Sunday, February 2, 2020

Liberian experiment: After one academic year, students in outsourced schools scored 0.18 σ higher in English and mathematics

Outsourcing Education: Experimental Evidence from Liberia. Mauricio Romero, Justin Sandefur, and Wayne Aaron Sandholtz. American Economic Review. Feb 2020, Vol. 110, No. 2: Pages 364-400.

Abstract: In 2016, the Liberian government delegated management of 93 randomly selected public schools to private providers. Providers received US$50 per pupil, on top of US$50 per pupil annual expenditure in control schools. After one academic year, students in outsourced schools scored 0.18 σ higher in English and mathematics. We do not find heterogeneity in learning gains or enrollment by student characteristics, but there is significant heterogeneity across providers. While outsourcing appears to be a cost-effective way to use new resources to improve test scores, some providers engaged in unforeseen and potentially harmful behavior, complicating any assessment of welfare gains. (JEL H41, I21, I28, O15)

Tyler Cowen says (
[...] The gains are real, and not the result of student selection.  That said costs are higher with the private contracting.  Better partner selection would have improved the program greatly, though the authors note that some of the most promising partners ex ante ended up being the biggest troublemakers ex post.  Some of the schools, for instance, allowed a possibly unacceptably degree of sexual abuse of the students.  There is perhaps potential for dynamic reoptimization of permissible partners to yield very real gains, though this may or may not be supported by the available political economy incentives.

The authors suggest, by the way, that outsourcing or contracting out to the private sector often does better when quality is relatively simple, such as with water services, food distribution, and simple forms of primary health care, such as immunization.  In their view, for advanced health care and prisons, contracting is less effective, due to the vaguer nature of product quality.

Unwantedness across birth order explains a substantial part of the documented birth order effects in education & employment; we find no birth order effects in families who have more control over their fertility

Birth order and unwanted fertility. Wanchuan Lin, Juan Pantano, Shuqiao Sun. Journal of Population Economics, April 2020, Volume 33, Issue 2, pp 413–440.

Abstract: An extensive literature documents the effects of birth order on various individual outcomes, with later-born children faring worse than their siblings. However, the potential mechanisms behind these effects remain poorly understood. This paper leverages US data on pregnancy intention to study the role of unwanted fertility in the observed birth order patterns. We document that children higher in the birth order are much more likely to be unwanted, in the sense that they were conceived at a time when the family was not planning to have additional children. Being an unwanted child is associated with negative life cycle outcomes as it implies a disruption in parental plans for optimal human capital investment. We show that the increasing prevalence of unwantedness across birth order explains a substantial part of the documented birth order effects in education and employment. Consistent with this mechanism, we document no birth order effects in families who have more control over their own fertility.

Keywords: Birth order Unwanted births Fertility intentions
JEL Classification: J13 J22 J24

The growth of behavioural complexity as well as the ex-vivo accumulation of human behaviour (non-genetically inherited behaviourome), cannot be explained by genetic/epigenetic mechanisms of inheritance

Mechanisms of a near-orthogonal ultra-fast evolution of human behaviour as a source of culture development. Christian P. Müller. Behavioural Brain Research, February 2 2020, 112521.

• A new mechanism for the recent time evolution of human behaviour is proposed
• Non-genetic inheritance (NGI) and accumulation of behaviour is crucial for culture
• The human behaviourome concept is introduced
• Mechanisms of a near-orthogonal and ultra-fast NGI of the behaviourome are suggested
• Behaviourome mutations can be target-directed
• Ex-vivo storage and -accumulation of the behaviourome are pivotal for culture

