In this concluding section, Diamond returns to Yali’s original question: Why did Europeans develop so much more cargo than the New Guineans? A concise answer can now be given: “the striking differences between the long-term histories of peoples of the different continents have been due not to innate differences in the peoples themselves but to differences in their environments.” In other words, Europeans had an environmental advantage that allowed them to pull ahead of New Guineans in the realm of technology. In fact, Diamond claims that, if the people who inhabited Eurasia had inhabited Australia, instead, then they would have found themselves to be a downtrodden population today. The crucial differences between New Guineans and Europeans are not cultural or biological, but purely environmental.
Four broad categories of environmental differences stand out as the most important ones. So far, Diamond has covered every explanation of these differences in detail. Now, he isolates the most notable four sets of them. The first is continental differences in wild plant and animal species that were available as starting materials for domestication. Areas that had more options for plants and animals that were suitable for domestication had an enormous advantage. This was because domestication of plants and animals was so crucial for increasing population density, making societies more complex and specialized, and thus developing germs and technology. The second set of factors consists of those that involved rates of diffusion and migration. On continents like Africa, diffusion and migration were more difficult because of natural barriers that made it hard for an idea or person to travel smoothly from one end to the other. In Europe, on the other hand, the relative lack of such barriers made diffusion faster. A third set of factors includes those affecting diffusion between different continents. Some continents are more isolated than others, which made it harder for them to adopt technologies developed in nearby continents. Fourth and last, continental differences in area or total population size also had a major effect. A larger area or population meant more potential inventors, competing societies, and more pressure to adopt innovation because nearby societies would overtake you if you didn’t.
Some scientists might accuse Diamond of “geographical determinism.” This label implies that human creativity is not important, or that humans are just helplessly swept along by natural phenomenon. It could be applied to Diamond’s text because of his emphasis on the impact environments had on human history. However, he points out that this label is misplaced and unfair. He does acknowledge that human inventiveness is important. All societies had inventors who contributed important new technology that moved the course of development along. However, some environments provided these inventors with greater materials and conditions for having their inventions be well-received. This is an important distinction to keep in mind: Diamond does not believe that nature accounts for every human action, but rather emphasizes that it provided the context for whether or not a human action had a big or a small impact on the course of human history.
After considering why some continents developed guns, germs, and steel earlier than others, Diamond now considers why, within Eurasia, European societies were the ones that took the lead over those of the Fertile Crescent or China. This is an important remaining question, which has not been addressed by Diamond’s analysis so far. It is clear that the Fertile Crescent and China must have lost their leads at some point, since Europe pulled ahead in terms of the development of technology, germs, and political centralization despite its late start of over a thousand years. Diamond points out that this is not as shocking a development as it may seem to be at first; in fact, the Fertile Crescent and China later suffered because of the very factors that originally gave them an advantage.
The Fertile Crescent was an early site of food production. However, over time, it became a desert-like environment dominated by steppes, because the land was so heavily eroded. It turns out that the Fertile Crescent was an ecologically fragile environment. Though it was remarkably fertile at first, its people quickly destroyed the land by over farming it. Over time, then, Europeans were able to pull ahead because their land was more durable. China’s decline is also due to its unique geography. However, in the case of China, it is its isolation and homogeneity that eventually doomed it to fall behind. China stopped sending fleets out to other countries after a power struggle between two factions at court, with the winning faction being opposed to maritime travel. This one political power struggle had a huge impact because China was so unified that one leader’s decision could impact the entire country. This could never have happened in Europe, which was fragmented between many different leaders. Moreover, China’s isolation meant that it was not pressured to re-adopt maritime technology, since its neighbors did not exert a strong influence on the country. Thus, as Europe pulled ahead by building its own fleets and exploring new territories, China eventually fell behind. China’s unity gave it early advantages when it came to quickly spreading technologies and developing food production over the whole continent. However, these advantages became disadvantages over time.
China and the Fertile Crescent were also both affected by other factors that varied over time. For example, the danger of barbarian invasions by horse-mounted nomads from Central Asia was more present in some areas than in others. Iran, Iraq, and parts of China were devastated by the Mongol invasions, which destroyed the regions’ irrigation systems. But these invaders barely made it past Hungary, into Western Europe. Overall, the diverging histories of the areas across Eurasia offer an important lesson: “circumstances change, and past primacy is no guarantee of future primacy.” This does not mean that the conclusions of this book are wholly irrelevant. Although modern circumstances are very different from those described by Diamond, they are heavily impacted by early historical patterns. In fact, new rules can be seen as variation son old ones. New nations rising to power today—such as the United States, Brazil, and Australia—are still those that were incorporated into the old centers of dominance based on food production, or were repopulated by peoples from those centers.
What about unique individuals, and their impact on history? Has that factor been neglected by Diamond in his analysis of broad historical patterns? He acknowledges that individual idiosyncrasies do throw wild cards into the course of history. They cannot be neatly accounted for by the environmental explanations Diamond applies to most of this book. However, he points out that even those who are most enthusiastic about the importance of individual leaders would admit that broad historical patterns cannot be attributed to a few important men. Although Alexander the Great, for example, may have pushed western Eurasia toward success, it was already a literate, food-producing, iron-equipped state; he did not impact these original factors, which were ultimately more important in Western Europe’s success relative to countries like Australia. Diamond does acknowledge, however, that the effect of unique individuals remains an open question.
