During a particularly meandering web-crawl, I came across a fascinating article describing the discovery of what some scientists believe to be the original wild yeast that enabled lager fermentation. Read the full article here
It turns out that lager yeast is actually a hybrid of our beloved ale yeast with a foreign yeast that enabled the characteristic of cryotolerance - ability to flourish in colder temperatures. Until this research was conducted, the source of the strain that contributed this additional characteristic remained a mystery, but scientific investigation happened upon the precise strain in the beech-tree forests of Patagonia in South America. It is believed that humans during the age of sail carried the yeast back to Europe from the New World, where it merge with ale yeast in the fermentation caves and cellars of Bavaria to form lagring yeast.
What's just as fascinating to me is that these lager yeast hybrid strains only persist through symbiosis with humans. Left to nature, they would die out, but because they are the perfects catalysts for the creation of human-consumed lagered beer, we humans have propagated and maintained a healthy population of these strains of yeast. We continue their existence and provide an environment in which they can thrive, and in exchange they produce lager beers for our consumption. Without humans, the lager yeast strains would quickly die out.