Guns, Germs, and Steel is Jared Diamond’s attempt to determine why societies historically took different paths. It was named one of TIME’s best non-fiction books of all time, awarded the Pulitzer Prize in 1998, and turned into a PBS documentary released in 2005.

After completing his doctorate at Cambridge University, Diamond did research among the remote tribes of New Guinea. It was there that he became interested in figuring out why the local tribespeople—whom he saw as every bit as intelligent and capable as he—never developed writing, steel tools, centralized governments, or a complex society like that of the British colonists who annexed New Guinea in the 19th century.

He became convinced that differences between such societies were caused by environmental factors that affected their historical development, not biological differences between the people of the societies. These differences led Eurasians—people living in Asia, Europe, and North Africa, by Diamond’s account—to historically have strategic advantages over non-Eurasians.

(Shortform note: Some of Diamond’s critics argue that his explanation for the differences between societies is oversimplified. Anthropologists in particular have criticized Diamond’s view, contending that he doesn’t account for the complexity of human individuals. This error, as they see it, is caused by Diamond’s generalist perspective: He’s a physiologist by training but, having worked in linguistics, history, and geography, he tries to synthesize diverse disciplines into an overarching explanation for the course of history. For anthropologists, this effort is wrongheaded because human societies are too complex to fit into overarching explanations—the job of the anthropologist is to develop an intricate view of that complexity.)

According to Diamond, these Eurasian advantages included:

• Advanced knowledge that led to written language, durable weapons, oceangoing vessels, and other sophisticated technologies
• Centralized governments that supported complex infrastructure and the efficient management of resources
• Infectious diseases to which they were largely immune

With these advantages, Eurasian colonists came to dominate much of the world. Diamond believes that each advantage was made possible by incidental geographic and environmental conditions that led to the rise of bountiful food production first in Eurasia.

(Shortform note: While we’ve described knowledge, governments, and diseases as advantages, Diamond isn’t arguing that humanity is better off for having developed in this way. In fact, he has suggested elsewhere that each of these advantages has ultimately left us worse off. For instance, he believes food production may have been humanity’s worst mistake.)

In our guide, we’ll see how Diamond draws the link between food production and these advantages, we’ll fact-check his ideas, and we’ll consider how Diamond’s view has been received by other experts.

It Started With Adequate Food Production

Diamond argues that the development of advanced civilizations depended first on the development of varied, abundant, and dependable food sources. This food production was achieved through the invention of agriculture, which gave rise to the strategic advantages listed above and which we’ll detail in the following sections.

(Shortform note: Some scholars claim that Diamond places too much stock in the idea that agriculture revolutionized the lifestyle of early humans. They feel there’s little evidence to distinguish foragers from farmers: Early civilizations practiced foraging while they farmed for millennia—so it’s not clear that farming should be seen as a starting point from which different societies diverged. Nevertheless, Diamond’s argument is supported by a population boom found in the archaeological record which suggests that the widespread adoption of farming did have significant effects on societies.)

Diamond says Eurasia could develop such food sources because it had geographic and environmental advantages over other regions of the world, so food production took off more readily in Eurasia than it did elsewhere. These advantages were:

• Domesticable plants
• Domesticable animals
• Geography favorable to food production

We’ll take a closer look at each of these.

Accused of Environmental Determinism, Diamond Disagrees

Diamond has been criticized for attributing too much significance to geographic and environmental conditions in the development of societies—what his critics call environmental determinism. The theory of environmental determinism was popular in the late 19th and early 20th centuries and held that physical and geographic features, including climate, terrain, and natural resources, are the main factors influencing the development of societies.

This idea fell out of favor by the 1950s: Critics argued that it ignored individual choice, cultural influence, and sociopolitical dynamics. Contemporary critics of the position insist that it was used to justify racism and imperialism and should be rejected as a relic of a bygone era. In criticizing Guns, Germs, and Steel, they allege that Diamond has done untold harm by repopularizing this antiquated idea.

Diamond rejects this interpretation of his view, contending that it’s an oversimplification of his argument. He’s not suggesting that geography is the only factor influencing the development of societies, and he recognizes that other factors—individual choice and sociopolitical dynamics, for instance—have a significant role to play. However, he insists that the influence of environment and geography can’t be ignored.

