How does an agricultural society naturally provide the opportunity to develop the proximate factors? This can be found in Chapter 4

There
are numerous proximate factors thatidentifies in Chapter 4; five of them appear at the bottom of
a chart. These are horses; guns, steel, and swords; ocean-going ships; political organization
and writing; and epidemic diseases. All of these developed at some point in agricultural
societies, but not all such societies developed all of those factors. Each of the specific
factors is part of a larger category that ultimately yielded items with narrowly defined
characteristics.

The outlier here seems to be epidemic diseases, as this is
the only obvious negative. Why does he include this? The category that creates disease is the
same one that leads to technology (e.g., steel, ships) and political organization: the
organization of agriculturally based people into large, dense, sedentary, stratified societies.
Here, size and density are the two primary factors leading to disease. When people live close
together, disease can spread more easily; the more people, the greater the epidemic can
become.

Thinking more abstractly, the general idea of spreading applies to
food crops as well as microbes. The ease of spreading increases the likelihood of domesticating
crops, but it also leads to changes that can create disease-bearing organisms.

Domestication, in turn, and an increase in both animal and plant species is likely to
create food surpluses, which in turns creates a need for storing the foods. When people have
food storage, they can survive harsh winters, becoming sedentary in a greater range of climates
and building larger settlements, even cities. These in turn create need for further political
organization because more rules are needed to govern behavior in close proximity. And, while
they are not busy growing food but can consume food already stored, people have time to make
complex tools and machines, and organize a more permanent labor force to operate those
things.