Countries with higher estimated IQs are *generally* more prosperous, better educated, more innovative, healthier, and more democratic

National Mean IQ Estimates: Validity, Data Quality, and Recommendations. Russell T. Warne. Evolutionary Psychological Science, Dec 19 2022. https://link.springer.com/article/10.1007/s40806-022-00351-y

Abstract: Estimates of mean IQ scores for different nations have engendered controversy since their first publication in 2002. While some researchers have used these mean scores to identify relationships between the scores and other national-level variables (e.g., economic and health variables) or test theories, others have argued that the scores are without merit and that any study using them is inherently and irredeemably flawed. The purpose of this article is to evaluate the quality of estimates of mean national IQs, discuss the validity of different interpretations and uses of the scores, point out shortcomings of the dataset, and suggest solutions that can compensate for the deficiencies in the data underpinning the estimated mean national IQ scores. My hope is that the scientific community can chart a middle course and reject the false dichotomy of either accepting the scores without reservation or rejecting the entire dataset out of hand.

Notes

1. This Flynn effect adjustment is often misunderstood. It does not increase or decrease the score of the country to reflect the age of the test. Rather, it adjusts the international IQ standard (where 100 = the mean in the UK) to the year of the test administration in a country so that the country’s measured IQ is compared to the estimated standard for the same year.

2. Only one sample had an overall quality rating of .18; it was collected in the United States. Four samples achieved an overall quality rating of .90. The data for these samples were collected in Tajikistan, the UK, the USA, and Yemen.

3. The width of a confidence interval is equal to ± 1.96(σn√)$\pm 1.96(\frac{\text{σ}}{\sqrt{n}})$, where σn√$\frac{\text{σ}}{\sqrt{n}}$ is equal to the standard error of the mean, σ = 15 (the default SD of a population on the IQ metric), and n is the combined sample size of all samples that contribute to a country’s mean IQ estimate (Warne, 2021, pp. 199–201).

4. These statistics are calculated using the absolute value of the differences between the QNW + SAS + GEO IQ in the Lynn and Becker (2019b) dataset and the IQ + GEO IQ for the previous version.

5. Listed in descending order of the magnitude of IQ change: Nicaragua (− 23.78 IQ points); Haiti (21.60 IQ points); Honduras (− 18.84 IQ points); Nepal (− 18.00 IQ points); Guatemala (− 17.71 IQ points); Saint Helena, Ascension, and Tristan da Cunha (− 17.01 IQ points); Belize (− 16.25 IQ points); Cabo Verde (− 16.00 IQ points); Morocco (− 15.39 IQ points); Yemen (− 14.39 IQ points); Mauritania (− 14.00 IQ points); Chad (11.83 IQ points); Saint Lucia (11.71 IQ points); Barbados (11.69 IQ points); Senegal (− 10.50 IQ points); Republic of the Congo (− 10.03 IQ points); Côte d’Ivoire (− 10.02 IQ points); and Vanuatu (10.02 IQ points). Positive values in this list indicate that the new IQ estimates from Lynn and Becker (2019b) are higher than the earlier estimate. Negative values indicate the new value is lower.

6. This finding also occurs in cross-national comparisons of educational achievement test scores. See, for example, Angrist et al. (2021), Gust et al. (2022), and Patel and Sandefur (2020).

7. The PERCE 1997 and SERCE 2006 data are taken from official publications reporting country means for each grade level and subject (Oficina Regional de Educación para América Latina y el Caribe/UNESCO, 2001, p. 176; 2008, Tables A.3.1, A.3.5, A.4.1, A.4.5, and A.5.1). TERCE 2013 and ERCE 2019 data can be downloaded at https://raw.githubusercontent.com/llece/comparativo/main/datos_grafico_1-1.csv

8. Cuba did not participate in TERCE 2013. Its ERCE 2019 data are much more similar to data from other countries in Latin America.

9. The 1995 SACMEQ test only produced reading scores. The 2000 and 2007 SACMEQ tests produced a reading and mathematics score. The 2000 and 2007 scores were combined as an unweighted mean for each country when calculating correlations with the estimated national-level IQs.

10. The correlations between PASEC scores and the GEO IQ scores from the Lynn and Becker (2019b) dataset—i.e., with Benin and Burkina Faso removed—are r = .142 (for PASEC grade 2 language), r = .153 (for PASEC grade 2 mathematics), r =  − .662 (for PASEC grade 6 language), and r = −.262 (for PASEC grade 6 mathematics). This does not change the conclusion that geographically imputed scores have a poor correspondence with data drawn from a country.

11. The national PIRLS/TIMSS scores and the chart to convert LLECE and PASEC scores to PIRLS/TIMSS scores to one another are available at https://www.cgdev.org/sites/default/files/patel-sandefur-human-capital-final-results.xlsx

12. I used the American mean in this calculation because the UK was not one of the countries in Patel and Sandefur’s (2020) study. The 2.5 IQ point adjustment is the standard adjustment that Lynn and Becker (2019b) used when examinees took a test normed in the USA instead of the UK.

13. Two regions, England and Northern Ireland, were part of the same country. When calculating correlations with QNW + SAS IQs, the Northern Ireland data were dropped, and the data for England was compared to QNW + SAS IQs for the entire UK.

14. Sear’s (2022) criticism of using IQ data from children to estimate IQs for an entire population shows that she does not understand that IQ scores are calculated by comparing examinees to their age peers. This functionally controls for age and allows scores from different age groups to have the same meaning. For an accessible explanation of how IQ scores are calculated, see Warne (2020), pp. 5–9.

15. Readers may be aware of Lim et al.’s (2018) study that measures human capital in 195 countries. These scores are not included in the discussion in this article because the underlying data are not solely cognitive/educational scores. Lim et al. (2018) also used health data and longevity/life expectancy data in the calculation of their human capital scores. Therefore, the Lim et al. (2018) data cannot be interpreted as a cognitive measure, which makes it inadequate to use for convergent validity purposes when studying the Lynn and Becker (2019b) dataset.

16. Available at https://datacatalog.worldbank.org/search/dataset/0038001.

17. This statistical truism is why the Flynn effect (a purely environmental effect) can coexist with high heritability (a variance statistic measuring the strength of generic influence on a phenotype in a population) of IQ. The same secular mean increase occurred in height (a phenotype with high heritability) in many countries during the twentieth century. Changes in the mean do not automatically result in changes in the variance—and vice versa.

