Men's almost universally greater tendency to overestimate their abilities is likely the heritage of a long evolutionary urge to achieve the upper hand in the mating game

The Cocksure Conundrum: How Evolution Created a Gendered Currency of Corporate Overconfidence. Richard Ronay, William W. Maddux & William von Hippel. Adaptive Human Behavior and Physiology, Aug 19 2022. https://rd.springer.com/article/10.1007/s40750-022-00197-5

Abstract: Biological differences between men and women mandate that women’s obligatory investment in reproduction is significantly greater than that of men. As a result, women have evolved to be the “choosier” of the two sexes and men have evolved to compete for female choice. To the degree that overconfidence is an effective tool for attracting mates and driving away competitors, greater competition among men suggests that they should express more overconfidence than women. Thus, sexual selection may be the primary reason why overconfidence is typically more pronounced in men than it is in women. Sexual selection may also be a distal, causal factor in what we describe as a cult of overconfidence pervading modern organizations and institutions. Whereas overconfidence was once regulated and constrained by features of ancestral life, levels of social mobility and accountability in contemporary society and modern organizations make it increasingly difficult to keep this gendered bias in check.

Why are People Overconfident?

Psychological explanations for the widespread tendency towards self-aggrandizement have focused primarily on intrapersonal hedonic benefits, such as higher self-esteem for those who believe they are better than others, and reduced reactivity to stressful events (e.g., Dunning et al., 1995; Taylor & Brown, 1988). An alternative possibility, however, is that overconfidence may be an evolved strategy of considerable utility for achieving status and other types of social currency, such as alliance formation, persuasion and influence, romantic attraction, and ultimately reproduction (von Hippel & Trivers, 2011a).

Individual differences in traits that lead to differential “fitness” within a given ecology result in reproductive variance (i.e., natural selection; Darwin, 1859; Andersson & Iwassa, 1996)). As a result, certain individuals’ expressed traits enable them to leave a greater genetic footprint than that of others. Across generations, this process leads to a proliferation of whatever genes assist in survival and reproduction. And so the footprint grows. The pan-cultural nature of the overconfidence bias (Sedikides et al., 2003) suggests that it may well be one such adaptive trait, selected for over many thousands of generations (Johnson & Fowler, 2011), likely predating the separation of our hominin ancestors from the ancestors of modern chimpanzees (e.g., Moore et al., 2009; Noë et al., 1980). Indeed, Daniel Kahneman speaks of overconfidence as being fundamentally built into the structures of human reasoning (Shariatmadari, 2015).

Given that overconfidence can lead to faulty assessments of one’s circumstances, and hence potentially perilous decisions, it seems odd that overconfidence might have provided an advantage in the context of natural selection. Believing oneself single-handedly capable of bringing down a woolly mammoth was unlikely to have been a winning attitude for our ancestors. Nonetheless, in competitive settings marked by uncertainty, overconfidence has the potential to maximize individual outcomes, so long as the associated costs of failure are outweighed by the benefits of possible success (Johnson & Fowler, 2011; Számadó, 2000). In other words, when the potential gains of achieving a particular goal outweigh the potential costs of failing, risky strategies such as overconfidence have adaptive utility (Adams & Mesterton-Gibbons, 1995; Számadó, 2003).

This perspective is consistent with Error Management Theory (Haselton & Buss, 2000), which predicts the emergence of psychological biases when; (1) the decision had recurrent impacts on fitness (reproductive success), (2) the decision is based on uncertain information, (3) the costs of false positives and false negatives were recurrently asymmetrical over evolutionary time. Overconfidence in one’s abilities meet these criteria quite well under many circumstances.

