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Unlike humans, chimpanzees only punish when they’ve been personally wronged

When Delta Airlines refused to let Arijit Guha board a plane because his T-shirt made passengers uncomfortable, others made Delta aware of their outrage. When Samsung infringed Apple’s copyright, a jury of independent peers awarded Apple more than $1 billion in damages. When Republican Todd Akin claimed that women could stop themselves from becoming pregnant if raped, people called for his head.

These recent events all illustrate a broad human trait: we seek to punish people who do wrong and violate our social rules, even when their actions don’t harm us directly. We call for retribution, even if we have nothing specific to gain from it and even if it costs us time, effort, status or money to do so. This “third-party punishment” is thought to cement human societies together, and prevents cheats and free-riders from running riot. If you wrong someone, and they’re the only ones who want to sanction you, the price of vice is low. If an entire society condemns you, the cost skyrockets.

Do other animals do the same thing? It’s not clear, but one group of scientists believes that our closest relative – the chimpanzee – does not. Katrin Riedl from the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany found that chimpanzees will punish individuals who steal food from them, but not those who steal food from others. Even if the victim was a close relative, the third party never sought to punish the thief. These were the first direct tests of third-party punishment in a non-human animal, and the chimps got an F.


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Charity of the apes – chimps spontaneously help each other

Compared to most other animals, humans are unusual in our tendency to help each other out. We donate to charity. We give blood. We show kindness to strangers, even when we stand to gain nothing in return. This behaviour is so odd that the natural question arises: are we alone in such selflessness? And if any animal could help to answer that question, it’s the chimpanzee, one of our closest relatives.

Dozens of scientists study the behaviour of chimps, looking at how these apes act towards their peers. But the results of these studies have been frustrating for many in the field. People who watch captive and wild chimps have documented hundreds of cases of seemingly altruistic behaviour. They have seen individuals helping each other to climb walls, consoling each other after fights, sharing food, risking death to save companions from drowning, and even adopting the babies of dead and unrelated peers. Anecdotes like these suggest that chimps, like humans, behave selflessly towards each other.

But experiments have often shown otherwise. In some studies, chimps choose to help their peers retrieve out-of-reach objects rather than doing nothing. But when chimps have a choice between two equal actions – say, cashing in a token that leads to personal gain versus another that also benefits a partner – they only looked out for themselves. One paper bore the title “Chimpanzees are indifferent to the welfare of unrelated group members”. Another concluded that “chimpanzees made their choices based solely on personal gain”.

Collectively, these studies championed a view of chimps as reluctant altruists, who only act selflessly in response to pressure, and who generally don’t help unfamiliar chimps, “even when they are able to do so at virtually no cost to themselves”. But Frans de Waal from the Living Links Centre at Emory University thinks that this portrait is wrong. He says, “The authors of these studies moved from not finding evidence for prosocial choice to thinking they had proven its absence.”

De Waal thinks that the previous tests handicapped the chimps by putting them in situations that masked their altruistic tendencies.  They couldn’t communicate, they had to cope with complicated equipment involving levers, and they often sat so far apart that they had little understanding of how their choices affected their fellows. With his colleague Victoria Horner, de Waal designed a new experiment to account for these problems. And, lo and behold, chimps spontaneously helped their partners, even without any prompting.


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How to make meerkats even more sociable

MeerkatMeerkats already look like a textbook case of a cooperative social animal. They live in groups of up to 50 individuals. All of them help to dig and guard the community’s burrows. They babysit, feed and teach the colony’s pups, regardless of whose offspring they are. The society already seems like the model of altruism, but there is a way of making meerkats even more cooperative – injecting them with a hormone called oxytocin.


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Slackers and parasites can sometimes make the best partners


As teenagers, we probably associate with different people to those whose company we keep as adults. At one point in our lives, we may want subversive influences, while preferring support and stability at other times. The same is true for other partnerships in nature.

