Sunday, May 23, 2021

Attention deficit hyperactivity disorder (ADHD) and autism spectrum disorder (ASD) are highly heritable neurodevelopmental disorders with a considerable overlap in their genetic etiology

Identification of shared and differentiating genetic risk for autism spectrum disorder, attention deficit hyperactivity disorder and case subgroups. Manuel Mattheisen et al. medRxiv, May 21 2021,

Abstract: Attention deficit hyperactivity disorder (ADHD) and autism spectrum disorder (ASD) are highly heritable neurodevelopmental disorders with a considerable overlap in their genetic etiology. We dissected their shared and distinct genetic architecture by cross-disorder analyses of large data sets, including samples with information on comorbid diagnoses. We identified seven loci shared by the disorders and the first five genome-wide significant loci differentiating the disorders. All five differentiating loci showed opposite allelic directions in the two disorders separately as well as significant associations with variation in other traits e.g. educational attainment, items of neuroticism and regional brain volume. Integration with brain transcriptome data identified and prioritized several significantly associated genes. Genetic correlation of the shared liability across ASD-ADHD was strong for other psychiatric phenotypes while the ASD-ADHD differentiating liability correlated most strongly with cognitive traits. Polygenic score analyses revealed that individuals diagnosed with both ASD and ADHD are double-burdened with genetic risk for both disorders and show distinctive patterns of genetic association with other traits when compared to the ASD- only and ADHD-only subgroups. The results provide novel insights into the biological foundation for developing just one or both of the disorders and for driving the psychopathology discriminatively towards either ADHD or ASD.

Motivations for Engaging in Consensually Non-Monogamous Relationships

Motivations for Engaging in Consensually Non-Monogamous Relationships. Jessica Wood, Carm De Santis, Serge Desmarais & Robin Milhausen. Archives of Sexual Behavior, May 14 2021.

Abstract: Sexual, romantic, and intimate relationships provide opportunities for individual and interpersonal fulfillment and the enhancement of well-being. Though research has identified that consensual non-monogamy (CNM) offers unique relational benefits, little work has examined why individuals pursue CNM relationships. Both self-determination theory and self-expansion theory provide frameworks for understanding the range of intra- and interpersonal motives for choosing or negotiating a multipartnered relationship. We explored the reasons for which people engage in CNM and discuss how motivations for CNM might be linked to well-being and need fulfillment. Our study used a qualitative approach to examine the motivations individuals report for engaging in CNM relationships. As part of a larger online survey, participants completed open-ended questions examining motivations for, and experiences of, CNM relationships. Data from participants who indicated that they were currently in a CNM partnership was selected for the analyses (n = 540). Data were analyzed using thematic analysis, within a critical realist framework. Motivations were organized into six interconnected themes: reasons related to autonomy, beliefs and value systems, relationality, sexuality, growth and expansion, and pragmatism. Individuals reported diverse reasons for engaging in CNM relationships; reasons addressed both individual and relational needs and well-being. Findings contrast with stereotypic views of CNM relationships as unstable/unfulfilling or that individuals engage in CNM because of relationship problems. The findings may facilitate therapeutic interventions for counselors working with individuals who are in the process of negotiating or re-negotiating relationship boundaries.

Check also Desire, Familiarity, and Engagement in Polyamory: Results From a National Sample of Single Adults in the United States. Amy C. Moors, Amanda N. Gesselman2 and Justin R. Garcia. Front. Psychol., March 23 2021.

Australia: Women who identify as “mainly heterosexual” report poorer health, greater health-risk behaviors, and higher rates of victimization than women identifying as “exclusively heterosexual"

Prevalence and Sociodemographic Correlates of Identifying as Mainly Heterosexual: Stability and Change across Three Cohorts of Australian Women. Francisco Perales, Alice K. Campbell, Bethany G. Everett, Ruth McNair & Tonda L. Hughes. Archives of Sexual Behavior, May 18 2021.