First, overconfidence potentially impacts fitness by helping individuals compete for sexual opportunity (Murphy et al., 2015) as well as other material and social resources that contribute to reproduction, such as status, prestige, and material rewards (e.g., Henrich & Gil-White, 2001). Second, uncertainty would have been a necessary condition for overconfidence to evolve, as certainty does away with the need for competition and signaling. In such cases, the strongest or most obviously qualified rival simply takes the desired resource. Indeed, as the uncertainty of contested outcomes increases, so too does the utility of overconfidence (Johnson & Fowler, 2011). Third, the costs in lost opportunities associated with being underconfident, or even accurate, are often greater than the costs associated with being overconfident, particularly when people compete with each other over limited resources (Soldà et al., 2021).

As a result of these processes, in situations where the potential gains of overconfidence outweigh the potential risks of overclaiming, overconfident individuals may have an advantage. If so, then overconfident displays may be a functional adaptation that help individuals acquire material and social benefits, depending on the relative magnitude of the risks and rewards that a given situation affords (Adams & Mesterton-Gibbons, 1995; Számadó, 2000, 2003). Consistent with the above reasoning, overconfident people gain a host of social and material benefits, such as increased perceptions of competence and a rise in social status and perceived leadership potential (Anderson et al., 2012; Ronay et al., 2019). As status increases, physiological markers of stress such as cortisol decrease (Sherman & Mehta, 2020) and dopamine sensitivity increases (Morgan et al., 2002), providing proximate, secondary mechanisms for the relationship between overconfidence and the maintenance of positive affect in response to social stressors (Ronay et al., 2019). Thus, it comes as no surprise that overconfidence is selected for in CEO appointments, despite the higher probability of overconfident leaders initiating value-destroying investments (Goel & Thakor, 2008) and financial reporting fraud (Schrand & Zechman, 2012). And perhaps, as we outline below, no surprise that fewer than 5% of CEO positions in the US and Europe are held by women (Edgecliffe-Johnson, 2018).

Why are Overconfident People So Often Men?

This distally focused, status-enhancing account of overconfidence has at least one important moderating factor: The available evidence strongly suggests that men tend to be more overconfident than women. For example, men exhibit more overconfidence than women in academic achievement (Bengtsson et al., 2005), finance and trading (Cueva et al., 2019; Prince, 1993), conflict and competitions (Johnson et al., 2006; Niederle & Vesterlund, 2007), science and mathematics (Ehrlinger & Dunning, 2003; Hyde et al., 1990), past performance (Reuben et al., 2012), intelligence (Steinmayr & Spinath, 2009), and on general knowledge and cognitive tasks (O'Laughlin & Brubaker, 1998; Pallier, 2003). By way of example, in one study, 70% of men and 30% of women, overestimated their work performance and professional skills (Lindeman et al., 1995). While under-confidence is generally the exception, it is more often women than men who err on the side of excessive humility (Lenney, 1977; Small et al., 2007), underestimating their chances of success across various outcomes (Erkut, 1983; Mura, 1987). Even successful women are more likely to attribute their triumphs to external causes, such as others in their team, or luck, rather than to personal aptitude (Campbell & Hackett, 1986; Haynes & Heilman, 2013; LaNoue & Curtis, 1985).

One potential origin of these observed gender differences is biased sampling, in that prior research has often assessed overconfidence in what are considered traditionally masculine domains. However, we argue that overconfidence is not a direct product of domain importance, expertise, or even stereotypicality; rather it is a product of the desire to persuade others of one’s competence in a given domain (Hoffman & Yoeli, 2022; von Hippel & Trivers, 2011a). As such, it is not so much the male-bias of the domains that matters, but the degree to which perceived ability in the domain can help people compete with members of the same sex or attract members of the opposite sex.

Thus, our theorizing also suggests that in contexts that stimulate competition between women, we might see stronger expressions of female overconfidence. For instance, given the importance of social support to female reproductive success (Campbell, 2004; Taylor et al., 2000), we might expect greater female overconfidence in domains related to emotional intelligence, such as empathy (Muthukrishna et al., 2018). And given that attractiveness is a primary dimension of competition for women (Blake et al., 2018; Buss, 1989), we might also see greater overconfidence in attractiveness among women than among men. A finding that is potentially consistent with this possibility is that the correlation between self- and other-ratings of physical attractiveness is substantially lower for women (r = 0.29) than it is for men (r = 0.53) (Marcus & Miller, 2003; see also Pereira et al., 2019).

