Diseases have been the biggest killers of humans. Some of the deadliest diseases that have afflicted humanity, including smallpox, the flu, tuberculosis, malaria, the bubonic plague, measles, and cholera, are "infectious diseases that evolved from diseases of animals, even though most of the microbes responsible for our own epidemic illnesses are paradoxically now almost confined to humans." By around 10,000 B.C. agricultural communities and domesticated animals were appearing. Along with the perks of agriculture, such as a generally more reliable and nutritious food supply, came some major setbacks, like epidemics of crowd diseases, some of which were previously mentioned. Crowd diseases could "not sustain themselves in small bands of hunter-gatherers and slash-and-burn farmers." An entire group could be wiped out by a disease from the environment or a foreigner due to the lack of antibodies among the small groups, leaving diseases unable to transition to an epidemic status as the populations had limited interactions. They did have infections, "but only of certain types," with some "caused by microbes capable of maintaining themselves in animals or in the soil, with the result that the disease [didn't] die out but remain[ed] constantly available to infect people," while others were chronic diseases, and some were "nonfatal infections against which [people] don't develop immunity to," meaning the same person can become re-infected after recovering (Diamond, 197- 204). According to Jared Diamond, the crowd diseases "could have arisen only with the buildup of large, dense human populations," which "began with the rise of agriculture . . . and then accelerated with the rise of cities starting several thousand years ago" (Diamond, 204-205). Hunter-gatherers had frequently shifted camp and left behind trash and fecal matter, whereas sedentary populations have lived amid their own sewage, "thus providing microbes with a short path from one person's body into another's drinking water" (Diamond, 205). Irrigation, fish farming, and forest clearings can also be breeding grounds for various microbes or carriers of certain diseases. In past years it has been proven that many of the "crowd" infectious diseases originated from diseases carried by domesticated animals. As is the case with humans, "epidemic diseases require large, dense populations" among animals and are "confined mainly to social animals providing the necessary large populations. Hence when [humans] domesticated social animals, such as cows and pigs, they were already afflicted by epidemic diseases just waiting to be transferred to" humans (Diamond, 206).