The Jomon People existed in what was essentially Japan's neolithic age.  Tools were slowly becoming present through technological advancements an likely trade.  Jomon hunters eventually developed bows for hunting game.  Living in a state of almost constant starvation, fertility was a struggle for the Jomon people.  Many experienced their teeth rotting out completely due to their poor diets.  There are several theories as to what actually happened to the Jomon people, ranging from completely dying off to migrating to what is now North America and actually being the ancestors of the Native Americans.  More than likely, it is a combination of these two things as well as some assimilation into the upcoming Yayoi and Emishi people.