Testosterone! Aggression!

Could low testosterone be what made us modern humans?!

The hormone, associated with both biologically male characteristics and aggression, makes skulls grow those heavy brows we associate with our evolutionary ancestors…The key, the researchers claim, could be found in the feminized skulls that became more prevalent around that time. A rounder face in humans isassociated with less testosterone, and less testosterone can mean better cooperation between individuals. Less head clubbing and more community building, basically.

The paper is pretty heavy on speculation – human skulls have gotten less masculinized over time, though obviously that could be for reasons beyond changing levels of testosterone; something downstream or different altogether could be the cause. But I think this is a good time to review some things about testosterone. From Sapolsky’s The Trouble With Testosterone:

Okay, suppose you note a correlation between levels of aggression and levels of testosterone among these normal males. This could be because (a) testosterone elevates aggression; (b) aggression elevates testosterone secretion; (c) neither causes the other. There’s a huge bias to assume option a, while b is the answer. Study after study has shown that when you examine testosterone levels when males are first placed together in the social group, testosterone levels predict nothing about who is going to be aggressive. The subsequent behavioral differences drive the hormonal changes, rather than the other way around…

Yes, it’s going to be on the final, and it’s one of the more subtle points in endocrinology—what is referred to as a hormone having a “permissive effect.” Remove someone’s testes and, as noted, the frequency of aggressive behavior is likely to plummet. Reinstate precastration levels of testosterone by injecting that hormone, and precastration levels of aggression typically return. Fair enough. Now this time, castrate an individual and restore testosterone levels to only 20 percent of normal and . . . amazingly, normal precastration levels of aggression come back. Castrate and now generate twice the testosterone levels from before castration—and the same level of aggressive behavior returns. You need some testosterone around for normal aggressive behavior—zero levels after castration, and down it usually goes; quadruple it (the sort of range generated in weight lifters abusing anabolic steroids), and aggression typically increases. But anywhere from roughly 20 percent of normal to twice normal and it’s all the same; the brain can’t distinguish among this wide range of basically normal values…

Round up some male monkeys…number 3, for example, can pass his day throwing around his weight with numbers 4 and 5, ripping off their monkey chow, forcing them to relinquish the best spots to sit in, but, at the same time, remembering to deal with numbers 1 and 2 with shit-eating obsequiousness…Take that third monkey and inject him with testosterone.  Inject a ton of it in him…And no surprise, when you check the behavioral data, it turns out that he will probably be participating in more aggressive actions than before…Is he now raining aggressive terror on any and all in the group, frothing in an androgenic glaze of indiscriminate violence?  Not at all.  He’s still judiciously kowtowing to numbers 1 and 2 but has become a total bastard to numbers 4 and 5. This is critical: testosterone isn’t causing aggression, it’s exaggerating the aggression that’s already there.

And don’t forget that the “effect of testosterone” can be culturally contingent:

However, subjects who believed that they received testosterone—regardless of whether they actually received it or not—behaved much more unfairly than those who believed that they were treated with placebo. Thus, the folk hypothesis seems to generate a strong negative association between subjects’ beliefs and the fairness of their offers, even though testosterone administration actually causes a substantial increase in the frequency of fair bargaining offers in our experiment.

And, revisiting this somewhat-embarrassing early post of mine about the role of testosterone in social domination (and physical displays associated with it):

However, if you go ahead and stick a needle in the other birds – the ones that didn’t get the testosterone injection – they also had an increase in testosterone level.  In fact, they had the same level of testosterone in their bloodstream as those with the injection.  But these birds had smaller combs [dominance displays]! …So testosterone levels per se don’t mediate dominance.  It’s also not at all clear whether testosterone is needed for aggression…Dark-eyed juncos will defend their territory by squawking at unwanted intruders…But at least for [some] behaviors, testosterone surges aren’t associated with aggressive social behavior.

Testosterone and social aggression

Testosterone will probably always be linked in people’s minds with aggressive behaviors, but its role in behavior is a source of controversy.  Why it rises when it does – and whether it causes aggression or merely responds to it – is not clear, although recent studies that directly inject testosterone into an animal has begun to clarify things a little.  A little.  But we still don’t know whether increases in testosterone cause increases in aggression.