Despite these possibilities, there are two important caveats that suggest male overconfidence is more important than female overconfidence in attracting a mate. First, with greater variability on a trait, competition for that trait becomes more important. In short-term mating the playing field among females is much more equal than it is among males (Brooks, 2021), suggesting that overconfidence is more likely to be wielded by males than females in short-term mating contexts. In long-term mating, competition among females is more focused on male traits that confer status, and as such, we might expect female status competition to increase with greater variability in male status and income. Support for this prediction can be seen in the finding that women’s self-sexualization occurs to a greater extent in environments that are economically unequal (Blake et al., 2018). Maximizing one’s beauty is a fruitful strategy for attracting high-status male partners (Udry & Eckland, 1984), which historically, has been an important strategy (indeed, sometimes the only strategy) for female survival and social mobility (Blake & Brooks, 2019).

But this possibility leads to our second point, which is that competition among females for long term mates is more focused on male traits that are not directly observable and hence can only be detected with greater uncertainty (e.g., the capacity to gain resources and assist in parental care giving; Taylor et al., 2000). As noted above, uncertainty magnifies the impact of overconfidence. As a consequence, overconfidence has more potential to enhance perceptions of important male traits (such as competence) than it does to enhance perceptions of important female traits (such as physical attractiveness). Perhaps for this reason, Blake (2018) finds that expenditure at beauty salons and women’s clothing stores also covaries with economic inequality, as adornments may be a more viable means of amplifying physical attractiveness than overconfidence. Women’s relative overuse of image-enhancing filters and photo editing (Dhir et al., 2016) may stem from similar motivations. The bottom line here is that males’ internal assets are more readily distorted via overconfident claims.

These differences in adaptive pressures are not unique to humans, and although cognitive tools such as language, theory of mind, and episodic foresight have dramatically enhanced the scope of human deception (Dor, 2017; Suddendorf et al., 2022), false signaling in the context of sexual competition is widespread. For instance, Noë et al. (1980) examined the role of dominance in explaining social rank within chimpanzee hierarchies, identifying three categories of dominance displays – agonistic, bluff, and competitive. They found that male chimpanzee’s social rank to be tied to displays of agonistic dominance (direct physical dominance) and bluff displays (closest to overconfidence). Females social rank was linked only with dominance in competition for space – such as giving way when another is approaching; and social competition – such as refraining from interacting with another partner because another chimp usually acts as partner to the third. Consistent with the human data, overconfidence has the greatest utility in the context of agonistic confrontations and bluff displays.

We can see similar effects further afield from our genetic roots: consider male fig wasps who signal their fighting ability during territorial competitions by displaying their impressive mandibles (Moore et al., 2009). Wasps with large mandibles are intimidating as they can inflict significant damage on opponents. Capitalizing on this advantage, there is an atypical male phenotype that develops mandibles 50% larger than expected for body size. These males are competitive signalers and engage in fewer fights than typical males but have higher mating success. Nonetheless, when compelled to combat, they fare poorly and incur more injuries than a typical male. Taken together, these examples from our near and distant cousins suggest that male sexual competition frequently takes the form of exaggerated signaling, a strategy that may be well served by self-deceptive overconfidence (see Angilletta et al., 2019).

New Deal, New Patriots: How 1930s Government Spending Boosted Patriotism During WWII

New Deal, New Patriots: How 1930s Government Spending Boosted Patriotism During WWII. Bruno Caprettini, Hans-Joachim Voth. The Quarterly Journal of Economics, qjac028, June 30 2022. https://doi.org/10.1093/qje/qjac028

Abstract: We demonstrate an important complementarity between patriotism and public-good provision. After 1933, the New Deal led to an unprecedented expansion of the US federal government’s role. Those who benefited from social spending were markedly more patriotic during WWII: they bought more war bonds, volunteered more, and, as soldiers, won more medals. This pattern was new—WWI volunteering did not show the same geography of patriotism. We match military service records with the 1940 census to show that this pattern holds at the individual level. Using geographical variation, we exploit two instruments to suggest that the effect is causal: droughts and congressional committee representation predict more New Deal agricultural support, as well as bond buying, volunteering, and medals.

