Guns, Germs & Steel by Jared Diamond: Summary & Notes

Front cover of Guns, Germs & Steel by Jared Diamond.

In short

Guns, Germs & Steel investigates why some continents and civilizations developed much faster than others, and why those trajectories are different. Diamond concludes that the course of history is shaped to a large extent by environmental and geographical reasons, rather than cultural or religious ones.

Meaning: the geographic orientation of the continents (east-west vs. north-south), the terrain, and the availability of domesticable plants and animals were key drivers of societal development.

Although the book has had its fair share of critique and doesn’t make for light reading, it’s still a very interesting perspective on why the world’s civilizations developed as they have.

For more details and reviews go to Amazon.

Book Summary & Notes

All text between quotation marks is taken directly from the book.

The central question of the book is why human development happened at different rates on different continents. Those rates of development are “history’s broadest pattern” and determined the interactions between different peoples in the past, but they even continue today.

The one-sentence summary by Diamond: “History followed different courses for different peoples because of differences among peoples’ environments, not because of biological differences among peoples themselves.”

Human history started to accelerate about 50,000 years ago, in a period that Diamond calls the Great Leap Forward. This is the period in which stone and bone tools are found, the first jewellery was unearthed, and when more and more archaeological evidence becomes available. Why did this happen? Diamond argues that it could be due to the development of the voice box, which is essential for language and thus creativity, but it could also be a change in brain organization.

One of the greatest collisions of peoples was the encounter between Inca emperor Atahuallpa and conquistador Francisco Pizarro. The latter had an army of 168 soldiers, in unknown terrain, with no possibility of reinforcements; the latter 80,000 and in the middle of his own kingdom. The result? Pizarro captures the Incan emperor within a few minutes and held him hostage for 8 months. While this example is extreme it is indicative of all colonizers and native people around the world.

Farmer power

The availability of domesticable plants and animals that yield more food allows human populations to grow. While hunter-gatherers often cannot get a huge surplus of food, the sedentary lifestyle of farmers does allow this. As a result, they can have more children – farmers had a birth interval of 2 years, hunter-gatherers double that. Having food surpluses also allows for specialists such as kings and bureaucrats that can help with storing food surpluses, taxation, and political activities.

Only a few areas of the world independently developed food production (fertile crescent, China, Mesoamerica, and some others), but these farmers slowly replaced hunter-gatherers in those areas. This head start meant that these peoples were also the first on the path towards guns, germs and steel, and they were also the ones to clash with the “have-nots” of the world.

The change of food production from hunting to farming didn’t happen all at once, but rather gradually. Domestication takes time, and so people slowly moved from hunting to a combination of farming and hunting, and finally to mostly farming.

Diamond argues that food production is an autocatalytic process, meaning a positive feedback cycle. It’s not much that higher population density forced people to adopt farming, or that farming directly produced higher population densities. Rather, a gradual increase in population density for hunter-gatherers – led by improvement in techniques, tools, method, et cetera – made people look for more food. Once they had more food, they became more sedentary, which meant they could have more children, which forced them to look for more food, et cetera. The paradox here is that while they had more food, they probably had fewer calories than the average hunter-gatherer – the population density increase more rapidly than the available food.

Plant Domestication

The start of plant domestication involved characteristics that people could see, things as the size of the fruit, fibre length, bitterness, et cetera. People would select those wild plants that had the characteristics they were seeking and as a result started the process of domestication.

But farmers didn’t just select from visible plant traits. Things like seed dispersal mechanisms, germination inhibition, and reproductive biology were also selected for, by using and developing mutations when they appeared.

This process of selection was not just due to farmers; plants and animals also ‘selected’ themselves through natural selection. A classic example is that melanism of moths became more common in the 19th century since in the darker, dirty industrial environment darker moths were harder to detect and could escape predators more easily.

Even though there are over 200,000 species of plants, not all areas in the world ended up with food production through farming. While this number might seem like a lot, humans only eat a few thousand plants, and only a few hundred have been more or less domesticated. A dozen of these plants provide >80% of the production of crops nowadays (wheat, corn, rice, barley, sorghum, soybean, potato, manioc, sweet potato, sugarcane, sugar beet, banana), and supply more than half of calories consumed in the world.

