From Aileen Fyfe:
At early Royal Society meetings, research findings were presented, often demonstrated and frequently discussed. But while it is possible to say that this means they had undergone scrutiny by well-informed scholars, that could be deemed to be peer review only to the extent that material presented nowadays at workshops and conferences (or on preprint servers) can be said to have been peer-reviewed. A modern journal editor might, as Oldenburg was in effect doing, scout for potential submissions at a conference and take heed of the tenor of the discussions; but those discussions are part of the oral culture of scientific communication, which help a researcher firm up their analysis and interpretation before seeking publication. They serve a purpose of their own, distinct from any editorial process.