Plagues and Peoples
By: William H. McNeill
• McNeill considers the influence that
disease has had on human history and
how the two have evolved together.
• It explores the impact disease had on
cultures and how in affected every area of
world history including the political,
demographic, ecological, and
psychological aspects.
The evolution of disease coincides
with the evolution of humanity.
Man The Hunter
Food Chain
Before human populations evolved, our ancestors fit into an ecological balance which was
mainly supported by the food chain.
They preyed upon some forms of life, and they in turn were preyed upon by others
Parasites also sought food in our ancestors’ bodies and became a important element in
balancing the system that humans were a part of.
Our Ancestors
Pre-human and proto-skeletal bones and tools that have been discovered
abundantly in sub-Saharan Africa points to an arboreal habitat for our
ancestors meaning that they lived in the trees.
Dentition also suggests an omnivorous diet based on nuts, fruit,
vegetable shoots instead of animal flesh until about 500,000 years ago.
Man the Hunter
In the warmth and moisture of a rainforest a single cell parasite
can survive outside of a host for a long period of time.
This means that even if there are few hosts to be found in the forest, the
parasite can wait .
Applied to our human ancestors, it was still possible for them to pick
up a lot of parasites
The rainforest, for millions of years, had a highly evolved natural
balance between the things humans ate and the things that ate us.
Non-biological Evolution
Because biological evolution is so slow, any change that would occur in
humans could be compensated for in the genetic makeup and behavioral
patterns of both prey and predator.
As long as the biological evolution of our ancestors kept pace with the
evolution of parasites, predators and prey, the ecological balance could
remain stable.
When humankind began to acquire new skills and elaborate learned
behavior into symbolic meanings, the biological balance was disturbed.
Development of weapons and tools allowed for the killing of large
animals that were on the grasslands of the African savanna.
Language and New muscular skills allowed new precision in hunting
What does this have to do with Disease?
When our ancestors started to come down from the trees to run walk, run, and hunt
in the open grassland they were susceptible to new kinds of diseases.
As rainforest types of infection thinned out new parasites contracted from animals
in the savanna start to affect humankind
 Meat from the hunted animals contained a lot of disease.
 Ex. Various types of worms can transfer to humans when we consume their
eggs contained in meat
 Tsetse fly contains trypanosome that causes sleeping sickness. It causes no
sickness in the fly (an example of stable, ancient parasite), but when
injected into a human it causes death. This fly basically set limits on where
early humans could hunt for game.
The new skills that our ancestors acquired allowed for a much larger food supply
which in turn caused human numbers increase.
 As human numbers increased, opportunities for transfer of parasites multiply
because there are more hosts
Parasites Evolving
Many of the parasites in Africa do not provoke
immune reactions which helps maintain an
ecological balance.
If human numbers increase, the rate of
infection also increases.
As hunting bands started to cause extinction of many of the large animals that were
feeding them they had to find food elsewhere.
Invention of clothes
 Allowed for bands of hunters to move north and attack animal populations that
could not be reached previously.
 Consequences were similar to what happened when our ancestors came down
from the trees.
 Hunting bands entered Australia about 40,000 yrs. ago, 5,000 – 15,000 yrs.
Ago crossed Bering Strait from Asia and entered into Americas. In the next few
thousand years, expanded across North and South America
First time a large-bodied species was able to spread across the globe
Cultural adaptation and invention (which can happen almost instantly) made
biological adjustment (which can take thousands of years) unnecessary
 Warm clothing
 housing
The hunting communities were still facing the problem of
killing off their food supply.
 One calculation suggests that human hunters exterminated
most large-bodied game in 1,000 years.
Parasites were still lurking and waiting.
They were able to travel with the hunting communities as
long as the infection acted slowly and did not kill off too
many human hosts or incapacitate them too suddenly
Food Production
Hunting communities realized they couldn’t keep
killing off all the animals.
Food Production
 The evolution of agriculture and domestication of
animals permitted a rapid rise in the number of
people that could thrive in a community. Led to
rise of cities and civilizations.
 Once humans started to form large communities
and cities, an optimal hunting ground was created
for potential parasites and diseases.
Food Production
Slash and burn methods of agriculture cleared the
way for multiplied breeding of a kind of mosquito
that carries malaria and that prefers to feed on human
Irrigation farming recreated favorable
conditions for parasites that prevailed in moist
tropical conditions
Blood fluke - involves mollusks and men as
hosts. Moves from one to the other freely in
water. Affects 100 million people today.
