The Black Death and European Intelligence:

An Evolutionary Perspective

December 5th, 2005

There has been much recent discussion in psychological and sociological circles on the notion that the European plagues of the Fourteenth through Eighteenth centuries had the effect of boosting genotypic intelligence throughout Europe in a way which precipitated the scientific and cultural advances of the Enlightenment. While any conclusive analysis of history is necessarily impossible due to the obvious restrictions on data collection, this subject seems nevertheless to be worthy of some consideration. If it is correct that the plagues increased genotypic intelligence in Europe, then two things must be true, the first being that intelligence is a characteristic with substantial heritability, the second being that the plague disproportionately affected the survival and fertility of the less intelligent relative to their more intelligent neighbors.

That the Black Death acted as a selection event is not a controversial idea. Many researchers believe that the increased AIDS resistance of ethnic Europeans is directly traceable to the plague epidemic of the Fourteenth Century.1 When one third or more of a population dies off, there will evidently be genetic consequences of one kind or another, and the most obvious consequence of selection by disease is genetic resistance to disease. The high incidence of Sickle-Cell in African populations is an example of this process at work-a single copy of the Sickle-Cell allele grants immunity to malaria, the endemic plague of that region of the world. So the concept that diseases such as the Black Death can alter the allelic frequencies in a population group is uncontroversial. The question is whether the Black Death could have had an impact on characteristics besides those directly related to disease resistance.

Even before considering the specific details of the spread and effect of the Black Death, there is good reason to assume that psychological characteristics were of substantial importance in determining which individuals succumbed, and which survived. In the modern world, intelligence is known to correlate positively with the following:2

• height,
• health,
• fitness,
• metabolism,
• lung capacity,
• infant survival,
• longevity, and
• facial symmetry.

These correlates demonstrate a biological link between intelligence and vitality that should logically transcend temporal and cultural barriers which might prevent modern psychometric analyses from being applied to the Fourteenth century. If individuals with less innate intelligence had reduced health and fitness compared to their peers, then the plague should have had a more severe impact on the less intelligent - an impact which would inevitably lead to increased intelligence throughout the entire population.

Intelligence probably served even better as a direct preventative than as an indirect one. Figuring out how to survive an outbreak of plague would have presented a difficult challenge to those alive during the Middle Ages, and while healthier and higher status medievals likely had better odds of surviving plague, those with foresight would have been much better at avoiding the disease entirely. Marchione di Coppe Stefani gives a horrific account of the events in his contemporary Florentine Chronicle, writing that "There was such a fear that no one seemed to know what to do."3 Yet there were many who did manage to reason out a solution of one kind or another; consider Boccaccio's words in the Decameron:

(T)here were those who thought that to live temperately and avoid all excess would count for much as a preservative against seizures of this kind. Wherefore they banded together, and dissociating themselves from all others, formed communities in houses where there were no sick, and lived a separate and secluded life, which they regulated with the utmost care, avoiding every kind of luxury, but eating and drinking moderately of the most delicate viands and the finest wines, holding converse with none but one another, lest tidings of sickness or death should reach them, and diverting their minds with music and such other delights as they could devise.4

Compare this with another prevalent strategy for coping with the horrors of the Black Death:

Others, the bias of whose minds was in the opposite direction, maintained, that to drink freely, frequent places of public resort, and take their pleasure with song and revel, sparing to satisfy no appetite, and to laugh and mock at no event, was the sovereign remedy for so great an evil: and that which they affirmed they also put in practice, so far as they were able, resorting day and night, now to this tavern, now to that, drinking with an entire disregard of rule or measure, and by preference making the houses of others, as it were, their inns, if they but saw in them aught that was particularly to their taste or liking; which they, were readily able to do, because the owners, seeing death imminent, had become as reckless of their property as of their lives; so that most of the houses were open to all comers, and no distinction was observed between the stranger who presented himself and the rightful lord.4

It is not difficult to see why the former strategy would be not only more successful at boosting survival chances, but would have had greater appeal for the more intelligent, as it requires an orientation towards the future rather than towards immediate gratification. The failure to properly integrate present and future in human thinking is described by Jensen as being a classic manifestation of low intelligence:

(L)ow IQ individuals have a short time horizon; that is, they are present-oriented and more lacking in foresight than most people. Persons with low IQ fail to adequately and realistically imagine the future consequences of their actions. Their immediate behavior is therefore less thoughtful and more impulsive. 2

While other personality traits (such as Extroversion), and other cultural beliefs (such as religious fatalism or a sense of helplessness in the face of divine retribution) probably influenced the decision to make merry and risk death by plague, this does not by any means point to the conclusion that intelligence had no ability to influence the outcome of an individual's decision. Consider for instance the example of Isaac Newton; although he wasn't alive during the original outbreak of plague in Europe, Newton left London to avoid a then-current outbreak of plague, and survived to ultimately become one of the most respected men of science.

