Educational attainment is associated with unconditional helping behaviour

Educational attainment is associated with unconditional helping behaviour. Grace Westlake,  David Coall and Cyril C. Grueter. Evolutionary Human Sciences, Volume 12019 , e15. Dec 11 2019. https://doi.org/10.1017/ehs.2019.16

Abstract: Altruism is a universal human trait, but little is known about its within-population variation. Socio-economic status (SES) has been found to positively impact altruism, but the specific socio-economic variables behind this relationship have remained elusive. This study aimed to determine which facets of SES predict altruism using a lost letter paradigm and a novel lost letter method. Six hundred letters (half dropped on the pavement, half sent to residential addresses) were distributed in 20 suburbs of Perth (Australia) differing in socio-economic variables. Letters distributed in high-SES neighbourhoods were more likely to be returned than letters distributed in low-SES neighbourhoods. Educational attainment and occupation status were the specific socio-economic variables underlying this association, while economic resources and crime rate were not associated with the likelihood of a letter being returned. These results suggest that altruism blossoms in neighbourhoods that are populated with highly educated individuals working in high-status jobs. The relationship between education and prosocial inclinations may be mediated by cognitive ability, self-control and high levels of socialization. Having experienced sustained exposure to norm-abiding models, more educated people may also be better at internalizing cultural norms of helping behaviour, thus creating a more altruistic environment where they reside.

Discussion

The current study revealed substantial and systematic variation in altruistic tendencies across urban suburbs of different socio-economic characteristics. This variance appears to be conditioned by the education and occupation level of residents in the suburb, and was not consistently influenced by economic resources or crime rate.

Socio-economic status

Both the original lost letter experiment and the novel, modified letterbox method provided support for the hypothesis that area-level SES (measured by IRSAD) was positively correlated with helping behaviour. This result is in consensus with previous research reporting a link between SES and letter return rates in the lost letter experiment (Brown and Reed 1982; Grueter et al. 2016; Holland et al. 2012; Nettle et al. 2011; Silva and Mace 2014). Multiple drivers underlying the lower levels of prosociality in low-SES areas are conceivable, for example time constraints resulting from the need to make ends meet (Holland et al. 2012; Lynam et al. 2000), lower sense of control over the environment (e.g. Gallo et al. 2005) or – more mundanely – higher tolerance of litter rates (see Khatib et al. 2007).

However, the above finding is in conflict with studies by Piff et al. (2010, 2012) who found upper-class individuals to be less prosocial and more unethical in measures such as willingness to cooperate with a game partner and attitudes on charitable donations. Côté et al. (2015) recently showed that higher-income individuals are not more selfish across the board but a tendency to be less generous emerges only under conditions of high economic inequality. Piff et al. (2012) suggested that – among others – this was because high-SES people have abundant resources to deal with the downstream costs of unethical behaviour (e.g. money for a speeding fine), while lower-SES individuals may need to be more careful as they incur greater relative consequences for social deviation. Piff et al. (2012) proposed that low-SES individuals have a greater interest in the wellbeing of others because it affects their ability to draw resources from them. Thus lower-class individuals’ willingness to engage in altruistic behaviour can be seen a function of economic interdependence. Relatedly, Amir et al. (2018) invoked an uncertainty management framework to account for the greater prosociality observed in economic games among economically deprived children. In this framework, cooperation with social partners and prosociality reflect the adaptive internalization of a risk-mitigating strategy in the face of uncertain returns associated with early life deprivation.

The difference between the results of Piff et al. (2010, 2012) and lost letter-based studies could stem from the fact that the former analysed variation at the individual level, whereas the latter examined neighbourhood-level differences (Holland et al. 2012). Perhaps high-SES neighbourhoods foster altruism, yet within any one neighbourhood, the poorer individuals are more altruistic than the wealthier ones (Holland et al. 2012).

Another reason for the difference between our findings and those of Piff et al. (2010, 2012) could be that their experiments measured altruistic tendencies towards people in general (no specific group) in a range of environments. In contrast, the lost letter experiment used in this study measured altruistic behaviours within one's own ‘home environment’ (their suburb or street) towards (presumably) members of their own group; individuals who encountered lost letters would have probably assumed that the letter was distributed by a resident when walking through the area.

Lastly, as suggested by Holland et al. (2012), the experiments used to analyse altruism by Piff et al. (2010, 2012) may be more competitive than the small, cooperative task of returning a lost letter, resulting in different behaviours. For example, upper-class individuals may be more likely than lower-class individuals to return a letter in a cooperative task, but they may also be more likely to deceive another player in a laboratory-based economic game. Future studies should incorporate multiple measures of altruistic behaviour (such as those used by Piff et al. 2010, 2012) to determine if the patterns seen in this study are unique to the lost letter experiment.

Socio-economic variables

The principal aim of this study was to disentangle the association of different socio-economic variables with altruistic behaviour. Crime was predicted to reduce altruism by lowering trust, but a suburb's crime rate was largely unrelated to the expression of prosocial behaviour. Only in the model where economic resources were included did crime rate become significant. Therefore, the variance explained by crime rate may be accounted for by other SES characteristics such as education, which was included in all other models. It may also be that crime has a threshold effect and needs to be at a certain rate before it begins to affect peoples’ altruistic tendencies. The suburbs analysed in this study may not have had sufficient crime rates to demonstrate this effect.

Economic resources, as a characteristic of SES, also did not have a significant effect on letter return rate. This suggests that demographic factors such as individuals’ assets, house prices and average household income are not related to suburb-level altruistic behaviours. Holland et al. (2012) suggested that low-SES individuals may be too preoccupied with meeting their individual needs to be willing to spend time helping others. This hypothesis suggests that individuals with more economic resources will be better equipped to meet their needs and will, therefore, have more time and energy to engage altruistically with others. The current dataset does not rule out the hypothesis that, when time itself is not a limited resource, people may be more willing to engage in prosocial behaviours. It should be noted that the location of this study does not experience widespread socio-economic deprivation where a great proportion of individuals do not have access to basic needs such as clean water, food and housing. Perhaps this hypothesis may be relevant in more economically deprived contexts where economic resources may influence altruism.

IEO was found to be significantly associated with whether a letter would be returned or not. The effect of IRSAD on letter return rate may largely be explained by the composite variables that it shares with IEO. This finding suggests that the component of SES that affects a neighbourhood's letter return rate is the education and occupation status of individuals in that suburb. To our knowledge this is a novel finding that has not been reported previously. However, along a similar vein, there is one recent study which documented a positive correlation between historical rates of primary education and civic honesty (Cohn et al. 2019). Because IEO incorporates both education and occupation variables, we cannot distinguish whether both, or just one or the other, of these variables influence altruistic behaviour within a suburb.

