Human scent

Most and Bruckner (1936) found human tracks to be complex. A track contains a human species odor and an individual odor, both extruded through boots, but also the odors of crushed plants, disturbed soil, and leather or other shoe material. Dogs still tracked correctly after removal of one or several of these components. To separate the track components, the authors built a chair lift and a track wheel (Fig. 13.5). The rim of the metal wheel (approximately 2m in diameter) carried raised replicas of shoes at stride intervals. Pulled over the terrain, the wheel makes a track of crushed plants and disturbed soil without human scent. The lift consists of a chair suspended on a steel cable about 1.5 m above the ground. Although a person riding this chair leaves no foot imprints or disturbed soil, he/she still sheds odorous rafts of skin cells. A trained dog uses one or the other of these track components, as terrain and surface change. 

FIGURE 13.5 Analysis of tracking components, a) A chairlift, (b) The track wheel was used to separate a human track into a person s olfactory footprint and odors emanating from crushed soil and vegetation. The track wheel has wooden footpads on a metal rim, spaced at an average human stride. The wheel produces a track that lacks human scent and consists entirely of odors from disturbed soil and vegetation. (From Most and Bruckner, 1936.)... 

Wear latex gloves to prevent human scent from interfering with the experiment. Cut filter paper so it fits on the bottom of live trap. Place into the trap. With an eyedropper, apply 0.12 ml of scent solution on the filter paper. 

In the afternoon or early evening before the beavers emerge from their lodge, build a scent mound from mud, scooped up from the pond, just as the beavers do. Use a little garden trowel, or in a pinch, a plastic tub. Wear rubber or plastic gloves to avoid contamination with human scent. About 1 1 of mud suffices. Place the scent sample on top of the scent mound. If you use commercial, dried, and ground beaver castoreum, sprinkle a teaspoon full over the mud. For dissolved scent samples, place a large cork or bottle cap on scent mound. 

If one individual deposits a scent mark on top of the mark of another individual, then the top scent is necessarily fresher (more recent) than the scent that was deposited first. Thus, relative scent age is one way that mammals (or other species) could evaluate scent over-marks to determine which animal had marked most recently. The hypothesis that mammals use scent age as the relevant cue is attractive because it is already known that changes in odor quality may provide information about scent age. Although there has been little research that demonstrates how individuals of any species perceive or use this information, it is clear that some rodents respond differently to fresher versus older scents (Johnston Lee, 1976 Johnston Schmidt, 1979 Wellington et al., 1981 Ferkin et al., 1995a). There is also evidence suggesting that dogs may be able to determine the direction of a human scent trail by differences in scent quality due to differences in age of footprints along the trail (Steen Wilsson, 1990). 

It should be noted that our use of the term, kin recognition, in Study 1 does not imply any particular type of instinctual process, nor does the term, recognition, used in Study 2. A reliable preference for either of the two scents used in Study 1 would show that the subjects responded discriminatively, thus conforming with Sherman and Holmes s (1985) definition of kin recognition cited above. A reliable preference for either of the two human scents used in Study 2 would also justify our use of the term, recognition, but only in the same limited sense as in Study 1. For a more detailed discussion of this issue see Johnston and Jemigan (1994). 

The reason why human scents have been preserved during evolution might be based upon a connection between the perception of odour and the major histocompatibility complex (MHC).[13J... 

J. A. Nolen et al., Method, apparatus and compositions for inhibiting the human scent tracking ability of mosquitoes in environmentally defined three dimensional spaces, Washington, DC U.S. Trademark and Patents Office (U.S. Patent No. 6,362,235), 2002. 

Area repellents are materials that are intended to keep animals away from a broad area. They include predator scent such as Hon or tiger manure, blood meal, tankage such as putrefied slaughterhouse waste, bone tar oil, rags soaked in kerosene or creosote, and human hair (84). Although few controlled tests have been mn on these materials in the past, more recent investigations of predator odors have shown promise (85). 

