Areas and Consequences of the Mismatch Between Ancestral and Modern Conditions on Mate-Retention Capacity

Abstract

Several people in contemporary postindustrial societies experience difficulties retaining intimate partners. This paper investigates the proximate reasons (the immediate causes of reduced capacity) and the ultimate reasons (the evolutionary causes behind those proximate mechanisms) that lead to such difficulties. I argue that the mechanisms or adaptations involved in partner retention evolved in ancestral preindustrial contexts and may not be effective in contemporary postindustrial settings. Relevant mismatches include the protection of human rights, dependence on intimate partners, freedom in mate choice, and access to parenting resources. I further argue that these mismatches have affected adaptations involved in partner retention, including the expression of undesirable traits, such as aggression and jealousy, insufficient mating effort, poor initial mate choice, and an impaired ability to meet the demands of parenting. As a consequence, many individuals today experience reduced mate-retention capacity, with implications that I explore.

1. Introduction

Many people living in contemporary postindustrial societies face considerable difficulties in attracting and retaining mates. For example, a study with 7181 participants from 14 countries found that, in the pooled sample, 48.2% reported difficulties attracting an intimate partner and 38.4% reported difficulties keeping one (Apostolou et al., 2023b). Given the evolutionary importance of mating (Buss, 2016), these rates are exceptionally high, raising the question of why evolutionary forces have allowed such variation in the population. The purpose of the present paper is to theorize on the reasons behind the difficulties people face in retaining mates and to explore the implications of reduced capacity in this dimension.

There are proximate and ultimate reasons behind any behavioral phenomenon, including reduced mate-retention capacity (Scott-Phillips et al., 2011). Proximate reasons refer to the immediate causes, for example, having an aggressive disposition toward an intimate partner. Ultimate reasons refer to the evolutionary causes behind those proximate mechanisms, namely, why selection forces have allowed or favored such dispositions (Alcock, 2018). The ultimate hypothesis advanced here is that mating environments in ancestral human societies differed substantially from those in contemporary postindustrial societies, so several mechanisms or adaptations involved in retaining mates do not function optimally today, which reduces mate-retention capacity. In the first part of the paper, I examine ultimate reasons, in the second part, I examine proximate reasons, and in the third part, I examine the consequences of reduced mate-retention capacity as well as directions for future research. The arguments put forward are summarized in Figure 1.

2. Ultimate Reasons: The Mismatch Problem

2.1. The Nature of Human Behavior

Life on Earth likely began about four billion years ago with the emergence of a self-replicating molecule, possibly similar to RNA. Copying errors produced variation among replicators, and scarce resources created competition. Variants that used resources more efficiently left more copies and displaced less efficient types. Evolution is this process. In environments with limited resources, an imperfectly copying replicator changes across generations as successful variants become more frequent (Fisher, 1958). Selection repeatedly favored efficient variants, so lineages adapted to their ancestral conditions. These simple ingredients, heredity with variation, competition, and differential replication or selection, generated increasing complexity that eventually spread across the planet (Dawkins, 2016).

Greater complexity requires more information, encoded in genes, the physical medium that stores it. Information is instantiated in molecules but expressed through development and interaction with environments. From this perspective, organisms are collections of mechanisms or adaptations that interact with their surroundings in ways that raise the odds that the genes that code for them are represented in future generations, termed fitness. Reproduction is the primary route, yet survival is a prerequisite for reproduction. Genes can increase their representation by coding for traits that enhance survival and reproduction. Because relatives share genes, tendencies that motivate helping kin can also raise a gene’s representation in future generations (Dawkins, 2016).

Viewed this way, bodily mechanisms function to increase fitness by supporting survival, reproduction, or aiding genetic relatives. The human brain is part of this system, bundling specialized mechanisms that motivate behaviors with these effects. Genetically influenced patterns of behavior, therefore, tend, in expectation, to promote the persistence of the genes that code them (Barkow et al., 1992). Consider hunger. The feeling of hunger prompts eating, which supports survival and thus the chance of reproduction. Offspring can inherit genetic architectures that generate hunger and feeding responses. The proximate reason people eat is that they feel hungry, whereas the ultimate reason is that the hunger mechanism evolved because it increased the chances of survival. Similar logic applies to other motivations, such as seeking mates, caring for offspring, and cooperating with kin. However, several factors can cause evolved mechanisms to function suboptimally.

