Weekly Blogging Assignment No. I

We read an article that talked about how the median age of "puberty onset" in girls is movin' on up, and how very young, developed girls are more common these days. I remembered reading a while ago about that one Peruvian girl (Lina Medina, I believe?) showed signs of puberty at the tender age of three, and got pregnant at age five. This was a while back, too - maybe in the forties or fifties. Her father was arrested for incestual, statutory rape, but he was later acquitted of all charges.
It's absolutely terrifying, in my opinion. Especially the last part - girls don't just randomly get pregnant without any sexual contact (unless you're Mary... but how the crap does that work, anyway?), so that means that SOME man had some form of sex with her. Aside from that, it's kind of scary, anyway. I saw a picture of her when she was pregnant and she looked so... young. Completely unequipped to carry a baby at her age. She delivered by cesarean section, of course, or the baby probably would have split her open.
The family treated the baby like a "younger brother", and Lina preferred to play with toys more than she did her child. He was not told of his "sister's" actual relation to him until he was older.
This is probably, hopefully, a once-in-a-blue-Moon case, but relating to the article we read, what is the possible evolutionary benefit to entering puberty at such a young age? Correct me if I'm wrong, but, aren't most qualities attained through evolution somehow beneficial to the current people that have them (but not necessarily the later ones - I'm looking at you, fear of spiders!). I just can't muster the brainpower to even comprehend why this could possibly be due to actual evolution - with our life expectancies so high, why would we need to attain the ability to become pregnant so much more early?