This study has isolated education and occupation as the likely leading socio-economic variables behind the often found relationship between SES and letter return rates. However, we still do not fully understand the mechanism behind this link. We do not know what aspects of education and occupation status may lead individuals within a suburb to behave more altruistically. Education and occupation may also be associated with a third variable that may be driving the patterns in the results. For example, individuals who have achieved a high education level or who are in high-status jobs are more likely to possess greater cognitive abilities (Schmidt and Hunter 2004; Strenze 2007). It may thus be possible that the significant effect of IEO on letter return rate reflects an underlying effect of cognitive ability. Previous studies in behavioural economics have shown a link between cognitive ability and altruistic behaviour (Jones 2008). Cognitive ability has been found to be negatively correlated with a preference for immediate rewards and impulsivity (Jensen 1998; de Wit et al. 2007). Cognition in more stressful and harsh environments associated with lower SES may be focused more on temporal discounting and lower levels of self-control (Coall et al. 2012; Frankenhuis et al. 2016; Mullainathan and Shafir 2013; Sheehy-Skeffington and Rea 2017), conditions that discourage altruistic behaviour (Osiński et al. 2017). It is important to note that extrapolating from SES at a relatively crude area-level analysis to individual differences in cognitive ability (and thus altruism) is problematic. The relationship between these factors and education is probably more complex, and dependent on many factors (e.g. opportunity, value placed on education, etc.).

An evolutionary mechanism underlying the finding that education and occupation are the primary drivers of prosocial behaviour may be that educated people have more opportunities to learn, to be taught and to receive feedback and thus are more likely to adopt or maintain cultural norms of prosociality. Individual behavioural decisions (as to whether to act proscocially) are influenced by expectations of the behaviour of others in the local social environment (Bichierri and Xiao 2009). In turn, these decisions also influence the local social environment, by conveying to others information about local norms of cooperative behaviour (cf. Schroeder et al. 2014).

Modified lost-letter experiment

The novel letterbox method incorporated in this study featured a significantly lower return rate compared with the original pavement method. Both methods, however, exhibited the same SES patterns in the data. One explanation for the differing return rates is that ignoring a letterbox letter ends all future possibilities for the letter to be returned, but pavement letters may be picked up by someone else (however, one could also argue that receiving a lost letter in someone's letterbox increases the recipient's pressure to do something about it). Another possible explanation is that returning a pavement letter may incur a smaller cost in terms of time and effort, because an individual could already be heading in the direction of a post box, compared who a letterbox recipient who would have to make a separate trip. Furthermore, individuals may behave more prosocially when encountering pavement letters because there is a chance that their actions are being observed by bystanders and influence their reputation (sensu Raihani and Bshary, 2015). Additionally, there remains the possibility that letterbox recipients may have uncertainty about what to do with the wrongly addressed letter.

The similar socio-economic patterns found in the results from both methods suggest that the letterbox method may be a useful alternative to the pavement method as it may not be as susceptible to some of the potentially confounding variables such as non-residents encountering the letters and differing rates of pedestrian foot traffic in different neighbourhoods. The letterbox method has additional advantages that should be considered for future experiments. The method enables the letter to be distributed at any time, unlike pavement letters, which must be distributed on wind- and rain-free evenings. The letterbox method also eliminates the lengthy process of distributing letters by hand and provides easy access to remote or rural areas. Additionally, the letterbox method allows for more letters to be distributed in any given area, owing to the elimination of the possibility of individuals encountering multiple letters while walking through a neighbourhood.

Cultural group selection and prosociality

Cultural group selection theory posits that groups whose members engage altruistically with each other are more successful in intergroup competition than groups whose members lack such locally stable cooperative cultural norms (Henrich 2004; Richerson et al. 2016). However, the great variation in altruistic tendencies exhibited by the different suburbs suggests that cultural group selection does not function at the scale of the city. Instead, we may see large populations splitting up into smaller sub-groups with their own set of altruistic norms which may be the result of cultural group selection operating on this smaller scale. However, since populations of city suburbs are not natural groups but administrative divisions, it is unclear if these are subject to cultural group selection. Alternatively, variation in altruism attributed to different cultural norms could in fact reflect individual adaptations to different environments with varying levels of socio-economic harshness (Mace and Silva 2016).

Higher neuroticism was associated with more cognitive failures (momentary lapses in memory, perception, or action), whereas Conscientiousness and Agreeableness were associated with fewer failures

Five Factor Model personality traits and subjective cognitive failures. Angelina R. Sutin et al. Personality and Individual Differences, Volume 155, 1 March 2020, 109741. https://doi.org/10.1016/j.paid.2019.109741

Abstract: Momentary lapses in memory, perception, or action, known as cognitive failures, are relatively common. These lapses may reflect, in part, aspects of psychological functioning, such as personality traits. The present research addresses how Five Factor Model personality traits and facets are associated with cognitive failures, and whether these associations are accounted for by depressed affect. Participants (N = 5,133; 50% female) who ranged in age from 18 to 91 completed an online survey that assessed their personality traits, cognitive failures, and depressed affect. Higher neuroticism was associated with more cognitive failures, whereas Conscientiousness and Agreeableness were associated with fewer failures, controlling for sociodemographic characteristics. Controlling for depressed affect reduced the associations in most cases by about 50%, but most relations were still apparent. Facet-level analyses provided a more detailed picture of how the traits are associated with cognitive failures. Subjective perceptions of lapses in cognition are associated with basic personality traits and may reflect, in part, processes related to those traits beyond depressed affect.

Are universities left‐wing bastions? Professors are more liberal & left‐leaning than other professionals, but there is a diversity of opinions which is similar to what professionals would find in other occupations

Are universities left‐wing bastions? The political orientation of professors, professionals, and managers in Europe. Herman G. van de Werfhorst. The British Journal of Sociology, December 10 2019. https://doi.org/10.1111/1468-4446.12716

Abstract: Universities are accused of being left‐wing bastions, unwelcoming to conservative and right‐wing professors. However, we know little about the political orientation of professors in comparison to other professionals, which would be the right comparison group if we want to know whether universities are potentially hostile environments to conservatives. Examining culturally and economically oriented political orientations in Europe, it is demonstrated that professors are more liberal and left‐leaning than other professionals. However, there is no greater homogeneity of political orientations among the professoriate relative to other specific professions, suggesting that there is a diversity of opinions which is similar to what professionals would find in other occupations. One exception concerns attitudes towards immigration, on which professors have more liberal orientations and comparatively low residual variance around that more liberal mean. Importantly, the difference between professors and other professionals is not so clear within graduates from the social sciences, but emerges more clearly among graduates with a medical, STEM, economics or law degree. An important political cleavage exists between professionals and managers, a group of similar social standing.