18. It is important to recognize that mean QNW + SAS IQs below 70 are also found in some Central American nations (Belize, El Salvador, Guatemala, Honduras, Nicaragua), the Caribbean (Dominica and Saint Vincent and the Grenadines), and Morocco, Nepal, and Yemen.

19. For the 2018 PISA, the SD for the UK data was 93 for math scores and 99 for science scores (Schleicher, 2019, pp. 7–8). In these calculations, I used the standard deviation of 99 to be more conservative. My choice of standard deviation will not affect any correlations, but it will change differences between these IQs and others and make outlier national mean IQs slightly less extreme.

20. This is not an artifact of the extrapolation based on nearby countries’ data that Gust et al. (2022) used. The correlation between scores for the 12 countries that had imputed data in both datasets was r = .608; for the 13 countries that had geographically imputed scores in the Lynn and Becker (2019b) dataset and scores based on educational achievement testing data in the Gust et al. (2022) dataset, the correlation was r = .511. The average difference between the two sets of scores is also similar.

21. Gust et al. (2022, p. A1) noted that Angrist et al.’s (2021) method overestimates academic achievement HLOs, compared to the Gust et al. (2022) method. The average scores in Table 2 are much more similar than would be expected because of the different means for the UK that were used to calculate z-scores and IQs. The HLO mean for the UK is 527.8 in the Angrist et al. (2021) data, compared to the Gust et al. (2022) mean of 503.2. The higher HLO mean for the UK provides a correction to the HLO scores, when converted to IQs, and makes the weighted mean IQs for both datasets in Table 2 much more similar.

22. The QNW + SAS IQs for these countries are 69.45 (Botswana), 60.98 (Ghana), and 69.80 (South Africa). However, note that these are not independent of the PIRLS and TIMSS data because Lynn and Becker (2019b) used the educational achievement data to calculate SAS IQs, which contributed data to the QNW + SAS IQs.

23. The largest discrepancies were for the Dominican Republic (+ 20.11 IQ points), Yemen (+ 19.34 IQ points), Tunisia (+ 12.39 IQ points), Argentina (+ 11.45 IQ points), Kuwait (+ 10.59 IQ points), and Honduras (− 10.47 IQ points). In this list, positive numbers indicate a higher QNW + SAS score in the Lynn and Becker (2019b) dataset, and negative numbers indicate a higher IQ derived from the Patel and Sandefur (2020) study.

24. The four countries with geographically imputed IQs in Lynn and Becker’s (2019b) dataset that have discrepancies of at least 10 IQ points are Paraguay (+ 17.26 IQ points), Senegal (− 15.76 IQ points), Chad (+ 13.92 IQ points), and Niger (+ 10.10 IQ points). In this list, positive numbers indicate a higher QNW + SAS + GEO score in the Lynn and Becker (2019b) dataset, and negative numbers indicate a higher IQ derived from the Patel and Sandefur (2020) study.

25. The largest discrepancies were for Cambodia (+ 26.4 IQ points), Venezuela (− 23.1 IQ points), Cuba (− 20.6 IQ points), Pakistan (+ 18.4 IQ points), Nicaragua (− 15.9 IQ points), Sri Lanka (+ 15.9 IQ points), Guatemala (− 15.4 IQ points), the Dominican Republic (+ 15.3 IQ points), the Philippines (+ 14.8 IQ points), Kyrgyzstan (+ 13.1 IQ points), Argentina (+ 12.4 IQ points), Haiti (+ 12.2 IQ points), Morocco (− 11.4 IQ points), Mongolia (+ 10.8 IQ points), and the United Arab Emirates (− 10.1 IQ points). In this list, positive numbers indicate a higher QNW + SAS score in the Lynn and Becker (2019b) dataset, and negative numbers indicate a higher IQ derived from the Gust et al. (2022) study. The inclusion of Cuba on this list is due to the use of SERCE 2006 data in the Gust et al. (2022) paper. As I stated earlier in this article, the Cuban data for this test are an outlier and likely fraudulent. This shows that when national IQ discrepancies arise in different datasets, it does not always indicate that Lynn and Becker’s (2019b) data are wrong.

26. In descending order of the magnitude of the discrepancy, these countries were Honduras (22.62 IQ points lower), Botswana (18.52 IQ points lower), South Africa (13.80 IQ points lower), and Egypt (11.65 IQ points lower).

27. Testing students one grade higher typical is standard practice for South Africa when administering PIRLS and TIMSS tests.

28. The Burundi data are clearly an outlier. Patel and Sandefur (2020) reported that 43% of examinees in Burundi met or exceeded the TIMSS low international benchmark in reading, which is typical of PASEC countries (PASEC, 2015, p. 50). The discrepancy between Burundi’s math and reading performance originates in the PASEC data and is not an error in Patel and Sandefur’s conversion of PASEC scores to TIMSS scores.

29. Pupil age is another factor to consider in making these comparisons. Repeating a grade is much more common in sub-Saharan Africa than it is in Western countries. However, these older pupils score worse on the PASEC than their classmates who have never repeated a grade (PASEC, 2015, pp. 78–81). Unlike testing students in a higher grade, the inclusion of these older students does not increase the countries’ percentages of students who meet the TIMSS low international benchmark.

30. I only compared mathematics scores here because language differences (e.g., one language being easier to learn to read than another) make comparing reading scores and competency less straightforward than comparing proficiency in mathematics (Gust et al., 2022). Additionally, many children in African learn to read in a non-native language (i.e., Swahili, or a colonial language instead of their local African language), which would be a penalty when comparing reading scores to children in economically developed nations where most children are tested in their native language.

31. There are three versions of the Raven’s: the Colored Progressive Matrices, Progressive Matrices, and Advanced Matrices (listed in ascending order of difficulty).

32. Countries with a low NWQ + SAS IQ (≤ 75) based solely on matrix test data are Benin, the Republic of the Congo, Djibouti, Dominica, Eritrea, Ethiopia, The Gambia, Guatemala, Malawi, Mali, Morocco, Namibia, Nepal, Saint Vincent and the Grenadines, Sierra Leone, Somalia, South Sudan, Syria, Tanzania, Yemen, and Zimbabwe.

33. This is why I have preferred to use the QNW + SAS IQs whenever possible in this article. QNW + SAS IQs are based on the most data and do not include countries with geographically imputed mean IQs.

34. That is, unless one does not believe that educational performance, life outcomes, health and disease, economic prosperity, and strong civic institutions are important.

