[1] http://brassgoggles.co.uk/forum/index.php/topic,43672.0.html [2] http://www.ebay.com/itm/272286062507
But it's not the ancestor of the computer printer.
The Selectric's main ancestor is the Blickensderfer_typewriter [1], from 1892. This used a curved type element rather than a typeball, but had a similar method of turning key presses into typing element positions. As with the Selectric, the font could easily be changed. There was a proportional-spacing successor to the Blickensderfer, the Vari-Typer, and IBM imitated that, too, with the IBM Selectric Composer.
The Selectric had a moving print head rather than moving paper, with cables on moving idlers used to transmit position to the print head. That mechanism is from the Teletype Model 28/35, from the early 1950s. Moving the print head rather than the paper was a Teletype concept - it worked much better with roll paper, and the machine was narrower.
The Selectric mechanism was not designed for electrical inputs and outputs. The add-on mechanism for that was an afterthought, and kind of a hack. The unit had to be built into a table, and the mechanism for the keyboard extended below the tabletop. IBM and Remington had previously built typewriters with electrical I/O, and those were used with some early mainframe computers.
Many computers, before and after the Selectric, used Teletype machines as I/O devices. That lasted until daisy-wheel printers and cheap CRT terminals were invented.
(Mechanical line printers have a completely separate history. They descend from the Potter Flying Typewriter.[2])
[1] https://en.wikipedia.org/wiki/Blickensderfer_typewriter [2] https://www.computer.org/csdl/proceedings/afips/1952/5041/00...
The whole world isn't quite like that yet; a few years ago I visited a factory in India that made portable generators. Aluminium ingots and copper wire came in one end and generators came out the other. None of the labor was automated. They could have, with some effort, changed products.