4 DISCUSSION

The evidence for the left‐wing bastion hypothesis is mixed. Overall, when we examine the average positions of different occupational groups, we see a pattern that is in line with sociological theories positing a central role to occupations for the formation of life styles and political orientations. In particular, we find evidence for a relationship between the dominance of cultural and economic capital for the political orientation of occupational groups. Professors and artists stand out as having a more left‐wing/liberal orientation than most other professions (as can be predicted from their dominance of cultural capital), and especially CEOs and small business managers stand out as more conservative and right‐wing (fitting the dominance of economic capital in these occupational groups). Also in line with this idea is the average position taken by engineers and medical doctors, groups for which none of the two types of capital can be considered dominant according to Bourdieu (1984).
However, with regard to the residual variance, as a measure of homogeneity within occupational groups, the pattern is less clear. Professors do not stand out as having a low dispersion of orientations. If universities were exclusionary organizations where diversity of opinions is undesired and conservative scholars are excluded, one would expect this would have resulted in a high level of homogeneity of opinions. The fact that that seems not to be very clearly the case is reassuring for the contemporary debates on ideological diversity in higher education.
Also, when we split out the results by fields of study, professors with a humanities degree are more left‐wing and liberal on most indicators, but this is not the case for professors with a social science degree. Importantly, professors are more tolerant to immigration than other professional graduates of three fields that are usually not seen as left‐wing bastions: the (para‐) medical field, economics/business, the STEM fields, and law. This finding fits less well with the “conflict of the faculties” noticed by Bourdieu (1988); the professoriate is comparatively more liberal in the powerful fields (compared to non‐professors). So, overall graduates from the humanities and social sciences may be more left‐wing and liberal (professors or not), but this is not an organizational feature of the universities, as Bourdieu seems to have suggested.
A common explanation for the more liberal orientation of professionals (including professors) relative to managers concerns their attachment to education. While the evidence is mixed on the question whether education has a causal effect on political orientations (Cavaillé & Marshall, 2019; Hillygus, 2005; Lancee & Sarrasin, 2015) people with higher levels of education, and educated in the social sciences and humanities, identify typically more strongly as left‐wing in the political sphere. The more left‐leaning orientation of more educated individuals is consistent with several well‐known explanations for the formation of political values. These include the theory that intelligence is an important driver of occupational group differences in political orientation (especially on cultural issues, Carl, 2015), the theory that education socializes values especially in the social and humanistic sciences (Stubager, 2008), and the theory that consensus in orientations results from scientific wisdom rather than bias (Fuller & Geide‐Stevenson, 2014).
To further illustrate the relevance of education, it is worth emphasizing that we used model predictions of occupational group differences for respondents with a college degree, and almost all predicted outcomes are above zero (indicating above the overall average on the z‐standardized variables), except for the support for economic redistribution. Also managers and workers in other social classes with a college degree have above‐average scores on a liberal and left‐wing political orientation.
While we cannot test the theory that conservatives are reluctant to take up an academic career because of their atypical political orientations, the results point to the possibility that universities form an unwelcoming environment to conservatives (Gross, 2013; Rothman, Lichter, & Nevitte, 2005). Even if there is the same level of variability within the universities as elsewhere, the mean difference implies that societies’ intellectuals responsible for teaching the next generation have a more left‐leaning orientation than the rest of society. Whether this is worrying from an educational perspective is yet another question—there is no evidence that professors bring their political orientation into the classroom.

Of malevolence and morality: Psychopathy dimensions are conducive to helping in highly-distressing moral dilemmas due to greater focus on helping execution vs. consequences

Of malevolence and morality: Psychopathy dimensions are conducive to helping in highly-distressing moral dilemmas. Gregory K.Tortoriello, William Hart, Christopher J. Breeden. Personality and Individual Differences, Volume 155, March 1 2020, 109759. https://doi.org/10.1016/j.paid.2019.109759

Highlights
•    Psychopathy predicted greater self-reported helping in distressing moral dilemmas.
•    Greater focus on helping execution vs. consequences partially explained relations.
•    Psychopathy also predicted inducing greater distress in an ostensible partner.
•    This relation did not depend on whether distress was framed as helpful or harmful.
•    Meanness dimension of psychopathy generally produced the strongest effects.

Abstract: We proposed a context-dependent account of psychopathy and morality which argues that any psychopathy dimension―including those typically theorized to be maladaptive―can be conducive to helping others under appropriate contexts. In Study 1, a college sample (N = 331; Mage = 18.68) completed two-factor and Triarchic psychopathy measures and reported helping behavior, psychological distress, and task prioritization (i.e., greater attentional focus on helping execution vs. helping consequences) after simulating highly-distressing moral dilemmas. In Study 2, a college sample (N = 256; Mage = 18.55) completed the same psychopathy measures and selected one of five intervention tasks—incrementally ranging from slightly to extremely distress-inducing—for an ostensible phobic to perform under conditions in which more distressing tasks were framed as either helpful or harmful. In Study 1, psychopathy dimensions were related to greater helping, which was generally explained best by greater task prioritization. In Study 2, psychopathy dimensions generally related to selecting more distressing tasks for the phobic, even when more distressing tasks were framed as helpful. Thus, psychopathy dimensions appeared conducive to helping in highly-distressing moral dilemmas. Findings contribute preliminary empirical support for a context-dependent account and the possibility of moral manifestations within psychopathy.


7.3. General discussion

A context-dependent account of psychopathy and morality argues
that behavioral manifestations of psychopathy (e.g., causing others
harms) can either be helpful or harmful to others depending on the
context. Across two studies, we obtained correlational (Study 1) and
experimental (Study 2) support for this account in the context of
helping others in various highly-distressing moral dilemmas. In Study 1,
Triarchic and two-factor dimensions of psychopathy were moderatelyto-
strongly related to greater self-reported helping across simulated,
highly-distressing moral dilemmas. In Study 2, participants scoring
higher in psychopathy dimensions generally selected more distressing
intervention tasks for an ostensible partner believed to be diagnosed
with a phobic disorder; however, we observed no strong or compelling
evidence that these effects depended on whether the distress was
framed as more or less effective for treating the partner's phobia. This
supports a context-dependence assumption which predicts that psychopathic
people cause others greater distress irrespective of when it is
framed as helpful or harmful for others, meaning that the context determines
the morality of this psychopathic expression. This assumption
is theoretically consistent with psychophysiological accounts which
posit that psychopathic people are less sensitive to processing distress
cues (Blair, 2007b; Glenn et al., 2009). Our account and findings,
however, offer a novel perspective by suggesting that reduced distress
sensitivity in psychopathy can sometimes confer prosocial benefits.