2.2. The Mismatch Problem

Adaptations address challenges posed by the environments in which they originally evolved. When the environment changes, these adaptations may no longer address the new challenges effectively, which reduces fitness. Environmental change then imposes selection pressures that shape adaptations to function better in the novel conditions (Irons, 1998). Gene replication is reliable but imperfect, so some copies differ from the original. Some mutations can be more adaptive in the novel environment, meaning they shape mechanisms to address new challenges more effectively. As a result, those mutations are more likely to be represented in future generations than the original genes. They increase in frequency in the gene pool, and the mechanisms they code for change, eventually functioning more effectively in the new environment. Accordingly, evolutionary change occurs when environmental change provides the engine and mutation supplies the fuel (Dawkins, 2016; Irons, 1998).

Adaptation to a novel environment usually requires many generations. Because evolutionary change is slow, there is often a considerable time lag before selection pressures adjust adaptations to new conditions. During this period, many individuals have mechanisms that are not well adapted to the novel environment, suffering in effect fitness penalties. This mismatch problem affects many aspects of human behavior (Crawford, 1998; Li et al., 2018).

Environmental change does not imply that all aspects of the environment change. Some features remain the same, while others change dramatically. Adaptations that address relatively stable features will be less affected by mismatch. Adaptations that address features that have changed will be affected, and the magnitude of the mismatch depends on the degree of change. If the relevant features change only slightly, mismatch will be limited, and those adaptations will still function reasonably well. If change is substantial, mismatch will be substantial, and those adaptations will not address the demands of the novel environment effectively. There are good reasons to believe that the contemporary environment related to retaining intimate partners has been considerably different than the ancestral one, negatively affecting the capacity to retain mates. I will explore the areas of divergence next.

2.3. Areas of Mismatch in Retaining an Intimate Relationship

2.3.1. The Evolutionary Importance of Intimate Relationships

Humans have prolonged development, so offspring require substantial parental investment before reaching maturity. This level of investment is difficult for a single parent to bear. Long-term intimate relationships in which partners cooperate to raise children are, therefore, of high evolutionary importance because they facilitate offspring survival to sexual maturity (Lancaster & Lancaster, 1987). In addition, an intimate partner is an important source of protection and of financial and emotional support, which can substantially enhance survival prospects, especially in preindustrial contexts without a welfare state (Buss, 2016). In total, forming lasting intimate relationships can greatly increase fitness, so selection pressures have shaped the human mind to seek and form such relationships.

From this argument follows the hypothesis that strong selection pressures favored adaptations that enable individuals to retain mates, and it is predicted that most people have a good such capacity. This prediction is not confirmed, since a considerable proportion of people perform poorly on this dimension (Apostolou et al., 2023b). One reason is the mismatch problem. Ancestral conditions relevant to retaining intimate partners differed substantially from those in the contemporary context. As a result, some mechanisms may not address contemporary demands effectively, and many people today experience a compromised capacity to retain mates (Apostolou & Wang, 2020). I next discuss the main areas of discrepancy between ancestral and modern environments that are relevant to maintaining intimate relationships.

2.3.2. Protection of Human Rights

In preindustrial contexts, human rights were not well protected, which allowed intimate partners to exercise physical coercion against each other. For instance, among the Cheyenne of North America, husbands could mutilate the noses of their wives in cases of actual or suspected infidelity (Grinnell, 1923). Such behavior was not punished by law and was considered culturally appropriate, although it could have negative consequences, for example, retaliation by the victim’s kin (Campbell, 1964). Similarly, having an abusive spouse was a frequent cause of divorce in preindustrial settings (Betzig, 1989). In contemporary postindustrial societies, physical coercion is not tolerated culturally or legally. Physical aggression against an intimate partner is illegal and is punishable, including with incarceration. Physical and verbal abuse are also socially unacceptable and often lead to the end of a relationship (Amato, 2010).

2.3.3. Dependence on Intimate Partners for Material and Nonmaterial Resources

In every human society, there are continual threats from internal and external aggressors. Internal aggressors include thieves and rapists who might use force to obtain material or reproductive resources. External aggressors include enemy groups that use force to seize a group’s resources. Consequently, individuals must rely on others, including friends and family, for protection (Hruschka, 2010). This network includes one’s spouse and their family (Apostolou et al., 2023a). For example, a woman’s husband might protect her from potential rapists, and a man might rely on his wife’s brothers for protection from groups attempting to seize his property.

