Intersexual aggression and male sexual activity in captive rhesus macaques

Rape has been posited to be an outgrowth of male reproductive strategies. Forced copulations may have evolved as a consequence of the low parental investment made by males in producing and raising offspring. We designed a laboratory experiment which paired rhesus macaque males with females in order to assess the influence of intersexual aggression on male sexual activity. Younger and older adult males had comparable levels of sexual behavior, but younger males were more aggressive towards females than were older males. In addition, females threatened younger males more than older males. Male attacks on females did not result in sexual intercourse. On the contrary, a negative correlation existed between male aggression towards females and male success at achieving intromissions. Female aggression towards males appeared to be an effective tactic which reduced the chances of sexual intercourse. We conclude that intersexual aggression acts either as a mechanism of dominance assertion or as a means to increase spatial distance between individuals. These data do not support the idea that rape in humans has an evolutionary foundation derived from male reproductive strategies.     

Positional inference in rhesus macaques

Animal Cognition - Understanding how organisms make transitive inferences is critical to understanding their general ability to learn serial relationships. In this context, transitive inference...     

Serial expertise of rhesus macaques

Here we describe the development of serial expertise in 4 experimentally naive rhesus monkeys that learned, by trial and error, the correct order in which to respond to 3-, 4-, and 7-item lists of arbitrarily selected photographs. The probabilities of guessing the correct sequence on 3-, 4-, and 7-item lists were, respectively, 1/6, 1/24, and 1/5040. Each monkey became progressively more efficient at determining the correct order in which to respond on new lists. During subsequent testing, the subjects were presented with all possible pairs of the 28 items used to construct the four 7-item lists (excluding pairs of items that occupied the same ordinal position in different lists). Subjects responded to pairs from different lists in the correct order 91% of the time on the first trials on which these pairs were presented. These features of subjects' performance, which cannot be attributed to procedural memory, satisfy two criteria of declarative memory: rapid acquisition of new knowledge and flexible application of existing knowledge to a new problem.     

Affiliative vocalizations in infant rhesus macaques (Macaca mulatta).

In Experiment 1, infant rhesus monkeys (Macaca mulatta) were separated and then reunited with mothers, united with a male, or placed in an empty cage. Infants girned more when with mothers or the male than when alone. Girns declined over time when infants were united with the male. Coo rates were high when the infant was alone or with the male. Shrieks, barks, and fear-related behavior were higher with the male. In Experiment 2 the vocalizations of infants were examined during separation when alone or when mothers or a male were in the same room. Infants cooed more when mothers or a male were present. Cooing increased over time, with a greater increase in the mothers' presence. Girns were given to both mothers and males, but more were given to mothers. Coos and girns are both affiliative vocalizations but are differentially modulated as infants cease cooing when they receive contact comfort.     

Predictors of dominance in male Betta splendens

The formation of dominance/subordinancy relations in pairs of male Siamese fighting fish was examined in six experiments. Dominant animals typically were those fish that built the largest nests and that attacked an image of a live, displaying male most intensely prior to combat. However, pretest performance on an operant task and reaction to an animal's own mirror image were not useful predictors of subsequent dominance. These findings are consistent with the suggestion that domesticated Bettas have a territorial social strategy that includes both nest-building and fighting behaviors.     

Visual preferences for sex and status in female rhesus macaques

Most primates are both highly visual and highly social. These qualities predict that visual cues to social variables, such as identity, sex, social status, and reproductive quality, would be intrinsically valuable and systematically attract attention. Supporting this idea, thirsty male rhesus macaques (Macaca mulatta) will forego fluid reward to view images of the faces of high-ranking males and the sexual skin of females. Whether female rhesus macaques, who experience dramatically different social pressures and reproductive costs than male macaques, also systematically and spontaneously value visual cues to social information remains untested experimentally. We probed the preferences of female rhesus macaques, given the opportunity to display an image from a known class of social stimuli or touch a second target to display a blank screen. We found that females preferred faces of high-status males and also images of the perinea of both males and females, but were not motivated to display images of subordinate males or control stimuli. These findings endorse the view that both male and female rhesus macaques—and presumably other highly social primates—seek information about other individuals in a way that matches the adaptive value of that information for guiding social behavior.     

Signature size signals sociable dominance and narcissism

Handwritten signatures have been traditionally associated with personality traits. In this study, we examined the relationship of signature size with intrasexual competition, aggressive and sociable dominance, narcissism, and self-esteem in a sample of Uruguayan university students (N = 340). The study went methodologically beyond current research by examining three different operationalizations of signature size, and by controlling for potential confounders: number of characters in the printed name, average character area in the printed name—a proxy for overall writing size—, and signature style. After controlling for these potential confounders and demographic variables, our results showed a significant link between signature size and sociable dominance, both for males and females, while narcissism was only in females significantly associated with signature size.     

