Where did the Jōmon people come from? Were they
the ancestors of modern Japanese?

southeast Asia , the Yayoi and Jomon

Explanation:

The Jomon originated in southeast Asia and spread to Japan about 12,000 years ago. The Jomon or the Yayoi were the true ancestors of the modern Japanese.

 Experts now conclude that the prehistoric Japanese people and ancestors of the Jomon people originated from somewhere around Lake Baikal area in Russia (currently called Buryatia which is known to have been inhabited as long ago as 23,000 years ago).

Explanation:

Hope this helps :)

length of the cultivating season was not a problem of new england agriculture

it's lower nubia : ) good luck