Prolonged or permanent settling brought many risks of parasitic invasion.
 Increased contact with human feces as it accumulated in close living
quarters could allow for intestinal parasites to move freely
 In contrast, a hunting band constantly on the move could avoid this
 Contaminated water supplies
In regions where food crops were being domesticated human population
density became 10-20 times greater than hunting densities had ever been in
the same areas in just a few hundred years.
Eventually agricultural populations became dense enough to sustain
bacterial and viral infections even without a non-human intermediate host.
Civilized societies began to form and disease
became a unknowingly potent biological
Trade, war, and exploration also brought the
exchange of disease – sometimes wiping out or
“digesting” whole societies.
500 B.C.TO A.D. 1200
 People were exposed to new types of parasites with
the expansion of irrigation farming and frequent
wading in irrigation water
 Those who wrote at this time paid no attention to the
life conditions of the peasantry
 Earliest references to epidemic diseases date back
to 2000 B.C., had been time for other infectious
diseases to establish themselves that were not
mentioned or recorded
 People moved southward to better farming regions to
increase development of rice paddies and urban
 Sharp climatic difference between northern and
southern China
 Warmer climates of the south allowed a larger variety
of parasites to flourish (compared to the north)
 Those from the north did not have built up immunities
to these foreign parasites
 Diseases in the south included: malaria, yellow fever,
 Extensive kingdoms developed in the Ganges Valley
around 600 B.C.
 Buddha articulated a world view that became widely
 The Ganges Valley experienced monsoons providing
abundant rainfall and shelter from the Himalayas;
temperatures never approached freezing
 Climate permitted a variety of parasites to develop as
soon as human populations came to existence in the
 Today the Ganges region contains: cholera, malaria,
dengue fever and other diseases characteristic of
cities and civilizations
 Civilizations cultivated wine and oil through vines and olives that
already existed in the region (men of power)
 Grain growers of remote coastlands were forced to feed the city
dwellers and get nothing in return
 Coastlands however offered a relatively disease free
environment for populations to expand
 Cropping patterns are not believed to have brought new
diseases to the Mediterranean
 Population growth attributed to the rise of disease, one that we
are sure of is malaria
 Hippocrates concluded that diphtheria, tuberculosis and
influenza also existed at this time
 He did not however account for smallpox, measles or bubonic
 Remained a relatively healthy place for human beings
Human population growth appears to
survive and multiply for a few generations
until natural limits again interfere
 Warm climatic conditions such as those in India better
allow for the survival of infectious organisms
 For that reason the assumption that smallpox
originated in India may be perfectly sound
 Bubonic plague and cholera may also be indigenous
to India
 Disease traveled less easily overland than by sea
 Long distance traveling by humans, whether by land
or sea, allowed for the possibility of new infections to
be brought to “virgin host populations”
 “Virgin” populations- those groups of people who
have never been exposed to a particular disease and
therefore lacked the ability to buildup an immune
system to it
 Often times disease was carried through the process
of trading
 This only occurred in profitable trading where the
demand for the goods desired was high enough that it
was worth the risks and costs of the long and
dangerous journeys that had to be endured
 Trade between the eastern Mediterranean, India and
China operated on a regular basis
 Regular movement back and forth created exchanges
of infections as well as goods
 New and unfamiliar diseases spread to susceptible
 Second century A.D. populations in the
Mediterranean and China were said to have
experienced “sever blows” from epidemic disasters
 Evidence suggests that India and the Middle East
were effected little by the presence of new infections
 Second to third centuries where when these diseases
are said to have broken out in the Mediterranean
 A.D. 165 and 180
 A.D. 251 to 266
 No overall estimate of population loss has been made
 Must have been very high because civil unrest was
also occurring on Roman frontiers
 Christians had an advantage over their pagan
contemporaries because they recognized caring for the
sick as a religious duty
 Strengthened Christian churches when most other
institutions where being discredited
 Teachings made life meaningful amid all the death and
The Impact of the Mongol
Empire on Shifting Disease
Mongol Movement
• Intensified overland caravan movement
across Asia
– Communication: post messengers were
capable of traveling 100 miles a day for
– Traveled new routes intensively
– Political/Military reasons
Before Mongol Movement