Eurasia Had Plants Well-Suited to Domestication

Diamond explains that wild plants are generally good prospects for domestication if they have some of the following attributes:

1. They show natural traits that are useful to humans, such as being sweet, oily, fibrous, or easy to gather.

2. They have successful germination attributes (such as producing many seeds that can stay dormant for years at a time) that enable them to survive bouts of bad weather.

3. They reproduce by means that allow humans to control and predict the usefulness of the plant’s offspring.

Domesticated Plants Have Invisible Useful Traits

The traits scientists look for when identifying domesticated plants are in many cases traits the foragers domesticating them would not have recognized. While early foragers may have noticed obvious visible traits, such as fruit size and color, experts don’t believe they would have noticed less visible traits, such as successful germination attributes or good reproduction characteristics. In most cases, these positive invisible traits—whether they were present in the wild form of the plants or not—would become more commonplace in the plants humans used.

Given enough time, wild plants that were consistently used by humans—whether they had recognizable desirable traits in the wild or not—changed on a genetic level to become more dependent on human care and more useful for humans. Scientists study these genetic features of domestication.

One such trait stands out as a clear sign of past domestication for these scientists: seed retention. Plants that are genetically disposed to hold on to their seeds were probably used by humans for many generations because seed retention is otherwise a poor adaptation for plant survival—it’s better for a plant to scatter its seeds. For humans, however, plants that don’t drop their seeds make the job of harvesting easier.

Typically, then, domesticated plants have attributes like these that make it hard for them to survive without human care, indicating that some factor beyond natural selection affected their genetic evolution. These genetic changes would have proceeded slowly and gone largely unnoticed by the humans using the plants.

The Fertile Crescent (the modern-day Middle East) was the first place where plant domestication occurred independently in the world because the plants of that region were well suited to it. Diamond offers several potential reasons why domestication was so successful there.

(Shortform note: While Diamond argues that the Fertile Crescent independently developed plant domestication earliest (8500 BCE by his account), he doesn’t suggest that it was the only place plant domestication independently arose. Current evidence indicates that, in addition to the Middle East (the Fertile Crescent), it also arose in South Asia, East Asia, New Guinea, Africa, South Arabia, North America, Mesoamerica, and South America.)

First, the climate of that region—mild, wet winters and long, hot, dry summers—resulted in many annuals that lived for one growing season and put most of their energy into producing large seeds capable of surviving the hot, dry season to sprout when the weather turned mild and wet again. This survival strategy resulted in more edible material (seeds) per plant than is common with perennial plants. Perennial plants such as trees often put more energy into growing long-lived, inedible material (such as woody stems) than into producing seeds that can survive for the next growing season. Thus, in places where perennial plants dominated, food production was slower to take off.

(Shortform note: Recent research indicates that, contrary to Diamond’s emphasis on annuals, a perennial plant was likely the first domesticated crop: the fig tree. Archaeobotanists have found evidence that the fig tree was cultivated in the Fertile Crescent nearly 1,000 years before common annual crops such as wheat, barley, and legumes.)

Second, the abundant edible wild plants in the Fertile Crescent produced huge quantities of domesticable seeds that hunter-gatherers could easily store. The sheer volume of useful, storable seeds encouraged tribal bands to establish settlements rather than stay on the move seeking other food sources. This kick-started the practice of maintaining crops. In places where plants produced less abundant edible and storable material, hunter-gatherers were slower to settle down.

(Shortform note: Archaeological evidence backs up Diamond’s suggestion that hunter-gatherers in the Fertile Crescent lived in long-term settlements before the dawn of agriculture. For example, excavation reports from a village in the Euphrates Valley of Syria show that hunter-gatherers established a settlement that was occupied from approximately 9,050 BCE to 5,000 BCE. In the early phase of this settlement, the inhabitants were foraging for wild plants and animals, but by the later phase, they were cultivating grains and tending herds of animals.)

Finally, according to Diamond, many of the edible wild annual plants in the Fertile Crescent tended to reproduce by self-pollination: They’d fertilize themselves and produce identical offspring. This was valuable because it ensured future generations would maintain the desirable traits of their parents. Importantly, however, many of these plants could also reproduce by cross-pollination. This meant two parent plants could be bred with each other to produce a daughter plant with a combination of the parent traits. This was helpful because occasionally, plants that reproduced this way resulted in daughter plants with better traits than the parents.

