In reply to RichardMc:
Hero loops, both the objects and the name, originated in Yosemite, probably in the late fifties or early sixties, but quite it bit before 1968. We used to carry ten or so stuffed into our pockets for tying off aid pins. But tied-off pins were needed for free-climbing protection too, so folks started making up some hero loops from 9/16 inch tape, which was much more robust than the half-inch webbing used for aid hero loops. It was inevitable that those beefier loops would also end up being used to extend piton placements, but the quickdraw wasn't born until someone decided to carry the extenders pre-made rather than just having some webbing in your pockets and fiddling with each placement.
I first saw these pre-made quickdraws in Yosemite in 1970; I don't know how much earlier they were in use, but it is worth noting that this seems to be about ten years earlier than people here are saying quickdraws appeared in the UK, and their adoption predates both the use of nuts in the US and sport climbing. The term "quickdraw" was also coined by Yosemite climbers, and is a play on the same term as it applies to old West gunfighters.
As for chaining biners, many American climbers knew of Mark Powell's accident, in which chained carabiners unclipped, resulting in a long fall and badly shattered ankle, an injury that changed the course of Mark's career and has remained a serious problem for his entire life. For this reason, we didn't trust chained carabiners from the late fifties on, and always used some sort of sling as part of the extending mechanism.