Chimpanzee social intelligence: selfishness,altruism, and the mother–infant bond

To better understand the human mind from an evolutionary perspective, a great deal of research has focused on the closest living relative of humans, the chimpanzee, using various approaches, including studies of social intelligence. Here, I review recent research related to several aspects of social intelligence, including deception, understanding of perception and intention, social learning, trading, cooperation, and regard for others. Many studies have demonstrated that chimpanzees are proficient in using their social intelligence for selfish motives to benefit from their interactions with others. In contrast, it is not yet clear whether chimpanzees engage in prosocial behaviors that benefit others; however, chimpanzee mother–infant interactions indicate the possibility of such behaviors. Therefore, I propose that chimpanzees possess rudimentary traits of human mental competence not only in terms of theory of mind in a broader sense but also in terms of prosociality involving regard for others. Mother–infant interactions appear to be particularly important to understanding the manifestation of social intelligence from an evolutionary perspective.     

Rehabilitation of research chimpanzees: stress and coping after long-term isolation

We report on the permanent retirement of chimpanzees from biomedical research and on resocialization after long-term social isolation. Our aim was to investigate to what extent behavioral and endocrine measures of stress in deprived laboratory chimpanzees can be improved by a more species-typical social life style. Personality in terms of novelty responses, social dominance after resocialization and hormonal stress susceptibility were affected by the onset of maternal separation of infant chimpanzees and duration of deprivation. Chimpanzees, who were separated from their mothers at a younger age and kept in isolation for more years appeared to be more timid personalities, less socially active, less dominant and more susceptible to stress, as compared to chimpanzees with a less severe deprivation history. However, permanent retirement from biomedical research in combination with therapeutic resocialization maximizing chimpanzees' situation control resulted in reduced fecal cortisol metabolite levels. Our results indicate that chimpanzees can recover from severe social deprivation, and may experience resocialization as less stressful than solitary housing.     

Marriage: an evolutionary perspective

Marriage is universal, and pair bonding is found in other species too with highly dependent young. So marriage functions as a reproductive social arrangement that traditionally involved the extended family. The sexes are not identical in their biological contributions to children's survival, so they seek somewhat different attributes in a mate. Men seek a young, attractive, sexually faithful bride. Women seek a man who is older, taller, and (as in many other species) socially dominant. Both sexes prefer a kind, healthy, attractive, similar mate who is emotionally attached to them. A spouse who fails to maintain sufficiently high mate value is vulnerable to divorce. Infertility and sexual dissatisfaction predict divorce, as does death of a child, but the more children, the stabler the marriage. Cross-cultural data suggest that cruel or subdominant men (e.g., poor providers) and unfaithful women are prone to divorce. Marriages in which the wife dominates the husband in economic contributions, nonverbal behavior, and decision making tend to be less satisfying. In societies in which wives are economically independent of husbands, divorce rates are high. As women's economic power has risen with industrialization, divorce rates have climbed. Economic and fitness considerations also help explain cultural differences in polygyny, age at marriage, arranged marriage, concern with the bride's sexual chastity, and marriage ceremonies. Other factors also affect marital dynamics, such as state subsidies to families, the sex ratio, and influence of the couple's parents.     

Machiavellian intelligence

The hypothesis that intelligence is an adaptation to deal with the complexity of living in semi-permanent groups of conspecifics, a situation that involves the potentially tricky balance of competition and cooperation with the same individuals, has been influential in recent theorizing about human mental evolution. It is important to distinguish among distinct versions of this general idea, for they predict different cognitive consequences and apply to different species of animal. Empirical support is strong in primates for links between (i) social complexity based on evolved tactics that require a good memory for socially relevant information, (ii) neocortical enlargement, and (iii) size of social groupings. However, the evolution of computational thought and the ability to understand other individuals' intentions are not well explained as products of selection for Machiavellian intelligence. Quite different explanations may therefore be required for increases in intelligence that occurred at different times in human ancestry.     