(Shortform note: Botanists argue that a main advantage self-pollinating plants had for domestication was that they’d produce daughter plants that couldn’t be fertilized by related wild plants. By contrast, open pollinated plants are prone to fertilization by wild relative plants, which can result in unexpected changes in plant attributes. Experts observe that the majority of cultivated plants today reproduce by self-pollination and that this trait can be traced back to the wild ancestors of these plants. This means that the wild ancestors of domesticated plants already had this trait, which made them better suited to eventual domestication.)

Early Fertile Crescent settlers, therefore, had good, abundant plant stock to work with. Because of this, they had an easier time domesticating their local wild plants than settlers in many other regions of the world.

Eurasia Had More Domesticable Animals

In addition to having good plants to work with, Eurasia had many wild animal candidates that were suitable for domestication. Diamond identifies seven attributes that wild animals must have to be good candidates for domestication, including the following four:

1. They must have a diet that’s sustainable under domestic conditions: That is, they must eat a type and amount of food that early farmers could provide. Non-picky herbivores or omnivores were better candidates than picky eaters or carnivores.

(Shortform note: Experts describe this attribute as being a generalist eater, as opposed to a specialist eater. Specialist eaters only eat particular foods—for example, the Canada lynx mainly eats snowshoe hares. By contrast, the raccoon eats a wide variety of plants, animals, and insects. In a domestic environment, the more specialized an animal’s diet, the less likely it is to survive.)

2. They must grow quickly. Animals that don’t reach maturity or reproduce for years are unsuitable for domestication.

(Shortform note: Not all experts include fast growth as a trait that makes an animal more suitable for domestication. However, other reproductive attributes that have similar benefits are often included in lists of traits considered favorable for domestication: For example, polygamous mating habits are better for domestication than pair bonding habits. One reason for this is that polygamous mating habits enable herds to produce many offspring so the herd grows quickly (producing abundant edible product), even if each individual offspring is slow to mature. Diamond doesn’t note several attributes, such as this, that other domestication experts consider valuable traits.)

3. They must have a relatively tolerant disposition. If they’re too aggressive, they won’t be suitable for domestication.

4. They must be relatively calm and not quick to spook and run. Otherwise, they’d be completely unmanageable.

(Shortform note: These last two traits (being tolerant and calm) are often grouped together under the term tameness. Specialists note that all domesticated animals—whether they were inadvertently or purposefully domesticated—were selected for being tamer than wild relatives. These animals, they believe, had to have been comfortable being close to, or even handled by, humans. As a result, they suggest that tameness is the primary trait that makes it possible for an animal to be domesticated.)

Only 14 ancient animals in the world had all the attributes Diamond describes. Eurasia was the continent with the greatest number of candidates: It had 13. No other continent had nearly as many. For this reason, Eurasia had the most potential for developing animal domestication.

(Shortform note: Diamond develops this point to suggest that Eurasians ended up with more domesticated animals because they had more candidates to start with. This assumes that domestication is inevitable if it’s possible. Given this, Diamond believes societies on other continents would have domesticated any animals they could have domesticated. Other scholars disagree, arguing that, in at least some cases, societies chose not to domesticate animals they could have domesticated. For example, the Aztecs had five domesticable candidates they never domesticated. Scholars argue, then, that choice has as much to do with domestication as opportunity.)

Diamond suggests three reasons Eurasia had so many animals that met these qualifications, while other continents didn’t.

First, Eurasia simply had more animals that were potentially good for domestication before humans even began living on the continent. This was mainly due to its extremely large land area and favorable ecological conditions, which together supported a diverse array of animals.

(Shortform note: Diamond doesn’t reference any sources to support the claim. A recent study comparing the number of large prehistoric herbivores (good candidates for domestication) on each continent didn’t support Diamond’s assertion—it found that South America had the most (77) and Eurasia had the least (31). This discrepancy may be because the researchers distinguished between Eurasia and Tropical Asia. If these two regions are combined, the total number of animal candidates becomes 92, according to this study. Diamond’s overall thesis doesn’t depend on this point, but it’s clear that details like this are open to interpretation among experts.)

Second, it didn’t lose as many animal candidates to prehistoric extinctions as other continents, such as Australia and the Americas. Diamond suggests this is because the animals on those continents were first exposed to humans later in human history, when we were more developed as hunters. Because those animals were unafraid of humans (having never encountered them before), the hunters could hunt them to extinction. In Eurasia, by contrast, animals and humans interacted throughout the long process of human evolution, so animals became more accustomed to the danger humans posed and developed successful survival strategies.

