Overconfidence in wargames: experimental evidence on expectations, aggression, gender and testosterone

Overconfidence has long been noted by historians and political scientists as a major cause of war. However, the origins of such overconfidence, and sources of variation, remain poorly understood. Mounting empirical studies now show that mentally healthy people tend to exhibit psychological biases that encourage optimism, collectively known as 'positive illusions'. Positive illusions are thought to have been adaptive in our evolutionary past because they served to cope with adversity, harden resolve, or bluff opponents. Today, however, positive illusions may contribute to costly conflicts and wars. Testosterone has been proposed as a proximate mediator of positive illusions, given its role in promoting dominance and challenge behaviour, particularly in men. To date, no studies have attempted to link overconfidence, decisions about war, gender, and testosterone. Here we report that, in experimental wargames: (i) people are overconfident about their expectations of success; (ii) those who are more overconfident are more likely to attack; (iii) overconfidence and attacks are more pronounced among males than females; and (iv) testosterone is related to expectations of success, but not within gender, so its influence on overconfidence cannot be distinguished from any other gender specific factor. Overall, these results constitute the first empirical support of recent theoretical work linking overconfidence and war.     

Asymmetry in host and parasitoid diffuse coevolution: when the red queen has to keep a finger in more than one pie

BACKGROUND: Coevolution between pairs of antagonistic species is generally considered an endless "arms race" between attack and defense traits to counteract the adaptive responses of the other species. PRESENTATION OF THE HYPOTHESIS: When more than two species are involved, diffuse coevolution of hosts and parasitoids could be asymmetric because consumers can choose their prey whereas preys do not choose their predator. This asymmetry may lead to differences in the rate of evolution of the antagonistic species in response to selection. The more long-standing the coevolution of a given pair of antagonistic populations, the higher should be the fitness advantage for the consumer. Therefore, the main prediction of the hypothesis is that the consumer trophic level is more likely to win the coevolution race. TESTING THE HYPOTHESIS: We propose testing the asymmetry hypothesis by focusing on the tritrophic system plant/aphid/aphid parasitoid. The analysis of the genetic variability in the virulence of several parasitoid populations and in the defenses of several aphid species or several clones of the same aphid species could be compared. Moreover, the analysis of the neutral population genetic structure of the parasitoid as a function of the aphid host, the plant host and geographic isolation may complement the detection of differences between host and parasitoid trophic specialization. IMPLICATIONS OF THE HYPOTHESIS: Genetic structures induced by the arms race between antagonistic species may be disturbed by asymmetry in coevolution, producing neither rare genotype advantages nor coevolutionary hotspots. Thus this hypothesis profoundly changes our understanding of coevolution and may have important implications in terms of pest management.     

Is military incompetence adaptive?: An empirical test with risk-taking behaviour in modern warfare

In battles, opponents exhibit positive illusions in both believing they can win. With great costs of failure and uncertain success, this represents extreme risk-taking behaviour. Conflict may be expected if one side is cornered, a sacrificial pawn in an overall war strategy, or demanded into action by politicians. However, in many cases even patently weaker forces fight despite nonviolent options. This is “military incompetence”, a failure in the assessment of winning probability. Previous explanations (stupidity, psychological deviance and cognitive constraints) have been rejected. Recently, Wrangham [Evol. Hum. Behav. 20 (1999) 3.] proposed that such risk-taking could be adaptive through one of two effects: (1) Performance Enhancement through exaggerated resolve or (2) Opponent Deception by bluffing. Although adaptive if they confer a tendency to win, both processes promote risk-taking behaviour and are therefore potentially responsible for military incompetence. These hypotheses can be distinguished because the Performance Enhancement hypothesis predicts positive illusions in any type of conflict. In contrast, the Opponent Deception hypothesis predicts them in battles but not in surprise attacks, where lack of communication disables any bluff. We conducted a test of these hypotheses using data collected by the US Historical Evaluation Research Organisation, mainly from the Arab–Israeli and Second World Wars. The Opponent Deception hypothesis is supported over the Performance Enhancement hypothesis, but other explanations are not ruled out.     

The Social Bayesian Brain: Does Mentalizing Make a Difference When We Learn?

