Jeans became the symbol of rebellion and passionate youth worn by the sex symbols of the day. James Dean, Marlon Brando, and Elvis wore their jeans straight and slim. Although women in the 50's didn't often wear jeans; Audrey Hepburn, Sandra Dee, and Marilyn Monroe wore the 50's fashion of slim, close fitting pants that had the same sexy silhouette as today's skinnies.
By the 60's women's jeans were more common (even though the zipper was in the back) and they continued to have that skinny silhouette. The look could be super sweet like the girl next door, or sexy and rebellious like those greaser chics in the musical and movie of the same name. Rock and Roll was coming of age and tight jeans were the uniform.