Lastly, intelligence also shows merit as a candidate for selection by the plague because of its correlates in the social arena - possibly the most effective way in which intelligence could affect disease survival is through social status and wealth. In the modern era, the correlates of intelligence also include income the following:2

• socioeconomic status of origin,
• achieved socioeconomic status,
• voluntary migration,
• functional literacy,
• accident avoidance, and
• freedom from alcoholism.

Many of these have larger correlation coefficients than those related to general health, and all would have offered protection against plague. Whether these social variables would have been related to intelligence during the High Middle Ages is an interesting question which lacks a definitive answer. Yet the relationship between intelligence and social status is likely to be robust, given that, according to David Buss' famous cross-cultural survey, intelligence is universally valued as an attractive characteristic in a spouse in wealthy and developing nations alike;2 this indicates an old selective bias favoring intelligence which should logically allow individuals with higher intelligence to climb the social ladder no matter what the circumstances. Knowing also that intelligence in the modern world grants improved performance in even the most mundane of tasks such as cooking eggs or supermarket shopping,2 it is difficult to imagine why intelligence would have lacked utility in the High Middle Ages. After all, omelets and town markets are hardly an innovation of the modern world; nor is social status, which was, if anything, of more pronounced importance throughout the High Middle Ages.

Of course, many historians imply that the Black Death could not have acted as a selection event, making statements such as:

Few (families) can have been spared some loss, since the plague killed indiscriminately, striking at rich and poor alike6

And:

Filth running in open ditches in the streets, fly-blown meat and stinking fish, contaminated and adulterated ale, polluted well water, unspeakable privies, epidemic disease, were experienced indiscriminately by all social classes.7

If it is true that the plague struck indiscriminately, then there would have been no way for any character trait to have been affected by the plague. Yet contemporary accounts belie this interpretation; John of Fordun wrote of Scotland that "This sickness befell people everywhere, but especially the middling and lower classes, rarely the great."8

This should come as no real surprise. The people of Europe were already weakened before the onset of the plague by famine, brought about in part by high population. More people in Europe meant that more land had to be brought under cultivation, but much of the best land had already been parceled off. But the wealthiest individuals would have scarcely noticed food shortages; although perhaps not so ignorant of hardship and food scarcity as Marie Antoinette, many noble families, and even successful trades families living in the High Middle Ages would have had more to eat for the entirety of their lives than the lower classes, and would have therefore been in better physical condition to resist plague. In other words, while there was no perfect defense against plague, being rich and powerful was quite helpful - and having rich and powerful relatives was the next best thing.

It is useful to have this information on class effects, since there is no good way that contemporaries could have estimated whether the plague struck indiscriminately within social classes or had a disproportionate effect on the less intelligent. The best that modern scholars can do is attempt to make conceptual arguments and show that the research carried out on modern populations, if it were applicable to medievals, leads to the conclusion that the plague would have had a positive net effect on genotypic intelligence in Europe.

But does psychometric research carried out on modern populations really have any validity when applied to social groups which lived and died six centuries ago? This is perhaps the lynch-pin of the evolutionary argument: the assumption that medieval society was, even if it differed in certain aspects, broadly comparable to modern societies. Dunnigan and Nofi provide a brief and lucid summary which should help to address this subject:

Medieval society was different, but not so different as to be totally alien to what we experience in the 20th century. In the 14th century, people were born, grew up, fell in love, married, had children, and died. People ate, got sick, took baths, dressed up for special occasions, went to church, attended wedding receptions, gossiped, got drunk, went to work with hangovers, committed adultery, beat their spouses, looked after their elderly parents, grieved for their dead, went off to war, engaged in unprotected sex as adolescents, celebrated Christmas, went skinnydipping, kept dogs as pets, and consulted horoscopes.9

But most important of all is this simple statement:

You can still find medieval living conditions and sensibilities in Third World nations.9

Fortunately, most of these quirks can be largely subsumed into variation which exists in the modern day. For instance, one of the most profound differences between Fourteenth Century Europe and the modern West is the existence of a powerful religious monopoly: the Roman Catholic Church. Following the events of the Reformation, there has been no such monopoly in the modern West to serve as a comparison; the character of Catholicism has mellowed significantly in the last several centuries. Still, the Islamic world may provide a useful parallel to the medieval Church with its fervent religious legalism, ritualistic devotional practices, powerful hierarchy, and militaristic theological doctrines. While the comparison is of course not perfect, the fact that institutions similar to the old Church do exist in the modern world prevents the medieval religious structure from creating an insurmountable barrier to comparisons between modern and medieval societies: a modern data set is, in theory, at least, broad enough to account for medieval religion.

