Random Thought: Mind your P's and Q's

So I wonder, the saying "Mind your P's and Q's" was that an early sign of Dislexia? Did people have to remind people to be careful when writting a p and a q to ensure the line was on the right side of the o....? Kinda makes you think, how "new" are ADHD, Dislexia, Autism.... are they a result of our environment, the food we eat, the innoculations we are forced to take... or have we always had them and we're just getting much much better at classifying them?