Abstract: In recent decades, the ways in which sexual minorities identify have changed dramatically. In response, social and health surveys have begun offering a greater range of response options within sexual orientation questions—for example, intermediate categories for “mainly heterosexual” and “mainly lesbian/gay” alongside the more common response options of “heterosexual,” “bisexual,” and “lesbian/gay.” Recent studies indicate that women who identify as “mainly heterosexual” report poorer health, greater health-risk behaviors, and higher rates of victimization than women identifying as “exclusively heterosexual.” However, we know very little about the demographic profile of women who choose the “mainly heterosexual” identity label compared to the adjacent “exclusively heterosexual” or “bisexual” labels or about changes over time in the prevalence and correlates of “mainly heterosexual” identification. This study addressed these knowledge gaps by modeling unique, high-quality survey data from three national cohorts of Australian women (Australian Longitudinal Study on Women’s Health, 2000–2017, n = 76,930 observations). Consistent with the facilitative environments model, we document stark cross-cohort increases in the percentage of Australian women identifying as “mainly heterosexual”—from ∼1% of those born in 1946–1951 to ∼26% of those born in 1989–1995, coinciding with comparable declines in the percentage of women identifying as “exclusively heterosexual.” We also found evidence of cohort differences in the associations between key sociodemographic factors—such as age, education, and socioeconomic status—and the likelihood of women identifying as “mainly heterosexual.” Finally, our results indicate that same-sex sexual attractions were more strongly associated with “mainly heterosexual” identification than was same-sex sexual behavior.

Large scale human cooperation needs to be explained as an adaptation, likely rooted in the distinctive features of human biology, grammatical language, increased cognitive ability, and cumulative cultural adaptation

Boyd, Robert, and Peter J. Richerson. 2021. “Large-scale Cooperation in Small-scale Foraging Societies.” EcoEvoRxiv. May 17. doi:10.32942/

Abstract: We present evidence that people in small-scale, mobile hunter-gatherer societies cooperated in large numbers to produce collective goods. Foragers engaged in large-scale communal hunts, constructed shared capital facilities; they made shared investments in improving the local environment; and they participated in warfare, alliance, and trade. Large-scale collective action often played a crucial role in subsistence. The provision of public goods involved the cooperation of many individuals, so each person made only a small contribution. This evidence suggests that large-scale cooperation occurred in the Pleistocene societies that encompass most of human evolutionary history, and therefore it is unlikely that large-scale cooperation in Holocene food producing societies results from an evolved psychology shaped only in small group interactions. Instead, large scale human cooperation needs to be explained as an adaptation, likely rooted in the distinctive features of human biology, grammatical language, increased cognitive ability, and cumulative cultural adaptation.

Irrespective of COVID, improved mood, less perceived stress were significanlty associated with some personality traits like neuroticism (lower), extraversion (higher), agreeableness (higher), and conscientiousness (higher)

Rettew DC, McGinnis EW, Copeland W, Nardone HY, Bai Y, Rettew J, et al. (2021) Personality trait predictors of adjustment during the COVID pandemic among college students. PLoS ONE 16(3): e0248895. May 17 2021. doi:10.1371/journal.pone.0248895.

Abstract: Personality traits have been found to be related to a variety of health outcomes. The aim of this study was to examine how personality traits were associated with adjustment to the COVID pandemic in college students. The sample included 484 first-year university students (76% female) attending a northeastern university who completed the Big Five Inventory (BFI) personality assessment at the beginning of a semester that was disrupted by the COVID pandemic. Using a phone-based app, students completed daily ratings of mood, perceived stress levels, and engagement in a number of health promotion activities (exercise, mindfulness, adequate sleep, etc.) throughout the semester both before and after the onset of the pandemic (e.g., a within-person longitudinal design). Results, as expected, showed that mood and wellness indices generally declined during the COVID period, although stress levels actually decreased. Further, irrespective of COVID, improved mood, less perceived stress and greater participation in health promotion activities were significantly associated with a number of personality traits including neuroticism (lower), extraversion (higher), agreeableness (higher), and conscientiousness (higher). Of primary interest, mixed-effects models were used to test how major personality traits interacted with any changes in daily ratings from the pre-COVID to COVID period. Significant interactions terms were found suggesting differential impacts of the COVID epidemic for students with low versus high levels of particular traits. Higher levels of extraversion, for example, were found to be related to decreases in mood as the pandemic progressed in contrast to those with lower extraversion, for whom there was a slight increase in mood over time. These data support the conclusion that personality traits are related to mental health and can play a role in a person’s ability to cope with major stressful events. Different traits may also be more adaptive to different types of stressors.