Birds are very territorial animals that have evolved signals to prevent the need from actually fighting over territory (too much).  Some of them have pretty fun ways to show off, too; the male red grouse grows a comb over its eyes almost like a rooster, with larger combs being a way to show off dominance.  Don’t want to mess with that guy, he’s got a really large red thing on his head!  In many animals, dominance and aggressive behaviors go hand-in-hand.  If your fellow red grouse is going to beat you silly over and over again, you’ll probably let him do what he wants.  But if aggression and testosterone are somehow related, and if aggression and dominance are somehow related, does testosterone control dominance?  We can start to answer this question by looking at red grouse comb size.

It turns out that testosterone kind of controls comb size.  When Vergara and Martinez-Padilla injected birds with testosterone, over time they grew larger combs, just as one would presuppose.  However, if you go ahead and stick a needle in the other birds – the ones that didn’t get the testosterone injection – they also had an increase in testosterone level.  In fact, they had the same level of testosterone in their bloodstream as those with the injection.  But these birds had smaller combs!  The lack of relationship between testosterone level and comb size (ie, dominance) shows that it doesn’t control displays of dominance.  Perhaps it’s a measure of one individual’s testosterone versus the population’s?  Or perhaps the birds who had increased testosterone started a feedback cycle in the population where everybody needed more testosterone, but only those birds with the initial increase got the rewards from it?

So testosterone levels per se don’t mediate (historical) dominance.  It’s also not at all clear whether testosterone is needed for aggression.  Take the example of another bird, the dark-eyed junco.  Dark-eyed juncos will defend their territory by squawking at unwanted intruders.  Some researchers like to go out and mess with these poor juncos by placing a little toy bird equipped with a speaker in the junco territory.  The result is a lot of swooping in, harassment and yelling at the decoys, in a futile attempt to make them go away.  And if you measure junco testosterone levels before and after introducing the fake bird, you’ll see the levels increase.  Now, if you go and put out just a speaker box – but not a fake bird – the local birds will still come out and and harass the speaker; they’ll approach close up and scream and throw a general fit.  But their testosterone levels don’t increase!  When Rosvall et al examined the baseline testosterone levels, though, it seems like these levels are (very weakly) correlated with how quickly the birds will quickly they’ll approach the speaker and how close they’ll get.  They can see this in a PCA analysis, but don’t mention the raw data so I don’t know if that’s significant; and it certainly isn’t for number of songs.  Just looking at the data makes me worry about outliers but who knows?  But at least for certain behaviors, testosterone surges aren’t associated with aggressive social behavior.

Aggressive behaviors clearly do not all require increases in testosterone, but perhaps it depends on the type of behavior.  In the Rosvall study, maybe the birds did not think they were in physical danger because they could never actually see the darn thing.  And maybe testosterone isn’t the right thing to measure at all!  Androgen and oestregon receptors regulate other genes after being activated by testosterone, and aromatase is a step required for testosterone to be useful.  If you measure the mRNA levels of these genes, they are significantly correlated with aggressive behaviors.  So the behavioral difference between individuals may not be the result of higher levels of the hormone itself, but levels of the receptor.  And since this is measured so quickly after the birds are observed to react to the false bird for six minutes (a mean of 4.5 minutes after the behavior), it seems unlikely that the transcript levels are changing because of the fake bird, but rather was there beforehand.

What role does testosterone play in aggression?  It doesn’t seem to be causing it, because aggressive behaviors happen without changes in testosterone.  It certainly doesn’t control dominance, because you can get the same increase in testosterone levels in birds with different levels of dominance displays.  But this doesn’t mean that testosterone is unrelated to aggression, because it could be receptor level that causes differences in behavior; one bird can do more with the testosterone it has than another.