When it comes to interpreting others'' behaviour, we almost irrepressibly engage in the attribution of mental states (beliefs, emotions…). Such "mentalizing" can become very sophisticated, eventually endowing us with highly adaptive skills such as convincing, teaching or deceiving. Here, sophistication can be captured in terms of the depth of our recursive beliefs, as in "I think that you think that I think…" In this work, we test whether such sophisticated recursive beliefs subtend learning in the context of social interaction. We asked participants to play repeated games against artificial (Bayesian) mentalizing agents, which differ in their sophistication. Critically, we made people believe either that they were playing against each other, or that they were gambling like in a casino. Although both framings are similarly deceiving, participants win against the artificial (sophisticated) mentalizing agents in the social framing of the task, and lose in the non-social framing. Moreover, we find that participants'' choice sequences are best explained by sophisticated mentalizing Bayesian learning models only in the social framing. This study is the first demonstration of the added-value of mentalizing on learning in the context of repeated social interactions. Importantly, our results show that we would not be able to decipher intentional behaviour without a priori attributing mental states to others.     

Self-Deceived Individuals Are Better at Deceiving Others

Self-deception is widespread in humans even though it can lead to disastrous consequences such as airplane crashes and financial meltdowns. Why is this potentially harmful trait so common? A controversial theory proposes that self-deception evolved to facilitate the deception of others. We test this hypothesis in the real world and find support for it: Overconfident individuals are overrated by observers and underconfident individuals are judged by observers to be worse than they actually are. Our findings suggest that people may not always reward the more accomplished individual but rather the more self-deceived. Moreover, if overconfident individuals are more likely to be risk-prone then by promoting them we may be creating institutions, including banks and armies, which are more vulnerable to risk. Our results reveal practical solutions for assessing individuals that circumvent the influence of self-deception and can be implemented in a range of organizations including educational institutions.     

Temporal variation can facilitate niche evolution in harsh sink environments

We examine the impact of temporal variation on adaptive evolution in "sink" environments, where a species encounters conditions outside its niche. Sink populations persist because of recurrent immigration from sources. Prior studies have highlighted the importance of demographic constraints on adaptive evolution in sinks and revealed that adaptation is less likely in harsher sinks. We examine two complementary models of population and evolutionary dynamics in sinks: a continuous-state quantitative-genetics model and an individual-based model. In the former, genetic variance is fixed; in the latter, genetic variance varies because of mutation, drift, and sampling. In both models, a population in a constant harsh sink environment can exist in alternative states: local maladaptation (phenotype comparable to immigrants from the source) or adaptation (phenotype near the local optimum). Temporal variation permits transitions between these states. We show that moderate amounts of temporal variation can facilitate adaptive evolution in sinks, permitting niche evolution, particularly for slow or autocorrelated variation. Such patterns of temporal variation may particularly pertain to sinks caused by biotic interactions (e.g., predation). Our results are relevant to the evolutionary dynamics of species' ranges, the fate of exotic invasive species, and the evolutionary emergence of infectious diseases into novel hosts.     

Resource holding potential, subjective resource value, and game theoretical models of aggressiveness signalling

Empirical evidence suggests that aggressiveness (willingness to enter into, or escalate an aggressive interaction) may be more important than the ability to win fights in some species. Both empirical and theoretical traditions treat aggressiveness as a distinct property from the ability (RHP) or motivation (subjective resource value) to win a fight. I examine how these three traits are clearly distinct when modelled using a simple strategic model of escalation. I then examine game theoretical models of agonistic communication and demonstrate that models in which aggressiveness is signalled require: (1) a trait, aggressiveness, which is neither a correlate, nor consequence of RHP or motivation, (2) a handicap which negates any benefit to be gained through the use of a particular signal, and (3) the absence of any other asymmetry which could be used to assign roles to players. I conclude that it is unlikely that these assumptions are ever met, and that empirical examples of "aggressiveness" are far more likely to represent long-term differences in subjective resource value.     

Effect of Mating Activity and Dominance Rank on Male Masturbation Among Free‐Ranging Male Rhesus Macaques

