Worth noting that if you listen to early jazz, you will have heard some variant of most of the folk melodies above, major and minor. "St. James Infirmary" is a kissing cousin to "Star of the County Down", and neither are more than a stone's throw from "Greensleeves".

Also, if you remember that all the world has folk music--there are many places, such as the Balkans, where the major melodies are heavily outnumbered by minor melodies--