This is the term for the step-by-step changes that relate to the biological (physical) features of a person’s sex. The development of sex begins at conception with the combining of sex chromosomes from the mother’s egg and the father’s sperm. Sex development continues in the womb with the prenatal development of the internal sex organs (including the gonads) and the external sex organs (like the penis, clitoris, labia, and scrotum). For most people, sex development continues naturally little by little through all stages of life, including most noticeably at puberty (which brings many changes including altered sexual arousability, fat distribution, voice pitch, hairline, pubic, underarm, and body hair, genital and nipple appearance, breast development, skin oil and texture, and body odor) and at menopause.