Saturday, May 7, 2022

Humans have domesticated over 1000 plant, animal, fungal and bacterial species, some just for their good looks

What is domestication? Michael D. Purugganan. Trends in Ecology & Evolution, May 6 2022. https://doi.org/10.1016/j.tree.2022.04.006

Highlights

. The study of domestication has seen enormous strides in recent years, but the concept of domestication has been unclear.

. The core nature of domestication is as the coevolution between domesticator and domesticate.

. Evolutionary and ecological studies with both human-associated domestication and non-human domesticators can help us understand the nature of this phenomenon.

Abstract: The nature of domestication is often misunderstood. Most definitions of the process are anthropocentric and center on human intentionality, which minimizes the role of unconscious selection and also excludes non-human domesticators. An overarching, biologically grounded definition of domestication is discussed, which emphasizes its core nature as a coevolutionary process that arises from a specialized mutualism, in which one species controls the fitness of another in order to gain resources and/or services. This inclusive definition encompasses both human-associated domestication of crop plants and livestock as well as other non-human domesticators, such as insects. It also calls into question the idea that humans are themselves domesticated, given that evolution of human traits did not arise through the control of fitness by another species.

Keywords: mutualismcoevolutionhuman domesticationinsect farmingperi-domesticatesweedscommensalsagricultural originsornamental species


Are humans domesticated?

The question of whether humans are domesticated has a long history and Darwin considered this question briefly in Descent of Man [65]. The idea of human domestication, especially the concept of ‘self-domestication’, has gained momentum in recent years based on the assertion of similarities in traits between humans and domesticate mammals, including evolution of smaller body sizes, shortening of the face and a reduction in tooth size, reduced sexual dimorphism, and a reduction in cranial capacity [66.67.68.69.]. More importantly, these morphological changes are accompanied by a decrease in reactive aggression and increase in docility and prosociality [68,69]. Finally, the concept of self-domestication has been extended to include bonobos [70].

Invoking the term ‘self-domestication’ as applied to humans (and bonobos) is problematic. Darwin dismissed the idea of human domestication, as he understood that humans had not been subject to the control of its fitness, which is one of the critical hallmarks of domestication [65]. Moreover, the idea of self-domestication is untenable, since domestication as a biological concept is rooted in a mutualistic interaction with another species. Finally, defining domestication based on shared phenotypic similarities is also fraught with problems, given that such similarities could also arise outside the context of domestication [71,72].

While there are some trait similarities between H. sapiens and domesticate animals, in humans these do not appear to have evolved as a direct result of the mutualistic interaction with domesticate species. Such phenotypic similarities may arise from parallel/convergent evolution [71,72], possibly associated with secondary effects of the domestication process (for example, increased population density or sedentism) [68,69] but arguably do not directly spring from the human/crop, human/livestock, and human/pet mutualisms. Those who have remarked on these similarities need to explore other mechanisms to explain these evolutionary convergences.

Concluding remarks

Here, I have attempted to provide a broad but rigorous biologically centered definition of this unique phenomenon. In this overarching biological conception, domestication has the following critical elements. It is: (i) an evolutionary process, (ii) arising from mutualistic ecological interaction, (iii) involves constructing an environment where there is control of the fitness of one species by another, (iv) occurs so that the domesticator can garner resources and/or services from the domesticate, (v) leads to fitness benefits that accrue to both partners, and (vi) is agnostic to the interacting species. The pace of domestication is governed by the strength of the selection exerted by the domesticator (and the environment it provides) and the genetic and ecological characteristics of the target domesticate.