Assessing the effects of social environment on blood pressure and heart rates of baboons

The objective of this publication is to report on the feasibility of using a tether system for obtaining data on blood pressure and heart rates of socially housed primates and to evaluate the extent to which housing environment alters cardiovascular responses (mean arterial blood pressure and heart rate). Blood pressure and heart rates of adult male baboons (Papio cynocephalus hamadryas) were evaluated over a 6 week period under three different housing conditions: social companion, individual, and socially unfamiliar. Social environment was manipulated in a specially designed cage that incorporated removable panels of either woven wire or solid sheet metal. The design of the cage permitted nonhuman primates to engage in species-typical social behaviors such as grooming and aggression. Using a tether and catheter system, we monitored cardiovascular physiology. We tested the hypothesis that individual housing, housing with social companions, and housing with social strangers would produce different mean arterial blood pressure and heart rate responses. Individual housing and housing with strangers produced resting mean arterial blood pressures that were elevated relative to blood pressure responses with social companions. Individual housing and housing with social strangers produced different patterns of cardiovascular response. Individual housing resulted in lowered heart rates and elevated blood pressures relative to the social companion condition. Housing with social strangers resulted in both elevated blood pressure and elevated heart rate, relative to the social companion condition. Responses observed during this study demonstrated the sensitivity of blood pressure and heart rates to differences in social environment.     

Contesting "Culture": The Perspectives of Hmong American Female Students on Early Marriage

This article complicates the meanings of early marriage among Hmong American female students. It moves beyond explanations of cultural difference in the examination and explication of the discourse and practice of early marriage among female adolescents in the Hmong community. Drawing on the perspectives and experiences of Hmong American female students, this article reveals that early marriage may be an expression of students' opposition to the structures of and experiences with school and family. The significance of this analysis is its recognition and illumination of the fluidity of cultural and social practices, and the tensions between and within ethnic groups.     

Feasting, Craft Specialization, and the Ritual Mode of Production in Small-Scale Societies

Economic intensification has been documented in a diversity of small-scale societies. The existing archaeological theory concerning such intensification has tended to privilege economic and political explanations and largely ignores social action and ritual performance as motivations for economic change. In this article, 1 use both ethnographic and archaeological data to argue that ceremonial feasting and the need for socially valued goods, which are critical for ritual performance and necessary for a variety of social transactions, create the demand that underwrites and sustains economic intensification in small-scale societies. Food for large-scale feasts is acquired through the intensification of food production and procurement targeted specifically for feasting, rather than from the surplus available from routine subsistence production. Large-scale demands for socially valued goods tend to result in specialization on the production of "extraordinary" material culture, which is characterized by two modes of circulation, in networks of social obligations or as offerings in sacred locations. [Key words.craft specialization, exchange, feasting, ritual]     

Marriage, Social Inequality, and Women's Contact with Their Natal Families in Alliance Societies: Two Tamang Examples

Anthropological and other approaches to women's natal kin links demonstrate a relationship between these linkages and the reproduction of social inequality, in addition to noting implications for the social standing of women themselves. Few studies have, however, dynamically considered the simultaneous dimensions of individual history, community context, and interfamilial politics influencing such contact. Using data from two Tamang communities in Nepal, this article examines the impact of changing individual experience and interfamilial relations on home visits in the first year of marriage. Explicit attention is given to these forms of social action as a critical moment in the construction of social inequality. Informant testimony is combined with statistical analysis to demonstrate the salience of these natal visits in the early months of marriage for individual and wider social relationships. The visits are shown to be strongly related to the nature of interfamilial relations organized by marriage in addition to earlier life-course experiences of women. Different community contexts, however, condition the direction of effects for these variables in ways consistent with enduring structures of relationship.     

Unemployment and marital status in Great Britain.

