Plagues & molecules?

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Two interesting articles out in the PNAS early release feed.

Molecular insights into human daily behavior:

Human beings exhibit wide variation in their timing of daily behavior. We and others have suggested previously that such differences might arise because of alterations in the period length of the endogenous human circadian oscillator. Using dermal fibroblast cells from skin biopsies of 28 subjects of early and late chronotype (11 “larks” and 17 “owls”), we have studied the circadian period lengths of these two groups, as well as their ability to phase-shift and entrain to environmental and chemical signals. We find not only period length differences between the two classes, but also significant changes in the amplitude and phase-shifting properties of the circadian oscillator among individuals with identical “normal” period lengths. Mathematical modeling shows that these alterations could also account for the extreme behavioral phenotypes of these subjects. We conclude that human chronotype may be influenced not only by the period length of the circadian oscillator, but also by cellular components that affect its amplitude and phase. In many instances, these changes can be studied at the molecular level in primary dermal cells.

Weird. ScienceNow notes some implications:

…raises the possibility of an inexpensive and objective test of a person’s “owlness” or “larkness.” Such a test would be no small matter, given the prevalence of sleep disorders and the fact that many drugs, including cholesterol medications and chemotherapy, work more effectively if administered at certain points in a person’s sleep/wake cycle. Pinpointing individual clock cycles could pave the way for personalized sleep and drug therapies, says Achim Kramer, a Free University chronobiologist who helped design the study.

Selectivity of Black Death mortality with respect to preexisting health:

Was the mortality associated with the deadliest known epidemic in human history, the Black Death of 1347-1351, selective with respect to preexisting health conditions (“frailty”)? Many researchers have assumed that the Black Death was so virulent, and the European population so immunologically naive, that the epidemic killed indiscriminately, irrespective of age, sex, or frailty. If this were true, Black Death cemeteries would provide unbiased cross-sections of demographic and epidemiological conditions in 14th-century Europe. Using skeletal remains from medieval England and Denmark, new methods of paleodemographic age estimation, and a recent multistate model of selective mortality, we test the assumption that the mid-14th-century Black Death killed indiscriminately. Skeletons from the East Smithfield Black Death cemetery in London are compared with normal, nonepidemic cemetery samples from two medieval Danish towns (Viborg and Odense). The results suggest that the Black Death did not kill indiscriminately-that it was, in fact, selective with respect to frailty, although probably not as strongly selective as normal mortality.

We’ve all read Farewell to Alms, so we know the argument that quick die offs can be good for standards of living by relieving some of the Malthusian pressure. Though if you ever took a normal medieval history course you’d probably be told about the premium on labor which emerged after the Black Death due to shortages and its affect on the collapse of the old manorial system (I was). But this data is interesting because it confirms that the most economically productive proportion a society where muscle power might was of essence have increased as a proportion of the population after these sorts of epidemics swept through. Perhaps these are the sorts of shocks that social systems need to shift toward another equilibrium? (I know, morbid)

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  1. As a general rule there are always social class differentials in mortality, with people getting healthier and longer lived as they get wealthier.  
    Underlying this health/ mortality differential are significant social class differences in average IQ.  
    Gottfredson has made this the basis of a theory of the relatively) recent evolution of intelligence.  
    When you combine social class IQ differences with social class health and mortality differences (and differences in reproductive success), this could well have constituted a major selection basis for the increase of intelligence in human populations which have inhabited complex agricultural societies.  

  2. Excuse my naivety, but wouldn’t it be more useful to compare Black Death cemeteries in England with other cemeteries in England? Preferably in the same geographical area, and both urban, or both rural.

  3. BGC, 
    I totally agree! 
    In the Great Irish Famine of the mid-1840′s in Ireland, the poorest 15-20% of the population died – they were largely servants, laborers and so on, they mostly subsisted on the potato and lived in the West of the country. The emigrants to the US and elsewhere were from the small farmer class. The large farmers not only survived but prospered in tis era. I grew up in the East of the country – where the land is very fertile and traditionally grain crops are grown and not too many potatoes – and know of some very prosperous families, whose fortune was made during the famine, when they greatly increased their land holdings, by offering a pittance to the destitute for their small farms.

  4. David B, 
    I thought the same when I read it! 
    They are surely comparing Apples and Oranges – as the London area was densely populated and had many urban slums – ideal habitats for rats – whereas Viborg and Odense are little more than towns…

  5. “Underlying this health/ mortality differential are significant social class differences in average IQ.” 
    Consider this toy model for an average community: 
    Over 90% were low class who were often starving before winter ended. They would have been malnourished and sickly. 
    The upper class would never starve and would regularly eat meat. They would be healthy and strong. 
    High status men would regularly father bastards in the lower classes. Also upper class families would expand and displace the lower classes. 
    Alleles would regularly flow from the upper class to the lower class. Strong selection pressure in the lower class would eliminate the low fitness alleles. In this model the lower class would average more high fitness alleles than the upper class. However, due to differences in nutrition and health, the upper class phenotype would be significantly better. 
    In this toy model, selection for intelligence might occur within the upper class but the between class genetic differences should have little affect on long term community genetics. 
    In a society with abundant, nutritious food and high social mobility, class differences may be largely genetic. It is not clear to me that this was commonly true in the Middle Ages.