This definition has the advantage that it is grounded in evolutionary and ecological concepts, first recognized by Darwin [52,53] and later on championed by others [7,10,14.15.16.17.18.19.20.21.22.23.24.25.]. Like any definition, it struggles for both inclusivity and exclusion and there may well be cases that present some ambiguity. Indeed, domestication has understandably come to mean many other things and undoubtedly its varied usage will continue. It is expected, however, that the biologically oriented view presented here can provide a more precise conceptualization of domestication, help sharpen discussion of cases as they arise, and focus attention on major issues surrounding fundamental aspects of this phenomenon (see Outstanding questions). With a comparative, evolutionary, and ecological framework [1,2,10,16,19,26,27,73], there is an opportunity to understand the nature of this coevolution and the dynamics of this unique mutualism.

Outstanding questions

What are the ecological and evolutionary pathways that lead to domestication?

To what extent do the partner species rely on the mutualism for their survival and reproduction?

Does every individual domesticated organism have to impart a fitness benefit to the domesticator?

How do we determine whether a species is domesticated?

In human-associated domestication and subsequent diversification, what are the relative roles of conscious versus unconscious selection?

How do we understand domestication and selection for aesthetic traits?


The economic costs of crime in North America attributable to people with psychopathic personality disorder

Gatner, D. T., Douglas, K. S., Almond, M. F. E., Hart, S. D., & Kropp, P. R. (2022). How much does that cost? Examining the economic costs of crime in North America attributable to people with psychopathic personality disorder. Personality Disorders: Theory, Research, and Treatment. Advance online publication. May 2022. https://doi.org/10.1037/per0000575

Abstract: Cost of illness research has established that mental disorders lead to significant social burden and massive financial costs. A significant gap exists for the economic burden of many personality disorders, including psychopathic personality disorder (PPD). In the current study, we used a top-down prevalence-based cost of illness approach to estimate bounded crime cost estimates of PPD in the United States and Canada. Three key model parameters (PPD prevalence, relative offending rate of individuals with PPD, and national costs of crime for each country) were informed by existing literature. Sensitivity analyses and Monte Carlo simulations were conducted to provide bounded and central tendency estimates of crime costs, respectively. The estimated PPD-related costs of crime ranged from $245.50 billion to $1,591.57 billion (simulated means = $512.83 to $964.23 billion) in the United States and $12.14 billion to $53.00 billion (simulated means = $25.33 to $32.10 billion) in Canada. These results suggest that PPD may be associated with a substantial economic burden as a result of crime in North America. Recommendations are discussed regarding the burden–treatment discrepancy for PPD, as the development of future effective treatment for the disorder may decrease its costly burden on health and justice systems.


Antibody patents are being struck down left and right, victims of the Federal Circuit’s recent shift to strengthen two doctrinal areas of patent law—enablement and the written description requirement

Lemley, Mark A. and Sherkow, Jacob S., The Antibody Paradox (February 11, 2022). Yale Law Journal, Forthcoming, SSRN http://dx.doi.org/10.2139/ssrn.4032912

Abstract

Antibodies constitute a staggering $145 billion annual market—an amount projected to almost double by 2026. Consequently, patents covering antibodies are among the most valuable in the patent system. But antibody patents are being struck down left and right, victims of the Federal Circuit’s recent shift to strengthen two doctrinal areas of patent law—enablement and the written description requirement. For each, the Federal Circuit has heightened requirements that patentees disclose or teach how to make and use the “full scope” of their inventions.

There are good reasons to be skeptical of the Federal Circuit’s attack on genus claims in chemistry generally. But it seems to be a particular problem for antibodies. Applying the Federal Circuit’s reinvigorated written description and enablement requirements to antibodies and their chemical structure fits poorly with the science underlying the molecules themselves. Immune receptor production—a semi-random and galactically expansive process—produces antibodies that are startingly different in both structure and function. There is no way to genus claims to antibodies that satisfy the court’s current tests. The science simply doesn’t allow it. At the same time, this change in the Federal Circuit’s jurisprudence is a legitimate reaction to some of the problems with the long-standing (and long-permitted) practice of claiming antibodies in functional terms. Functional claiming can lead to overbroad patents that stifle future innovation, as it has done in the software industries. Perhaps the Federal Circuit is wary of a similar result in biotechnology.