This study aimed to examine the link between major personality dimensions and change in mental health functioning through the COVID pandemic in a group of college students. We utilized daily ratings of subjective mood, stress levels, and engagement in wellness activities such as mindfulness, healthy eating, and exercise obtained from a smartphone app that started before students were sent home due to COVID concerns and then continued as they completed the semester at home.

As has been reported in many studies examining the association between personality traits and various indices of well-being and functioning, we found robust associations with many of the higher-order personality traits. Lower levels of neuroticism and higher levels of extraversion were generally found to be related to improved mood, lower stress levels and more engagement in healthy activities. Higher levels of openness, agreeableness, and conscientiousness were also significantly related to better mood and more wellness engagement but were not significantly related to stress levels. Some of these significant main effects need to be interpreted with caution given the interactions found for some of these traits as levels changed between the pre-COVID and COVID period. High levels of agreeableness and conscientiousness showed particularly strong associations with better mood across the study period while higher levels of neuroticism were prominently and expectedly related to higher levels of perceived stress. High conscientiousness was significantly related to more participation in wellness activities and healthy activities. Conscientiousness refers to the tendency to be both goal oriented and to abilities that help people obtain goals such as reliability and organization. As such, this trait has often been associated with better health and well-being [23] and has been called the “most valuable psychological asset” a person can have when it comes to major personality traits [10].

The COVID pandemic also appeared to have a negative impact on our mental health indicators, although not as uniformly as we had expected. Comparing ratings between the pre-COVID and COVID period, mood and engagement in wellness activities generally decreased. Stress levels, however, significantly fell across the study period, although the magnitude of this drop was quite modest. Such a drop was hypothesized for students high in the trait of neuroticism but was found more globally. These results underscore how stressful college life can feel for some students [24]. It also may suggest some independence between mood and stress, the latter of which may be described more closely as anxiety. While mood and anxiety levels typically are found to move together–so much so that the two areas in combination are considered the core of “internalizing” problems [25], the COVID pandemic may present an important example of conditions that can separate the two domains. The college experience for many students provides engagement and relationships but, as has been well documented of late, can also be quite challenging and anxiety provoking [26]. With many exceptions, it is possible that the college environment, for those who do not find the experience overwhelming, represents an example of “good stress” that might contribute to a higher mood [27]. The COVID pandemic brought more isolation and inactivity but also some relief from the regular stresses of this environment and this may have overall depressed both mood and perceived levels of stress. Of course, it is possible that a more prolonged duration of disruption in regular life from COVID, as is now occurring, will result in perceived stress levels to rise. Further investigations with this sample and others will help reveal the long-term impact of COVID on experienced stress levels.

For the most part, associations between personality traits and mental health/wellness were preserved across the time period from before the COVID pandemic in January 2020 through the end of the semester in May. As previously mentioned, however, some interactions effects were found, suggesting a differential response to the COVID epidemic based on levels of specific traits. The dimension of extraversion was especially involved, with significant interaction effects found for mood, stress, and wellness participation. For mood, we found that those with higher levels of extraversion experienced a decrease in their mood as the COVID period progressed while mood ratings among those with lower levels of extraversion rose slightly. When it came to stress levels, however, those in the high extraversion groups felt decreased stress during the COVID period while those with lower extraversion experienced slightly more. There isn’t a straightforward interpretation of this combination of findings, but we speculate that, as hypothesized, more extraverted people might find the stimulation and challenges of busy academic life to be more rewarding. Leaving this environment for home isolation thus could have resulted in feeling less stressed but more bored and lonely, resulting in a decrease in mood. This finding partially supported our hypothesis, although it is important to note that students with higher levels of extraversion, despite having a clear decrease in mood with COVID, still reported an overall more positive mood than their low extraversion peers.

A similar, though less pronounced, pattern was found with neuroticism in which those with lower levels experienced a larger drop in mood levels with COVID compared to students with high neuroticism (although the higher neuroticism group continued to report lower mood overall). It is possible that this finding comes from a “floor effect” as students with higher levels of neuroticism had a lower mood at baseline. Alternatively, it is possible that the disruption from COVID represented a relatively bigger “loss” for those with lower levels of neuroticism.

