Forensics Researchers Reveal Pubic Hair's Unique Crime Solving Potential

"Clearly a single hair comes from a single contributor." 

pubic hair

While the rest of the world was debating the ethics, privacy concerns, and utility of using fitness trackers or DNA to solve crimes, a lab in California was slowly mining the forensic power of pubic hair. In a paper published in Scientific Reports, they reveal that pubic hair has some serious crime-busting potential — perhaps even more so than hair from other parts of the body.

Hair can be invaluable in a forensic investigation, but pubic hair, interestingly, is an entirely different ballgame. In their analysis, published in May, a team of scientists at the Lawrence Livermore National Laboratory show that pubic hair is far more complex than arm or even head hair, displaying more individual-specific markers that could help identify potential suspects.

The LLNL is a federally funded lab, specifically intended to “deliver solutions for the nation’s most challenging security problems.” With just a single strand of pubic hair, says Deon Anex, a lab chemist at LLNL and paper co-author, scientists can make a dent a particularly prescient problem in United States sexual assault cases.

“Pubic hair is often collected as evidence of a sexual assault. In many cases, DNA evidence is collected as a fluid that can compromise multiple contributors. These mixtures can be hard to deconvolute to identify one particular contributor,” he tells Inverse. “Clearly a single hair comes from a single contributor and can be used to aid in a positive identification.”

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With further testing, the team suggests that a single strand of pubic hair could potentially identify someone in a population of 10 million. 

Hair, in general, can prove invaluable to forensic investigations for several reasons. For one, it contains a “minimal” amount of nuclear DNA, and small unique genetic markers in that DNA can be used to pin down a suspect. But hair is also rich in proteins and peptides that these scientists believe can also be used to identify individuals.

In their analysis, Anex and his team dove deep into the chemistry of hair. By studying nine head hair samples, they found that one inch of head hair can yield an average of 142 proteins and 1,031 unique peptides. A subset of those peptides, they found, were “genetically variant peptides.” That means that they might differ according to someone’s unique genetic profile, and thereby might be used to identify a person.

But a single inch of pubic hair, they write, yields more proteins, unique peptides, and amino acids than both head and arm hair, making it even more useful for identification purposes. With further tests, they suggest, it could be used to identify one person in a crowd of a 10 million people.

“The identification markers reside in the peptides that we derive from the samples,” Anex says. “The more protein we have, the better the measurements we can make — we see more markers and have higher confidence.”

Ideally, this type of analysis would be conducted in tandem with DNA analysis that could further narrow down a suspect’s identity even more. But while these early results are promising, it’s unlikely we will see them used right away, says Anex:

“The process is often years before new forensic methods are accepted in courts. We are probably a couple of years out from legal application,” he adds.

From there, it may still be a long way until this kind of evidence is admissible in court. But publication in a journal, like Scientific Reports, could be pubic hair’s first step into a unique place in forensic science.

Abstract:

Human hair contains minimal intact nuclear DNA for human identification in forensic and archaeological applications. In contrast, proteins offer a pathway to exploit hair evidence for human identification owing to their persistence, abundance, and derivation from DNA. Individualizing single nucleotide polymorphisms (SNPs) are often conserved as single amino acid polymorphisms in genetically variant peptides (GVPs). Detection of GVP markers in the hair proteome via high-resolution tandem mass spectrometry permits inference of SNPs with known statistical probabilities. To adopt this approach for forensic investigations, hair proteomic variation and its effects on GVP identification must first be characterized. This research aimed to assess variation in single-inch head, arm, and pubic hair, and discover body location-invariant GVP markers to distinguish individuals. Comparison of protein profiles revealed greater body location-specific variation in keratin-associated proteins and intracellular proteins, allowing body location differentiation. However, robust GVP markers derive primarily from keratins that do not exhibit body location-specific differential expression, supporting GVP identification independence from hair proteomic variation at the various body locations. Further, pairwise comparisons of GVP profiles with 8 SNPs demonstrated greatest interindividual variation and high intraindividual consistency, enabling similar differentiative potential of individuals using single hairs irrespective of body location origin.