In Chapter 13, Diamond argues that most people think that necessity is the mother of invention. Diamond argues, however, that it is really inventions that bring about the needs. He says that people figure out ways to use inventions just as often as they figure out inventions to fill a given need.
To see examples of how this is so, we can look at p. 243 in the paperback edition of the book. There, Diamond discusses the invention of the record player by Thomas Edison. He tells us that Edison invented the record player without having any real idea that its main use would be to play music. Instead, Edison though it would be used to do things like recording the last words of dying people or books that were being read for the blind. Diamond tells us that Edison thought the invention had no commercial value and that
Only after about 20 years did Edison reluctantly conceded that the main use of his phonograph was to record and play music.
This would be an example of an invention giving rise to a necessity, not the other way around.
Diamond makes this point because he does not want us to see invention as a “heroic” process in which smart people invent things to fill needs. This is important to him because he does not want us to believe that societies that did not invent many things failed to invent because they were somehow deficient.