Taking the lead from man's best friend, the military wants to turn odor recognition into a science.

Credit: John Davey

The Defense Advanced Research Projects Agency, or DARPA, the government’s primary agency for military research and development, has the time and resources to dream up some of the most groundbreaking ideas that modern science will allow. This pie-in-the-sky thinking can lead to great breakthroughs, though over the years there have been a few spectacular flops—Anyone remember weaponized bees?

    When a biology graduate student submits a doctoral thesis on the physiological benefits of REM sleep, DARPA saw an opportunity to research and develop a pill that could eliminate a soldier’s need for sleep. When chemists discovered a vaccine against a biological agent, DARPA identified a portable defense against biological weapons. At its essence, the agency thrives on its ability to find exotic military uses for otherwise mundane scientific breakthroughs.

    “Throughout the government you would be hard pressed to find a group that focuses more on blue sky projects and thinks more out of the box than DARPA,” said Noah Shachtman, editor of the blog DefenseTech. “If you have an idea that is just so crazy it might work, DARPA is one of the places you can go to try it. There is no punishment for failure, and that’s really not the case with most military or government offices.”

Between the end of the Cold War and the start of the War on Terror, DARPA’s focus has shifted from developing weapons to researching the practice of intelligence gathering. Some of its current projects involve lasers that can detect biological agents at stand-off distances, a cognitive program to improve soldier information intake under stress and creating “fiber-biotics” that can digest indigestible fiber.

    The “Unique Signature Detection Project,” formerly known as the “Odortype Detection Program,” is designed to help identify terrorists based on scents they secrete in their sweat, tears, urine and other bodily fluids. According to experts, a person’s smell is so unique it offers the military an alternative method of identification, as effective as retinal scans and fingerprinting but far less invasive.

    “[It can be used] to identify and distinguish specific ‘high-level-of-interest individuals’ within groups of enemy troops or combatants,” said DARPA spokeswoman Jan Walker via e-mail.

    If successful, a Unique Signature Detection program could give the military advantages in identification that retinal scans just can’t match. Unlike eyelids, a person’s smell is not under their direct control. Even after leaving the scene of a crime, a terrorist’s scent could spread over a large distance and linger for a considerable time, said Gary Beauchamp, director of the Monell Chemical Senses Center and a researcher for the DARPA-funded project.

    Although the science behind this field is nascent, says Beauchamp, evidence to support the theory of odor detection is all around us. Countless animals rely on odor to find food, identify one another and mark territory. USDA researchers even trained wasps to act as hound dogs, sniffing out drugs, bombs and cadavers.

    “We see, even in insects, that they are using odor signatures in a very detailed way to go about their natural activities,” said entomologist W. J. Lewis. “These wasps could detect different species of closely related host insects based on the trail odors associated with them.”

    Researchers believe the unique smell that we each emit is tied to the make-up of the major histocompatibility complex, a group of genes found on T-cell surfaces that are crucial to the immune system. These genes lend themselves perfectly to creating an idiosyncratic pattern for every person’s immune system, says Beauchamp, because they are “the most varied in all of nature.” In fact, this complex is what makes the process of organ transplants so specific and therefore complicated. Because T-cells are designed to recognize a body’s specific histocompatibility proteins and attack anything it determines is foreign, if a donor’s organ comes from someone whose immune system differs too much from the recipient’s, it will be rejected. In addition, scientists have found that mice, which like dogs characterize individuals by their unique odor-type, can differentiate between two individuals whose genetic make-up differs by only one amino acid in the histocompatability complex.

    “We’ve proven a million times over that these genes, in ways that we still are not clear how, code for individual differences in smell,” said Beauchamp. “The next question would be, ‘Is this the same for people?’ and that is the focus of the research.”

    Substantial hurdles remain in the path of researchers wishing to make scent detection an everyday technology. For one, as Beuchamp mentioned, scientists aren’t sure how these genetic differences translate into different smells. More daunting is that researchers don’t know how environmental factors, such as diet, health or even shampoo selection, can alter one’s natural smell. Beauchamp points out that dogs and other animals with more sophisticated olfactory systems seem to be able to smell past these surface alterations.

    “It’s as if there is a core individual-identifying smell that is not changed by that,” said Beauchamp.

    As part of the Novel Sensors for Force Protection Program, over $15 million has been allocated to smell detection research from the 2007 DARPA budget, up from under $10 million in 2004.

    “If we identify an exploitable, robust signature, the program will then pursue detector development,” said Walker, a DARPA spokesperson.

    While a working smell detector as sophisticated as the one Walker describes is years off, Beauchamp believes there are other uses for the military funded research that, like the Internet, will benefit civilians.

    If the immune system does in fact create a unique smell that helps identify individuals, the process could also be reverse-engineered, allowing scientists to track down a specific type of immune system. This would be beneficial for organ transplantation: If a donor’s odor-type is similar enough to a recipient’s, doctors can be reasonably confident that the latter’s body will accept a donated organ. Also, if specific diseases can alter a person’s odor, smell detection could prove to be an effective tool for early diagnosis.

    “The idea of having some way of being able to diagnose a disease early, non-invasively and inexpensively,” Beauchamp said, “is one of the ancillary payoffs that may come from this research.”

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Originally published June 5, 2006

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