There is a develompent in the Singer round bobbin models from model 15, 9W7 to 115 and 101 and 201. There's model 66 in 1900 and I have always though of 101 and 201 as a development from the drop in bobbin machine.

Some early German models are rotary, with similar bobbin case as model 15, but not identical setup. I don't know if it's possible to sort out the lines of development, dating and origins at this point, a 100 years down the road.

Likely impossible...
The Featherweight has combos of other older machines, too. I wonder how much industrial machines influenced....?
Not much effective innovation ever since is there? And even then what there was wasn't necessarily an improvement just cost control.
Then there is the ZZ ability + fancy stitches and how that has evolved from one machine to another.

I know various overlock stitches, fancy stitches, emobroidery, and zigzag were invented before 1900; industrial versions of course. The first domestic swing needle was possibly a Mundlos-Victoria machine in the early 1920s. Development has come in steps forwars but often resulted two steps back in other areas. We are very driven by the new, an almost frantic fascination for innovation.I wonder why plastic materials were used in all areas increasingly from the 1950s? Is steel that much more expensive? Hardened steel parts tend to be rather expensive, but mass production often evens it out. I'm not sure.

Almost all the features we have today we find in non-computerized domestic versions from the 1950s, Auto-threaders, buttonholer function, overlock type fancy stitches, models with over 100 stitch patterns, presser bar knee lift,... I guess the auto bobbin winding function with out having to take it out of the bobbin case was introduced in the 60s. Not sure when the first auto thread cutter was introduced?

At some point computerised machines were forced upon up (I don't think there is a single mechanical cam function left in production, it's all step motors and compuerize circuit boards even on the simplest machines). I guess that's the new part (started with a Pfaff in 1968?). When was needle up/down introduced? Among the new is having all the fancy features integrated in one machine. The fancy overlock stitches on new machines have stitch windth function the 1950s models didn't have, and there are 7 and 9 millimeter wide zigzag on the top models these days. Embroidery is much more advanced than 20 years ago, but I don't do that.

I still feel all the auto features to a large degree has to do with what we get used to and how we find ways about things. My favorite machine to use the last two years has been a 201 I fixed up.

There is a Singer model (I think it was) bragging to have the first pyramid shaped feed dog pins (or is teeth a better word?) "a new exclusive feature" the odd thing is Elna had this in the early 1950s and no one really bothers to correct them lol

When Corvette came out with hide a away headlights in 1963, some of us knew that Cord had them much earlier.
Still waiting for a modern two spool....

Sorry about the messed up typing, I really should not post more than a line or two from the phone.