A touch of generosity
Aug 14th 2008
From The Economist print edition
Touch can inspire munificence towards those you trust
PEOPLE touch each other a lot, even strangers. We shake hands, slap backs, kiss and caress. Such behaviour can increase co-operation, which is good from an evolutionary point of view. It has even been shown that waitresses who touch patrons tend to be tipped more generously.
It is known that stroking rats can raise the level of oxytocin, a hormone active in the brain and implicated in various social interactions, such as maternal attachment. In humans higher oxytocin levels have been linked to physiological phenomena like contractions during childbirth, or orgasm. But the link to physical contact is so far unclear. Interestingly, the level of hormone appears to rise in people who are trusted. And more of it seems to inspire greater generosity towards strangers.
This prompted Vera Morhenn of the University of California, San Diego, and her colleagues, to examine the physiological mechanism underlying this and to see whether munificence towards strangers could be manipulated through touch. In their experiment, published in Evolution and Human Behavior, they split 96 male and female graduate students into three groups. The first and second received a professional massage but the third did not. Then the first and third group took part in a “trust game”.
Participants were paired at random and seated in front of a computer, physically removed from their anonymous partner. Each also got $10 in cash, supposedly for showing up. The rules stipulated that for each pair, one person, the giver, could cede a part of their money to the other, the trustee. This amount would then be tripled and credited to the trustee, who was subsequently prompted by the computer to sacrifice a part of his stash by returning some to the giver.
Standard game theory predicts that in an anonymous one-off exchange like this the trustee ought to keep the gift and not reciprocate. The giver, too, ought to refrain from donating, since his sacrifice is bound to remain unrequited. Yet that is not what tends to happen with real people. Givers often give and trustees frequently return the favour. (Studies of identical and non-identical twins suggest that co-operative behaviour in trust games is heritable.) In effect, the giver’s donation reflects his confidence in the trustee’s willingness to reciprocate. In other words, it signals trust.
To test the physiology, Dr Morhenn took blood samples at the start and end of each game and looked for changes in oxytocin levels. She found no effect in the massaged group who did not participate in the game, implying that trust does indeed act as some sort of trigger. But in the players the hormone rose in those who were massaged and fell slightly in those who were not.
Despite receiving statistically identical trust signals from givers, the massaged trustees with their higher oxytocin levels returned a whopping 243% more than their unrubbed counterparts. A clue to why evolution might favour such a double-trigger mechanism may come from the other finding that women appear more susceptible than men to tactile manipulation. Perhaps that is to ensure maternal care of their own brood. If so, such effects seem to extend beyond the mother’s bosom.
30 de agosto de 2008
23 de agosto de 2008
Facing the truth
Physiognomy
Facing the truth
Aug 21st 2008
From The Economist print edition
The shape of your face betrays how aggressive you are—if you are a man
PHYSIOGNOMY, the art or science of predicting inward character from outward form, has had its ups and downs over the years. A century ago, the idea that a person’s character could be seen in his face was more or less taken as given. It then fell out of favour, along with the idea that behaviour is genetically determined, as Marxist ideas of the pliability and perfectibility of mankind became fashionable. Now, it is undergoing something of a revival. It has been found, for example, that women can predict a man’s interest in infant children from his face. Trustworthiness also shows up, as does social dominance. The latest example comes from a paper just published in the Proceedings of the Royal Society by Justin Carré and Cheryl McCormick, of Brock University in Ontario, Canada. This suggests that in men, at least, it is also possible to look at someone’s face and read his predisposition to aggression.
The thesis developed by Mr Carré and Dr McCormick is that aggressiveness is predictable from the ratio between the width of a person’s face and its height. Their reason for suspecting this is that this ratio differs systematically between men and women (men have wider faces) and that the difference arises during puberty, when sex hormones are reshaping people’s bodies. The cause seems to be exposure to testosterone, which is also known to make people aggressive. It seems reasonable, therefore, to predict a correlation between aggression and face shape.
To test their thesis, Mr Carré and Dr McCormick looked at the fine, old Canadian sport of ice hockey. This is, famously, not a gentle game. It is also a game in which the rules provide a plausible proxy for aggressiveness, namely the amount of time a player spends off the ice in the penalty box for such infringements as knocking his opponent’s teeth out with a well-aimed stick.
The two researchers obtained photographs of several university and professional ice-hockey teams, and measured the facial ratios of the players. They also obtained those players’ penalty records. Just as they expected, the wider a player’s face, the more time he spent in the cooler.