Andrew Sluyter’s Critique of Diamond

One critic of Diamond, Andrew Sluyter, cites this particular point as an instance of Diamond’s logical inconsistency. As he frames it, Diamond contradicts himself by arguing on the one hand that only geography determined the availability of domesticable animals and on the other hand that early humans determined that availability in the Americas by hunting them to extinction. If the Americas are an exception to the geographic determinism rule, why is it a rule at all?

However, this appears to be an uncharitable reading of Diamond. First, Sluyter seems to misread Diamond’s argument about geographic determinism as an absolute rule. Diamond never indicates this, instead only arguing that geography influenced the course of societies (including the availability of domesticable animals).

Second, Sluyter fails to note a key part of Diamond’s argument. As we’ve summarized it here, Diamond argues that the reason hunters could extinguish the population of domesticable animals in the Americas but not Eurasia was because they arrived there later in history than humans arrived in Eurasia. These late arrivals were more advanced hunters than their Eurasian ancestors had been.

The evidence for this theory (archaeologist Paul Martin’s overkill hypothesis) is open to criticism, but Sluyter doesn’t question it in his critique of Diamond—he doesn’t account for it at all. This is a problem because the overkill hypothesis provides a reason why the circumstances in the Americas were different than the circumstances in Eurasia.

Finally, more of the surviving Eurasian animals were good for domestication than were the surviving animals of other continents. Diamond observes that 18% of the surviving animal candidates in Eurasia were suitable for domestication—in the Americas, only 4% were, and there were no native animal candidates in Australia or Sub-Saharan Africa.

(Shortform note: Recent evidence suggests that Sub-Saharan Africa may have had more domesticable animals than Diamond indicates here. While certain species, such as the cow and goat, are up for debate (scholars are unsure whether they originated in Africa or Eurasia), the donkey and the guinea fowl almost certainly originated in Sub-Saharan Africa.)

Eurasia’s Geographic Conditions Supported the Rise and Spread of Food Production

In addition to having domesticable plants and animals, Diamond contends that Eurasia benefited from having geographical features that supported the rise and spread of food production.

A Favorable Axis Orientation

His main argument on this point is that Eurasia’s average north-south distance across the continent is shorter than the average east-west distance across the continent. He describes this as the continent’s axis orientation: Eurasia (including present-day Asia, Europe, and North Africa) has a predominantly east-west orientation. In contrast, the orientation of the Americas is north-south, as is the remaining portion of Africa.

(Shortform note: While the dominant axis of the Americas is north-south (about 9,000 miles north-to-south versus 3,000 miles east-to-west), Africa’s axes aren’t that different from one another (the difference is about 400 miles). Therefore, axis orientation may not be as relevant to the development of agriculture there as Diamond believes it was elsewhere. Instead, evidence suggests that other ecological barriers (such as differences in regional soil quality) were a bigger obstacle to the spread of food production in Africa.)

Diamond contends that an east-west axis facilitates the development and spread of food production more easily than a north-south axis because plants adapt to grow within similar latitudes: Plants suited to a certain seasonal day length can’t easily spread to another latitude where the seasonal day length differs. By contrast, continents with a north-south axis encompass more latitudes. If humans on these continents tried to spread crops to other latitudes, those crops wouldn’t thrive. Regions that face these geographic limitations to the spread of crops, therefore, face limitations to the spread of food production, which is largely based on maintaining crops.

Did Plants Spread, or Were They Independently Domesticated?

Diamond’s argument about the importance of latitude is built on the idea that domesticated plants spread outward from the Fertile Crescent: Plants from the Fertile Crescent were transferred to neighboring farmers along latitudinal lines because they were suited to the common climate. However, archaeologists debate whether the plants that were domesticated throughout Eurasia came from crops that originated in the Fertile Crescent.

Some argue that crops were domesticated independently in different regions throughout Eurasia—this indicates that the diffusion of crops along an east-west axis wasn’t as important as Diamond believes. In this scenario, regional foragers began cultivating their own local crops (not crops they obtained from latitudinal neighbors). From a genetic standpoint, these independently cultivated crops shouldn’t have Fertile Crescent ancestor crops.

Others argue that crops were domesticated once in the Fertile Crescent and then transposed from there across the continent. Recent evidence in support of this view is that most of the domesticated plants and animals throughout western Europe have genetic links to the earliest Fertile Crescent crops. If crops from the Fertile Crescent were the ancestors of these western European crops, scholars argue that Fertile Crescent crops must have been transferred to these distant places at some point in history. There’s no consensus among scholars on which model of Eurasian plant domestication describes what actually happened in the past.

