Skepticism Surrounding Sex

It’s a basic truth of the human condition that everybody lies; the only variable is about what

One of my favorite shows from years ago was House; a show centered around a brilliant but troubled doctor who frequently discovers the causes of his patient’s ailments through discerning what they – or others – are lying about. This outlook on people appears to be correct, at least in spirit. Because it is sometimes beneficial for us that other people are made to believe things that are false, communication is often less than honest. This dishonesty entails things like outright lies, lies by omission, or stretching the truth in various directions and placing it in different lights. Of course, people don’t just lie because deceiving others is usually beneficial. Deception – much like honesty – is only adaptive to the extent that people do reproductively-relevant things with it. Convincing your spouse that you had an affair when you didn’t is dishonest for sure, but probably not a very useful thing to do; deceiving someone about what you had for breakfast is probably fairly neutral (minus the costs you might incur from coming to be known as a liar). As such, we wouldn’t expect selection to have shaped our psychology to lie about all topics with equal frequency. Instead, we should expect that people tend to preferentially lie about particular topics in predictable ways.

Lies like, “This college degree will open so many doors for you in life”

The corollary idea to that point concerns skepticism. Distrusting the honesty of communications can protect against harmful deceptions, but it also runs the risk of failing to act on accurate and beneficial information. There are costs and benefits to skepticism as there are to deception. Just as we shouldn’t expect people to be dishonest about all topics equally often, then, we shouldn’t expect people to be equally skeptical of all the information they receive either. This is point I’ve talked about before with regards to our reasoning abilities, whereby information agreeable to our particular interests tends to be accepted less critically, while disagreeable information is scrutinized much more intensely.

This line of thought was recently applied to the mating domain in a paper by Walsh, Millar, & Westfall (2016). Humans face a number of challenges when it comes to attracting sexual partners typically centered around obtaining the highest quality of partner(s) one can (metaphorically) afford, relative to what one offers to others. What determines the quality of partners, however, is frequently context specific: what makes a good short-term partner might differ from what makes a good long-term partner and – critically, as far as the current research is concerned – the traits that make good male partners for women are not the same as those that make good females partner for men. Because women and men face some different adaptive challenges when it comes to mating, we should expect that they would also preferentially lie (or exaggerate) to the opposite sex about those traits that the other sex values the most. In turn, we should also expect that each sex is skeptical of different claims, as this skepticism should reflect the costs associated with making poor reproductive decisions on the basis of bad information.

In case that sounds too abstract, consider a simple example: women face a greater obligate cost when it comes to pregnancy than men do. As far as men are concerned, their role in reproduction could end at ejaculation (which it does, for many species). By contrast, women would be burdened with months of gestation (during which they cannot get pregnant again), as well as years of breastfeeding prior to modern advancements (during which they also usually can’t get pregnant). Each child could take years of a woman’s already limited reproductive lifespan, whereas the man has lost a few minutes. In order to ease those burdens, women often seek male partners who will stick around and invest in them and their children. Men who are willing to invest in children should thus prove to be more attractive long-term partners for women than those who are unwilling. However, a man’s willingness to stick around needs to be assessed by a woman in advance of knowing what his behavior will actually be. This might lead to men exaggerating or lie about their willingness to invest, so as to encourage women to mate with them. Women, in turn, should be preferentially skeptical of such claims, as being wrong about a man’s willingness to invest is costly indeed. The situation should be reversed for traits that men value in their partners more than women.

Figure 1: What men most often value in a woman

Three such traits for both men and women were examined by Walsh et al (2016). In their study, eight scenarios depicting a hypothetical email exchange between a man and woman who had never met were displayed to approximately 230 (mostly female; 165) heterosexual undergraduate students. For the women, these emails depicted a man messaging a woman; for men, it was a woman messaging a man. The purpose of these emails was described as the person sending them looking to begin a long-term intimate relationship with the recipient. Each of these emails described various facets of the sender, which could be broadly classified as either relevant primarily to female mating interests, relevant to male interests, or neutral. In terms of female interests, the sender described their luxurious lifestyle (cuing wealth), their desire to settle down (commitment), or how much they enjoy interacting with children (child investment). In terms of male interests, the sender talked about having a toned body (cuing physical attractiveness), their openness sexually (availability/receptivity), or their youth (fertility and mate value). In the two neutral scenarios, the sender either described their interest in stargazing or board games.