7.4. Explanations for a context-dependent account: evidence and theory

Study 1 illuminated some possible explanations for the relations
between psychopathy dimensions and greater helping that are theoretically
anticipated from a context-dependent account. Psychopathy dimensions
were related to reduced psychological distress and greater
task prioritization across highly-distressing moral dilemmas. The
former relations, however, were weaker for disinhibition and secondary
psychopathy relative to other dimensions, which is consistent with research
indicating that disinhibition and secondary psychopathy are less
immune to cognitive-affective expressions of distress compared to other
dimensions (e.g., Almeida et al., 2015; Lishner, Hong, Jiang, Vitacco &
Neumann, 2015). Of these two theoretically-inspired explanations,
greater task prioritization broadly fit the data better, such that it more
strongly mediated the relations between psychopathy dimensions and
greater helping. Indeed, reduced psychological distress either mediated
effects extremely weakly or not at all (i.e., secondary psychopathy). Our
data are congruous with a response-modulation hypothesis (Gorenstein
& Newman, 1980) which argues that psychopathic people have a
dominant response set impervious to peripheral cues. In the case of
highly-distressing moral dilemmas, psychopathic people may be better
equipped at focusing on helping task execution relative to adverse
helping consequences, which should promote greater helping.
In Study 2, evidence supporting a context-dependence assumption is
inconsistent with a harm-intent explanation. Indeed, the drive to harm
others has been an explanation for egregious and violent psychopathic
behavior (Porter & Woodworth, 2006), but we did not observe evidence
supporting a harm-intent hypothesis for effects in Study 2. In fact, although
the interaction coefficients between most psychopathy dimensions
and task effectiveness generally approached zero, the direction of
the interactions for secondary psychopathy (and less so for disinhibition)
suggested a possible contradiction of a harm-intent hypothesis
(i.e., more distressing tasks are selected when distress is framed as
helpful vs. harmful). This contradiction is consistent with research
suggesting that some socially-aversive behavior associated with psychopathy
manifests from lesser, not greater, harmful intent (Tortoriello,
Hart & Richardson, 2019).

7.5. Re-conceptualizing morality in psychopathy: a case for meanness

Investigations into the potential morality in psychopathy have been
constrained by assumptions of “successful psychopathy” models such as
dual-process (Hall & Benning, 2006) and differential-configuration accounts
(Lilienfeld et al., 2015). Essentially, these accounts assume that
certain dimensions of psychopathy are generally adaptive (e.g., boldness)
and other dimensions are generally maladaptive (e.g., meanness
and disinhibition). This assumption has inspired theses that the most
adaptive dimension(s) of psychopathy should be conducive to helping
others, whereas other, more maladaptive dimensions should inhibit
helping (e.g., Patton et al., 2018). While we generally agree that
boldness might have the most “generalizable” moral manifestations (at
least in Western cultures), we also maintain that the potential moral
behavior (e.g., helping) associated other psychopathy dimensions
should not be neglected.
Evidence across our studies corroborated this perspective. In addition
to boldness, primary psychopathy and meanness also revealed
evidence of greater helping across studies. In particular, and perhaps
even counterintuitively, one could argue that meanness―a dimension
that blends lack of concern for others and violence/aggression―could
be the best psychopathic candidate for helping others in highly-distressing
moral dilemmas. Although boldness and meanness were each
similarly related to greater helping across dilemmas in Study 1, evidence
suggests that meanness, relative to boldness, may have been
more strongly related to greater task prioritization―which predicted
helping―across dilemmas. In Study 2, the bcs regressing task selection
on meanness was nearly twice as large as that on boldness. In sum, in
highly-distressing moral dilemmas, meanness may rival boldness for its
prosocial consequences. Still, more broadly, the dimensions most emblematic
of interpersonal and affective features (boldness and primary
psychopathy) received moderate-to-strong overall support for a context-
dependent account, while dimensions most emblematic of lifestyle
and antisocial features (disinhibition and secondary psychopathy) received
relatively weaker support.
The novelty of a context-dependent account for understanding
moral manifestations of psychopathy should be considered in light of
other accounts of successful psychopathy. Our perspective has commonalities
with a moderated-expression account (e.g., Hall & Benning,
2006; Lilienfeld et al., 2015), which argues that successful expressions
of psychopathy are determined by moderating factors. However, one
criticism of this account is its focus on dispositional moderating factors
(Steinert, Lishner, Vitacco, & Hong, 2017), such as executive functioning
or conscientiousness. Interactions between psychopathy dimensions
and dispositional variables which theoretically oppose a
psychopathic constitution are less appealing for understanding moral
manifestations of psychopathy because they are fundamentally different
than theorized psychopathy. For example, psychopathy is
marked by low conscientiousness, so the combination of high conscientiousness
and high psychopathy no longer represents psychopathy
per se. A context-dependent account is robust to these issues because it
changes the implications of psychopathy, not its conceptual composition.
Indeed, an elaborated moderated-expression account (Steinert,
Lishner, Vitacco, & Hong, 2017) accommodates the possibility of situational
context as a moderator for determining moral manifestations
of psychopathy. Our research suggests that this perspective has promise.

7.6. Limitations and future directions

Self-report. Study 1 relied on a self-report methodology which is
susceptible to bias and erroneous responding. Also, Study 1 used simulations
of highly-distressing moral dilemmas, so the degree to which
psychopathic people could accurately simulate their internal psychological
states and, therefore, accurately report on their likely behavior
remains unknown. Although Study 2 partially addressed these limitations
by including a behavioral indicator of helping and devising a realworld
moral dilemma, an informant-reports study should be considered
because it addresses self-report bias, common method variance, and
limited ecological validity. An informant-reports methodology further
bestows the advantage of assessing helping effectiveness. Our evidence
only suggests that psychopathy dimensions are more conducive to
helping decision-making in highly-distressing moral dilemmas, not necessarily
that they are more conducive to better helping outcomes for
others. Nevertheless, we would not be surprised if the latter is also
supported, which would further augment a context-dependent account.
Restricted range of psychopathy scores. Data were derived from
college samples. As one consequence, “relatively high” scores on each
psychopathy dimension (i.e., one standard deviation above the mean)
failed to exceed the respective scale's midpoint, meaning that relatively
high scorers were not “absolutely” high scorers. This issue of restricted
ranges can result in the attenuation of observed effects, suggesting that
samples representing a more expansive range of scores on psychopathy
dimensions might yield stronger effects on helping outcomes. However,
how the observed effects actually manifest in clinical samples, wherein
scores on psychopathy dimensions are absolutely high, remains unknown.
Thus, we encourage future research to explore these issues.
Alternative explanations. We entertain the possibility that other
state-based explanations beyond greater task prioritization (and to a
lesser degree, reduced psychological distress) might exist. Indeed, relations
observed across studies between psychopathy dimensions and
greater helping could be explained by activated thrill-seeking motives
(Porter & Woodworth, 2006). This explanation is compatible with a
context-dependent account. Future research should consider testing
various theoretically-anticipated explanations using rigorous experimental
methodologies that are more receptive to drawing causal inferences
(e.g., manipulating a theorized mechanism). In this vein, future
research should also consider isolating the specific personality and
individual-difference constituents within psychopathy dimensions (e.g.,
lack of concern, tolerance for uncertainty) that might be driving the
observed relations.