Fortunately, we think there is a middle ground—a new (or, really, quite old) form of patent claim drafting that gives inventors effective control over true substitutes without giving them the power to block real improvements: means-plus-function claims and infringement by the equivalents. Those doctrines limit patentees to claiming only the specific structural features of antibodies they both possessed and described, but also entitle them to assert their patents against antibodies with equivalent functions but different structural characteristics. If the economics of intellectual property center on balancing a need for protection beyond the literal invention and allowing improvements, this seems a step in the right—or, at least doctrinally permissible and economically sensible—direction.

Whether patentees go for such a solution remains to be seen. Recent empirical evidence on antibody claims has yet to document such a shift. Patent attorneys may need to get over their historical reluctance in writing their claims in such a fashion. Our solution won’t give patentees everything they want. But they just might find it gives them what they need.


Special forces commandos have discernible personality profiles, with low neuroticism, more conscientiousness, and markedly less openness to experience

Huijzer, R., Jeronimus, B. F., Reehoorn, A., Blaauw, F. J., Baatenburg de Jong, M., de Jonge, P., & den Hartigh, R. J. R. (2022). Personality traits of special forces operators: Comparing commandos, candidates, and controls. Sport, Exercise, and Performance Psychology, May 2022. https://doi.org/10.1037/spy0000296

Abstract: Dutch special forces operators, also known as commandos, perform in mentally and physically tough environments. An important question for recruitment and selection of commandos is whether they have particular personality traits. To answer this question, we first examined differences in personality traits between 110 experienced Dutch male commandos and a control sample of 275 men in the same age range. Second, we measured the personality traits at the start of the special forces selection program and compared the scores of candidates who later graduated (n = 53) or dropped out (n = 138). Multilevel Bayesian models and t tests revealed that commandos were less neurotic (d = −0.58), more conscientious (d = 0.45), and markedly less open to experiences (d = −1.13) than the matched civilian group. Furthermore, there was a tendency for graduates to be less neurotic (d = −0.27) and more conscientious (d = 0.24) than dropouts. For selection, personality traits do not appear discriminative enough for graduation success and other factors need to be accounted for as well, such as other psychological constructs and physical performance. On the other hand, these results provide interesting clues for using personality traits to recruit people for the special forces program.

Author's Perspective - Comparing the Personality of Commandos, Civilians and Recruits

What is it about? Special forces operators perform in mentally and physically tough environments. For instance, they need to complete high-stakes missions, such as saving a hostage, successfully even when dehydrated or sleep deprived. As a consequence, the special forces training is very challenging and the great majority of recruits drop out during the selection period. In order to find out which types of people become successful commandos, we examined whether (a) Dutch commandos differ in their personality traits from a matched group of “normal” Dutch men, and (b) recruits who graduate from the selection program differ in their personality traits from the dropouts. Differences between commandos the matched group of Dutch men, and between the recruits were indeed found. Amongst others, commandos and successful recruits were relatively less neurotic and more conscientious.

Why is it important? Why are some people able to become a commando, whereas others are not? Does it have to do with personality whether one can become a commando? Such questions are crucial to recruit and select special forces operators. In our study, we investigated the personality of commandos, a matched group of Dutch men, and recruits, and found that personality traits do make a difference between these groups. Having a clearer picture of the personality traits that matter allows for a better targeted recruitment and selection of special forces operators.


Friday, May 6, 2022

In search of gratification: Psychological Benefits of Believing Conspiracy Theories

Psychological Benefits of Believing Conspiracy Theories. Jan-Willem van Prooijen. Current Opinion in Psychology, May 5 2022, 101352. https://doi.org/10.1016/j.copsyc.2022.101352

Highlights

• Despite their negative effects, many people find conspiracy theories appealing.

• Conspiracy theories can be rewarding by providing a sense of meaning and purpose.

