Guns, Germs, and Steel

Hunter-gatherers turned to food production whenever they could, based on geographic and environmental factors. The first factor that prompted a shift towards farming was a decline in the availability of wild foods and animals, or even animal extinction—this would reward domesticating wild plants. Another influence was the development of technologies for collecting, processing, and storing wild foods. A final factor came into play once the population of food-producing areas had grown in density. Though sheer numbers, food producers were able to displace or kill remaining hunter-gatherers.

Plant domestication involves growing a plant and causing it to change genetically from its wild ancestor. Some plants were seen as easier or more inviting to domesticate than others. Animal domestication means breeding animals in captivity and over time selecting for traits that will render the animal different from its wild ancestors. These traits could be size, greater retention of wool, higher milk yields, smaller brains, and less developed sense organs. 

Germs infect individual humans, and in high-density populations, the most successful germs create epidemics. The rise of crowd diseases is linked with the rise of agriculture around 10,000 years ago and it accelerated with the development of cities. One reason for this is that farming communities were densely packed and sedentary, which meant that they lived amid their own sewage. In the survival contest between humans and our pathogens, epidemics produce no cases for a long time, unleash a flood of cases, and then lie dormant once again. Such epidemics—which include tuberculosis, cholera, and the bubonic plague—spread quickly and victims either die or recover within a short space of time. It is also notable that these epidemics are typically limited to humans, as the microbes responsible do not tend to live in the soil or in other animals.

Societies that have undergone epidemics create survivors with resistance to these pathogens. They then transport these germs to societies that have yet to be exposed as part of successful conquest.

Inventing a language would seem to be a difficult task, and this explains why there are only a few instances of such inventions throughout history. The oldest known writing system is Sumerian cuneiform, a system that consisted of a complex mixture of three types of sign: logograms (referring to a whole word or name), phonetic signs (used for spelling syllables, letters, grammatical elements, or parts of words), and determinatives (which were not pronounced but were used to solve ambiguities). The indigenous societies of Mesoamerica have also provided evidence of independent writing, organized along similar lines to those of Sumerian writing.

The principles of writing systems spread in two ways: “blueprint copying,” which involves copying or modifying an available blueprint; or “idea diffusion,” which occurs when one receives only a basic idea and has to reinvent the details. While blueprint copying and modification are the simplest options for transmitting technology, these methods are sometimes unavailable; for example, blueprints may be unreadable or kept secret. The knowledge of such inventions may nevertheless inspire others to formulate their own methods to achieve the desired result. Indeed, Diamond notes that idea diffusion probably led to many of the ancient writing systems.