The Fertile Crescent saw the development of society because they had the availability of not just domesticable plants such as three types of cereals, four pulses, four domestic animal, and plants for fibre and oil. “Thus, the crops and animals of the Fertile Crescent’s first farmers came to meet humanity’s basic economic needs: carbohydrate, protein, fat, clothing, traction, and transport.”

Animal domestication

Large domesticated animals are small in number: only 14 in total with the most widespread being the “major 5”: cow, sheep, goat, pig and horse. That’s not to say more animals species have not tamed (elephants for example), but they were never domesticated. That is: selectively bred in captivity to serve some human purpose that’s different from the original, wild version of the animal.

Eurasia was the place where most animal domestication happened, but this was due to the highest number of species available.

Why did most domestication efforts fail? Diamond calls this the Anna Karenina principle: most human and animal species create an unhappy marriage. This could be due to the animal’s diet (for example, eating food humans also eat), their growth rate, mating habits, general disposition, a tendency to panic, or unique social hierarchy structures.

The impact of geography

Why did domesticated plants spread so quickly from the Fertile Crescent? Diamond states that the east-west axis of Eurasia (in contrast to the north-south axis of the Americas & Africa) helped enormously. With the same latitude came the same length of day, and the same seasons. Often there also was a similarity in diseases, temperature and rainfall. Since plants are adapted to a certain set of parameters, they spread much more rapidly in an east-west axis than in a north-south axis.

But it’s not just plants that spread more quickly on the east-west axis, also writing systems and technologies such as the wheel. These things are not linked to any natural states, it’s just that societies that exchanged in crops or livestock exchange were more likely to exchange writing and technologies as well.


Food production meant that farmers slowly gained an advantage over hunter-gatherers due to things like population density, literacy, technology, centralized government, and more lethal germs.

Being around animals, especially in large, dense populations, can cause the spread of microbes to humans as well. Many of the famous epidemic diseases originate in our domesticated livestock: measles, smallpox, flu, and tuberculosis.

This helps to explain why the New World didn’t have any major epidemics – they had less domestic animals, and the livestock that they had – like llamas – were kept in smaller herds and without close association to people.


Most writing systems seem to be derived from Sumerian or Mesoamerican writing, with the possible exception of Egyptian, Chinese and Easter Island writing. This is because inventing a writing system is very difficult, and that the independent development of new writing systems was preempted by Sumerians and Mesoamericans, i.e. there was no opportunity to independently create a new system.

How did writing spread? Probably through two types of transmissions that are common for all inventions: 1) blueprint copying or modification, i.e. directly using the invention, or 2) idea diffusion, i.e. receiving the basic idea or information and then fleshing out all the ideas yourself. If something can be done, it helps to stimulate people to do it as well (and the result doesn’t have to look like the original).

One of the best examples of idea diffusion in writing, which is well documented, is the invention of the Cherokee script. Sequoyah received the idea of a writing system, some paper, the idea of using separate characters in an alphabet, but he didn’t speak English and so he couldn’t understand any of the details. This led him to recreate a syllabary.

Writing was developed late in human evolution and only in those societies that were hierarchical, complex, and with centralized politics. Writing serves political needs, which explains why writing was never developed in hunter-gatherer societies.


The saying ‘necessity is the mother of invention’ is only sometimes true (e.g. atomic bomb, steam engines for pumping water out of mines), but most of the time something is developed without a clear use case or need. It’s a case of tinkering, curiosity, development and only then finding a need for it (e.g. light bulbs, airplanes, cars, transistors, et cetera).

Invention is usually also an iterative process; we praise the genius inventors like Edison, Wright brothers, and Morse, but they all build their inventions based on previous versions. Instead, they developed improvements for existing products that gave them better or wider use cases. Diamond lists multiple examples of this.

