Chemical signals of love and fear
Saturday, 6 December 2008
Syed Fattahul Alim
Pheromones are chemical messages sent by one member of a living organism to another belonging to the same species. Of the various pheromones, those related with sex have been most widely studied. The first such pheromone ever synthesised about half a century back (1959) was Bombykol, which is released by the silk moth. It is not just insects and other lower animals that release pheromones in the air to attract members of the opposite sex or communicate some socially significant signals to fellow members.
Some scientists are deeply convinced that chemical attractants like pheromones are active even among human beings, especially between opposite sexes. One would often hear about perfumes that are able to bias males and females towards one another. But so far genuineness of such claims could not be proved scientifically. Majority of the scientists studying the phenomena are of the view that the particular organ responsible for receiving the chemical signal pheromone has become extinct in the process of evolution. That particular pheromone receptor, the vomeronasal organ (VNO) is found within the nose of lower mammalians. Human nose does not contain such kind of pheromone receptors, if any, to respond to other humans, especially those belonging to opposite sex. But there may be other pathways to release and receive such chemical messengers. In that case the receptor may not necessarily in the nose. And it may not also be only signals about sex that such chemical messengers are busy conveying. The area may be far broader than it was first thought to be. Caroline Williams of the New Scientist magazine tells below the researches and their various explanations and theories about the chemical signals that carry signatures of deep human instincts like sexual attraction, fear, and the like and how those are conveyed to the fellow beings of the same species.
Ever had a feeling come over you that you just can't explain? Like suddenly getting all warm and fuzzy when you meet someone for the first time, while somebody else who looks just as good leaves you cold? Or experiencing a sudden pang of fear on a plane even though you're totally at ease with flying?
These seemingly unrelated and illogical human reactions may have a reasonable explanation after all, although one that not everyone will be happy to hear. They may be reactions to other people's pheromones.
Pheromones are something of a sensitive subject in human biology. Though they are found across the animal world from insects to mammals, research into human pheromones has been dogged by flaky experimental designs and dubious commercial endorsements, with the result that the entire field has a whiff of the disreputable about it. "It's not so much that the jury is out, but that the jury has been dismissed before the trial has begun," says Mike Meredith, a neuroscientist at Florida State University in Tallahassee, who studies animal pheromones.
In recent years, though, this has begun to change. Evidence that animal pheromones don't always work in they way we thought, backed up by a growing number of brain-imaging studies in humans, is convincing some researchers that we really do make and respond to pheromones. As a result some think it's time to stop asking if human pheromones exist and start investigating exactly how they affect our behaviour.
The term pheromone was coined in 1959 to describe chemicals released by insects to trigger hard-wired behaviours in other members of the same species. The classic example is female moths releasing sex pheromones to attract a mate. When pheromones were discovered in mammals, their more complex behaviour meant this definition no longer fitted the bill. Researchers have been debating the meaning of the word ever since. One useful working definition is that pheromones are chemicals which send a message that, in evolutionary terms, benefits both sender and receiver.
Whatever definition you go for, pheromones are a big part of the animal world. Animals use pheromones to transmit useful information about themselves, such as gender or sexual receptiveness; to change others' physiology, for example by stimulating ovulation; and to directly affect others' behaviour. Examples of these behaviour-changing or "releaser" pheromones include sexual attractants and the alarm pheromones many mammals - among them rats and deer - use to put others on alert without giving away their location with an alarm call.
For many years, it was assumed that humans did not produce or respond to any of these types of pheromones. In part that was down to a reluctance to admit that humans might respond in such an "animal" way. There is also no clear mechanism for how they might act on the human brain. In animals, pheromones are usually detected by the vomeronasal organ (VNO), a pair of mini-nostrils inside the nose which detect airborne pheromones and relay messages directly to the brain. Although humans have something resembling a VNO, there are no neurons linking it to the brain. And while we have the genes required for a working VNO, they no longer code for functional pheromone receptor proteins. The obvious conclusion was that we had lost this method of communication at some point in our evolution.
