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There absolutly is selection involved. First, you create a selective environment to culture a subset of environmental organisms (yeasts). Then, by infusing fresh media (flour/water) into the cultures each day, you are essentially passaging a live culture or organisms. It's not rational selection, like that practiced by plant breeders, since you aren't hand ...


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That is not Darwinian selection, because you are not selecting anything. As you mention yourself, it doesn't matter which half you discard and which half you keep. In fact, you can keep the entire thing. Discarding just makes it more practical. If all conditions are fine, yeast will grow exponentially, meaning your amount of yeast will double every 2 hours ...


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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....


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