Sourdough bread, olives, pickles, undergo fermentatios by the same or similar bacteria.
All mammals produce milk.
Man has been drinking milk from many mammal species for a long time. In cool climates, like northern Europe, the milk is comonly drunk in the sweet, fresh state. In warm climates, like Africa, the milk sours so rapidly due to bacteria growth that usually only sour milk is available. Therefore, humans from the two regions have differing enzymes for digesting milk. Sour milk separates into solid white curd and clear liquid whey.