Abstract: Current human culture is characterized by an increasing rate of accumulating potential and actually performed behaviours. The growth of behavioural complexity as well as the ex-vivo accumulation of human behaviour, here identified as the non-genetically inherited (NGI) behaviourome, cannot be explained by genetic/epigenetic mechanisms of inheritance. As human beings derive their socio-cultural identity predominantly from their behaviourome, mechanisms of heritability should predominantly consider inheritance and accumulation of the NGI behaviourome. Here we propose key mechanisms of a near-orthogonal and ultra-fast evolution of the NGI human behaviourome that provide a foundation not only of unique human culture development, but also of its recent acceleration. Thereby, the evolution of the human NGI behaviourome underlies similar features as genetically based evolution. However, specific mechanisms of mutation and selection work largely independent (orthogonal) from genetic/epigenetic mechanisms. We suggest a mechanism of how adaptive changes (mutations) in the NGI behaviourome work target-directed and how selection works on an ultra-fast time scale. Selection results are mostly not fatal for the individual which allows for a much increased mutation rate. For crucial accumulation of the NGI behaviourome, ex-vivo storage and retrieval systems of virtually unlimited capacity are described. We discuss the great potential of the human NGI behaviourome in respect of speculative human super-reproduction and homosexual reproduction success, as well as a possible unique human way to avoid reproduction failure in childlessness. Altogether, this model of human behavioural reproduction and accumulation of behaviour may provide a base for better understanding and prediction of uniquely human cultural development.

Keywords: behaviouromebehavioural accumulationcultural evolutionex-vivo storagenear-orthogonal evolutionnon-genetic inheritancereplication failure, super-reproductiontargeted mutationultra-fast selection


9. Childless and homosexual reproduction success

It is speculated that a considerable part of the human population which appears threatened by reproduction failure are childless and homosexual man and women, which were denied a direct genetic reproduction. In non-human animals, the lack of genetically-related offspring and homosexuality leads to a general reproduction failure which may, however, be partly overcome by supporting kin and their offspring [182]. In humans, the individual NGI behaviourome constitutes a large part of the personal identity. This can be passed on in a gradual way, from almost complete to small traces of the individual NGI behaviourome. The individual NGI behaviourome may very well be inherited in small or even large proportions by NGI mechanisms, may it be to foster children or even children not being in any legal care responsibility. By that way, also childless and/or homosexual human individuals may reproduce their individual behavioural phenotype to a considerable extent. The degree of this reproduction may even be so large that genetically unrelated foster children are seen as a fully accepted biological offspring [242]. For example, many cuckoo children are not recognized by their fathers as not-genetically related, especially when the inherited paternal NGI behaviourome is copied to a significant degree [17].
Behavioural teaching in humans is often outsourced from the pedigree, e.g. in the kinder garden, in schools, or universities. There, teachers not only teach the macro social environment shared part of the NGI behaviourome (e.g. common knowledge and social behaviour), but also to some extent their own individual NGI behaviourome. As such, pupils may inherit always some parts of their teacher’s individual NGI behaviourome. And depending on the teacher, this can be quite large and influential for the non-kin recipients. Based on the above described proximal mechanisms of NGI, this may be one reason why teachers often prefer and treat in a more affectionate and supportive way those pupils that show a strong similarity in their individual behaviourome to the own one. When a non-kin relationship between teacher and pupil is likely or known, similarity in the NGI behavioural phenotype is preferred to similarity in the physical phenotype which would otherwise serve as a proxy indicator of genetic overlap. This may go as far as considering non-kin pupils like a “son in mind” (and behaviour), although being well aware that they are non-kin.
Even super-reproduction of the NGI behaviourome appears possible for childless and/or homosexual individuals by whom the behaviourome is transmitted to a very large population of recipients. This may or may not include homosexuality and related behaviours. Famous artists may serve here as outstanding examples for behavioural reproduction, such as e.g. Leonardo da Vinci or Oscar Wilde. Their live records (as behavioural instructions) and achievements as artists (as successful results of their NGI behaviourome) are still serving as blue prints for young artist’s attitudes and working modes. They are often seen as brilliant examples of their profession.
An as yet unanswered question in human evolution has been why do homosexuals not die out when their genome is not inherited [182]? A potential new answer to this question may be provided by NGI of the behaviourome. Homosexual partner preference and associated behavioural patterns may readily be assumed to be part of the NGI behaviourome, which is not inherited from genetic parents. At least, no genetic source for this behaviour has been discovered; neither as a preserved genetic base, nor in the shape of de novo genetic mutations [207]. Nevertheless, homosexual behaviour can be copied from non-kin and from ex-vivo sources (e.g. written records), or may be established as a de novo behaviour. Likewise, it may be passed on effectively to next generation non-kin, and become ex-vivo stored. But how is it providing any fitness benefit for those who copy and express it? The advantage may be in saving on resources that heterosexual individuals have to spend on genetic reproduction. This may set capacity free to innovate new NGI behaviours and to develop more sophisticated NGI behaviouromes that can contribute more than average to the general population NGI behaviourome pool and, thus, to culture. And as long as cultural advancement, i.e. the qualitative or quantitative expansion of the NGI behaviourome, is rewarded in a human society and enhances chances of survival for the individual, this behavioural trait may remain in the NGI behavioural pool. Nonetheless, it should be noted that certain societies do actively punish the behavioural trait of homosexuality and its in-vivo and ex-vivo inheritance and replication. Gay people are threatened by death penalty and books/movies about this behavioural phenotype are prohibited and prosecuted. The relative persistence of this behaviour may arise from the delayed nature of the cultural benefit. While the perceived threat of genetic replication failure is immediately perceived by a group, the potential benefits in cultural advancement are delayed. As such, the behavioural trait of homosexuality is submitted to a reward discounting in a group/society, which can yield opposite outcomes depending on how immediate vs. delayed reward are valued. If the immediate risk of replication failure is valued higher, the behavioural trait may become supressed, i.e. actively punished by society. If the delayed reward is valued higher, homosexuality may become accepted and even actively rewarded.

