[Solved] What is the difference between an if statement and an if/else statement? Fraternal Birth-Order Effect: A phenomenon where the more older brothers a man has, the higher his likelihood of being homosexual. Genetic Basis: The underlying genetic makeup or heritable factors that contribute to the physical and behavioral characteristics of an organism. Erotic Plasticity: The degree to which an individual's sex drive or sexual interests can be shaped and altered by cultural, social, and situational factors. Hypothalamus: A small region of the brain that plays a crucial role in many essential functions, including hormone regulation, temperature, and appetite control.