Unit 2
Geographic Luck
Guns, Germs & Steel: The Fates of Human Society
By Jared Diamond
Excerpts from Chapter 10 – Spacious Skies and Tilted Axes
On the map shown to the
left of the world, compare
the shapes and
orientations of the
continents. You’ll be struck
by two things: 1)
everything looks more
“stretched” than maps you
have seen in the past. This
is called the “Peter’s
Projection”. It was
revealed in 1973, and is an
equal-area projection. So
areas of equal size on the
globe are also equally
sized on the map; and 2). The Americas span a much greater distance north-south (9,000 miles) than east-west:
only 3,000 miles at the widest, narrowing to a mere 40 miles at Panama. That is, the major axis of the
Americas is north-south. The same is also true, though to a less extreme degree, in Africa. In contrast, the
major axis of Eurasia is east-west. What effect, if any, did those differences in the orientation of the continents’
axes have on human history?
The Spread (or lack thereof) of domesticated crops
Scientific research suggests that there were no more than 9 areas of the globe, perhaps as few as five, where
food production arose independently. Yet, even in prehistoric times, food production became established in
many other areas besides those original 5 to 9 areas of origin. All those other areas became food producing
regions as a result of the spread of crops, livestock, and knowledge on how to grow them, and in some cases,
as a result of the migrations of farmers and herders themselves.
The main such spreads of food production were from the Middle East to Europe, from North and West Africa
to East and South Africa, from China to tropical southeast Asia, and from Mesoamerica [modern day Central
Mexico to Costa Rica] to North America. Of course, some regions were much more suitable than others for
food production – the ease of its spread also varied greatly around the world. Some areas that are ecologically
very suitable for food production never acquired it in prehistoric times at all, even though areas of food
production existed nearby.
Unit 2
Geographic Luck
For instance, both farming and herding failed to reach Native North American California from the US
Southwest. The same can be said for Australia, which had both farming and herding practically next door in
New Guinea and Indonesia. The opposite is also true. Some farming and herding traveled very, very fast. For
instance food and herding traveled rapidly from the Middle East both west to Europe and Egypt and east to the
Indus Valley (as fast as 3.2 miles/year). At the opposite extreme was the slow spread along the north-south
axes. Corn and beans spread from Mexico northward to the US Southwest at less than 0.3 miles/year.
There were also great differences
in the completeness of with
which groups of crops and
livestock spread, again implying
stronger or weaker barriers to
their spreading. For instance,
while most of the Middle East’s
crops and livestock did spread
west to Europe and east to the
Indus Valley and modern day
India, neither of the domestic
mammals of the Andes in South
America (the llama/alpaca and
the guinea pig) ever reached
Mesoamerica in ancient times.
This failure of spreading cries out
for explanation. There were very
Llamas – present in South America but never made it to Mesoamerica
dense farming populations and
very complex cities in Mesoamerica, so there can be no doubt that domestic animals (if they had been
available) would have been valuable for food, transport, and wool. Except for dogs, Mesoamerica was
completely without mammals to fill those needs. However, some crops made it, such as sweet potatoes and
peanuts. What selective barrier let some crops through but didn’t allow llamas and guinea pigs?
SINGLE VS MULTIPLE DOMESTICATIONS
Most WILD plant species from which our crops were derived were very different genetically from area to area.
This is because each area would have established (naturally) different mutations necessary for survival. When
humans brought about the changes required to transform WILD plants into DOMESTICATED crops, different
wild mutations were selectively bred, and then those same mutated crops spread to other communities. So,
what that means is that scientists today can look at the genetics of crops today and see if they were developed
in just one area and spread or else developed independently in several areas.
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Geographic Luck
If one looks at the genetic analysis for major ancient crops of the Americas, many of them prove to include two
or more of alternative wild variants. This suggests that the crops were domesticated independently in at least
two different areas. Botanists conclude that lima beans and chili peppers were all domesticated on at least two
separate occasions, once in Mesoamerica and once in South America. Likewise, squash was also domesticated
independently at least twice, once in Mesoamerica and once in the eastern United States. In contrast, most
crops of the ancient Middle East have just one alternative wild variant mutation, suggesting that all modern
varieties of that crop stem from only a single domestication.
But what does all that mean? What does it imply if the same crop has been repeatedly and independently
domesticated in several different regions, and not just once in a single area? Well, we know (historically and
from common sense) that if a productive domesticated crop is already available, farmers will surely proceed to
grow it rather than start all over again by gathering the crop’s not yet so useful wild relative and domesticating
it. Evidence for
just a single
domestication of a
plant suggest that
once a plant was
domesticated, it
The “Three Sisters” of Mesoamerica: Squash, Maize (Corn) and Beans
spread quickly to
other areas
throughout the plant’s range, making the need for other independent domestications of the same plant
pointless. However, when we find evidence that the same wild plant was domesticated in several different
areas, we infer [conclude] that the crop spread too slowly to stop its domestication elsewhere. The evidence
for single domestications in the Middle East but frequent multiple domestications in the America might provide
more subtle evidence that crops spread more easily out of the Middle East than in the Americas.
