Consequences of the Black Death

The Black Death, the third deadliest^{[citation needed]} pandemic in human history, which peaked in Europe between 1349 and 1351, led to several major social, economic and religious consequences in Europe.

Depopulation

See also: Medieval demography

Figures for the death toll vary widely by area and from source to source as new research and discoveries come to light. It killed an estimated 75–200 million people in the 14th century.^[1][2][3] According to medieval historian Philip Daileader in 2007:

The trend of recent research is pointing to a figure more like 45% to 50% of the European population dying during a four-year period. There is a fair amount of geographic variation. In Mediterranean Europe and Italy, the South of France and Spain, where plague ran for about four years consecutively, it was probably closer to 75% to 80% of the population. In Germany and England it was probably closer to 20%.^[4]

Asia

Estimates of the demographic impact of the plague in Asia are based on both population figures during this time and estimates of the disease's toll on population centers. The initial outbreak of plague in the Chinese province of Hubei in 1334 claimed up to ninety percent of the population, an estimated five million people. During 1353–54, outbreaks in eight distinct areas throughout the Mongol/Chinese empire may have possibly caused the death of two-thirds of China's population, often yielding an estimate of twenty-five million deaths. China had several epidemics and famines from 1200 to the 1350s and its population decreased from an estimated 125 million to 65 million in the late 14th century.^[5][6][7]

Europe and Middle East

It is estimated that between one-quarter and two-thirds of the European population (35 million people) died from the outbreak between 1348 and 1350.^[8][9] Contemporary observers, such as Jean Froissart, estimated the toll to be one-third—less an accurate assessment than an allusion to the Book of Revelation meant to suggest the scope of the plague.^[10] Many rural villages were depopulated, mostly the smaller communities, as the few survivors fled to larger towns and cities leaving behind abandoned villages.^[11] The Black Death hit the culture of towns and cities disproportionately hard, although rural areas (where most of the population lived) were also significantly affected. A few rural areas, such as Eastern Poland and Lithuania, had such low populations and were so isolated that the plague made little progress. Parts of Hungary and, in modern Belgium, the Brabant region, Hainaut, and Limbourg, as well as Santiago de Compostela, were unaffected for unknown reasons (some historians^[12] have assumed that the presence of resistant blood groups in the local population helped them resist the disease, although these regions would be touched by the second plague outbreak in 1360–63 and later during the numerous resurgences of the plague). Other areas which escaped the plague were isolated mountainous regions (e.g. the Pyrenees). Larger cities were the worst off, as population densities and close living quarters made disease transmission easier. Cities were also strikingly filthy, infested with lice, fleas, and rats, and subject to diseases related to malnutrition and poor hygiene. According to journalist John Kelly, "[w]oefully inadequate sanitation made medieval urban Europe so disease-ridden, no city of any size could maintain its population without a constant influx of immigrants from the countryside".(p. 68) The influx of new citizens facilitated the movement of the plague between communities, and contributed to the longevity of the plague within larger communities.

In Italy, Florence's population was reduced from 110,000 or 120,000 inhabitants in 1338 to 50,000 in 1351. Between 60 to 70% of Hamburg and Bremen's population died. In Provence, Dauphiné, and Normandy, historians observe a decrease of 60% of fiscal hearths. In some regions, two thirds of the population was annihilated. In the town of Givry, in the Bourgogne region in France, the friar, who used to note 28 to 29 funerals a year, recorded 649 deaths in 1348, half of them in September. About half of Perpignan's population died in several months (only two of the eight physicians survived the plague). Over 60% of Norway's population died from 1348 to 1350.^[13] London may have lost two-thirds of its population during the 1348–49 outbreak.^[14] England lost 70% of its population, which declined from 7 million before the plague, to 2 million in 1400.^[15]

All social classes were affected, although the lower classes, living together in unhealthy places, were most vulnerable. Alfonso XI of Castile was the only European monarch to die of the plague, but Peter IV of Aragon lost his wife, his daughter, and a niece in six months. Joan of England, daughter of Edward III, died in Bordeaux on her way to Castile to marry Alfonso's son, Pedro. The Byzantine Emperor lost his son, while in the kingdom of France, Joan of Navarre, daughter of Louis X le Hutin and of Margaret of Burgundy, was killed by the plague, as well as Bonne of Luxembourg, the wife of the future John II of France.

