Male-male relationships in chimpanzees and the evolution of human pair bonds

The evolution of monogamy has been a central question in biological anthropology. An important avenue of research has been comparisons across "socially monogamous" mammals, but such comparisons are inappropriate for understanding human behavior because humans are not "pair living" and are only sometimes "monogamous." It is the "pair bond" between reproductive partners that is characteristic of humans and has been considered unique to our lineage. I argue that pair bonds have been overlooked in one of our closest living relatives, chimpanzees. These pair bonds are not between mates but between male "friends" who exhibit enduring and emotional social bonds. The presence of such bonds in male-male chimpanzees raises the possibility that pair bonds emerged earlier in our evolutionary history. I suggest pair bonds first arose as "friendships" and only later, in the human lineage, were present between mates. The mechanisms for these bonds were co-opted for male-female bonds in humans.

Evolution of affiliation: patterns of convergence from genomes to behaviour

Affiliative behaviours have evolved many times across animals. Research on the mechanisms underlying affiliative behaviour demonstrates remarkable convergence across species spanning wide evolutionary distances. Shared mechanisms have been identified with genomic approaches analysing genetic variants and gene expression differences as well as neuroendocrine and molecular approaches exploring the role of hormones and signalling molecules. We review the genomic and neural basis of pair bonding and parental care across diverse taxa to shed light on mechanistic patterns that underpin the convergent evolution of affiliative behaviour. We emphasize that mechanisms underlying convergence in complex phenotypes like affiliation should be evaluated on a continuum, where signatures of convergence may vary across levels of biological organization. In particular, additional comparative studies within and across major vertebrate lineages will be essential in resolving when and why shared neural substrates are repeatedly targeted in the independent evolution of affiliation, and how similar mechanisms are evolutionarily tuned to give rise to species-specific variations in behaviour. This article is part of the theme issue 'Convergent evolution in the genomics era: new insights and directions'.

Dog ownership satisfaction determinants in the owner-dog relationship and the dog's behaviour

Dog ownership satisfaction relates to the quality of life of both owner and dog, and when seriously compromised may even lead to dog abandonment. Knowledge on determinants of dog ownership satisfaction is limited, obstructing solutions for promoting satisfaction, and here we quantified causes making dog owners less than very satisfied with their dog. We focused on the owner perceived relationship with the dog, unwanted dog behaviour, and dog obedience class attendance. The study population included only few seriously dissatisfied dog owners, preventing discrimination of multiple levels below 'very satisfied'. Consequently, existing relationships in the entire population may have been missed or underestimated and the findings apply specifically to dog owners that are relatively contented with dog ownership. Nine hundred seventy-seven Dutch dog owners completed an online questionnaire and we found the probability of being very satisfied to associate with all three subscales of the Monash Dog Owner Relationship Scale. Most strongly with perceived costs of ownership and less so with shared activities between owner and dog, and perceived emotional closeness to the dog. Aggression and/or disobedience related directly to high perceived ownership costs and to an increased probability of being less than very satisfied. Interaction effects indicated that dog disobedience was less influential on ownership satisfaction at high levels of aggression. Surprisingly, dog ownership satisfaction was unrelated to dog obedience class attendance, raising questions about the effectiveness of these classes in establishing satisfying dog-owner relationships. Training aids used during classes could play a role here, as choke chain use associated with high perceived costs and increased probabilities of being less then very satisfied with dog ownership. Ownership satisfaction in relatively contented dog owners, seems more influenced by unwanted dog behaviour and perceived costs of ownership, than by perceived emotional closeness to the dog, shared activities and dog obedience class attendance.

Lactobacilli with probiotic potential in the prairie vole (Microtus ochrogaster)

Background

Recent research suggests integration of the intestinal microbiota in gut-brain communication which could lead to new approaches to treat neurological disorders. The highly social prairie voles are an excellent model system to study the effects of environmental factors on social behavior. For future studies on the role of probiotics in ameliorating disorders with social withdrawal symptoms, we report the characterization of intestinal Lactobacillus isolates with probiotic potential from voles.

Methods and results

30 bacterial strains were isolated from the vole intestine and found to be distinct but closely related to Lactobacillus johnsonii using 16S rRNA gene sequencing and Random Amplification of Polymorphic DNA fingerprinting. In vitro characterizations including acid and bile tolerance, antimicrobial effects, antibiotic susceptibility, and adherence to intestinal epithelial cells were performed to assess the probiotic potential of selected strains. Since previous studies revealed that mercury ingestion triggers social deficits in voles, mercury resistance of the probiotic candidates was evaluated which could be an important factor in preventing/treating these behavioral changes.

Conclusions

This study demonstrates that lactobacilli with probiotic potential are present in the vole intestine. The Lactobacillus isolates identified in this study will provide a basis for the investigation of probiotic effects in the vole behavioral model system.

Electronic supplementary material

The online version of this article (doi:10.1186/s13099-015-0082-0) contains supplementary material, which is available to authorized users.