The adaptive function of male masturbation is still poorly understood, despite its high prevalence in humans and other animals. In non‐human primates, male masturbation is most frequent among anthropoid monkeys and apes living in multimale–multifemale groups with a promiscuous mating system. In these species, male masturbation may be a non‐functional by‐product of high sexual arousal or be adaptive by providing advantages in terms of sperm competition or by decreasing the risk of sexually transmitted infections. We investigated the possible functional significance of male masturbation using behavioral data collected on 21 free‐ranging male rhesus macaques (Macaca mulatta) at the peak of the mating season. We found some evidence that masturbation is linked to low mating opportunities: regardless of rank, males were most likely to be observed masturbating on days in which they were not observed mating, and lower‐ranking males mated less and tended to masturbate more frequently than higher‐ranking males. These results echo the findings obtained for two other species of macaques, but contrast those obtained in red colobus monkeys (Procolobus badius) and Cape ground squirrels (Xerus inauris). Interestingly, however, male masturbation events ended with ejaculation in only 15% of the observed masturbation time, suggesting that new hypotheses are needed to explain masturbation in this species. More studies are needed to establish whether male masturbation is adaptive and whether it serves similar or different functions in different sexually promiscuous species.     

Multiple Quantitative Trait Analysis Using Bayesian Networks

Models for genome-wide prediction and association studies usually target a single phenotypic trait. However, in animal and plant genetics it is common to record information on multiple phenotypes for each individual that will be genotyped. Modeling traits individually disregards the fact that they are most likely associated due to pleiotropy and shared biological basis, thus providing only a partial, confounded view of genetic effects and phenotypic interactions. In this article we use data from a Multiparent Advanced Generation Inter-Cross (MAGIC) winter wheat population to explore Bayesian networks as a convenient and interpretable framework for the simultaneous modeling of multiple quantitative traits. We show that they are equivalent to multivariate genetic best linear unbiased prediction (GBLUP) and that they are competitive with single-trait elastic net and single-trait GBLUP in predictive performance. Finally, we discuss their relationship with other additive-effects models and their advantages in inference and interpretation. MAGIC populations provide an ideal setting for this kind of investigation because the very low population structure and large sample size result in predictive models with good power and limited confounding due to relatedness.     

Avoiding injury and surviving injury: two coexisting evolutionary strategies in lizards

Congenital morphological differences between injured and intact individuals in a population may reflect adaptations to avoid injury, to survive injury, or both. We explore the possible occurrence of such adaptations, analysing the relationship between tail state (original, O; regenerated, R) and morphology (20 scale characters) in 23 taxa of Lacertidae. In some taxa, such as Acanthodactylus opheodurus , morphologies of O and R lizards differed significantly. In these, usually O individuals were morphologically typical (modal), while R individuals were extreme; in others, the contrary occurred. Indices of pattern similarity detected fewer differences between O and R lizards than those based on absolute values. We developed unbiased estimates of classification rates of discriminant analysis. The order of inclusion of characters in the discriminant functions of males and females of the same species differed more than the order for the same sex in other species. Some morphological differences between O and R lizards seem adaptive or linked by pleiotropy to adaptive traits. Congenital morphological differences between O and R lizards are probably more frequent than detected because we show that age and geographical heterogeneity of our samples are confounding factors to O–R differences. R-morphologies might reflect microevolution in favour of paedotypic forms, possibly possessing greater regenerating capacities than relatively more peratypic forms.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 78 , 307–324.     

How to identify (as opposed to define) a homoplasy: examples from fossil and living great apes

There is much debate on the definitions of homoplasy and homology, and on how to spot them among character states used in a phylogenetic analysis. Many advocate what I call a "processual approach," in which information on genetics, development, function, or other criteria help a priori in identifying two character states as homologous or homoplastic. I argue that the processes represented by these criteria are insufficiently known for most organisms and most characters to be reliably used to identify homoplasies and homologies. Instead, while not foolproof, phylogeny should be the ultimate test for homology. Character states are assumed to be homologous a priori because this is falsifiable and because their initial inclusion in the character-state analysis is based on the assumption that they may be phylogenetically informative. If they fall out as symplesiomorphies or synapomorphies in a phylogenetic analysis, their status as homologies remains unfalsified. If they fall out as homoplasies, having evolved independently in more than one clade, their status as homologous is falsified, and a homoplasy is identified. The character-state transformation series, functional morphology, finer levels of morphological comparison, and the distribution and correlation of characters all help to explain the presence of homoplasies in a given phylogeny. Explaining these homoplasies, and not ignoring them as "noise," should be as much a goal of phylogenetic analysis as the production of a phylogeny. Examples from the fossil record of Miocene hominoids are given to illustrate the advantages of a process-informs-pattern-recognition-after-the-fact approach to understanding the evolution of character states.     