Furthermore, resurgences of the plague in later years must also be counted: in 1360–62 (the "little mortality"), in 1366–69, 1374–75, 1400, 1407, etc. The plague was not eradicated until the 19th century.

The precise demographic impact of the disease in the Middle East is very difficult to calculate. Mortality was particularly high in rural areas, including significant areas of Judea and Syria. Many surviving rural people fled, leaving their fields and crops, and entire rural provinces are recorded as being totally depopulated. Surviving records in some cities reveal a devastating number of deaths. The 1348 outbreak in Gaza left an estimated 10,000 people dead, while Aleppo recorded a death rate of 500 a day during the same year. In Damascus, at the disease's peak in September and October 1348, a thousand deaths were recorded every day, with overall mortality estimated at between 25 and 38 percent. Syria lost a total of 400,000 people by the time the epidemic subsided in March 1349. In contrast to some higher mortality estimates in Asia and Europe, scholars such as John Fields of Trinity College in Dublin believe the mortality rate in the Middle East was less than one-third of the total population, with higher rates in selected areas.

Social and economic effects

Monks, disfigured by the plague, being blessed by a priest. England, 1360–75

The governments of Europe had no apparent response to the crisis because no one knew its cause or how it spread. In 1348, the plague spread so rapidly that before any physicians or government authorities had time to reflect upon its origins, about a third of the European population had already perished. In crowded cities, it was not uncommon for as much as fifty percent of the population to die. Europeans living in isolated areas suffered less, and monasteries and priests were especially hard hit since they cared for the Black Death's victims.^[16]

Because fourteenth century healers were at a loss to explain the cause, Europeans turned to astrological forces, earthquakes, and the poisoning of wells by Jews as possible reasons for the plague's emergence.^[16] No one in the fourteenth century considered rat control a way to ward off the plague, and people began to believe only God's anger could produce such horrific displays. There were many attacks against Jewish communities. In February 1349, 2,000 Jews were murdered in Strasbourg. In August of the same year, the Jewish communities of Mainz and Cologne were exterminated.^[17]

Where government authorities were concerned, most monarchs instituted measures that prohibited exports of foodstuffs, condemned black market speculators, set price controls on grain, and outlawed large-scale fishing. At best, they proved mostly unenforceable. At worst, they contributed to a continent-wide downward spiral. The hardest hit lands, like England, were unable to buy grain abroad: from France because of the prohibition and from most of the rest of the grain producers because of crop failures from shortage of labour. Any grain that could be shipped was eventually taken by pirates or looters to be sold on the black market. Meanwhile, many of the largest countries, most notably England and Scotland, had been at war, using up much of their treasury and exacerbating inflation. In 1337, on the eve of the first wave of the Black Death, England and France went to war in what would become known as the Hundred Years' War. Malnutrition, poverty, disease and hunger, coupled with war, growing inflation and other economic concerns made Europe in the mid-fourteenth century ripe for tragedy.

The plague did more than just devastate the medieval population; it caused a substantial change in economy and society in all areas of the world. Economic historians like Fernand Braudel have concluded that Black Death exacerbated a recession in the European economy that had been under way since the beginning of the century. As a consequence, social and economic change greatly accelerated during the fourteenth and fifteenth centuries. The church's power was weakened and, in some cases, the social roles it had played were taken over by secular groups. Also the plague led to peasant uprisings in many parts of Europe, such as France (the Jacquerie rebellion), Italy (the Ciompi rebellion, which swept the city of Florence), and in England (the English Peasant Revolt).

Europe had been overpopulated before the plague, and a reduction of 30% to 50% of the population could have resulted in higher wages and more available land and food for peasants because of less competition for resources^{[citation needed]}. In 1357, a third of property in London was unused due to a severe outbreak in 1348–49.^[14] However, for reasons that are still debated, population levels declined after the Black Death's first outbreak until around 1420 and did not begin to rise again until 1470, so the initial Black Death event on its own does not entirely provide a satisfactory explanation to this extended period of decline in prosperity. See Medieval demography for a more complete treatment of this issue and current theories on why improvements in living standards took longer to evolve.