Take the whistling-thorn acacia. This African tree forms partnerships with four different species of ants. Some provide a valuable service as bodyguards (even routing elephants), while others have been written off as freeloaders and parasites. But Todd Palmer has found that these labels are too simplistic. In fact, none of the ants is a perfect partner. The tree actually does best by switching its alliances throughout the course of its life. At certain times, partnering with a parasite is actually its best course of action.


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Attack of the cloned soldier worms

Soldier_queenIn the body of a snail, a war is waging. It’s so violent that the only reason there isn’t blood everywhere is that the combatants don’t have any blood. The fighters are flatworms, simple parasites that have taken over the snail. Its body is now theirs, a shell in which they mate, cooperate, and produce more flatworms. But they don’t have it all to themselves – other colonies, and even other species of flatworms can invade the same snail. When that happens, war breaks out and the flatworms wage it with something more commonly associated with ants or humans – a caste of soldiers.


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Charitable bacteria protect vulnerable sisters from antibiotics


Humans are capable of great charity, taking hits to their bank accounts and bodies to benefit their peers. But such acts of altruism aren’t limited to us; they can be found in the simple colonies of bacteria too.

Bacteria are famed for their ability to adapt to our toughest antibiotics. But resistance doesn’t spring up evenly across an entire colony. A new study suggests that a small cadre of hero bacteria are responsible for saving their peers. By shouldering the burden of resistance at a personal cost, these charitable cells ensure that the entire colony survives.


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Bonobo males get sex with help from their mums


Most human men would be appalled at the idea of their mothers helping them to get laid. But then again, we’re hardly as sexually carefree as bonobos. While these apes live in female-led societies, the males also have a strict pecking order. For those at the bottom, mum’s assistance may be the only thing that allows them to father the next generation.


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Suicidal menopausal aphids save their colony by sticking themselves to predators

A ladybird larva is on the prowl on a witch hazel plant. The youngster is a voracious predator and it’s hunting for aphids. It seems to have found a bountiful feast – a swollen structure called a gall that houses an entire aphid colony. With so many meals in one place, the colony seems easy prey, but it has staunch defenders.

As the ladybird approaches, aphids pour out of the gall and grab the predator by their jaws and legs. It’s a suicide defence. The aphids secrete massive amounts of waxy liquid from their bodies, which quickly solidifies and glues the ladybird to the plant. Unable to walk or bite, the ladybird dies and the aphids go with it. In the video below, you can see what happens when one of these aphids is prodded with a needle.

There is more to these suicidal protectors that meets the eye. Keigo Uematsu and University of Tokyo found that all of them are ‘menopausal’. They are the parents of the other aphids in the gall but their reproductive days are long behind them. With no further opportunities to raise the next generation, their final role is to defend their offspring, with their lives if necessary.


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Pay it forward? Cooperative behaviour spreads through a group, but so does cheating

Ever wonder if acts of kindness or malice really do ripple outwards? If you give up a seat on a train to a stranger, do they go onto “pay it forward” to others? Likewise, if you steal someone’s seat, does the bad mood you engender topple over to other people like a set of malicious dominoes? We’d all probably assume that the answers to both questions were yes, but James Fowler and Nicholas Christakis think they have found experimental evidence for the contagious nature of cooperation and cheating.

The duo analysed data from an earlier psychological experiment by Ernst Fehr and Simon Gachter, where groups of four volunteers had to decide how much money to put in a public pot. For every unit they chipped in, each member would get 0.4 back. So any donations represent a loss to the donor, but a gain to the group as a whole. The best way for the group to benefit would be for everyone to put in all their money, but each individual player could do even better by putting in nothing and feeding off their peers’ generosity.  

This “public goods game” went on for six rounds. At the end of each one, the players were told what their other comrades did, although everyone’s identities were kept secret. The groups were shuffled between rounds so that players never played with each other more than once.

Fowler and Christakis found that the volunteers’ later moves were influenced by the behaviour of their fellow players. Each act of generosity by an individual influenced the other three players to also give more money themselves, and each of them influenced the people they played with later. One act became three, which became nine. Likewise, players who experienced stingy strategies were more likely to be stingy themselves.