Here’s my current working hypothesis: testosterone is more important as a way to prepare the body for the effects of aggression than for aggression itself.  Look at the studies above – the researchers only detected surges in testosterone level when it seemed like the bird saw another bird – when it thought it would need to be prepared to fight.  And since testosterone’s effect seems to be changes in gene transcription rather than direct depolarization of neural membranes, it is the role of the receptors to prepare the brain to respond to a different level of environmental aggression.  But hey, I’m new to the testosterone field so we’ll see what I think next week 😉

References

Rosvall KA, Bergeon Burns CM, Barske J, Goodson JL, Schlinger BA, Sengelaub DR, & Ketterson ED (2012). Neural sensitivity to sex steroids predicts individual differences in aggression: implications for behavioural evolution. Proceedings. Biological sciences / The Royal Society, 279 (1742), 3547-55 PMID: 22673360

Vergara P, & Martínez-Padilla J (2012). Social context decouples the relationship between a sexual ornament and testosterone levels in a male wild bird. Hormones and behavior PMID: 22841824

KA Rosvall, DG Reichard, SM Ferguson, DJ Whittaker, & ED Ketterson (2012). Robust behavioral effects of song playback in the absence of testosterone or
corticosterone release Hormones and Behavior DOI: 10.1016/j.yhbeh.2012.07.009

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Investigating Wall Street through neuroscience

There’s a good collection of links on metafilter about decision-making in finance, and includes a bit about John Coates, who investigates the role of testosterone and cortisone in decision-making.  This article from Businessweek about how this ex-trader got interested in neuroscience:

The more Coates learned, the more he became convinced that traders were, as he put it, “a clinical population.” The stimuli of a trading floor triggered chemical changes in people’s brains, emotionally whipsawing them. During the tech bubble, he recalls, “People just really slipped their moorings: They were motor-mouthing, they weren’t sleeping, they were on this high. It was initially reasonable to assume it was cocaine, but I don’t know many traders that do that. There was something going on, it was just incredibly noticeable, and I realized that at times I had also felt that way.”

I think this is true not just about financial traders, but about anyone in a high-stress occupation during good times.  I know I get this way when everything is working perfectly in lab.

With enough victories, though, testosterone can reach levels that make the animal act foolishly. He picks fights he can’t win, tries to claim too much territory, and roams around in the open where predators might pick him off. A human being on a trading floor might take massive, risky bets on the strength of the American housing market or on U.S. corporate bonds. One of the traders Coates studied went on a hot streak, making twice his average profit-and-loss ratio for five days in a row. By the end of it his testosterone levels had risen 80 percent. If Coates had followed the trader long enough, he believes, there was a good chance “he would be irrationally exuberant and blow up.”

For losers, the effect is the opposite: The stress and worry of losing money cause the endocrine system to flood the body with cortisol, which makes people afraid to take even favorable bets. In the wake of a financial crisis, it’s not just Wall Street traders who suffer from this, but anyone making decisions about money, whether it’s an employer who balks at hiring or a bank officer leery of making a loan even when the Federal Reserve is offering her free money to do so.

Obviously, testosterone and cortisol have wider effects, and the effects they have are contingent on a lot of other environmental variables.  Studying testosterone and cortisol on the trading floor will elucidate just one (important!) aspect of their function.

Papers of the week, 6/10 – 6/17

Joint attention, social-cognition, and recognition memory in adults

“The early emerging capacity for Joint Attention (JA), or socially coordinated visual attention, is thought to be integral to the development of social-cognition in childhood…We tested the validity of the differentiation of IJA [initiating joint attention] and RJA [responding to joint attention] in our paradigm in two studies of picture recognition memory in undergraduate students. Study 1 indicated that young adults correctly identified more pictures they had previously viewed in an IJA condition (67%) than in a RJA (58%) condition, η2 = 0.57. Study 2 controlled for IJA and RJA stimulus viewing time differences, and replicated the findings of Study 1.”

The biological bases of conformity

“We review the relevant literature considering the causation, function, history, and ontogeny of conformity, and describe a computer-based experiment on human subjects that we carried out in order to resolve ambiguities. We found that only when many demonstrators were available and subjects were uncertain was subject behavior conformist. A further analysis found that the underlying response to social information alone was generally conformist. Thus, our data are consistent with a conformist use of social information, but as subjects’ behavior is the result of both social and asocial influences, the resultant behavior may not be conformist.”