That hasn't stopped researchers from making claims about human pheromones. In 1971 Martha McClintock, a social psychologist at Harvard University, famously reported that women who live together gradually synchronise their menstrual cycles. McClintock, now at the University of Chicago, suggested that this might be mediated by pheromones. In 1998, along with her Chicago colleague Kathleen Stern, McClintock found evidence to support this idea, showing that sweat from women in different stages of their menstrual cycle either extended or shortened the cycles of other women. Despite this evidence, McClintock's conclusions remain contentious because nobody has yet isolated the actual chemicals that cause the effect.
Sexy scents: More controversial still are claims that pheromones are involved in human sexual attraction. This is partly due to some high-profile yet scientifically questionable research done by David Berliner and Luis Monti-Bloch of the University of Utah in the mid-1990s. They claimed that when they exposed people to reproductive hormones from the opposite sex, they could see an electrical response from the part of the nose where the vomeronasal organ would be.
In women, cells in this region responded most strongly to extracts containing androstadienone, a hormone related to testosterone found in male sweat. Men reacted similarly to estratetraenol, which is found in female urine. The same team also reported that releasing these compounds into the air subconsciously altered mood, having a calming effect on the opposite sex. The research was widely greeted with scepticism because of Berliner's financial interest in a brand of perfume called Realm, which was laced with the supposed pheromones. The team's insistence that the pheromones act through the VNO also raised eyebrows. With no convincing evidence for a functional human VNO, many people dismissed the research outright.
Despite this chequered past, there are still plenty of researchers who insist that human pheromones are alive and well. One is Johan Lundstrom, a neuropsychologist at the Monell Chemical Senses Center in Philadelphia. He has shown that women can consistently sniff out their sisters from friends and strangers even when they are not consciously aware of any difference in odour. A similar effect is our well-known ability to select mates based on genetic signatures evident in their body odour - a subconscious indicator of the compatibility of their immune system.
To Lundstrom, this is convincing evidence that human pheromones are real - it's just that most researchers have a blind spot when it comes to using the P-word. "If you asked scientists whether one human can convey some sort of social message to another in their body odour, 99.9 per cent of them would say yes," he says. "If you ask them if humans have pheromones they'll say 'that hasn't been demonstrated'. It's a semantic issue."
That may all be about to change, thanks in part to the recent discovery that some animals detect pheromones using their normal olfactory system, not the VNO. "There are several well-established examples of pheromone communication in animals that don't require the VNO," says Meredith, who specialises in the animal VNO. For example, a recent study found that mice detect alarm pheromones via a bundle of nerve cells at the tip of their nose that is wired into the normal olfactory system.
Brain-imaging studies have also helped revive the idea that humans may respond to sex pheromones. In a series of recent experiments, neuroscientist Ivanka Savic of the Karolinska Institute in Stockholm, Sweden, exposed people to androstadienone and watched what happened in their anterior hypothalamus, a part of the brain thought to be involved in sexual behaviour.
In one study, published in 2005, Savic found that androstadienone activated that brain region in heterosexual women and homosexual men, but not in heterosexual men or homosexual women. She later found the opposite effect with estratetraenol.
Brain-imaging studies are also providing tantalising evidence that humans release and respond to alarm pheromones. These have been less well studied than those thought to be involved in attraction, but a handful of psychological studies have claimed to show that humans can detect the "scent of fear". In 1999, Denise Chen, a psychologist now at Rice University in Houston, Texas, asked a group of volunteers to sniff sweat from people who had watched either funny or scary film clips. More than half of the volunteers successfully identified a sample of fearful sweat despite not being able to consciously smell any difference in the samples.
In a similar study in 2002, Kerstin Ackerl from the University of Vienna in Austria reported that women seemed to be able to detect the scent of fear. The 60 women rated sweat from women who had watched a scary movie as stronger, less pleasant and smelling more "like aggression" than sweat from women who had watched a neutral movie.
