Does the process of making a sourdough starter involve Darwinian selection? In essence - to make a sourdough starter: 1. Put flour and water in a jar, and leave it in a warm place overnight 2. Divide the remaining mixture in half, throw out half, add half as much flour and water again. 3. Repeat for 7 days. I don't see why you couldn't just add all the ingredients required at the start, open it once a day to let more yeast drop in and give it a stir, and keep in a warm place every day. The vague idea comes to me that throwing out half the mixture every day has a Darwinian element, but it doesn't involve any 'selection', you're simply casting out half, regardless of adaptability. My question is: **Does the process of making a sourdough starter involve Darwinian selection?** EDIT: There is no 'choice' involved in throwing out half the sourdough. It is entirely arbitrary - and both halves look equally the same.

Yes, continually diluting the mix like this encourages the organisms (bacteria, yeasts, fungi) to have more constant conditions (maximum nutrients, fewer waste products) and be in log phase growth. The mix selects for particular faster-growing organisms. if you did not dilute, the nutrient levels would change (lower) and waste products accumulate much faster. Then the conditions would be more different day-to-day.

Practically, the dilution adds more nutrients while still allowing the pH to fall. Without the dilution, particular bacteria tend to take over and lactic-acid producers dont get a chance.

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