I've been doing a lot of research about traditional dance music from the celtic nations. I've learned that most of what we think of as "traditional Irish" music is not Irish at all. In fact, much of the music came originally to the new world (Virginia, US) by immigrants from Ulster Cty, mostly young men from Scotland unable to make a living there. They came first to build the new communities and sent for their brides later. They brought their music, dance and song with them, which largely was responsible for "country music" at first and later "old timey music", which influenced Bill Monroe and gave him the impetus to start up the Blue Grass boys.
But Scotland didn't create those dance forms, they came from the Normans who sacked England in the 12th century. The original dance form, the Carole (12/8) came from Crete in 900 BC and settled in what became Gaul, and later France. All western dance forms evolved from the Carole: 12/8 (the slide), 9/8 (slip jig), 6/8 (single and double jig), 4/4 (reel, strathspay, hornpipe), 2/4, 3/2, etc. The polka came from eastern Europe originally and only entered the lexicon in the 20th century.
Chief O'Neill, who is credited for collecting a myriad of melodies he called Irish, gave us the first compendium of traditional dance tunes. But the provenance of those tunes is unclear. Chances are they are mostly 19th century melodies largely from England and Irish-English cities such as Dublin and Cork, no doubt influenced by the keys, modes and forms from Scotland and England.
The most popular dance form that made it's way to the Americas was the hornpipe. The dance was largely a solo dance, done by men. In the south it was known as "buck dancing" and in the north, "clogging". Here's an example of the style in the south:
Many of the original "old timey" tunes became "bluegrass" tunes in the 20th century: Red Haired Boy, Hull's Victory, Boys of Bluehill, Fisher's Hornpipe, etc.
These were all hornpipe forms. We don't know who wrote them, which is why they can't be nailed down, but if you look closely at the melody form, you notice the 3 quarter not sequence at the end of each 8 bar section, indicating it's a hornpipe.
Many other tunes, probably written in the 20th century, follow this rule and are included in the Bluegrass lexicon.