Humans evolved to live in groups, and group success depends on specialization (Aronson, 1980). In agricultural preindustrial societies, for instance, some people farm the land, others make tools for farming, and others process farm products into food. One consequence of specialization is that individuals cannot generate all the resources necessary for survival on their own, so they must rely on others, including intimate partners and their families (Apostolou et al., 2023a). Even when individuals can generate sufficient resources, periods of hardship arise when they cannot. A hunter might be injured and unable to hunt, for example. In such scenarios, people rely on their intimate partners and their kin to provide support.

Overall, in all human societies, intimate partners constitute important sources of physical protection and material resources. This importance is much lower in the postindustrial context than in the preindustrial one. Postindustrial societies have institutions, such as the police and the military, that protect people from internal and external threats. Individuals can use wages to purchase the goods necessary for subsistence. Financial institutions, such as banks and insurance companies, enable people to save resources for periods when they cannot work. Social protection institutions, such as sick leave and unemployment benefits, also support individuals when they cannot work.

2.3.4. Freedom over Mate Choice

In the preindustrial context, the primary form of long-term mating was arranged marriage, in which parents chose spouses for their daughters and sons (Coontz, 2006). One study that analyzed anthropological evidence from 190 contemporary hunting and gathering societies found that arranged marriage was the most frequent mode of long-term mating in about 70% of cases (Apostolou, 2007). A subsequent study, using a smaller sample from the Standard Cross-Cultural Sample, a dataset of 186 relatively independent preindustrial societies, found that first marriages were predominantly arranged and that this institution was more prevalent in agropastoral than in hunting and gathering societies (Apostolou, 2010). Another study analyzed the historical record for 16 preindustrial societies, including Classical Athens and Imperial Rome, and found that in 15 of them, marriages were typically arranged, while for one society, the evidence was inconclusive (Apostolou, 2012).

Furthermore, across human evolution, men often formed coalitions that engaged in conflict with other groups over resources, including sexual access to women (Chagnon, 1992). Evidence from anthropology, history, and behavior indicates that this conflict ranged from small-scale raids to large-scale wars. In foraging societies, men sometimes organized raiding parties to capture women from neighboring groups (Chagnon, 1992; Chapman, 1982). Historical records indicate that in preindustrial societies, victorious leaders, such as kings and emperors, frequently monopolized large numbers of women (Betzig, 1986).

Even in cultural contexts characterized by arranged marriages and forced mating by dominant men, individuals retained some agency in mate selection. Opportunities for personal choice arose in casual or extra-pair relationships and in later marriages when parental influence diminished (Apostolou, 2017). This autonomy was limited, however, because parents and spouses often used measures such as mate guarding to prevent disapproved relationships (Apostolou, 2014). Overall, in preindustrial contexts, long-term mates were predominantly provided by parents or obtained through coercion by dominant males. This pattern contrasts with contemporary postindustrial societies, where individuals usually choose their own mates, parental involvement is limited, and forced mating is illegal.

2.3.5. Online Dating

Until very recently in human evolutionary history, mate choice was taking place offline; the usual process would be for individuals or their parents to interact with prospective mates or in-laws face to face. On the other hand, in contemporary postindustrial societies, much of mate choice takes place online. In particular, people meet prospective mates on social media platforms, like Facebook, or on dedicated dating applications, like Tinder. For instance, a 2023 Pew Research Center study found that approximately 30% of U.S. adults have used online dating sites or apps, with higher rates among younger demographics (McClain & Gelles-Watnick, 2023).

2.4. Parenting

Access to Supporting Kin

Anthropological and historical evidence indicate that, in preindustrial contexts, most couples live in very close proximity to extended kin, including parents, grandparents, siblings, and cousins (Hareven, 1994; Laslett, 1972). These individuals are genetically related to the couple’s children and, therefore, have vested interests in their welfare, which makes them more willing to assist with child-rearing. As a result, parents have access to a network of relatives who provide meaningful assistance. Families also tend to be extended in this context (Laslett, 1972), so this network is usually large. In addition, people typically have children at younger ages, which means their parents are relatively young and able to help, and grandparents are often alive and able to contribute. There is also evidence that nonparental help in child-rearing is common, often termed alloparental care; for example, younger women receiving help from older women whose children are more independent and later providing help in turn (Hrdy, 2009).

