Another teeth theory: My grandmother always said a child can't be potty trained until he/she gets 2 year molars. She also said that kids who don't crawl 9skip that stage and go right to walking) will have a hard time learning to read.
LOL - Love these theories! DD did have her 2yo molars when she toilet trained - but she got them very early (hence the early loosing teeth). She didn't crawl, went straight to walking and yet read at 2.5... goodness imagine if she'd crawled!
Another I read about was someone who said that if children didn't crawl they'd never be able to dance! That one still makes me giggle.