In the future, aliens who have invaded earth are conducting a survey of teenagers. when examining body modifications, they conclude that piercing is a polygenic trait. they reached this conclusion by examining only the number of piercings in a teenager, and the number of piercings in their parents. why might they conclude that the propensity for piercings is a polygenic trait? explain your answer fully in words, no equations please, including all observational patterns that might have led the aliens to their conclusions.