Overall, in the preindustrial context, parents generally have access to a large network of relatives and nonrelatives who assist with child-rearing. This contrasts with the postindustrial context, in which many couples lack such access. People frequently move away from their extended families, relocating to different neighborhoods, cities, or countries for employment (Molloy et al., 2011). Contemporary postindustrial families also tend to be smaller than preindustrial ones, which reduces the size of the close-kin network. Individuals tend to have children later in life, so their parents may be older and in poorer health, sometimes requiring help themselves, and grandparents may be absent due to mortality (Coall & Hertwig, 2010). Additionally, contemporary postindustrial societies are highly individualistic (Triandis, 1995), which means that meaningful alloparenting does not take place.

3. Proximate Reasons: Predictors of Reduced Capacity to Retain Mates

Differences between ancestral and modern conditions indicate that mechanisms involved in mating and parenting evolved in contexts very different from those in which they now operate. The Industrial Revolution and the transition to postindustrial economies, in which most people work in the service sector, began in the eighteenth century in the United Kingdom (Allen, 2009). This shift is very recent in evolutionary terms, so selection pressures have had insufficient time to adjust adaptations for retaining an intimate partner to modern conditions. It follows that many people today have mechanisms or adaptations that constrain the maintenance of intimate relationships. In this section, I will discuss adaptations that are likely to have been affected by the mismatch problem.

3.1. Undesirable Traits

3.1.1. Aggressive Behavior

Men have often competed with one another for access to women using physical aggression, which selected for traits such as larger stature, stronger musculature, and higher aggression. As a result, men are, on average, larger, stronger, and more aggressive than women (Puts, 2016). These traits function as “weapons” in male–male competition and have also been used to control women. In the mating domain, men have used physical aggression, or the threat of it, to keep intimate partners aligned with their wishes (Buss, 2000). To take an extreme example among the Yanomamo of South America, “Some Yanomamo men often mistreat their wives, they beat them with pieces of firewood, shoot them with barbed arrows in a nonfatal part of their bodies, chop their arms and upper bodies with axes and machetes, press burning chunks of firewood against their bodies, and do other things that most of us would find revolting and vile” (Chagnon, 2013, p. 218).

In preindustrial contexts, where human rights are poorly protected and men dominated women, physical coercion was often effective for partner retention. Women might fear severe punishment for leaving their husbands or for cheating with other men. It is, therefore, reasonable to argue that men evolved a predisposition to use physical coercion to exercise control and retain partners. In contemporary postindustrial contexts, where rights are protected and men do not dominate women, this strategy is likely to have the opposite effect, making men less likely to keep an intimate partner. Although some women may be intimidated and remain, many will leave an abusive partner.

Because the transition to environments in which physical coercion is ineffective is recent, selection pressures have not had enough time to eliminate such predispositions. Men can adjust their strategies to local conditions, yet the mismatch argument implies that many fail to do so. Consequently, some men today struggle to refrain from coercive behavior and, therefore, face difficulties retaining partners. Consistent with this argument, in one study, participants, especially men, identified being physically abusive as a factor that hindered relationship maintenance (Apostolou & Wang, 2020). Partner aggression is also a frequently reported reason for divorce (Amato, 2010; Amato & Previti, 2003).

3.1.2. High Romantic Jealousy

Intimate partners often have incentives to cheat or to leave for more desirable alternatives (Buss et al., 2017; Grelling & Buss, 2000). One adaptive problem is how to prevent a partner from cheating or leaving. Romantic jealousy appears to be a mechanism that evolved to address this problem (Buss, 2000). Cues of infidelity or interest in another mate trigger jealousy that motivates corrective action, for example, spying on partners, threatening partners or rivals with aggression, and guarding partners more closely (Buss & Shackelford, 1997). Yet, once a partner has cheated or formed an emotional bond with someone else, it is often too late to save the relationship. Accordingly, jealousy tends to operate preemptively. People may feel jealous even in the absence of clear signs of outside interest, which motivates closer guarding and reduces exposure to potential mates. In this respect, romantic jealousy can increase the capacity to keep intimate partners, as individuals who experience little or no jealousy may be more likely to lose partners to competitors.

Selection likely tuned the jealousy mechanism to ancestral preindustrial conditions in which rights were weakly protected, and individuals depended on partners for material and nonmaterial benefits. Such conditions likely favored higher jealousy. Intense jealousy could motivate surveillance and close guarding that limited contact with potential competitors, and intimate partners might tolerate it in order to retain relationship benefits. Intense jealousy might also trigger aggression that deters contact with prospective mates, and such behavior could be tolerated or accepted socially.

