If you take a 1 pound batch of starter and use it once a week, each time removing half then replenishing the missing half with flour and water, in 1 year, there will only be 10 trillionths of a gram of the original starter in your 1 lb batch of starter.
Of course, as you are adding the flour, the original organisms will proliferate in the replenished starter, causing them to continue on. However, the yeasties and lactos contained in the flour which you are replenishing your starter with, will have a huge affect on the starter. In fact, you could end up, eventually, with a starter that has none of the original organisms. Unlikely, but it is possible. Temperature has a huge affect on which organisms will win out in the end.