During the Gold rush in California Sourdough became a legend. Even though commercial yeast was around, it was scarce and chuck wagon cooks and prospectors had to use the old method of sourdough baking to feed themselves and others. Prospectors were known to take their starters to bed with them to keep the yeast warm---and alive. The Boudin family who where well known bakers moved from France to the San Francisco area and set up the Boudin Bakery.
Since 1849 they have been using the same sourdough culture, which they call a "Mother dough" and the same recipe, flour, water, a pinch of salt and some of this "Mother Dough". So important is their "Mother Dough" it was heroically saved by Louise Boudin during the Great San Francisco Earthquake of 1906.
The health benefits are significant. The slow fermentation process makes the bread far more digestible with dramatically improved nutritional properties. It has a GI (glycemic index) 30% lower than other breads. The next time you bite into a piece of sourdough bread, remember it's not just bread; it's also a piece of history.