Perhaps one difference with greater importance to this discussion is the medieval castle. Lacking well developed military technology, the stone fortress was an unrivaled symbol of autocratic mastery. Armies defending in castles were so difficult to defeat that the only reliable method for taking a castle required an overwhelming numerical advantage applied over half a year's time, or longer - siege warfare. This allowed nobles to firmly entrench themselves within their private fortresses and easily resist attack from all but the most dedicated, well armed, and well supplied of enemies. And city walls of course provided similar defense for those residing within them. This would have given medievals a sense of continuity and stability lacking from the modern era, where firearms have become ubiquitous in a way which renders the castle totally obsolete. Rocket launchers and machine guns are common even in the developing world, preventing useful fortresses from being built on the same scale as those of the medieval era; this probably has the effect of making modern societies more unstable than medieval ones.

But most other differences between medieval and modern societies can be chalked up to technological differences, educational differences, and differences in family structure, all of which are readily observed to exist throughout the modern era. Thus, it is reasonable to bring up cross-cultural research in order to compare societies which are not only separated by geographic distance, but societies separated by temporal distance.

Gerhard Meisenberg carried out a 2004 study on the World Values Survey which is excellent for this purpose, titled "Talent, Character, and the Dimensions of National Culture." In the abstract, he reports the following (emphasis added):

This study investigates the dimensions of cultural variation in the modern world as assessed by the World Values Survey. It confirms the previously reported existence of two major dimensions of cultural variation that can be described as 'modern' and 'postmodern,' respectively. Modern values are characterized by skepticism and critical thinking, with a rejection of religion and traditional authority along with an interest in politics. In multiple regression models, modern values are directly related to the IQ of the population. Postmodern values are characterized by trust, tolerance, and self-realization. In multiple regression models, they are inversely related to corruption. Subjective well-being is positively related to postmodern values and negatively to modern values. Modern values are interpreted as the emancipation of reason from the constraints of traditional custom and religion, and postmodern values as the emancipation of pleasure-seeking and social emotions from the constraints of dysfunctional social systems.10

Meisenberg's description of "modern" values is highly consistent with general descriptions of value systems flourishing during the Renaissance. The Middle Ages were generally characterized instead by a broad acceptance of religion, metaphorical and literary thinking, and defense of traditional authority and custom. Of course, it would probably be inaccurate to claim that the medieval era was the intellectual wasteland Enlightenment thinkers often described it as being, but by the same token it is generally accepted that the Enlightenment was characterized more by skepticism, critical thinking, a rejection of religion and traditional authority, and an interest in politics, than the preceding era. That such values correlate with the average IQ of existing populations serves as useful evidence suggesting that something - even if not necessarily the Black Death - boosted the average intelligence in Europe during the centuries preceding in a way that encouraged such values to grow.

It may be tempting to dismiss this unusual argument on the grounds that evolution can't proceed over the span of a few generations. Yet Vining found that genotypic IQ in the 1980's was dropping, due to differential fertility alone, at the rate of 1.6 points per generation in a white sample, and 2.4 points per generation in a black sample.11 Herrnstein & Murray showed that a shift of IQ 3 points produces dramatic changes in societal functioning, changing crime rates, education rates, and poverty rates by over ten percent.12 It is also generally reported that most creative advances come from those with IQs above the 130 IQ mark (for instance, the chance of earning a Nobel Prize reaches its peak at 130 IQ);13 a 6-point shift in average IQ from 97 to 103 would change the number of individuals above 130 IQ from 14 per thousand to 36 per thousand, roughly doubling the creative potential of a society undergoing such a shift.

