system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do you get a PhD in a field nobody else has a PhD in?

Til about Dr David Clutton who's the only person with PhD in Gin, however stupid that sounds.   
How do you get a phd in a discipline where there's no-one to grant you that phd? How was it done in the past?
gpt
All PhDs are technically within a field where nobody else knows anything. That is sort of the definition of a PhD thesis paper. In order to earn a PhD degree you need to demonstrate that you are able to do your own base research and contribute to the common shared knowledge of humanity. So when David Clutton got his PhD in Gin he had to do some sort of research or experiments on gin himself and then publish those findings. He would get help from professors within related fields who would guide him and then the paper would be evaluated by other doctors within these similar fields. After getting his paper published and defended he would get his PhD.