Ice hockey, though, is mostly a man’s game (women might argue that they are too sensible to get involved, although the Canadian ladies did win a gold medal at the last winter Olympics). To find out whether the theory was true for females as well, Mr Carré and Dr McCormick turned to that stock experimental subject, the university undergraduate. They recruited several dozen of both sexes and got them to play a game against what they thought was a person in another room but was actually a computer. Various measures of aggression taken during this game suggest that men are the same everywhere, be they students or sportsmen. Aggression was not, however, predictable in women students—or, at least, not from the shapes of their faces.
It seems, therefore, that facial ratio in men is a biologically honest signal of aggressiveness. Honest signals are those, such as luxuriantly feathered tails, that cannot be mimicked by individuals who would like the benefits without the costs. In the case of aggressiveness, the benefit to the aggressive individual is, paradoxically, that he will not have to get into fights in order to prove the point. The fear induced by his face should be enough by itself. At least, that is the hypothesis. The experiment to prove it has yet to be done.
Facing the truth
Aug 21st 2008
From The Economist print edition
The shape of your face betrays how aggressive you are—if you are a man
PHYSIOGNOMY, the art or science of predicting inward character from outward form, has had its ups and downs over the years. A century ago, the idea that a person’s character could be seen in his face was more or less taken as given. It then fell out of favour, along with the idea that behaviour is genetically determined, as Marxist ideas of the pliability and perfectibility of mankind became fashionable. Now, it is undergoing something of a revival. It has been found, for example, that women can predict a man’s interest in infant children from his face. Trustworthiness also shows up, as does social dominance. The latest example comes from a paper just published in the Proceedings of the Royal Society by Justin Carré and Cheryl McCormick, of Brock University in Ontario, Canada. This suggests that in men, at least, it is also possible to look at someone’s face and read his predisposition to aggression.
The thesis developed by Mr Carré and Dr McCormick is that aggressiveness is predictable from the ratio between the width of a person’s face and its height. Their reason for suspecting this is that this ratio differs systematically between men and women (men have wider faces) and that the difference arises during puberty, when sex hormones are reshaping people’s bodies. The cause seems to be exposure to testosterone, which is also known to make people aggressive. It seems reasonable, therefore, to predict a correlation between aggression and face shape.
To test their thesis, Mr Carré and Dr McCormick looked at the fine, old Canadian sport of ice hockey. This is, famously, not a gentle game. It is also a game in which the rules provide a plausible proxy for aggressiveness, namely the amount of time a player spends off the ice in the penalty box for such infringements as knocking his opponent’s teeth out with a well-aimed stick.
The two researchers obtained photographs of several university and professional ice-hockey teams, and measured the facial ratios of the players. They also obtained those players’ penalty records. Just as they expected, the wider a player’s face, the more time he spent in the cooler.
Ice hockey, though, is mostly a man’s game (women might argue that they are too sensible to get involved, although the Canadian ladies did win a gold medal at the last winter Olympics). To find out whether the theory was true for females as well, Mr Carré and Dr McCormick turned to that stock experimental subject, the university undergraduate. They recruited several dozen of both sexes and got them to play a game against what they thought was a person in another room but was actually a computer. Various measures of aggression taken during this game suggest that men are the same everywhere, be they students or sportsmen. Aggression was not, however, predictable in women students—or, at least, not from the shapes of their faces.
It seems, therefore, that facial ratio in men is a biologically honest signal of aggressiveness. Honest signals are those, such as luxuriantly feathered tails, that cannot be mimicked by individuals who would like the benefits without the costs. In the case of aggressiveness, the benefit to the aggressive individual is, paradoxically, that he will not have to get into fights in order to prove the point. The fear induced by his face should be enough by itself. At least, that is the hypothesis. The experiment to prove it has yet to be done.
Helicobacter Pylori
Symbiosis
The twists and turns of fate
Aug 21st 2008
From The Economist print edition
Helicobacter pylori has a reputation for causing ulcers and cancer. Hunting it to extinction, however, may be a mistake
Science Photo Library
MOST people feel a twinge of regret at reports that an animal or plant is becoming rare. Should they feel the same pangs for a bacterium? With Helicobacter pylori, so-called because of its twisty-turny shape, and famous for causing stomach ulcers and gastric cancer, the reaction would probably be “good riddance”. And H. pylori is, indeed, endangered in many parts of the planet. It is fast vanishing from the rich world, thanks to antibiotics and improved hygiene. Yet, as conservationists of larger organisms are quick to remind you, extinctions can have unexpected consequences. And that may prove to be the case with H. pylori.