The foundation of kinship: households

Men's hunting has dominated the discourse on energy capture and flow in the past decade or so. We turn to women's roles as critical to household formation, pair-bonding, and intergenerational bonds. Their pivotal contributions in food processing and distribution likely promoted kinship, both genetic and affinal, and appear to be the foundation from which households evolved. With conscious recognition of household social units, variable cultural constructions of human kinship systems that were sensitive to environmental and technological conditions could emerge. Kinship dramatically altered the organization of resource access for our species, creating what we term "kinship ecologies." We present simple mathematical models to show how hunting leads to dependence on women's contributions, bonds men to women, and bonds generations together. Kinship, as it organized transfers of food and labor energy centered on women, also became integrated with the biological evolution of human reproduction and life history.

The neurobiological link between compassion and love

Love and compassion exert pleasant feelings and rewarding effects. Besides their emotional role and capacity to govern behavior, appetitive motivation, and a general ‘positive state’, even ‘spiritual’ at times, the behaviors shown in love and compassion clearly rely on neurobiological mechanisms and underlying molecular principles. These processes and pathways involve the brain’s limbic motivation and reward circuits, that is, a finely tuned and profound autoregulation. This capacity to self-regulate emotions, approach behaviors and even pair bonding, as well as social contact in general, i.e., love, attachment and compassion, can be highly effective in stress reduction, survival and overall health. Yet, molecular biology is the basis of interpersonal neurobiology, however, there is no answer to the question of what comes first or is more important: It is a cybernetic capacity and complex circuit of autoregulation that is clearly ‘amazing’.

Does fertility trump monogamy?

Monogamous animals face an interesting dilemma: if and when to terminate a nonproductive relationship. To address this issue, we asked whether reproductive compatibility is a criterion for maintaining a monogamous pair-bond between mates. Prairie voles (Microtus ochrogaster), are small rodents that form long-term, monogamous pair-bonds evidenced by a strong preference for their familiar partners, and thus are an excellent model animal in which to study mate-fidelity. Accordingly, we examined partner-preferences by male prairie voles and related their behavior to the reproductive status of their mates. We found that, when given a choice between their familiar female partner and a stranger, male prairie voles differ in their responses depending on the pregnancy status of the partner. Males that were paired with females for two weeks displayed mate-fidelity only when mating had been initiated within ~48 hours after pairing. In contrast, males whose mates experienced a delay in the onset of sexual receptivity displayed non-selective affiliative behavior. We also found that, in addition to being appropriately timed, mating must be successful. Males that mated with ovariectomized females for whom pregnancy was precluded did not display mate-fidelity even though mating was initiated within the proper timeframe. These observations of mate-fidelity only when the partner's pregnancy was sufficiently advanced relative to the duration of the pairing suggest that mating must be both successful and timely. Thus, reproductive compatibility can influence mate-fidelity.

Following the Whitings: The Study of Male Pregnancy Symptoms

In their long careers, John and Beatrice Whiting inspired investigation into a great variety of topics. Of these inquiries, men’s experience of pregnancy-like symptoms occupied the interest of the late Ruth Munroe and the author for some years. Men’s symptoms-morning sickness, lassitude, and so on-vary greatly both among individuals and across cultures. At the upper extreme, men average as many as five pregnancy-related symptoms in some culture groups, where they also display other behaviors related to the reproductive process (e.g., male “menstruation”). Tests and behavioral responses among such men (and among similar males elsewhere) typically reveal female-like choices on covert measures but also a surprising pattern of defensively masculine choices at the overt level (e.g., drinking, wife beating). A case study invites still other questions. To help resolve some of the issues raised by these findings, the author proposes a new program of research focusing on potential hormonal correlates of male symptomatology.

The ABC of demographic behaviour: how the interplays of alleles, brains, and contexts over the life course should shape research aimed at understanding population processes

This paper proposes core innovations in the strategy of research on demographic behaviour. One aim is a shift of attention away from events and towards a focus on dynamic processes and their interplay: away from a preoccupation with marriage and divorce, births, deaths, migrations, and household structure towards a broader perspective that takes account of partnership and intimacy, parenthood, potential and well-being, position in society and space, and personal ties. Another aim is a much closer engagement with genetics, neuroscience, psychology, and behavioural economics. A third aim is a strategy that pays more attention to pathways within the individual, to the processes entailed when the individual interacts with various contexts, and to progressions that involve the interplay of the pathways and processes through the life course. These shifts of emphasis, which have already begun to occur, require a systematic reassessment of priorities for research on demographic behaviour.

The neural correlates of maternal and romantic love

Romantic and maternal love are highly rewarding experiences. Both are linked to the perpetuation of the species and therefore have a closely linked biological function of crucial evolutionary importance. Yet almost nothing is known about their neural correlates in the human. We therefore used fMRI to measure brain activity in mothers while they viewed pictures of their own and of acquainted children, and of their best friend and of acquainted adults as additional controls. The activity specific to maternal attachment was compared to that associated to romantic love described in our earlier study and to the distribution of attachment-mediating neurohormones established by other studies. Both types of attachment activated regions specific to each, as well as overlapping regions in the brain's reward system that coincide with areas rich in oxytocin and vasopressin receptors. Both deactivated a common set of regions associated with negative emotions, social judgment and 'mentalizing', that is, the assessment of other people's intentions and emotions. We conclude that human attachment employs a push-pull mechanism that overcomes social distance by deactivating networks used for critical social assessment and negative emotions, while it bonds individuals through the involvement of the reward circuitry, explaining the power of love to motivate and exhilarate.