Explain why, according to Guns, Germs, and Steel, epidemic diseases almost never originate or are sustained in hunter-gatherer societies, though they can have devastating results when they do break out.
The answer to this question can be found in Chapter 11. Pieces of the answer are scattered throughout the chapter. One place to find much of the answer is in the pages beginning with p. 205 in the paperback edition of the book.
Epidemic diseases do not usually originate in hunter-gatherer societies because they are closely tied to animals. On p. 207, Diamond provides Table 11.1, in which he lists some major diseases that have come to human populations from animals. These include such killer diseases as measles and smallpox. Hunter-gatherer societies do not typically live in close proximity with animals in the way that farming societies do. Therefore, epidemic diseases do not pass from animals to people as readily in such societies.
Epidemic diseases cannot sustain themselves in hunter-gatherer societies. They need to have large populations in order to survive. This is because epidemic diseases kill large numbers of people. Diamond discusses on p. 204 the fact that epidemic diseases tend to kill nearly everyone in a hunter-gatherer society. This is bad for the disease because it robs it of hosts for the germs. Therefore, these diseases can only sustain themselves in large populations where there are plenty of people who can survive the epidemics and keep the germs alive.