During the past decade, the marriage rate has declined and the divorce rate has increased in Great Britain. Becker (1981) attributes such changes to improvements in the economic status of women, in that high-wage women gain less from marriage relative to other women. However, an empirical analysis of data from the General Household Survey 1985 in Great Britain shows that male unemployment is another important determinant of changes in marital status. High rates of male unemployment reduce the incidence of marriage and increase the likelihood of divorce.     

Female Choice in Humans: A Conditional Mate Selection Strategy of the Krummhörn Women (Germany, 1720–1874)

The suitors' ownership of land influenced the marriage age of the women in the Krummhörn population (Germany, 1720–1874). This led to a characteristic distribution of the categories of land ownership of husbands by the wife's age at marriage: the younger the brides, the higher was the percentage of high-status males among their bridegrooms. But the natal status of brides did not exert any significant influence on their age at marriage. Moreover, socially hypergamous women married younger than those whose marriage meant a social drop. We have interpreted these findings as the expression of a conditional female choice strategy with age-dependent decrease in demands on a marriage partner: “If you are young, be very choosy and marry only a high-quality mate; the older you become, the more you must reduce your initial standards!” On the average this strategy was adaptive, because in this population land ownership correlated with the local reproductive success of a family.     

Biological explanations and social responsibility

The aim of this paper is to show that critics of biological explanations of human nature may be granting too much to those who oppose such explanations when they argue that the truth of genetic determinism implies an end to critical evaluation and reform of our social institutions. This is the case because when we argue that biological determinism exempts us from social critique we are erroneously presupposing that our social values, practices, and institutions have nothing to do with what makes biological explanations troublesome. My argument is that what constitutes a problem for those who are concerned with social justice is not the fact that particular behaviours may be genetically determined, but the fact that our value system, and social institutions create the conditions that make such behaviours problematic. Thus, I will argue that even if genetic determinism were correct, the requirement of assessing and transforming our social practices and institutions would be far from superfluous. Biology is rarely destiny for human beings and the institutions they create.     

Impact of 'living apart together' on postoperative recovery of mice compared with social and individual housing

Social housing is the optimal way of housing female laboratory mice. However, individual housing may be required in experimental designs, for example after surgery. We therefore investigated whether housing two female mice in a cage, separated by a grid partition ('living apart together', LAT), counters the adverse effects of individual housing on postoperative recovery. Ten individually housed (IND) mice, nine socially housed (SOC) mice and nine mice, housed LAT, were surgically implanted with a telemetry transmitter. From one week prior to surgery until three weeks thereafter, several physiological and behavioural parameters were measured in the mice subjected to surgery. The telemetry transmitter measured heart rate (HR), body temperature and activity continuously. Body weight, food and water intake were scored regularly, as were wound healing, ease of handling, nest building and behaviour. Results indicated that SOC mice appear to be less affected by abdominal surgery than IND mice, as indicated by HR and behaviour. LAT, however, did not appear to be beneficiary to the mice. Increased HR levels and differences in behaviour as compared with both SOC and IND animals indicate that LAT may even be the most stressful of the three housing conditions. We therefore conclude that mice benefit most from social housing after surgery. If, however, social housing is not possible, individual housing appears to be a better option than separating mice by a grid partition.     

The genetic implications of biological and cultural structuring processes during hominid evolution

Human populations are genetically structured through biological reproduction but reproduction is socially structured through culturally expressed systems of marriage, hence the need to take into account the cultural dimension of human societies when considering the genetic structure of modern human populations. The interplay between these two structuring processes is examined through the implications of a biologically based primate form of social organization versus a culturally based foraging form of social organization for an anomaly between the genetic differentiation implied by micro-evolutionary genetic models versus the species-wide pattern of morphological change implied by hominid fossil evidence. Simulation is used to derive the pattern for genetic differentiation at the level of the living group for both forms of social organization and a competition model is added to the genetic model as a way to resolve the anomaly. The importance of the competition model for the transition from a biologically based to a culturally based form of social organization is discussed.     

