I've been reading a fascinating book by Mark (Shakespeare in Love) Norman called What Happens Next, A History of American Screenwriting, which is pretty much what the title says it is. I've reached the 1930's, but I've run across a few interesting tidbits:
1. Most early screenwriters (during the silent films) were women, though no one seems to know why.
2. One, Gene Gauntier, was inadvertently responsible for authors of source material (like books and plays) being paid for the right to use their work when she did a 15 minute adaptation of Ben Hur and the Wallace estate sued.
3. Thomas Ince is responsible for the way a screenplay looks on paper when he wanted to make movie production to be as efficient as possible.
Also, a quote. In talking about the basic formula and structure that was started in silent film (though dates from Aristotle) and is still used today:
"This often monotonous narrative structure answered many studio needs. For an industry increasingly compelled to churn out products, it streamlined production; screenwriters learned to mold and hew their output to fit the template and save time; and it provided the front office with a basis to judge a writer's screenplay and a vague but finite vocabulary to use when it set out to change or improve it."
I.e., the reason that this formulaic structure (often seen in many books on how to write screenplays) was adopted was not because this was the only way to make a story work for an audience, it was because it was the most efficient way of churning out product.