Yep like pat said they did not waste materials, as is evidenced in the used up arrow heads that have been found. Also there were some spiral fletches also, using one feather. The fletch is basically like a kite tail, to keep the back from going in a different direction, and helping it to recover from the fishtailing, due to the compression of the arrow upon release, and compressing the arrow in an arc. I am sure there must have been some experimental research and development, among the various groups of the earlier people. After all it was a means of survival. If one group used two, or three, and another used one in a spiral, if it worked for a particular group, that is what they used. No need to go further. It shot straight, that was all they were after. Maybe some experimenting with fletch height, for sound, and speed. There is just so much of archeology that is pure conjecture, whether it is based on sound reasoning, or purely a wild guess. How and why one group chose one style of fletch over another is purely guessing. Till we can bend the lines of time (E=EMC2) and travel back and observe, it is anybody's guess.
Just my own opinion, and you know what they say about those......
Wayne