• This meaning and purpose sparks feelings of importance, legitimacy, and excitement.

• The benefits of conspiracy theories are likely a form of instant gratification.

Abstract: Many people believe conspiracy theories, even though such beliefs are harmful to themselves and their social environment. What is the appeal of conspiracy theories? In this contribution I propose that conspiracy theories have psychological benefits by imbuing perceiver’s worldview with meaning and purpose in a rewarding manner. Conspiracy theories enable an alternative reality in which perceivers (a) can defend a fragile ego by perceiving themselves and their groups as important, (b) can rationalize any of their beliefs and actions as legitimate, and (c) are entertained through the opportunity to uncover a mystery in an exciting tale. These are short-term benefits, however, suggesting that conspiracy theories provide people with a form of instant gratification.

Keywords: Conspiracy TheoriesPsychological BenefitsAlternative RealityInstant Gratification

1.3. Conspiracy theories as entertainment

A third way in which conspiracy theories contribute to meaning and purpose is by creating an alternative reality that is exciting, attention-grabbing, and spectacular. Conspiracy theories typically portray an archetypical struggle between good and evil, and introduce mystery about the potentially dubious role of powerful and important societal actors (e.g., politicians; celebrities). It is therefore not surprising that the plotlines of many works of fiction – including novels, theater plays, and movies – center around conspiracies [47]. Believing conspiracy theories turns perceivers into active players in such spectacular narratives, and gives them the opportunity – much like lay detectives – to uncover a mystery. Believing conspiracy theories hence offers people entertainment.

At first blush, this psychological benefit might seem discrepant with the notion that conspiracy theories can increase negative emotions such as anxiety [24]. Note, however, that many popular sources of entertainment are likely to increase anxiety (e.g., scary movies; detective novels; gambling; bungee jumping). People often do not avoid such negative emotions; instead, people are drawn to events that provide intense emotional experiences, which may include emotions that are negative, positive, or both [48]. Such intense emotional experiences are exciting, and make people feel alive.

Research supports the notion that people experience conspiracy beliefs as entertaining. Conspiracy beliefs are associated with dispositional aversion to boredom [49], and with the more general trait sensation-seeking, reflecting people’s desire for intense sensations and experiences [50]. Sensation-seeking also predicts a range of phenomena closely related with conspiracy beliefs, including radicalization and participation in violent extremist groups [51,52], and supernatural beliefs [53,54]. Moreover, conspiracy beliefs are associated with not only negative but also positive emotions [55].

Experimental studies underscore the entertainment value of conspiracy theories. Participants rated a conspiratorial text (about the Notre Dame fire or the death of Jeffrey Epstein) as more entertaining than a text describing the official account of these events. These entertainment appraisals subsequently predicted increased belief in these conspiracy theories. An additional study showed that people more strongly believed that an election event was rigged if it was described in an entertaining rather than a boring manner [50]. These findings illuminate that people find conspiracy theories entertaining, which motivates increased belief in them.

Small effects: Adolescents with more extraverted mothers were more likely to be sexually active; sexually active girls were also more likely to use contraception if their fathers scored higher on conscientiousness

Parent personality traits and adolescent sexual behaviour: Cross-sectional findings from the Longitudinal Study of Australian Children. Mark S.Allen, Sylvain Laborde. Personality and Individual Differences, Volume 195, September 2022, 111682. https://doi.org/10.1016/j.paid.2022.111682

Highlights

• Parent personality traits were related to adolescent sexual behaviour.

• Mothers' extraversion and conscientiousness were most important for sexual activity.

• Mothers' openness and conscientiousness were most important for pornography viewing.

• Fathers' extraversion was related to pornography viewing in adolescent boys.

• Fathers' conscientiousness was related to condom use among sexually active girls.