These findings need to be interpreted with appreciation for some of the limitations of this study. First, these data were obtained from college students at a single university. As such, the generalizability of this study to other populations may be limited. Secondly, it is also not possible to prove with these data that is was the COVID pandemic and not another unmeasured factor that was responsible for any changes in the mental health ratings. Small but meaningful changes in personality have been documented in college students under “normal” conditions, although this has generally been found to occur over longer periods of time [28]. Finally, we note that both the personality and mental health assessments were obtained from self-report.

This study, however, also has some noticeable strengths. The use of daily ratings of our mental health indices may have provided a more valid assessment of these parameters over time and minimized bias inherent in more retrospective reporting. Personality assessment was also performed using a well-validated instrument based on a widely accepted and researched personality model.

The Himba, spousal separation & female sexual autonomy: In such a harsh environment, having a mix of formal and informal romantic partners may be less costly and more beneficial than a system of monogamous marriage

Scelza, Brooke; Prall, Sean; Starkweather, Kathrine. 2021. "The Role of Spousal Separation on Norms Related to Gender and Sexuality among Himba Pastoralists" Soc. Sci. 10, no. 5: 174. May 17 2021.

Abstract: The gender-specific labor demands of arid pastoralism often lead to spousal separation. Men typically respond in one of two ways: engage in mate guarding tactics, or loosen restrictions on female sexuality. Among Himba pastoralists in northwest Namibia, the latter strategy is dominant. Rooted in a history of matriliny, Himba have strong norms promoting female sexual autonomy. We propose that these conditions, combined with a stochastic resource base, have led to women utilizing a combination of formal and informal partnerships to meet their needs and the needs of their children. Aspects of Himba socioecology also increase the costs of mate guarding for men and lower the costs of extra-pair paternity, further bolstering a concurrency strategy. Using a mix of quantitative and qualitative data, we show how spousal separation, female autonomy, and concurrency are linked, and suggest that in this harsh environment having a mix of formal and informal romantic partners may be less costly and more beneficial than a system of monogamous marriage.

Keywords: spousal separation; female autonomy; multiple mating

5. Discussion

Here we bring together data on various aspects of Himba lives and livelihoods in order to understand how the particular socioecological context of contemporary Himba life affects their marital and reproductive decision-making. In particular, we are interested in understanding why a normative system of concurrent partnerships and sexual autonomy for women exists in this pastoral system, instead of the more typical pattern of strong mate guarding and restrictions on women’s autonomy.
Like many pastoralists, Himba must contend with a stochastic resource base, moving livestock in response to seasonal rainfall patterns and with them, various members of the household. As Bollig describes, these ecological constraints greatly affect household composition:
Himba pastoralism depends on independent movements of livestock camps (ozohambo) and households (ozonganda). After a few weeks of heavy rain (usually January to March) the entire household herd gathers at the main homestead…. In an average year they stay together for three to four months while the major gardening work is done…. However, a cattle camp … will be established long before grazing resources become depleted…. Later, in July or August, male goats and sheep are separated from the household and either a separate small stock camp is established or the small stock herd joins the cattle camp…. At the height of the dry season, between September and December, a number of households shift all their remaining cattle to their cattle camp…
Depending on how many camps are established, and how many able-bodied adults are available for herding, various members of the household might be separated. Our data reflect the general pattern Bollig describes in that husbands and wives are most likely to be separated during the early dry season when the herd is split between the main household and the cattle camp.
Our data also point to a pathway from spousal separation to extra-pair paternity. We show both that spousal separation can lead to long periods of abstinence between spouses, and that sex with boyfriends is common enough to lead to extra-pair paternity. Although more than a quarter of respondents noted that it had been at least a month since they had had sex with their husband, sex with a nonmarital partner was reported to have occurred within the last month in 37% of cases. Several interlocutors mentioned spousal separation explicitly as the cause of their abstinence, noting that their partner was at the cattle post. Although these separations can be long, they do not necessarily indicate marital strife. As one woman who had been apart from her husband for many months explained, “You know you are divorced if you are in the same place and he doesn’t come to you. But if you are just in different places, then you are still together.”
Similarly, interlocutors also remarked that spousal separation is instrumental to maintaining relationships with non-marital partners. Although it is widely seen as normative to have lovers, there is a set of rules that all parties are expected to follow in conducting those relationships. Boyfriends arrive after dark and leave just before dawn, and they often try to determine ahead of time whether their partner is alone. With cell phones becoming increasingly common, this can often be accomplished directly between partners, but as one Himba man explains, others are often enlisted in the process: “I see her when her husband is not around. I can ask around, even kids you can ask, to see if the husband is around. In the evening I would go to a house of someone I know nearby and tell someone to let her know I’m there. Then I go there late at night to see her. We wake up early, before the roosters, and I leave to go back home.” For their part, husbands are expected to sleep away from home if they are out after dark (e.g., chasing a rogue cow after sunset). This reduces the chance that a husband and lover will mistakenly encounter each other.
Our aim in this paper was not just to illustrate the correlation between spousal separation and a normalized system of concurrent partnerships, but also to understand why they co-occur. We believe there are three distinct, but interrelated, reasons why spousal separation is associated with sexual autonomy and concurrent partnerships among Himba: (1) Phylogenetic inertia sets the stage for norms promoting female autonomy, while also increasing the costs of mate guarding; (2) demographic and economic factors reduce the costs of lost paternity for men; and (3) the stochastic resource base makes concurrency a viable way for men and women to improve their fitness.