Martin Blaser, a microbiologist at the New York University School of Medicine, and his team have already linked the bug’s disappearance with increased levels of obesity and with the rise of cancer of the oesophagus. Last month they added asthma to the list by publishing a study showing that children who had not been infected by H. pylori were more likely to suffer from the condition than those who had.
It is a mistake, according to Dr Blaser, to think of H. pylori as just another pathogen. He reckons that it is better perceived as a symbiont that is sometimes helpful and sometimes harmful. The evidence suggests that its relatives have been living in mammalian stomachs since the mammals began, some 150m years ago. It, itself, has been around for at least 60,000 years and until about 50 years ago it infected 70-80% of the human population. Now, as a consequence of the routine use of antibiotics for such things as ear infections, only 5% of American children have it. That change, he thinks, is having consequences.
Give and take
Dr Blaser has discovered, for example, that H. pylori helps to regulate stomach-acid levels in a way that is usually helpful to both itself and its host. If the human side of the loop gets too strong, and the stomach becomes too acid, the bug may produce a substance called cag. The intended effect of this, Dr Blaser thinks, is to say “turn down the acid level”. However, cag also has a side-effect. It is toxic to the stomach lining, and it is this toxicity that provokes the ulcers and cancers for which H. pylori is notorious.
The obvious medical temptation—and, indeed, what has happened in practice—is to annihilate the bacterium with antibiotics. That works as an anti-ulcer treatment, but when H. pylori goes its homeostatic effect goes with it, allowing the strength of the stomach acid to rise chronically. This acid has a tendency to spill out of the top of the stomach and into the oesophagus. That has unpleasant consequences. In fact the recent drop in H. pylori infections has almost exactly matched the rise in gastroesophageal reflux disease (which feels like bad heartburn). Over time, the damage the excess acid does to the walls of the oesophagus may cause cancer.
The link with asthma has a different mechanism. When Dr Blaser and his colleague Yu Chen analysed a health and nutrition database called the National Health and Nutrition Examination Survey, they found that American children between the ages of three and 13 who are infected with H. pylori are 60% less likely to have asthma than their uninfected contemporaries. They believe this is because H. pylori makes the immune system more robust. The lack of it lowers the threshold for responding to a foreign protein that might come from a pathogen. As a result, things like pollen and mites trigger responses even though they are not, actually, dangerous. This idea is similar to the “hygiene hypothesis” that the super-clean environment of the modern world fails to challenge children’s immune systems enough for their own good, and thus opens the way for conditions such as asthma. It differs, however, in that Dr Blaser thinks humanity has co-evolved with the bugs that prime the immune system, rather than picking them up at random.
Moreover, even the link between H. pylori and gastric cancer and ulcers is complicated. Just having the bacterium does not automatically mean you will get an ulcer. In the past, most people were infected with H. pylori from their childhoods until they died. Ulcers, however, generally emerge when a patient is in his 30s or 40s. In addition, they are three times more common in men than in women. H. pylori-infection rates, however, are the same in both sexes.
H. pylori also has an effect on two of the hormones that control appetite—ghrelin, which makes you feel hungry, and leptin, which does the opposite. People without H. pylori produce more ghrelin than those with. Though the connection has not been established for sure, Dr Blaser suspects the bacterium’s disappearance could thus be contributing to the epidemic of obesity that is sweeping the rich world.
What all this suggests is that rather than trying to eradicate H. pylori, a better strategy would be to manage its relationship with humanity in a more sophisticated way. Some people are, genetically, more susceptible to ulcers and gastric cancer than others. For these unfortunates eradication may be the best option. However, if your genes predispose you to asthma or obesity, eradication may be unwise.
Moreover, people are not born with H. pylori in their stomachs. Rather, they get infected when they are young. That means a parent or doctor could choose which strain of the bacterium a child ends up carrying, rather than leaving the matter to chance. H. pylori is genetically variable (not all strains, for example, make cag). Dr Blaser envisages a future in which doctors run routine checks on babies’ genes to find out their susceptibilities, and then colonise those babies’ stomachs with the strain or strains that are best for them. If that happens, H. pylori can come off the endangered species list for good.
