Why do girls now begin to menstruate earlier than they used to?

Answer 1

Well, puberty is when the body begins to mature. One aspect of a girl's body being mature (and this is similar in a male's body, too) is that of being able to reproduce. This, for a girl, is when she menstruates. During and after puberty, a girl is able to reproduce and will have her period. Before puberty, a girl has an un-mature body that cannot yet reproduce, and thus she does not menstruate.

Answer 2

Puberty and menstruation are triggered by estrogen, of which high quantities are released by the Pituitary gland in the brain.
That's a bit like asking why it doesn't get dark until sunset.

Puberty is the name for the phase when the body is growing big/mature enough to be able to become a parent. And for girls/women, they can't become parents unless they're menstruating. So for girls/women puberty and menstruating are tied together.

Answer 3

Because puberty is the name given to the process which changes a child's body into that of an adult. The defining feature of a woman as opposed to a girl is the ability to bear children. Menstruation is part of the process of puberty which enables woman to bear children so therefore any female who can menstruate is technically a woman wereas before puberty they were a girl child. Simply, menstruation is part of puberty.

Answer 4

Cause the walls in your uterus are breaking, so you bleed. It means you can now get preggers.