We thus have many different factors all converging on the same conclusion: that food production spread more
readily out of the Middle East than in the Americas, and possibly also than in sub-Saharan Africa. These factors
include some food’s complete failure to reach some ecologically suitable areas; the differences in the rate and
selectivity of spread of food; and the differences in whether the crops were single or multiple domestications
and the role that would play in the speed and success of certain foods. So…what was it about the Americas
and Africa that made the spread of food production more difficult there than in Eurasia?
THE EURASIAN EAST-WEST AXIS
Soon after food production arose in the Middle East (the Fertile Crescent), somewhat before 8000 BCE, it
spread to other parts of western Europe and North Africa. These plants were not independently domesticated.
The crops of Europe and India and North Africa were mostly obtained from the Fertile Crescent. For most of
Unit 2
Geographic Luck
the Fertile Crescent’s founding crops, all cultivated varieties in the world today share only a single mutation.
The rapid spread of domesticated crops from the Middle East actually stopped any other possible attempts to
domesticate the same wild ancestor plants. Once the crop had become available, there was no further need to
gather it from the wild and start domesticating it again.
Why was the spread of crops from the Middle East so rapid? Communities distributed east and west of each
other at the same latitude share exactly the same day length and seasonal variations. To a lesser degree, they
also tend to share the same diseases, temperature and rainfall and types of vegetation. For example, Portugal,
northern Iran and Japan are all located at about the same latitude despite the fact that they are 4,000 miles
east or west of each other. They are more similar to each other in climate than each is to a location lying even
a meager 1,000 miles south.
The germination, growth and disease resistance of plants are adapted to precise features of climate. Seasonal
changes of day length, temperature, and rainfall send signals that stimulate seeds to germinate, seedlings to
grow, and mature plants to develop flowers, seeds and fruit. Those signals are very different with latitude. For
example, the growing season – that is, the months with temperatures and day lengths suitable for plant growth
– is shortest at high latitudes and longest towards the equator.
Imagine a Canadian farmer foolish enough to plant
a race of corn adapted to growing farther south, in
Mexico. The unfortunate corn plant, following the
signals and code, would prepare to thrust up out of
the ground in March, only to find itself buried in 10
feet of snow. Even if the plant could be genetically
programed to shoot up at a time better suitable for
Canada, like late June, the corn plant would still be
in trouble for other reasons. Its genes would be
telling it to grow slowly over 5 months. That is a
perfectly safe strategy in Mexico’s mild climate, but
in Canada it would only lead to death by autumn
frost before it had produced any mature corn cobs.
The plant would also lack genes for resistance to
diseases of northern climates. All those features
make low-latitude plants poorly adapted to highlatitude conditions, and vice versa.
Animals too are adapted to latitude-related
features of climate. Look at humans. Some of us
can’t stand cold northern winters with their short
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Geographic Luck
days and germs, while others can’t stand hot tropical climates with their own diseases. In recent centuries
overseas colonists from cool northern Europe have preferred to migrate to the similarly cool climates of North
America, Australia and South Africa. Northern Europeans who were sent out to hot tropical lowland areas used
to die in mass of diseases such as malaria, to which tropical people had evolved some genetic resistance.
Therefore, Eurasia’s west-east axis allowed Fertile Crescent crops quickly to launch agriculture over the
temperate latitudes from Ireland to the Indus Valley, and to enrich the agriculture that arose independently in
eastern Asia. While Eurasia provides the world’s widest band of land at the same latitude, and the most
dramatic example of the rapid spread of domestication, there are other examples as well. Almost as fast was
the eastward spread of subtropical crops and animals from South China, the Philippines and Indonesia
(bananas, taro, yams, chickens, pigs and dogs) some 5,000 miles into the tropical Pacific to reach the islands of
Polynesia.
THE NORTH-SOUTH AXIS OF AFRICA
Contrast the ease of east-west diffusion in Eurasia with the difficulties of diffusion along Africa’s north-south
axis. Most of the Fertile Crescent crops reached Egypt very quickly and then spread as far south as the cool
highlands of Ethiopia, beyond which they didn’t spread. South Africa’s Mediterranean climate would have been
idea for the crops, but
the 2,000 miles of
tropics between
Ethiopia and South
Africa posed an
impossible barrier.
Instead, African
agriculture south of
the Sahara Desert was
launched by the
domestication of wild
Sorghum in the field and cooked on the plate
plants like sorghum
and African yams
that were indigenous to West Africa, and adapted to the warm temperatures, summer rains and constant day
lengths of those low latitudes.
Similarly, the spread south of Fertile Crescent domestic animals through Africa was stopped or slowed by
climate and disease. The horse never became established farther south than West Africa’s kingdoms north of
the equator. The advance of cattle, sheep and goats halted for 2,000 years at the northern edge of the
Serengeti Plains. Domesticated sheep, cattle and goats finally reached South Africa, but it was 8000 years after
Unit 2
Geographic Luck
livestock was domesticated in the Fertile Crescent. The domesticated animals never made it through the
tropical climate of the middle of Africa, and were also halted by the diseases carried by certain insects, like the
Tsetse fly.
