What is the first sexual characteristic of human beings?

Human primary sexual characteristics refer to various reproductive organs involved in human reproduction. Men include testis, epididymis, penis, seminal vesicle, vas deferens, prostate and urethral glands. Among women, the primary sexual characteristics mainly include: ovary, fallopian tube, uterus, vagina, lips and so on. The secondary sexual characteristics of human body refer to the special signs of different sexes except reproductive organs, such as pubic hair, armpit hair, breast, beard, Adam's apple and voice change. Before puberty, the development of reproductive organs and secondary sexual characteristics is very slow and almost stagnant. After puberty, under the action of gonadotropins and sex hormones, the human reproductive organs developed rapidly, and secondary sexual characteristics gradually appeared, which gradually transformed boys and girls into mature individuals of different sexes. That is, from appearance and reproductive system and function to maturity, and finally achieve the function of reproducing the next generation.