Effects of age, sex, and  neuropsychological performance on financial decision-making

“Results indicated that Older participants significantly outperformed Younger participants on a multiple-choice test of acquired financial knowledge. However, after controlling for such pre-existing knowledge, several age effects were observed. For example, Older participants were more likely to make immediate investment decisions, whereas Younger participants exhibited a preference for delaying decision-making pending additional information…In terms of sex differences, Older Males were more likely to pay credit card bills and utilize savings accounts than were Older Females. Multiple positive correlations were observed between Older participants’ financial decision-making ability and performance on neuropsychological measures of non-verbal intellect and executive functioning. Lastly, the ability to justify one’s financial decisions declined with age, among the Older participants.”

Efficient coding and the neural representation of value

“Although normative theories of choice have outlined the theoretical structure of these valuations, recent experiments have begun to reveal how value is instantiated in the activity of neurons and neural circuits. Here, we review the various forms of value coding that have been observed in different brain systems and examine the implications of these value representations for both neural circuits and behavior. In particular, we focus on emerging evidence that value coding in a number of brain areas is context dependent, varying as a function of both the current choice set and previously experienced values. Similar contextual modulation occurs widely in the sensory system, and efficient coding principles derived in the sensory domain suggest a new framework for understanding the neural coding of value.”  By Paul Glimcher, so of course you should read this.

Orbitofrontal cortical activity during repeated free choice

“OFC neurons encode important features of the choice behavior. These features include activity selective for exceptionally long runs of a given choice (stay selectivity) as well as activity selective for switches between choices (switch selectivity). These results suggest that OFC neural activity, in addition to encoding subjective values on a long timescale that is sensitive to satiety, also encodes a signal that fluctuates on a shorter timescale and thereby reflects some of the statistically improbable aspects of free-choice behavior.”

Physical competition increases testosterone among Amazonian forager-horticulturalists: a test of the ‘challenge-hypothesis’

“We tested whether the Tsimane, pathogenically stressed forager-horticulturalists of the Bolivian Amazon, would express acute T increases in response to physical competition…Linear mixed-effects models were used to establish that T increased significantly immediately following competition (β = 0.23, p < 0.001), remaining high 1 h later (β = 0.09, p = 0.007); equivalent to 30.1 and 15.5 per cent increases in T, respectively. We did not find larger increases in T among winners (p = 0.412), although T increases were positively associated with self-rated performance (β = 9.07, p = 0.004). These results suggest that despite lower levels of T than US males, Tsimane males exhibit acute increases in T at the same relative magnitude reported by studies in industrialized settings, with larger increases in T for those who report better individual performance.”  I covered this partly in my introduction to testosterone earlier in the week.

Individual plastic responses by males to rivals reveal mismatches between behavior and fitness outcomes

“Behaviour (mating duration) was remarkably sensitive to the level of competition and fully reversible, suggesting that substantial costs arise from the incorrect expression of even highly flexible behaviour. However, changes in mating duration matched fitness outcomes (offspring number) only in scenarios in which males experienced zero then high competition. Following the removal of competition, mating duration, but not offspring production, decreased to below control levels. This indicates that the benefit of increasing reproductive investment when encountering rivals may exceed that of decreasing investment when rivals disappear.”

The dynamics of coordinated group hunting and collective information transfer among schooling prey

“Predators were found to frequently form coordinated hunting groups, with up to five individuals attacking in line formation. Attacks were associated with increased fragmentation and irregularities in the spatial structure of prey groups, features that inhibit collective information transfer among prey. Prey group fragmentation, likely facilitated by predator line formation, increased (estimated) per capita risk of prey, provided prey schools were maintained below a threshold size of approximately 2 m2.”

