Environment History Science What I read

Guns, Germs, & Steel

Why is it that Eurasians colonised the Americas? Why, until European colonisation, did the Americas lag behind the Old World in population density and social organisation? Jared Diamond explores the far-reaching consequences of geographical differences on the emergence of densely populated, militaristic civilisations in Eurasia vs. the Americas.

[Image source]

NOTE: This is not a book review; it is a summary of the book’s argument. I will do a review at some point.


Guns, Germs, and Steel (1997) was inspired by a simple question: why have peoples on different continents experienced history so differently? Throughout history Eurasians have conquered, and ruled or exterminated, peoples in the New World and Australia, and to a smaller degree Africa. Technological progress has occurred at dramatically different rates across the globe: the last remaining tribes of hunter-gatherers in the Amazon and Australia today have stone tools and social organisation more primitive than did many paleolithic communities elsewhere in the world 10,000 years ago.

Diamond calls this Yali’s question, after the new Guinean who posed it to him. This question is integral to human history, but has yet to be investigated systematically. That progress has varied dramatically between and within continents is obvious. But why? We either don’t ask, or we answer the question with supposed genetic differences between peoples. Some peoples, we assume, are more innovative, receptive to change, or culturally superior, and this explains why they progressed more rapidly and conquered other peoples. What else could explain why – even though humans had reached all the continents except Antarctica 13,000 years ago – we live today in a world with such stark differences?

Diamond argues that these differences in outcome were caused by differences not in the peoples, but rather in their environments. He examines the key developments that catalysed human progress, and then examines why these developments occurred at different rates in different places.

The key development is agriculture. Agriculture provides many more calories per acre than hunting and gathering. It thus supports a higher population, and also frees a subset of the population from production. This subset can then devote itself to administrative, military, and priestly functions. Supported by peasants, this elite directs irrigation, terracing, and other works to maximise food yields; collects taxes for public works; defends and expands territory; and provides people with a spiritual basis for unity as well as sanctions for intergroup aggression. Another crucial subclass created by agricultural food surpluses are craftspeople: technologists who allow innovate better techniques for food storage and preparation, better tools and weapons, public works and shipping (important in exploratory and colonial expeditions) and the other support systems for a booming population. Agriculture and population growth are autocatalytic: increases in one cause increases in the other. The vast majority of populations shifting from hunting-gathering to agriculture experienced a rapid population boom. On average, a larger population is a bonus whenever one people comes into contact with another.

In most parts of the world, agriculture and animal husbandry arose simultaneously. Domesticated animals are used for meat, milk, fibres for clothing, and manure; big mammals are further in used transport, trade, traction (ploughing), power (running wind and water mills to generate power and to grind grains), and war. Agriculture and animal husbandry together offer a formidable package for population growth and the emergence of the specialised non-productive classes. Agriculture also creates the demand for central organisation: to direct farming and husbanding activities, to organise labour, and to distribute raw materials, finished goods, and tools. Agriculture and the central organisation necessary for it also create the demand for, and rudiments of, writing: to direct and track planting and harvests, and for tax collection.

In most cases, agriculture demanded a sedentary lifestyle. This, in addition to labour specialisation and population explosion, allowed for technological progress. Nomadic hunter-gatherers, and even nomadic pastoralists, have little use for or ability to carry around pottery, sophisticated tools, or writing utensils. Sedentary agricultural peoples need, and can accumulate, these things. One important kind of technological progress involved metalworking: first bronze, then iron, and finally steel were forged into ever more versatile and durable tools and weapons.

Thus agriculture and animal husbandry together constitute a major force of progress. Peoples who domesticated plants and animals earlier than others got a headstart on developing a numerous, specialised, well-organised, and in many cases literate society equipped with advanced weapons and steel tools and ships.

Writing initially served administrative and record-keeping functions. But it also played a crucial role in conquest. When individuals of Culture A which was literate encountered peoples of Culture B which was nonliterate, individuals of Culture A were able to communicate with each other navigational directions – as well as the size, defensive capabilities, and attitude of Culture B – much more accurately, directly, and rapidly, than could Culture B, relying only on word of mouth. Writing was an important factor, for example, in organising, motivating (with religious justifications) and executing the conquest of the Incan empire by Spain.