Rapid cognitive flexibility of rhesus macaques performing psychophysical task-switching

Three rhesus monkeys (Macaca mulatta) performed a simultaneous chaining task in which stimuli had to be sorted according to their visual properties. Each stimulus could vary independently along two dimensions (luminosity and radius), and a cue indicating which dimension to sort by was random trial to trial. These rapid and unpredictable changes constitute a task-switching paradigm, in which subjects must encode task demands and shift to whichever task-set is presently activated. In contrast to the widely reported task-switching delay observed in human studies, our subjects show no appreciable reduction in reaction times following a switch in the task requirements. Also, in contrast to the results of studies on human subjects, monkeys experienced enduring interference from trial-irrelevant stimulus features, even after exhaustive training. These results are consistent with a small but growing body of evidence that task-switching in rhesus macaques differs in basic ways from the pattern of behavior reported in studies of human cognition. Given the importance of task-switching paradigms in cognitive and clinical assessment, and the frequency with which corresponding animal models rely on non-human primates, understanding these differences in behavior is essential to the comparative study of cognitive impairment.     

The social origins of male dominance

Writings in psychoanalytic theory and social science that discuss the basis of men's motive to dominate women are reviewed. Both men's fear and envy of women and men's tenuous masculine identity arise from the exclusive early mother-child tie. It is suggested that an important step in altering the development of the motive underlying male dominance would be to have men, as well as women, care for infants. The possibility of greater equality in the family and in the economy is discussed.This article represents a considerable expansion of the first part of a paper entitled Sex Role Development and Sex Discrimination: A Theoretical Perspective by Jean Stockard, Miriam M. Johnson, Joan Acker, and Marion Goldman, presented at the annual meetings of the American Sociological Association in San Francisco in 1975. We wish to thank Joan Acker and Marion Goldman for the earlier discussions we had with them which led to this article.     

Dimensions of response to novelty are associated with social engagement and aggression in adult male rhesus macaques (Macaca mulatta)

In this study, the authors tested the hypothesis that behavioral response across social and nonsocial, novel and familiar conditions may be guided by the same trait(s) related to impulsivity in adult male rhesus macaques. The authors assessed 23 individuals' behavioral response to a series of nonsocial novel scenarios, as well as aggression and sociality within familiar and novel social contexts. Factor analysis of responses to nonsocial novelty identified two factors: Caution, which reflected latency to engage different novel situations, and Interest in Novelty, which consisted of duration and quality of exploration. Each dimension was associated with different social manifestations. Caution was negatively correlated with social aggression in novel and familiar social circumstances; Interest in Novelty was positively associated with social engagement in familiar, but not novel, social circumstances. The authors conclude that traits influencing impulsive response to novelty contribute to risky and normal social behavior across social contexts.     

Retrospective and prospective metacognitive judgments in rhesus macaques (Macaca mulatta)

A growing body of research suggests that some non-human animals are capable of making accurate metacognitive judgments. In previous studies, non-human animals have made either retrospective or prospective judgments (about how they did on a test or how they will do on a test, respectively). These two types of judgments are dissociable in humans. The current study tested the abilities of two rhesus macaque monkeys to make both retrospective and prospective judgments about their performance on the same memory task. Both monkeys had been trained previously to make retrospective confidence judgments. Both monkeys successfully demonstrated transfer of retrospective metacognitive judgments to the new memory task. Furthermore, both monkeys transferred their retrospective judgments to the prospective task (one, immediately, and one, following the elimination of a response bias). This study is the first to demonstrate both retrospective and prospective monitoring abilities in the same monkeys and on the same task, suggesting a greater level of flexibility in animals’ metacognitive monitoring abilities than has been reported previously.     

The evolution of intergroup bias: perceptions and attitudes in rhesus macaques

Social psychologists have learned a great deal about the nature of intergroup conflict and the attitudinal and cognitive processes that enable it. Less is known about where these processes come from in the first place. In particular, do our strategies for dealing with other groups emerge in the absence of human-specific experiences? One profitable way to answer this question has involved administering tests that are conceptual equivalents of those used with adult humans in other species, thereby exploring the continuity or discontinuity of psychological processes. We examined intergroup preferences in a nonhuman species, the rhesus macaque (Macaca mulatta). We found the first evidence that a nonhuman species automatically distinguishes the faces of members of its own social group from those in other groups and displays greater vigilance toward outgroup members (Experiments 1-3). In addition, we observed that macaques spontaneously associate novel objects with specific social groups and display greater vigilance to objects associated with outgroup members (Experiments 4-5). Finally, we developed a looking time procedure-the Looking Time Implicit Association Test, which resembles the Implicit Association Test (Greenwald & Banaji, 1995)-and we discovered that macaques, like humans, automatically evaluate ingroup members positively and outgroup members negatively (Experiments 6-7). These field studies represent the first controlled experiments to examine the presence of intergroup attitudes in a nonhuman species. As such, these studies suggest that the architecture of the mind that enables the formation of these biases may be rooted in phylogenetically ancient mechanisms.     

