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What can a single strand of human hair tell crime scene investigators and pathologists?
We’ve all seen it; a cop pulls out a pen, uses it to pick up a single strand of hair, pops that hair into an empty crisp packet, takes it to be boys down the crime lab and boom, the victim is identified. But is that possible, can you get a complete DNA match of a victim or perpetrator from a single thread of human hair?
No. You can’t.
Currently, it is not possible to identify a person by a single strand of hair, although it is a vital piece of evidence in any enquiry. You can learn a lot from a single strand of human hair, as (unless it’s cut) a human hair normally grows for up to two to six years before it falls out, so you can determine some details: what racial group a person is from (whether European, Asian or African), their hair colour (whether natural or dyed), what chemicals, toxins or heavy metals they’ve been exposed to, the types of foods they eat, possible diseases, genetic disorders, health issues, and if they smoke, drink or do drugs. Gulp! If you’re worried… the drugs which can be tested includes cannabis, cocaine, opiates, amphetamines, methamphetamines, benzodiazepines, methadone, ketamine, most prescription drugs, antidepressants, neuroleptics, steroids and GHB, all from a single strand of hair. And while a urine test will reveal if you’ve used drugs in the last several days, hair testing (depending on the sample) can show if you’ve used drugs over the past 3 months.
On average, a person sheds 100-150 strands of hair a day, and although the hair shaft contains some mitochondrial DNA – this DNA is easily degraded by bacteria, fungi, ultraviolet light, bleaches, dyes and the weather, rendering it useless for testing – but it’s actually the root pulp at the end of the shaft which contains the nDNA (nuclear DNA), which is vital for identifying a person. Sadly, the hairs we shed, do not contain root pulp, but they do if they are yanked out in a violent struggle.
The problem is that even this nDNA found in the hair’s root quickly degrades when exposed to light, moisture or heat, making it almost useless (but not entirely useless) for identification, so the best hair strands for DNA testing are those pulled directly from the victim or perpetrators’ head with the root pulp still attached, prior to testing, and in order for the laboratory to accurately determine a person’s identity, they wouldn’t need one single hair, they would need at least one hundred.
So, the next time you see a TV detective picking up a single eye-lash with their tweezers and getting a match to a known felon within an hour, call “bulls**t”, and check the DVD extras to see if there’s an additional scene where he spends fifty-two days on his hands and knees, scouring the floor for ninety-nine more and praying the felon has a genetic disorder, so unique, they named a disease after him.
So why am I bald? Nature’s been cruel to me, that’s all.
If you found this interesting? Check out the Mini Mile episodes of the Murder Mile UK True-Crime Podcast, or click on the link below to listen to an episode.
Michael J Buchanan-Dunne is a writer, crime historian, podcaster and tour-guide who runs Murder Mile Walks, a guided tour of Soho’s most notorious murder cases, hailed as “one of the top ten curious, quirky, unusual and different things to do in London”, nominated "one of the best true-crime podcasts at the British Podcast Awards 2018", and featuring 12 murderers, including 3 serial killers, across 15 locations, totaling 50 deaths, over just a one mile walk
Michael J Buchanan-Dunne is a crime writer, podcaster & tour guide of Murder Mile Walks, hailed as one of the best "quirky curious & unusual things to do in London".
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