I am sure I will get this wrong and that Ron will be able to clarify but it appears that two forensic yeast researchers have determined that lager yeast came into existence twice during two separate events:
...the team discovered that it happened at least twice in two separate locations in Europe, giving rise to the two different lager families...The hybrid, which makes lager instead of ale, probably evolved in Bavarian beer-brewing cellars during the 16th century. The team also found that Saaz yeasts have a single copy of each parent yeast's genome, whereas the Frohberg yeasts have an extra copy from S. cerevisiae. They believe this difference affects the flavour of the lager, as well as how quickly the yeasts can ferment the hops.
OK, so the egg heads in lab coats don't know that hops do not do the fermenting. Forgive them. Take a breath. There, that's better. Apparently, that there are Saaz and Frohberg strains of lager yeast has been long known. But what was not known was that they developed independently from each other - as this article in today's New Scientist explains in further detail. Sadly, they cannot trace back to which Bavarian cave gave birth to which strain and when. Even more detail here including this interesting tidbit:
Studying the spread of the two groups provides a genetic snapshot of lager brewing in Europe during the past 600 years: one lineage is associated primarily with Carlsberg breweries in Denmark and others in what is now Czechoslovakia, while the other group localizes to breweries in the Netherlands, including Heineken.
Neato. The team's full research results will be published tomorrow by Genome Research.