Adopt a Daughter-in-Law, Marry a Sister: A Chinese Solution to the Problem of the Incest Taboo

In stressing the social advantages of the familial incest taboo, most explanations of the taboo ignore the fact that it makes marriage the enemy of the family. The stranger intruded by marriage often poses a threat to existing domestic relationships. The Chinese solution to this problem is to circumvent the taboo by adopting female children who are raised as wives for their foster parents' sons. The family choosing this form of marriage sacrifices prestige and dependable affinal ties, but by socializing their own daughters-in-law they preserve domestic harmony. The fact that many Chinese arrange marriages within the family as a means of preserving the family suggests that widely accepted explanations of the incest taboo exaggerate the dangers of incest and ignore the dangers of the taboo.     

Determinants of infant and child mortality in the West Bank and Gaza Strip

Infant and child mortality in the West Bank and Gaza Strip has steadily reduced since 1967, even though fertility has remained extremely high. In this paper the determinants of infant and child mortality are discussed, with particular emphasis on the role of consanguineous marriages, short birth spacing and maternal education. It is shown that short birth spacings and type of marriage are more important determinants of infant mortality than maternal education. Moreover, the relative role of consanguineous marriages appears to increase with time.     

How does marriage affect length of life? Analysis of a French historical dataset from an evolutionary perspective

There are broadly two explanations for why human longevity appears to be extended by marriage. First, there is the social explanation, whereby the companionship, division of labour and the economic support that marriage offers is thought to extend life. Second, there is a selective explanation, whereby those individuals with high potential longevity are more attractive to the opposite sex and therefore more likely to get married. Here we analyse the “TRA” dataset from 19th century France, using an evolutionary approach to address the question of why marriage is linked to longevity, focussing particularly on sex differences. The dataset is based on death and marriage records from all of France between 1798 and 1901 and includes information on age at death, marriage and wealth for individuals whose surnames began with the letters TRA. We find that marriage is positively associated with longevity, particularly for men. In part, this is related to the higher rate of deaths for single males during marriageable age, as compared to a higher rate of deaths for females during marriage. There is a positive association between wealth (at death) and longevity for individuals who were single or married at death, with a stronger effect for singles. Analysis of the effect of spousal age gap on duration of survival after first marriage indicates that men who were married to younger women lived longer, whereas the longevity of women was not associated with the spousal age gap. We put forward an evolutionary perspective on marriage and longevity, hypothesizing that there is an important role for sexual selection in the association between marriage and longevity, with women selecting on characteristics associated with longevity, whilst men select on characteristics associated with reproductive potential.     

A comparison of cell-mediated immune responses in rhesus macaques housed singly, in pairs, or in groups

A variety of psychosocial factors have been shown to influence immunological responses in laboratory primates. The present investigation examined the effects of social housing condition on cell-mediated immune responses, comparing rhesus macaques (Macaca mulatta) in three housing conditions (single, pair, and group). Subjects included 12 adults of both sexes in each housing condition (N=36). Multiple blood samples (0, 4, 8, and 12 months) were collected for immunological analyses, including lymphocyte subsets, lymphocyte proliferation to pathogens and nonspecific mitogens, natural killer cell activity, and cytokine production. CD4(+) to CD8(+) ratios differed significantly across housing conditions and singly caged subjects had significantly lower CD4(+)/CD8(+) after the 4-month timepoint than did socially housed (pair and group) subjects. CD4(+) to CD8(+) ratios were positively correlated within subjects, suggesting a trait-like aspect to this parameter. Lymphocyte proliferation responses to all four gastrointestinal pathogens differed across housing conditions (at least at the 0.08 level), as did proliferation responses to StaphA, and the production of cytokines (IFN-gamma, IL-2, and IL-10). Proliferation responses of singly caged monkeys did not differ from socially housed monkeys and the highest levels of both IFN-gamma and IL-10 were produced by group housed subjects. The data demonstrate that social housing condition affects immune responses. While not unidirectional, these effects generally suggest enhanced immune responses for socially housed animals. Since rhesus monkeys live socially in nature, and the immune responses of singly housed animals differed from those housed socially, there is considerable motivation and justification for suggesting that the use of singly housed rhesus macaques may complicate interpretations of normal immunological responses. This may have important implications for the management, treatment, and selection of primate subjects for immunological studies.     

