You're right - given that there is really only a finite number of ways that chromosomes and genes can replicate themselves over time, and the highly probably possibility that in other dimensions, like attracts like and the same people are drawn together, eventually we all may have a doppleganger in another dimension, which increases the probability of said doppleganger showing up here as the rest of us have, and in fact it really isn't surprising at all if you think about it.