Our findings suggest though that liberals view emotion as a feature of rationality while conservatives view it as a bug

Do liberals value emotion more than conservatives? Political partisanship and Lay beliefs about the functionality of emotion. Minyoung Choi, Melissa M. Karnaze, Heather C. Lench & Linda J. Levine. Motivation and Emotion, Dec 19 2022. https://link.springer.com/article/10.1007/s11031-022-09997-4

Abstract: Relying on feelings to guide thoughts and plans may be functional from the perspective of the individual but threaten the cohesion of social groups. Thus, liberals, who prioritize caring and fairness for individuals, may view emotion as more functional than do conservatives, who prioritize preserving social groups, hierarchies, and institutions. To test this, participants in three studies (total N = 1,355) rated political partisanship, beliefs about the functionality of emotion, and well-being. Study 3 also assessed how much participants prioritized “individualizing” versus “socially binding” values (Graham et al., 2011). Across all studies, the more liberal participants were, the more they viewed emotion as functional, despite reporting less emotional well-being. In Study 3, the link between liberalism and valuing emotion was mediated by more liberal participants’ greater endorsement of individualizing than socially binding values. These results suggest that emotion is viewed as more functional by those who prioritize the needs of individuals, but as less functional by those who prioritize the cohesion of social groups.

General discussion

As the gap between liberals and conservatives widens to a chasm, and each group accuses the other of being either heartless or bleeding hearts, it becomes critically important to understand partisan perspectives on emotion. This investigation examined the relation between people’s political orientation and their beliefs about the functionality of emotion. The results across three studies were strikingly similar. The more liberal participants were, the more they viewed emotion as functional despite also reporting less well-being. In Study 3, the link between liberal partisanship and viewing emotion as functional was mediated by liberals’ greater endorsement of “individualizing” than “socially binding” moral values. These findings suggest that emotion is viewed as more functional by those who prioritize the needs of individuals, and as less functional by those who prioritize the cohesion of social groups.

Liberals value emotion more than conservatives

Powerful emotion, and appeals for greater rationality, are prevalent on both sides of the political continuum (Finkel et al., 2020; Frimer et al., 2019). Our findings suggest though that liberals view emotion as a feature of rationality while conservatives view it as a bug. Across three studies, liberals viewed emotion as more functional than conservatives – that is, as a healthy source of information about the self that provides direction in life rather than as a weakness and a waste of time. This link between liberalism and viewing emotion as functional remained after taking into account participants’ gender (in all studies) and religiosity (assessed in Studies 1 and 2). In Study 1, participants also reported the intensity with which they typically experience emotion and how they regulate emotion. The more liberal participants were, the more they reported experiencing intense emotion and the less they reported suppressing the expression of emotion. Further, viewing emotion as more functional mediated the association between liberal partisanship and reports of experiencing more intense emotion and engaging in less suppression. Thus, beliefs about the functionality of emotion may help to explain why people who are more liberal value emotional expressiveness more (Matsumoto et al., 2008), whereas people who endorse conservative policies are more motivated to avoid emotion (Leone & Chirumbolo, 2008).

Social values explained the Link between partisanship and Lay beliefs about emotion

In Study 3, we investigated whether participants’ social values explained the association between liberal partisanship and valuing emotion. Emotions provide information and guide action in a manner that is often functional for attaining the goals of the individual (Keltner & Gross, 1999; Scherer, 2019). However, relying on personal feelings to guide thoughts and plans may disrupt the harmonious functioning of social groups which include individuals with disparate goals (Mooijman et al., 2018). Thus, we expected participants who were primarily concerned with the needs of individuals to view emotion as more functional than those who were more attuned to the needs of social groups. We tested this by examining participants’ responses to the Moral Foundations Questionnaire (Graham et al., 2011).

Consistent with prior research, when judging actions as right or wrong, the more liberal participants were, the higher they scored on progressivism (Graham et al., 2009, 2011). That is, more liberal participants prioritized the “individualizing” moral foundations of caring and fairness, which address the needs of individuals, to a greater extent than the “binding” moral foundations of loyalty, authority, and sanctity, which help to maintain the cohesion of social groups. As expected, the link between liberalism and viewing emotion as functional was mediated by liberals’ greater endorsement of individualizing than binding social values. Thus, prioritizing the needs of individuals more than the cohesion of social groups helped explain the association between liberal partisanship and viewing emotion as more functional.

Openness to experience and well-being

We also assessed whether participants’ openness to experience (Study 1) or well-being (all three studies) could account for the link between liberal partisanship and viewing emotion as more functional. In Study 1, participants who were more open to experience viewed emotion as more functional. However, in contrast to past research (e.g., Desimoni & Leone, 2014; Sibley et al., 2012), openness to experience was not associated with political partisanship in our sample. Thus, this personality trait did not explain the association between partisanship and beliefs about emotion. Study 1 included relatively few conservative participants, so we interpret this finding with caution. Future research sampling a broader range of political partisanship should examine whether conservatives’ preference for stability and certainty over novelty and ambiguity contributes their view of emotion as less functional.

With respect to well-being, past research shows that feeling threatened and anxious can lead people to endorse more conservative views (e.g., Jost et al., 2003; Oxley et al., 2008). We found that participants who reported less well-being viewed emotion as less functional (Karnaze & Levine, 2018, 2020; Luong et al., 2016). But the link found between conservatism and viewing emotion as less functional was not explained by poorer well-being. In all three studies, more conservative participants viewed emotion as less functional despite reporting greater well-being. In summary, participants’ social values, but not their openness to experience or well-being, helped explain the association between liberal partisanship and viewing emotion as more functional.

Emotional responses to specific events

Finally, we explored whether participants’ beliefs about the functionality of emotion explained associations between partisanship and emotional responses to specific events. In Study 2, we assessed participants’ emotional responses to a personal experience of success or failure – receiving a favorable or unfavorable grade on an exam. After adjusting for the appraised importance of their grade and the specific letter grade received, participants’ feelings about their grades were not related to political partisanship. Irrespective of partisanship, those who viewed emotion as more functional felt happier about getting the grade they expected or higher. Emotion beliefs were not related to the unhappiness participants felt about receiving a grade that was lower than expected. In Study 3, we assessed participants’ emotional responses to a political experience of success or failure – Biden’s victory in the 2020 U.S. presidential election. After adjusting for how important the election outcome was for participants, and how much they agreed that Biden’s election was good for the country, partisanship did not predict how happy participants felt about Biden’s victory, but more conservative participants reported more anger and fear. Participants’ beliefs about the functionality of emotion were not related to the intensity of happiness, anger, or fear they reported.