5.1. Phylogenetic Inertia

Himba arrived in Namibia via the Bantu expansion, and only became ethnically distinct from their close relatives, the Herero, in the last 100 years (Bollig 2006). Holden and Mace (2003) analyzed shifts in the inheritance structures and modes of production of Bantu groups as they moved across the continent, and depict a general pattern where the adoption of pastoral production led to a shift from matrilineal to patrilineal inheritance. Himba/Herero are unique in that they transfer livestock matrilaterally, and links to one’s matriclan are culturally and functionally important (Malan 1995Gibson 1956). The Bantu language tree that Holden and Mace used to conduct their analysis shows that of the five groups Herero are most closely related to, one practices double descent similar to Herero, and the other four have matrilineal inheritance (Figure S3). Further back, Holden and Mace show that Herero are in the half of the phylogenetic tree with the majority of matrilineal Bantu populations.
Their deep history of matriliny helps to explain why norms promoting female autonomy are likely prominent among Himba. Early ethnographies of Herero describe many of the same sexual practices that exist today, including frequent divorce, high rates of nonmarital sex, acceptance of children born outside of marriage, and senior wives being included in the process of choosing a co-wife (Gibson 1959). Our data compliment these findings, showing that Himba women have relatively high freedom of movement, including lengthy visits unaccompanied by their husbands (Figure 3). These visits serve a dual purpose, keeping up relationships with natal kin, and allowing women opportunities to maintain concurrent relationships. Relatives can also serve as conduits for resource transfers. As one man described, “You cannot give it straight to the woman if she is married. You give ‘behind.’ You can send it [the gift] to her father or sister, then when she goes there she gets it and she can say it was given to her by her family.”
However, the picture of Himba autonomy is complex. Although they have more freedoms than women in many pastoral societies, the limits placed on them indicate that some mate guarding is occurring For example, husbands are most reticent about their wives traveling alone to a funeral or ceremony, which is commonly described by both men and women as being a place where lovers frequently meet. Intimate partner violence is not uncommon, and violence in response to extra-marital sex was second only to child neglect in its acceptability among men and had the highest acceptability rating among women. Women and men both linked sexual jealousy to IPV, and several of the women in our interviews mentioned being hit by their partners. One woman explained, “My husband is very jealous. He beats me because he loves me. He doesn’t tell me to leave. He just beats me.”
There are also complicated notions about non-marital partnerships at play, as evidenced by our vignette study. The majority of men stated that a married woman having a boyfriend is unacceptable, and almost every respondent reported that they knew about this happening. We see similar variation in the types of punishments men reported, ranging from nothing, to mild verbal warnings, to severe physical harm. Several of our respondents described a situation where a husband who found out about his wife’s boyfriend snuck into his compound at night (when he knew they would be together) and attacked and killed the boyfriend. We do not know that our interlocutors were all describing the same event or different ones as we did not ask people to give names when they told these stories, but regardless, this exemplifies how dangerous concurrency can be, even in this population where the practice is largely normalized. However, other men described much more measured responses. One reported, “The husband asked the boyfriend not to sleep with his wife. The boyfriend continued anyway. One day the husband met an agemate who told him the man was still sleeping with his wife. That night he didn’t come home. Later, he caught the boyfriend again. He called the community and they met and fined the boyfriend 10 cows.”