Abstract: Parent personality traits are thought to influence offspring outcomes through inherited traits and parenting styles. This study sought to test associations between parental personality traits and adolescent sexual behaviour. In total, 3089 Australian adolescents (1576 boys, 1513 girls; age 16–17 years) provided information on their sexual activity, with personality data available for 92% of mothers and 60% of fathers. In total, 64.6% of boys and 18.2% of girls reported viewing pornography. Results showed that mothers' personality traits were most important for adolescent sexual behaviour. Adolescents with more extraverted mothers were more likely to be sexually active, and those with more conscientious mothers tended to have their first sexual encounter at a later age. Girls were more likely to view pornography (and more frequently view pornography) if their mothers scored higher on openness, whereas boys were more likely to view pornography (and more frequently view pornography) if their mothers scored lower on conscientiousness. Sexually active girls were also more likely to use contraception if their fathers scored higher on conscientiousness. Effect sizes were small in all instances. Overall, these findings provide initial evidence that parent personality traits relate to offspring sexual behaviour in mid-late adolescence.

Keywords: Big fiveConscientiousnessExtraversionFive-factor modelSexuality


Male witches were mostly accused by males (blood-relatives or not), often in connection to disputes over wealth & status; accusations of women were mainly from kin by marriage (mostly husbands & co-wives)

Same-sex competition and sexual conflict expressed through witchcraft accusations. Sarah Peacey, Olympia L. K. Campbell & Ruth Mace. Scientific Reports volume 12, Article number: 6655, Apr 22 2022. https://www.nature.com/articles/s41598-022-10315-8

Abstract: There is significant cross-cultural variation in the sex of individuals most likely to be accused of practising witchcraft. Allegations of witchcraft might be a mechanism for nullifying competitors so resources they would have used become available to others. In this case, who is targeted may result from patterns of competition and conflict (same-sex or male–female) within specific relationships, which are determined by broader socio-ecological factors. Here we examine patterns of sex-specific accusations in historic cases from sub-Saharan Africa (N = 423 accusations). Male ‘witches’ formed the greater part of our sample, and were mostly accused by male blood-relatives and nonrelatives, often in connection to disputes over wealth and status. Accusations of women were mainly from kin by marriage, and particularly from husbands and co-wives. The most common outcomes were that the accused was forced to move, or suffered reputational damage. Our results suggest that competition underlies accusations and relationship patterns may determine who is liable to be accused.

Discussion

The data used here provides evidence that particular relationships may determine sex-specific patterns of witchcraft accusation. Cases where women were targeted frequently came from affinal kin, while those directed at men were often from unrelated individuals and blood relatives. Most previous research on factors that determine the sex of accused ‘witches’ has largely consisted of qualitative studies of a single society or a few societies48, or historical studies that have not tested for correlations49. Our findings, in support of the overarching hypothesis that accusations may be driven by various forms of competition, can be tentatively aligned with evolutionary literature on patterns of intrasexual and kin competition, intersexual conflict and polygamous mating30,31,50.

Men were more often accused than women in our sample, although we did not have a prediction in relation to this. But the finding suggests how overall patterns of competition within relationships may contribute to societal ‘phenotypes’ of witches as male or female. The ethnography of the Ndembele perhaps indicates why women were less frequently targeted in Bantu societies: ‘in a case of witchcraft, the complainant is actuated by caprice, jealousy or pique; and the defendant is a person of wealth or popularity, and is always a man, for the women have neither wealth nor honor worth coveting’51.

