Question: how can we know for sure that everyone's fingerprints are unique?

Richard Case answered on 12 Jun 2011:

Good Question! This is a tricky one that always gets asked in courts…..

You have to have faith in nature that it never replicates itself…. the number of ways that the patterns (and the tiny amounts of detail) on your fingers, palms, toes and feet, can be produced are infinite. Even in identical twins their fingerprints are different due to being subject to different conditions and positions within the womb.

I have seen hundreds of thousands (maybe millions) of fingerprints in my career, and the only matching ones have been made by the same person. In over 100 years where fingerprints have been used for identifications all over the world, there have been thousands of people doing a similar job to mine… and nobody else has ever found matching fingerprints from different people.

Within the last 20 years we have seen the creation of computers that search millions of fingerprints every minute… and none of these have found fingerprints from different people to be the same.

Unfortunately fingerprints do not lend themselves to be easily explained numerically, (like they say the likelihood of 2 DNA matches from different people being 1 in a billion), but there are some clever mathematicians that are trying to develop some statistical models.

I hope that answers your question 🙂