Aging-related increases in behavioral variability: relations to losses of dopamine D1 receptors

“Increasing ISDs [intraindividual standard deviation] were associated with increasing age and diminished D1 binding in several brain regions (anterior cingulate gyrus, dorsolateral prefrontal cortex, and parietal cortex) for the interference, but not control, condition. Analyses of partial associations indicate that the association between age and IIV in the interference condition was linked to D1 receptor losses in task-relevant brain regions. These findings suggest that dysfunctional DA modulation may contribute to increased variability in cognitive performance among older adults.”

Testosterone: cooperation or competition?

In my last post, I gave an introduction into a couple aspects of testosterone: how it rises and falls, and how it affects decision-making.  I forgot to mention that, neurally, it appears to act substantially through three areas of the brain: the nucleus accumbens, amygdala, and orbitofrontal cortex (OFC).  The nucleus accumbens is a major dopaminergic center, the molecule generally seen as responsible for decision-making and action selection.  Amygdala, as we all know, mediates fear and emotional responses (generally…).  The more interesting area is OFC, which is typically thought to be an area that is involved in self-control.  I couldn’t find many papers that I really wanted to talk about on this aspect of testosterone, so I’ll wait for another day to delve into it.

So let’s look at how testosterone affects social behavior.  In what must have been the Most Fun Study To Participate In Ever, Oxford et al. asked subjects to play Unreal Tournament in teams.  When men are playing the game against other teams, the players that contribute the most show increases in testosterone.  However, when men are forced to play against their own teammates, they have decreased testosterone!  And the subjects who contributed the most to a win showed the largest change.

But if testosterone is increasing during competition against other groups, what affect might it have on social behavior?  Eisenegger et al. used the ultimatum game, where a pair of subjects are given a small amount of money.  One of the subjects then makes an offer of part of the money to the other subject, who can either accept the money or reject it; when the second subject rejects it, neither subject gets any money.  It is well-known that people will generally reject unfair offers.  Following the framework of past studies, female subjects were given either testosterone or placebo and asked to play the game.  They found that subjects who were given testosterone made larger offers than placebo subjects.  Although the authors try to make the claim that this is because being turned down is a ‘status concern’, it could just be because they think that they will make more money that way?  Maybe this is risk-aversion?  I should also note that different study found that subjects given testosterone and asked to be the second subject will also reject more unfair offers.  But the most interesting part about the study is that the subjects who thought that they had received testosterone made much smaller offers – presumably because they already thought they knew what testosterone should do, even though they were wrong!

In a response, van Honk et al. tried using a different game.  He used the ‘public good game’ which is where all players receive 3 moneys, and can contribute some to the public good.  When at least two players contribute to the public good, all players receive 6 moneys.  Note that in this version of the game, with the contribution rate of other players, the expected value is highest when you contribute to the public good.  And subject who have testosterone administered to them give more often to the public good!  So it’s not clear whether they are being more pro-social or just smarter…

The interesting thing about this paper, though is that they also measured the ratio of ring to index finger.  This is a measure of prenatal testosterone exposure, although it doesn’t predict adult levels of testosterone.  Those with a high 2D:4D ratio (ie, those with low maternal testosterone, figure left) are most likely to contribute to the common good, and the less prenatal testosterone, the more of an effect the testosterone given to subjects has.  van Honk et al. suggest that prenatal exposure may change something physically to make subjects more receptive to testosterone, whether it is metabolism or receptor level.  They had found a similar result in a previous study which showed that suspicious individuals didn’t become any more suspicious from testosterone, but the most trusting individuals became much more suspicious when given testosterone (figure right).

The data is a bit hard to interpret, but the general feeling now is that testosterone can act as either a pro-social hormone, or one that makes you more concerned about your social status (egocentrism?).  Although I’d love to give a good clean explanation here, I cannot come up with – and have not yet found – a good unifying framework that unites all the social effects of testosterone .

