Under what kinds of conditions does technology develop and how and why did technological development differ from one place to another?

Jared Diamond's book, Guns, Germs, and Steel, is an attempt to understand the causes of unequal development of technology in different cultures and regions. He argues that the causes are not, as racists claim, due to inherent differences in intelligence between people of different races and cultures, but rather due to environmental factors.
For Diamond, several major preconditions are needed for the development of advanced technology. The first is the neolithic transition to agriculture to provide enough of a food surplus to enable people to devote time to tasks that are not directly involved in food production. This creates a virtuous cycle in which people can specialize in technology such as making pottery or metal work or food production technology creating a virtuous cycle of increasing efficiency in food production leading to freeing up more people to specialize in various crafts and technology. Easily accessible natural resources such as metals and clay contribute to this process.
Two key environmental elements for technological development are living in a region with readily domesticable plants and animals and being in an area that has no barriers to east-west travel and communication, something which enables rapid sharing of ideas and trade in goods.