Even though the groups swapped every time, the contagious nature of generous or miserly actions carried on for at least three degrees of separation. You can see an example of one such cascade in the diagram below. Eleni contributes some money to the public pot and her fellow player, Lucas, benefits (one degree). In the next round, Lucas himself offers money for the good of the group, which benefits Erika (two degrees), who gives more when paired with Jay in her next game (three degrees). Meanwhile, the effects of Eleni’s initial charity continue to spread throughout the players as Lucas and Erika persist in their cooperation in later rounds.



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Prejudice vs. biology – testosterone makes people more selfish, but only if they think it does

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.

Hulk.jpgIf 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

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Envious capuchin monkeys react badly to raw deals

This article is reposted from the old WordPress incarnation of Not Exactly Rocket Science.

Two years ago, Sarah Brosnan and Frans de Waal at the Yerkes National Primate Research Center found that brown capuchin monkeys also react badly to receiving raw deals. Forget bananas – capuchins love the taste of grapes and far prefer them over cucumber. If monkeys were rewarded for completing a task with cucumber while their peers were given succulent grapes, they were more likely to shun both task and reward.

Envious capuchin monkeys react badly to raw dealsThat suggested that the human ability to compare own efforts and rewards with those of our peers evolved much earlier in our history than we previously thought. Of course, animal behaviour researchers always need to be careful that they’re not reading too much into the actions of the animals they study.

It’s easy to suggest that the monkeys were motivated by envy, fuelled by directly weighing up their rewards with those of others. But they could equally be driven by greed of frustration. They could simply have coveted the better reward regardless of the fact that it was given to their partner. Alternatively, they could have been frustrated at being given grapes in previous trials and having to contend with cucumbers.

To rule out these alternative explanations, de Waal and Brosnan tasked graduate student, Megan van Wolkenten with repeating their earlier study with subtle tweaks. Their new results firmly show that monkeys can indeed spot unjust deals and respond with envy and apathy.

The trio worked with 13 capuchins who were asked to hand over a small granite rock in exchange for a cucumber or grape reward. They tested the monkeys in pairs, sat in adjacent wire cages so that each individual could see what its partner was getting.

If both partners were rewarded equally, they completed the task about 90% of the time, regardless of whether they were given grapes or cucumbers. Even if they were shown their future rewards before the experimenters reached for the rock tokens, they didn’t make any special efforts to earn the grapes.

That suggests that they’re not being greedy after all and are more than happy to work for a cucumber reward if their peers are rewarded equally. However, if monkeys were given cucumbers while their partners received grapes, they only cooperated 80% of the time and as the trials continued, they were more and more likely to refuse.

The researchers also found that monkeys were just as likely to hand over the tokens, regardless of whether they received a grape or a cucumber in the previous round. That effectively discounts the frustration angle, which suggests that cucumbers fail to meet the lofty expectations set by grapes.

The trio of researchers also found that the monkeys weren’t just fussed about rewards. They also compared their efforts to those of their partners and were less likely to cooperate if they had gone to more trouble to get their rewards.

If one monkey exchanged tokens for cucumbers while their partner got one for free, it was still happy to complete the task 90% of the time. But if it had to hand over three rocks for the same reward, it only complied 75% of the time. The monkeys became even more indignant if their slacker partners were given grapes for slacking. Now, they were making more effort and getting poorer rewards and their tendency to hand over rocks fell to new lows.

However, if both partners were given grapes, they were willing to do whatever it took to get them, inequity be damned. It seems that capuchins aren’t willing to act disdainfully in the face of really good rewards.

Together, these new results show that capuchins react negatively to unequal rewards and are motivated neither by greed nor frustration. Capuchins hunt squirrels as a team and once food is found, they willingly share it out among the group. Their intolerance for unequal handouts would foster greater cooperation among monkey troupes by preventing any individuals from monopolising the spoils.

In other studies, pairs of capuchins who cooperate for unequal rewards do better in the long run if they swap who gets the lion’s share. De Waal speculates that this need to share the spoils of a hunt could be the origin of our own disdain for inequality.