Finally, the participants were asked to rate (on a 1-5 scale) how deceitful they thought the sender was, whether they believed the sender or not, and how skeptical they were of the claims in the message. These three scores were summed for each participant to create a composite score of believability for each of the messages (the lower the score, the less believable it was rated as being). Those scores were then averaged across the female-relevant items (wealth, commitment, and childcare), the male-relevant items (attractiveness, youth, and availability), and the control conditions. (Participants also answered questions about whether the recipient should respond and how much they personally liked the sender. No statistical analyses are reported on those measures, however, so I’m going to assume nothing of note turned up)

The results showed that, as expected, the control items were believed more readily (M = 11.20) than the male (M = 9.85) or female (9.6) relevant items. This makes sense, inasmuch as believing lies about stargazing or interests in board games aren’t particularly costly for either sex in most cases, so there’s little reason to lie about them (and thus little reason to doubt them); by contrast, messages about one’s desirability as a partner have real payoffs, and so are treated more cautiously. However, an important interaction with the sex of the participant was uncovered as well: female participants were more skeptical on the female-relevant items (M = about 9.2) than males were (M = 10.6); similarly, males were more likely to be skeptical in male-relevant conditions  (M = 9.5) than females were (M = 10). Further, the scores for the individual items all showed evidence of the same sex kinds of differences in skepticism. No sex difference emerged for the control condition, also as expected.

In sum, then – while these differences were relatively small in magnitude – men tended to be more skeptical of claims that, if falsely believed, were costlier for them than women, and women tended to be more skeptical of claims that, if falsely believed, were costlier for them than men. This is a similar pattern to that found in the reasoning domain, where evidence that agrees with one’s position is accepted more readily than evidence that disagrees with it.

“How could it possibly be true if it disagrees with my opinion?”

The authors make a very interesting point towards the end of their paper about how their results could be viewed as inconsistent with the hypothesis that men have a bias to over-perceived women’s sexual interest. After all, if men are over-perceiving such interest in the first place, why would they be skeptical about claims of sexual receptivity? It is possible, of course, that men tend to over-perceive such availability in general and are also skeptical of claims about its degree (e.g., they could still be manipulated by signals intentionally sent by females and so are skeptical, but still over-perceive ambiguous or less-overt cues), but another explanation jumps out at me that is consistent with the theme of this research: perhaps when asked to self-report about their own sexual interest, women aren’t being entirely accurate (consciously or otherwise). This explanation would fit well with the fact that men and women tend to perceive a similar level of sexual interest in other women. Then again, perhaps I only see that evidence as consistent because I don’t think men, as a group, should be expected to have such a bias, and that’s biasing my skepticism in turn.

References: Walsh, M., Millar, M., & Westfall, S. (2016). The effects of gender and cost on suspicion in initial courtship communications. Evolutionary Psychological Science, DOI 10.1007/s40806-016-0062-8

Musings About Police Violence

I was going to write about something else today (the finding from a meta-analysis that artificial surveillance cues do not appear to appreciably increase generosity; the effects fail to reliably replicate), but I decided to switch topics up to something more topical: police violence. My goal today is not to provide answers to this on-going public debate – I certainly don’t know enough about the topic to consider myself an expert – but rather to try and add some clarity to certain features of the discussions surrounding the matter, and hopefully help people think about it in somewhat unusual ways. If you expect me to take a specific stance on the issue, be that one that agrees or disagrees with your own, I’m going to disappoint you. That alone may upset some people who take anything other than definite agreement as a sign of aggression against them, but there isn’t much to do about that. That said, the discussion about police violence itself is a large and complex one, the scope of which far exceeds the length constraints of my usual posts. Accordingly, I wanted to limit my thoughts on the matter to two main domains: important questions worth answering, and addressing the matter of why many people find the “Black Lives Matter” hashtag needlessly divisive.

Which I’m sure will receive a warm, measured response

First, let’s jump into the matter of important questions. One of the questions I’ve never seen explicitly raised in the context of these discussions – let alone answered – is the following: How many people should we expect to get killed by police each year? There is a gut response that many would no doubt have to that question: zero. Surely someone getting killed is a tragedy that we should seek to avoid at all times, regardless of the situation; at best, it’s a regrettable state of affairs that sometimes occurs because the alternative is worse. While zero might be the ideal world outcome, this question is asking more about the world that we find ourselves in now. Even if you don’t particularly like the expectation that police will kill people from time to time, we need to have some expectation of just how often it will happen to put the violence in context. These killings, of course, include a variety of scenarios: there are those in which the police justifiably kill someone (usually in defense of themselves or others), those cases where the police mistakenly kill someone (usually when an error of judgment occurs regarding the need for defense, such as when someone has a toy gun), and those cases where police maliciously kill someone (the killing is aggressive, rather than defensive, in nature). How are we to go about generating these expectations?