11. Empirical testing of the proposed mechanisms of a near-orthogonal ultra-fast evolution of human behaviour in culture development

Here, we described a mechanism of human NGI behaviourome evolution that was characterized as near-orthogonal and ultra-fast acting compared to genetic/epigenetic based evolution and claimed it to be a major source of present day human culture. As this is currently only a speculative account, all components of this claim would need empirical testing and the opportunity of falsification. This may be done by addressing each feature separately.
The “near-orthogonal” claim can be falsified when evidence shows that the human NGI behaviourome has a predominant genetic/epigenetic base that essentially displays the same temporal dynamic change as the human behavioural phenotype. For that, it would be an important research goal to empirically classify the full human NGI behaviourome in all its current complexity and to empirically monitor its changes closely from now on. From the starting point of a categorized present day human NGI behaviourome, one should estimate backwards its dynamic change over the last five thousand years. This may be paralleled by measurements of the human genome/epigenome development backward and forward. Behavioural and genetic/epigenetic data may then allow testing of whether and to what extent the dynamic development of the human behaviourome over that time is best described by a process near-orthogonal and, thus, largely independent from genetic/epigenetic evolution. Likewise the “ultra-fast” nature can be tested by comparing time scales and the degree of behaviourome change. Time scales for alterations of the human genome/epigenome that are known to have changed human behaviour and the dynamic of behavioural changes for which no genetic base can be identified, may be compared in the relevant 5000 years.
A proposed unique characteristic of the evolution of the human NGI behaviourome is its capability for targeted mutations of behaviour, e.g. during puberty. Thereby, the proposed Lamarckian mechanism may be experimentally tested in longitudinal studies where single parental behaviours may be artificially introduced that would be mildly maladaptive for the offspring, and trans-generational mutation rate is measured together with rate and quality of newly invented behaviours that can replace the abandoned/non-replicated ones. However, when ethical concerns should limit this experimental approach, also quasi-experimental post hoc analysis of behavioural mutations during puberty would provide some clues.
If the claim that the presented mechanism is a major driving force for human culture, it would be critical to test for an accumulation of the NGI behaviourome, i.e. the sheer number of human behaviours should increase in the relevant time span, which should not be paralleled by an increase in behaviourally relevant genes or epigenetic modifications.

12. Summary and outlook

If a biological, psychological or cultural theory of evolution wishes to explain development and current diversity of life, it also has to capture the present appearance of human beings. It has to provide a reasonable account of its radical transformation in the last few thousand years. Here we tried to identify and characterize mechanisms of a near-orthogonal and ultra-fast evolution of human behaviour which serve as an essential prerequisite for human cultural development in the last 5.000 years of human history. In that they are not meant to replace a genetic/epigenetic based evolution, but to largely expand them by mechanisms which allow to better explain many features of human culture that cannot be readily captured by genetic evolution. The Darwinian account of evolution comprises all living beings on earth, may they express behaviour or not. Human behavioural evolution theory, in contrast, captures only a relatively small aspect of biology, the NGI component of the human behaviourome. Nevertheless, this is the one that has submitted the surface of earth to probably the most profound changes induced by living species ever recorded in the history of life on earth, with significant effects on virtually all other species and on inanimate nature. Among those changes is what we consider as human culture, a vast array of NGI behaviours that are no longer genetically coded, but inherited, externally stored, spread and accumulated. In that the present account attempts to provide an explanatory scheme of how distinct genetically inherited features gave rise to human culture.

