You Are Not As Unique As You Think

One of the stories on BBC News today talks about concerns over the national DNA database. Right now in the UK, anyone who is arrested is entered into the database. Not convicted, just arrested. But what’s the problem? DNA evidence has revolutionized police work in recent years, and many scientists will tell you the chances of two people sharing the same DNA profile are 1 in 113 Billion!

Only….. that’s not quite true. In fact, it’s probably an outright lie. The chances of two people having exactly the same DNA are effectively zero, but we don’t compare two people’s DNA against their entire DNA sequence. We compare them against a small section of DNA, at 13 individual locations on particular chromosomes that will supposedly identify an individual with a margin for error as low as 1 in 113 Billion.

So you can imagine the surprise of lab technician Kathryn Troyer, who in 2001 found dozens of similar matches between unrelated individuals in one DNA database. A DNA database that contained only 65,000 profiles. It defies logic. In the years that followed many scientists and organizations attempted to launch investigations into Kathryn’s findings, but were blocked at every step of the way. To my knowledge, no actual public study or investigation into the actual reliability of DNA evidence has been conducted [can someone confirm or disprove this?].

Which I think raises serious questions over the validity and safety of a national DNA database, crammed full of innocent people. DNA evidence is something of a silver bullet in a courtroom. It will place you at the scene of a crime and is paraded in front of a jury as evidence so infallible, God may as well have descended from heaven to point his finger at the accused himself (or Allah, Buddha et al). People are even convicted of a crime on DNA evidence alone, in the absence of any other evidence of any sort. But if that evidence is as unreliable as the findings of Kathryn Troyer seem to indicate, then it’s highly likely that innocent people are being convicted of crimes they didn’t commit, on the strength of evidence that no one can question.