The twists and turns of fate
Aug 21st 2008
From The Economist print edition
Helicobacter pylori has a reputation for causing ulcers and cancer. Hunting it to extinction, however, may be a mistake
Science Photo Library
MOST people feel a twinge of regret at reports that an animal or plant is becoming rare. Should they feel the same pangs for a bacterium? With Helicobacter pylori, so-called because of its twisty-turny shape, and famous for causing stomach ulcers and gastric cancer, the reaction would probably be “good riddance”. And H. pylori is, indeed, endangered in many parts of the planet. It is fast vanishing from the rich world, thanks to antibiotics and improved hygiene. Yet, as conservationists of larger organisms are quick to remind you, extinctions can have unexpected consequences. And that may prove to be the case with H. pylori.
Martin Blaser, a microbiologist at the New York University School of Medicine, and his team have already linked the bug’s disappearance with increased levels of obesity and with the rise of cancer of the oesophagus. Last month they added asthma to the list by publishing a study showing that children who had not been infected by H. pylori were more likely to suffer from the condition than those who had.
It is a mistake, according to Dr Blaser, to think of H. pylori as just another pathogen. He reckons that it is better perceived as a symbiont that is sometimes helpful and sometimes harmful. The evidence suggests that its relatives have been living in mammalian stomachs since the mammals began, some 150m years ago. It, itself, has been around for at least 60,000 years and until about 50 years ago it infected 70-80% of the human population. Now, as a consequence of the routine use of antibiotics for such things as ear infections, only 5% of American children have it. That change, he thinks, is having consequences.
Give and take
Dr Blaser has discovered, for example, that H. pylori helps to regulate stomach-acid levels in a way that is usually helpful to both itself and its host. If the human side of the loop gets too strong, and the stomach becomes too acid, the bug may produce a substance called cag. The intended effect of this, Dr Blaser thinks, is to say “turn down the acid level”. However, cag also has a side-effect. It is toxic to the stomach lining, and it is this toxicity that provokes the ulcers and cancers for which H. pylori is notorious.
The obvious medical temptation—and, indeed, what has happened in practice—is to annihilate the bacterium with antibiotics. That works as an anti-ulcer treatment, but when H. pylori goes its homeostatic effect goes with it, allowing the strength of the stomach acid to rise chronically. This acid has a tendency to spill out of the top of the stomach and into the oesophagus. That has unpleasant consequences. In fact the recent drop in H. pylori infections has almost exactly matched the rise in gastroesophageal reflux disease (which feels like bad heartburn). Over time, the damage the excess acid does to the walls of the oesophagus may cause cancer.
The link with asthma has a different mechanism. When Dr Blaser and his colleague Yu Chen analysed a health and nutrition database called the National Health and Nutrition Examination Survey, they found that American children between the ages of three and 13 who are infected with H. pylori are 60% less likely to have asthma than their uninfected contemporaries. They believe this is because H. pylori makes the immune system more robust. The lack of it lowers the threshold for responding to a foreign protein that might come from a pathogen. As a result, things like pollen and mites trigger responses even though they are not, actually, dangerous. This idea is similar to the “hygiene hypothesis” that the super-clean environment of the modern world fails to challenge children’s immune systems enough for their own good, and thus opens the way for conditions such as asthma. It differs, however, in that Dr Blaser thinks humanity has co-evolved with the bugs that prime the immune system, rather than picking them up at random.
Moreover, even the link between H. pylori and gastric cancer and ulcers is complicated. Just having the bacterium does not automatically mean you will get an ulcer. In the past, most people were infected with H. pylori from their childhoods until they died. Ulcers, however, generally emerge when a patient is in his 30s or 40s. In addition, they are three times more common in men than in women. H. pylori-infection rates, however, are the same in both sexes.
H. pylori also has an effect on two of the hormones that control appetite—ghrelin, which makes you feel hungry, and leptin, which does the opposite. People without H. pylori produce more ghrelin than those with. Though the connection has not been established for sure, Dr Blaser suspects the bacterium’s disappearance could thus be contributing to the epidemic of obesity that is sweeping the rich world.
What all this suggests is that rather than trying to eradicate H. pylori, a better strategy would be to manage its relationship with humanity in a more sophisticated way. Some people are, genetically, more susceptible to ulcers and gastric cancer than others. For these unfortunates eradication may be the best option. However, if your genes predispose you to asthma or obesity, eradication may be unwise.
Moreover, people are not born with H. pylori in their stomachs. Rather, they get infected when they are young. That means a parent or doctor could choose which strain of the bacterium a child ends up carrying, rather than leaving the matter to chance. H. pylori is genetically variable (not all strains, for example, make cag). Dr Blaser envisages a future in which doctors run routine checks on babies’ genes to find out their susceptibilities, and then colonise those babies’ stomachs with the strain or strains that are best for them. If that happens, H. pylori can come off the endangered species list for good.
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