Individuals who are more socially conservative or religious tend to have lower sexual disgust thresholds; this relationship is hypothesized to be motivated to avoid contact with pathogens

Six dimensions of sexual disgust. Courtney L.Crosby et al. Personality and Individual Differences, Volume 156, April 1 2020, 109714. https://doi.org/10.1016/j.paid.2019.109714

Abstract: Sexual disgust is an emotion hypothesized to deter individuals from engaging in sexual activities that are probabilistically detrimental to fitness. Existing measures of sexual disgust are limited in treating sexual disgust as a unitary construct, potentially missing its multidimensional nature, and inadvertently ignoring important adaptive problems that this emotion evolved to solve. We conducted three studies to address these limitations. In Study 1, women and men (N = 225) nominated over 2,300 unique items that they considered sexually disgusting across a variety of different contexts. Study 2 (N = 331) identified a six-factor structure of the 50 most frequently nominated items: Taboo, Oral sex, Promiscuity, Hygiene, BDSM, and Same-sex attraction. Moreover, this study established construct validity with significant associations between sexual disgust and major dimensions of personality. Correlations between the Three Domains of Disgust Scale and our six-factor measure of sexual disgust established convergent validity. Study 3 (N = 318) confirmed the factor structure found in Study 2, established further convergent validity and examined sex differences and other individual differences in sexual disgust. Discussion focuses on the theoretical importance and psychometric validity of the Sexual Disgust Inventory–a new six-factor measure of sexual disgust.



3.1.3. Sexual disgust, religiosity, and political ideology
Individuals who are more socially conservative or religious tend to have lower disgust thresholds (Inbar, Pizarro, Iyer & Haidt, 2012; Olatunji, 2008). This relationship is hypothesized to exist as a function of the behavioral immune system, which motivates individuals to avoid contact with pathogens (Schaller & Duncan, 2016). This is a robust association; however, previous research has focused mostly on pathogen disgust. By measuring the associations between these variables with our measure of sexual disgust, we hope to clarify how conservatism or religious affiliation influences disgust experienced towards specific sexual acts.


5. General discussion
Sexual disgust is an understudied emotion of great importance from
an evolutionary perspective. Previous research suggests there is interesting
individual variation in the activation of this emotion. To
understand how individual variation in sexual disgust sensitivity can
persist under the winnowing forces of sexual selection, we must consider
the role of context and personality dimensions in the conceptualization
of sexual disgust. The primary focus of the studies presented
in this paper was to address the limitations of current measures
of sexual disgust, while systematically creating and testing a novel instrument
for use in future studies.

5.1. Limitations and future directions
The studies presented in this paper have several limitations that
should be considered. First, although our studies attempted to broaden
the age range and demographic distribution of the participants, selection
issues common in psychological research might still be at play.
Recruiting individuals from the university's subject pool is a common,
inexpensive way to increase sample size; however, this often results in a
young, liberal sample. The use of Amazon's Mechanical Turk helps
mitigate this issue, but only participants living in the US with internet
access could participate. Participants were demographically similar
across the three studies in terms of ethnicity, age, and sexual orientation.
However, there was variation between each study, which may
account for differences in results between Studies 2 and 3. We did not
collect data on the political orientation of individuals in Study 1. It is
possible that the individuals who participated in this nomination procedure
are not representative of politically diverse populations that
exist outside of western, economic, industrialized, rich, and democratic
samples (WEIRD; Henrich, Heine & Norenzayan, 2010). Cross-cultural
research is needed to address these issues.
It is also possible that the items generated in Study 1 do not map
exactly onto a functional analysis of sexual disgust during human
evolutionary history, but rather are a better representation of items that
individuals find disgusting within the modern environment. For example,
our measure does not include items about mating with an unattractive
person or someone with cues indicative of disease such as
open lesions, sores, or STIs. These problems, among others not included
on our measure, were presumably important deterrents during the EEA.
Future research could examine if inclusion of such items alters the latent
structure of sexual disgust.
We find it surprising that most of the sex differences that were found
in Study 2 did not replicate in Study 3, except for a significant sex
difference on the “Promiscuity” factor. The other factors of the SDI
should also be relevant for women and men's mating strategies and
should be differentially activated according to the adaptive problem
being represented. This should be especially true for items regarding
incest and rape. We believe this might be because of our sample (majority
of which was obtained through Amazon's Mechanical Turk) and
may not represent the true nature of sex differences in this emotion or
on this measure. Additional research is needed to test the robustness of
sex differences in sexual disgust across factors.
Although the studies presented in this paper provide evidence in
support of previous research relating sexual disgust to various personality
dimensions, we cannot reasonably establish the direction of
causality between these variables. It is not clear, for example, whether
conservative worldviews cause higher levels of sexual disgust or, alternatively,
whether higher levels of sexual disgust lead people to
support conservative worldviews that stigmatize sexual acts. Some links
between sexual disgust and other individual difference variables may
be the result of sexual disgust thresholds creating patterns of thoughts,
feelings, and behavior. Other links may result from pre-existing
personal characteristics—such as immune functioning, relationship
status, or formidability—involved in the calibration of sexual disgust
across development. Future research should work to disentangle the
causality of these relationships.

5.2. Hypothesized functions of the six factors of sexual disgust

Studies 2 and 3 determined a six-factor organization of sexual disgust.
These six dimensions of sexual disgust may map on to solutions to
six partially distinct adaptive problems. Understanding the proper domain
of each facet is of critical importance in predicting and interpreting
individual differences. We have hypothesized the adaptive
function of each factor below. Future research will need to examine
whether the six dimensions of sexual disgust reflect unique adaptations
that evolved in response to different adaptive problems.

5.2.1. Taboo
Engaging in the activities under the “Taboo” factor pose various
social and biological costs. Several of the items within the “Taboo”
factor are considered illegal or unusual across cultures (e.g., rape, sex
with children, sex with animals, sex with the use of human feces) while
others refer to sex with close genetic relatives. Both categories of behaviors
are often moralized and deemed unacceptable by the majority
of people. Engaging in sexual acts deemed unacceptable by one's social
group poses a serious adaptive problem: being socially ostracized.
Experiencing sexual disgust towards these activities might aid in
avoiding behaviors that can lead to social devaluation, alongside prospective
shame (Sznycer et al., 2016). Further, engaging in sex with
genetic relatives can lead to deleterious phenotypic effects in offspring.
Sexual disgust should prevent participation in these acts and promote
negative moralization of individuals who engage in these acts.