In summary, our findings with respect to partisan differences in emotional experience were mixed. On one hand, as noted above, viewing emotion as functional explained more liberal participants’ reports of generally experiencing more intense emotion and engaging in less expressive suppression. On the other hand, when participants reported their actual emotional responses to specific events, we found few associations between emotional experience and partisanship after accounting for their appraisals of those events. The one partisan association found – between conservatism and greater anger and fear about Biden’s victory – was not related to beliefs about the functionality of emotion. Overall, these findings were in keeping with past research showing that group differences in emotion values (e.g., differences in the emotions people ideally want to feel) are more pronounced and consistent than group differences in people’s actual feelings in response to concrete day-to-day events (Tsai et al., 2006).

Limitations and directions for Future Research

This investigation extended the emerging literature on lay beliefs about emotion to address an increasingly contentious and defining feature of people’s identity – political partisanship. Our findings suggest that prioritizing the needs of individuals over those of social institutions contributes to the association between liberal partisanship and the belief that emotions are functional. A limitation of this investigation, however, is that the causal direction of the relationship between partisanship and beliefs about emotion cannot be determined from correlational data. Future research could assess if experimentally manipulating whether people prioritize the needs of individuals over groups increases the value they place on the directive and expressive functions of emotion.

A second limitation is that factors in addition to social values may contribute to partisan differences in valuing emotion. For example, children’s early experiences shape both their political orientation and their attitudes about emotion. Children tend to adopt their parents’ political ideology (Boshier & Thom, 1973) and, when it comes to responding to children’s emotions, the parenting philosophies and practices of liberals and conservatives differ. Liberal parents encourage children to identify and communicate emotions rather than suppress them (Friedlmeier et al., 2011). What liberals consider to be sensitive and responsive emotion coaching, conservatives consider irresponsibly indulgent (Schreiber et al., 2013). Future research should explore how these parenting approaches shape liberals’ and conservatives’ differing beliefs about the value of emotion.

A third limitation is that, Studies 2 and 3 used the most common unidimensional measure of U.S. political partisanship which ranges from strongly conservative to strongly liberal. A recent meta-analysis showed that the association between moral progressivism (that is, individualist vs. binding values) and political partisanship is stronger for social than economic political orientation, varies modestly across countries with different political histories, and even varies across U.S. demographic and political groups (Kivikangas et al., 2021). For example, when libertarians make more decisions, they rely less on emotion, less on all five moral foundations, and more on considerations of individual freedom, than both liberals and conservatives (Iyer et al., 2012). Thus, extending the research beyond a unidimensional measure of partisanship, and to demographic groups from non-university samples, may yield further insights about the generalizability of the findings and the relations among political orientation, social values, and beliefs about the functionality of emotion.

Finally, participants in our studies may have interpreted questions about the functionality of emotion as referring to individuals’ emotional responses to events that impact their personal goals. Future research should examine whether conservatives value emotions as much or more than liberals when emotions are experienced and expressed on behalf of their social groups and institutions. For example, compared to liberals, conservatives may place greater value on feelings of pride toward family, community, and country, and anger toward perceived threats to these institutions (Porat et al., 2016). Compared to both liberals and conservatives, libertarians may value pride in individual achievement and anger about infringements on individual autonomy (Iyer et al., 2012).

Human capacity for emotional experiences of pleasure and pain spans an incredibly wide range of intensity, a minimum of two orders of magnitude between the most mild and the most intense experiences

Gómez-Emilsson, Andrés, and Chris Percy. 2022. “The Heavy-tailed Valence Hypothesis: The Human Capacity for Vast Variation in Pleasure/pain and How to Test It.” PsyArXiv. December 19. psyarxiv.com/krysx

Abstract: This paper proposes the "Heavy-Tailed Valence” (HTV) hypothesis: the notion that human capacity for emotional experiences of pleasure and pain spans an incredibly wide range of intensity, a minimum of two orders of magnitude between the most mild and the most intense experiences. We set out a thought experiment, the "integer experiment test", to demonstrate that such a capacity is not arbitrary: a wide range could not simply be mapped onto a narrow range without losing something tangible.

In directional support of the hypothesis, we discuss three stylized facts, based on heavy-tailed neurological functions, the application of pain/discomfort scales, and the existence of extreme events. We also present five intuitions against the hypothesis and suggest reasons to reject these counter-intuitions. Recognizing this theoretical ambiguity, we turn to specifying additional assumptions under which the hypothesis results in testable empirical claims.

A pilot survey (n=97) investigated how people describe their most intense experiences, finding tentative support for the hypothesis in preparation for a larger survey revised based on insights from the pilot. Over half said their most intense painful experience was at least three times more intense than the second most intense. Simulations further suggest an underlying heavy-tailed distribution of experience valences is more consistent with the survey responses. The results also raise doubts over the cardinal interpretation at the high end of 0-10 scales for pleasure or pain, with over 80% of respondents appearing to compress experienced intensity in order to report high values.

Finally, we discuss how a larger future survey could mitigate the limitations in the pilot study and discuss potential implications of the hypothesis for wellbeing economics, ethics, and personal life choices.

We found that androgynous group reported themselves to be more creative than the gender conforming group, but they did not score higher than the latter on behavioral creativity

Liu, T., & Damian, R. I. (2022). Are androgynous people more creative than gender conforming people? Psychology of Aesthetics, Creativity, and the Arts, Dec 2022. https://doi.org/10.1037/aca0000536

Abstract: Psychological androgyny refers to possessing both masculine and feminine characteristics. Sandra Bem (1974) proposed that androgynous people are more creative, because they are less limited by gender boundaries. This so-called androgyny-creativity effect contributes to the gender equality movement by ameliorating stereotypes about people who stepped out of gender boundaries. However, the evidentiary value of the available research testing this hypothesis has been limited by suboptimal (by current standards) methodology, such as small samples, antiquated statistical analysis, and inconsistent measurement. The current study attempted to replicate the androgyny-creativity effect in a large sample (N = 672), with both self-report and behavioral measures of creativity, and following both original and optimized statistical analyses. We found that androgynous group reported themselves to be more creative than the gender conforming group, but they did not score higher than the latter on behavioral creativity. This suggests that the androgyny-creativity effect (a) could be just a popular lay theory, (b) might only hold for certain types of creativity, and (c) might be a true effect but no longer exist due to societal changes in gender roles.

The great decline in adolescent risk behaviours, 1999—2019: Unitary trend, separate trends, or cascade?

