Science
A sourdough starter is a complex mix of yeast and bacteria. The result of these two types of microbes are carbon dioxide bubbles (from the yeast) and acids (from the bacteria), which are what gives sourdough its fluffy crumb and tangy taste.
Due to naturally-occuring enzymes in the flour, hydrated flour will automatically start breaking down its starches into mono- and disaccharides. Typically, the sourdough bacteria (such as L. sanfranciscensis) will metabolize maltose, while common yeasts such as S. exiguus and C. humilis prefers glucose, sucrose, and fructose, so they’re not directly competing for resources.
Waste products of fermentation include lactic acid and acetic acid, which are what gives sourdough that characteristic tang. Even more importantly, though, they lower the pH of the culture. Common sourdough microbes prefer this highly acidic environment (an average pH of about 4), which is nearly inhospitable to “rival” bacteria and yeasts. This makes your starter pretty difficult to spoil. Symbiosis, baby.
Many people begin their own sourdough starters by just leaving flour and water uncovered on their countertops. There are enough wild yeasts and bacteria to populate it in just a few weeks! However, you don’t always get the best yeasts and bacteria, which is why the history of this particular starter is so great...
History
This batch of sourdough is a descendant of a (claimed) 100+-year-old sourdough starter from Alaska. The “pedigree” of a starter doesn’t actually matter that much (scientists believe that the culture will mostly adapt to its local climate regardless of where it has lived in the past), but I chose Alaskan starter because of its history [1] (and because San Francisco sourdough is too mainstream).
Historians believe that sourdough began because of beer brewing thousands of years ago. Early bakers and brewers noticed that skimming off the top of a hoppy brew and mixing it in with their flour caused the bread to rise. From there, they began keeping a bit of leftover dough each day in order to make the next loaf rise.
Sourdough came to the U.S. pretty early: legend has it that Christopher Columbus brought a crock of sourdough starter with him in his famous 1492 voyage. However, the tang of classic sourdough fell out of fashion, and most early American bread bakers got their yeast from beer brewers. This resulted in a white bread that rose without the sour acidity added by the bacteria. When brewers changed their yeast, though, it was no longer as good for baking, and commercial yeast was invented. Sourdough cultures were seen as uncultured, and it seemed like sourdough might be a thing of the past. BUT THEN...
Sourdough made a comeback in the California Gold Rush (1849ish). Hungry miners were forced to bake for themselves, and commercial yeast (which didn’t keep as long as a sack of flour would) was hard to come by in the wild west. French bakers brought back the technique and starter to the northern California area, which is why San Francisco is famous for its sourdough today. In fact, there is a strain of bacteria called Lactobacillus sanfranciscensis (though it has been found in sourdoughs around the world, not just in SF).
As the gold search slowly made its way north, miners brought their starters with them. The next famous sourdough rush is characterized by the Yukon gold rush in Canada/Alaska (1896-1899). However, the Yukon territory’s harsh winters threatened to kill the starters (don’t freeze your starter -- it will die!). In order to protect their starters (and their bread fluffy for another year), Yukon explorers were known to sleep with their starters to keep them warm. That’s so adorable. “Sourdough” even became a term for a backcountry Yukon explorer.
In fact, this particular sourdough starter is the descendant of a starter used by a fortune-seeker in the Yukon gold rush (1896-99). When was it actually started? That’s lost to history, but you could have a flour particle in there from over 100 years ago (gross). The starter has been living in Wrangell, Alaska for the last few decades, and I purchased it from a local there.
Tl;dr: you’re holding a starter that an old crusty Alaskan might have slept with.