Infidelity, jealousy, and wife abuse among Tsimane forager–farmers: testing evolutionary hypotheses of marital conflict

Abstract

The role of men's jealousy over a wife's infidelity in precipitating marital conflict and wife abuse is well documented. The role of women's jealousy over a husband's infidelity has received little attention, which is puzzling given high potential costs to women of withdrawal of paternal investment. We address this gap by investigating marital conflict and wife abuse among Tsimane forager–farmers of Bolivia. We test predictions derived from male jealousy and paternal disinvestment hypotheses, which consider threats and consequences of infidelity by women (male jealousy hypothesis) and men (paternal disinvestment hypothesis). The paternal disinvestment hypothesis proposes that wife abuse is employed by husbands to limit wives' mate retention effort and maintain men's opportunities to pursue extrapair sexual relationships. Interviews were conducted among husbands and wives in the same marriages using a combination of open-ended and structured items. Spouses agree that the most frequently reported type of marital argument is women's jealousy over a husband's infidelity (N=266 arguments). Roughly 60% of abusive events occurred during arguments over men's diversion of household resources (N=124 abusive events). In multivariate analyses, likelihood of wife abuse is greater in marriages where husbands have affairs, where wives are younger, and where spouses spend more time apart (N=60 husbands, 71 wives). While we find strong support for both male jealousy and paternal disinvestment hypotheses, it is men's infidelity, not women's, that precipitates most instances of marital conflict and wife abuse. We conclude that men's aggression towards their wives facilitates men's diversion of family resources for their selfish interests.

Introduction

What causes marital conflict, and which marital conflicts are more likely to result in men's violence against their wives? It has long been argued that men's jealousy over women's infidelity is the strongest impetus to men's lethal and nonlethal violence against female partners (reviewed in Daly & Wilson, 1988; also see Goetz, 2008 and references therein). Less is known about the extent to which women's jealousy over men's infidelity precipitates men's violence against female partners. Husbands are more likely than wives to commit infidelity (Atkins, Jacobson, & Baucom, 2001), and men and women report a similar frequency and intensity of jealous emotions during recalls of potential infidelity (Shackelford, LeBlanc, & Drass, 2000). If men are likely to use time and resources for pursuit of extramarital sexual relationships, wives' jealousy may play a critical role in mate retention, but at potential cost of instigating marital arguments and violence against wives. Given men's greater size and strength, violence against wives may be used as a “bargaining” tool to strategically leverage a selfish outcome, despite potential costs to the victim, aggressor, and offspring.

This is the first study to document content and prevalence of marital arguments and prevalence of men's violence against wives during such arguments in a small-scale society, the Tsimane of Bolivia. We show that men's diversion of resources from the family is a major source of arguments between spouses and husbands' violence against their wives. We argue that husbands employ violence to limit wives' mate retention effort and maintain men's opportunities to pursue extramarital sexual relationships. We define violence against wives as any physical contact initiated by a husband with intent to harm a wife (hereafter termed wife abuse). The research design minimizes response and sampling bias in two ways: (1) data are obtained independently from both spouses instead of only one spouse, permitting assessment of spousal consistency in reporting (Szinovacz & Egley, 1995), and (2) couples are not self-selected for a high degree of marital conflict.

Jealousy is experienced when a relationship is threatened, leading to responses reducing or eliminating the threat (Buss, 2000, Daly et al., 1982). The possibility of paternity uncertainty promotes the evolution of male jealousy. Jealous responses either deter same-sex competitors from mate theft or deter mates from pursuing other sexual relationships. Wife abuse might be used as a “mate retention behavior,” functioning to maintain exclusive access to a mate and ensure that paternal investment is directed toward biological offspring (Buss, 1988, Goetz and Shackelford, 2006, Kaighobadi et al., 2008). Risk of women's infidelity, men's jealousy, and wife abuse should therefore be linked.

Existing evidence supports these links. Two factors associated with risk of women's infidelity are the woman's mate value and the amount of time partners spend apart from each other. A woman's mate value is the degree to which she enhances a man's reproductive success, and is often proxied by age or reproductive condition. Younger women are preferred partners across cultures (e.g., Borgerhoff Mulder, 1988, Buss, 1989) and therefore likely have more extrapair mating opportunities than their older counterparts. Younger women are more likely to conceive following sexual encounters and have higher reproductive value (expected future fertility). This increases the cost to men of losing a young wife. Indeed, a wife's young age is associated with an increase in her husband's mate retention effort (Buss & Shackelford, 1997). Similarly, couples engage in aggressive interactions (verbal or physical) more frequently when a woman may be more likely to conceive (Flinn, 1988).