Paranoia,self-deception and overconfidence

Self-deception, paranoia, and overconfidence involve misbeliefs about the self, others, and world. They are often considered mistaken. Here we explore whether they might be adaptive, and further, whether they might be explicable in Bayesian terms. We administered a difficult perceptual judgment task with and without social influence (suggestions from a cooperating or competing partner). Crucially, the social influence was uninformative. We found that participants heeded the suggestions most under the most uncertain conditions and that they did so with high confidence, particularly if they were more paranoid. Model fitting to participant behavior revealed that their prior beliefs changed depending on whether the partner was a collaborator or competitor, however, those beliefs did not differ as a function of paranoia. Instead, paranoia, self-deception, and overconfidence were associated with participants’ perceived instability of their own performance. These data are consistent with the idea that self-deception, paranoia, and overconfidence flourish under uncertainty, and have their roots in low self-esteem, rather than excessive social concern. The model suggests that spurious beliefs can have value–self-deception is irrational yet can facilitate optimal behavior. This occurs even at the expense of monetary rewards, perhaps explaining why self-deception and paranoia contribute to costly decisions which can spark financial crashes and devastating wars.     

Global temperature stability by rule induction: An interdisciplinary bridge

Rules incorporating influences on global temperature, an estimate of radiation balance, were induced from astronomical, geophysical, and anthropogenic variables. During periods of intermediate global temperatures (generally like the present century), the influences assume cancelingroles; influences cancel the effects of extreme states potentially imposed by other influences because they are, in aggregate, most likely to be assuming opposite values. This imparts an overall stability to the global temperature. To achieve cold or hot global temperature, influences assume reinforcingroles. CO ₂ is an active influence on global temperature. By virtue of its constancy in the atmosphere, it can be expected to sponsor frequent hot years in combination with the other influences as they cycle through their periods. If measures were implemented to maintain warm or cool global temperatures, it could retain the status quoof present global agricultural regions. They are probably more productive than hot world regions would be because of narrow storm tracks.     

Male attractiveness covaries with fighting ability but not with prior fight outcome in house crickets

In many species males that tend to win fights against othermales are more attractive to females. There are three ways inwhich male fighting ability and attractiveness may be associated:(1) attractiveness and fighting ability are influenced by thesame underlying traits (e.g., body size), (2) females prefermales that have directly observed winning fights, or (3) winningprevious fights indirectly improves a male's chance of beingpreferred by females. The last possibility may arise as a consequenceof the "loser effect"; in many species when a male loses a fighthis probability of losing subsequent fights increases. Thereare, however, no studies testing whether such a "loser effect"also influences male attractiveness. Here we show that maleattractiveness and fighting ability are positively correlatedin the house cricket, Acheta domesticus. Our experiment wasdesigned so that females could not directly observe the outcomeof fights, thus eliminating possibility (2) above. We then testedbetween possibilities (1) and (3) by making use of the factthat in some cricket species the "loser effect" can be eliminatedexperimentally by ‘shaking’ a male and stimulatingthe motor program for flying. We showed that in A. domesticus‘shaking’ does affect the outcome of subsequentfights. Males that had won two previous fights were less likelyto win a fight after being ‘shaken’ than when subjectto a control treatment. In contrast, males that had lost twoprevious fights were more likely to win a fight after being‘shaken’ than when they were not shaken. There was,however, no effect of ‘shaking’ on male attractiveness.We conclude that the "loser effect" does not alter the tendencyfor large, dominant males to be attractive to females. Instead,it appears that there are traits correlated with both fightingability and attractiveness. One such trait is body size. Fightwinners were significantly larger than losers and attractivenesswas positively correlated with male body size.     

Early Comers Become Owners: Effect of Residency Experience on Territorial Contest Dynamics in a Lycaenid Butterfly

A positive relationship between ownership and contest success is widespread among territorial butterflies. We tested the hypothesis that owners win simply because they have a longer experience occupying a given territory than do intruders in territorial butterflies. Using the lycaenid butterfly Chrysozephyrus smaragdinus , we staged contests between two males that had experienced different residency periods at the same contested territory, similar to owners and intruders in natural contests. We found that males that had occupied the contested territory for a longer period (a day) always defeated the shorter occupancy males (15 min). Therefore, residency period plays a key role in settling territorial contests. As residency confers advantages in a time-dependent manner, the mechanism of owner dominance could be an increase in motivation to fight as local familiarity increases. Moreover, this result predicts a population-level territorial dynamics. If residency period per se confers advantages in each contest, males arriving at a territory early in their adult season should acquire territorial dominance because they can remain there for a certain period with only a few rivals; late-appearing males do not have this advantage. As predicted, we found that males appearing at territory sites early in the season were more likely to hold their territories. This finding provides new evidence for the evolution of protandry in butterflies.     

