Everything about Pheromones totally explained
A
pheromone (from
Greek φέρω phero "to bear" +
‘ορμόνη "
hormone") is a
chemical that triggers a natural behavioral response in another member of the same species. There are
alarm pheromones,
food trail pheromones,
sex pheromones, and many others that affect behavior or physiology. Their use among
insects has been particularly well documented, although many
vertebrates and
plants also communicate using pheromones.
Background
The term "pheromone" was introduced by Peter Karlson and Martin Lüscher in 1959, based on the Greek
pherein (to transport) and
hormone (to stimulate). They proposed the term to describe chemical signals from
conspecifics which elicit innate behaviours soon after Butenandt characterized the first such chemical,
Bombykol (a chemically well-characterized pheromone released by the female
silkworm to attract mates).
Types
Aggregation pheromones
Produced by one or the other sex, aggregation pheromones attract individuals of both sexes.
Alarm pheromones
Some species release a volatile substance when attacked by a predator that can trigger flight (in aphids) or aggression (in bees) in members of the same species. Pheromones also exist in plants: certain plants emit alarm pheromones when grazed upon, resulting in tannin production in neighboring plants. These tannins make the plants less appetizing for the herbivore.
Epideictic pheromones
Recognized in insects, epideictic pheromones are different from territory pheromones. According to Fabre (translated from French), "Females who lay their eggs in these fruits deposit these mysterious substances in the vicinity of their clutch to signal to other females of the same species so that that'll clutch elsewhere."
Releaser pheromones
Releaser pheromones are powerful attractant molecules that some organisms may use to attract mates from a distance of two miles or more. This type of pheromone generally elicits a rapid response but is quickly degraded. In contrast, a primer pheromone has a slower onset and a longer duration.
Primer pheromones
Primer pheromones trigger a change of developmental events.
Territorial pheromones
Laid down in the environment, territorial pheromones mark the boundaries of an organism's territory. In dogs, these hormones are present in the urine, which they deposit on landmarks serving to mark the perimeter of the claimed territory.
Trail pheromones
Trail pheromones are common in social insects. For example, ants mark their paths with these pheromones, which are non-volatile hydrocarbons.
Certain ants lay down an initial trail of pheromones as they return to the nest with food. This trail attracts other ants and serves as a guide. As long as the food source remains, the pheromone trail will be continually renewed. The pheromone must be continually renewed because it evaporates quickly. When the supply begins to dwindle, the trailmaking ceases. In at least one species of ant, trails that no longer lead to food are also marked with a repellent pheromone.
Sex pheromones
In animals, sex pheromones indicate the availability of the female for breeding. Male animals may also emit pheromones that convey information about their species and genotype. Many insect species release sex pheromones to attract a mate, and many lepidopterans can detect a potential mate from as far away as 10 kilometers (6 mi). Pheromones can be used in gametes to trail the opposite sex's gametes for fertilization. Pheromones are also used in the detection of oestrus in sows. Boar pheromones are sprayed into the, and those sows which exhibit sexual arousal are known to be currently available for breeding.
Other pheromones (not yet classified)
This classification, based on the effects on behavior, remains artificial. Pheromones fill many additional functions.
- Nasonov pheromones (worker bees)
- Royal pheromones (bees)
- Calming (appeasement) pheromones (mammals)
Uses
Animals
Pheromones of the pest insect species, such as the
Japanese beetle and the
gypsy moth, can be used to induce many behaviors. This facilitates trapping for monitoring purposes and population control by creating confusion, disrupting mating and preventing them from laying eggs.
In
mammals and
reptiles, pheromones may be detected by the
vomeronasal organ, or Jacobson's organ, which lies between the nose and mouth and is the first stage of the
accessory olfactory system. Some pheromones in these animals are detected by regular
olfactory membranes.
Humans
Few well-controlled scientific studies have ever been published suggesting the possibility of pheromones in humans. The best known case involves the reported synchronization of
menstrual cycles among women based on unconscious odor cues (the
McClintock effect, named after the primary investigator,
Martha McClintock, of the University of Chicago). This study proposes that there are two types of pheromone involved: "One, produced prior to ovulation, shortens the ovarian cycle; and the second, produced just at ovulation, lengthens the cycle". However recent studies and reviews of the of the McClintock methodology have called into question the validity of her results.
Other studies have suggested that people might be using odor cues associated with the immune system to
select mates who are not closely related to themselves. Using a brain imaging technique,
Swedish researchers have shown that
homosexual and
heterosexual males' brains respond differently to two odors that may be involved in sexual arousal, and that the homosexual men respond in the same way as heterosexual women. The study was expanded to include homosexual women; the results were consistent with previous findings meaning that homosexual women were not as responsive to male identified odors, but their response to female cues was similar to heterosexual males. According to the researchers, this research suggests a possible role for human pheromones in the biological basis of
sexual orientation.
Another study demonstrated that the smell of
androstadienone, a chemical component of male
sweat, maintains higher levels of
cortisol in females. The scientists suggest that the ability of this compound to influence the
endocrine balance of the opposite sex makes it a human pheromonal chemosignal. In 2002 a study published in the quarterly journal
Physiology and Behavior showed an unnamed synthetic chemical in women's perfume appeared to increase intimate contact with men. The authors hypothesize, but don't demonstrate, that the observed behavioural differences are olfactory mediated.
In 2006 it was shown that a second mouse
receptor sub-class is found in the
olfactory epithelium. Called the
trace amine-associated receptors (TAAR), some are activated by volatile
amines found in mouse urine, including one putative mouse pheromone.
Orthologous receptors exist in humans providing, the authors propose, evidence for a mechanism of human pheromone detection.
Some body spray advertisers claim that their products contain human sexual pheromones which act as an
aphrodisiac. In the 1970's "copulins" were patented as products which release human pheromones, based on research on
rhesus monkeys. Subsequently, androstenone, axillary sweat, and "vomodors" have been claimed to act as human pheromones. Despite these claims, no pheromonal substance has ever been demonstrated to directly influence human behavior in a
peer reviewed study.
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