Final answer:
As humans evolved to walk upright, anatomical and behavioral changes influenced human sexuality, with the visibility of sexual characteristics becoming more pronounced. Cultural and social norms, influenced by researchers like Kinsey, have evolved to recognize sexuality as a continuum and to understand sexual behavior and orientation in more depth.
Step-by-step explanation:
When humans began walking upright, several anatomical and behavioral changes occurred that influenced human sexuality. As the Homo genus evolved, walking upright led to the digestive organs moving into a smaller space, necessitating a different diet that possibly allowed for increased brain development and complex social behaviors associated with sexuality. Throughout history, including the Jazz Age and beyond, cultural and social norms around sexuality have evolved as well, influenced by thinkers like Sigmund Freud and researchers like Alfred Kinsey. Kinsey's work began a more open dialogue on human sexuality and identified that sexual orientation exists along a continuum through the Kinsey Scale. Moreover, Masters and Johnson's research in the 1960s on sexual physiology further influenced the understanding of human sexual behavior.
Changes in sexuality associated with bipedalism may not directly relate to social customs but did emphasize a shift in reproductive structures and possible mate selection processes. As per the options given in the question, it can be inferred that option 2) 'The placement of the genitals became less important for intercourse' might be related to the anatomical adjustments resulting from bipedalism. However, it's essential to note that as the upright posture evolved, visibility of sexual and reproductive cues such as secondary sexual characteristics likely became more pronounced.