Like all social dancing, Scottish Country Dancing was originally not only an enjoyable activity in its own right but also a major opportunity for young males and females to size each other up. It's a sad fact that many young males were only spurred on to participate at all by the competition for the females; once they had found long-term partners, many simply gave up whereas most females continued to enjoy dancing for its own sake. The outcome is that most Scottish Country Dancing groups have a predominance of female members, many of whom have to spend much of their time dancing as Men. In an all male environment, such as the prisoner-of-war camp where The Reel of the 51st Division was devised, every Lady's Place had to be danced by a male.
Having females dancing as Men is well established everywhere, even at a formal Ball; in a teaching environment, they should wear an identifying band. Where a group or event does not include enough males to fill the Men's roles, it would be a crime if that were to leave disappointed wallflowers; far better to have everyone on the floor who wants to dance.
The situation with males dancing as Ladies is much rarer; the MC or teacher must recognize that many less experienced dancers may be confused on finding a male dancing as a Lady in the same Set and a few experienced dancers may be upset. Scottish Country Dancing is mostly unisex in the sense that there are not many situations which specifically imply a female for the Lady's part and so it should not be too strange to have a few males dancing as Ladies; the main potential problems are with some Hand positions, Precedence, Corners, Allemande and Promenade, especially when the Dancers involved are not Partners.