This topic could also be addressed in another way of looking at it, sort of "outside the box' if it were.
While I am not going to sit hear and preach to you about nature vs. nurture, or the evolutionary road that seems to split the Christians from the scientists, but I do believe that some of the two above mentioned thing has to have some sort of factoring into the changes we are seeing in the generations that follow us. Some of these changes are easily tracked while other are not so much.
For example, my mother started her period when she was either close to 13 or just turned 13. I started when I was either close to 12 or right after 12, and my girls both started at 11, and oh what a huge blessing that was, trust me. Now given this information, it would make sense that their children would be starting around the age of 10, but I have serious doubt as to that every happening. Evolution does't quite work that fast. But, like I said, that's just one example.
I also believe that hormones in food products also aide in some of the recent changes we have been seeing. Also one has to factor in the child's home environment too. Children are being forced harder, quicker, and sooner to grow up, take responsibilities, take care of them selves because Mom and Dad both have to work to make ends meat, in turn, leaving kids often having to fend for them selves, mine included. On one hand I wouldn't allow either of them to get a job while they were in school because I did't want that sort of pressure put on them, which I don't regret to this day. But the double edged sword to that line of thinking is that while I have protected them from having to grow up too fast, now I'm starting to wonder if I have even let them grow up at all? Only time will tell I guess?
Mashie.