  You may have noticed that girls seem to have a growth spurt sometime around the sixth grade or so. Many of them are taller than the boys in their class, and they stay that way right through Junior High. But by the time everyone has reached the end of high school, most of the boys will be taller than most of the girls! How come?? The growth spurt that both boys and girls undergo during puberty is caused by rising levels of hormones called androgens. These hormones are released by the ovaries or testes, and adrenal glands, and they start working in girls before they do in boys. Androgen makes bones grow, and shoulders get wider. Increasing levels of androgen in girls makes them become taller before boys do. Another type of hormone released into boys' and girls' bodies is estrogen. It also influences bone growth. Girls' bodies require more estrogen than boys' do, however, in order to help them develop breasts, hips, and a layer of under-skin fat. But high levels of estrogen also slow and eventually stop the growth of bones ... so as girls develop, they usually stop growing taller. This lets the boys catch up. The result is that the boys who were shorter than the girls in grade six usually end up being taller by grade eleven or twelve. The boys kept growing taller, but the girls stopped. Incidentally, did you know that the average age when girls reached puberty in 1840 in North America was 16.5 years? It's now about 12. Improved diet, health, medicine, and medical knowledge are the cause. |