The great decline in adolescent risk behaviours: Unitary trend, separate trends, or cascade? Jude Ball et al. Social Science & Medicine, December 16 2022, 115616. https://doi.org/10.1016/j.socscimed.2022.115616

Abstract: In many high-income countries, the proportion of adolescents who smoke, drink, or engage in other risk behaviours has declined markedly over the past 25 years. We illustrate this behavioural shift by collating and presenting previously published data (1990–2019) on smoking, alcohol use, cannabis use, early sexual initiation and juvenile crime in Australia, England, the Netherlands, New Zealand, and the USA, also providing European averages where comparable data are available. Then we explore empirical evidence for and against hypothesised causes of these declines. Specifically, we explore whether the declines across risk behaviours can be considered 1) a ‘unitary trend’ caused by common underlying drivers; 2) separate trends with behaviour-specific causes; or 3) the result of a ‘cascade’ effect, with declines in one risk behaviour causing declines in others. We find the unitary trend hypothesis has theoretical and empirical support, and there is international evidence that decreasing unstructured face-to-face time with friends is a common underlying driver. Additionally, evidence suggests that behaviour-specific factors have played a role in the decline of tobacco smoking (e.g. decreasing adolescent approval of smoking, increasing strength of tobacco control policies) and drinking (e.g. more restrictive parental rules and attitudes toward adolescent drinking, decreasing ease of access to alcohol). Finally, declining tobacco and alcohol use may have suppressed adolescent cannabis use (and perhaps other risk behaviours), but evidence for such a cascade is equivocal. We conclude that the causal factors behind the great decline in adolescent risk behaviours are multiple. While broad contextual changes appear to have reduced the opportunities for risk behaviours in general, behaviour-specific factors have also played an important role in smoking and drinking declines, and ‘knock-on’ effect from these behavioural domains to others are possible. Many hypothesised explanations remain to be tested empirically.

Introduction

Throughout much of the developed world, adolescent smoking, drinking, underage sex, and juvenile crime declined dramatically between the late 1990s and around 2015 (Ball et al., 2018; Pape et al., 2018; Twenge, 2017), yet the reasons for this widespread and long-term trend are not well understood. Better understanding of what caused declines in risk behaviours is vital if we are to predict and influence future trends. Trends for some risk behaviours plateaued or even began to reverse in some countries in the 2015–2019 period, adding urgency to the need to understand what drives teen trends and apply the lessons to preventive efforts.

In this narrative review we document this shift in adolescent behaviour and discuss evidence to date on possible causes. Potential causes are explored within three overarching hypotheses which are not mutually exclusive: 1) declines represent a ‘unitary trend’ with common underlying causes resulting in simultaneous declines in many risk behaviours; 2) declines in various risk behaviours are separate, caused by behaviour-specific factors; and 3) declines in certain risk behaviours have caused declines in others (the ‘cascade’ hypothesis).

To contextualise the changes in risk behaviours it is important to consider how the lives of adolescents have changed over recent decades within the economic, social, cultural and technological spaces they inhabit. Contextual changes over time in the labour market, regulatory environment, school environment, parenting norms, youth culture, and information technology, for example, have undoubtedly shaped the experiences of young people as well as their worldviews, attitudes and behaviours. The idea that young people's development and behaviour are influenced by the contexts in which they grow up has been termed the social ecological approach (Brofenbrenner, 1977; Sallis et al., 2008). This approach provides an overarching theoretical framework within which we explore the recent shift in adolescent behaviour and possible causes.

This review has two parts. In the first, we present an overview of recent international trends in substance use, sexual behaviour and juvenile crime, highlighting long-term changes. In the second we discuss the plausibility of selected causal hypotheses for the simultaneous decline in multiple risk behaviours, drawing on theory and empirical evidence to date.

Short-term effective radiative forcing trends are difficult to verify, so caution is required in predictions/policy judgments that depend on them, such as the time remaining to, or the outstanding carbon budget consistent with, 1.5C warming

Is Anthropogenic Global Warming Accelerating? Stuart Jenkins et al. Journal of Climate, Vol 35, Issue 24, Pages 4273–4290, Nov 22 2022. https://doi.org/10.1175/JCLI-D-22-0081.1

Abstract: Estimates of the anthropogenic effective radiative forcing (ERF) trend have increased by 50% since 2000 (from +0.4 W m−2 decade−1 in 2000–09 to +0.6 W m−2 decade−1 in 2010–19), the majority of which is driven by changes in the aerosol ERF trend, as a result of aerosol emissions reductions. Here we study the extent to which observations of the climate system agree with these ERF assumptions. We use a large ERF ensemble from the IPCC’s Sixth Assessment Report (AR6) to attribute the anthropogenic contributions to global mean surface temperature (GMST), top-of-atmosphere radiative flux, and we use aerosol optical depth observations. The GMST trend has increased from +0.18°C decade−1 in 2000–09 to +0.35°C decade−1 in 2010–19, coinciding with the anthropogenic warming trend rising from +0.19°C decade−1 in 2000–09 to +0.24°C decade−1 in 2010–19. This, as well as observed trends in top-of-atmosphere radiative fluxes and aerosol optical depths, supports the claim of an aerosol-induced temporary acceleration in the rate of warming. However, all three observation datasets additionally suggest that smaller aerosol ERF trend changes are compatible with observations since 2000, since radiative flux and GMST trends are significantly influenced by internal variability over this period. A zero-trend-change aerosol ERF scenario results in a much smaller anthropogenic warming acceleration since 2000 but is poorly represented in AR6’s ERF ensemble. Short-term ERF trends are difficult to verify using observations, so caution is required in predictions or policy judgments that depend on them, such as estimates of current anthropogenic warming trend, and the time remaining to, or the outstanding carbon budget consistent with, 1.5°C warming. Further systematic research focused on quantifying trends and early identification of acceleration or deceleration is required.

4. Consequences of alternative aerosol forcing trends

Successive IPCC reports have given assessments of the level of anthropogenic global warming, but no equivalent assessment of the rate of human-induced warming has been made. This is despite the rate of warming offering arguably more policy relevance at the present day in determining the time remaining to key goals of the Paris Agreement. This study highlights the key contributors to a perceived acceleration in the anthropogenic rate of warming since 2000 and uses observations of the climate system to constrain the forced response. Section 2 breaks down an ERF dataset that suggests anthropogenic ERF accelerated between 2000 and 2020, shown to arise because of aerosol forcing trends becoming positive around 2010 in the ERF ensemble. In section 3 we then step through three observational records to search for evidence supporting this assessed trend change.