Animal domestication also led to the emergence of crowd diseases: epidemic and endemic diseases including, respectively, smallpox, cholera, and measles, and malaria and tuberculosis. The pathogens that communicate these diseases to humans are now species-specific, but they originated, without exception, from pathogens borne by domesticated animals. Peoples who domesticated animals early were thus exposed to these pathogens, which killed many individuals but which also, over generations, bestowed on survivors both genetic and acquired immunity. Only peoples with domesticated animals (which in most cases went together with domesticated animals) thus acquired an accidental but potent weapon: the deadliest germs of human history.

When agricultural peoples encountered peoples without domesticated animals, in a large majority of cases the germs decimated the latter within a few decades or even years of first contact. When Europeans bearing crowd diseases arrived in the New World, which had no domesticated large mammals, up to 95% of the original native population was wiped out by diseases against which New World peoples had no immunity. In a few cases, Europeans deliberately infected New World peoples. Either way, Eurasian germs played an enormous role in facilitating Eurasian colonisation.

Domesticated animals, in most cases horses, offered another crucial military advantage. The charge of a horse can terrify people who have never seen one, and can mow down and outrun footbased opponents. The most spectacular illustration of how horses and advanced weapons can tip the scales comes from 1593 in Cajamarca, Peru: where the Spaniard Francisco Pizarro, with 168 soldiers including 62 horsemen, defeated an Incan army of almost 80,000, captured and later executed the emperor Atahuallpa, and struck in one day a big blow for the total extermination-cum-conquest of the Incas by Spain. The Incas were already in trouble: germs from previous Spanish encounters had killed many Incas including the previous emperor. At the encounter in Cajamarca, the Spaniards were armed with guns and steel swords, and they and their horses had steel armour. The Incas had only spears and arrows and light padded armour. Spain was a literate empire, and Cortez benefited from Spanish records of previous encounters with Incas. He had come prepared to conquer, and was able to deceive Atahuallpa, emperor of the largest contemporary empire without writing, and thus without a crucial medium of insight into the existence and mindsets of other peoples. With so many factors in their favour, the 168 Spaniards beat the odds of sheer numbers and killed, terrorised, and scattered 80,000 Incas.

The encounter at Cajamarca is the most striking demonstration of the advantage that guns, germs, and steel offer to some peoples. But history, and this book, offer many more such examples around the world.

The date at which a people acquired lethal crowd diseases, technology, and weapons depended on the date at which it had domesticated animals and plants. Societies which began agriculture earlier got a headstart on population growth, class specialisation, and sociopolitical sophistication, as well as on accumulating the weapon of lethal crowd diseases. Why then did peoples around the world adopt agriculture at different rates, while many peoples never developed it at all – and instead either had to wait to acquire it from neighbours, or were exterminated by invading agricultural peoples?

After beginning the book with a brief history of human evolution, Diamond addresses this crucial question. Grains are crucial in the history of agriculture. Most peoples who independently pioneered agriculture grew grains as a major and early staple. Grains and legumes were more nutritionally dense, and yielded more tonnage per acre, than other crops: and were thus capable of supporting denser populations than most nongrain crops. Grains keep for longer than fruit and vegetable crops, allowing storage of surpluses to tide the community over years of crop failure – and thus easing the transition from a hunter-gatherer lifestyle. Finally, by biological accident grains have been relatively easy to domesticate. Many other species of plants have either proved nondomesticable (e.g. oaks), or their domestication has required more intensive technology (grafting, in the case of apples and pears), or breeding (such as breeding a mutant cultivar lacking normal plant toxins, as with almonds).

Grains were domesticated from wild grass species. Yet the distribution of suitable wild grass grain-bearing species across the globe is extremely uneven. Most of these wild ancestors were concentrated in the Mediterranean. Not surprisingly, the earliest records of agriculture in the world are in the Fertile Crescent in modern Iraq. Peoples in this area domesticated emmer wheat, as well as barley, olives, and peas, as early as 8500 BCE. The Fertile Crescent had yet another favourable environmental factor that allowed it to become the cradle of civilisation: the presence of nearly all the major domestic animals. Easily domesticated and high-yielding grains, and animals for food and traction – and, later, the world’s first writing system – made the Fertile Crescent home to a series of cultures who conquered or influenced other peoples and played a key role in early human history.