JEL D64 - Altruism; PhilanthropyD74 - Conflict; Conflict Resolution; Alliances; RevolutionsD91 - Role and Effects of Psychological, Emotional, Social, and Cognitive Factors on Decision MakingH53 - Government Expenditures and Welfare ProgramsH56 - National Security and WarI38 - Government Policy; Provision and Effects of Welfare ProgramsN31 - U.S.; Canada: Pre-1913N41 - U.S.; Canada: Pre-1913P16 - Political Economy

5 Conclusion

Patriotism is widespread today – in 48 out of 52 countries, according to the World Value Survey, more than 80% of citizens are "quite proud" or "very proud" of their country (Beauchamp, 2014). At the same time, an important literature views nation-states and nationalist sentiment as artificial inventions that are socially constructed based on shared myths and narratives (Anderson, 2006; Colley, 1992). In the words of Yuval Harari: "We can weave common myths such as .. the nationalist myths of modern states. Such myths give Sapiens unprecedented ability to cooperate flexibly in large numbers... with countless strangers"(Harari, 2014). Instead of common narratives and myths as sources of patriotism, we focus on the contractual origins of state capacity, and in particular, intrinsic reciprocity towards the nation (Besley, 2020; Sobel, 2005). We demonstrate that where the US federal government provided help and support in times of crisis during the 1930s, patriotic deeds became much more common. Roosevelt’s New Deal ushered in an unprecedented expansion of federal spending, fundamentally changing the role of the Federal Government in American society (Schlesinger, 1957). Where the New Deal offered more support, Americans were more likely to help their country in wartime. By observing the same, costly actions – volunteering and medal awards – in both WW I and II, we can examine what factors changed attitudes. Importantly, New Deal spending was not targeted at areas that were already more patriotic during WW I; it created a new geography of patriotism. These results hold both at the county level and at the individual level, examining patterns of volunteering among the 12 million American men of military age in 1940. Our findings have implications for two literatures. First, they offer insight into the synergy between civic capital and pro-social behaviors on the one side, and state capacity on the other. An emerging literature in economics analyzes the origins of capable states and the role of armed conflict (Besley and Persson, 2009; Acemoglu, 2005; Gennaioli and Voth, 2015). It often focuses on war shocks, military spending needs, and taxes as a key dimension of state building (Levi, 1989; Scheve and Stasavage, 2010). The case of US patriotism during WW II suggests that the complementarity between government intervention and civic capital goes far beyond taxation and direct, legal obligations – with social spending and government support inducing a form of generalized, intrinsic "reciprocity" towards the country as a whole (Besley, 2020; Sobel, 2005). In this way, the New Deal helped to overcome a fundamental distrust of the federal government (Wallis, 2010). The US pattern after 1940 therefore bears out a general mechanism that led conservative politicians from Bismarck to Churchill to advocate greater social spending to enhance military prowess. Second, a large literature has demonstrated that culture — the combination of attitudes, prac23 tices, and beliefs governing everyday life — can persist over long periods (Becker et al., 2016; Guiso et al., 2016; Voigtländer and Voth, 2012; Nunn and Wantchekon, 2011). Research on the determinants of changes in attitudes is in its infancy (Giuliano and Nunn, 2021). Here, we demonstrate how government spending can fundamentally transform patriotic attitudes in a relatively short space of time, creating a new geography of patriotism. 