The "diversity equity and inclusion statement" required of anyone hired by the University of California: Only those statements scoring high enough are passed on for scholarly review

Wokeademia. John Cochrane. Thursday, January 30, 2020.

I'm working on an economic view of political polarization. One aspect of that project is the extent to which many institutions in our society have become politicized. Today's post is one little data point in that larger story. It tells a little story of how to politicize an institution and silence dissenters.

Jerry Coyne reports on the "diversity equity and inclusion statement" required of anyone hired by the University of California, or desiring a raise or promotion. This is a required statement each candidate must write "Demonstrating Interest in and Ability to Advance Diversity, Equity, and Inclusion." It's not about whether you are "diverse," meaning belonging to a racial, gender, or sexual-preference group the University wishes to hire. It is a statement, as it says, of your active participation in a  political movement.

Jerry's news in this post is that the statements are now being scored numerically, and only the files of those scoring high enough are passed on for scholarly review. 


The university not only requires the statements, but gives
these statements precedence in the hiring process, so that if your statement doesn’t exceed a minimum numerical cutoff for promoting diversity, increasing it in your past, and promulgating it in the future should you be hired, your candidacy is terminated


Jerry links to the UC Rubric to assess candidate contributions to diversity equity and inclusion. It's lovely that they are so secure they don't think they have to hide this sort of thing.

 [Impressive, read it all:]

Much more details, links at the original post.

When facing others who hold beliefs different from our own, we do not find these encounters disturbing because of the different beliefs per se, but because we are convinced that others hold false beliefs

The Othello Effect: People are more disturbed by others' wrong beliefs than by different beliefs. Andras Molnar, George Loewenstein. Carnegie Mellon University, PA, January 2020.

Abstract: We propose an alternative account to the theory of belief homophily--that people have an intrinsic distaste for encountering differences in beliefs. We argue that when people face others who hold beliefs different from their own, they do not find these encounters disturbing because others hold different beliefs per se, but because they are convinced that others hold false beliefs. In three preregistered studies (N = 1408) featuring self-recalled personal experiences and vignette scenarios, we demonstrate that participants are more disturbed when others hold false beliefs, compared to cases in which others' beliefs are different, even when participants' objective knowledge about the validity of beliefs is held constant. This effect is robust across contexts and types of social interactions, and is present among all ages and both sexes. We also show that higher confidence that others hold wrong beliefs, but not different beliefs, evokes stronger negative emotions.

How do voters react to information about aggregate turnout? Do high turnout levels mobilize or discourage citizens to vote? We argue that it depends on individuals’ degree of conformity

Conformity and Individuals’ Response to Information About Aggregate Turnout. André Blais, Rafael Hortala-Vallve. Political Behavior, February 1 2020.

Abstract: How do voters react to information about aggregate turnout? Do high turnout levels mobilize or discourage citizens to vote? We argue that it depends on individuals’ degree of conformity. We argue that in addition to the classic calculus of voting, conformist voters have an added incentive to ‘follow the pack’ and vote when turnout is high while abstain when turnout is low. We conduct two separate experiments, the first a survey experiment with a representative sample of the UK population and the second a lab experiment in Canada. Both studies confirm our hypothesis. These findings highlight the importance of taking individuals’ level of conformity into account when explaining their decision to vote or abstain.