Selection pressures likely favored relatively high jealousy, so many individuals today experience high levels of it. In postindustrial contexts, where human rights are well protected and dependence on partners is lower, high jealousy can reduce mate-retention capacity. Partners are less willing to tolerate spying, invasions of privacy, or aggression driven by jealousy. Because the transition to modern contexts is relatively recent, selection has had limited time to recalibrate jealousy to more optimal levels, so many people today experience levels of jealousy that harm relationship stability. Consistent with this argument, participants report that being very jealous impedes their ability to keep an intimate partner (Apostolou & Wang, 2020), and jealousy is a common reason for divorce (Amato, 2010; Amato & Rogers, 1997).

3.1.3. Selfishness and Inflexibility

Traits such as selfishness and inflexibility can, in some circumstances, increase fitness by helping individuals persist in acquiring desired outcomes across domains, including mating (Hawley, 1999; Jonason et al., 2009). For example, a selfish individual may demand more time and attention from a partner, and an inflexible individual may refuse to deviate from such demands. Having a partner with these traits imposes costs. Still, in preindustrial contexts, the benefits of a relationship could outweigh these costs, so individuals might tolerate partners’ selfishness or inflexibility to continue receiving those benefits. The fitness gains associated with these traits, coupled with limited reproductive costs under ancestral conditions, would have favored their persistence and increased their frequency (Hawley, 1999).

In postindustrial contexts, where relationship benefits of this kind are reduced, tolerance for selfishness and inflexibility is lower. Selection pressures have not had sufficient time to adjust the prevalence or expression of these traits to modern conditions, so many people today may behave selfishly or inflexibly toward partners and therefore struggle to maintain relationships. More broadly, ancestral conditions favored or permitted several personality traits at relatively high frequencies. Due to mismatch, these traits can constrain mate-retention capacity today. Studies of divorce identify character issues, including inflexibility, as common reasons for marital dissolution (Amato & Previti, 2003; Caughlin et al., 2000).

3.1.4. Insufficient Mating Effort

Mating effort can refer to the effort of people to attract new mates, including extra-pair ones, as well as to the effort to keep current mates. With respect to the latter, maintaining an intimate relationship requires effort, for example, attending to a partner’s needs, offering support through challenges, and providing sexual satisfaction. The mechanisms that motivate such effort evolved in contexts with strong extrinsic incentives to keep relationships, including material and nonmaterial support from partners. In the presence of strong incentives, less effort is required to maintain relationships. Because effort is costly, selection pressures likely calibrated mechanisms to provide only what was necessary.

What effort is necessary is higher in contemporary postindustrial than in preindustrial contexts because extrinsic incentives are reduced. Yet, the recent transition has not allowed sufficient time for relevant adaptations to recalibrate upward. As a result, many people today do not exert the effort needed to sustain their relationships. Insufficient effort strains relationships and can lead to dissolution.

Sexual interest in a partner also tends to decline as relationships progress (Byers, 2005). In preindustrial contexts, the material and nonmaterial benefits of a relationship could make sexual satisfaction a secondary concern. As those incentives are reduced in modern contexts, sexual satisfaction becomes more important. Because mechanisms underlying sexual desire evolved where a partner’s sexual satisfaction was less critical for relationship stability, for many people, desire for a partner subsides soon after relationship formation, which strains the relationship. In sum, inadequate mating effort, including insufficient provision of sexual satisfaction, impairs mate-retention capacity. Consistent with this argument, participants have identified not making the necessary effort and losing sexual interest in a partner as important constraints on maintaining intimate relationships (Apostolou & Wang, 2020).

3.1.5. Poor Choice of Long-Term Mates

Some prospective mates possess traits, for example, strong preferences for monogamy, that make them more likely to remain in a relationship, whereas others lack such traits and are less likely to commit long-term. Similarity between partners in traits such as attractiveness, age, intelligence, and personality predicts relationship stability (Luo, 2017). For instance, an introverted partner paired with an extraverted partner may face frequent disagreements over leisure time, creating strain.

