This chapter addresses the biological, psychological, and sociological aspects of gender. Anatomic sex: based on the physical differences between females and males. Sexual differentiation: the process by which males and females develop distinct reproductive anatomy. Prenatal sexual differentiation: aristotle believed that the anatomical differences between men and women were due to the heart of semen at the time of sexual, hot semen- generated males, whereas cold semen- generated women relations. The basic blueprint of the human embryo is female. The role of sex hormones in sexual differentiation. Each wolffian duct develops into an epididymis, vas deferens, and seminal vesicle. The external genitals, including the penis, begin to take shape at about the eighth week of development under the influence of another androgen, dihydrotestosterone (dht) Each embryo possesses primitive external genitals, a pair of sexually undifferentiated gonads, and two sets of primitive duct structures, the mullerian (female) ducts and the wolffian (male) ducts.