What do you think a group of women would do if they were given a dose of testosterone before playing a game? Our folk wisdom tells us that they would probably become more aggressive, selfish or antisocial. Well, that’s true… but only if they think they’ve been given testosterone.
If they don’t know whether they’ve been given testosterone or placebo, the hormone actually has the opposite effect to the one most people would expect – it promotes fair play. The belligerent behaviour stereotypically linked to testosterone only surfaces if people think they’ve been given hormone, whether they receive a placebo or not. So strong are the negative connotations linked to testosterone that they can actually overwhelm and reverse the hormone’s actual biological effects.
If ever a hormone was the subject of clichés and stereotypes, it is testosterone. In pop culture, it has become synonymous with masculinity, although women are subject to its influence too. Injections of testosterone can make lab rats more aggressive, and this link is widely applied to humans. The media portrays “testosterone-charged” people as sex-crazed and financially flippant and the apparent link with violence is so pervasive that the use of steroids has even been used as a legal defence in a US court.
Christoph Eisenegger from the University of Zurich tested this folk wisdom by enrolling 60 women in a double-blind randomised controlled trial. They were randomly given either a 0.5 milligram drop of testosterone or a placebo. He only recruited women because previous research shows exactly how much testosterone you need to have an effect, and how long it takes to do so. We don’t know that for men.
The women couldn’t have known which substance they were given, but Eisenegger asked them to guess anyway. Their answers confirmed that they couldn’t tell the difference between the two drops. But they would also confirm something more startling by the trial’s end.
Each woman was paired with a partner (from another group of 60) and played an “Ultimatum game” for a pot of ten Swiss francs. One woman, the “proposer”, decided how to allocate it and her partner, “the responder” could choose to accept or refuse the offer. If she accepts, the money is split as suggested and if she refuses, both players go empty-handed. The fairest split would be an equal one but from the responder’s point of view, any money would be better than nothing. The game rarely plays out like that though – so disgusted are humans with unfairness that responders tend to reject low offers, sacrificing their own meagre gains to spite their proposers.
Overall, Eisenegger found that women under the influence of testosterone actually offered more money to their partners than those who received the placebo. The effect was statistically significant and it’s exactly the opposite of the selfish, risk-taking, antagonistic behaviour that stereotypes would have us predict.
Those behaviours only surfaced if women thought they had been given testosterone. Those women made lower offers than their peers who believed they had tasted a placebo, regardless of which drop they had been given. The amazing thing is that this negative ‘imagined’ effect actually outweighed the positive ‘real’ one. On average, a drop of testosterone increased a proposer’s offer by 0.6 units, but belief in the hormone’s effects reduced the offer by 0.9 units.
The difference between these values is not statistically significant, so we can’t conclude that the negative effect outweighs the positive one, but the two are certainly comparable. Either way, it is a staggering result. It implies that the biological effect of a behaviour-altering hormone can be masked, if not reversed, by what we think it does. It’s somewhat similar to the nocebo effect, where people experience unwanted side effects from a drug because they believe that such effects will happen.
How can we explain these results? Certainly, Eisenegger accounted for the volunteers’ levels of testosterone before the experiment, as well as their levels of cortisol (a stress hormone), their mood and their feelings of anxiety, anger, calmness or wakefulness. None of these factors affected his results.
It’s possible that people who are naturally inclined towards selfish, aggressive or dominant behaviour would find it easier to rationalise their actions if they felt that they were under the spell of testosterone. However, these personality traits weren’t any more common among the recruits who thought they were given testosterone than those who thought they had a placebo.
Instead, Eisenegger suggests that testosterone’s negative stereotype provided some of the women with a licence to misbehave. Their beliefs relieved them from the responsibility of making socially acceptable offers because they thought they would be driven to make greedy ones.
At first, this work seems to contradict the results from earlier studies, which suggest that high testosterone levels are linked with risk-taking, selfishness and aggression. But these studies can’t tell us whether the former causes the latter. Indeed, another randomised trial that I’ve blogged about before found that doses of testosterone didn’t affect a woman’s selflessness, trust, trustworthiness, fairness or attitude to risk. This study also used an Ultimatum game but it only analysed the behaviour of the responder rather than the proposer.
The alternative hypothesis says that testosterone plays a much subtler role in shaping our social lives. When our social status is challenged, testosterone drives us to increase our standing; how we do that depends on the situation. Traders might take bigger financial risks, while prisoners might have a dust-up. Eisenegger thinks that this is the right explanation, and his results support his view. In his experiment, women who received testosterone would be more inclined towards acts that boosted their social status, and the best way of doing that was to make a fair offer.
