This is a topic discussed by Henry Petroski, who has written several books on the history of design and engineering, in several of his books but most extensively in The Pencil: A History of Design and Circumstance where it's discussed in the context of why this layout has become ubiquitous and how the same factors continue today despite the existence of "better" keyboard layouts, specifically the Dvorak.

The origin of the QWERTY keyboard in the late 1870s was indeed to reduce the incidence of jams in contemporary typewriters, not by slowing the action of the typist, but by physically separating the most commonly used keys. Mechanical typewriter keys have a direct physical linkage to the letter being typed, and the action of pressing the key provide the power to swing the letter forward and stamp on the paper. By laying out the keyboard such that common letter combinations, e.g. "S-T", don't involve adjacent letters, it's less likely for a jam to occur in normal typing. This design constraint, combined with the need to still make the most common keys easily accessible (there's a reason why "Q" and "Z" are off in the corners, for example), led to the QWERTY layout as a solution.

As to the rest of your question, I highly recommend reading the book as it's a surprising complicated story involving not just the ergonomics and utility of the design for users but also the interaction with other technology and even the economy of the day.