Frequently used pairs of letters were separated in an attempt to stop the typebars from intertwining and becoming stuck
The position of the letters however determine also the ergonomics and the speed of the typing. This is why they invented alternative keyboard layouts, the most known of which is the Dvorak Simplified Keyboard with a greater focus of the position of the letters.
When I come to know that, having learned myself touch typing, I was quite interested and did some research on the net. That is how I came across the colemak layout, specifically designed for computers and specially made to allow an easy transition from QWERTY. I've started to practice 3 days ago and am able to write using 16 letters so far. For my day to day use I'm still on the standard QWERTY and the two don't seem to interfer.