Relaxed genetic constraint is ancestral to the evolution of phenotypic plasticity

Phenotypic plasticity--the capacity of a single genotype to produce different phenotypes in response to varying environmental conditions--is widespread. Yet, whether, and how, plasticity impacts evolutionary diversification is unclear. According to a widely discussed hypothesis, plasticity promotes rapid evolution because genes expressed differentially across different environments (i.e., genes with "biased" expression) experience relaxed genetic constraint and thereby accumulate variation faster than do genes with unbiased expression. Indeed, empirical studies confirm that biased genes evolve faster than unbiased genes in the same genome. An alternative hypothesis holds, however, that the relaxed constraint and faster evolutionary rates of biased genes may be a precondition for, rather than a consequence of, plasticity's evolution. Here, we evaluated these alternative hypotheses by characterizing evolutionary rates of biased and unbiased genes in two species of frogs that exhibit a striking form of phenotypic plasticity. We also characterized orthologs of these genes in four species of frogs that had diverged from the two plastic species before the plasticity evolved. We found that the faster evolutionary rates of biased genes predated the evolution of the plasticity. Furthermore, biased genes showed greater expression variance than did unbiased genes, suggesting that they may be more dispensable. Phenotypic plasticity may therefore evolve when dispensable genes are co-opted for novel function in environmentally induced phenotypes. Thus, relaxed genetic constraint may be a cause--not a consequence--of the evolution of phenotypic plasticity, and thereby contribute to the evolution of novel traits.     

The coevolution of warning signals

It has long been recognized that defended prey tend to be conspicuous. Current theories suggest that the association ('aposematism') has arisen because predators more readily learn to avoid attacking defended phenotypes when they are conspicuous. In this paper, I consider why such psychology has evolved. In particular, I argue that aposematism may have evolved not because of an independent and pre-existing receiver bias, but because the conspicuousness of a prey item provides a reliable indicator of its likelihood of being defended. To develop my case I consider how warning signals might coevolve in a system containing a number of predators, whose foraging behaviour is also subject to selection. In these cases, models readily show that the greater the conspicuousness of a novel prey item, the more likely that it has been encountered by other predators and survived. As a consequence, naive predators should be less likely to attack highly conspicuous novel prey on encounter, or at least more inclined to attack them cautiously. This adaptive predator behaviour will greatly facilitate the spread of aposematic phenotypes from extreme rarity, which in turn will enhance selection for forms of predator behaviour under which aposematism will coevolve even more readily.     

Abundance and generalisation in mutualistic networks: solving the chicken‐and‐egg dilemma

A frequent observation in plant–animal mutualistic networks is that abundant species tend to be more generalised, interacting with a broader range of interaction partners than rare species. Uncovering the causal relationship between abundance and generalisation has been hindered by a chicken‐and‐egg dilemma: is generalisation a by‐product of being abundant, or does high abundance result from generalisation? Here, we analyse a database of plant–pollinator and plant–seed disperser networks, and provide strong evidence that the causal link between abundance and generalisation is uni‐directional. Specifically, species appear to be generalists because they are more abundant, but the converse, that is that species become more abundant because they are generalists, is not supported by our analysis. Furthermore, null model analyses suggest that abundant species interact with many other species simply because they are more likely to encounter potential interaction partners.     

Sexual mimicry in hyenas

Genital masculinization in female spotted hyenas has been widely explained as an incidental consequence of high androgen levels. High androgen levels, in turn, were supposed to be favored because they led to adaptive aggressive behavior. Incidental androgenization is no longer a tenable hypothesis, however, because genital masculinization has been shown to proceed in the absence of androgenic steroids. Thus, an alternative hypothesis is required. The genitals of spotted hyena females are not simply masculinized, but exhibit a detailed physical resemblance to the male genitalia. In the absence of satisfactory alternative explanations, we propose that selection may have favored sexual mimicry in females because they are more likely than males to be targets of aggression from other females. Male-like camouflage could theoretically be protective in three contexts: neonate sibling aggression, infanticide by conspecific females, and interclan territoriality. Current data suggest that if sexual mimicry is important, its effects are strongest among infants.