Let's explore how natto came to be created and loved and passed down from generation to generation.
Was natto actually invented, or it was discovered by accident that wrapping boiled soybeans in rice straw or dried grass and leaving it would eventually produce fermentation that made the soybeans delicious? The answer to that question is unknown.
The origins of natto are a mystery because natto likely dates back to a time before writing was invented.

We know that people were already cultivating soybeans in the middle of the Jomon period (around 4,000 years B.C.). So it would not be unusual if natto was "invented" at the same time.
However, no evidence has been discovered to prove definitively that natto culture began in the Jomon period. In addition, the period of time that we call the Jomon period is vast, encompassing more than 10,000 years.