• The plague was endemic in one or more natural
foci among communities of burrowing rodents
where human populations had found a
customary pattern of behavior that minimized
chances of infection
• Natural focus points: borderland b/n India,
China, and Burma in the Himalayan foothills,
another in central Africa
– The Eurasia steppelands not yet focus of plague
After Mongol Movement
• In the 2nd half of the 13th century Mongol
horsemen penetrated Yunnan and Burma
– C.1252-53
– They entered regions where the rodents host the bacillus on
a chronic basis
– Mongol invaders into this region disregard local rules to
protect humans from plague
– The great speed of the horsemen meant infection was able
to travel great distances
– For nearly 100 years it moved from one rodent community
To the next
Effect of Mongol Movement on
• Traveled by the black rats getting on ships
from Asia for trade purposes
• 1291- a Genoese admiral opened the
Strait of Gibraltar to Christian shipping for
the first time by defeating Moroccan forces
• Then circumstances turned for the worst
Europe and the Plague
• Severity of winters caused crop devastation and
resulting deaths and more migration
• Initial shock of the “Black Death” in 1346-50 was
severe because of these situations
• Fleas, Human
• MR: 60-70%
• The plague would come and go several times to
the same areas
• Socioeconomic shifts
Main Idea
• The disease disasters that attacked the people
of the steppes in the 13th and 14th centuries due
to the Mongols were soon followed by 2 other
– The circumnavigation of Africa by European seamen
– Systematic opening up of sea routes b/n Europe and
other major centers of civilization.
• After this the caravans were no longer most economic way of
moving goods
• Habits/customs
Effect of Mongols
• Response to changed Communication
• Massive epidemics due to military/political
– And the rodents that came along for the ride
• Greater interests in travel and exchange
led to more travel and movement causing
plague to spread
Transoceanic Exchanges
• Amerindian epidemics and disease before
Spaniards erroneous
• First instance of epidemic on the
Amerindians found in Aztec’s
• There were no human populations dense
enough to sustain human-human disease
Transoceanic Exchanges
• Only dense areas of population were areas
in Mexico and Peru where a considerable
amount of crops were grown.
• These areas are where epidemics began.
– Decline of Amerindian populations began after
Cortez allowed exchanges b/n Amerindian and
European settlements
• The population of Mexico shrunk 90%
Transoceanic Exchanges
• Once again with more military and political
movement came the spread of such
diseases as smallpox, measles, and typhus
• People coming to America rarely
contracted any diseases from the
Amerindians and this made the Indians
feel as if they were naturally inferior
Pre-Columbus to 1700
Impact of diseases in the new and old
Transoceanic Exchanges
• In 1616-1617 a great pestilence of some sort swept
through the Massachusetts bay area. (God prepared
the way for the pilgrims).
• 1633 smallpox outbreak convinced colonists that
Divine Providence was indeed on their side in conflicts
with the Indians.
• Malaria and yellow fever establish themselves in the
New World from Africa, both affected settlement and
survival in tropical and subtropical parts. Contrary
evidences show that they two diseases existed in the
America’s before Columbus.
•Malaria completed the annihilation of Amerindians in
the tropical lowlands.
Transoceanic Exchanges
• Yellow fever announced its successful transfer from west Africa to the
Caribbean in 1648. Yucatan and Havana were the first reports.
Specialized species of mosquito Aedes aegypti arose. It is highly
domesticated, for its breading places were small bodies of water that
doesn’t have natural mud or sand, but in a water cask, cistern, or calabash
for laying eggs. Crossed over on a ship, couldn’t propagate at first until
weather conditions were met (72 degrees F).
Mosquito’s carrying yellow fever would travel from sailor to sailor and
remained on these ships for weeks. “Yellow Jack” dreaded by sailors of the
Caribbean and other tropical seas.
African Americans took place of the Amerindians along the Caribbean coast
and neighbor islands because of the human labor needed for the Caribbean
plantation enterprises. Africans loss to malaria and yellow fever was very
minimal because of past exposure.
Amerindians populations drastic die-offs decreased to ratios of 20:1 and
Transoceanic Exchanges
• In 1450-1550 three new infectious diseases break out in
Europe. “English sweats”, syphilis, and typhus.
Syphilis and typhus appeared in Europe during the
Italian wars (1494-1559) first breaking out in the army
spreading the diseases to all far and wide adjacent
Syphilis was considered a new disease in Europe even
though in 1498 there was a break out in India as wells
as China and Japan in 1505. The disease being new to
the Old World it was thought that a strain of spirochete
from America causing yaws found a way to shortcirculating the increasingly ineffective path of skin-skin.
