[Solved] What does a spectroscopic binary show periodic variations in? A) brightness B) motion perpendicular to the line of sight C) motion along the line of sight D) spectral type Birth-Order Effect: The theoretical impact that a person's rank by age among siblings has on their personality, intelligence, and behavior. Sexual Orientation: A persistent attraction pattern that is emotional, romantic, or sexual towards men, women, both, neither, or a different gender. Natural Selection: A process in evolutionary biology where organisms with traits better suited to their environment are more likely to survive and reproduce, thus passing those traits on to future generations. Erotic Plasticity: The degree to which an individual's sex drive, sexual preferences, and sexual identity can change throughout their lifetime.