Pheromones are chemical messages sent by one member of a living organism to another belonging to the same species. Of the various pheromones, those related with sex have been most widely studied. The first such pheromone ever synthesised about half a century back (1959) was Bombykol, which is released by the silk moth. It is not just insects and other lower animals that release pheromones in the air to attract members of the opposite sex or communicate some socially significant signals to fellow members.
Some scientists are deeply convinced that chemical attractants like pheromones are active even among human beings, especially between opposite sexes. One would often hear about perfumes that are able to bias males and females towards one another. But so far genuineness of such claims could not be proved scientifically. Majority of the scientists studying the phenomena are of the view that the particular organ responsible for receiving the chemical signal pheromone has become extinct in the process of evolution. That particular pheromone receptor, the vomeronasal organ (VNO) is found within the nose of lower mammalians. Human nose does not contain such kind of pheromone receptors, if any, to respond to other humans, especially those belonging to opposite sex. But there may be other pathways to release and receive such chemical messengers. In that case the receptor may not necessarily in the nose. And it may not also be only signals about sex that such chemical messengers are busy conveying. The area may be far broader than it was first thought to be. Caroline Williams of the New Scientist magazine tells below the researches and their various explanations and theories about the chemical signals that carry signatures of deep human instincts like sexual attraction, fear, and the like and how those are conveyed to the fellow beings of the same species.
Ever had a feeling come over you that you just can't explain? Like suddenly getting all warm and fuzzy when you meet someone for the first time, while somebody else who looks just as good leaves you cold? Or experiencing a sudden pang of fear on a plane even though you're totally at ease with flying?
These seemingly unrelated and illogical human reactions may have a reasonable explanation after all, although one that not everyone will be happy to hear. They may be reactions to other people's pheromones.
Pheromones are something of a sensitive subject in human biology. Though they are found across the animal world from insects to mammals, research into human pheromones has been dogged by flaky experimental designs and dubious commercial endorsements, with the result that the entire field has a whiff of the disreputable about it. "It's not so much that the jury is out, but that the jury has been dismissed before the trial has begun," says Mike Meredith, a neuroscientist at Florida State University in Tallahassee, who studies animal pheromones.
In recent years, though, this has begun to change. Evidence that animal pheromones don't always work in they way we thought, backed up by a growing number of brain-imaging studies in humans, is convincing some researchers that we really do make and respond to pheromones. As a result some think it's time to stop asking if human pheromones exist and start investigating exactly how they affect our behaviour.
The term pheromone was coined in 1959 to describe chemicals released by insects to trigger hard-wired behaviours in other members of the same species. The classic example is female moths releasing sex pheromones to attract a mate. When pheromones were discovered in mammals, their more complex behaviour meant this definition no longer fitted the bill. Researchers have been debating the meaning of the word ever since. One useful working definition is that pheromones are chemicals which send a message that, in evolutionary terms, benefits both sender and receiver.
Whatever definition you go for, pheromones are a big part of the animal world. Animals use pheromones to transmit useful information about themselves, such as gender or sexual receptiveness; to change others' physiology, for example by stimulating ovulation; and to directly affect others' behaviour. Examples of these behaviour-changing or "releaser" pheromones include sexual attractants and the alarm pheromones many mammals - among them rats and deer - use to put others on alert without giving away their location with an alarm call.
For many years, it was assumed that humans did not produce or respond to any of these types of pheromones. In part that was down to a reluctance to admit that humans might respond in such an "animal" way. There is also no clear mechanism for how they might act on the human brain. In animals, pheromones are usually detected by the vomeronasal organ (VNO), a pair of mini-nostrils inside the nose which detect airborne pheromones and relay messages directly to the brain. Although humans have something resembling a VNO, there are no neurons linking it to the brain. And while we have the genes required for a working VNO, they no longer code for functional pheromone receptor proteins. The obvious conclusion was that we had lost this method of communication at some point in our evolution.