Even so, de Waal notes that the monkeys’ aversion to injustice isn’t on a par with humans. They don’t like getting less than their peers, but they don’t react to getting more. If anything, this worsens any inequality since monkeys that do badly end up shunning the task and its reward altogether, while the one that’s better off continues to be rewarded.

It may be that in a more realistic situation, monkeys that were ripped off could just leave and find other social partners, but only further research would tell.

Reference: van Wolkenten, M., Brosnan, S., de Waal, F. (2007). Inequity responses of monkeys modified by effort.Proceedings of the National Academy of Sciences, 104(47), 18854-18859.


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How to lose friends and alienate people by disrupting the brain

Oscar Wilde once said, “One can survive everything nowadays, except death, and live down anything, except a good reputation.” All well and witty, but for those of us who aren’t Victorian cads, reputation matters. It’s the bedrock that our social lives are built upon and people go to great lengths to build and maintain a solid one. A new study shows that our ability to do this involves the right half of our brain, and particularly an area called the lateral prefrontal cortex (PFC).

Disrupting the neurons in this area hampers a person’s ability to build a reputation while playing psychological games. They can still act selflessly, and they still know what they would need to do in order to garner good repute. They just find it difficult to resist the temptation to cheat, even though they know it will cost them their status among other players. Most of us know from personal experience that knowing what’s best for us is very different to acting on it – this study shows that this distinction exists at a neurological level.

Daria Knoch and colleages from the University of Basel focused on the PFC because it’s a key player in mental abilities that centre around self-control, including planning, decision-making and attention. These “executive processes” must surely play a key part in building a good reputation, for doing so typically involves a cost (such as time, effort or money) and a tradeoff between current and future benefits. For example, I might return a dropped wallet so that I’ll be seen in a good light, rather than pocket the cash and be done with it.

Other studies have compared neural activity in the PFC with people’s behaviour, but these brain scans can’t tell us whether the activity caused the behaviour or vice versa.  To do that, Knoch decided to take the PFC out of the game entirely. She used a technique called transcranial magnetic stimulation (TMS) where rapidly changing magnetic fields induce weak electric currents in specific parts of the brain the suppresses the buzz of the local neurons.

After going through this treatment, 87 volunteers played a “trust game” in pairs. In each round, an investor decides how many points (out of 10) to donate to a trustee. These are quadrupled, and the trustee decides how many of these to give back.  Some games were played anonymously and the investors never knew about the trustees’ decisions. With the investor in the dark, the trustees had no strategic incentive to return any points at all, and doing so is a measure of their selflessness.


In other games, the trustee’s last three decisions were public knowledge and that brought reputation into play. The trustee could achieve a good reputation by equalising the shares or paying back even more, or shatter their credibility by paying back nothing or very little. The latter option nets big rewards in the short-term, but the trustees needed to override their immediate self-interests for bigger gains in the long-term. And if the initial investment is greater, the trustees also need more self-control for the amount they have to return is greater.

This worked in practice. If trustees always equalised their payoffs, they had a 71% chance of being trusted with the full 10 point investment; if they gave nothing back, this probability fell to 6%. In the long run, those who always cooperated until the last hurdle earned 43% more points than constant cheats. And trustees cared about their reputation – when the game was anonymous, they send back around a quarter of their investment, but if their status was on the line, they gave back 44%. 

TMS didn’t affect the trustees’ choices in the anonymous games, or in the reputational ones if investments were low. But when big points were on the table, things changed. Targeting their right lateral PFC significantly reduced their likelihood of paying back the investors to 30%, down from 41% for a fake round of TMS, or 48% for a burst directed to the left brain.

In fact, the trustees whose right brains were targeted with TMS behaved in exactly the same way regardless of whether the investors knew about their choices or not. Anonymous or transparent, it didn’t matter – even though their reputation was on the line, their behaviour didn’t change.


Knoch also found that the TMS didn’t affect the volunteers’ perceptions of fairness. They knew that hoarding large investments was unfair, and they knew that if they did so, the investors would probably give them fewer points in the future. They knew all of this – they just couldn’t put it into useful practice. They couldn’t put off the short-term gains of having lots of points, in favour of earning even more in the long-term – a basic skill when it comes to building a reputation.

