants on one’s survival but they are less significant (p.687).
The authors have described a feed-forward loop linking grandparental nutrition with their grandchildren health. They attribute the causes of this process to epigenetic factors but admit any further explanation remain elusive. For the records, the spermediated INS – IGF2 – H19 imprinted domain is a good candidate to carry these changes accross generations.
Beyond the interest as such of this research, it shows clearly that our understanding of the biological factors affecting human life are yet to be significantly improved. And this is particularly true for the social scientists. Epigenetic inheritance is particularly interesting for historians due to their spontaneity (unlike selection) and their trans-generational characteristics. This article for instance ought to affect the way we understand the effects of the positive Malthusian checks. Other researchers have shown (for chickens) the influence on an individual’s IQ of her grandparents level of stress. This in turn may have major implications on the way we understand innovation.
In anyway, it appears that the individual cannot remain the last black box of social sciences. The environment affects us in such ways that the rationality warranted to the historical actors has to be complemented with hard-wired mechanisms such as the ones described above. One can only dream that one day psychology and biology classes will be compulsory in every economics and historical curricula.