In addition, animals adapt to thrive within certain latitudes and climates. It would have been harder, therefore, for domesticated animals to spread along a north-south axis with its drastically different climates than to spread along an east-west axis.

(Shortform note: Recent research finds that plants and animals respond to climate differences in similar ways: They gradually adapt to survive within a certain range of environmental conditions. Hot-weather plants and animals don’t thrive in cold weather, and vice versa. This suggests that Diamond is right: Early domesticated animals would have spread more readily to environmentally similar regions than to environmentally different regions. Taking altitude and other microclimate factors into account, climate conditions tend to be more similar along a line of latitude than along a line of longitude.)

Fewer Topographic or Ecological Obstacles

A second factor affecting the spread of food production is the presence of topographic or ecological obstacles. It’s not quite enough to have an east-west axis, according to Diamond—over time, humans had to be able to spread crops and animals along that axis without encountering obstacles that threatened the survival of the plants, animals, or humans.

In Eurasia, there were historically few obstacles to the spread of domesticated plants and animals from the Fertile Crescent westward. Archaeologists find that food production spread quickly in that direction. However, the Fertile Crescent plants and animals weren’t well adapted to the different rainfall conditions of eastern India, so they were delayed in their spread eastward. Nevertheless, Fertile Crescent crops spread over the majority of Eurasia earlier and faster than crops on other continents.

In North America, for instance, early domesticated crops spread extremely slowly from the US Southeast to the US Southwest—which share the same latitude—because infertile desert conditions barred the way. Ecological barriers therefore affected the spread of food production across North America more than the spread of food production across Eurasia.

The Spread of Food Production in the Americas

Researchers find that agriculture spread quickly from the Fertile Crescent to northwestern Europe within about 3,000 years. Some evidence suggests that migrant farmers from the Fertile Crescent gradually moved west during this period, bringing their agricultural practices with them. By contrast, crops from Central America spread about half that distance—northwest to the modern-day US Southwest—over a period of about 2,000 years. Some archaeologists suggest that differences in moisture conditions affected the pace of this spread in the Americas.

However, there’s no expert consensus on the reason eastern American crops didn’t spread to western America. While ecological barriers could have been an important factor, there were many other factors as well, including the bountiful wild food sources available to the Native Americans of eastern North America: Food production there was practiced alongside foraging, and tribes had few reasons to disperse westward because their region supported them well.

For these reasons—an abundance of domesticable plants and animals, and favorable geographic conditions—Eurasia got a head start on food production compared to the rest of the continents.

Diamond argues that this head start, combined with the favorable conditions that enabled it, led to the three strategic advantages we mentioned at the start of the guide. We’ll now take a look at each of these below.

The Advantage of Knowledge

Eurasians developed advanced knowledge leading to innovations that gave them advantages over societies whose knowledge was more limited, writes Diamond.

Some of these key innovations were: durable metal weapons, armor, and tools; efficient means of transport such as the wheel and oceangoing ships; navigational equipment; and written language. When Eurasians traveled across the ocean to the Americas, their metal armor and guns were superior to the wood, bone, leather, and stone weapons and armor of the indigenous peoples. Moreover, the written languages of the Eurasians facilitated clear communication, which both inspired and coordinated expeditions and conquest. For these and other reasons, the invaders quickly subdued the Native Americans despite their having been established on the continent for millennia.

(Shortform note: Some scholars believe that Diamond has sugarcoated colonialism and contributed to the destructive spirit of conquest. The problem with Diamond’s view, as they see it, is that he makes conquest and colonialism an inevitable outcome of the environment’s effects on societies—some people just end up with all the advantages. Because of this, they argue that colonizers and conquerors are let off the hook.)

Diamond argues that Eurasians didn’t develop this advanced knowledge because of some unique set of special abilities. Let’s look at the factors he believes led to this knowledge.

Factors That Contributed to the Rise and Spread of Knowledge

Diamond identifies three factors that contributed to the rise and spread of knowledge in Eurasia:

1. Early onset of food production: Food production led to the development and spread of knowledge because it created food surpluses and increased population density. Because Eurasia had a head start on food production, it had a head start on creating these conditions.

(Shortform note: Researchers have found that the earliest cities in the world (such as Uruk, the main city in The Epic of Gilgamesh) emerged first in the Fertile Crescent. This suggests that the early onset of agriculture may have influenced population density there.)

