The use of the 8th beat as the starting point for most solo jazz dance moves can be traced back to the origins of jazz music and dance in the early 20th century. Jazz music is known for its syncopated rhythms, which emphasized the offbeat and created a swing feel. This swing feel was reflected in jazz dance, where the dancer's movements would accent the offbeat and give the dance a swinging quality.
One of the key features of jazz dance is improvisation, and starting the dance on the 8th beat allows for greater improvisational freedom. The 8th beat provides a strong downbeat, which serves as a foundation for the dancer to build their movements and phrasing. Starting on the 8th beat also allows for a more relaxed feel, as the dancer can settle into the rhythm before starting their movements.
In addition, starting on the 8th beat helps to distinguish jazz dance from other forms of dance that may have similar movements but different rhythms. By starting on the 8th beat, jazz dance retains its unique swing feel and remains distinct from other forms of dance.
It's important to note that while most solo jazz dance moves do start on the 8th beat, this is not a hard and fast rule. Dancers are encouraged to experiment and find their own phrasing, and starting on a different beat can add variety and interest to the dance.
In conclusion, the use of the 8th beat as the starting point for most solo jazz dance moves is rooted in the syncopated rhythms of jazz music and the improvisational nature of jazz dance. Starting on the 8th beat provides a strong downbeat and allows for greater freedom and creativity in the dance, while also maintaining the distinct swing feel of jazz dance.