One popular method seems to be comparisons of police shootings cross-nationally. The picture that results from such analyses appears to suggest that US police shoot people much more frequently than police from other modern countries. For instance, The Guardian claims that Canadian police shoot and kill about 25 people a year, as compared with approximately 1,000 such shootings in the US in 2015. Assuming those numbers are correct, once we correct for population size (the US is about ten-times more populated than Canada), we can see that US police shoot and kill about four-times as many people. That sure seems like a lot, probably because it is a lot. We want to do more than note that there is a difference, however; we want to see whether that difference violates our expectations, and to do that, we need to be clear about why our expectations were generated. If, for example, police in the US face threatening situations more often than Canadian police, this is a relevant piece of information.

To begin engaging with that idea, we might consider how many police die each year in the line of duty, cross-nationally as well. In Canada, the number for 2015 looks to be three; adjusting for population size again, we would generate an expectation of 30 US police officer deaths if all else were equal. All else is apparently not equal, however, as the actual number for 2015 in the US is about 130. Not only are the US police killing four-times as often as their Canadian counterparts, then, but they’re also dying at approximately the same rate as well. That said, those numbers include factors other than homicides, and so that too should be taken into account when generating our expectations (in Canada, the number of police shot was 2 in 2015, compared to 40 in the US, which is still twice as high as one would expect from population size

. There are also other methods of killing police, such as the 50 US police killed by bombs or cars; 0 for Canada). Given the prevalence of firearm ownership in the US, it might not be too surprising that the rates of violence between police and citizens – as well as between citizens and other citizens – looks substantially different than in other countries. There are other facts which might adjust our expectations up or down. For instance, while the US has 10 times the population of Canada, the number of police per 100,000 people (376) is different than that of Canada (202). How we should adjust the numbers to make a comparison based on population differences, then, is a matter worth thinking about (should we expect ratio of police officers to citizens per se to increase the number of them that are shot, or is population the better metric?). Also worth mentioning is that the general homicide rate per 100,000 people is quite a bit higher in the US (3.9) than in Canada (1.4). While this list of considerations is very clearly not exhaustive, I hope it generates some thoughts regarding the importance of figuring out what our expectations are, as well as why. The numbers of shootings alone are going to be useless without good context. 

Factor 10: Perceived silliness of uniforms

The second question concerns bias within these shootings in the US. In addition to our expectations for the number of people being killed each year by police, we also want to generate some expectations for the demographics of those who are shot: what should we expect the demographics of those being killed by police to be? Before we can claim there is a bias in the shooting data, we need to both have a sense for what our expectation in that regard are, why they are such, and only then can we look at how those expectations are violated.

The obvious benchmark that many people would begin would be the demographics of the US as a whole. We might expect, for instance, that the victims of police violence in the US are 63% white, 12% black, about 50% male, and so on, mirroring the population of the country. Some data I’ve come across suggests that this is not the case, however, with approximately 50% of the victims being white and 26% being black. Now that we know the demographics don’t match up as we’d expect from population alone, we want to know why. One tempting answer that many people fall back on is that police are racially motivated: after all, if black people make up 12% of the population but represent 26% of police killings, this might mean police specifically target black suspects. Then again, males make up about 50% of the population but represent about 96% of police killings. While one could similarly posit that police have a wide-spread hatred of men and seek to harm them, that seems unlikely. A better explanation for more of the variation is that men are behaving differently than women: less compliant, more aggressive, or something along those lines. After all, the only reasons you’d expect police shootings to match population demographics perfectly would be either if police shot people at random (they don’t) or police shot people based on some nonrandom factors that did not differ between groups of people (which also seems unlikely).

One such factor that we might use to adjust our expectations would be crime rates in general; perhaps violent crime in particular, as that class likely generates a greater need for officers to defend themselves. In that respect, men tend to commit much more crime than women, which likely begins to explain why men are also shot by police more often. Along those lines, there are also rather stark differences between racial groups when it comes to involvement in criminal activity: while 12% of the US population is black, approximately 40% of the prison population is, suggesting differences in patterns of offending. While some might claim that prison percentage too is due to racial discrimination against blacks, the arrest records tend to agree with victim reports, suggesting a real differential involvement in criminal activity.