Having extra food meant that a society could support non-farming specialists—such as craftspeople and bureaucrats—who could focus their time and energy on advancing their specialized knowledge. Craftspeople who may initially have developed specialized tools for farming, for example, could in time develop specialized weapons for warfare. Likewise, bureaucrats responsible for organizing harvests and building projects had to keep records and collect and transfer information: According to Diamond, this was a necessary condition for the invention of written language.

(Shortform note: Research supports Diamond’s idea that record-keeping and transferring information were necessary preconditions for the invention of written language. Scholars find that the earliest precursor to writing was used for transferring numerical (how much) and categorical (what type) information. Tokens were simply objects, such as a shell or a special stone, that were used to represent a quantity and type of object (for example, a jar of grain or three fish). This earliest use of non-spoken language indicates that one condition leading to the invention of written language was the need to quantify information and relay it accurately.)

In hunter-gatherer societies, by contrast, all members of the society had to spend most of their time and energy on collecting enough food to survive, so they weren’t free to advance their knowledge in other areas, and they had little use for innovations such as written language.

(Shortform note: Because hunter-gatherer societies shared the responsibility for foraging equally, there were no sharp distinctions between members of the society. Experts argue that the practice of food production changed this, causing an unequal social division of labor: Not only did specialists emerge, but tasks also began to split along gender and age lines in a way that wasn’t seen before.)

2. Large area and population size: We’ve already seen that Eurasia had earlier and better food production than other continents, but it also happened to be the largest continent by far, and larger continents could support larger populations. Having more people provided more opportunities for ideas to arise and spread.

Diamond explains that Eurasia (including North Africa) is nearly eight million square miles (21 million km²) larger than the next largest continent group: North and South America. Similarly, the current population of Eurasia is many times larger than any other continent. While the ancient population size isn’t known, Diamond contends that Eurasia likely had the largest population in the past, also.

(Shortform note: Estimates show that the combined population of Asia and Europe (Eurasia) was greater than any other continent from at least as early as 10,000 BCE and has remained so up to the present. Furthermore, current measurements of Eurasia’s landmass (including North Africa) indicate that it’s around 56 million km². The landmass of the Americas is over 42 million km². While this 14 million km² difference isn’t identical to Diamond’s figure, rounding errors and other variations may account for the discrepancy: For instance, Diamond never defines what areas he includes in North Africa. Nevertheless, Eurasia is larger and more populous than the Americas by any definition—this is consistent with Diamond’s argument.)

3. Ease of diffusion: The same reasons that gave Eurasia advantages in the spread of food production gave it the upper hand in the diffusion of knowledge: a dominant east-west axis and fewer geographic obstructions.

A dominant east-west axis free of major obstructions facilitated the spread of knowledge because knowledge moved with people. As groups crossed Eurasia and set up farms and villages, they brought ideas and skills with them. Once new ideas emerged, they replaced or corrected old ideas and stimulated more new ideas, which led to more innovation.

(Shortform note: Recent studies back up Diamond’s hypothesis that an east-west (E-W) axis made the diffusion of knowledge easier. In an analysis of ancient and early modern technology adoption, researchers found that technologies spread more quickly along an E-W axis than along a north-south axis. Another recent study indicates that languages change more readily along an E-W axis, as well.)

Because of these factors, Diamond believes Eurasia had an advantage over other regions of the world for advancing knowledge since any idea that arose was more likely to spread and develop across a large network of people.

(Shortform note: Researchers observe that knowledge spreads through the diffusion of ideas and the migration of people. Population size and density have been shown to affect the rate of this spread, suggesting that Eurasia did have an advantage over less populous regions.)

The Advantage of Centralized Government

In addition to having more advanced knowledge, Eurasia benefitted from having more centralized governments, contends Diamond. Societies that had centralized governments, organized with hierarchies of authority and specialized roles, came to dominate societies that didn’t organize themselves this way.

Centralized societies were better able to initiate and coordinate complex activities such as construction projects and wars of conquest. Rulers could give unilateral commands and mobilize armies through numerous subordinate leaders. They could justify wars and individual sacrifice by appealing to religious authority and the spirit of social unity. By contrast, egalitarian societies that viewed everyone as basically equal couldn’t easily unite around a single authority, so they were less able to coordinate large-scale cooperation and encourage self-sacrifice for a common good.