5.2.2. BDSM
Items that constitute the “BDSM” factor involve activities that are
potentially violent or dangerous. Although these items have become
less stigmatized over time (Weiss, 2006) they are still considered less
typical sexual activities. It is possible that these items are sexually
disgusting because these activities are triggering our evolved psychology
of punishment or harm avoidance, or because several of the
items represent behaviors commonly used in sexual coercion. Even
though these activities can be completely safe, sexual disgust may
function to reduce participation, thereby decreasing the potential risks
associated with harm.

5.2.3. Same-sex attraction
The “Same-sex attraction” factor may have arisen due to the way
that “disgust interacts with the ‘moral’ system” (Lieberman &
Patrick, 2018, pg. 134). Individuals engaging in sexual activities with
the same-sex have a low expected sexual value for heterosexual individuals,
and are considered a “minority group”. In our ancestral environment,
sexual disgust might have functioned to cognitively label
these individuals to eliminate the costs associated with channeling resources
or time into attempting to mate with such individuals.
Another reason this factor may have emerged centers around the
mental association between short-term mating orientation, promiscuity,
and homosexuality (Pinsof and Haselton, 2017, Pinsof &
Haselton, 2016). We found no evidence to support the idea that shortterm
mating orientation is associated with levels of disgust on the
“Same-sex attraction” factor in these studies. However, we did find that
disgust towards the “Promiscuity” factor was positively, highly correlated
with disgust towards “Same-sex attraction” in Studies 2 and 3.
Future research should work to disentangle potential reasons that this
factor emerged.

5.2.4. Promiscuity
The items that constitute the “Promiscuity” factor represent interest
in sexual variety. By engaging in acts of uncommitted, promiscuous
mating, individuals are at risk of having sex with someone whom will
not continue to be a future sexual partner, signaling themselves as an
unreliable, uncommitted mate to those in the surrounding environment,
or contracting sexually transmitted infections with increased exposure
to sexual partners and activities.
While individuals interested in sexual variety might not consider the
items on this factor overtly sexually disgusting, a potential mate who
engages in these behaviors could be costly as a long-term mate. The
replicable sex difference in levels of disgust experienced by men and
women on this factor may reflect women's desire for committed, longterm
mating as well as the costs women historically incurred from
short-term mating (Buss, 2016; Symons, 1979). Sexual disgust on this
factor should therefore function to deter individuals from facing the
potential social and health risks that are faced when one engages in
promiscuous sex (e.g., reputational damage; contracting a sexually
transmitted disease) and aid in mate selection. Future research should
examine the extent to which disgust towards “Promiscuity” is associated
with sexual regret.

5.2.5. Oral sex
The function of the “Oral sex” factor of the SDI is hypothesized to
deter participation in sexual activities that could lead to increased rates
of transmission of harmful pathogens or diseases, tapping into our
evolved psychology of disease avoidance. Genitals harbor bacteria that
can be dangerous when transmitted to other areas, either orally or
through penile-vaginal penetration (American Sexual Health
Association, 2016; Schneede, Tenke & Hofstetter, 2003). Being disgusted
by cues to increased risk of disease or pathogen transmission by
genital to mouth contact might function to protect individuals from
contracting these diseases.
Disgust towards “Oral sex” is different from disgust towards the
“Promiscuity” factor in several important ways. While it is certainly
true that engaging in promiscuous sex promotes higher disease risk,
there are a variety of other adaptive challenges that are also closely
associated with promiscuity, such as reputational damage and ensuring
investment. This is less true for “Oral sex,” because oral sex consists of
this unique, adaptive problem involving potential disease transmission
from intimate genital to mouth contact. Interestingly, the items that
constitute this factor involve acts of performing oral sex, not receiving.
It remains unclear why this asymmetry exists. Future research should
examine predictors of variation in this facet of sexual disgust.

5.2.6. Hygiene
The extraction of a factor about “Hygiene” is not surprising from an
evolutionary perspective,; but it is particularly interesting because it
provides evidence that within sexual disgust, elements of pathogen
avoidance are critical. Similar to the “Oral sex” factor, disgust towards
these items likely taps into our evolved psychology of disease avoidance.
Avoiding contact with contaminated vectors is of utmost importance
within sexual contexts. Any attempt to decrease exposure to
the pathogens involved in sexual activities would have been advantageous.
Further, bad hygiene might have been a reliable cue to increased
levels of pathogen load during our evolutionary history. Our psychology
should function to deter engaging in sexual activities that
would expose us to harmful diseases or vectors. Sex is already a risky
activity to engage in. If one is disgusted by cues to pathogens, then the
presence of bad breath or bad hygiene should further increase disgust,
inhibiting participation in sexual activities.


Future research should disentangle the adaptive function of each
factor of the SDI. If our speculations are correct, then these factors
could be linked to variation in legal rules or systems, parasite prevalence,
sexual strategies, sexual dysfunction, sexual coercion, or
childhood co-residence.. While the problems associated with the factors
of the SDI should be consistent cross-culturally, varying levels of context-
specific input might result in cross-cultural differences in sexual
disgust activation. Ecologies vary in parasite prevalence, for example,
which may evoke cultural differences in sexual disgust thresholds.
Mating pools vary in operational sex ratio, which may downregulate
“Promiscuity” disgust when there is a surplus of women, which activates
more frequent short-term mating. Cross-cultural research can test
these hypotheses, as well as examine the universality and cultural
specificity of the six factors of sexual disgust discovered in the current
studies.

Some macaques and capuchins are able to discriminate appearance from reality; seems that the evolutionary apparition of this cognitive ability was sooner than commonly believed

Are monkeys able to discriminate appearance from reality? Marie Hirel et al. Cognition, Volume 196, March 2020, 104123. https://doi.org/10.1016/j.cognition.2019.104123

Abstract: The understanding that the perceptual appearance of the environment can differ in several ways from the reality underlies the ability to discriminate appearance from reality. Being able to realize when a misperception can lead us to behave in inappropriate ways confers an evolutionary advantage and may be a prerequisite to develop a Theory of Mind. Understanding that our own perception can differ from reality seems indeed necessary to attribute to others perceptions or beliefs different than ours. This appearance-reality discrimination ability has recently been demonstrated in great apes but no information is currently available regarding this ability in other nonhuman species. In a comparative study, we tested Tonkean macaques (Macaca tonkeana), an Old World primate species, and brown capuchins (Sapajus apella), a New World primate species. We provided monkeys with two experiments using visual illusions of size and quantity to test their ability to discriminate appearance from reality, with an experimental setup similar to the one developed by Krachun et al. (2016) on chimpanzees. A large number of brown capuchins, from different ages and both sexes, as well as two Tonkean macaques succeeded in the two experiments. By ruling out all alternative explanations (i.e. visual tracking or associative learning), our study brings the first evidence that some Old World and New World monkeys are able to discriminate appearance from reality. Our results suggest moving the evolutionary apparition of this cognitive ability earlier in time. Finally, it suggests that humans could share more Theory of Mind components with more nonhuman species than we previously thought.

