About being literate or semi-literate to vote: Isn't that why the symbols, elephant for republican, and donkey for democrat, were invented?

I remember when I was a little kid and accompanied my dad into the voting booth -- everybody used plain paper ballots back then, and marked an X in a box -- I saw that the ballot was divided into columns, one column per party. If you wanted to vote a "straight ticket", i.e. vote the same party for every office, there was a box at the top of the column where you could indicate that, and you didn't have to put an X next to every candidate's name. Also, at the top of each column was an animal symbol. (I remember one symbol was an eagle, but I don't remember what party that was.) I asked my dad why they printed the symbol and he said, "It's for people who can't read." This would have been in Missouri in the 1950's.