The great population loss brought economic changes based on increased social mobility, as depopulation further eroded the peasants' already weakened obligations to remain on their traditional holdings. In the wake of the drastic population decline brought on by the plague, authorities in Western Europe worked to maintain social order through instituting wage controls.^[18] These governmental controls were set in place to ensure that workers received the same salary post-plague as they had before the onslaught of the Black Death.^[18] Within England, for example, the Ordinance of Labourers, created in 1349, and the Statute of Labourers, created in 1351, restricted both wage increases and the relocation of workers.^[19] If workers attempted to leave their current post, employers were given the right to have them imprisoned.^[19] The Statute was strictly enforced in some areas. For example, 7,556 people in the county of Essex were fined for deviating from the Statute in 1352.^[20] However, despite examples such as Essex, the Statute quickly proved to be difficult to enforce due to the scarcity of labour.

In Western Europe, the sudden shortage of cheap labour provided an incentive for landlords to compete for peasants with wages and freedoms, an innovation that, some argue^{[weasel words]}, represents the roots of capitalism, and the resulting social upheaval "caused" the Renaissance, and even the Reformation. In many ways the Black Death and its aftermath improved the situation of surviving peasants, notably by the end of the 15th century. In Western Europe, labourers gained more power and were more in demand because of the shortage of labour. In gaining more power, workers following the Black Death often moved away from annual contracts in favour of taking on successive temporary jobs that offered higher wages.^[21] Workers such as servants now had the opportunity to leave their current employment to seek better-paying, more attractive positions in areas previously off limits to them.^[21] Another positive aspect of the period was that there was more fertile land available to the population; however, the benefits would not be fully realized until 1470, nearly 120 years later, when overall population levels finally began to rise again.

In Eastern Europe, by contrast, renewed stringency of laws tied the remaining peasant population more tightly to the land than ever before through serfdom. Sparsely populated Eastern Europe was less affected by the Black Death and so peasant revolts were less common in the fourteenth and fifteenth centuries, not occurring in the east until the sixteenth through nineteenth centuries. Since it is believed to have in part caused the social upheavals of fourteenth- and fifteenth-century Western Europe, some see the Black Death as a factor in the Renaissance and even the Reformation in Western Europe. Therefore, some historians have cited^{[citation needed]} the smaller impact of the plague as a contributing factor in Eastern Europe's failure to experience either of these movements on a similar scale. Extrapolating from this, the Black Death may be seen as partly responsible for Eastern Europe's considerable lag in the move to liberalise government by restricting the power of the monarch and aristocracy. A common example is that by the mid-sixteenth century, England began the process that ultimately ended serfdom there and gave rise to representative government; meanwhile, Russia did not formally abolish serfdom until an autocratic tsar decreed so in 1861.

Furthermore, the plague's great population reduction brought cheaper land prices, more food for the average peasant, and a relatively large increase in per capita income among the peasantry, if not immediately, in the coming century. Since the plague left vast areas of farmland untended, they were made available for pasture and put more meat on the market; the consumption of meat and dairy products went up, as did the export of beef and butter from the Low Countries, Scandinavia and northern Germany. However, the upper class often attempted to stop these changes, initially in Western Europe, and more forcefully and successfully in Eastern Europe, by instituting sumptuary laws. These regulated what people (particularly of the peasant class) could wear, so that nobles could ensure that peasants did not begin to dress and act as a higher class member with their increased wealth. Another tactic was to fix prices and wages so that peasants could not demand more with increasing value. This was met with varying success depending on the amount of rebellion it inspired; such a law was one of the causes of the 1381 Peasants' Revolt in England.

The increase in social mobility that the Black Death contributed to may have been one means by which the Great Vowel Shift was propagated.^{[citation needed]}

Persecutions

Jews are burnt alive.

As previously mentioned in reference to the plague's sociocultural impacts, renewed religious fervor and fanaticism bloomed in the wake of the Black Death. Some Europeans targeted "various groups such as Jews, friars, foreigners, beggars, pilgrims",^[22] lepers^[22][23] and Roma, thinking that they were to blame for the crisis. Lepers, and other individuals with skin diseases such as acne or psoriasis, were singled out and exterminated throughout Europe.^{[citation needed]} Anyone with leprosy was believed to show an outward sign of a defect of the soul.^{[citation needed]}

Differences in cultural and lifestyle practices also led to persecution. Because Jews had a religious obligation to be ritually clean they did not use water from public wells and so were suspected of causing the plague by deliberately poisoning the wells. European mobs attacked Jewish settlements across Europe; by 1351, sixty major and 150 smaller Jewish communities had been destroyed, and more than 350 separate massacres had occurred.