Remember, all that is necessary for natural selection to act on a trait is for that trait to carry substantial heritability; in the modern era, the heritability for measured IQ is approximately 75%, as reported by the American Psychological Association.14 Could this heritability have been lower during the Middle Ages? Indeed, it probably was. Poor nutrition and widespread teratogens (such as alcohol, which was consumed ubiquitously by medievals, even pregnant mothers) would have added environmental variation to intelligence differences existing within the population. This would not, however, have eliminated the genetic contribution to intelligence, merely watered it down. Even a more modest heritability of 60% or even 40% would have been easily enough to allow for selective forces to act on intelligence through a few hundred years of pestilence and plague.

As a final check on the utility of this model, it is useful to compare the areas in Europe which were hit hardest with those that suffered less overall from plague deaths. Because genetic diffusion has taken place over the many generations since the primary selection event represented by the onset of the Black Death in the middle of the Fourteenth Century, the end of the plague in Europe during the Eighteenth Century, and the start of the Twenty First Century, it will not be possible to consider smaller areas and sub-populations, but the hypothesis should still be testable at the larger scale. According to Wikipedia, the Black Death struck Eastern Europe less hard than Western Europe because of lower population density towards the East;15 thus, the evolutionary model predicts higher overall intelligence for Western than Eastern Europe. Does the data bear this out? According to IQ studies compiled by Richard Lynn and Tatu Vanhanen, Eastern Europe is significantly lower in average IQ than Western Europe; here are the IQ figures themselves (all given relative to a British mean of 100):16

102 IQ: 101 IQ: 100 IQ: 99 IQ: 98 IQ: 97 IQ: 96 IQ: 95 IQ: 94 IQ: 93 IQ: 92 IQ: 90 IQ:

Austria, Germany, Italy, Netherlands Sweden, Switzerland Belgium, United Kingdom Hungary, Poland Denmark, France, Norway Czech Republic, Finland, Spain Russia Portugal, Slovenia Romania Bulgaria, Ireland Greece Croatia

Despite a few outliers (namely, Portugal and Ireland), and further despite some inescapable margin for error resulting from problems in data collection and test design, it is apparent that the Western European nations do indeed have higher overall averages than the Eastern European nations in measured IQ, just as predicted.

Thus, the evolutionary argument can be considered complete: the trait in question not only shows good heritability and apparent sensitivity to selection by plague, but this model generates testable hypotheses which are upheld by the available data. In a sense, then, what medievals perceived as an act of divine retribution for their sinfulness was instead a whetstone which honed their minds in such a way as to allow for the scientific explosion modern historians describe as "The Enlightenment."

But the outliers in the above table are worth further consideration. Portugal has a substantial African element in its gene pool, as does Greece, and it is therefore unsurprising to see these two countries scoring low in IQ. But Ireland is more of a puzzle. Why would modern Ireland score fully 7 IQ points below neighboring Great Britain? One common answer, casually offered by Matt Nuenke, is that Ireland, too, underwent a recent selection event after the Black Death: the potato famine.17 Roughly a third of the Irish migrated from Ireland, leaving half of the remainder to starve. Voluntary migration is correlated with IQ, probably for many reasons touched on above such as foresight or sufficient wealth for traveling abroad; the more intelligent left Ireland and experienced higher survival rates than the less intelligent.

This was observable in the recent New Orleans disaster, where it was primarily the poorest and most strongly Black element of the population that remained behind to suffer the brunt of hurricane Katrina. It is especially interesting to note that New Orleans has a large Creole population which, despite being socially identified as "Black," was notably absent in disaster footage, indicating that they generally fled the area alongside the ethnic Europeans. Given that the heritability of racial IQ differences is somewhere on the order of 50%,2 this is compelling evidence that the selective model presented in this paper is in effect during many different kinds of disasters, not only disease epidemics. It seems especially effective with disease, however, given the extremely high rates of HIV and AIDS in contemporary Black and Latino populations relative to those of more intelligent racial groups.

One question this analysis cannot answer is "Why didn't East Asia experience a Renaissance if Europe did?" East Asia also experienced plague deaths, possibly more than Europe did, and shows a significantly higher average IQ. This presents a problem for any explanation on the European Renaissance which relies entirely on disease and intelligence, and demonstrates the necessity of bringing other explanations to bear. It is worth pointing out that historians have never needed evolutionary or psychometric models to explain the changing value systems of the Enlightenment period; there have always been reasonable military, political, religious, social, and economic explanations available. Some probable environmental causes for the rise of the European Enlightenment include:

1. Weapons technology, such as gunpowder and the crossbow which together undermined the authority of the aristocracy by outmoding its knights, and cannons, which greatly lessened the societal stability created by castles,
2. The rise of cities, which further weakened the power of the aristocracy by developing the economic power to rival and ultimately surpass that of most nobles;
3. Increasing education and literacy of the peasant classes;
4. Increasing anticlericalist sentiments germinated around the Fourteenth century which weakened Church authority; and also
5. The plague itself, which destabilized the social system and created a labor shortage which increased the economic power of skilled tradesmen.