It appears that Himba hold a dual notion of concurrency. On the one hand, they stated that informal partnerships are an integral part of their culture, socially acceptable, and very common. On the other hand, both men and women reported sexual jealousy and there are efforts to constrain spouses’ relationships with lovers, especially if they become too frequent and become a threat to the marital union. As one man summed it up, “You don’t want other people to sleep with your wife, but it’s the tradition.” There are several explanations for this tension. Although it may be socially advantageous for men not to buck the current system, individually they may be motivated to maintain as much paternity certainty as possible. Alternatively, as with many double descent systems, Himba may be in a state of disequilibrium, in the process of shifting their social structures from matriliny to patriliny (Scelza et al. 2019). We show here that older men are more likely to be accepting of women’s concurrency. Age also had a negative but non-significant effect on men’s beliefs about IPV, with older men less likely to believe IPV is acceptable under varying circumstances. These results could represent a generational shift, with more patrilineal, patriarchal norms becoming more prominent. Another possibility is that older men are less incentivized to mate guard because they are further along in their reproductive careers (Pazhoohi et al. 2016).
In addition to the direct impact of matriliny on female autonomy, the particular form of double descent that Himba practice, which involves largely matrilateral inheritance of cattle, impacts the costs and benefits of paternity certainty for men. When wealth can be aggregated and distributed, it can be used to generate fitness-related benefits such as bride-price payments and multiple wives via polygyny. This tends to benefit sons’ reproductive success more than daughters’, and has been used to explain the correlation between patriliny and pastoral production (Holden and Mace 2003). However, parents must balance the gains that their sons can accrue from inherited wealth with any costs of misallocated investment due to paternity uncertainty.
When cows are inherited matrilaterally, a different calculation becomes relevant. Paternity certainty pertains mainly to relatedness between siblings (as a man is giving to his sister’s son). Classic interpretations of the “paternity threshold model” of matrilineal inheritance require levels of paternity uncertainty that are highly unlikely, even in populations such as Himba where extra-pair paternity rates are the highest ever recorded (Greene 1978; but see Rogers 2013 for further discussion). However, when the paternity threshold is considered alongside other socioeconomic factors, stable strategies for this type of matrilineal inheritance can emerge. Fortunato (2012) shows that both polygyny and polyandry can make diagonal transfers (from uncle to nephew) beneficial to men’s fitness. With their combination of formal polygyny and informal polyandry, and a system of diagonal transfers of wealth, Himba may be a prime example of how high rates of extra-pair paternity, via women’s concurrency, can be fitness beneficial to men. If this combined system of polygyny and polyandry alongside matrilateral inheritance is beneficial to men, they may be more tolerant of spousal separation and less incentivized to spend time and energy on mate guarding.