Of course, the lateral PFC is probably only part of the story. It’s fashionable to try and discover the brain region “responsible for” different abilities or behaviours, but the PFC is no more the brain’s “reputation centre” than a steering wheel is a car’s “driving centre” – clearly other parts like the wheels, axle and engine help too. Knoch (more so than many neuroscientists), is aware of this and says, ” In highly complex processes such as reputation formation, brain areas do not act in isolation, but rather must work together as a network.” Her next goal is to investigate how different parts of the brain interact when reputation is on the line.

Reference: PNAS 10.1073/pnas.0911619106

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Cooperating bacteria are vulnerable to slackers

As a species, we hate cheaters. Just last month, I blogged about our innate desire to punish unfair play but it’s a sad fact that cheaters are universal. Any attempt to cooperate for a common good creates windows of opportunity for slackers. Even bacteria colonies have their own layabouts. Recently, two new studies have found that some bacteria reap the benefits of communal living while contributing nothing in return.

Cooperating bacteria are vulnerable to slackersBacteria may not strike you as expert co-operators but at high concentrations, they pull together to build microscopic ‘cities’ called biofilms, where millions of individuals live among a slimy framework that they themselves secrete. These communities provide protection from antibiotics, among other benefits, and they require cooperation to build.

This only happens once a colony reaches a certain size. One individual can’t build a biofilm on its own so it pays for a colony to be able to measure its own size. To do this, they use a method ‘quorum sensing’, where individuals send out signalling molecules in the presence of their own kind.

When another bacterium receives this signal, it sends out some of its own, so that once a population reaches a certain density, it sets off a chain reaction of communication that floods the area with chemical messages.

These messages provide orders that tell the bacteria to secrete a wide range of proteins and chemicals. Some are necessary for building biofilms, others allow them to infect hosts, others make their movements easier and yet others break down potential sources of food. They tell bacteria to start behaving cooperatively and also when it’s worth doing so.

Steve Diggle and colleagues from the Universities of Nottingham and Edinburgh have found that bacterial slackers can exploit this system. They studied an opportunistic species called Pseudomonas aeruginosa, that preys on the weak. It’s a major cause of hospital infections, setting up shop in burn victims, cystic fibrosis patients and others with weakened immune systems.

The bug’s success hinges on quorum sensing, which allows it to thrive in limited environments by cooperating. When Diggle cultured the bacteria in a nutritionally poor liquid containing only proteins as the only food source, they grew happily nonetheless. That’s because the chemical signals exchanged as part of quorum sensing also triggers the release of proteases, enzymes that can digest proteins.

Pseudomonas aeruginosaDiggle then tested two mutant forms of P.aeruginosa that are commonly found in nature. The first – the ‘signal-negative’ version – can’t produce signalling molecules but can react to them. It obeys orders to secretes the right chemicals but never passes the orders along. As such, it doesn’t secrete enough proteases and grows poorly in a protein-only solution. However, it picked up the pace if it was artificially doused in signalling molecules to cope with its deficiency.

The ‘signal-blind’ mutant is even more of a slacker – it can’t react to signals at all, so it doesn’t help or communicate. This strain also grew poorly in the protein-only liquid and only matched the normal strain if it was artificially given extra proteases.

If quorum sensing provides such obvious benefits, you might expect all bacteria to take part. But there is a catch – it’s also quite draining. Making signals and proteases takes up energy, and when Diggle placed the different strains in a rich, nutritious solution, the mutants vastly outgrew the normal strain. With an abundance of easily digested food, it was every bacterium for itself and the mutants, that weren’t busy making expensive signals and proteases, did better.

Quorum sensing may be good for the group, but for each individual bacterium, it pays to sit back and let your peers do all the work. Diggle demonstrated this by allowed the normal and mutant strains to compete in the protein-only liquid, in a real-time experiment in evolution. The mutant strains were engineered with luminescent genes so that the team could track their growth by the light they gave off.