Global temperatures show a clear change in trend between 2000 and 2020, characterized by temperatures remaining stable at around +1.0°C above preindustrial levels in the first decade, whereas in the second decade temperatures increase rapidly (with the rate of warming peaking at over +0.3°C decade−1). The reduced warming trend around 2000 has been discussed in the context of ocean heat uptake and natural variability (Masson-Delmotte et al. 2021; IPCC et al. 2013), but less research has focused on a possible warming acceleration in the following decade induced by aerosol ERF trend changes. By attributing the temperature trends to anthropogenic and natural ERFs we show that the forcing time series from Fig. 2 capture the broad warming contributions over the previous two decades (Fig. 4). However, significant variations around the anthropogenic best fit are still present (e.g., see the period of early Arctic warming in Fig. 4a), and alternative forcing trend change assumptions can be applied with little indication of a worse fit. A three-way regression isolates the aerosol contribution over history in Fig. 5, fitting the mid-twentieth-century GMST more successfully by downscaling the aerosol contribution. Hence, the aerosol ERF trend change contribution since 2000 is also downscaled, with best-estimate anthropogenic warming trend change around +0.05°C decade−1 between 2000–09 and 2010–19 (the 5th–95th-percentile range spans 0.01°–0.08°C decade−1). The aerosol contribution to this is +0.03°C decade−1 between 2000–09 and 2010–19 (the 5th–95th-percentile range spans 0.00°–0.07°C decade−1).

In the CERES record, LW TOA flux contributions are explained by recent GMST and forcing trends combined, while there is greater uncertainty in the contributors to the SW and net flux anomalies. In the SW anomaly, unforced variability in temperature and TOA flux time series precludes clear assessments of the aerosol ERF contribution, supporting the assessment that significant contributions from ENSO and PDO are present in recent TOA flux trend changes. Given this, TOA flux trends cannot rule out little to no anthropogenic ERF trend change over the two decades, despite the best-estimate anthropogenic ERF time series agreeing well with both TOA fluxes and temperature anomalies. Figure 6’s middle column (atmosphere-only TOA flux anomalies) and right column (coupled-model TOA flux anomalies) confirm the major role played by natural variability processes in these TOA flux records, demonstrating that the trend change induced in the SW TOA flux anomaly, where we expect to observe a large trend change induced by aerosols (Fig. 6h), is small relative to the trend change caused by unforced variability over the previous two decades (Fig. 6e). Continued funding for new satellites to study the outgoing radiative balance of the Earth system (such as the recently announced FORUM mission; ESA 2021) is vitally important in order to maintain long-term records and constrain radiative feedbacks with greater certainty.

Satellite observations and CMIP6 models agree that a relatively small AOD trend change has occurred over the last two decades, despite significant reductions in anthropogenic aerosol emissions in the Northern Hemisphere. Exploring a linear relationship between AOD and aerosol ERF trends (based on the mean response of CMIP6 models) allows us to estimate the ERF trend change expected in response to the observed AOD trend change since 2000. This analysis again supports the best estimate ERFs in Fig. 2, but also suggests that little-to-no trend change remains a possible assessment for ERF trends since 2000 in observations. The spatial pattern of aerosol emissions also may play a role in determining the aerosol ERF level (Stier et al. 2013), causing nonlinearities in the AOD and ERF responses to globally averaged aerosol emissions reductions. Further research of ERF trends and feedbacks using their full spatiotemporal signal in AMIP GCM experiments where forcing time series are known, and conducting regional aerosol perturbation experiments in coupled models (Wilcox et al. 2022), will provide more insight.

Overall, this assessment suggests that aerosol emissions reductions have contributed to an increase in the rate of anthropogenic warming since 2000, but both to a lesser degree than is suggested in the ERFs presented in Fig. 2, and with a substantial uncertainty range including the possibility of little contribution over two decades. The forced behavior coincides with a period of considerable internal variability, meaning that isolating the aerosol-induced ERF trend change from observations is challenging, and that a wide range of ERF scenarios offer plausible explanations of the past 20 years. Some of these possibilities are not well represented in the ERF ensemble shown in Fig. 2: for example, a zero-trend-change aerosol ERF scenario between 2000 and 2020 (shown in Fig. 2 as an dashed orange line, with the corresponding anthropogenic ERF a black dashed line), is considered possible in the analysis of all three observation datasets but is not represented well in the ERF ensemble of Fig. 2. Using a zero-trend-change aerosol ERF to attribute the anthropogenic contribution to global warming results in a similar quality fit to GMSTs (see dashed orange and black lines in Fig. 5, left panel), but substantially reduces the anthropogenic warming trend change that occurs since 2000 (orange and black dashed lines in Fig. 5, right panel). A comprehensive ERF ensemble of the recent time-history of anthropogenic ERF should offer these alternative scenarios, including scenarios with reduced aerosol ERF trend change since 2000 and with alternative rescalings for all pollutants using global energy balance constraints [e.g., those in Smith et al. (2021a) or Fig. 5].

The importance of continuing to track and constrain the early twenty-first century’s forcing trends is underappreciated, and future work should focus on providing better constraints to near-term forcing trends as well as their levels. Short-term ERF trends are vital to accurately assess this decade’s warming rate, with tangible, real-time impacts for global mitigation policy.

Think-tank employees favor military intervention much more than professors; those who favor interventionist policies are more likely to pursue positions to increase their policy influence

What Do Think Tanks Think? Proximity to Power and Foreign Policy Preferences. Richard Hanania, Max Abrahms. Foreign Policy Analysis, Volume 19, Issue 1, January 2023, orac031, https://doi.org/10.1093/fpa/orac031

Abstract: Through the use of survey methods, the study presents the first systematic comparison of America-based international relations professors to think tank employees (TTEs) in terms of their preferred conduct of the United States in international affairs. The difference between the two groups in their support for military intervention is stark. TTEs are 0.47 standard deviations more hawkish than professors based on a standard measure of militant internationalism (MI). Controlling for self-described ideology mitigates this effect although it remains statistically significant. Beyond quantifying their relative foreign policy preferences, this study helps to resolve why TTEs tend to assume more hawkish policies. The authors find evidence that hawkishness is associated with proximity to power. Professors who have worked for the federal government score higher on MI, as do TTEs based at institutions located closer to Capitol Hill. In general, the results point to a self-selection mechanism whereby those who favor interventionist policies are more likely to pursue positions to increase their policy influence, perhaps because they know that powerful institutions are more likely to hire hawks. Alternative explanations for differences, such as levels or kinds of foreign policy expertise, have weaker empirical support.