Our predictions about how the sex of accused ‘witches’ might be associated with particular relationship categories were supported. The majority of accusations targeting men came from unrelated individuals, which is unsurprising, as inclusive fitness52 would not mitigate the effects of competition between them. Blood relatives were the next most common relationship category directing accusations at men. This aligns with more recent studies indicating that witchcraft fears between family members are significant in parts of Africa, to the extent that they can be construed as ‘the dark side of kinship’53. In evolutionary terms, kin may compete with one another in environments where resources are limited30,31,50 and in societies with patrilineal inheritance related males, and particularly brothers, compete for resources in order to marry31. This aligns with an ethnographic observation that among the Banyoro witchcraft accusations often occurred between brothers over inheritance, but not between brothers and sisters, whose interests did not conflict21. The situations relating to accusations of men were also often connected to the acquisition of wealth and status, such as rivalry over village headmanships32, power struggles between a chief’s counsellors54 or disputes over inheritance55. These connections can be found in more recent contexts such as twentieth century Ghana, where notions of obtaining political power and wealth through occult means involving human sacrifice were pervasive56.

Accusations of women were more likely to come from affines. Husbands were the largest category of affinal kin to accuse women (Supplementary Fig. 2). The higher rate of accusations from husbands to wives than wives to husbands aligns with evolutionary perspectives suggesting male coercion of females is a strategy to maximize male reproductive success39,41. Accusations of wives who were suspected of being unfaithful can be interpreted as a strategy for reducing investment in unrelated offspring35,41. In a case from the Shona a woman gave birth to a stillborn child. This was attributed to an affair before marriage, and was followed by divorce and the repayment of bridewealth to her husband, who commented she was ‘a witch, a woman who had killed her own child’48. Other ethnographic accounts suggest accusations of wives by husbands were an attempt to gain control within the marital relationship55.

A significant number of accusations of women by affinal kin were from co-wives in polygynous marriages, and these were often notably associated with jealousy connected to a husband’s attention and investment32. Evolutionary models predict competition for reproductive resources would occur among co-resident breeding women57, as has been found to occur among the Mosuo of southwest China58. In the patrilocal social systems that are predominant in our sample, women disperse at marriage and are isolated from kin, so conflict may be more extreme30. This is consistent with ethnographic observations reporting that the relationship between co-wives in polygynous marriages was often (although not always) marked by conflict, and liable to produce witchcraft accusations38,59.

There were accusations of women from other categories of their affinal kin (Supplementary Fig. 2). These again may result from competition for a husband’s time and resources between his kin and wife. New wives may be vulnerable in environments where they enter their husband’s families as unrelated strangers, and are potentially expendable, at least before the arrival of offspring. Some accounts of accusations indicate that accusations of wives by in-laws in patrilocal households are common29.

Accusations directed at elderly individuals targeted women more often than men. This may form part of a broader pattern of geronticide: societies close to subsistence-level are documented as sometimes accepting the abandonment or killing of elderly people19,60. In modern Tanzania, ‘witches’ are mostly post-reproductive women, who are more likely to be murdered in periods of income shock19. This is also the case in contemporary Ghana, where accusations are frequently directed at middle-aged or elderly women, whose families may subsequently cease to provide them with financial or material assistance61. In our sample, elderly women may have been targeted more frequently as a result of longer female lifespans: in a polygynous society, men may marry younger women, so wives would be widowed at an earlier age than husbands. Among the Bantu, older men were accused, but some were possibly protected by their status.

Accusers’ payoffs from accusations are not always explicit but they can be inferred. The most common outcome of accusations in our sample was that accused ‘witches’ were exiled from their communities or forced to move from where they were living. This would mean resources and cooperative assistance they would have used became available to their accusers or others nearby. Where the accused acquires a negative reputation, which was the second most common outcome, there may be a subtle removal of benefits, which may be preferred to direct ‘punishment’ as it is less costly62. Accusers’ gains need not be direct, as harming behaviours may reduce the overall pressure of competition in an environment28. 8% of accusations in the sample resulted in the acquisition of either resources or political positions from the accused, or in preventing the accused from acquiring them. Where the accused were penalised in other ways, such performing ceremonies to reconcile with accusers, this is perhaps akin to classic cooperation models involving the punishment of defectors (although the accused may not actually be uncooperative)11, providing accusers with subordinate partners who offer fitness benefits to avoid more serious allegations63. Where an accusation does not ‘stick’, ethnographic accounts sometimes indicate it was reversed through divination or ordeal54. In other cases, for various reasons accusations are short-lived and forgotten about4. Finally, although not tested in this dataset, accusers may gain informal prestige and dominance, an outcome analogous to competitive punishment63.

