Cheese was discovered when humans began carrying and preserving milk in stomachs of cows as they did with carrying water. The stomach bacteria found happiness in the milk and what do you know, they reached their destination in yogurt form (which explains why yogurt is so good for your digestion - it has the same bacteria your body needs to produce). Yogurt is so alive that it makes a perfect hairloom. Just take a tablespoon of your old yogurt, dip it in milk, incubate it and you get a copy of the old yogurt.
Similarly, with cheese cultures, it is very common to create a "mother culture" and heirloom it between cheeses. You can also rub a mature rind on a new one to get it to catch on and grow a new rind on the new cheese. (recently I had an Irish cheddar in my fridge that was infected by a Camembert and grew a beautiful tasty velvety rind of Penicilum Candidum).
In many places around the world cheese is still made by dipping a piece of cow or pig stomach in the milk. Sometimes a dry piece can work, in other times it is better to do this with a fresh piece. The results and success rate varies tremendously and some of the undesired bacteria can also find a new home in your cheese. Commercial cultures though are far more accurate; they are the same exact bacteria and enzymes, still produced from animal stomachs and then reproduced in a friendly lab environment without the undesirable bacterias. The benefit is that you can control the strength and have a predictable process and results. Moreover, it enables you to exercise full control of a wide range of flavor and texture profiles.
In the old world, cheese would vary regionally because the livestock had different feed, humidity, heat and seasonal habits in every geographic area. It developed different milk and different strains digestion enzymes in their stomachs which gave its character to the local cheese. People lived their whole lives eating local cheese that was based on the same milk, process and character. They didn't have the ability or even the knowledge of other cheeses produced thousands of miles away. Today, we know and expect more and that's where the commercial stuff comes in handy.
Commercial bacteria can give you the same exact collection of bacterias and enzymes of a sheep in Andalusia or a mountain goat in the French Alps at the comfort of your California kitchen or factory in Holland. Used with milk that corresponds with local character, it brings upon exciting new flavors and textures. It makes the trade in cheese culture as irresistible as trade in any spice.