That hasn't stopped researchers from making claims about human pheromones. In 1971 Martha McClintock, a social psychologist at Harvard University, famously reported that women who live together gradually synchronise their menstrual cycles. McClintock, now at the University of Chicago, suggested that this might be mediated by pheromones. In 1998, along with her Chicago colleague Kathleen Stern, McClintock found evidence to support this idea, showing that sweat from women in different stages of their menstrual cycle either extended or shortened the cycles of other women. Despite this evidence, McClintock's conclusions remain contentious because nobody has yet isolated the actual chemicals that cause the effect.
Sexy scents: More controversial still are claims that pheromones are involved in human sexual attraction. This is partly due to some high-profile yet scientifically questionable research done by David Berliner and Luis Monti-Bloch of the University of Utah in the mid-1990s. They claimed that when they exposed people to reproductive hormones from the opposite sex, they could see an electrical response from the part of the nose where the vomeronasal organ would be.
In women, cells in this region responded most strongly to extracts containing androstadienone, a hormone related to testosterone found in male sweat. Men reacted similarly to estratetraenol, which is found in female urine. The same team also reported that releasing these compounds into the air subconsciously altered mood, having a calming effect on the opposite sex. The research was widely greeted with scepticism because of Berliner's financial interest in a brand of perfume called Realm, which was laced with the supposed pheromones. The team's insistence that the pheromones act through the VNO also raised eyebrows. With no convincing evidence for a functional human VNO, many people dismissed the research outright.
Despite this chequered past, there are still plenty of researchers who insist that human pheromones are alive and well. One is Johan Lundstrom, a neuropsychologist at the Monell Chemical Senses Center in Philadelphia. He has shown that women can consistently sniff out their sisters from friends and strangers even when they are not consciously aware of any difference in odour. A similar effect is our well-known ability to select mates based on genetic signatures evident in their body odour - a subconscious indicator of the compatibility of their immune system.
To Lundstrom, this is convincing evidence that human pheromones are real - it's just that most researchers have a blind spot when it comes to using the P-word. "If you asked scientists whether one human can convey some sort of social message to another in their body odour, 99.9 per cent of them would say yes," he says. "If you ask them if humans have pheromones they'll say 'that hasn't been demonstrated'. It's a semantic issue."
That may all be about to change, thanks in part to the recent discovery that some animals detect pheromones using their normal olfactory system, not the VNO. "There are several well-established examples of pheromone communication in animals that don't require the VNO," says Meredith, who specialises in the animal VNO. For example, a recent study found that mice detect alarm pheromones via a bundle of nerve cells at the tip of their nose that is wired into the normal olfactory system.
Brain-imaging studies have also helped revive the idea that humans may respond to sex pheromones. In a series of recent experiments, neuroscientist Ivanka Savic of the Karolinska Institute in Stockholm, Sweden, exposed people to androstadienone and watched what happened in their anterior hypothalamus, a part of the brain thought to be involved in sexual behaviour.
In one study, published in 2005, Savic found that androstadienone activated that brain region in heterosexual women and homosexual men, but not in heterosexual men or homosexual women. She later found the opposite effect with estratetraenol.
Brain-imaging studies are also providing tantalising evidence that humans release and respond to alarm pheromones. These have been less well studied than those thought to be involved in attraction, but a handful of psychological studies have claimed to show that humans can detect the "scent of fear". In 1999, Denise Chen, a psychologist now at Rice University in Houston, Texas, asked a group of volunteers to sniff sweat from people who had watched either funny or scary film clips. More than half of the volunteers successfully identified a sample of fearful sweat despite not being able to consciously smell any difference in the samples.
In a similar study in 2002, Kerstin Ackerl from the University of Vienna in Austria reported that women seemed to be able to detect the scent of fear. The 60 women rated sweat from women who had watched a scary movie as stronger, less pleasant and smelling more "like aggression" than sweat from women who had watched a neutral movie.