I find it interesting no one has used a five-letter word in this thread: horse. The lack of an equestrian class (specifically horseback riders) has led many cultures into unbifurcated garments for the lower extremities. Frequently, as Richard Willham, a lecturer in the history of animal husbandry, explained to us at Iowa State University, such cultures, when they did use horses, drove chariots or other types of wagons. See ancient Greece and Rome.