Keywords: Conformity Turnout Survey experiment Lab experiment


Our research highlights the importance of including social conformity in the study of political phenomena. Recent research in political psychology has focused on the Big Five personality traits (see especially Mondak et al. ) but our study suggests that we should go beyond these personality traits. Politics is very much about collective decision-making, so there is an underlying tension between the desire for personal autonomy and the need for social norms that are respected and followed by everyone in the community. Citizens strike a different balance between these two considerations, and this is bound to shape their behavior.
We have combined a survey experiment conducted in Britain and a lab experiment performed in Canada to test our hypothesis. Both studies produced remarkably similar findings: in both instances, people who score higher on the social conformity scale are more prone to vote (abstain) when they know that most other people vote (abstain) while those who score low on the conformity scale have exactly the opposite reaction. If a predicted high turnout makes conformists more inclined to vote and if there are many conformists in the electorate, then a relatively high turnout would be an equilibrium.
The implications of our study hinge in good part of the distribution of individuals across the conformity scale in a given society at a given point in time. To the best of our knowledge there are no time-series or cross-section data about the distribution of conformity across societies or over time. The data that we have collected in Britain (see Fig. A1 in Online Appendix A1) suggest a relatively normal distribution, with the mean (7.52 on a 0 to 17 scale) indicating a slight majority of non-conformists. The point remains that, at least in our representative poll of British society, there are many people with conformist leanings.
We therefore end with a call for more attention to be paid to an individual’s social conformity. A huge literature exists in social psychology about the role of conformity, yet little research has been devoted to its impact in political life. Our study suggests that it is a crucial variable in the decision to vote or abstain. There are good reasons to believe that it shapes other political phenomena such as the decision to participate in demonstrations or to engage in strategic or bandwagon voting. It makes sense to assume that many people pay attention to information about what others in the community are likely to do when deciding whether to vote or abstain. Political scientists need to integrate such considerations into their models and analyses.
Our study also raises important questions about the relationship between social conformity and other factors that may affect voter turnout. One such question pertains to the relationship between social conformity and sense of civic duty. Are conformists more prone to believe that they have a moral obligation to vote? Are both attitudes shaped by personality traits? Another set of questions is about the relationship between social conformity and social pressure. We would expect conformists to pay attention to social pressure. But what kind of social pressure? In this study, we have examined how conformists react to information about aggregate turnout. But what happens when conformists are exposed to conflicting information, if/when for instance they learn that turnout in the country is going to be high but that most friends/relatives are going to abstain? These are big questions about which we have no clear answer.

Macaques in the wild cooperating for copulation: Males actively shared the mating opportunities, i.e., a male copulated with a female, while his ally waited his turn and guarded them

Cooperation for copulation: a novel ecological mechanism underlying the evolution of coalition for sharing mating opportunities. Aru Toyoda, Tamaki Maruhashi, Suchinda Malaivijitnond, Hiroki Koda, Yasuo Ihara. bioRxiv, January 31, 2020.

Abstract: Cooperation, or the act of benefiting others at the cost of the benefactor's fitness, has been a central issue in evolutionary theory. Non-human animals sometimes show coalitions or male-male cooperation to confront a male rival and challenge the rank hierarchy. Here we observed novel types of coalitions in wild stump-tailed macaques; multiple males actively shared the mating opportunities, i.e., a male copulated with a female, while his ally waited his turn and guarded them. Our mathematical simulations revealed that lack of estrous signs, as well as large numbers of males in a group, possibly enhance facultative sharing of females. This is the first demonstration of the sharing of females in non-human primates, and shed light on the evolutionary theory of cooperation.


