Animals carry a number of germs that were first passed on to humans in a variety of ways. Moreover, human proximity to domesticated livestock is what caused certain deadly germs to develop in sedentary, food-producing societies instead of hunter-gatherer communities. For this reason, new crowd diseases do not develop in small societies-hunter-gatherer tribes do not have enough population density to beget their own deadly diseases that they could pass to larger sedentary societies. In small hunter-gatherer societies, of course, such diseases would very quickly kill everyone and thus die out themselves. This kind of “crowd disease” can only be sustained in large populations, where there are enough people to spread amongst that the germs can continue to pass themselves along otherwise, the germs would quickly die out as all people in the society died out.

Over time, human populations exposed to a given germ came to have a high proportion of people with genes for resistance, since they were selected for survival of such epidemics.

In an epidemic, germs are particularly quick and deadly, and can kill otherwise healthy individuals. Germs have a vested interest in passing from one person to another, and in making sure that they have enough available hosts to stay alive. Germs make us “sick” in order to pass themselves from one host to another for example, coughing is a strategy by which a germ can transfer through the air to a new host. This leads to a key question: why was the exchange of nasty germs between Europe and the Americas so unequal? To answer this, Diamond considers why some microbes make us sick and others don’t, why many diseases run in epidemics, and how diseases pass from humans to animals. This third section will explore how the ultimate cause, food production, led to more proximate causes such as germs, literacy, technology, and centralized government.ĭiseases were a crucial proximate cause of domination by one society over another in the majority of wars, most deaths were caused not by warfare itself but by the exchange of diseases. The advantages that do distinguish these men come from factors related to their differing strategies for food production: societies with agriculture have denser populations, breathe out nastier germs, own better weapons, and live in centralized governments with elites who can wage war. If a farmer and a hunter-gatherer fought each other one-on-one and naked, for example, neither one would have a large advantage over the other. It is only an ultimate cause, or a basic prerequisite for certain other factors that directly determined modern differences. However, food production is not a proximate cause. In the second section, Diamond explained the ways in which food production contributed to differences in ancient societies.

Diamond guns germs and steel