Not all of the cases in our dataset support the hypothesis that witchcraft accusations are a mechanism for competition. There is a significant proportion where the accusation of a particular individual appears to be incidental, or dependent a on circumstantial association between the ‘witch’ and a negative event. Such accusations are unlikely to provide accusers with a competitive advantage. There are several possible explanations for such cases. They are in line with the hypothesis that witchcraft belief arises from attempts to identify the cause of an impactful misfortune3,4. Cultural evolutionary explanations of witchcraft beliefs suggest that they are a maladaptive attempt to explain misfortune. Although it is inaccurate, belief in witches is maintained through bias and selective inattention to evidence that would otherwise counter it64. Alternatively this could be viewed under the contention that superstitious beliefs (or errors in attributing cause and effect) are broadly adaptive if they occasionally lead individuals to acts which provide them with fitness benefits65.

Although witchcraft accusations may be a mechanism for mitigating the damage to accusers’ reputations in harmful competitive acts, as with any behavioural strategy it is not without risks. Accusers may suffer costs in the form subsequent reputational damage or counter-accusations, as with punishment63, depending on factors such the level of support for an accusation by other members of the community.

One limitation of our dataset is that it contains realized allegations of witchcraft, that cannot be tested against baseline population measures. We could not examine the risk that a particular individual, such as an elderly woman, would be accused. Instead, the analysis shows the odds, given an accusation occurred, that the ‘witch’ was male or female, given certain predictors. For example, if the accused was elderly, there are increased odds they were female rather than male.

A dataset using historic witchcraft cases is almost certainly affected by selection bias. Cases with sensational outcomes are more likely to be reported, and cases that are dismissed or where the accused removes themselves from their accusers are liable to be overlooked19. Most incidents in our sample were reported anecdotally. Obtaining a random sample of witchcraft accusations within a population is challenging, if not impossible1,66. Attempts to systematically collect cases within a given location and timeframe cannot guarantee that all are brought to the attention of researchers19. Comparative studies of this kind usually use all the data that is available and control for confounding effects. Our sensitivity analyses suggest the large number of accusations of men in the dataset probably reflects patterns of accusations in these societies, rather than male-focused bias from ethnographers. There are many accounts of cultures where witches are predominantly male33,34,49. But the accuracy of historic ethnographic accounts cannot be verified, especially in relation to one-off events such as witchcraft accusations, just as it is unclear how much uncertainty there is in the ethnographic record overall67. Ethnographers may not always have noted the characteristics of the individuals involved, or there may be times where they were mistaken in reporting the circumstances surrounding an accusation. There are several explanations for cases where the identities of accusers or purported victims of witchcraft were not reported. Not all cases had identifiable ‘victims’, for example when the accused was thought to have used witchcraft to promote their own success, or ethnographers could not denote the relationship between the accused and their accusers when suspicions of witchcraft were communicated through general gossip. In a small number of cases, ethnographer perspectives on accusations (and possible inability to access further information) are salient, as they may ascribe more importance to one relationship over another in reporting a case, such as a witch’s envy of their victim, or a witch’s argument with an accuser.

