My Identical Twin

When I was younger, I used to think it would have been cool to have an identical twin. Cool for me, I mean, not so much for my parents. One of me was waaaaaay more than enough, I can't imagine what a nightmare two of me would have become. I used to think of all the things that I could do with a brother the exact same age instead of a stinky little sister.
   Make no mistake, I love my sister dearly, and I promised my parents long ago never to mention the crooked carnies we bought her from when she was a baby. Still, you can't exactly practice lighting your farts with your little sister, but it's an obligation when you have a twin brother.
   Anyway... I was reading in Scientific American the other day - the October 2010 issue - that humans have about 20,000 genes, with about 3 billion nucleotide pairs. Not a whole heck of a lot, actually. Most of the human genome is identical from person to person, there are differences only in about 1 in 1000 nucleotide pairs. Which means that from me to you there would only be a maximum difference of about 3 million pairs, and that's only if every single nucleotide sequence was different. Chances are good you and I have far fewer than 3 million different genes. Maybe only on the order of a few hundred.
   So I got to thinking. If the maximum difference between two people was 3 million nucleotide pairs, and if there are 6 billion people on the planet...
   There's an extremely good chance that somewhere out there - right this moment - there is a man who has EXACTLY the same genome as I do. He could be older, he could be younger, but with so few possibilities for differences in genes, the probability is solidly in the positive range. The math is simple enough to do, it's not even calculus.
   Somewhere in the world I have a genetic twin, who is walking around, blissfully unaware that he and I are the same down to our very last strands of DNA.
   And why is this important? Other than being a way for me to get the twin brother I never had, it would be good to find my genetic twin just in case I run up against any problems. You know, accidents, disease, that kind of thing. If I can find this guy then I'll have someone whose organs I can harvest when the going gets tough.
   Of course, maybe that guy has the same idea about me.... We are exactly the same, after all.