At first, the signal-blind cheats made up just 1% of the population but after 2 days, they accounted for 45% of it. In a separate culture, the proportion of signal-negative cheats went from 3% to 66%. Among P.aeruginosa, cheaters can indeed prosper and then some – they outgrew their cooperating cousins by 60 to 80 times.

In a separate study with the same species, Kelsi Sandoz from Oregon State University found that cheaters evolve naturally. Like Diggle, she grew a normal strain of P.aeruginosa in conditions where they needed to make proteases to survive.

After 12 days, she managed to isolate specific colonies that weren’t pulling their weight. All of them had developed mutations in a key gene involved in quorum sensing which meant that they were only secreting a very small amount of protease. Within 20 days, these cheats made up 40% of the cultures. 

Cheaters prosper

Why then, do any individuals bother cooperating at all? If slacking is so profitable, why doesn’t everyone do it? For a start, cheating pays fewer dividends if you do it at the expense of your relatives who share your genes. This is especially true for bacteria colonies that reproduce asexually and spawn genetically identical clones.

In this case, helping your neighbour pays off because it ensures that your genes are passed on to the next generation. Diggle found that when the bacteria were very closely related to each other, mutants were much less likely to gain a foothold in a population of co-operators.

There is another reason though, and it’s probably more important. Both studies found that as the proportion of cheaters increased, their growth rate dropped because the value of cheating diminished.

Slackers only prosper if they can cadge of a hard-working population – if every bacterium took the easy way, there would be no proteases and no food. Sandoz found that when this happened, the entire population suffered and overall growth plummeted. If there were enough cheaters, the signalling molecules became too dilute, the ‘quorum’ fell apart and the population crashed.

However, Sandoz also found that the bacteria usually evolved compensatory measures in time to stop this from happening. During her study, she saw that many cheaters developed further mutations that restored protease production. Faced with a sinking ship, there was strong evolutionary pressure for them to swap sides and start cooperating again.


Diggle, S., Griffin, A., Campbell, G., West , S. (2007). Cooperation and conflict in quorum-sensing bacterial populations. Nature, 450, 411-415.

Sandoz, K., Mitzimberg, S., Schuster, M. (2007). Social cheating in Pseudomonas aeruginosa quorum sensing. . Proceedings of the National Academy of Sciences, 104(40), 15876-15881.

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Genes affect our likelihood to punish unfair play

This article is reposted from the old WordPress incarnation of Not Exactly Rocket Science. The blog is on holiday until the start of October, when I’ll return with fresh material.

As a species, we value fair play. We’re like it so much that we’re willing to eschew material gains in order to punish cheaters who behave unjustly. Psychological games have set these maxims in stone, but new research shows us that this sense of justice is, to a large extent, influenced by our genes.

When it comes to demonstating our innate preference for fair play, psychologists turn to the ‘Ultimatum Game‘, where two players bargain over a pot of money. The ‘proposer’ suggests how the money should be divided and the ‘receiver’ can accept of refuse the deal. If they refuse, neither player gets anything and there is no room for negotiation. In a completely rational setting, the proposer should offer the receiver as little as possible, and the receiver should take it – after all, a very little money is better than none at all.

Of course, that’s not what happens. Receivers typically abhor unfair offers and would rather that both parties receive no money than accept a patronisingly tiny amount. Across most Western countries, proposers usually offer the receivers something between 40% and 50% of the takings. Any offers under 10% are almost always rejected.

The uniformity of responses across Western countries suggests that culture has a strong effect on how people play the game, but until now, no one had looked to see how strongly genes asserted their influence. Bjorn Wallace and colleagues from the Stockholm School of Economics decided to do just that, and they used the classic experiment for working out heritability – the twin study.


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Paper wasps – caring mothers evolved into selfless workers

This article is reposted from the old WordPress incarnation of Not Exactly Rocket Science. The blog is on holiday until the start of October, when I’ll return with fresh material.

Imagine that one day, you make a pact with your brother or sister, vowing to never have children of your own and instead spend your life raising theirs. You’ll agree to do the grocery shopping, cook for them, clean their rooms and bathe them, until you die.

