I have just released two more of my past Patreon essays for sale on Amazon, as The Early History of Shinto. These two essays cover the archaeology of Shinto in the Kofun period of Japanese history, roughly 300 CE to 650 CE, and the early records of matsuri, Shinto rituals, as preserved mainly in the early eighth century.
The origin of Shinto is a very interesting topic, because it is very controversial. Some people say that Shinto goes back to the Jōmon culture of the Japanese archipelago, back to 10,000 BCE. Others say that Shinto only really starts to exist in the Kofun period, or around 700 CE, or around 1000 CE, or around 1200 CE, or around 1500 CE, or in 1868. All of these claims have some sort of grounds, although I tend to think that the earliest and latest are very hard to support.
The problem arises because it is hard to define “Shinto”. With no founder, and no consistent set of religious rules, it is always possible to acknowledge that rituals were happening, but deny that they were Shinto. My personal stance is that it is most useful to talk about changes in Shinto over time, and that we should start talking about Shinto from the first period where we have solid evidence for rituals that show continuity with later Shinto. That is the Kofun period, and so that is what these essays are about.