Alan Lomax in his "Land Where The Blues Began" writes of the Levy camps and similar gang labor situations where as the use of team drawn machinery came in the use of black labor proliferated because the blacks could handle mules. One of the things separating low land whites from low land blacks was that the whites used horses and the blacks used mules. Obviously this can be overdrawn. Highland whites and lowland blacks had both mules and independent song traditions. Hmmm? Could there be some correlation? Nahhh. Hmmm.

"I like to work, I'm rolling all the time, (2x)
I can pop my initials on a mule's behind."

from the Woody Guthrie version on Daddy's 78.