Final answer:
Secondary sexual development occurs during puberty, which typically begins between 11 and 12 in boys and between 9 and 10 in girls. It involves the development of secondary sexual characteristics like pubic hair and facial hair for boys, and breast development and pubic hair for girls.
Step-by-step explanation:
Secondary Sexual Development in Adolescents
Secondary sexual development typically begins during puberty, which is a period of physical changes when a child's body matures into an adult body capable of sexual reproduction. In boys, puberty generally starts between the ages of 11 and 12 years old and is usually completed by the age of 18. During this time, secondary sexual characteristics such as pubic hair, facial and body hair, and the deepening of the voice emerge. In girls, puberty typically starts between the ages of 9 and 10, with the development of breast and pubic hair, and is usually completed by the ages of 14 to 16 years old. The timing of these events can vary greatly among individuals, but the sequence of changes is generally predictable.
The onset of puberty is triggered by a concerted release of hormones from the hypothalamus (GnRH), the anterior pituitary (LH and FSH), and the gonads (testosterone or estrogen). These hormones are responsible for the maturation of the reproductive system and the development of both primary and secondary sex characteristics.
It's important to note that while the adolescent growth spurt is a prominent feature of puberty, including rapid growth in height and weight, it is the hormonal changes that lead to the development of secondary sexual characteristics, differentiating between males and females.