The message from this study is clear, and Eisenegger sums it up best himself:
“Whereas other animals may be predominantly under the influence of biological factors such as hormones, biology seems to exert less control over human behaviour. Our findings also teach an important methodological lesson for future studies: it is crucial to control for subjects’ beliefs because the [effect of a pure substance] may be otherwise under- or overestimated.”
Reference: Nature doi:10.1038/nature08711
More on hormones and placebo:
Some people go out of their way to help their peers, while others are more selfish. Some lend their trust easily, while others are more suspicious and distrustful. Some dive headlong into risky ventures; others shun risk like visiting in-laws. There’s every reason to believe that these differences in behaviour have biological roots, and some studies have suggested that they are influenced by sex hormones, like testosterone and oestrogen.
It’s an intriguing idea, not least because men and women have very different levels of these hormones. Could that explain differences in behaviour between the two sexes? Certainly, several studies have found links between people’s levels of sex hormones and their behaviour in psychological experiments. But to Niklas Zethraeus and colleagues from the Stockholm School of Economics, this evidence merely showed that the two things were connected in some way – they weren’t strong enough to show that sex hormones were directly influencing behaviour.
To get a clearer answer, Zethraeus set up a clinical trial. He recruited 200 women, between 50-65 years of age, and randomly split them into three groups – one took tablets of oestrogen, the second took testosterone tablets and the third took simply sugar pills.
After four weeks of tablets, the women took part in a suite of psychological games, where they had the chance to play for real money. The games were designed to test their selflessness, trust, trustworthiness, fairness and attitudes to risk. If sex hormones truly change these behaviours, the three groups of women would have played the games differently. They didn’t.
Their levels of hormones had changed appropriately. At the end of the four weeks, the group that dosed up on oestrogen had about 8 times more than they did at the start, but normal levels of testosterone. Likewise, the testosterone-takers had 4-6 time more testosterone and free testosterone (the “active” fraction that isn’t attached to any proteins) but normal levels of oestrogen. The sugar-takers weren’t any different. Despite these changes, the women didn’t play the four psychological games any differently.
Animals have distinct personalities and temperaments, but why would evolution favour these over more flexible and adaptible mindsets? New game theory models show that animal personalities are a natural progression from the choices they make over how to live and reproduce.
Any pet owner, wildlife photographer or zookeeper will tell you that animals have distinct personalities. Some are aggressive, others are docile; some are bold, others are timid.
In some circles, ascribing personalities to animals is still a cardinal sin of biology and warrants being branded with a scarlet A (for anthropomorphism). Nonetheless, scientists have consistently found evidence of personality traits in species as closely related to us as chimpanzees, and as distant as squid, ants and spiders.
These traits may exist, but they pose an evolutionary puzzle because consistent behaviour is not always a good thing. The consistently bold animal could well become a meal if it stands up to the wrong predator, or seriously injured if it confronts a stronger rival. The ideal animal is a flexible one that can continuously adjust its behaviour in the face of new situations.
And yet, not only do personality types exist but certain traits are related across the entire animal kingdom. Aggression and boldness toward predators are part of a general ‘risk-taking’ personality that scientists have found in fish, birds and mammals.
Max Wolf and colleagues from The University of Groningen, Netherlands, have found a way to explain this discrepancy. Using game theory models, they have shown that personalities arise because of the way animals live their lives and decide when to reproduce.
It’s mid-October. For most of us, our New Year’s resolutions have long been forgotten and our bad habits remain frustratingly habitual. The things that are bad for us often feel strongly compelling, be they high-fat foods, gambling or alcohol. And nowhere is the problem of addiction more widespread, serious and dangerous than the case of cigarette smoking.
Smoking is the leading preventable cause of death in the developed world, and in the UK, it kills five times more people than all non-medical causes combined. The dangers of smokers are both well-established and well-known, and surveys repeatedly show that the majority of smokers want to quit. But weaning oneself off a substance as addictive as nicotine is not easy.
People often view quitting smoking as a question of willpower – a problem of the mental world. But like all mental processes, addiction eventually boils down to physical matter, to our brains and the chemicals that reside within. Neurological studies have found that smoking causes long-term changes to various parts of the brain including the dopamine system involved in feelings of pleasure, and the amygdala, involved in emotional responses. Even cues associated with smoking such as the smell of smoke or the sight of a cigarette, can trigger distinctive patterns of activity in these areas, and are likely to contribute to the urges that smokers feel.