References

Eisenegger, C., Naef, M., Snozzi, R., Heinrichs, M., & Fehr, E. (2010). Prejudice and truth about the effect of testosterone on human bargaining behaviour Nature, 463 (7279), 356-359 DOI: 10.1038/nature08711

van Honk, J., Montoya, E., Bos, P., van Vugt, M., & Terburg, D. (2012). New evidence on testosterone and cooperation Nature, 485 (7399) DOI: 10.1038/nature11136

Oxford, J., Ponzi, D., & Geary, D. (2010). Hormonal responses differ when playing violent video games against an ingroup and outgroup Evolution and Human Behavior, 31 (3), 201-209 DOI: 10.1016/j.evolhumbehav.2009.07.002

Testosterone: an introduction

Today I want to talk about testosterone.  I had intended for this post to be a short one, but then I kept digging and digging and, well, it turns out that testosterone is a pretty interesting subject.  What I’m going to do today is give a bit of a review on it, and talk about the effect that it has on personal decision-making.  In the next post, I’ll relate testosterone to social decision-making.

Testosterone does a lot of things, and most of them seem to revolve around social status effects – although that simplification may end up making things more confusing.  What testosterone does do is, over time, enhance muscle performance and redistribute immune resources to prepare for injury (remember my post on social status and healing?).  Several things cause increased levels of testosterone, with competition and sex being foremost among them.  This isn’t just physically aggressive competition, either; chess will give you bursts of testosterone.  Historically, calorically stressed populations will see seasonal variations in testosterone levels when men need to suppress aggressive behaviors during child rearing, or get ready for fighting and healing from fighting for status and mates.  But don’t think that testosterone directly will make an individual wildly aggressive.  As Robert Sapolsky notes in The Trouble With Testosterone

Round up some male monkeys…number 3, for example, can pass his day throwing around his weight with numbers 4 and 5, ripping off their monkey chow, forcing them to relinquish the best spots to sit in, but, at the same time, remembering to deal with numbers 1 and 2 with shit-eating obsequiousness…Take that third monkey and inject him with testosterone.  Inject a ton of it in him…And no surprise, when you check the behavioral data, it turns out that he will probably be participating in more aggressive actions than before…Is he now raining aggressive terror on any and all in the group, frothing in an androgenic glaze of indiscriminate violence?  Not at all.  He’s still judiciously kowtowing to numbers 1 and 2 but has become a total bastard to numbers 4 and 5.

Males in industrialized societies, however, don’t have any caloric needs causing them to suppress testosterone.  In order to examine testosterone in a more ‘natural’ setting, Trumble et al. turned to ‘pathogenically stressed forager-horticulturalists of the Bolivia Amazon’ (ie, poor and hungry people of the Amazon) who do indeed have lower testosterone levels.  These tribal people were brought together and organized into teams for a soccer tournament.  They found that testosterone was higher after the game in all participants, whether they won or lost.  But pay attention to this: the individuals who thought they performed better had larger increases in testosterone immediately following the game.  An hour later?  The difference disappeared.

It’s this type of effect of confidence that caused (Wright et al. 2012) to examine the effect of testosterone on group collaboration.  They put pairs of female subjects in a room and gave them a visual task where they had to decide which of two sets of bars were brighter.  When the subjects disagreed, they were allowed to discuss it and then one of the pair had to make a decision based on the joint beliefs.  But some of those subjects were given testosterone injections!  And the ones who were given testosterone were more likely to trust their own injections.  Although this seems like a nice result, we don’t really know what is happening during the verbal discussion.  Does the testosteroned subject just verbally browbeat the other subject?  What’s going on there?

So testosterone may act to reinforce egocentric behavior.  How about risk-taking?  That’s a little more complicated.  In a gambling game – with the subject only competing against themselves – (Stanton et al. 2011) showed that high risk taking in a gambling task is associated with high testosterone, but the same group later showed that (Stanton et al. 2011 [2]) there is actually a U-shaped curve.  Subjects with intermediate levels of testosterone are actually risk-averse, while low and high levels are risk-neutral.  This is an important point, and something to keep in mind; often we are not sampling the whole distribution of testosterone levels, and the simple ‘high’ versus ‘low’ dichotomy may be misleading.

So we have seen that testosterone probably goes up and down based on caloric resources and in the presence of competition and mates (or mating).  We’ll conclude next time with a discussion of how testosterone affects sociality, and how things are even more complicated than high/low or U-shaped.

