I've always wondered if the fact that if your teeth were straight depended on how you lost your previous teeth.....

I have a brother and a sister.  My brother, like me, would always yank his loose teeth out, not letting it "fall out by itself".  My sister would always be careful, and would wait until the teeth fell out on their own.  

Well, it turns out that my brother and I have a perfect set of teeth, while my sister's....... well..... they aren't bad. They could be better.  

So that led me to thinking that maybe if you yanked out your baby teeth earlier, it might make more room for the new teeth, letting it grow out straighter.