THE NORTH-SOUTH AXIS OF THE AMERICAS
The distance between Mesoamerica and South America is only 1,200 miles, approximately the same as the
distance in Eurasia separating the Balkans from the Middle East. The Balkans provided ideal growing
conditions for most Middle Eastern crops and livestock, and they spread rapidly. The highlands of Mexico and
the Andes in Southern America would similarly had been suitable for many of each other’s crops and domestic
animals. A few crops, notably Mexican corn, did indeed spread along the north-south axis.
But other crops and domestic animals failed to spread between Mesoamerica and South America. The cool
highlands would have been ideal conditions for raising llamas, guinea pigs, and potatoes, all domesticated in
the cool high lands of the South American Andes. Yet the northward spread of those crops and animals was
stopped completely by the hot lowlands of Central America. 5,000 years after llamas had been domesticated in
the Andes, the Maya, Aztecs and all other native societies of Mexico remained without pack animals and
without any edible domestic animals except for dogs.
On the other hand, domestic turkeys of Mexico and domestic sunflowers of the eastern United States might
have thrived in the Andes, but their southward spread was stopped by the tropical climates in-between. Only
700 miles of north-south distance prevented Mexican corn, squash and beans from reaching the US Southwest
for several thousand years. For thousands of years after corn was domesticated in Mexico, it failed to spread
northward into eastern North America, because of the cooler climates and shorter growing season. It wasn’t
until 900 CE, after hardy varieties of corn adapted to northern climates had been developed, could corn-based
agriculture contribute to the most complex Native American society of North America, the Mississippian culture
– a brief flowering ended by European introduced germs arriving after Columbus.
Remember that most Fertile Crescent crops prove, upon genetic study, to come from only a single
domestication process. In contrast, many apparently widespread native American crops prove to consist of
genetically distinct varieties of the same species, independently domesticated in Mesoamerica, South America
and the eastern United States. Those legacies of multiple independent domestications provide further
testimony to the slow movement of crops along the Americas’ north-south axis.
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Geographic Luck
FINAL ISSUES THAT NEED TO BE ADDRESSED
I have been dwelling on latitude because it is a major factor of climate, growing conditions, and ease of the
spread of food production. However, latitude
is not the only such factor. It isn’t always true
that places close together at the same
latitude have the same climate. Land and
ecological barriers and also logically
important obstacles to diffusion.
For instance, crop diffusion between the US
Southeast and Southwest was very slow even
though these two regions are on the same
latitude. That’s because much of the inbetween area of Texas and the southern
plains was dry and unsuitable for agriculture.
Another example within Eurasia involved the
eastern limit of Fertile Crescent crops. As the
The Central Asian desert called Karakum – it makes of 70% of the
land now called Turkmenistan.
crops spread east, there was a shift from
predominantly winter rainfall to
predominantly summer rainfall that
contributed to a much more delayed extension of agriculture, involving different crops and farming techniques.
Even farther east, temperate areas of China were isolated from western Eurasian areas with similar climates by
the Himalayas and the Central Asian desert. The initial development of food production in China was therefore
independent of that at the same latitude in the Fertile Crescent, and gave rise to entirely different crops.
The differences in axis orientation affected the spread not only of food production but also of other
technologies and inventions. For example, around 3,000 BCE the invention of the wheel in or near the Middle
East spread rapidly west and east across much of Eurasia within a few centuries, whereas the wheels invented
independently in prehistoric Mexico never spread south the Andes. The principle of alphabetic writing,
developed in the western part of the Fertile Crescent by 1500 BCE, spread west to what is now Italy and east to
the India within about a thousand years, but the Mesoamerican writing systems that were successful in
Mesoamerica for 2000 years never reached the Andes.
Unit 2
Geographic Luck
Wheels and writing weren’t linked
to latitude and day length the way
crops are. Instead, the links are
indirect. The earliest wheels were
parts of ox-drawn carts used to
transport agricultural produce.
Early writing was restricted to elites
supported by food-producing
peasants, and it was for complex
food-producing societies (such as
inventories of goods, record
keeping and royal propaganda). In
general, societies that engaged in intense exchanges of crops, livestock and technologies related to food
production were more likely to become involved in other exchanges as well.
America’s patriotic song “America the Beautiful” mentions spacious skies, amber waves of grain, from sea to
shining sea. Actually, that song reverses geographic realities. As in Africa, in the Americas the spread of native
crops and domestic animals was slowed by skies and environmental barriers. No waves of native grain ever
stretched from the Atlantic to the Pacific. However, amber waves of wheat and barley did come to stretch from
the Atlantic to the Pacific across Eurasia.
To bring us all these differences isn’t to claim that widely distributed crops are admirable, or that they testify to
the superiority of early Eurasian farmers. They reflect, instead, the orientation of Eurasia’s axis compared with
that of the Americas or Africa. Around those axes turned the fortunes of history.
Excerpts from:
Guns, Germs & Steel
Pages 176-191
Jared Diamond, 1999