answer:Most people think sushi was an ancient traditional dish of the Japanese. It was not. Although its current form came about in the middle of the Edo period (~1700) it was a delicacy only afforded to the upper classes – in Edo. Peasants (the majority of Japanese at the time) did not eat Sushi in Edo, much less all of Japan. A guy named Hanaya Yohei is credited with “inventing” nigiri sushi (Kanto style – where Tokyo is located) around 1830 as a “fast food”, bringing it to the people. (Edo was renamed Tokyo in 1868.) Food carts where all the rage (not unlike taco trucks all over my very own Los Angeles today.) The huge 1923 earthquake that devastated Kanto (a 7.9!!) is credited with making all those local sushi chefs spread throughout Japan. So sushi – as we know it – was not widespread in Japan until the 1930’s. To answer your question though, how has it changed in form since around 1900 (other than its spread through Japan and then the world) – variety is the main thing. Today you can get thousands of combinations with every fish and roll combination imaginable. Back in the day it was limited to what fish were caught in Edo Bay. Sushi was originally called Edomae zushi (Edo Bay). “Sushi” in Japanese actually means vinegared rice (to make it sticky) not the fish toppings/ingredients. For eons Asians were eating fish and rice combos, mostly fermented, and created/wrapped for storage. The big change was when it was prepared fresh to be eaten immediately. All that said, I’ll bet you could find tuna sushi (nigiri maguro) and a hand roll (temakizushi) in 1900 Edo not much changed from what you find today. You just probably wouldn’t find much else. (This is all my limited understanding, over simplification, and personal opinion.)