How are bite mark forensics a poor measure of determining whether a suspect matches the evidence found?
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Bites are very rarely uniform or neat. Also depending on medium the bite is in, it can deform differently and how a different bite to what it actually was.
On top of that, teeth can change and be moved. Overall they’re an inconsistent way to measure or collect evidence.
The issue is not that it is bad hypothetically, it’s that it’s bad in practice.
Meaning, sure, people’s teeth are fairly distinct and their may be times that you can clearly establish person X made bite Y, but more often then not it’s ambiguous with a lot of room for pseudo-scientific and subjective analysis.
1. Human skin doesn’t preserve marks very well.
2. In practice, the process of matching bite marks often involves pressing a mold of the suspect’s teeth into the bite marks, which can alter the marks (and make it appear that the teeth match even when they don’t).
3. There’s no objective standards for qualifying matching, and very little in the way of consistent training for practitioners.
If you want a fascinating (and terrifying) look at the “science” of bite marks and several other types of “forensics” that aren’t nearly as accurate as often claimed, there’s a great book by Radley Balko called *The Cadaver King and the Country Dentist* which really goes through how the whole “science” of bite mark analysis came about.
It wasn’t actually developed as a real science. When real science methods were applied to it, it turned out that it would never have had publishable results.
Vox made a whole video about it, which I think is really cool: https://youtu.be/EO6kYkoCEsA
There’s is a good Netflix documentary about the guy who singlehandedly developed bitemark forensics, and it was eventually proven it was total bullshit. The method was unscientific and pretty much allowed the operator to ‘make the bites match’ in a semi convincing way to juries. It was proven bullshit years later when DNA evidence started showing that the people convicted with it were innocent.
Almost always a bite mark is used to try and rule someone out vs rule them in. Almost all evidence is like that actually, even DNA. DNA matches are never given as “yes, it’s that person’s DNA and only their DNA” it’s always given as “the chances of that DNA belonging to anyone else are 1 in 10 billion” or whatever, meaning there aren’t enough people on the planet for it to reasonably be someone else, but, there’s still a slim chance you could find one other person who matches. Bite marks are similar, but with much wider error. If Sally shows up saying she was attacked and her assailant bit her on the upper arm, and she thinks it was that dude with long hair and brown eyes over there, a bite mark examiner could look and see “ok, in this bite mark on Sally, we can see 6 teeth outlined, and the front two are very crooked”. Then they could look at that long haired dude over there and if they can see his front teeth are really straight, or he doesn’t have front teeth, or his mouth is too big/small to have reasonably made the mark, then they have some idea that it probably wasn’t him who bit Sally so they can look for someone else. But any good examiner would never say “yes, those are that dude’s teeth marks on Sally’s” arm
Project Innocence had some good documentaries of innocent people convicted on the basis of bite marks. At the time, there were a few scientists trying to make a science out of it but without being aware of it hitting into all sorts of their own cognitive biases, such that they convinced themselves of the reliability of the identification. Prosecutors liked anyone who sounded convincing, and free legal aid wasn’t good at questioning such scientists.
It was declared a pseudoscience because it wasn’t reproduceable. When blind tests were administered to the experts asking them to identify which bite mark was human, from a bite, or simply a normal bruise, the results were nowhere near consistant. Unfortunately some people were in prison for a decade or more until their cases were revisited, and those convinced solely on bite marks were released.
Bite mark study is now used as a cautionary tale for how easy it is to start a pseudoscience without truly independent verification. Even the most intelligent scientists convince themselves of a result if it’s in their benefit.
A famous example in early science of this tendency is Blondlot , who “discovered” N rays as the new X ray. [https://en.wikipedia.org/wiki/Prosper-Ren%C3%A9_Blondlot](https://en.wikipedia.org/wiki/prosper-ren%c3%a9_blondlot) . He was a good scientist, but made a complete fool of himself over the subject and ruined his career. It’s even more a cautionary tale of observer bias.
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