Seeing two faces together: preference formation in humans and rhesus macaques

Humans, great apes and old world monkeys show selective attention to faces depending on conspecificity, familiarity, and social status supporting the view that primates share similar face processing mechanisms. Although many studies have been done on face scanning strategy in monkeys and humans, the mechanisms influencing viewing preference have received little attention. To determine how face categories influence viewing preference in humans and rhesus macaques (Macaca mulatta), we performed two eye-tracking experiments using a visual preference task whereby pairs of faces from different species were presented simultaneously. The results indicated that viewing time was significantly influenced by the pairing of the face categories. Humans showed a strong bias towards an own-race face in an Asian–Caucasian condition. Rhesus macaques directed more attention towards non-human primate faces when they were paired with human faces, regardless of the species. When rhesus faces were paired with faces from Barbary macaques (Macaca sylvanus) or chimpanzees (Pan troglodytes), the novel species’ faces attracted more attention. These results indicate that monkeys’ viewing preferences, as assessed by a visual preference task, are modulated by several factors, species and dominance being the most influential.     

Sexual harassment in the context of double male dominance

It has been suggested that numerically male-dominated workplaces propagate cultural norms that support sexual bravado, sexual posturing, and the denigration of feminine behaviour (Sbraga & O'Donohue, 2000 Sbraga, T. P. and O'Donohue, W. 2000. Sexual harassment. Annual Review of Sex Research, 11: 258–285. [Taylor & Francis Online] , [Google Scholar]). These cultural norms are features of normative male dominance, which have been shown to increase the risk of sexual harassment. This implies that the effect of numerical male dominance on sexual harassment may be mediated by the level of normative male dominance in the work environment. The aim of this study was to test this assumption. Our sample consisted of 1295 police women, who filled out an Internet questionnaire. The results suggest that normative male dominance indeed mediates the relation between numerical male dominance and sexual harassment. We add to the sexual harassment literature by building on Gruber's concept of double dominance. Our study helps to make clear why women are at greater risk of sexual harassment in work situations where men outnumber women than in more gender-balanced workplaces.     

Weber's Law influences numerical representations in rhesus macaques (Macaca mulatta)

We present the results of two experiments that probe the ability of rhesus macaques to match visual arrays based on number. Three monkeys were first trained on a delayed match-to-sample paradigm (DMTS) to match stimuli on the basis of number and ignore continuous dimensions such as element size, cumulative surface area, and density. Monkeys were then tested in a numerical bisection experiment that required them to indicate whether a sample numerosity was closer to a small or large anchor value. Results indicated that, for two sets of anchor values with the same ratio, the probability of choosing the larger anchor value systematically increased with the sample number and the psychometric functions superimposed. A second experiment employed a numerical DMTS task in which the choice values contained an exact numerical match to the sample and a distracter that varied in number. Both accuracy and reaction time were modulated by the ratio between the correct numerical match and the distracter, as predicted by Weber's Law.     

Dynamic object individuation in rhesus macaques: a study of the tunnel effect

A manual-search experiment with rhesus monkeys (Macaca mulatta) explored dynamic object individuation in the tunnel effect: Subjects watched as a lemon rolled down a ramp and came to rest behind a tunnel (Occluder 1) and then as a kiwifruit emerged and became occluded at the end of its path behind a screen (Occluder 2). When the kiwifruit emerged at about the time that the lemon should have (had it continued its motion), subjects searched for food only behind Occluder 2-apparently perceiving the lemon to have transformed into a kiwifruit on the basis of spatiotemporally continuous motion. In contrast, when a brief pause interrupted the occlusion of the lemon and the emergence of the kiwifruit, monkeys searched for food behind both occluders. With further control conditions, this experiment demonstrates a spatiotemporal bias-similar to a bias found in adult visual perception-in the computation of object persistence in the context of a dynamic correspondence problem.     

Factors influencing sexual performance in male rhesus monkeys.

A 5-yr retrospective study of the sexual behavior of eight adult male rhesus monkeys showed that sexual vigor declined over the years but testosterone levels in peripheral vein plasma did not. Two prospective experiments were then carried out on these males during the sixth year. (a) The four poorest performers were injected daily for 28 days with testosterone propionate (1 mg/kg of body weight). There was no significant increase in level of performance, and behavior was not correlated with plasma levels of testosterone either before or 24 hr after the last hormone injection. (b) All eight males were exposed to novel nonspecific sensory stimulation during tests of sexual behavior. Eight different adult male rhesus strangers-present in the room but not in the test cage-were used as stimuli, one for each experimental test. Sexual behavior during experimental and control tests did not differ.     

Self-control in rhesus macaques (Macaca mulatta): controlling for differential stimulus exposure

Previous research on self-control using macaques (Macaca fascicularis) showed these animals have a strong bias for a delayed, larger reinforcer (Self-control) over an immediate, smaller reinforcer (Impulsive). Typical studies of self-control have used a discrete trials methodology with a secondary discriminative stimulus during the delay periods. This results in a greater exposure to the stimulus representing the self-controlled option and may account for some of the early exclusive preference for self-control observed. The present experiment examined self-control bias in three rhesus macaques (Macaca mulatta) while controlling for differential durations of stimulus exposure. Subjects were presented stimuli via a computer monitor and made choices by touching the stimulus at which point both stimuli were removed for the delay periods. All three subjects displayed a nearly exclusive bias for the delayed, larger reinforcer self-control). These results are consistent with previous studies, despite the variations in methodology and species.