The genetically determined smell that is unique to each person.
Hot on the scent of a suspected terrorist? Darpa the Defense Advanced Research Projects Agency hopes to give literal meaning to the phrase. It wants someone to develop a sniffing machine that can detect individuals by their body odor.
The idea is not as rank as it may seem. Dogs are said, at least by dog handlers, to recognize the scents of individual people. Researchers have found that mice can detect from body odor and urine how closely they are related to one another, a useful way to avoid inbreeding. So Darpa, the grand patron of exotic military arts (not everything it does works, but it did have a hand in creating the precursor of the Internet), is soliciting "innovative proposals to (1) determine whether genetically-determined odortypes can be used to identify specific individuals, and if so (2) to develop the science and enabling technology for detecting and identifying specific individuals by such odortypes."
With the high-tech identification industry going into full gear with machines that recognize fingerprints and scan the iris, why is Darpa messing with something as old-fashioned as B.O.? Dr. Gary Beauchamp, director of the Monell Chemical Sense Center in Philadelphia, notes that odors can be detected through just a handful of molecules. Also, unlike sight and sound, the smells from a fugitive can linger for hours or days.
Nicholas Wade, "On the Scent of Terrorists," The New York Times, January 5, 2003
The immune system can distinguish self from non-self, which is a fundamental property of individual recognition. This capacity is determined in large part by a linked set of more than 50 genes known as the Major Histocompatibility Complex (MHC)...Together with other Monell scientists Yamazaki went on to show that MHC-determined odors (now termed "odortypes") can be altered by varying a single gene within the MHC.
A relevant question is whether odortypes play a role in human communication and behavior. While urine is most likely not an appropriate source of information for humans. Yamazaki's research suggests that odor cues regarding identity may also be conveyed through more suitable mediums, such as sweat, saliva, or mother's milk. A recent study indicates that human fetuses have distinctive odortypes. It is possible that mothers and infants may use smell as an early form of identification, and perhaps as an aid to bonding.
"The Scent of Immunity," AROMAtherapy 2037, Summer 1997
Yamazaki K, Beauchamp GK, Shen FW, Bard J, Boyse EA., "Discrimination of odortypes determined by the major histocompatibility complex among outbred mice," Proceedings of the National Academy of Sciences, 1994
Olfactory researchers have come up with some interesting findings related to human smells. For example, it has been known for a while that newborn babies can identify their mothers on the basis of smell alone. Not to be outdone, new mothers can identify their infants by smell within 24 hours of giving birth. Siblings, too, can recognize each other by smell. Dogs, with their ultra-sensitive noses, can distinguish between fraternal twins based on smell, but they can't distinguish between identical twins. All of this suggests that each person except identical twins has a distinctive smell, and that this smell is gene-based. (See the earliest citation for more details on this.) Since the visible expression of an organism's genes is called its phenotype, researchers have labeled this gene-based smell the odortype.