4. Discussion
This study brings the first evidence that monkeys are able to discriminate
appearance from reality. All our subjects passed the preference
tests of both the Lens and Mirror experiments and thus demonstrated
a strong natural preference for larger or higher number of
food items, as well as a good size and quantity discrimination ability.
Then, in the Lens experiment, all but two subjects of each species
passed successfully the basic test and the tracking control tests, demonstrating
that they were capable of ignoring the misleading appearance
of the magnified grape to choose the truly bigger one, without
being able to visual track the grapes (see Fig. 2). Afterwards, the large
number of successful brown capuchins, from different ages and both
sexes, in the last learning control brings strong evidence that they are
able to discriminate appearance from reality. In Tonkean macaques, our
results are less clear, with only one individual succeeding in the avoidlens
control (see Fig. 2). Thus, we are unable to say with confidence
whether or not this species possesses appearance-reality discrimination
ability. However, our procedure with lenses might have not allow us to
highlight AR discrimination ability in a larger scale in this species and
could provide results underestimating it (see methodological issues
discussed below). This is supported by Tonkean macaques’ good performances
in the Mirror experiment. Indeed, the two Tonkean macaques
and all but one brown capuchin that were tested in this second
experiment passed the visual tracking and the avoid-mirror tests. By
validating all controls, they demonstrated they are able to discriminate
perceived from real quantity.
We found that all except two individuals who were successful in the
Mirror experiment had also succeeded in the Lens experiment.
Successes in both of our experiments provides evidence for a general
understanding in our animals, that perceptual appearance of objects
can be different in several ways from reality. Nevertheless, we should
approach this conclusion with caution for the few individuals that
needed more than two sessions to succeed. Even by limiting the number
of sessions allowed to reach a success, our and other procedures of
progressive sessions generate an increasing probability of false positives.
To account for this multiple testing issue, one option is to look out
group performances. In this respect, brown capuchins succeeded significantly
in all tests of the Lens and Mirror experiments. For Tonkean
macaques, their succeeded significantly in all tests except for the avoidlens
tests n°1 and n°2. These results confirm our inability to conclude of
an AR discrimination ability presence for Tonkean macaques with the
Lens experiment. However, we still able to maintain confidence in our
results demonstrating AR discrimination ability in both experiments for
brown capuchins and in the Mirror experiment for Tonkean macaques.
In summary, even if more subjects of both species are necessary to make
a reliable conclusion at a species scale, results of the Mirror experiment
confirmed those of the Lens experiment and together suggest that these
monkeys could be able to discriminate appearance from reality.
The ability to discriminate appearance from reality was demonstrated
in great apes by previous studies of Karg et al. (2014) and
Krachun et al. (2009, 2016). Now, our study suggests the presence of
this ability in Tonkean macaques, an Old World monkey species, and
brings strong evidence in brown capuchins, a New World monkey
species. Therefore, the hypothesis of the emergence of AR discrimination
ability in a common ancestor dating back to at least the capuchin
monkey genus is conceivable. However, our results certainly need to be
strengthened by further research on more individuals and other species
of macaques to make a more reliable conclusion. Since only two Tonkean
macaques were compared to eight brown capuchins in both experiments,
alternative hypotheses of convergent evolution cannot be
completely ruled out. Thus, instead of looking at phylogenetic relatedness
only, our interest should go towards the socio-ecological aspects
that are characteristic of these species in order to improve our knowledge
about the development of such cognitive abilities during evolution.
Indeed, as example, many similarities were found between genus
Sapajus and Pan: long life spans, explorative and manipulative behaviours,
tool using, omnivorous diet, socially complex behaviours such
as coalitions and cooperation and so forth (Visalberghi & McGrew,
1997).
One of the major aims of this study was to compare performances of
monkey species with those of chimpanzees (Krachun et al., 2016) using
a same experimental paradigm. Like chimpanzees, brown capuchins
performed high scores in the two AR experiments and passed each test
within a small amount of sessions. Not all of them succeeded but the
proportion of successful brown capuchins is still greater than observed
in chimpanzees. Hence, the performance of brown capuchins is likely to
be comparable to those of chimpanzees in these AR discrimination
experiments. It brings more evidence that monkeys can perform like
apes in demanding cognitive tasks, for example like prerequisite ToM
tests, contrary to previous scientists’ common beliefs. These previous
studies that found differences between performances of monkeys and
apes in cognitive tasks, have normally compared apes that are highly
habituated to experiments with naive monkeys (Amici et al., 2010). In
addition to using similar standardized paradigm, our study tested
highly habituated monkeys. Thereby, a comparison between our results
and those on chimpanzees appears more reliable and appropriate.
Several recent studies on cognitive abilities comparing different
monkey and ape species found no strong evidence of a difference between
their performances (Amici et al., 2010; Meunier, 2017; Schmitt
et al., 2012; Tomasello et al., 1998). Instead, Amici et al. (2010) revealed
a link in their results between cognitive capacities and social
organisation: performances of species living in systems with fissionfusion
dynamics (e.g. chimpanzees, bonobos, orangutans, and spider
monkeys) exceeded those of species living in more stable groups (e.g.
long-tailed macaques, gorillas and capuchin monkeys). Thereby, the
type of social organisation seems to impact the physico-cognitive skills
of primates (i.e. spatial memory, quantities, causality, etc.) and may
provide better predictor of performance in some cognitive tasks than
phylogenetic relatedness (Schmitt et al., 2012). This led to the development
of the social intelligence hypothesis, which claims that primate
intelligence evolved in response to challenges of living in large and
complex groups (Byrne & Bates, 2010; MacLean et al., 2012; Schmitt
et al., 2012). However, both for Tonkean macaques and brown capuchins,
this explanation does not apply because they are not living in
fission-fusion dynamics but instead in stable female-bonded groups
with comparable social complexity, and are described as socially tolerant
(Hare et al., 2003). These other social features could then interfere
in their cognitive abilities’ development. Thus, as socio-ecological
conditions might better explain the presence of some cognitive abilities,
instead of comparing monkeys and apes, we should focus on comparison
between particular species. Studying with the same paradigm other
nonhuman primates either closely related or presenting different social
organisations (e.g. lemurs, white-faced capuchins, or long-tailed macaques)
should provide insights about the origin of this ability and
could help to clarify the social intelligence hypothesis (Byrne & Bates,
2010; Humphrey, 1976; MacLean et al., 2012; Schmitt et al., 2012).
The positive results in both experiments could be explained by
several alternative mechanisms of learning. First of all, an association
learning between large or big food item and negative outcome could be
a possibility. However, it seems to be an unlikely explanation because