That said, criminal activity per se shouldn’t get one shot by police. When generating our expectations, we also might want to consider factors such as whether people resist arrest or otherwise threaten the officers in some way. In testing theories of racial biases, we would want to consider whether officers of different races are more or less likely to shoot citizens of various demographics (that is to ask whether, say, black officers are any more or less likely to shoot black civilians than white officers are. I could have sworn I’ve seen data on that before but cannot appear to locate it at this time. What I did find, however, was a case-matched study of NYPD officers, reporting that black officers were about three times as likely to discharge their weapon as white officers at the scene, spanning 106 shooting and about 300 officers; Ridgeway, 2016). Again, while this is not a comprehensive list of things to think about, factors like these should help us generate our expectations about what the demographics of police shooting victims should look like, and it is only from there that we can begin to make claims about racial biases in the data.

It’s hard to be surprised at the outcomes sometimes

Regardless of where you settled on your answer to the above expectations, I suspect that many people would nonetheless want to reduce those numbers, if possible. Fewer people getting killed by police is a good thing most of the time. So how do we want to go about seeing that outcome achieved? Some have harnessed the “Black Lives Matter” (BLM) hashtag and suggest that police (and other) violence should be addressed via a focus on, and reductions in, explicit, and presumably implicit, racism (I think; finding an outline of the goals of the movement proves a bit difficult).

One common response to this hashtag has been the notion that BLM is needlessly divisive, suggesting instead that “All Lives Matter” (ALM) be used as a more appropriate description. In turn, the reply to ALM by BLM is that the lack of focus on black people is an attempt to turn a blind eye to problems viewed a disproportionately affecting black populations. The ALM idea was recently criticized by the writer Maddox, who compared the ALM expression to a person who, went confronted with the idea of “supporting the troops,” suggests that we should support all people (the latter being a notion that receives quite a bit of support, in fact). This line of argument is not unique to Maddox, of course, and I wanted to address that thought briefly to show why I don’t think it works particularly well here.

First, I would agree that “support the troops” slogan is met with a much lower degree of resistance than “black lives matter,” at least as far as I’ve seen. So why this differential response? As I see it, the reason this comparison breaks down involves the zero-sum nature of each issue: if you spend $5 to buy a “support the troops” ribbon magnet to attach to your car, that money is usually intended to be designated towards military-related causes. Now, importantly, money that is spent relieving the problems in the military domain cannot be spent elsewhere. That $5 cannot be given to both military causes and also given to cancer research and also given to teachers and also used to repave roads, and so on. There need to be trade-offs in whom you support in that case. However, if you want to address the problem of police violence against civilians, it seems that tactics which effectively reduce violence against black populations should also be able to reduce violence against non-black populations, such as use-of-force training or body cameras.

The problems, essentially, have a very high degree of overlap and, in terms of the raw numbers, many more non-black people are killed by police than black ones. If we can alleviate both at the same time with the same methods, focusing on one group seems needless. It is only those killings of civilians that effect black populations (24% of the shootings) and are also driven predominately or wholly by racism (an unknown percent of that 24%) that could be effectively addressed by a myopic focus on the race of the person being killed per se. I suspect that many people have independently figured that out – consciously or otherwise – and so dislike the specific attention drawn to race. While a focus on race might be useful for virtue signaling, I don’t think it will be very productive in actually reducing police violence.

“Look at how high my horse is!”

To summarize, to meaningfully talk about police violence, we need to articulate our expectations about how much of it we should see, as well as its shape. It makes no sense to talk about how violence is biased against one group or another until those benchmarks have been established (this logic applies to all discussions of bias in data, regardless of topic). None of this is intended to be me telling you how much or what kind of violence to expect; I’m by no means in possession of the necessary expertise. Regardless, if one wants to reduce police violence, inclusive solutions are likely going to be superior to exclusive ones, as a large degree of overlap in causes likely exists between cases, and solving the problems of one group will help solve the problems of another. There is merit to addressing specific problems as well – as that overlap is certainly less than 100% – but in doing so, it is important to not lose sight of the commonalities and distance those who might otherwise be your allies. 

References: Ridgeway, G. (2016). Officer risk factors associated with police shootings: a matched case-control study. Statistics & Public Policy, 3, 1-6.

