The book begins with a preface in which Diamond claims that the main purpose of his text is to explain why different countries developed in different manners. Diamond mentions Yali, a New Guinean politician interested in the history of his country and the colonization of New Guinea. Yali asks Diamond why some societies flourished more than the others—this is the question Diamond will try to answer in the book. Diamond makes a point of insisting that he doesn’t believe that one society is better than any other, and that he will try to remain impartial in his analysis. For a long time, the Europeans and those from advanced industrial nations believed that the reason why some nations were less developed was that some peoples were naturally inferior to others. However, Diamond argues, this view doesn't hold up to examination, and part of the point of his book will be to disprove that view. Diamond even argues that hunter-gatherer societies are in some ways superior to industrial ones today because their members have to rely on their intelligence to survive, and spend more time exploring and planning ways to get their food. The real reason for varied rates of development amongst different societies must lie elsewhere.
In the first part of his book, Diamond analyzes the history of human evolution. It is generally believed that the closest evolutionary relatives the humans have are the apes, who at one point evolved and then migrated to other parts of the world about half a million years ago. The first settlers populated Eurasia and then moved to Australia and America somewhere around 14,000 years ago. In America, just as in other places, the settlers exterminated some of the larger animal species during their hunting activities. Some places of the world remained unpopulated until quite recently. On the other hand, we know that people lived in Africa from the beginning of humanity. Thus, historians have asked themselves why Africans didn’t evolve technology much faster than the rest of the world, since they had such a head start.
Diamond uses Polynesia as a prime example for trying to explain why some communities chose to remain hunter-gatherers and why some turned to agriculture to survive. In Polynesia, many islands were populated roughly around the same time. Because some islands were not fertile, the people on then became hunters and then pillaged other islands in search for food. But those who lived on the farmable islands also fought among themselves, because owning land meant having more resources and possibilities to live a good and long life. The environmental differences between one island and the other influenced the way the tribes developed. Though in the beginning they were all the same, after a while they changed and developed diverse societies. Those who grew crops and domesticated animals were those who had a better chance of survival, and had more time and energy for developing technology. The islands that could provide better food became more heavily populated, and as a result these societies developed more complex social structures. On a much larger scale, a similar thing happened to other societies all over the world: those that developed plant and animal domestication earlier became more dense, more diverse, and more complex.
A well-known story of conquest involves the Spanish conquistador, Francisco Pizarro, defeating the great Incan emperor, Atahuallpa. Why was Francisco able to come to America with so few troops, and defeat such a large Incan army? A number of factors explain this disparity. The Spanish had a writing system to transmit information, a well-established government system, and the materials and knowledge to build ships and sail to distant lands. These technological advancements would have been impossible without the agricultural advancements that had begun almost 11,000 years previously. Agriculture and controlled farming was more efficient than hunting and gathering and so social specialization appeared; a small group controlled the workers and owned the land, and a larger group of peasants worked for the first group. People also had time to learn new skills and develop personally because they no longer had to spend all their days hunting for food. Because of this, they could go to war against other nations.
Humankind turned to agriculture out of necessity. Large species of animals that were hunted disappeared and cities and other settlements became harder to sustain just through hunting and gathering. Humans learned slowly what plants were good to eat, and were able to domesticate some plant species over time. The food was selectively bred to be bigger, to grow faster and to be sweeter. However, the number of plants domesticated is low in comparison to the number of plants existing all over the world. No new plants have been domesticated recently, which goes to show that our ancestors domesticated almost every available plant that could be useful. In fact, not every plant is easy or possible to domesticate. The same principle applies to animal domestication. Agriculture flourished in Mesopotamia because this area had many native grains and animals that could be domesticated and put to work on the fields. In other places in the world with the same climate and soil, agriculture did not develop the same as in Mesopotamia because these areas either did not have indigenous plants like wheat or barely, or because they did not have the same domesticable animals as in Mesopotamia. This was the case in New Guinea, for example. Another reason agriculture and farming spread more quickly in Eurasia than on continents like America is the relative lack of climactic barriers. Natural features, like mountain ranges, could determine whether a given technology spread more or less easily across a continent.
As societies began to domesticate animals, they also became prone to diseases. Many major diseases were first passed from animals to humans. These included smallpox, measles, and even AIDS. Thus, Eurasians also had the advantage of first being exposed to these diseases, to which they could develop immunity. These kinds of diseases typically spread in epidemics, which meant that they required a very dense population in order to arise. For this reason, only societies like those in Eurasia, which had developed food production early and thus become more dense, could establish such diseases. Similarly, it was these kinds of societies that invented or adopted writing and other technologies. Geographical isolation, on the other hand, could stop a country from adapting new inventions, and even those that did end up in those countries had a higher chance of being abandoned in a shorter period of time.
In the epilogue, Diamond answers the question posed by Yali: differences in environment influenced whether a given society had more or less “cargo.” He concludes by pointing out that there are a number of factors that determine whether a nation evolves or not. The most important of these include the number of plants and animals than can be domesticated, the lack or presence of natural barriers, and population density. He argues that no person is born naturally superior or inferior. Instead, every societal advantage and disadvantage can be explained by analyzing the natural environment. Diamond also includes a defense of historical studies in his conclusion; he points out that history is often disparaged for being less rigorous than the hard sciences, but argues that, through natural experimentation and prediction, it can achieve some of the same methodologies and levels of rigor as fields like physics do. Understanding human history, from a perspective that includes ecology, archeology, linguistics, biology, etc., is crucial for understanding how the world works today. Diamond’s book offers a new explanation of this history—one that emphasizes environmental differences as a key factor in explaining societal differences.