basically, eliciamarie is right. It does go back to the early 20th century where typing skills were required of women or men entering the work field. I use to have the name of the woman who invented the pattern of the letters on the keyboard but I can't recall it right now. I took typing lessons in high school and when my children grew, they were amazed at my speed on the key board.
The qwerty style keyboard was arranged so that commonly used letters were placed in an order where your fingers were easier to reach them when placed on the middle row of keys. It is also said that it dates back to the old type writers and had something to do with the speed of typing. (sorry, i can't exactly remember, but it's something along those lines) :)