Why Women Are More Depressed Than Men

Women are more likely to be depressed than men; about twice as likely here in the US, as I have been told. It’s an interesting finding, to be sure, and making sense of it poses a fun little mystery (as making sense of many things tends to). We don’t just want to know that women are more depressed than men; we also want to know why women are more depressed. So what are the causes of this difference? The Mayo Clinic floats a few explanations, noting that this sex difference appears to emerge around puberty. As such, many of the explanations they put forth center around the problems that women (but not men) might face when undergoing that transitional period in their life. These include things like increased pressure to achieve in school, conflict with parents, gender confusion, PMS, and pregnancy-related factors. They also include ever-popular suggestions such as societal biases that harm women. Now I suspect these are quite consistent with the answers you would get if queried your average Joe or Jane on the street as to why they think women are more depressed. People recognize that depression often appears to follow negative life events and stressors, and so they look for proximate conditions that they believe (accurately or not) disproportionately affect women.

Boys don’t have to figure out how to use tampons; therefore less depression

While that seems to be a reasonable strategy, it produces results that aren’t entirely satisfying. First, it seems unlikely that women face that much more stress and negative life events than men do (twice as much?) and, secondly, it doesn’t do much to help us understand individual variation. Lots of people face negative life events, but lots of them also don’t end up spiraling into depression. As I noted above, our understanding of the facts related to depression can be bolstered by answering the why questions. In this case, the focus many people have is on answering the proximate whys rather than the ultimate ones. Specifically, we want to know why people respond to these negative life events with depression in the first place; what adaptive function depression might have. Though depression reactions appear completely normal to most, perhaps owing to their regularity, we need to make that normality strange. If, for example, you imagine a new mouse mother facing the stresses of caring for her young in a hostile world, a postpartum depression on her part might seem counterproductive: faced with the challenges of surviving and caring for her offspring, what adaptive value would depressive symptoms have? How would low energy, a lack of interest in important everyday activities, and perhaps even suicidal ideation help make her situation better? If anything, they would seem to disincline her from taking care of these important tasks, leaving her and her dependent offspring worse off. This strangeness, of course, wouldn’t just exist in mice; it should be just as strange when we see it in humans.

The most compelling adaptive account of depression I’ve read (Hagen, 2003) suggests that the ultimate why of depression focuses on social bargaining. I’ve written about it before, but the gist of the idea is as follows: if I’m facing adversity that I am unlikely to be able to solve alone, one strategy for overcoming that problem is to recruit others in the world to help me. However, those other people aren’t always forthcoming with the investment I desire. If others aren’t responding to my needs adequately, it would behoove me to try and alter their behavior so as to encourage them to increase their investment in me. Depression, in this view, is adapted to do just that. The psychological mechanisms governing depression work to, essentially, place the depressed individual on a social strike. When workers are unable to effectively encourage an increased investment from their employers (perhaps in the form of pay or benefits), they will occasionally refuse to work at all until their conditions improve. While this is indeed costly for the workers, it is also costly for the employer, and it might be beneficial for the employer to cave to the demands rather than continue to face the costs of not having people work. Depression shows a number of parallels to this kind of behavior, where people withdraw from the social world – taking with them the benefits they provided to others – until other people increase their investment in the depressed individual to help see them through a tough period.

Going on strike (or, more generally, withdrawing from cooperative relationships), of course, is only one means of getting other people to increase their investment in you; another potential strategy is violence. If someone is enacting behaviors that show they don’t value me enough, I might respond with aggressive behaviors to get them to alter that valuation. Two classic examples of this could be shooting someone in self-defense or a loan-shark breaking a delinquent client’s legs. Indeed, this is precisely the type of function that Sell et al (2009) proposed that anger has: if others aren’t giving me my due, anger motivates me to take actions that could recalibrate their concern for my welfare. This leaves us with two strategies – depression and anger – that can both solve the same type of problem. The question arises, then, as to which strategy will be the most effective for a given individual and their particular circumstances. This raises a rather interesting possibility: it is possible that the sex difference in depression exists because the anger strategy is more effective for men, whereas the depression strategy is more effective for women (rather than, say, because women face more adversity than men). This would be consistent with the sex difference in depression arising around puberty as well, since this is when sex differences in strength also begin to emerge. In other words, both men and women have to solve similar social problems; they just go about it in different ways. 

