Boys start shorter than girls, yet end up about 13 centimetres taller
Before puberty, boys average about 2 centimetres shorter than girls. By adulthood men are roughly 13 centimetres taller. The reason is timing: the male growth spurt starts later and runs longer before bone growth plates fuse, largely because of the later rise and lower levels of the hormone estradiol.
Puberty is the set of bodily changes that turn a child into an adult capable of reproduction. The brain signals the gonads, ovaries or testicles, which respond with hormones that reshape bones, muscle, skin, hair, blood, breasts, sex organs and the brain itself. Height and weight surge in the first half of the process. The word comes from Latin for the age of maturity and refers to physical change, distinct from adolescence, the psychological passage to adulthood that overlaps it.
On average girls begin at about 10½ and finish between 15 and 17, while boys begin at 11½ to 12 and finish at 16 to 17. The first period, menarche, arrives around 12½; first ejaculation, spermarche, around 13. Girls reach reproductive maturity about four years after the first changes, whereas boys develop more slowly and keep growing for about six years. Adrenarche, a rise in adrenal androgens between ages 6 and 10, comes first and can bring early body hair that sometimes vanishes again.
The trigger is a surge of pulses of the hormone GnRH, which drives up LH and FSH, though what sets it off is unknown. Leptin is one candidate: its receptors sit in the hypothalamus, people lacking it never start puberty, and its levels climb at onset before settling. Genes matter too; mutations affecting neurokinin B can shift timing, perhaps via kisspeptin. In boys testosterone dominates. In girls testosterone is converted to estradiol at rates that vary widely between individuals, giving very diverse patterns of development.
Nineteenth-century averages were later, around 15 for girls and 17 for boys, a shift variously linked to better nutrition, more body fat or endocrine-disrupting chemicals. Yet archaeological work suggests growth spurts have long begun at 10 to 12, with later milestones delayed by poverty, poor diet and pollution. Studies find that early puberty tends to bring poorer outcomes for girls, often tied to body image, while early-maturing boys fare worse in adolescence but better as adults.
Source: Puberty
