We humans don't give ourselves a lot of credit for our sense of smell. We have about 5 million sensitive odor-detecting cells in our noses, compared to a dog's 200 million, which is why we generally leave it to dogs to sniff out things like bombs, drugs and missing people. And while forensic evidence detected by a dog schnoz routinely holds up in court, when it comes to human witnesses, we usually trust their eyes and ears before their noses.
That's because we have long believed our sense of smell is to be mostly perfunctory. This whole human's-can't-smell thing was first broached by Pierre Paul Broca, a 19th century anatomist who suggested that — compared to the noses of other animals like dogs — the human olfactory organ was so small as to be hardly any use at all. Research in the 1920's confirmed that, with calculations suggesting humans could only reliably distinguish between around 10,000 odors.
However, more recent research has suggested that not only is the part of our brain dedicated to detecting and processing smells much larger that Broca originally thought, our noses themselves are more sensitive and capable of differentiating between odors than we thought. For instance, a 1998 study found that our noses are sensitive enough to tell the difference between two molecules that are identical except for being mirror images of each other. And a 2014 study found that humans can actually detect and tell the difference between around a trillion different odors.
And now human noses may get their day in court — literally. New research published in the journal Frontiers in Psychology suggests we've underestimated our ability to accurately identify another person by body odor, and therefore to use our noses as forensic tools to solve crimes.
Professor Mats Olsson, an experimental psychologist at the Karolinska Institutet in Sweden, and a Portuguese research team suggest that since our olfactory sense is so closely tied to the emotional processing parts of our brains — the hippocampus and amygdala — we might be able to remember smells associated with highly stressful situations better than we remember sights and sounds.
To test this, they showed study participants video clips of a violent crime being committed, and accompanied the experience of watching the clip with a human body odor scent they told the participants belonged to the perpetrator of the crime. An individual's body odor signature stays pretty constant for their entire lives, though it might change a bit with age, diet, etc. Participants were also shown neutral video clips associated with human body odors.
Afterwards, when given a sniff line-up of body odors from different people, the participants were able to pick out the body odor of the correct perpetrator from the crime video almost 70 percent of the time, which was more often than they correctly identified the BO from the characters in the neutral video. That level of accuracy is about what you can expect from eyewitnesses (fallible as we are), and comparable to the 75-to-90-percent accuracy you can expect from a dog's nose.
"It worked beyond my expectation," said Olsson in a press release. "Most interestingly — participants were far better at remembering and identifying the body odor involved in the emotional setting."
Witness accuracy was reduced somewhat as the size of the lineup grew and as time passed, but that is also true for eye- and ear-witnesses reliability degrades similarly as well.
"Our work shows that we can distinguish a culprit's body odor with some certainty," said Olsson. "This could be useful in criminal cases where the victim was in close contact with the assailant but did not see them and so cannot visually identify them."