Theolinguistic Study of Directive Speech Acts Performed by an Islamic Preacher in Friday Sermon in Bandung, Indonesia

Theolinguistic Study of Directive Speech Acts Performed by Islamic Preacher in Friday Sermon in Bandung Indonesia. Cipto Wardoyo, Lina Marlina, Wahyudi Darmalakasana, Ija Suntana, and Dadang Kahmad. In Proceedings of the 2nd International Conference on Sociology Education (ICSE 2017) - Volume 1, pages 178-183, ISBN: 978-989-758-316-2. https://www.scitepress.org/Papers/2017/70950/70950.pdf

Abstract: Theolinguistic study tries to explain the relationship between linguistics and religion. Religious rituals in Islamic teachings are closely related to verbal activities such as pray, daily prayer, sermons, and wedding ceremony. One method of delivering the teachings of Islam is through Friday sermons. The speech of preacher in Islamic Friday sermons is relevant to be approached pragmatically by using the theory of speech acts. This research tries to focus on studying directive speech acts performed by khatib (Islamic preacher) in Friday sermons. The data in this study was taken from the recording Friday sermon mosque in the Bandung, West Java, Indonesia. The result shows that the strategy of directive speech acts using suffix “lash” and “kan” also has higher number among the finding data. The directive speech acts strategy using inclusive pronoun “kita” indicates that khatib want to be more polite. The strategy of directive speech acts using prohibition words also has quite high number. Khatib asked attendees to fear God, be thankful, always remember and pray to God, khatib supported his argument with Quranic verses and prophetic tradition.

Keywords: Theolinguistics, Speech Acts, Islamic Friday Sermon.

People fail to give prosocial input (complimenting someone), because of overestimation of the costs of doing so (e.g., making recipients uncomfortable); this reluctance to give prosocial input results in a short supply of kindness

Kindness in Short Supply: Evidence for Inadequate Prosocial Input. Jennifer E. Abel et al. Current Opinion in Psychology, August 20 2022, 101458. https://doi.org/10.1016/j.copsyc.2022.101458

Abstract: In everyday life, people often have opportunities to improve others’ lives, whether offering well-intentioned advice or complimenting someone on a job well done. These are opportunities to provide “prosocial input” (information intended to benefit others), including feedback, advice, compliments, and expressions of gratitude. Despite widespread evidence that giving prosocial input can improve the well-being of both givers and recipients, people sometimes hesitate to offer their input. The current paper documents when and why people fail to give prosocial input, noting that potential givers overestimate the costs of doing so (e.g., making recipients uncomfortable) and underestimate the benefits (e.g., being helpful) for at least four psychological reasons. Unfortunately, the reluctance to give prosocial input results in a short supply of kindness.

Keywords: prosocial behaviorsocial cognitionfeedbackadvicecomplimentsgratitude

Due to the male backlash channel, women in employment in India face significantly higher levels of intimate partner violence compared to women involved in domestic work only

Male Backlash and Female Guilt: Women’s Employment and Intimate Partner Violence in Urban India. Sowmya Dhanaraj & Vidya Mahambare. Feminist Economics, Volume 28, 2022 - Issue 1, Pages 170-198, Nov 25 2021. https://doi.org/10.1080/13545701.2021.1986226

Abstract: This study investigates the relationship between a married woman’s paid work participation and her exposure to intimate partner violence (IPV) in urban India. Results show that due to the male backlash channel, women in employment face significantly higher levels of IPV compared to women involved in domestic work only. The study does not find evidence that any autonomy women gain by doing paid work lowers their experience of IPV. Furthermore, this paper contributes to the literature on gender-based violence by introducing and testing for a “female guilt channel” – a phenomenon in which women in paid work justify IPV against them more than those not in paid work – that, in turn, further raises their IPV exposure. The paper finds weak evidence for the guilt channel in the overall sample and stronger evidence among women with intermediate levels of education.

Highlights

. Women in paid work in urban India are more likely to accept intimate partner violence (IPV), as well as experience a higher degree of marital controlling behavior by husbands.