Accordingly, people who choose mates with traits that favor long-term commitment and who are similar to themselves have a higher capacity to retain mates than those who do not. Selection forces should, therefore, shape mate-choice mechanisms that guide individuals toward choices that promote relationship longevity. Yet, until very recently in human evolution, parents typically chose long-term mates or dominant men enforced pairings, so selection pressures on individual mate-choice mechanisms were relatively weak. These pressures are stronger in postindustrial contexts, but the transition is too recent for this change to have had a substantial effect. Consequently, many people today have mate-choice mechanisms that are not effective at screening for traits that promote lasting relationships. Accordingly, people may choose unfaithful or incompatible partners, leading to short-lived unions.

Moreover, much of mate choice in contemporary societies takes place online, which is evolutionarily novel. In effect, individuals may have a harder time screening mates online and be more likely to end up with ones that have undesirable traits. Overall, poor initial mate choice, stemming from mismatch-affected mechanisms, reduces mate-retention capacity. Consistent with this argument, incompatibility is among the most frequently reported reasons for divorce (Amato & Previti, 2003; Gigy & Kelly, 1992; Scott et al., 2013).

3.1.6. Poor Ability to Meet the Demands of Parenting

Individuals receive substantial material and nonmaterial benefits from intimate partners, yet in evolutionary terms, the primary purpose of lasting intimate relationships is to have children and raise them to sexual maturity (Buss, 2016). If partners struggle to do so, relationship stability is compromised because its central function is threatened. Mismatch between ancestral and modern conditions in the parenting domain likely generates such difficulties and, in turn, difficulties in maintaining intimate relationships.

In preindustrial contexts, people could rely on extended kin and older children to help raise younger children. This is often not the case in postindustrial societies, where people frequently live far from family, kin networks are smaller, and couples have fewer children. Parents must, therefore, expend more effort themselves. Selection pressures may not have shaped sufficient capacity or motivation to meet these demands, particularly for men. In preindustrial contexts, most hands-on parenting was performed by mothers and their female relatives and friends (Hrdy, 2009). Fathers primarily provided resources and protection and were less involved in direct childcare. This division of roles would have produced differential selection pressures, making women more effective at childcare than men. In postindustrial contexts, mothers often lack access to female helpers, so more of the parenting effort must be shared with male partners, who may be less prepared for this task. Women may interpret such unpreparedness as a lack of interest in the child, which can diminish their perceptions of their partners.

Women may, therefore, bear the burden of parental care predominantly on their own, and they may not be fully prepared to handle this burden either, since in the past it was shared among female kin and allies. The additional load taxes parents and strains the relationship. In sum, the mismatch problem leads contemporary parents to face parenting challenges that, in turn, reduce their capacity to maintain intimate relationships. Consistent with this argument, a meta-analysis found that parenthood was associated with a modest but significant decline in marital satisfaction (Twenge et al., 2003).

3.2. Boundary Conditions

Contemporary postindustrial societies are heterogeneous, which means that the degree of the mismatch between ancestral and modern environments is likely to vary. For instance, contemporary societies tend to vary in the degree to which parents have access to supporting kin. To use an example, the Republic of Cyprus is a small island country, with most couples living within driving distance of other family members, such as their parents. On the other hand, the U.S. is a vast country, with people frequently moving around to find jobs, resulting in couples living away from their relatives. Accordingly, couples have easier access to kin-assistance in raising their children in Cyprus than in the U.S. Such variation in the mismatch between ancestral and modern conditions is likely to lead to variation in mate-retention capacity; ceteris paribus, people who live in societies where the mismatch is smaller would experience higher such capacity than people who live in societies where the mismatch is larger.

4. Consequences of Reduced Capacity to Retain Mates

I have argued that the mismatch between ancestral and modern conditions has negatively affected several mechanisms involved in retaining intimate partners. As a consequence, several people in contemporary postindustrial societies experience reduced mate-retention capacity. A compromised capacity to retain mates has several consequences, which I outline in this section.

To begin with, reduced mate-retention capacity is likely to lead to more fragile intimate relationships, which are likely to dissolve, leaving people single. Accordingly, this mismatch problem is one reason for the high prevalence of divorce and singlehood observed in contemporary postindustrial societies. Higher rates of singlehood, in turn, contribute to lower fertility, since people lack partners with whom to have children. Additionally, reduced capacity to keep intimate partners can substantially delay finding a suitable partner for family formation, as people pass through many failed relationships and spells of singlehood. At this point, women face another mismatch. During most of human evolution, women began reproducing in their late teens and concluded in their late thirties (Hill & Hurtado, 1996). Accordingly, the female reproductive system did not evolve for successful reproduction past these ages, and fertility approaches zero after age 45 (te Velde & Pearson, 2002). Consequently, delays in finding a partner for family formation can result in lower fertility due to advanced maternal age.