However, it is likely that ethnographers were for the most part accurate in documenting variables of interest such as the sex of an accused individual and their relationships with accusers. There is less certainty in relation to the situation connected to an accusation, especially taking into recent research that indicates the prevalence of phenomena such as the misperception of causation68,69. Our attempts to account for such possibilities with sensitivity analyses and meta-data on the production of ethnographies cannot conclusively provide reassurance that bias has not affected results, and so this section of the analysis should be treated with caution and regarded as exploratory. The situations documented in our study do however align with accounts of accusations from more contemporary observers and studies from different geographic locations, suggesting that similar causes of accusations arise convergently in different societies. For example in modern contexts accusations have led to accusers gaining land or property in India6 and cessation of the obligation to provide material and financial assistance to elderly relatives in Ghana61. One advantage of our cross-cultural data being drawn from numerous ethnographies is that it is not reliant on the perspective of one individual, meaning that random perceptual error or individual (as opposed to cultural) bias is more likely to be mitigated in the results than would be the case in the study of a single culture by one ethnographer.

As a further limitation, we were reliant on accessible ethnographic records from the best-documented societies. Although selection bias in favour of better described societies is present in our sample, this should not impact the main aim of this research, which is to understand the determinants of witchcraft accusations being directed at male or female targets.

Overall our findings may indicate allegations of witchcraft stem from diverse forms of competition between individuals. This aligns with evolutionary approaches to competition and conflict. Accusations may provide fitness benefits by allowing individuals to target competitors, but the exact form and direction of competition is determined by aspects of socio-ecology. This in turn influences which sex is most likely to be accused and the overall portrayal of witches in a society. Accusations may be more likely to occur in some relationships rather than others, when there is a gain for the accuser, as in disputes over inheritance and property, or where another individual may pose a threat, or by simply reducing numbers of competitors. The success of witchcraft accusations in removing competitors and their flexibility as an adaptive strategy may explain their widespread distribution.

It is increasingly recognized that sex chromosomes are not only the battlegrounds between sexes but also the Great Walls fencing off introgression between diverging lineages

Neo-sex chromosome evolution shapes sex-dependent asymmetrical introgression barrier. Silu Wang et al. xxx, May 5, 2022 | 119 (19) e2119382119 | https://doi.org/10.1073/pnas.2119382119

Significance: It is increasingly recognized that sex chromosomes are not only the battlegrounds between sexes but also the Great Walls fencing off introgression between diverging lineages. Here we dissect the multifaceted roles of sex chromosomes using experimental evolution, whole-genome resequencing, and theoretical modeling, taking advantage of hybrid populations between a Drosophila sister species pair in the early stage of speciation that have different sex chromosome systems. Our work sheds light onto the complex roles of neo-sex chromosome evolution in creating a sex-dependent asymmetrical introgression barrier at a species boundary, and we show how diverse population genetic forces act in concert to explain observed patterns of introgression across the genome.

Abstract: Sex chromosomes play a special role in the evolution of reproductive barriers between species. Here we describe conflicting roles of nascent sex chromosomes on patterns of introgression in an experimental hybrid swarm. Drosophila nasuta and Drosophila albomicans are recently diverged, fully fertile sister species that have different sex chromosome systems. The fusion between an autosome (Muller CD) with the ancestral X and Y gave rise to neo-sex chromosomes in D. albomicans, while Muller CD remains unfused in D. nasuta. We found that a large block containing overlapping inversions on the neo-sex chromosome stood out as the strongest barrier to introgression. Intriguingly, the neo-sex chromosome introgression barrier is asymmetrical and sex-dependent. Female hybrids showed significant D. albomicans–biased introgression on Muller CD (neo-X excess), while males showed heterosis with excessive (neo-X, D. nasuta Muller CD) genotypes. We used a population genetic model to dissect the interplay of sex chromosome drive, heterospecific pairing incompatibility between the neo-sex chromosomes and unfused Muller CD, neo-Y disadvantage, and neo-X advantage in generating the observed sex chromosome genotypes in females and males. We show that moderate neo-Y disadvantage and D. albomicans specific meiotic drive are required to observe female-specific D. albomicans–biased introgression in this system, together with pairing incompatibility and neo-X advantage. In conclusion, this hybrid swarm between a young species pair sheds light onto the multifaceted roles of neo-sex chromosomes in a sex-dependent asymmetrical introgression barrier at a species boundary.