Among older adults with subjective cognitive concerns, mindfulness training, exercise, or both did not result in significant differences in improvement in episodic memory or executive function at 6 months

Effects of Mindfulness Training and Exercise on Cognitive Function in Older Adults: A Randomized Clinical Trial. Eric J. Lenze et al. JAMA. 2022;328(22):2218-2229. doi:10.1001/jama.2022.21680

Key Points

Question  Does mindfulness training, exercise, or the combination of these interventions improve cognitive function in older adults with subjective cognitive concerns?

Findings  In this randomized clinical trial that included 585 participants, mindfulness training, exercise, or both did not result in significant differences in improvement in episodic memory or executive function composite scores at 6 months.

Meaning  The findings do not support the use of mindfulness training, exercise, or a combination of both for significantly improving cognitive function in older adults with subjective cognitive concerns.

Abstract

Importance  Episodic memory and executive function are essential aspects of cognitive functioning that decline with aging. This decline may be ameliorable with lifestyle interventions.

Objective  To determine whether mindfulness-based stress reduction (MBSR), exercise, or a combination of both improve cognitive function in older adults.

Design, Setting, and Participants  This 2 × 2 factorial randomized clinical trial was conducted at 2 US sites (Washington University in St Louis and University of California, San Diego). A total of 585 older adults (aged 65-84 y) with subjective cognitive concerns, but not dementia, were randomized (enrollment from November 19, 2015, to January 23, 2019; final follow-up on March 16, 2020).

Interventions  Participants were randomized to undergo the following interventions: MBSR with a target of 60 minutes daily of meditation (n = 150); exercise with aerobic, strength, and functional components with a target of at least 300 minutes weekly (n = 138); combined MBSR and exercise (n = 144); or a health education control group (n = 153). Interventions lasted 18 months and consisted of group-based classes and home practice.

Main Outcomes and Measures  The 2 primary outcomes were composites of episodic memory and executive function (standardized to a mean [SD] of 0 [1]; higher composite scores indicate better cognitive performance) from neuropsychological testing; the primary end point was 6 months and the secondary end point was 18 months. There were 5 reported secondary outcomes: hippocampal volume and dorsolateral prefrontal cortex thickness and surface area from structural magnetic resonance imaging and functional cognitive capacity and self-reported cognitive concerns.

Results  Among 585 randomized participants (mean age, 71.5 years; 424 [72.5%] women), 568 (97.1%) completed 6 months in the trial and 475 (81.2%) completed 18 months. At 6 months, there was no significant effect of mindfulness training or exercise on episodic memory (MBSR vs no MBSR: 0.44 vs 0.48; mean difference, –0.04 points [95% CI, –0.15 to 0.07]; P = .50; exercise vs no exercise: 0.49 vs 0.42; difference, 0.07 [95% CI, –0.04 to 0.17]; P = .23) or executive function (MBSR vs no MBSR: 0.39 vs 0.31; mean difference, 0.08 points [95% CI, –0.02 to 0.19]; P = .12; exercise vs no exercise: 0.39 vs 0.32; difference, 0.07 [95% CI, –0.03 to 0.18]; P = .17) and there were no intervention effects at the secondary end point of 18 months. There was no significant interaction between mindfulness training and exercise (P = .93 for memory and P = .29 for executive function) at 6 months. Of the 5 prespecified secondary outcomes, none showed a significant improvement with either intervention compared with those not receiving the intervention.

Conclusions and Relevance  Among older adults with subjective cognitive concerns, mindfulness training, exercise, or both did not result in significant differences in improvement in episodic memory or executive function at 6 months. The findings do not support the use of these interventions for improving cognition in older adults with subjective cognitive concerns.

Parental Income and the Sexual Behavior of Their Adult Children: A Trivers–Willard Perspective

Parental Income and the Sexual Behavior of Their Adult Children: A Trivers–Willard Perspective. John T. Manning, Bernhard Fink, and Robert Trivers. Evolutionary Psychology, December 12, 2022. https://doi.org/10.1177/14747049221142858

Abstract: Parental income is negatively and linearly related to the digit ratio (2D:4D; a proxy for prenatal sex steroids) of their children. Children of parents with high income are thought to be exposed to higher prenatal testosterone and develop lower 2D:4D. It is further hypothesized that 2D:4D relates to sexual orientation, although it is unclear whether the association is linear or curvilinear. Here, we consider patterns of parental income and its association with the sexual behavior of their adult children in a large online study (the BBC internet study). There were curvilinear relationships with parental income in male and female children. The highest frequencies of homosexuality and bisexuality were found in the lowest income group (bottom 25% of the population), the lowest frequencies in the income group representing the upper 50% of the population, and intermediate values in the other groups (low 50% and top 25% of the population). Parental income showed a U-shaped association with scores for same-sex attraction and an inverted U-shaped association with opposite-sex attraction. Thus, for the first time, we show that same-sex attraction is related to parental income. The curvilinear relationship between parental income and sexual behavior in their adult children may result from an association between very high fetal estrogen or testosterone and attraction to partners of the same sex. Among non-heterosexuals, and in both sexes, very high fetal estrogen may be associated with femme or submissive sexual roles, and very high fetal testosterone with butch and assertive sexual roles.

Check also High-income women may prenatally masculinize their sons at the expense of the fitness of their daughters; low-income women may prenatally feminize their daughters at the fitness expense of their sons:

Parental income inequality and children’s digit ratio (2D:4D): a ‘Trivers-Willard’ effect on prenatal androgenization? J.T. Manning et al. Journal of Biosocial Science, February 2021. https://www.bipartisanalliance.com/2021/02/high-income-women-may-prenatally.html

Discussion

The current study found that in male adult children, homosexuality was the most frequent non-heterosexual group and bisexuality was rare. For female adult children, bisexuality was more frequent than homosexuality. Parental income was related to the frequency of sexual orientation (heterosexuality, homosexuality, bisexuality) of their adult children. The association between parental income and sexual orientation of children was found in the total sample and when we considered the most numerous ethnic group (Whites) in the two largest national samples (UK and USA), thus confirming our prediction (i).

Parents with income that was “much lower than others” (bottom 25% of the population) had the highest frequencies of homosexuality and bisexuality for both male and female adult children. The lowest frequency of homosexuality was found in the male and female children of parents with an income “slightly higher than others” (upper 50% of the population). Parents with an income “much higher than others” (top 25% of the population) had male and female children with intermediate frequencies of homosexuality.