Differentiation can be defined as the process of specialisation in terms of shape and function. An example is cell differentiation in plants, animals and humans a young cell, which is initially multifunctional, gradually acquires one specific function and shape. Specialisation is a refinement that is expressed in terms of shape, scent and colour. For example, fruits ripen, leaves change colour in the autumn, the growth of a shoot ends in a terminal bud and seeds become dormant. The primary components are converted into secondary components such as phenols, vitamins, aromas, wax, and so on. Thus differentiation in this context has a broader meaning than only the formation of a new plant organ . 

The towels were impregnated with one odour 60 min before their introduction into the animals enclosure by spraying the stimulus over the entire surface of the cloths (2 ml almond, 3 ml cKl). Both scented cloths (almond, cKl) smelled equally strong to human subjects. No odour, other than that of the cloth, was detectable from the towel sprayed with distilled water (3 ml). Following odour impregnation, each cloth was sealed in a plastic bag and handled with plastic gloves worn by the experimenters. 

Stoddart, D.M. (1991) The Scented Ape. The biology and culture of human odour. Cambridge University Press, Cambridge. 

Schaal, B., Doucet, S., Sagot, P.,Herding, E. and Soussignan, R. (2006) Human breast areolae as scent organs morphological data and possible involvement in maternal-neonatal coadaptation. Dev. Psychobiol. 48, 100-110. 

Thornhill, R. and Gangestad, S.W. (1999) The scent of symmetry a human sex pheromone that signals fitness Evol. Hum. Behav. 20, 175-201. 

The Human Breast as a Scent Organ Exocrine structures, Secretions, Volatile Components, and Possible Functions in Breastfeeding Interactions... 

Many hunters react to their prey s overall scent or some of its components, perhaps the smell of fur or some less complex odor. One of the world s most injurious insects, the African malaria mosquito (Anopheles gambiae), prefers humans to other sources of a blood meal. Oddly, whenever possible the mosquitoes bite people on their feet. This predilection reflects their strong attraction to the mixture of fatty acids that we associate with smelly feet. Humans may find the odor offensive, but these mosquitoes know it as a fragrant guide to blood. The same fatty acids also draw them to another odor that offends some people, the smell of Limburger cheese. 

For this lifestyle to succeed, the wasp larvae obviously must avoid being recognized. If the ants were to detect them, they would suffer the fate of other intruders discovered in the nest expulsion or death. Although some intruders escape detection in ant nests because they resemble their ant hosts, Orasema larvae, pupae, and adults all are easily distinguishable from their hosts, at least by the human eye. Fire ants, however, are much more concerned with smell than physical appearance. Fire-ant odor and local colony odor are what matter to them. By these scents, ants identify their own nestmates as distinct from other species and even from fire ants belonging to rival colonies. The wasps strategy to avoid discovery is to smell just like fire ants. Larvae, pupae, and even adult wasps carry the distinctive scent of their particular fire ant colony. Shortly after the adult wasps leave the ant nest, this ant odor begins to fade. 

The sense of smell in humans is not limited to detection of those volatile molecules inhaled through the nose, termed orthonasal olfaction. Molecules released at the back of the mouth, particularly in the chewing of food, can make their way up through the nasopharynx to the olfactory epithelium, termed retronasal olfaction. This system is activated when air is exhaled. Orthonasal olfaction is used to detect the scent of flowers and perfumes, food aromas, the presence of skunks, and the like. Retronasal olfaction detects the volatile molecules released from food. It is retronasal olfaction that makes a major olfactory contribution to the taste of food. And it is retronasal olfaction that helped to elicit Proust s profound reaction to a madeleine dipped in tea. 

A subset of all odorants is pheromones, about which much more follows later. Basically, pheromones transmit chemical messages among members of the same species. Bombykol is a pheromone for the silkworm moth the scent of lilacs as perceived by a human being is not. Although the question of human pheromones is difficult, that for many mammals is not. The pheromones in mammals are not detected... 

In contrast to the evidence for primers, signalers, and modulators, there is no decent evidence to suggest that there are human releaser pheromones. That is not to argue that there are none but to state that there is no evidence for them at present. Nonetheless, products purported to be human releaser pheromones—specifically sex attractants—are widely available on the Internet. They go by such suggestive names as Scent of Eros, The Edge, Alter-ego, and Pheromone Additive. Many of these products contain either androstenone or androstenol, steroids of unknown influence on the human emotional state. 

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