The only other centres where agriculture is confirmed to have arisen indigenously are China (rice and millet, 7500 BCE), New Guinea (sugarcane and banana, 7000 BCE), Mesoamerica (corn, beans, and squash, 3500 BCE), the Andes (potato and manioc, also around 3500 BCE), and the eastern coast of the present United States (sunflower and goosefoot, 2500 BCE). Among these, the Chinese and Mesoamerican grains – rice and corn, respectively, are less protein-dense than Mediterranean grains. As well, unlike large-seeded Mediterranean wild grass species which were domesticated rapidly and with very little modification, the wild ancestor of corn, teosinte, began as a thumb-sized cob that required hundreds of years to breed into a viable staple with large cobs – and thus to offer a fruitful alternative to hunting-gathering.

Another environmental factor that skewed starting conditions in the intercontinental “race” was the presence of domesticable animals. Diamond describes the factors that constrain the domesticability of animals: how amenable they are to being captured, tamed, bred in captivity, and selected over generations to become species useful to humans. The list of domesticable animals, especially big animals, is tiny, and again is distributed unevenly. By the time of the neolithic revolution, only Eurasia had any domesticable large mammals left. Large mammals had been exterminated, most probably by human overhunting, in the Americas, Australia, and New Guinea; and Africa has many big mammals but no domesticable ones.

How can we be sure that peoples around the world did in fact attempt to domesticate all available wild plants and animals – that the gap in domestication was not due to innate traits of the peoples themselves? Modern scientists and farmers have attempted to domesticate new species of both animals and plants. However, even with advanced technology and central planning, no new animal or plant species of commercial significance has been domesticated since prehistoric times. Indigenous populations show thorough knowledge of their local fauna and flora, and regularly continue to attempt to use or domesticate new species. We can thus be confident that peoples around the world did try to domesticate all available plants and animals. Only a few species were successfully domesticated, and the distribution and nature of these species varied widely for geoclimatic reasons.

Civilisations with Mediterranean grains and several big domesticable animals thus got a headstart on civilisations with less suitable grain species and with no (or no large) domesticable animals. The farming communities in the eastern United States, New Guinea, Mexico, and the Andes had no domesticated big mammals at all – no mammals that could be used for traction, trade, transport, power generation, or war. Thus they remained dependent on human muscle power and footbased soldiers. Regions where agriculture and animal husbandry never arose independently were at an even bigger disadvantage, remaining at lower hunting-gathering population densities until encountered – and, in most cases, replaced, marginalised, exterminated, outbred, or conquered – by more advanced, more populous peoples.

A headstart in agriculture allowed China to achieve early internal unity, as well as to spread out to colonise much of Polynesia, replacing indigenous Pacific Islander populations. In contrast, New Guineans, lacking grains, never conquered other peoples, although they did domesticate small animals, develop resistance to crowd diseases, and resist conquest by Chinese settlers. The Andeans developed an empire based on local conquest, but never developed writing or the shipping and military technology necessary for intercontinental conquests.

Thus, among the peoples who adopted agriculture independently and early, differences in the success of the agricultural package were due to environmental variation. As well, whether or not the people of a region adopted agriculture at all was due to environmental variation in availability of wild animal and plant species suitable for domestication. Numerous factors disqualify a candidate plant or animal for domestication, the number of suitable candidates was a small fraction of the whole, and the distribution of these suitable candidates across the globe was very uneven. Because of all these environmental, accidental factors, some peoples gained massive headstarts on sedentary living, population expansion, specialisation of labour, and technological progress. The effects of these environmental differences were magnified over centuries: such that, while all continents except Antarctica had large human populations by 11,000 BCE, the outcomes for indigenous populations vary vastly. And it is these effects that continue to appear today in intercontinental and interregional differences in wealth and technological sophistication.

Guns Germs and Steel raises a key historical question, and provides a fascinating tour through history to argue for a simple, strong answer. Environmental variations in starting conditions, rather than differences between the peoples themselves, are the answer to Yali’s question.


Buy the book here. To save paper, consider buying a Kindle or audiobook copy.

By Amita Basu

I'm a writer based in Bangalore, India.

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