Time partners spend apart from each other increases opportunities for surreptitious pursuit of extrapair relationships. Time apart is associated with an increase in men's mate retention effort (Baker and Bellis, 1995, Buss and Shackelford, 1997, Shackelford et al., 2007, Starratt et al., 2007). Degree of men's mate retention effort increases with risk of female infidelity even after controlling for men's dominant personality (Goetz & Shackelford, 2009).

The male jealousy hypothesis generates the following predictions: a husband's jealousy over a wife's suspected infidelity should be (1) ranked highly as a common type of intense marital conflict; (2) a type of conflict frequently associated with wife abuse; (3) greater in marriages where a wife's mate value, using her age as a proxy, is higher (i.e., when she is younger); and (4) greater in marriages where spouses spend more time apart. In addition, likelihood of wife abuse should be (5) greater in marriages where a wife is younger and (6) greater in marriages where spouses spend more time apart. A husband's jealousy is operationalized dichotomously, as reporting an argument over a wife's suspected infidelity in the past year. Spousal time apart is also operationalized dichotomously, as whether a husband participated in multiday solitary wage labor in the past year.

Sex differences in potential reproductive rates affect optimal levels of reproductive effort (Trivers, 1972). Whereas male reproductive effort is limited to courtship and copulation in most mammals and primates (Clutton-Brock, 1991), humans have a history of high paternal investment (Gray & Anderson, 2010). While nonhuman primate females increase work effort during pregnancy and lactation, thereby increasing maternal mortality (Altmann, 1980), women decrease metabolism and store fat during pregnancy (Prentice & Goldberg, 2000) and decrease work effort during lactation (Hurtado, Hill, Kaplan, & Hurtado, 1992). This suggests significant energetic support of reproduction by men. Throughout much of life Tsimane fathers produce more calories consumed by children per day than mothers and grandmothers combined; wives consume over 250 calories per day produced by husbands (Kaplan, Gurven, Winking, Hooper, & Stieglitz, 2010). Tsimane men thus clearly direct resources toward their nuclear families.

Unlike men, women do not risk investing inadvertently in unrelated offspring. However, women do risk losing access to resources critical for reproduction if men divert resources to attract other women. Women experience jealousy as a response reducing or eliminating the threat of resource loss (Buss, 2000, Daly et al., 1982, Schutzwohl and Koch, 2004, Symons, 1979).

Paternal disinvestment is a construct representing men's diversion of resources from the family for individual fitness gain (Stieglitz, Kaplan, Gurven, Winking, & Vie Tayo, 2011). Men's infidelity is an obvious indicator of paternal disinvestment because time and resources invested in gaining and maintaining access to extrapair mates are unavailable for familial investment. Men's infidelity is expected to result in women's jealousy and women's mate retention effort. Tsimane wives frequently complain to husbands about husbands' suspected infidelity (Stieglitz et al., 2011). Wives' complaints to husbands are considered mate retention effort because complaints attempt to obstruct current and future male infidelity and resource diversions (cf. Buss, 1988). The paternal disinvestment hypothesis proposes that wife abuse is employed by husbands to limit wives' mate retention effort and maintain men's opportunities to pursue extrapair sexual relationships. Consistent with this logic, women's physical aggression against mates precipitates most instances of partner violence against women (O'Leary & Slep, 2006). Men's infidelity, women's jealousy, women's mate retention effort, and wife abuse should therefore be linked.

The paternal disinvestment hypothesis generates the following predictions: a wife's jealousy over a husband's suspected infidelity should be (1) ranked highly as a common type of intense marital conflict; (2) a type of conflict frequently associated with wife abuse; and (3) greater in marriages where a husband has an affair. In addition, likelihood of wife abuse should be (4) greater in marriages where a husband has an affair. The positive association between men's infidelity and rate of wife abuse should be mediated by marital arguments over wives' jealousy. A wife's jealousy is operationalized dichotomously, as reporting an argument over a husband's suspected infidelity in the past year.

It is important to note that predictions 5 and 6 generated by the male jealousy hypothesis (Section 1.1) do not follow exclusively from this hypothesis. If a husband's infidelity is more likely when a wife is younger, then an inverse relationship between a wife's age and rate of wife abuse is also consistent with the paternal disinvestment hypothesis. Similarly, if a husband's infidelity is more likely when spouses spend more time apart, then a positive correlation between spousal time apart and rate of wife abuse is also consistent with the paternal disinvestment hypothesis. We address implications of these shared predictions in the Discussion.