Without the reproductive system, new members of a species could not be produced and the species would become extinct. Although the foundation of reproductive organs exist at birth, it is not until about 10 years later that the full functioning of the system is spurred by the endocrine system, and its sudden change in hormone production to begin puberty. These same hormones are responsible for sex drive and secondary sex characteristics, including facial and genital hair, distribution of body fat and breast development. The hormones also affect emotions in both sexes. They are produced in the sexual organs themselves and in endocrine glands outside the reproductive system. In men, the main reproductive organs include the penis, the testes, ducts and the accessory sex glands [the seminal vesicles, bulbourethal glands and the prostate]. The testes [or testicles] are oval glands were sperm is produced and hormones are secreted. The testes are contained in a pouch called the scrotum. The muscle fibres in the scrotum regulate the temperature for the testes which is important to the survival of sperm; they must be kept 5.4°F [3°C] lower than the core body temperature or else they will die. In woman, the ovaries, uterus and vagina are the major reproductive organs. Once a month the ovaries will produce an egg, which will be released into one of two fallopian tubes at mid-cycle. This process is called ovulation. While the egg is in the fallopian tube, it may or may not be fertilized by sperm. The uterus prepares for possible fertilization by building up its walls to protect the fertilized egg when it arrives from the fallopian tube, and provide it with nutrients until the placenta takes over.