According to Joseph P. Byrne in his book, The Black Death, women also faced persecution during the Black Death. Muslim women in Cairo became scapegoats when the plague struck.^[24] Byrne writes that in 1438, the sultan of Cairo was informed by his religious lawyers that the arrival of the plague was Allah’s punishment for the sin of fornication and that in accordance with this theory, a law was set in place stating that women were not allowed to make public appearances as they may tempt men into sin. Byrne describes that this law was only lifted when “the wealthy complained that their female servants could not shop for food.”^[24]

Religion

Flagellants practiced self-flogging (whipping of oneself) to atone for sins. The movement became popular after general disillusionment with the church's reaction to the Black Death

The Black Death led to cynicism toward religious officials who could not keep their promises of curing plague victims and banishing the disease. No one, the Church included, was able to cure or accurately explain the reasons for the plague outbreaks. One theory of transmission was that it spread through air, and was referred to as miasma, or "bad air". This increased doubt in the clergy's abilities. Extreme alienation with the Church culminated in either support for different religious groups, such as the flagellants, which from their late 13th century beginnings grew tremendously during the opening years of the Black Death, and later to a pursuit of pleasure and hedonism. It was a common belief at the time that the plague was due to God's wrath, caused by the sins of mankind; in response, the flagellants traveled from town to town, whipping themselves in an effort to mimic the sufferings of Jesus prior to his crucifixion. Originating in Germany, several miraculous tales emerged from their efforts, such as a child being revived from the dead and a talking cow. These stories further fueled the belief that the flagellants were more effective than church leaders. It may have been that the flagellants' later involvement in hedonism was an effort to accelerate or absorb God's wrath, to shorten the time with which others suffered. More likely, the focus of attention and popularity of their cause contributed to a sense that the world itself was ending and that their individual actions were of no consequence.

Unfortunately, the flagellants may have more likely contributed to the actual spreading of the disease, rather than its cure. Presumably, there were towns that the flagellants visited or passed through which were largely unaffected by the plague until that point, only to be infected by fleas carried either by the flagellants' followers, or the flagellants themselves. This is a common ironic theme in how individuals at the time dealt with the plague—that in nearly all cases, the methods employed to defend against the plague encouraged its spread.

Because of the generosity of Christian service, the Black Death hit the monasteries very hard because of their proximity with the sick, who sought refuge there, so that there was a severe shortage of clergy after the epidemic cycle. This resulted in a mass influx of hastily-trained and inexperienced clergy members, many of whom knew little of the rigors of their predecessors. This led to abuses by the clergy in years afterward and a further deterioration of the position of the Church in the eyes of the people.

Other effects

Inspired by Black Death, Danse Macabre is an allegory on the universality of death and a common painting motif in late-medieval periods

Doktor Schnabel von Rom ("Doctor Beak of Rome"), engraving by Paul Fürst, 1656.
During the period of the Black Death and the Great Plague of London, plague doctors (physicians) visited victims of the plague.

After 1350, European culture in general turned very morbid. The general mood was one of pessimism, and contemporary art turned dark with representations of death.

In retrospect, it seemed as if everything the people thought to do at the time simply made the problem worse. For example, since many equated the plague with God's wrath against sin, and that cats, owls, and snakes were often considered in league with the Devil, these animals were killed en masse. Had this bias not existed, local rodent populations could have been kept down, lessening the spread of plague-infected fleas from host to host.^{[citation needed]}

The practice of alchemy as medicine, previously considered to be normal for most doctors, slowly began to wane as the citizenry began to realise that it seldom affected the progress of the epidemic and that some of the potions and "cures" used by many alchemists only served to worsen the condition of the sick. Distilled spirit, originally made by alchemists, was commonly applied as a remedy for the Black Death, and, as a result, the consumption of spirits in Europe rose dramatically after the plague. The Church often tried to meet the medical need.^{[citation needed]}

A plague doctor's duties were often limited to visiting victims to verify whether they had been afflicted or not. Surviving records of contracts drawn up between cities and plague doctors often gave the plague doctor enormous latitude and heavy financial compensation, given the risk of death involved for the plague doctor himself. Most plague doctors were essentially volunteers, as qualified doctors had (usually) already fled, knowing they could do nothing for those affected.^{[citation needed]}

A plague doctor's clothing consisted of:

• A wide-brimmed black hat worn close to the head. At the time, a wide-brimmed black hat would have identified a person as a doctor, much the same as how nowadays a hat may identify chefs, soldiers, and workers. The wide-brimmed hat may have also been used as partial shielding from infection.
• A primitive gas mask in the shape of a bird's beak. A common belief at the time was that the plague was caused by "bad air". There may have been a belief that by dressing in a bird-like mask, the wearer could draw the plague away from the patient and onto the garment the plague doctor wore. The mask also included red glass eyepieces, which were thought to make the wearer impervious to evil. The beak of the mask was often filled with strongly aromatic herbs and spices to overpower the miasmas or "bad air" which was also thought to carry the plague. At the very least, it may have dulled the smell of unburied corpses and sputum from plague victims.
• A long, black overcoat. The overcoat worn by the plague doctor was tucked in behind the beak mask at the neckline to minimize skin exposure. It extended to the feet, and was often coated head to toe in suet or wax. A coating of suet may have been used with the thought that the plague could be drawn away from the flesh of the infected victim and either trapped by the suet, or repelled by the wax. The coating of wax likely served as protection against respiratory droplet contamination, but it was not known at the time if coughing carried the plague. It was likely that the overcoat was waxed to simply prevent sputum or other bodily fluids from clinging to it.
• A wooden cane. The cane was used to both direct family members to move the patient, other individuals nearby, and possibly to examine patients without directly touching them.
• Leather breeches. Similar to waders worn by fishermen, leather breeches were worn beneath the cloak to protect the legs and groin from infection. Since the plague often tended to manifest itself first in the lymph nodes, particular attention was paid to protecting the armpits, neck, and groin.

It is not known how often or widespread plague doctors were, or how effective they were in treatment of the disease. It is likely that while the plague doctor's clothing offered some protection to the wearer, the plague doctors themselves may have actually contributed more to the spreading of the disease than its treatment, in that the plague doctor unknowingly served as a vector for infected fleas to move from host to host.

Although the Black Death highlighted the shortcomings of medical science in the medieval era, it also led to positive changes in the field of medicine. As described by David Herlihy in The Black Death and the Transformation of the West, more emphasis was placed on “anatomical investigations” following the Black Death.^[25] How individuals studied the human body notably changed, becoming a process that dealt more directly with the human body in varied states of sickness and health. Further, at this time, the importance of surgeons became more evident.^[25]

A theory put forth by Stephen O'Brien says the Black Death is likely responsible, through natural selection, for the high frequency of the CCR5-Δ32 genetic defect in people of European descent. The gene affects T cell function and provides protection against HIV, smallpox, and possibly plague,^[26] though for the last, no explanation as to how it would do that exists. This, however, is now challenged, given that the CCR5-Δ32 gene has been found to be just as common in Bronze Age tissue samples.^[27]

The Black Death also inspired European architecture to move in two different directions; there was a revival of Greco-Roman styles that, in stone and paint, expressed Petrarch's love of antiquity and a further elaboration of the Gothic style.^[28] Late medieval churches had impressive structures centered on verticality, where one's eye is drawn up towards the high ceiling. The basic Gothic style was revamped with elaborate decoration in the late medieval period. Sculptors in Italian city-states emulated the work of their Roman forefathers while sculptors in northern Europe, no doubt inspired by the devastation they had witnessed, gave way to a heightened expression of emotion and an emphasis on individual differences.^[29] A tough realism came forth in architecture as in literature. Images of intense sorrow, decaying corpses, and individuals with faults as well as virtues emerged. North of the Alps, painting reached a pinnacle of precise realism with Early Netherlandish painting by artists such as Jan Van Eyck (c. 1390– by 1441). The natural world was reproduced in these works with meticulous detail bordering on photography.^[30]

