The answer to this question can be found beginning on p. 242 of Guns, Germs, and Steel. There, Diamond tells us that necessity is not usually the mother of invention. Instead, he claims, invention is more often the mother of necessity. This is because most inventors invent things first out of their own curiosity or interest and then society finds ways in which to use those inventions.
Most people are familiar with the idea that necessity causes inventions. In this view, inventors see a need and devise something to fill that need. Diamond gives Eli Whitney’s cotton gin and James Watt’s steam engine as examples of this. However, Diamond says that this is not the most common process that drives invention.
Instead, Diamond says that the process happens in reverse order. On p. 243 he says that “invention is often the mother of necessity, rather than vice versa.” Diamond argues that this happens because inventors are motivated more by curiosity or interest. They simply like to tinker and they have ideas that they want to bring to fruition. On p. 242, he says
many or most inventions were developed by people driven by curiosity or by a love of tinkering, in the absence of any initial demand for the product they had in mind.
Once the inventors have created the new technology, they (or society) have to find a use for it. Diamond gives the example of Thomas Edison and the phonograph. Edison invented the machine without any demand for it. He published an article suggesting uses for it. However, society was not very interested in using it the way Edison wanted to and eventually started to use it for recording and replaying music.
The process then, goes as follows. An inventor has an idea that comes from his or her mind rather than from perceived societal need. The inventor tinkers around and comes up with new technology based on his or her idea. The invention does not have a use right away. Over time, either the inventor has to go out and create demand for the new invention or society learns of the invention and devises ways to use it. Eventually, they come to “need” the invention just as people came to “need” record players to listen to music. This is the process by which invention breeds necessity.