Sexual maturity is the change that most people associate with adolescence: puberty: all of the changes both seen and unseen needed for reproductive maturity. Major hormones that contribute to physical growth & development. Normal brain development and overall rate of growth. Some changes at puberty, particularly the development of secondary sex characteristics in girls. General growth hormone, thyroid stimulating hormone, and other activating hormones. Crucial in the formation of male genitals prenatally; also triggers the sequence of changes in primary and secondary sex characteristics in the male. Development of the menstrual cycle and breasts in girls; has less to do with other secondary sex characteristics than testosterone does for boys. Babies who lack thyroid hormone at birth are small and have insufficiently developed brains. Primary sex characteristics include growth of the testes and penis in the male, and of the ovaries, uterus, and vagina in the female.