Furthermore, relationship instability due to the mismatch problem, combined with limited access to extended kin in contemporary postindustrial contexts and greater reliance on partners for child-rearing, can lead people to decide to have fewer children. In particular, people may worry that the relationship will not last and that if they have children, or more children, they will end up raising them on their own. Overall, reduced mate-retention capacity likely contributes to low fertility through multiple pathways and thus may be one reason for the fertility crisis that many postindustrial societies currently face (OECD, 2024). This argument suggests that addressing one root cause may help. Psychological interventions could help people increase their capacity to keep intimate partners, which would yield more stable relationships and, in turn, more children.

Additionally, the welfare of children born to parents with poor mate-retention capacity can be negatively affected. In particular, reduced capacity can lead to tension, fights, and aggression between parents, which in turn negatively affects their children’s emotional wellbeing. Furthermore, weak mate-retention capacity makes relationships more fragile, meaning that children born into these partnerships are more likely to find themselves in single-parent households. This situation often results in fewer resources being available for healthcare and education. Consequently, reduced mate-retention capacity is likely to result in fewer children and, for those children, lower emotional wellbeing and limited access to resources.

Moreover, reduced mate-retention capacity is likely to lead to low-quality intimate relationships. In turn, low-quality relationships are associated with lower emotional wellbeing, including sadness, despair, and reduced life satisfaction (Apostolou et al., 2024). Singlehood and low fertility are also likely to cause negative emotions (Apostolou et al., 2024; Cousineau & Domar, 2007). Accordingly, mismatch in the mating domain lowers emotional wellbeing in contemporary postindustrial societies by increasing the number of low-quality intimate relationships, making singlehood more prevalent, and decreasing fertility (Figure 1).

4.1. Directions for Future Research

In the present paper, I advanced the hypothesis that mismatch between ancestral and modern conditions has resulted in many individuals experiencing a reduced capacity to retain intimate partners, and I have also discussed several behavioral mechanisms that may be affected. Empirical research is required to test this hypothesis and its predictions. More specifically, future studies need to develop a psychometric instrument to assess the capacity to retain intimate partners and thus be able to identify individuals with reduced capacity. This instrument can be objective or subjective. Starting from the former, it could include behavioral indicators such as frequency of relationship dissolutions across a fixed window and initiator of dissolutions, evaluative indicators such as partner-report scales of effort, jealousy, or aggression, as well as event indicators such as relationship duration and shared projects such as cohabitation and children. It can also be subjective, including items such as “I am generally satisfied with how long my intimate relationships tend to last.” Subsequently, traits nominated, such as high jealousy and aggressive disposition, can be measured to examine whether they indeed predict the capacity to keep an intimate partner. Additionally, future work should investigate the extent to which reduced capacity to retain partners predicts singlehood and fertility.

Another line of research can focus on developing psychological interventions that address the factors underlying reduced mate-retention capacity and help people improve on this dimension. For example, interventions could help people manage romantic jealousy so that it does not harm their relationships. This line of research could have considerable practical implications. Improved capacity to retain mates would be associated with higher-quality intimate relationships and higher emotional wellbeing. Greater capacity would also yield more stable relationships and, in turn, more children, which could help address the demographic challenges facing many contemporary postindustrial societies.

The present paper was based on an evolutionary perspective to understand variation in mate-retention capacity. Yet, other theoretical perspectives can offer additional insights. For instance, the Investment Model, where low investments and high-quality alternatives predict dissolution, attachment theory, with expected patterns in stability by attachment style, and sex-ratio and “economics of sex” perspectives linking partner/child costs and market imbalances to commitment, could offer valuable insights. Accordingly, future studies could attempt to synthesize the insights of different perspectives in a more inclusive theoretical framework that could be used for understanding mate-retention capacity.

4.2. Conclusions

Many people today experience a reduced capacity to retain mates, with consequences that include singlehood and lower emotional wellbeing. In this paper, I traced the ultimate cause of this reduced capacity to the mismatch problem and nominated several proximate mechanisms likely to be affected. Future work is needed to better understand how mismatch shapes these mechanisms and to develop ways to mitigate its negative effects.