Concerning adult children's scores for sexual attraction to others, in men, same-sex attraction was highest among children of parents with an income corresponding to the bottom and top 25% of the population, and the lowest scores were found in children of parents with an income “slightly higher than others” (upper 50% of the population). For women, same-sex attraction was greatest for adult children of parents with an “income much lower than others” (bottom 25% of the population), lowest in children of parents with an income “slightly higher than others” (as for men) and intermediate for children of parents with an income representing the top 25% of the population. Splitting the sample for ethnicity (Whites only) and nation (UK and USA), UK scores for adult children's same-sex attraction were lower than those for the US with the former reporting the highest scores for the income group representing the bottom 25% of the population and the latter reporting very high scores for the highest income group (top 25% of the population). Overall, for both the frequency of sexual orientation groups and the same-sex attraction scores, we found no evidence for linear relationships. Concerning same-sex attraction scores, post hoc tests confirmed a U-shaped association such that the frequency of homosexuality/bisexuality and the magnitude of same-sex attraction scores were highest in the adult children from parents with the lowest (bottom 25% of the population) and to a lesser extent in parents with the highest income (top 25% of the population). The nadir of the attraction scores was observed in adult children from parents with an income “slightly higher than others” (upper 50% of the population). Therefore, our prediction (ii) was rejected and prediction (iii) was supported.

The curvilinear relationships between parental income and the sexual behavior of their adult children are, to our knowledge, novel. Our interpretation of these relationships is through the lens of the “Trivers–Willard” hypothesis (Trivers & Willard, 1973). We suggest that parental income is a marker of maternal condition (Babones, 2008; Pickett & Wilkinson, 2015). Male children have a greater variance in reproductive success than female children in human and nonhuman animals (Bateman, 1948; Trivers & Willard, 1973). Male children of mothers in poor condition (lowest parental income) will have below-average male reproductive success, but in contrast, daughters from mothers with the lowest parental income will have reproductive success closer to the female mean. Thus, mothers will be selected to favor their daughters depending on parental income by reducing their prenatal testosterone and increasing their prenatal estrogen. If mothers cannot distinguish between their male and female fetuses this will mean they expose their male offspring to a feminized fetal environment. Conversely, mothers in good condition (highest parental income) will androgenize their fetuses of both sexes. We have found high frequencies of homosexuality and bisexuality and same-sex attraction scores in adult children of mothers with the lowest and highest parental income. This suggests that both a high fetal estrogen-to-testosterone ratio and a high fetal testosterone-to-estrogen ratio are related to an increase in the probability of non-heterosexuality in adult children. We speculate that among the former, there may be a high proportion of “receptive” male homosexuals and “femme” female homosexuals. Among the latter, there may be a preponderance of “insertive” male homosexuals and “butch” female homosexuals.

In conclusion, the current study builds on the finding that parental income is negatively related to 2D:4D in both adult female and male children (Manning et al., 2022). Insofar as 2D:4D is a correlate of prenatal sex steroids and prenatal sex steroids influence sexual behavior, we predicted that parental income would be associated with children's sexual orientation and same-sex scores for sexual attraction to others. Our prediction was confirmed, so that compared to adult children of parents with the lowest income and those with an income “slightly higher,” the former was associated with higher frequencies of homosexuality and bisexuality and high attraction scores toward the same sex for both male and female adult children. Moreover, a comparison between children from “slightly higher” income families and those that had “much higher” income also showed an increase in homosexuality, bisexuality, and same-sex attraction scores in the latter. We suggest that very high fetal estrogen and testosterone are both associated with nonheterosexual behavior in adult male and female children. That is, prenatal sex steroids are related to sexual orientation in a U-shaped fashion. The relationship between 2D:4D and sexual orientation should now be reexamined for curvilinear effects. 

Increasing Tweeter access yields less corporate misconduct; effect is stronger for facilities of more visible firms; effect is concentrated in non-financial violations (unsafe workplace conditions or inappropriate treatment of employees/customers)

Heese, Jonas and Pacelli, Joseph, The Monitoring Role of Social Media (November 16, 2022). SSRN: http://dx.doi.org/10.2139/ssrn.4278696

Abstract: In this study, we examine whether social media activity can reduce corporate misconduct. We use the staggered introduction of 3G mobile broadband access across the United States to identify exogenous increases in social media activity and test whether access to 3G reduces misconduct. We find that facilities reduce violations by 1.8% and penalties by 13% following the introduction of 3G in a local area. To validate social media activity as the underlying mechanism, we show that 3G access results in sharp increases in Tweet volume and that facilities located in areas with high Tweet volume engage in less misconduct. The effect of 3G access on misconduct is stronger for facilities of more visible firms and concentrated in non-financial violations, such as those involving unsafe workplace conditions and inappropriate treatment of employees and customers. Overall, our results demonstrate that social media plays an important role in monitoring corporate misconduct.

Keywords: corporate misconduct, social media, Twitter, mobile broadband.

JEL Classification: M40, M41, M43

Humans stand alone in nature in their ability to form lasting, peaceful and productive relationships with conspecifics from foreign groups

The Evolution of Peace. Luke Glowacki. Behavioral and Brain Sciences, December 16 2022. https://doi.org/10.1017/S0140525X22002862

Abstract: While some species have affiliative and even cooperative interactions between individuals of different social groups, humans are alone in having durable, positive-sum, interdependent relationships across unrelated social groups. Our capacity to have harmonious relationships that cross group boundaries is an important aspect of our species’ success, allowing for the exchange of ideas, materials, and ultimately enabling cumulative cultural evolution. Knowledge about the conditions required for peaceful intergroup relationships is critical for understanding the success of our species and building a more peaceful world. How do humans create harmonious relationships across group boundaries and when did this capacity emerge in the human lineage? Answering these questions involves considering the costs and benefits of intergroup cooperation and aggression, for oneself, one's group, and one's neighbor. Taking a game theoretical perspective provides new insights into the difficulties of removing the threat of war and reveals an ironic logic to peace—the factors that enable peace also facilitate the increased scale and destructiveness of conflict. In what follows, I explore the conditions required for peace, why they are so difficult to achieve, and when we expect peace to have emerged in the human lineage. I argue that intergroup cooperation was an important component of human relationships and a selective force in our species history in the past 300 thousand years. But the preconditions for peace only emerged in the past 100 thousand years and likely coexisted with intermittent intergroup violence which would have also been an important and selective force in our species’ history.