Puberty
Because of more hormones in the body, girls start to have more fat in their breasts, abdomen, hips, and thighs. At the age of ten years, the average girl has 6% more body fat than the average boy, but by the end of puberty, the difference is nearly 50%. The fat makes sure that a baby growing inside a pregnant woman will have enough nutrients. Also, the bones in the pelvis move further apart to make room for a larger uterus and ovaries, so there is space for a baby to grow in the uterus and to pass out of the body when it is born. The extra fat and wider hip bones that girls have give them a curvier shape.