“An answer that doesn’t depend on wide-spread sexism? How boring…”

Crucially, this explanation should also be able to account for within-sex differences as well: while men are more able to successfully enact physical aggression than women, not all men will be successful in that regard since not all men possess the necessary formidability. The male who is 5’5″ and 130 pounds soaking wet likely won’t win against his taller, heavier, and stronger counterparts in a fight. As such, men who are relatively weak might preferentially make use of the depression strategy, since picking fights they probably won’t win is a bad idea, while those who are on the stronger side might instead make use of anger more readily. Thankfully, a new paper by Hagen & Rosenstrom (2016) examines this very issue; at least part of it. The researchers sought to test whether upper-body strength would negatively predict depression scores, controlling for a number of other, related variables.

To do so, they accessed data from the National Health and Nutrition Examination Survey (NHANES), netting a little over 4,000 subjects ranging in age from 18-60. As a proxy for upper-body strength, the authors made use of the measures subjects had provided of their hand-grip strength. The participants had also filled out questions concerning their depression, height and weight, socioeconomic status, white blood cell count (to proxy health), and physical disabilities. The researchers predicted that: (1) depression should negatively correlate with grip-strength, controlling for age and sex, (2) that relationship should be stronger for men than women, and (3) that the relationship would persist after controlling for physical health. About 9% of the sample qualified as depressed and, as expected, women were more likely to report depression than men by about 1.7 times. Sex, on its own, was a good predictor of depression (in their regression, ß = 0.74).

When grip-strength was added into the statistical model, however, the effect of sex dropped into the non-significant range (ß = 0.03), while strength possessed good predictive value (ß = -1.04). In support of the first hypothesis, then, increased upper-body strength did indeed negatively correlate with depression scores, removing the effect of sex almost entirely. In fact, once grip strength was controlled for, men were actually slightly more likely to report depression than women (though this didn’t appear to be significant). Prediction 2 was not supported, however, with their being no significant interaction between sex and grip-strength on measures of depression. This effect persisted even when controlling for socioeconomic status, age, anthropomorphic, and hormonal variables. However, physical disability did attenuate the relationship between strength and depression quite a bit, which is understandable in light of the fact that physically-disabled individuals likely have their formidability compromised, even if they have stronger upper bodies (an example being a man in a wheelchair having good grip strength, but still not being much use in a fight). It is worth mentioning that the relationship between strength and depression appeared to grow larger over time; the authors suggest this might have something to do with older individuals having more opportunities to test their strength against others, which sounds plausible enough. 

Also worth noting is that when depression scores were replaced with suicidal ideation, the predicted sex-by-strength interaction did emerge, such that men with greater strength reported being less suicidal, while women with greater strength reported being more suicidal (the latter portion of which is curious and not predicted). Given that men succeed at committing suicide more often than women, this relationship is probably worth further examination.  

“Not today, crippling existential dread”

Taken together with findings from Sell et al (2009) – where men, but not women, who possessed greater strength reported being quicker to anger and more successful in physical conflicts – the emerging picture is one in which women tend to (not consciously) “use” depression as a means social bargaining because it tends to work better for them than anger, whereas the reverse holds true for men. To be clear, both anger and depression are triggered by adversity, but those events interact with an individual’s condition and their social environment in determining the precise response. As the authors note, the picture is likely to be a dynamic one; not one that’s as simple as “more strength = less depression” across the board. Of course, other factors that co-vary with physical strength and health – like attractiveness – could also being playing a roll in the relationship with depression, but since such matters aren’t spoken to directly by the data, the extent and nature of those other factors is speculative.

What I find very persuasive about this adaptive hypothesis, however – in addition to the reported data – is that many existing theories of depression would not make the predictions tested by Hagen & Rosenstrom (2016) in the first place. For example, those who claim something like, “depressed people perceive the world more accurately” would be at a bit of a loss to explain why those who perceive the world more accurately also seem to have lower upper-body strength (they might also want to explain why depressed people don’t perceive the world more accurately, either). A plausible adaptive hypothesis, on the other hand, is useful for guiding our search for, and understanding of, the proximate causes of depression.

References: Hagen, E.H. (2003). The bargaining model of depression. In: Genetic and Cultural Evolution of Cooperation, P. Hammerstein (ed.). MIT Press, 95-123

Hagen, E. & Rosenstrom, T. (2016). Explain the sex difference in depression with a unified bargaining model of anger and depression. Evolution, Medicine, & Public Health, 117-132

Sell, A., Tooby, J., & Cosmides, L. (2009). Formidability and the logic of human anger. Proceedings of the National Academy of Sciences, 106, 15073-78.