To the best of our knowledge, this is the first mammalian observation of collaborative
mate guarding by males, followed by facultative sharing of mating opportunities. Males in other
species, such as chimpanzees, olive baboons, and lions, also collaborate to guard females against
other males. The "cooperative mate guarding by coalition males" in these species appear to be
similar to those in the stump-tailed macaque; however, they fundamentally differ in social
relationships between/among coalition allies or non-allies. The stump-tailed macaque forms
multi-male multi-female societies, which includes a large number of males in the group, among
which only certain individuals tolerate sexual competition and show exclusive attitude toward
others. Male allies in a coalition exclude rivals and then share the mating opportunities with each
other. Thus, coalitions of stump-tailed macaques act as dominant males’ strategy for overcoming
reproductive competition within a group, by sharing the mating opportunities, as well as by
excluding other rivals. In the case of lions, a pride is the unit of a group, which mainly consists
of females and only few males, who collectively defend the females from other invasive males.
This is similar to coalitions of stump-tailed macaques, although alpha (the highest ranking) males
mostly monopolize the mating opportunities, whereas subordinate allies may either have no
access to the females or are allowed limited number of copulations, albeit not through active
sharing. Similarly, olive baboons are a well-known species forming male-male “coalition for
reproduction”, but differ from the stump-tailed macaques regarding the formation of coalitions.
The subordinate baboons form a coalition to jointly attack the dominant male, thereby increasing
their future access to females, while not showing any active sharing of copulations. The
observations made with one chimpanzee group might be comparable to our observations
regarding the stump-tailed macaque, where active sharing copulation (a female copulated with 8
males within a short period) was observed [29]. However, these were considered exceptions only
in the Ngogo population, which are considerably larger than the other populations [see section of
‘Contrasts with other chimpanzee communities’ in 29].
In stark contrast, stump-tailed macaques showed active sharing of mating opportunities
that they jointly obtain among the male allies. In this novel type of coalition, the alpha male
appeared to pay a reproductive cost by giving mating opportunities away to benefit his allies, and
the subordinate males in return repay in terms collaborative work efforts, as a result of which
they gain reproductive advantage as a team. Furthermore, the cooperation among three males is
another novel feature. Generally, coalition formation has been observed in the context of
aggression, characterized by triadic relations, such as the attacker, attack recipient, and supporter.
In the cognitive aspect, coalition formation may require higher abilities of social cognition,
termed "triadic awareness" [30–33], where the individual must recognize not only the dyadic
relationship between two individuals, but also the relationships with other individuals [34]. The
collaboration among three individuals, which is rarely observed in non-human animals, may
require the more expanded capacity of social cognition in this species. Hence, we consider
coalition formation in stump-tailed macaques as a unique instance of male-male cooperation to
achieve reproductive gain, which we believe is rare in non-human animals.
Why do male stump-tailed macaques, unlike males of closely related species, exhibit this
peculiar behavior? To put it in another way, what are the socio-ecological factors in stump-tailed
macaques that may have favored the evolution of this behavior? Here, we tentatively hypothesize
that the absence of signs of ovulation in female stump-tailed macaques is key to understanding
the evolution of male-male coalition, followed by facultative sharing. In many primate species,
the females exhibit visual or olfactory signs of ovulation during the fertile period of the
reproductive cycle. Conspicuous estrous signals such as sexual swellings enhance male-male
competition, providing females more opportunities for mate choice [35–37]. Advertisement of
female reproductive status is often seen in Old World monkeys living in multi-male multi-female
societies, such as most macaques, baboons, and chimpanzees [35–37]. When female
reproductive status is advertised, it is relatively easy for the alpha male to monopolize
fertilizations, as in that case he can concentrate all his guarding efforts on the females fertile at
that moment. On the other hand, when female ovulation is cryptic, the alpha male is no longer
able to adopt the selective guarding strategy, and reproductive monopoly is only possible if all
cycling females are guarded all the time. Our hypothesis is that the difficulty in establishing
reproductive monopoly by the alpha male due to concealed ovulation may have promoted
coalition formation of top-ranking males. Despite the low copulating frequency, it is surprising
that the males adopt a strategy to efficiently monopolize and share the copulating
opportunities—a critical reproductive resource—among multiple coalition males.
Our discovery of male-male coalition, followed by active sharing of mating opportunities
in stump-tailed macaques, demands a revision of the existing socioecological models in primate
social systems. To the best of our knowledge, this is the first documented case in non-human
primates of non-kin collaborative effort for acquiring resources based on active sharing among
allies. We have hypothesized that the lack of estrous signs in female stump-tailed macaques,
unlike many Old World monkeys, is a key factor enhancing male-male coalition coupled with
active sharing. Concealed ovulation is likely to reduce the extent to which fertilizations are