Before concluding his text, Diamond addresses the public’s misconceptions about historical studies in general. As he notes, “the discipline of history is generally not considered to be a science, but something closer to the humanities.” Diamond takes issue with this conception of history. In his own book, he has integrated historical evidence with scientific analysis. He has endeavored to use history to answer certain questions originally raised by the natural sciences. As he points out, four factors do separate history from other sciences: methodology, causation, prediction, and complexity. These factors are not as divisive as they may seem at first. It is true that historians cannot conduct experiments in labs, and are concerned with chains of proximate and ultimate causes. However, historians do make and test predictions about what future discoveries of data can show us about past events. And they do consider the complexity inherent in their data. For predictions, historians tend to make use of the comparative method or “natural experiments.” This means that they look to existing examples from which they can draw conclusions, instead of starting new experiments themselves. Overall, Diamond does acknowledge that it is more difficult to understand human history than it is to understand issues in the field of science, where history does not play a large part. However, he argues that successful methodologies for analyzing historical problems do exist; for example, the histories of dinosaurs, nebulas, and glaciers are now considered part of science. He shares his optimistic view that historical studies of human societies can be pursued just as scientifically as studies of dinosaurs.
Throughout his analysis in this final section, Diamond adheres rigorously to the scientific method. He does not slip into over-generalization, even while attempting to conclude the text as a whole. For example, when he makes the claim that, if Eurasian and Australian peoples had been switched, then Aboriginal Eurasians would be downtrodden today, he adds, “One might at first be inclined to dismiss this assertion as meaningless, because the experiment is imaginary and my claim about its outcome cannot be verified. But historians are nevertheless able to evaluate related hypotheses by retrospective tests…” Diamond then goes on to cite a number of tests that help to show how peoples who swapped places with other groups of peoples found themselves repeating the successes or failures of those they swapped with. This consistency in his application of the scientific method—meaning the establishment of a hypothesis that is backed up by experimentation and evidence—is particularly important because Diamond defends the study of history as a scientific one. In order to back up his claim that historical studies should be accepted as rigorous and important, he is careful to apply such rigor to his own statements.
Diamond is also sure to respond to potential philosophical objections, in order to leave his readers with all bases covered. For example, he acknowledges that other scholars might accuse him of “geographic determinism.” But he argues against this criticism by noting that, while all societies contain inventive people, “it’s just that some environments provide more starting materials, and more favorable conditions for utilizing inventions, than do other environments.” Diamond goes out of his way to raise these possible criticisms in his conclusion because this is the section in which he must definitively convince readers of the validity of his argument. Thus, to respond to criticism, he reemphasizes his central points and shows how his main arguments stand solid in the face of potential controversy.
This conclusion also acknowledges the complications that arise from the book’s complex scope. Diamond admits that “these answers to Yali’s question are longer and more complicated than Yali himself would have wanted. Historians, however, may find them too brief and oversimplified.” The main challenge of the book’s scope is that it is too detailed to fully satisfy someone who is not an expert, like Yali, but too broad to satisfy the keen eye of an expert, as well. Nevertheless, Diamond responds to this problem by pointing out that “the compression brings a compensating benefit: long-term comparisons of regions yield insights that cannot be won from short-term studies of single societies.” By this, he means that a focus on historical patterns is important in a different way: it allows for a fuller picture than more focused studies would. Thus, he justifies the scope of the book. Though it may seem both too detailed and too broad, depending on the audience, its middle-ground approach benefits from unique insights.
Much of the framing of this conclusion is reminiscent of the conclusion to a scientific journal. As he wraps up the text, Diamond explains that, “At present, we can put forward some partial answers plus a research agenda for the future, rather than a fully developed theory…The most straightforward extension of this book will be to quantify further, and thus to establish more convincingly the role of, intercontinental differences in the four sets of factors that appear to be most important.” Diamond makes note of the questions that remain unresolved by his book, and suggests areas for further research. He does not claim to have developed a full and perfect theory, but rather the beginning of an inquiry into a topic that deserves further attention. This kind of framing is typical for scientific studies, which tend to conclude by acknowledging what contributions they have made while also admitting to the incompleteness of their theory. Diamond wants his text to be seen as a serious scientific study, as well. To that end, he focuses on establishing what future studies should expand on: the role of intercontinental differences in his four important factors.
In his conclusion, Diamond also addresses the role of history as a methodology. He defends historical studies against unfair criticisms and biases; he knows that many people view history as a less “serious” and rigorous mode of study than hard sciences, like physics. However, much of Diamond’s inquiry has been based on historical evidence and analysis. Thus, it is important that he defend its credibility as a science that is just as important as the other sciences he invokes in this book, which include biology, archeology, genealogy, etc. By concluding with such a defense of history, Diamond emphasizes the extent to which his book really is a historical study, above all. Although it involves many different scientific elements, in its broadest sense it engages with historical patterns and historical modes of inquiry. Overall, this is a study of human history.