. Urban women and men with tertiary education are most likely to overcome gendered norms for paid work.

. IPV is higher among urban women in paid work whose husbands are not employed or earning less.

. Raising women’s economic opportunities alone may not lead to universally better outcomes for them inside households.

Keywords: Violence against womenwomen’s paid workgender relationsgender roles

JEL J12J16

Novel hypotheses that answer key questions about the evolution of sexual reproduction

The origination events of gametic sexual reproduction and anisogamy. Yukio Yasui & Eisuke Hasegawa. Journal of Ethology, Aug 19 2022. https://link.springer.com/article/10.1007/s10164-022-00760-3

Abstract: The evolution of gametic sex (meiosis and fertilization) and subsequent transition from isogamy (fusion between two equal-sized gametes) to anisogamy (dimorphism into eggs and sperm, namely, females and males) is one of the largest enigmas of evolutionary biology. Meiosis entails genome-dilution cost and anisogamy entails male-production cost. Despite much progress has been made for the maintenance mechanisms of sex, its origination events under such “twofold cost of sex” are still unsolved. Here, we posit two hypothetical scenarios as follows: the “Seesaw Effect” hypothesizes that automictic selfing between isogametes effectively purged deleterious mutations from an organism’s lineage and simultaneously fixed the sex-controlling allele and all other loci (no genome-dilution cost raised). The high relatedness among homoeologous cell colonies led to multicellularization. The “inflated isogamy” hypothesizes that multicellularity increased the reproductive investment of both mates, resulting in excessively large isogametes. This redundancy induced cheating of one sex (evolving to male) to reduce gamete size. However, the other sex (evolving to female) allowed this cheat because her cost did not change. Therefore, anisogamy originated as a kind of commensalism but turned into beneficial for females because it solved the gamete limitation problem inherent to isogamy. Thus, smooth transition to anisogamy had been attained.

Discussion

The first gametic sex and anisogamy

Many hypotheses successfully explain the maintenance mechanisms of sex but the mechanisms favoring the first individual bearing a sex mutation are still unclear. Likewise, the scenario enabling a smooth transition from isogamy to anisogamy imposing the twofold cost is not fully understood. We have explained these issues according to the seesaw effect and inflated isogamy. The seesaw effect of automictic selfing does not require another sexual individual at the origin of gametic sex. Mutations independently occurring in two genomes of the sexual individual (dms in diploidy) are unevenly divided into gametes (dms2+α$\frac{dms}{2}+\alpha$ and dms2−α$\frac{dms}{2}-\alpha$: α$\alpha$ is a positive value representing the deviation from the equal division of dms). This is the only necessary condition, which is satisfied in most cases (α≫1$\alpha \gg 1$).

Previous studies have considered automixis only in the sense of negative consequences, such as the loss of heterozygosity and inbreeding depression, and could not explain why automixis has been sustained across diverse taxa from yeast to insects and reptiles (Matsuura et al. 2004, 2009; Engelstadter 2017). This study shows that the seesaw effect achieved by automixis reduces deleterious genes. If thelytokous species usually produce clonal offspring without meiosis but periodically perform automictic selfing, they may purge the dms accumulated during asexual generations via the seesaw effect. If this is the case, the seesaw effect may be the key mechanism preventing these species from going extinct. Instead, in such reproductive modes, limited genetic diversity restricts adaptability to changing environments, but some thelytokous species could persist in specific niches (mostly as relic species such as Komodo dragons; Watts et al. 2006). Thus, automixis may have a positive function in certain situations.

Three cautions regarding the cost of sex

Here, we note three cautions that should be considered when arguing the cost of sex. First, meiosis does not necessarily always enforce the genome-dilution cost in sexual organisms. In fact, the authors of some previous studies (e.g., Dawkins 1976; Lehtonen et al. 2012) have argued that assortative mating can instantly fix the sex allele in a descendant lineage, and thereafter, the genome-dilution cost disappears because mating occurs only between the individuals bearing the sex allele. However, the first sexual individual could not find a mate. In contrast in our scenario, fusion between CS (clean and sexual) gametes in the form of automictic selfing is a mechanical necessity. Mate searching and discriminating, which are required in assortative mating are all unnecessary in our case.