References

Trumble, B., Cummings, D., von Rueden, C., O’Connor, K., Smith, E., Gurven, M., & Kaplan, H. (2012). Physical competition increases testosterone among Amazonian forager-horticulturalists: a test of the ‘challenge hypothesis’ Proceedings of the Royal Society B: Biological Sciences, 279 (1739), 2907-2912 DOI: 10.1098/rspb.2012.0455
Wright, N., Bahrami, B., Johnson, E., Di Malta, G., Rees, G., Frith, C., & Dolan, R. (2012). Testosterone disrupts human collaboration by increasing egocentric choices Proceedings of the Royal Society B: Biological Sciences, 279 (1736), 2275-2280 DOI: 10.1098/rspb.2011.2523

Stanton, S., Liening, S., & Schultheiss, O. (2011). Testosterone is positively associated with risk taking in the Iowa Gambling Task Hormones and Behavior, 59 (2), 252-256 DOI: 10.1016/j.yhbeh.2010.12.003

Stanton, S., Mullette-Gillman, O., McLaurin, R., Kuhn, C., LaBar, K., Platt, M., & Huettel, S. (2011). Low- and High-Testosterone Individuals Exhibit Decreased Aversion to Economic Risk Psychological Science, 22 (4), 447-453 DOI: 10.1177/0956797611401752
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How social status determines your health

You wouldn’t think how people perceive you could directly affect your health, would you?  Luckily, science is here to save the day and to tell you, you’re wrong.  A pair of papers published in PNAS in the last month have investigated the interaction between social status and health, and the findings compliment each other rather nicely.

The authors of the first paper tracked baboons over thirty years and made a compelling figure (show at right) showing that low-ranking males are sick more often, and for longer, than high-ranking males.  It has been theorized that the biological effects of high social status – testosterone, high glucocorticoids, high reproductive effort – would reduce health.  After all, if these high-ranking male baboons have to spend all their time and energy making sweet monkey love, there wouldn’t be much energy left over for healing, would there?  However, they found no evidence for this.  In fact, alpha males seemed to heal faster than anyone else.

The authors of the other paper examined the different genes that are regulated in low- and high-status female rhesus monkeys.  The previous paper tracked male animals in the wild, and this one kept female animals in the laboratory.  The authors took blood samples from the monkeys to profile gene expression – though only after dominance order had been established.  It would have been great had they done so before hand to see if there were genes predictive of social status, or if expression changed in any appreciable way.  But no matter.  By using a PCA analysis – basically, finding the combinations of genes that most explained the variance in the behavior – they found that the first principle component was predictive of social status.  This tells us that gene expression is intertwined with your social status.

Almost 1000 genes were found to be associated with rank, 535 of which were more enriched in high-ranking individuals and 452 of which were more enriched in low-ranking individuals.  So a lot is going on in there and getting changed!  Consistent with the previous paper, there was the largest cluster of enriched genes were immune-related.  This included interleukin signaling, T-cell activation, and chemokine/cytokine inflammation.  Perhaps, then, the reason high-ranking males heal faster is because the right immune-related genes were enriched.  But that leaves the question, why should that be so?

The paper included an excel spreadsheet of the enriched genes which can be a bit fun to scroll through; following on something I touched on in the previous post, I expected to find dopamine receptor genes enriched in one of the conditions but I didn’t.  Something to keep in mind.

I guess the moral of story here is: socializing is dangerous.  Or maybe not socializing is dangerous.  Either way, watch out!

References

Archie, E., Altmann, J., & Alberts, S. (2012). Social status predicts wound healing in wild baboons Proceedings of the National Academy of Sciences, 109 (23), 9017-9022 DOI: 10.1073/pnas.1206391109

Tung J, Barreiro LB, Johnson ZP, Hansen KD, Michopoulos V, Toufexis D, Michelini K, Wilson ME, & Gilad Y (2012). Social environment is associated with gene regulatory variation in the rhesus macaque immune system. Proceedings of the National Academy of Sciences of the United States of America, 109 (17), 6490-5 PMID: 22493251