References

1. ^ Dunham, Will (29 January 2008). "Black death 'discriminated' between victims". Australian Broadcasting Corporation. http://www.abc.net.au/science/articles/2008/01/29/2149185.htm. Retrieved 2008-11-03. 
2. ^ "De-coding the Black Death". BBC News. 3 October 2001. http://news.bbc.co.uk/2/hi/health/1576875.stm. Retrieved 2008-11-03. 
3. ^ Philipkoski, Kristen (3 October 2001). "Black Death's Gene Code Cracked". Wired. http://www.wired.com/medtech/health/news/2001/10/47288. Retrieved 2008-11-03. 
4. ^ Philip Daileader, The Late Middle Ages, audio/video course produced by The Teaching Company, 2007. ISBN 978-1-59803-345-8.
5. ^ Spengler, Joseph J. (October 1962). "Review (Studies on the Population of China, 1368–1953 by Ping-Ti Ho)". Comparative Studies in Society and History 5 (1): 112–114. JSTOR 177771. 
6. ^ Maguire, Michael (22 February 1999). "Re: How many people recovered from Black Death (Bubonic Plague)". MadSci Network. ID: 918741314.Mi. http://www.madsci.org/posts/archives/1999-02/919734037.Mi.r.html. Retrieved 2008-11-03. 
7. ^ King, Jonathan (2005-01-08). "World's long dance with death". The Sydney Morning Herald. http://www.smh.com.au/news/Asia-Tsunami/Worlds-long-dance-with-death/2005/01/07/1104832310525.html. Retrieved 2008-11-03. 
8. ^ Stéphane Barry and Norbert Gualde, in L'Histoire n° 310, June 2006, pp.45–46, say "between one-third and two-thirds"; Robert Gottfried (1983). "Black Death" in Dictionary of the Middle Ages, volume 2, pp.257–67, says "between 25 and 45 percent".
9. ^ Gottfried, Robert S. (1983). The Black Death. New York: The Free Press
10. ^ Jean Froissart, Chronicles (trans. Geoffrey Brereton, Penguin, 1968, corrections 1974) pp.111
11. ^ Joseph Patrick Byrne (2004). The Black Death. ISBN 0-313-32492-1. Page 64.
12. ^ Stéphane Barry and Norbert Gualde, "The Biggest Epidemic of History" (La plus grande épidémie de l'histoire, in L'Histoire n°310, June 2006, pp.45–46
13. ^ Harald Aastorp (2004-08-01). "Svartedauden enda verre enn antatt". Forskning.no. http://www.forskning.no/Artikler/2004/juli/1090833676.68. Retrieved 2009-01-03. 
14. ^ ^{a b} Kennedy, Maev (17 August 2011). "Black Death study lets rats off the hook". The Guardian. http://www.guardian.co.uk/world/2011/aug/17/black-death-rats-off-hook. Retrieved 18 August 2011. 
15. ^ Barry and Gualde 2006.
16. ^ ^{a b} Judith M. Bennett and C. Warren Hollister (2006). Medieval Europe: A Short History. New York: McGraw-Hill. p. 329. ISBN 0072955155. OCLC 56615921. 
17. ^ Bennett and Hollister, 329–330.
18. ^ ^{a b} Penn, Simon A. C.; Dyer; Christopher (August 1990). "Wages and Earnings in Late Medieval England: Evidence from the Enforcement of the Labour Laws". The Economic History Review 43 (3): 356–357. doi:10.1111/j.1468-0289.1990.tb00535.x. 
19. ^ ^{a b} Penn and Dyer, 357.
20. ^ Joseph P. Byrne, The Black Death (London: Greenwood Predd, 2004), 65.
21. ^ ^{a b} Penn and Dyer, 366.
22. ^ ^{a b} David Nirenberg, Communities of Violence, 1998, ISBN 0-691-05889-X.
23. ^ R.I. Moore The Formation of a Persecuting Society, Oxford, 1987 ISBN 0-631-17145-2
24. ^ ^{a b} Joseph P. Byrne, The Black Death (Westport, Conn.: Greenwood Press, 2004), 108.
25. ^ ^{a b} David Herlihy, The Black Death and the Transformation of the West (Cambridge, Mass.: Harvard University Press, 1997), 72.
26. ^ Jefferys, Richard; Anne-christine d'Adesky (March 1999). "Designer Genes". HIV Plus (3). ISSN 1522-3086. Archived from the original on 14 February 2008. http://web.archive.org/web/20080214110211/http://www.aidsinfonyc.org/hivplus/issue3/ahead/genes.html. Retrieved 2006-12-12. 
27. ^ Philip W. Hedrick; Brian C. Verrelli (June 2006). "'Ground truth' for selection on CCR5-Δ32". Trends in Genetics 22 (6): 293–6. doi:10.1016/j.tig.2006.04.007. PMID 16678299. 
28. ^ Bennett and Hollister, page 374.
29. ^ Bennett and Hollister, 375.
30. ^ Bennett and Hollister, 376.