The evolutionary context of postnatal depression

“Postnatal depression” denotes the syndrome of dysphoria, debility, and anxiety that follows childbirth in about 10–20% of women (as variously estimated). Its etiology is seen to be lodged in a variety of psychosocial as well as biological factors, among which the isolating and pressured culture of contemporary society (especially for women/mothers) is commonly singled out as a powerful precipitator. This view is extended here through the evolutionary perspective which casts maternal distress as a set of adaptive responses with the function, in ancestral environments, of soliciting support for a mother who feels that her maternal responsiveness may be threatened. As continuous caretaking of the infant is the active expression of evolved maternal responsiveness, departures from this pattern result in anxiety and distress that seek resolution. Manifestations of maternal distress in contemporary society are dysfunctional, however, since the present social structure does not provide spontaneous and immediate support that can spring forth within small, closely knit social units. Furthermore, for present-day mothers distress is self-perpetuating since the ingrained tendency toward continuing responsiveness rarely finds practical expression and is thus converted into anxious vigilance and depression. This view generates the hypothesis that the emotional and cognitive contents of maternal vigilance are associated with the needs of the infant and will therefore be focused on crying and feeding. A number of qualitative studies of women’s experiences during the postpartum bear out this prediction and support the feasibility of the evolutionary hypothesis of “postnatal depression” as a set of adaptive responses, now out of place in a novel environment.     

The Lonely Mouse – Single Housing Affects Serotonergic Signaling Integrity Measured by 8-OH-DPAT-Induced Hypothermia in Male Mice

Male BALB/c mice single-housed for a period of three weeks were found to respond with a more marked hypothermia to a challenge with a selective serotonergic agonist (8-OH-DPAT) than their group-housed counterparts. This effect of single housing was verified by screening a genetically heterogeneous population of male mice on a C57BL/6 background from a breeding colony. Enhanced activity of the implicated receptor (5-HT_1A) leading to an amplified hypothermic effect is strongly associated with depressive states. We therefore suggest that the 8-OH-DPAT challenge can be used to demonstrate a negative emotional state brought on by e.g. long-term single housing in male laboratory mice. The study emphasizes the importance of social housing, and demonstrates that male mice deprived of social contact respond with altered serotonergic signaling activity. Male mice not only choose social contact when given the option, as has previously been shown, but will also, when it is deprived, be negatively affected by its absence. We propose that the 8-OH-DPAT challenge constitutes a simple, but powerful, tool capable of manifesting the effect of social deprivation in laboratory mice. It potentially allows not only for an unbiased, biochemical evaluation of psychological stressors, but may also allow for determining whether the effect of these can be counteracted.     

Men's facial masculinity predicts changes in their female partners' sexual interests across the ovulatory cycle,whereas men's intelligence does not

A substantial body of work demonstrates that women's mate preferences change across the ovulatory cycle. When fertile in their cycles, women are especially attracted to masculine features (e.g., faces, voices, bodies), socially dominant behavior, and male scents associated with body symmetry and social dominance. Women may also find intelligent men particularly attractive when fertile, though findings are mixed. Related research shows that, on average, romantically-involved women report stronger sexual attraction to men other than their pair-bond partners, but not partners, when fertile, and especially when their partners lack features fertile women prefer (e.g., symmetry). In the current study, we examined whether women's patterns of sexual interests across the cycle are similarly moderated by partners' facial masculinity, facial attractiveness, and intelligence. Results revealed predicted effects of male partners’ facial masculinity but none for partners’ intelligence. Facial attractiveness may have effects, but we find no evidence that it does so independently of facial masculinity.