Monday, February 25, 2008

Forensic Science at Breakfast

The back of my kids' cereal box this morning was all about forensic science. Boy, cereal boxes have come a long way from when I was a kid!

One of the things mentioned was the "fact" that all fingerprints are unique. This is one of those facts that is right up there with no two snowflakes being alike and identical twins have identical DNA. Of course they're all true.

Actually, none of them are true. They are theories, not facts. Science doesn't call things facts that aren't observable or provable. And we're not doing our children any service by miseducating them about science.

Let's start with the identical or monozygotic twins (I happen to be one). How could you prove the theory? Well, you can't because you can't possibly test every past, present and future set of twins and we don't have a complete understanding of how twins happen (we have a pretty good understanding, but we're still learning). Over the years, there have also been cases where DNA testing showed identical twins to have different DNA. But these cases were viewed as exceptions, not the rule, and were generally explained away. Now there's a recent study (PDF) that many, if not all, identical twins have different DNA. Scientists have learned that all identical twins may actually differ genetically from their partners to some degree. See also

What about snowflakes? This "theory" was proposed by Wilson Bentley, a farmer and photographer, not a scientist. Again, you can't prove the theory, but you can disprove it and scientists have found small identical snowflakes. See also

And, finally, fingerprints. I'll leave this as an exercise for the reader. All you have to do prove the theory is explain exactly how fingerprints get created to the extent necessary to show that identical fingerprints cannot possibly be created. That there is some rule that means that a baby born today, in Seattle, cannot possibly share fingerprints with someone born fifty years ago, in Russia. That there is a mechanism that prevents that from happening. If you can't explain that, not only can't you prove the theory, but it's looking a lot more like it's false.

Or, you could just trust the cereal box.