A paper wasp foundress begins the task of building a hive.That seems like a crazy plan, but it’s one that some of the most successful animals in the world – the social insects – have adopted. It’s called ‘eusociality‘ and it’s a puzzle for evolutionary biologists. Why should an animal forgo the chance to reproduce in order to help rear its siblings and their young?

The strategy makes sense if you share enough genes with your close relatives. In helping them, you indirectly ensure the transmission of your own genetic material. But even if this explains the existence of eusociality, it doesn’t explain how such an extreme form of co-operation evolved.

Now, Amy Toth and colleages at the University of Illinois have found a clue in the genes of the paper wasp, Polistes metricus, which suggests that their altruistic actions evolved from motherly behaviour.

Scientists have suggested this theory before as a possible origin for eusociality. It doesn’t take a great leap of imagination to picture how a group of wasp sisters living together and communally looking after their young could become a society in which only a few individuals reproduce and the others share the care. But until now, that theory had never been tested at a genetic level.

Truly eusocial insects like honeybees have physically distinct castes with strongly segregated jobs. The queen’s sole purpose is to lay eggs and she never takes on the menial foraging and brood care of the smaller workers.

Paper wasps are only halfway down the road to eusociality, which makes them an ideal choice for studying its evolution. They have different castes, but they all look much the same and their castes are far less strictly segregated. The roles that individuals perform depends on the age of the colony and fall into four different groups.

Foundresses, females that establish new colonies and care for young as well as laying eggs. After creating the first generation, these females become queens and focus solely on laying more eggs. Their daughters, the workers, take up the task of caring for their new siblings to the exclusion of their own reproduction. Later on in the colony’s life, the queen gives birth to gynes, that neither care for young or lay eggs – their job is to mate with males and become foundresses themselves in the following spring.

Paper wasps join forces to build a nestToth decided to look at the patterns of gene activity in these four groups. She reasoned that if the workers’ altruistic actions had originated in maternal care, they would share similar genetic profile to the foundresses, the only other group that also cares for young.

Complex behaviours like caring for young and foraging were hardly going to be the province of a single gene. Toth needed a way to analyse a myriad of genes across the entire wasp genome – a genome that has not yet been fully sequenced.

To overcome this problem, the team took a streamlined approach. They specifically looked at genes that were strongly activated in the brains of 87 wasps from all four groups. Using a powerful sequencing technique from the 454 Life Sciences company, they identified almost 400,000 stretches of relevant DNA across their genomes.

Toth matched these hits to the genome of the closely related honeybee (Apis mellifera), which was fully sequenced last year. They focused on 32 genes, whose honeybee counterparts are involved in worker behaviour. Even though bees and paper wasps started down different evolutionary roads some 100 million years ago, the proteins encoded by these genes have remained very similar.

As predicted, Toth found that the activation pattern of these 32 genes was closest in workers and foundresses, and were distinct from those of queens and gynes, which don’t practice maternal care. Regardless of whether the wasps focused on their siblings or their young, their caring behaviour was governed by similar sets of genes, supporting the idea that eusociality evolved from maternal care.

Today, the vast majority of solitary wasps provide food for their helpless young, often in grisly or murderous ways. During the course of evolution, the twin behaviours of egg-laying and maternal care started to separate.

In the intermediary paper wasps, the behaviours are separated in time – the foundresses practice both at first and then focus on just one when they turn into queens. As this happens, their brain undergo dramatic changes and different sets of genes are switched on.

The final stage down this evolutionary path is the one seen in true eusocial wasps, where egg-laying and maternal care are separated in space, in the bodies of queens and workers.

The study also shows that many evolutionary problems can be addressed without the complete sequence of an animal’s genome. For every full genome we have, we can use next-generation sequencing technology to compare it to the partially sequenced genes of closely-related species, just as the bee and wasp proved here.

Reference: toth, Varala, Newman, Miguez, Hutchison, Willoughby, Simons, Egholm, Hunt, Hudson & Robinson. 2007. Wasp gene expression supports and evolutionary link between maternal behaviour and eusociality. Sceince

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