monopolized by dominant males. In our mathematical model, this effect is represented by the
reduction in parameter ". The model predicts that male-male coalition is more likely to occur
when " is small, confirming the logical consistency of our hypothesis. From the female's
perspective, monopolization by dominant males is indicative of limited opportunities for females
to select mates, particularly when they prefer copulations with subordinate or out-group males.
Thus, concealed ovulation may be considered as a female strategy to facilitate mate choice.
Further extending the argument, the formation of coalition followed by active sharing of mating
opportunities may be a counter strategy of dominant males. In other words, being unable to
control female reproduction on his own, the alpha male may be better suited surrendering some
fertilization opportunities to elicit cooperation by subordinates. Hence, the intensified sperm
competition in stump-tailed macaques may be a joint consequence of female concealment of
fertility states and male sharing of mating opportunities. In addition, a potentially relevant
observation is that female stump-tailed macaques do not produce copulation calls [38]. Although
the function of female copulation calls is still a matter of contention [39,40], a possible
interpretation is that female stump-tailed macaques do not make any effort to induce male mate
The present study has also revealed the importance of the number of males in a group as
a predictor for the formation of copulation coalitions among dominant males. In other words,
male-male coalition is more likely to be formed when there are more males in a group. In our
field site, we observed five groups of stump-tailed macaques consisting of 391 individuals, or on
an average 78.2 individuals per group. The relatively large group size is primarily due to the
semi-provisioning conditions in our study site, and this factor also appears to affect the
socioeconomic sex ratio, i.e., the ratio of the number of adult females to the number of adult
males. The average socioeconomic sex ratio in our sample is 1.33, while those that have been
previously reported for other populations of stump-tailed macaques are approximately 5.7 [18].
The smaller socioeconomic sex ratio indicates more intense male-male contest. Hence, both large
number of males per group and small socioeconomic ratio may have facilitated the occurrence of
coalition formation by dominant males in our study population.
Per our observational data, the coalition sizes were two or three, but did not exceed four;
however, our current model predicts the monotonic increase of the coalition size over four,
depending on the number of males in a group. This “discrepancy” might indicate three as the
limit of the coalition size in non-human animals. Actually, psychological experiments on
cooperative tasks revealed possibilities of collaboration by two or three subjects, but difficulties
were encountered with four or more subjects even in chimpanzees, probably due to the
limitations of social cognition. For the recognition of quadradic relations, an individual has to
recognize the possible combinations of dyadic and triadic relations, exponentially increasing the
socio-cognitive loading in the brain. Thus, such a socio-cognitive background might limit the
coalition size in stump-tailed macaques. In contrast, humans have evolved a hyper-cooperative
manner beyond the triadic allies, as suggested by the Machiavellian intelligence hypothesis.
We have also observed within-species variation to the extent to which copulations are
monopolized by dominant males, which is represented by " in our model. Despite the marked
ecological similarities between groups, the estimated "′ ranged from 0.30 to 0.97. In the Third
("Z = 0.97) and Wngklm ("Z = 0.78) groups, copulations were almost completely monopolized
by the alpha males, a situation that is called "despotic." This contrasts with the conventional
classification of primate societies, in which stump-tailed macaques are characterized as having
"egalitarian" societies [41], or class 3 social systems [42]. The traditional classification intends to
place each species on a single position on the despotic-egalitarian spectrum, based largely on the
species-level characterizations of ecological factors, such as whether or not a given species is
seasonal breeder, or the abundance and spatial distribution of food resources [43]. However, our
observations clearly suggest that the level of despotism as indicated by " is determined not
necessarily in such a top-down manner, but in a more bottom-up way, such that it may vary
within species according to the idiosyncrasies of each group. For example, our field observation
indicates that the despotic nature of the Third group may have been caused not only by the
physical strength of the alpha male, THR-M01, but by the absence of competent rivals; in fact,
other males seem either too old or immature to challenge him. Therefore, it appears that bottom5 up mechanisms determine " in each group, which then determines whether the alpha male will
adopt the solo monopolization strategy or the coalition strategy.
Finally, our model predicts the future dynamics in the stump-tailed macaque groups. For
example, when youngsters in the Third group become sufficiently mature to challenge the alpha
male, and as a consequence " is reduced, our model predicts that the alpha male will form
coalition with other males. We expect that a longitudinal observation of wild stump-tailed
macaques will confirm these model predictions. In conclusion, stump-tailed macaques are
characterized by societies ranging from despotism to egalitarianism, and from monopolization of
females by a dominant male to male-male coalition coupled with active sharing of mating
opportunities. Future studies on wild stump-tailed macaques may shed new light on the origins
and evolution of altruism and cooperation in mammalian societies, including the hypercooperation in human societies.