5.2. Demography and Economics

There are several aspects of Himba sociodemography that affect the costs and benefits of spousal separation and potentially lost paternity. The first is the adult sex ratio. We previously reported that Himba have an ASR of 0.71 (i.e., 71 men for every 100 women, see Scelza et al. 2020c). This was the lowest ASR in that sample of 11 populations, as well as another cross-cultural study of ASR (Schacht et al. 2014). Although the reasons underlying the imbalance in this population are not well understood, a female-biased sex ratio appears to be a long-term trend. Reports from the early 20th century also show a surplus of adult women among Herero, with a sex ratio of 0.75, based on a sample of 16,201 individuals (Malcolm 1924). Gibson reported similar numbers in the 1959 (Gibson 1959), as did Harpending and Pennington in the 1990s (Harpending and Pennington 1991). The ratio of males to females affects the stability of partnerships. When there are more women than men in a population, men face lower costs to deserting their current partner because there are more alternatives in the population to choose from. In other populations this has led to female-biased sex ratios being associated with less monogamous behavior (Schacht and Mulder 2015Schacht and Kramer 2016).
Another factor that must be considered is the value of child labor. When children contribute to household production, they offset some of their own costs, mitigating potential losses to men if they care for children who are not their biological offspring. Although we do not present data on child labor here, our previous findings lend support to this idea. Himba men have been shown to bias their investments in biological versus non-biological children, in what appears to be a functional response to their productive value (Prall and Scelza 2020b). Girls, who Himba resoundingly praise as being valuable laborers, have poorer anthropometric outcomes when they are believed to be omoka (non-biological offspring). Our data support the idea that this may be because girls have to work harder to “earn their keep” in this situation. One Himba woman said to us, “Sometimes when the child starts to grow up, the child will be working very hard and the husband might start to like that child, even more than his own child.” On the other hand, Himba boys, whose labor is generally considered to be less valuable, are more likely to be fostered out when they are believed to be omoka. One woman explained, “When the husband talks about that child, he hates him. When he sees him he tells you to take that child to your parents.” In this case, it seems that men may be lowering their own investment costs when paternity certainty is low and the net cost of the child is greater.

5.3. Benefits of Concurrency

Our data show that women can benefit directly from having multiple partners. Women with both husbands and boyfriends have greater food security than those who have partners of only a single type. Although it is difficult to identify a causal pathway from concurrency to greater food security, the mix of data we present serves to illuminate how husbands and lovers support women in different ways. Husbands tend to be more reliable partners, giving gifts more often and in greater quantities than boyfriends. Boyfriends are less likely to provide food or livestock than husbands, but more likely to give cash. Women have noted that this is useful because cash can be given discreetly, and can be used for a wide variety of purposes, including for food, medical care, or transportation. These data show that the bond between spouses is strong—women rely on their husbands as their primary sources of support, and husbands largely fulfill that role. Boyfriends, on the other hand, are less socially obligated to give, and so there is more variability in the frequency of their giving, and in fact, whether he gives her anything of note at all.
Our qualitative data reveal an important aspect of resource transfer patterns that did not show up in our quantitative data. Multiple women reported that boyfriends are called upon in critical times, either when there is an inordinately large expense, or when their husband is not available to help. One woman explained, “They [her friends] could tell him [her boyfriend] that I needed something, so he would know…. If he saw I was having a problem he would give something to me to help, because we have been together so long…. My child was sick and my friend went to tell [the boyfriend] and he came to me and gave me N$1000.” These rare events are unlikely to show up in the recall data described above, which is better suited for describing general transfer patterns. In addition, the safety net of knowing that you could ask if you needed something is also an important aspect of resource security, and one that would not be picked up in our quantitative data. As one woman stated, “He’s never given me anything but I love him. I know if I asked he would give me something.”
Boyfriends, therefore, help in ways that can be either complementary or supplementary. This may be particularly critical when spousal separation is common because there are long periods of time (particularly historically when cars and cell phones were less common) when husbands may be unable to help. If a child is sick, or an unexpected food shortage arises, boyfriends can step in. One woman stated, “If you are tired of asking the husband, you can ask the boyfriend. It’s good to have both to ask,” while another said, “You need to eat two times. From the husband and the boyfriend.”

It should be noted that where this trickles down to affect the well-being of a couple’s children, both the husband’s and the wife’s fitness can be positively affected by concurrency. This creates a system of generalized reciprocity for men. Husbands invest in their wives’ children, only some of which are his biological offspring—which comes at a cost. However, help comes in toward those children from his wives’ informal partners. In addition, a man may be providing some investment toward children he has with his lovers, but the majority of investment in those children comes from their social father. Formal modeling and more specific empirical data would be needed to know whether this results in a net benefit for most men, but our data point toward this being a stable response in a system with a stochastic resource base and high mate guarding costs. Men can accrue the kinds of standard gains to fitness that are predicted through sexual selection theory, and any paternity loss that occurs in their marriage is buffered by support from other men.