How did farmers conquer the world?

For most of the time since the ancestors of modern humans diverged from the ancestors of the living great apes, all humans on Earth fed themselves exclusively by hunting wild animals and gathering wild plants. It was only within the last 11,000 years that some peoples turned to what is termed food production: that is, domesticating wild animals and plants and eating the resulting livestock and crops. Today, most people on Earth consume food that they produced themselves or that someone else produced for them.

 

Different peoples acquired food production at different times in prehistory. Some, such as Aboriginal Australians, never acquired it at all. Of those who did, some (for example, the ancient Chinese) developed it independently by themselves, while others (including ancient Egyptians) acquired it from their neighbors.

 

Availability of more consumable calories means more people. Among wild plant and animal species, only a small minority are edible to humans or worth hunting/gathering. Most species are useless to us as food, for one or more of the following reasons: they are indigestible (like bark), poisonous, low in nutritional value, tedious to prepare, difficult to gather, or dangerous to hunt. Most biomass on land is in the form of wood and leaves, most of which we cannot digest (the giant panda, a carnivore with a vegetarian diet, faces pretty much the same set of problems).

 

By selecting and growing those few species of plants and animals that we can eat, we obtain far more edible calories per unit land area. As a result, one hectare can feed many more herders and farmers--typically, 10 to 100 times more--than hunter-gatherers. That strength of brute numbers was the first of many military advantages that food-producing tribes gained over hunter-gatherer tribes.

 

In human societies possessing domestic animals, livestock fed more people in four distinct ways: by furnishing meat, milk, and fertilizer and by pulling plows. First and most directly, domestic animals became the societies' major source of animal protein, replacing wild game. In addition, some big domestic mammals served as sources of milk and of milk products such as butter, cheese, and yogurt. Those mammals thereby yield several times more calories over their lifetime than if they were just slaughtered and consumed as meat. Animal manure was and remains a major source of crop fertilizer. Plow pulling mammals enabled people to till lands that were otherwise uneconomical for farming.

 

Infectious diseases like smallpox, measles, bubonic plague, tuberculosis, and influenza mutated from similar ancestral pathogens that had infected group-living animals. The humans who domesticated animals were the first to fall victim to the newly evolved germs, but those humans then evolved substantial resistance to the new diseases. When such partly immune people came into contact with others who had had no previous exposure to the pathogens, epidemics resulted in which up to 99 percent of the previously unexposed population was killed. Infectious diseases thus acquired ultimately from domestic animals played decisive roles in the European conquests of Native Americans, Australians, South Africans, and Pacific islanders.