Doubtless there was some method of cultivation: starchy yams and taro, almost certainly originating with the continent, ended up elevated, the starch from them formed into a kind of bread. This incipient agriculture appears to be related to a cultural florescence in mid-Jōmon occasions that lasted about 1,000 years. Encyclopaedia https://cocoagriculture48148.bleepblogs.com/29334191/the-basic-principles-of-shokupan-recipe