a common space & database for harmonic overtones
Yea, so "Frere Jacques" (Are You Sleeping Brother John?), "Row, Row, Row Your Boat", "The Farmer in the Dell", etc., are all playable on 1.2-1.5 meter long wooden trumpets (you can use a valved trumpet and play it like a bugle without valves). You can also see that the fanfare motif of these songs is the basis for courtly fanfares. So it's very possible that these tunes that we think of as banal, are actually what was played at court in the Early Middle Ages. It also means that the chasm between folk music and art music is not that at all. This music survived through the force of the Christian Church trying to force the ecclesiastical modes through using the diatonic scale. So these songs are in the "modus lascivus" (the major mode) that was forbidden by the early Church. You have to leap-frog over the influence of the Church to find their origin. So they probably date from before the first millennium (1,000 A.D.). You can also see the triadic nature of them and therefore why European art music is based on chords. You can't have chords (triads) in early art music since the thirds are so out-of-tune in Pythagorean tuning you can't use them (and they were therefore forbidden).
These simple songs and folk music being based on the natural scale completely un-ravel the mystery of medieval music theory.