Now, Nasir Naqvi and colleagues from the University of Iowa have tracked down the neurons that control the addictive urges of smokers to a part of the brain called the insula. Located deep inside the brain, the insula is involved in emotion. It collects and processes sensory information from the rest of the body, and translates them into conscious emotional experiences, such as cravings, hunger or pain. And in doing this, the insula could control cravings for cigarettes in response to smoking-related cues.
The art of auctioning is an ancient one. The concept of competitively bidding for goods has lasted from Roman times, when spoils of war were divvied up around a planted spear, to the 21st century, when the spoils of the loft are sold through eBay. But despite society’s familiarity with the concept, people who take part in auctions still behave in a strange way – they tend to overbid, offering more money than what they actually think an object is worth.
Some economists have suggested that people overbid because they are averse to risk. They would rather make spend more money to be sure of a win than to risk making a steal by gambling with a low bid. Others have suggested that it’s the element of competition that drives people to overbid – the joy of winning is what they’re after. Now, Mauricio Delgado and colleagues from Rutgers University have provided new evidence to show that neither theory is right.
With a combination of brain-scanning and psychological games, they have found that economists who suggested a social competition angle were moving along the right lines. But it’s not the joy of winning that’s important – it’s the fear of losing. People cough up too much because of simple social competition.
Delgado’s team (which included Elizabeth Phelps, whose work I have blogged about before) used a brain-scanning technique called functional resonance magnetic imaging (fMRI) to study the brains of 17 volunteers as they played two games – a two-player auction or a single-player lottery.
Financial trading is really risky business for individuals and economies alike. Millions of pounds and dollars rest on the fast decisions of stressed people, working under extreme pressure. With such high stakes, it’s worth remembering that traders, regardless of their intellect or experience, are as fallible as the rest of us and their brains and bodies are influenced by the same ensemble of hormones.
Testosterone is one of these, and it’s of particular importance to traders for it can influence a person’s confidence and attitudes to risk during competitive encounters. While it seems almost clichéd to talk of the testosterone-fuelled alpha-male, a new study shows that traders that enter the floor with higher levels of this hormone do tend to make significantly higher profits over the course of the day. The actions of testosterone and other hormones could have large effects on entire markets by affecting the decisions of people in the financial sector.
John Coates and Joe Herbert from the University of Cambridge shadowed 17 male traders over 8 working days as they went about their business in a mid-sized City of London trading floor (the City is the capital’s financial district for the non-Brits among us). The bulk of their work took place between 11 am and 4pm, and at these times, Coates and Herbert took saliva samples to measure how their hormone levels shifted in a real-life situation. At the end of each one, the duo recorded how much profit and loss each trader had made.
Would you gamble on a safe bet for the promise of something more? Would you risk losing everything for the possibility of greater rewards? In psychological experiments, humans tend to play it safe when we stand to gain something – we’re more likely to choose a certain reward over a larger but riskier one. Now, we’re starting to understand how our two closest relatives deal with risk – bonobos, like us, tend to be risk-averse while chimpanzees usually play the odds.
Sarah Heilbronner from Harvard University studied the attitudes of five chimps and five bonobos to risky decisions. All the animals had been born in captivity in the Liepzig Zoo, Germany and were fed well on a regular schedule. Heilbronner presented the apes with one of two upside-down bowls of different shapes and colours. One ‘fixed’ bowl always contained four grape pieces and the other ‘variable’ one had a fifty-fifty chance of concealing either one grape piece or seven.
After a few trials with each bowl to get them accustomed to the options, Heilbronner let the animals choose between the two. The chimps were most likely to take a gamble on the variable bowl and they only chose the fixed one 36% of the time. The bonobos on the other hand mostly liked to play it safe and picked the fixed bowl 72% of the time. On an individual level, all of the five bonobos showed risk-averse behaviour and four of the five chimps demonstrated a penchant for risk-taking.
It’s not that one of the two species learns about the choice more slowly than the other; the differences in their behaviour were apparent in the very first trials of the experiment, and only grew larger with experience. Nor was it the case that either chimps or bonobos had better mathematical skills than the other. When they were offered the bowls face-up and could see what was inside, they almost always picked the one with the most grape pieces.