Dogs are trained to sniff out a lot of things, and some of those “things” are human remains. Human remains, except those in a cemetery, are usually not out in the open; someone doesn’t want them found or there has been an accident. But bring your own Scooby Doo to the case, and you might have a fighting chance.
But how do dogs get into detection mode? Training can take many different forms, but customarily, trainers present dogs with a target odor (the smell of interest) and control odors (that are not of interest). They are trained to alert to the target odor and ignore the controls. Sometimes trainers use a scent detection board, like the one below that the University of Pennsylvania's Working Dog Center uses when training dogs to alert to ovarian cancer.
To train dogs to identify and ultimately find a particular scent, trainers need samples. For different types of cancer, these samples might come from the blood, urine or tissue of a person with the target cancer. But what do you use if you are training a dog in human remains detection (thankfully given the innocuous-sounding acronym HRD)? If you are a HRD handler, how do you train and practice with your dog? Where do you get your, um, samples? Is this Dexter's side gig?
One solution is to use nonhuman remains, as long as they are a suitable proxy for humans. A recent study by Cablk et al. (2012) compared the chemical compositions of decomposing tissue from a pig, cow, chicken and human. The researchers were investigating the volatile organic compounds (VOCs)—the “smell particles”—released by animals and humans.
The important question in the HRD field is: which VOCs are produced when a human body decomposes? Are they similar to or different from VOCs of decomposing animal tissue? Identifying the specific compounds—and their ratios—could help when training dogs, or in creating synthetic training samples. You know, so you don’t need a fridge full of—well, you get the picture.
When comparing decomposing animal and human tissue, the results were clear: “Although there were compounds common to both animal and human remains, the VOC signatures of each of the animal remains differed from those of humans.” Thank goodness. You are not a pig. Nor are you a cow. But yes, you are kind of a chicken: “The VOC signatures from chicken and human samples were most similar, sharing the most compounds of the animals studied.”
By contrast, VOCs in pig remains were not so similar to VOCs found in human remains. “In addition to sharing only seven of 30 human-specific compounds, an additional nine unique VOCs were recorded from pig samples, which were not present in human samples.”
HRD trainers sometimes use pig remains to train dogs, but given their VOC differences, are pig remains the best best? Is it better to train on human, synthetic human or even chicken remains?*
We don't usually confuse humans with chickens, but this similarity we just can't shake. It seems Marty McFly was wrong. Maybe we are chickens.
* Nowadays, training with pig remains is not the norm. I mention the use of pig remains in cadaver dog training because it was a major point in the Cablk research paper. And totally kidding about training on chicken remains. A subsequent post will expand on the issues raised here.
Photo: Chicken on Flicker by SMcGarnigle via Creative Commons
Acevedo et al. 2007. Volatile organic compounds produced by human skin cells. Biological Research, 40, 347–355.
Cablk et al. 2012. Characterization of the volatile organic compounds present in the headspace of decomposing animal remains, and compared with human remains. Forensic Science International, 220, 118–125.
Hoffman et al. 2009. Characterization of the volatile organic compounds present in the headspace of decomposing human remains. Forensic Science International, 186, 6–13.