our successful subjects have chosen the item that appeared larger or
bigger in the avoid tests, and they continued to choose the bigger or
larger amount of items in each warm up preference trials before each
session. Secondly, some might argue that successful individuals could
have done reverse contingency learning, i.e. choose the smaller food
item to obtain the larger one. However, this assumption is highly unlikely
for the following reasons. First, the avoid control test clearly rules
out this possibility. In fact, to validate this control, subjects needed to
choose the apparent bigger or larger food item to obtain the truly bigger
or larger one, and not the apparent smaller one as in previous tests.
Second, several studies have already demonstrated that this type of
contingency learning for both size and quantity of items is really difficult
for these species, even for great apes, and require hundreds of
trials to succeed in it (Anderson, Hattori, & Fujita, 2008; Boysen,
Berntson, & Mukobi, 2001; Krachun et al., 2009; Vlamings, Uher, &
Call, 2006).
In the Lens experiment, a few subjects did not succeed in different
tests. First, a significant left pointing bias can explain the failure of two
brown capuchins, one in the basic and the other one in the seen
tracking test. The fact that this bias was not present in the initial conditions
might indicate they do not understand the situation in the
follow-up conditions and thus could also suggest that a more ecological
procedure may have been necessary for these individuals for AR discrimination
to be revealed. Second, Tonkean macaques and brown capuchins
seem to have failed the Lens experiment in the last learning
control because they have performed learning strategies based on different
stimuli. Two Tonkean macaques and one brown capuchin obtained
really low scores, demonstrating a significant preference for the
truly smaller grape. This could be explained by a learning process to
avoid the magnifying lens or to choose the grape that appeared with the
size of the small one through the lenses. The other five unsuccessful
Tonkean macaques and one brown capuchin obtained medium scores,
which reflect a learning to choose the minimizing lens or the grape that
appeared with the size of the bigger one through the lenses. Because
neither the minimizing lens nor the grape appearing the size of the
bigger one through lenses were no more available in this control, individuals
could not anymore use these stimuli to succeed and so they
chose randomly. Moreover, these individuals who failed the test still
choose preferentially the bigger grape in warmup preference trials
before each session, suggesting their failure was not due to a change of
preference to smaller grapes.
In order to compare performances with those of chimpanzees, we
carried out a second avoid-lens test at the end of the Lens experiment
using exactly the same procedure as Krachun et al. in their study of
2016. Tonkean macaques’ results obtained in the avoid-lens test n°2 are
quite inconsistent with those of avoid-lens test n°1. In fact, one individual
succeeded in both but two individuals that failed avoid-lens
test n°1 then succeeded in the avoid-lens test n°2, within one or two
sessions only. For these two subjects, we carried out one more session
with the unseen test procedure, in order to check whether by changing
again sizes and lenses used, they will succeed (as before in the same
unseen tracking test) and thus demonstrate a truly understanding of the
illusion phenomena. However, both of them drastically failed by never
choosing the truly larger grape in this session. These results highlight a
learning strategy they must have developed during the four sessions of
the avoid-lens test n°1. Because avoid-lens test n°2 was carried out after,
individuals had the possibility to learn the new rule (larger grape
placed behind magnifying lens). In addition, the only subject that
passed the first avoid-lens control test needed four sessions to succeed
in this last control. His result should be interpreted with caution because
he could have also learned, faster than the others, i.e. within only
three sessions. Surprisingly, the other Tonkean macaques and brown
capuchins that have failed did not realise this potential quick learning:
they both failed the avoid-lens n°1 and the avoid-lens n°2. A comparison
between avoid-lens n°1 performances of Tonkean macaques and brown
capuchins with avoid-lens test performances of chimpanzees in the
study of Krachun et al. (2016) seems thus more reliable.
Instead of an absence of AR discrimination, individuals’ failure
could be interpreted by other explanations corresponding to methodological
issues like too many experimenter’s manipulations or isolation
from their social group. Our test procedure could have required too
much concentration, motivation and short-term memory for these animals,
difficulties faced by Krachun et al. (2016) in their study on
chimpanzees. Notably, poor performances of Tonkean macaques (poor
success ratio, higher means of sessions to succeed in each test) compared
to brown capuchins and chimpanzees may support this assumption:
as we carried out half-sessions for brown capuchins, they had
twice as many demo trials as Tonkean macaques and chimpanzees,
hence more opportunities to understand the effects of stimuli illusion.
Moreover, all brown capuchins came to the experimental room at least
once per day, whereas with some Tonkean macaques, several days
sometimes separated two successive sessions because they did not come
back in the experimental room regularly. Because of those delays,
Tonkean macaques might have faced memory challenges about the
impact of illusion. Our results could thus underestimate their AR discrimination
ability.
Given the pointing bias of some brown capuchins and the large
failure of Tonkean macaques in the Lens experiment, ecological relevance
of our paradigm has to be questioned. The better success ratio
in the Mirror experiment could be due to the applied illusion. The
mirror effect indeed creates a false presence of two raisins, which do not
exist in reality. Whereas lens is modifying properties of grapes that
already exist, it does not create new food items. Thereby, it is maybe
easier to understand the effect of a mirror than the subtle modification
of existent items created by lenses. One alternative paradigm to test size
illusion understanding could be the one developed by Karg et al.
(2014). In their comparative study between great apes and children on
AR discrimination, they created a size illusion using completion illusion,
i.e. part of an object is partially occluding by another, in order to
inverse size relation. As Tonkean macaques and brown capuchins are
semi-arboreal primates, they might more regularly face size illusion
challenges by completion illusion because of the dense vegetation in the
canopy rather than by distortion.
Further research using different complementary types of illusion,
e.g. colour or auditory illusions, could now bring more information
about the scope of the AR understanding of these species. Another
notable result is that several capuchins of various ages succeeded. Thus,
AR discrimination ability seems to appear early in the development of
brown capuchins. Further experiences on even younger individuals will
be helpful to determine if the development of AR discrimination occurs
around the same development stage as for human children and with the
same developmental pattern (e.g. Hansen & Markman, 2005; Karg
et al., 2014; Moll & Tomasello, 2012).
To conclude, our results support those of apes, demonstrating that
this AR discrimination ability is not unique to great apes. As we have
now demonstrated that even some monkey species seem to possess this
understanding, it seems these abilities are perhaps more evolutionary
ancestral than previously thought. More research on different monkey
species with similar standardized procedure is now more than ever
necessary to better understand evolution of our remarkable social
cognition.