Importantly, automictic selfing also fixes all other alleles in the genome at the time of the first reproduction event. Thereafter, the twofold cost disappears for entire genome, where the interests of all genes coincide. Moreover, because the evolutionary interests of all the homozygous alleles at all the loci in all individuals coincided within the offspring population (clonal colony), multicellularization as the necessary step toward anisogamy evolution would occur smoothly.

Instead, genetic diversity that is necessary for further evolution is lost by selfing. Newly occurring mutations and subsequent outcrossing (initially within the sib colony and later between non-kin individuals) would create heterozygosity at all loci in offspring populations and revive the twofold cost. The offspring of the NN genotype at the sex-controlling locus, which would be generated by selfing or sib mating between SN mutants, would return to asexuality and avoid the cost of sex, but this lineage is ultimately destined to go extinct again based on Muller’s ratchet. Thus, stabilizing selection would retain the SS genotype (i.e., sexuality), but sex would enforce the genome-dilution cost at the other heterozygotic loci, leading to intragenomic conflict. However, this conflict would result in the victory of the sex locus because the secondary asexuals soon go extinct and the other loci must require genetic diversity for further evolution, even if they incur a twofold cost. Therefore, all loci would finally reach a point of compromise leading to coexistence under sexuality.

Second, we should not confound investments with costs. Investments should be increased if they are beneficial, but costs should always be reduced. As life evolved from simple unicellular organisms to complex multicellular organisms, the construction cost increased enormously, but this may have been a high-return investment. This considerable investment in the body absorbed the mere twofold cost of eggs. Considering mammals that supply nutrition to their offspring via placentation and lactation, the sex difference in gamete size is no longer problematic. This study explains the evolution of anisogamy by assuming the occurrence of inflated isogamy (an intermediate step between smart isogamy and anisogamy; Fig. 4). Inflated isogamy is a necessary step because if one sex shows a reduced investment under smart isogamy, only the embryo (size << R) will die (male cheating is impossible; Fig. 4). Then, male–female coevolution would continue in either a synergistic or antagonistic (sexual conflict; Lessells et al. 2009) manner, leading to the present-day diversity of the reproductive system.

Third, we should not overlook the notion that complex multicellular organisms require anisogamy irrespective of its cost. When diploid multicellular organisms reproduce sexually, they have to produce haploid germ cells that represent their genetic information because it is impossible to fuse each of the billions of cells in a differentiated body with those of another individual, and somatic cells have lost the totipotency that is necessary for the organic differentiation of embryos. Multicellularization allows more advanced adaptations due to the division of labor among differentiated (but genetically identical) cells within individuals. However, relatedness among cells in a multicellular individual will necessarily decrease due to independent mutations occurring during differentiation. Gametic sexual reproduction, namely, restarting from a single stem cell, can solve specific problems of multicellularization at the same time: (1) it resets the relatedness in an individual body to 1, (2) it recovers totipotency, and (3) it purges deleterious genes from genetic lineages. Another reason why isogamy does not exist in the multicellular organisms larger than plankton is that they require large amounts of resources (large zygotes) for ontogeny, but fusion between two very large cells (two eggs) seems physically impossible. Among external fertilizers, a large amount of cytoplasm disturbs fusion, in addition to decreasing mobility (mate searching cost; Parker et al. 1972; Lehtonen et al. 2012). Among internal fertilizers, if a large nutritious egg is sent into the mate’s reproductive tract, it will be consumed by the mate (sexual conflict; Lessells et al. 2009). Therefore, gametic sex is possible only as isogamy between micro-sized gametes or as fusion between large eggs and small sperm that can penetrate the egg cytoplasm. All these factors would force anisogamy on higher organisms.