(Shortform note: While centralized societies may have been more successful in conquest, not all scholars believe they’re better forms of social organization. They point out that one reason centralized societies engaged in conquest in the first place was that they were more unstable than egalitarian societies. Whereas egalitarian societies valued group cooperation and altruism, centralized societies—built on inequality—valued hierarchy, competition, and dominance. These conditions created internal instability for centralized societies and led them to periodically split or expand and dominate those around them. The stability of cooperative, egalitarian societies, on the other hand, made them less prone to expand and dominate.)

Factors That Contributed to the Rise of Centralized Government

Why did Eurasian societies develop centralized government more than other societies? The two main reasons are related, writes Diamond: food production and population size.

As we’ve discussed, Eurasia’s population could grow due to its head start in food production. Diamond believes the size and density of the regional population was the biggest factor in determining how complex and organized societies became. He says there are several reasons for this.

Population Size and Density May Not Have Led to Political Organization

Some scholars take a different view of what led to the development of organized government. Whereas Diamond argues that environmental constraints compelled growing societies to become more complex, some archaeological evidence suggests that large and dense populations endured for thousands of years without signs of complex centralized organization.

For example, in The Dawn of Everything, anthropologist David Graeber and archaeologist David Wengrow insist that the archaeological record tells a different story than Diamond’s: Ancient hunter-gatherer societies adopted food production and lived in cities but maintained egalitarian societies by choice. Many of these societies left evidence of densely populated cities that were occupied for generations and had no palaces or other evidence of centralized authority. They even find that some civilizations adopted a centralized government for a period of time and then went back to decentralized organization.

Graeber and Wengrow argue that Diamond’s narrative misrepresents the facts: Many of our ancestors chose to live as equals because they evidently preferred it over hierarchy. This is important, they believe, because it means we, too, can choose to organize our societies in a more egalitarian manner.

First, larger and denser populations experienced more conflicts between strangers. These conflicts required more sophisticated mediation than family feuds or conflicts between people who knew each other. Sophisticated mediation, though, required more organized governance.

(Shortform note: Research supports this claim: Loose-knit societies with fewer kinship ties were more likely to have institutions and religions that emphasized universal morals than tight-knit communities that had more kinship ties. These institutions and religions served as organizational systems that justified cooperation between unrelated strangers.)

Next, larger societies needed more efficient and productive means of food production. Often this included large-scale projects such as irrigation systems or public buildings suitable for crop storage. These projects required a great deal of coordination, which created the need for management, planning, and even record keeping.

(Shortform note: An opposite explanation can also account for the organization of societies: Just as large societies grow more organized, more organized societies grow larger. Experts argue that well-organized societies—those that managed to increase their efficiency and coordinate complex tasks—outcompeted more poorly-organized societies. Over time, in a process mimicking natural selection, these societies became larger and more centralized.)

In addition, accomplishing large-scale projects also required a great deal of labor—this created a need for slaves. Because of this, victors in battle enslaved the losers and thereby grew their societies. Larger societies led to larger, more complex governments as the need to control and organize vast groups of people became more demanding.

Finally, if victors didn’t absorb societies around them, they often left them in place to extract tribute. Extracting tribute further increased societal complexity because facilitating the collection of tribute and the stratification of different classes of people (for example, slaves and citizens) created a need for complex organizational systems and specialized bureaucratic roles.

(Shortform note: These last two points suggest that warfare tended to increase societal complexity—victors in battle tended to become increasingly stratified and organized as they absorbed or controlled societies around them. Researchers tested this basic idea by designing a computer simulation to see how hypothetical societies would organize on the Eurasian continent in response to warfare and geographic features. The computer simulation produced a model of the distribution of complex societies on the Eurasian continent that resembled the historical distribution of these societies: The Fertile Crescent emerged as a center of states and empires. This simulation suggests that war may play a key role in the way societies develop.)

According to Diamond, of all the continents, Eurasia had the largest head start and the most favorable conditions for developing highly populated and complex societies with centrally organized governments.

The Advantage of Epidemic Diseases

Diamond claims the final advantage Eurasian societies had over other continents was a blessing in disguise: epidemic diseases.

For those encountering epidemic microbes for the first time, the results are often deadly. However, if a person has survived previous exposure, they typically have some level of immunity to the disease. Therefore, societies that had the chance to develop immunities to epidemic diseases had a significant advantage over those that didn’t.