By the end of the century syphilis began to recede.
Transoceanic Exchanges
• Typhus made its debut in European soil in 1490 when it
was brought to Spain by soldiers who had just been
fighting in Cyprus.
In 1526 it hit a French army forcing them to withdraw
due to the damage of the disease. It continued to spread
disrupting armies, depopulating jails, poorhouses, and
other institutions all the way to WWI when 2-3 million
had already died of this infection.
Typhus was a disease of crowding and poverty it brought
death quicker compared to the other infections present.
Transoceanic Exchanges
• The “English Sweats” had a opposite effect than typhus
socially for it affected the upper classes yet it
mysteriously disappeared by 1551.
Symptoms resembled scarlet fever though it did not have
a big enough effect all over the continent to be a
demographic effect on the continents.
During this time there were high rates of infant mortality
due to older persons high level of immunity through
prior exposures. For costs of giving birth and rearing
another child to replace one that had died was hard.
After these occurrences of epidemic disease and severe
weather conditions affecting crop northern Europe's
population continued to slowly increase.
Transoceanic Exchanges
• Doubling of recorded instances of epidemic disease in the sixteenth
century corresponds with which the epidemics arrived in China.
China’s population increased by 85million people between 14001600. The growth relates to the slowing of western europe’s
population growth in the same period.
Agriculture advances in Europe from American and China. Maize,
potatoes, tomatoes, chili peppers, peanuts, and manioc came from
America. Oranges originating from China.
Changes in diseases patterns and increase in productivity with the
spread of American food corps were the two main factors in
triggering population growth.
People became knowledgeable about diseases and prevention of
them. Europeans discovered that oranges prevented the disease
scurvy and bathing clothing and bodies was necessary was well to
prevent disease.
The Ecological impact of medical
science and organization since
• Medical schools and hospitals were significant in producing more
systematic responses to new disease experiments. For hospitals
gave opportunities for repeated observation of the symptoms and
course of the disease. If they found a cure once they would try it
again on anther patient.
• In England 1721 a deliberate resort to smallpox inoculation, it was
successfully immunized the next year with the royal children. They
transferred the infection into a slight wound on the patients skin.
Then in 1840’s the safer method of vaccination with cowpox was
• In 1850 the practice of medicine and the organization of medical
services begant to make large-scale differences in human survival
rates and population growth.
The Ecological impact of medical
science and organization since
• Cholera was introduced from Bengal to other parts of
Europe and seemed capable of penetrating any
quarantine. Though after Cholera is swallowed the
bacillus survives the stomach juices, it is capable of swift
multiplication in the human alimentary tract and
produces violent symptoms such as vomiting, fever, and
death often within a few hours of the first signs of the
Cario had 13% of total population got Cholera. A new
cholera epidemic arose in Bengal in 1826 it filtered all
over Europe. It got to America from Ireland and America
gave it to Mexico (1833).
Germs and Methods
• The first such germs to be detected were the bacilli of
anthrax and tuberculosis, discovered by Louis Pasteur
between 1877 and 1879 and Robert Koch.
Jame Lind installed sea-water distilleries and fresh
drinking water.
“Spit and Polish” was a ritual for cleanliness for the
European sailors.
Edwin Chadwick was to construct narrow sewers out of
the smooth ceramic pipe to flush out the sewage. Had to
develop more powerful pumps and pipes.
• 1829 bacillus was discovered and an effective vaccine
developed by 1896.
Diphtheria bacilli identified in 1883 and antitoxin was
effective in 1891.
1866 Board of health was established in New York City.
WWII chemicals-DDT, sulfas, penicillin, and Atabrine
1937 cheat and effect vaccine for yellow fever.
1948 World Heath Organization was set up.
“Birth control may in time catch up with death control”
(pg. 294)
The author is able to identify patterns in
the diseases that occurred with limited
amounts of data and statistics
The book describes the diseases that took
place over large periods of time and
throughout many countries
The author makes many connections
between disease and humanity that would
have otherwise gone unnoticed because
of the lack of data.
The book tends to jump around a lot between
the diseases that occurred in different countries
and those that occurred in differing time periods
Failed to describe the diseases themselves but
rather focused primarily on how they came
Draws conclusions on very sketchy evidence
and data.
Only discusses AIDS in the preface of the book.