Disputing the salience of these points would be counterproductive, since they all offer useful explanations for the events of the Renaissance. But many of these can only offer a speculative explanation for the lack of any obvious East Asian Renaissance, and all of them lack the benefit of a century of psychometric and sociological research, which the evolutionary explanation has behind it. Consider for example anticlericalism, which, although a reasonable explanation for the eventual Reformation with the added appeal of being restricted to Europe and not Asia, is nevertheless missing a scientific basis. There is also the further question of the timing of the Reformation, which is imperfectly consistent with anticlericalism as an explanation - opposition to the Church would have been strongest around the time of the onset of the Black Death, so why did the heresy of Wycliffe fail to take root when Martin Luther's Reformation succeeded? Of course, this is precisely what the evolutionary model would predict, since the early anticlericalism would have arisen before intelligence had changed sufficiently to encourage organized political action against oppressive religious regimes; the plagues continued to wash over the European populace for many centuries following the initial outbreak. The best use of the analysis detailed in this paper, then, is to apply it as a supplement to more traditional models rather than as a single overarching explanation for the Enlightenment in Europe.

Although the conclusions drawn in this paper are obviously tentative, they suggest a few interesting consequences for human society in the future. Perhaps some disaster, affecting billions of human beings over several generations, could once more raise intelligence to Enlightenment levels and beyond. Perhaps an effective eugenics program which raised the average intelligence by fewer than ten points could spur a new Renaissance in the populace which dared to apply it on itself. But most intriguingly, it appears that the consequences of rising intelligence are an increase in secularization, a rejection of traditional authority, and heightened political participation. This appears true on both an individual and national scale, given not only Meisenburg's analysis above, but the evidence that IQ relates on an individual level to liberalism,13 to a rejection of traditional religion,13 and to the personal decision to vote in democratic elections.12 This being the case, it appears that the survival of traditional religious and governmental forms such as monotheism and centralized monarchies would be jeopardized by the application of global-wide eugenics. Or, stated another way, perhaps the only hope of substantially increasing human intelligence through eugenic means resides in the adoption of modern religious and governmental forms which anticipate the higher intelligence of future human beings.

References

1. Trinkl, Alice. "A Relative Of Smallpox Is First Virus Found To Invade Cells As Hiv Does." December 2, 1999.

2. Jensen, Arthur. The g Factor: The Science of Mental Ability. (1998)

3. Stefani, Marchione di Coppo. Cronaca Fiorentina. Rerum Italicarum Scriptores, Vol. 30. , ed. Niccolo Rodolico. Citta di Castello: 1903-1913

4. Boccaccio, Giovanni. The Decameron. M. Rigg, trans. Vol. 1, pp. 5-11. London: David Campbell. (1921)

5. ABC Radio National Science Program. "Descent of Man: Stone Age Minds in Modern Skulls." (2000)

6. Bolton, ed. Ormrod and Lindley. The World Upside Down: Black Death in England. (1996)

7. Holt and Rosser, The English Medieval Town. (1990)

8. John of Fordun, Scotichronicon. (1384)

9. Dunnigan, James F. and Nofi, Albert A. "Medieval Life and the Hundred Years War." Hundred Years War Archives. (1997)

10. Meisenburg, Gerhard "Talent, Character, and the Dimensions of National Culture." Mankind Quarterly. (2004)

11. Vining, D. R. "On the possibility of the re-emergence of a dysgenic trend with respect to intelligence in American fertility differentials." Intelligence, 6, 241-264. (1982)

12. Herrnstein, Richard and Murray, Charles. The Bell Courve: Intelligence and Class Structure in American life Free Press (1994)

13. Henshaw, Mark W. These Hidden Truths: Psychometrics, Society, and the Unspeakable Heresies of Our Time Iuniverse (2005)

14. Neisser, Ulric. et al. "Intelligence: Knowns and Unknowns." Washington, DC: American Psychological Association. (1996)

15. Wikipedia: The Online Encyclopedia.

16. Lynn, Richard and Tatu, Vanhanen. IQ and the Wealth of Nations. (2002)

17. Nuenke, Matt. "A Review of The Book Eugenics: A Reassessment by Richard Lynn."