Such societies could unwittingly wipe out a population of previously unexposed people without ever wielding a weapon, thereby clearing the way for new settlements on once-occupied land. For example, according to Diamond, archaeologists estimate that the population of the Americas declined by as much as 95% in the years following Columbus’s arrival—much of this was due to the spread of diseases such as smallpox.

(Shortform note: Recent estimates indicate that the population of the Americas declined by 90% after the arrival of Europeans (who carried numerous epidemic diseases with them, including typhus and smallpox). The population loss was approximately 10% of the total world population at the time. Experts believe that the magnitude of this loss—and the accompanying reduction in farming—led to a period of global cooling as unmanaged land became overgrown and began absorbing more carbon.)

Factors That Contributed to the Development and Spread of Infectious Diseases

Why did societies in Eurasia harbor so many infectious diseases that worked to their advantage? Diamond suggests that the reasons are again linked to food production—namely, living close to domesticated animals and other humans.

As Eurasian societies incorporated more animals into their growing, sedentary, food-producing towns and cities, they spent more time in close contact with those animals and with each other. This was the perfect breeding ground for disease.

(Shortform note: Specialists observe that the first major epidemic diseases, such as measles and smallpox, emerged among human populations in cities of around 10,000 to 20,000 residents. They note that cities of this scale were established in Eurasia long before they were established in other places, and suggest—in agreement with Diamond—that the practice of food production accounted for these denser populations.)

According to Diamond, scientists discovered that the major infectious diseases of recent history—including smallpox, tuberculosis, malaria, plague, measles, and cholera—have microbial ancestors that still infect common farm animals, such as pigs and cows. At some point in history, they believe, these microbial ancestors transferred from animals to humans, allowing humans to contract diseases that were previously exclusive to livestock.

(Shortform note: Experts note that the likelihood that an animal disease will pass to a human depends on four factors: First, the number of possible animal hosts; second, the percentage of those animals infected; third, how often humans encounter those infected animals; fourth, the genetic similarity between the animal and the human. Taking these factors into account, it becomes clear that the domestication of mammals—which involved gathering them in large groups and interacting with them often—increased the odds that humans would become infected by those animals.)

Once a microbe transfers from an animal host to a human host, it can begin to spread among the human population. When people live in relatively close proximity, this is easy. Diamond argues that Eurasian towns and cities, organized as they were around agriculture, provided numerous opportunities for diseases to spread among the population. Not only did people live and work close to one another, but they also used animal and human waste as fertilizers for their crops.

(Shortform note: Many microbes never manage to spread widely among humans. Experts find that a pathogen’s ability to spread efficiently between humans depends on its ability to find new ways to transfer from one host to another. New practices often create these opportunities. In ancient times, these new practices included fertilizing with manure and living close to humans and domestic animals. Today, blood transfusions, injections, antibiotic resistance, and commercial food production offer numerous opportunities for pathogens to develop new ways to infect hosts.)

Eurasians, therefore, had many opportunities to be infected by these microbes, says Diamond—epidemics were common throughout their history. After an epidemic wiped out a large portion of a society, people that survived tended to have genetic features that made them immune to the microbes that caused the epidemic. Thus, the Eurasian survivors and their children were largely protected from these deadly infections by the time they encountered the inhabitants of other continents, though they would still get sick from the microbes periodically.

(Shortform note: Immunity had devastating consequences not only for the conquest of the New World, but also for the early American colonies. Experts believe Eurasians had immunity to temperate diseases (such as smallpox and measles) because of their long history with them but that they were susceptible to tropical diseases, including yellow fever and cholera. Historians contend this affected the economics of slavery in America. They argue that slavery in the southern US was more profitable than in the northern US partly because enslaved Africans were less susceptible to the tropical diseases that thrived in the warm American South. By contrast, in the North, enslaved Africans succumbed to temperate diseases in the colder climate.)

In this way, Eurasians acted as vectors, carrying with them microbes that could no longer kill them but could easily kill those without immunities. Eurasians’ germs went ahead of them, hitching a ride on explorers’ ships and landing on the shores of the Americas and isolated islands, wiping out entire civilizations without any armed conflict.

(Shortform note: Researchers have found that the health of the pre-Columbian Americans (before contact with Europeans) was significantly declining long before Europeans arrived. While they insist that this doesn’t change the fact that Europeans transferred numerous epidemic diseases to the Native Americans, it does indicate that there were other factors contributing to population decline in the New World. Specifically, researchers see a correlation between the Native American adoption of agriculture and declining health—farming wasn’t as healthy as hunting and gathering.)