After an invention, the inventor will have to persuade people to use it. What promotes the use of a new invention? Diamond lists 1) the “the relative economic advantage compared with existing technology”, 2) “social value and prestige”, 3) “compatibility with vested interests”, and 4) “the ease with which their advantages can be observed”.

We might characterize some countries or continents as innovative or open to innovation, but this is not true. “On any given continent, at any time, there are innovative societies and also conservative ones. In addition, receptivity to innovation fluctuates in time within the same region.”

Why did technology first start on the Eurasian continent? Because of three factors: “time of onset of food production, barriers to diffusion, and human population size”. Eurasia is the largest continent, with many different societies, and also had two origins in food production: the Fertile Crescent and China. Due to the east-west axis innovation spread quickly, temperatures and climates were comparable, and the continent doesn’t have severe geographical barriers. All this meant that technology developed faster than in other continents.


“The difference between a kleptocrat and a wise statesman, between a robber baron and a public benefactor, is merely one of degree: a matter of just how large a percentage of the tribute extracted from producers is retained by the elite, and how much the commoners like the public uses to which the redistributed tribute is put.”

How did kleptocrats stay in power? By arming the elite (and disarming the citizens), by redistributing wealth into popular projects or ways, by using force to maintain order and stopping violence, and by building an ideology or religion that supports the kleptocracy.

Religion or ideology also helps to solve the problem of people from different backgrounds living together, by focusing on a common element. It also gives people a reason for altruistic actions and sacrificing themselves for society.

Does increased food production lead to more complex societies, or does a more complex society lead to more food production? It’s not an either-or question and both stimulate each other – more population leads to more complex societies, while more complex societies also lead to more food production and higher population growth.

Human history as a science

The trajectories of human development had different rates due to a few important factors: 1) the availability of starting materials for domestication (plants, animals), 2) things affected rates of diffusion and migration, such as geographical orientation (east-west vs. north-south), or ecological barriers, 3) diffusion between continents, that would help to increase the number of domesticable plants, animals, and the spread of technology and ideas, and 4) differences in area and population size – the higher the population in a certain area, the more competition and pressure to innovate and develop.

The original Fertile Crescent is not as fertile nowadays, being mostly a desert or semi-desert area. But originally it was a very productive area for food production until societies there committed ecological suicide. Due to low rainfall, vegetation only grew slowly and could not compensate for the ongoing destruction. This is why the power base shifted further and further to Western Europe which has a higher rainfall, higher vegetation growth, and able to support intensive agriculture for a longer period.

China enjoyed an early advantage in technology and exploration and built massive fleets to explore and trade – until after a power struggle the opposing party decided to stop all that. Since the entire region was unified it stopped everything; not just the ships, but also the shipyards, and knowledge itself. Contrast this downside of unification to Europe: Columbus was for example rejected by many kings and countries until he finally found a sponsor. Exactly this fragmentation allowed for this, and similar examples can be seen with the inventions of cannons, electric lighting, printing, firearms, and others. “Each was at first neglected or opposed in some parts of Europe for idiosyncratic reasons, but once adopted in one area, it eventually spread to the rest of Europe.”

While unification gave China an early head start, in the end, it became a disadvantage because a single person or party could halt progress or innovation. This is in contrast to the “geographic balkanization” of Europe with dozens of independent states and centres of creativity. “If one state did not pursue some particular innovation, another did, forcing neighbouring states to do likewise or else be conquered or left economically behind.”

Looking through history you can see that circumstances change (for example, the Fertile Crescent) and primacy at one point holds no guarantees for the future.

Has the impact of geography become irrelevant in the modern world? Diamond argues no, even the new rising powers today (Taiwan, Korea, Malaysia, etc.) were dominant thousands of years ago. The history of civilization, food production, technology, literacy, is still of importance today.

Even today “countries with a long history of agriculture, and of the state governments that resulted from agriculture, have higher average per-person incomes than do countries with short histories of agriculture and state government, even after economists control for other variables. That effect of agricultural history is a big effect. It accounts for about half of the explained variance in differences in average income between countries.”

Interested in Guns, Germs & Steel? Get the book on Amazon.

Or, browse all book notes here.