The evolution of female sexuality and mate selection in humans

Understanding female sexuality and mate choice is central to evolutionary scenarios of human social systems. Studies of female sexuality conducted by sex researchers in the United States since 1938 indicate that human females in general are concerned with their sexual well-being and are capable of sexual response parallel to that of males. Across cultures in general and in western societies in particular, females engage in extramarital affairs regularly, regardless of punishment by males or social disapproval. Families are usually concerned with marriage arrangements only insofar as those arrangements are economically or politically advantageous, but females most often have a voice in arranged marriages. Extended families also concentrate on a couple’s future reproduction rather than on sexual exclusivity. Although marriage for females is often compromised by male or family reproductive interests (which may not in fact differ from female interests), females appear to exercise their sexuality with more freedom than has previously been suggested. Notions of human females as pawns in the male reproductive game, or as traders of sex for male services, should be dispelled.     

Oscillatory dynamics in rock-paper-scissors games with mutations

We study the oscillatory dynamics in the generic three-species rock-paper-scissors games with mutations. In the mean-field limit, different behaviors are found: (a) for high mutation rate, there is a stable interior fixed point with coexistence of all species; (b) for low mutation rates, there is a region of the parameter space characterized by a limit cycle resulting from a Hopf bifurcation; (c) in the absence of mutations, there is a region where heteroclinic cycles yield oscillations of large amplitude (not robust against noise). After a discussion on the main properties of the mean-field dynamics, we investigate the stochastic version of the model within an individual-based formulation. Demographic fluctuations are therefore naturally accounted and their effects are studied using a diffusion theory complemented by numerical simulations. It is thus shown that persistent erratic oscillations (quasi-cycles) of large amplitude emerge from a noise-induced resonance phenomenon. We also analytically and numerically compute the average escape time necessary to reach a (quasi-)cycle on which the system oscillates at a given amplitude.     

Marriage Timing over the Generations

Strong relationships have been hypothesized between the timing of marriage and the familial environment of the couple. Sociologists have identified various mechanisms via which the age at marriage in the parental generation might be related to the age at marriage of the children. In our paper we study this relationship for historical populations. We use a dataset consisting of several hundreds of thousands of marriages contracted in three of the 11 Dutch provinces between 1812 and 1922. We identified the generational links between the brides, grooms, their parents, and grandparents. We studied (a) whether there is a relationship between ages at marriage of (grandfathers) fathers and sons, and ages at marriage of (grandmothers) mothers and daughters and (b) whether this relationship might be explained by social class. We find evidence for a clear effect of the family on age at marriage and substantial intergenerational transmission. The impact that the family of origin has on age at entry into marriage can partly be attributed to social class. We also observed positive effects of grandparents’ age at marriage on their offspring’s age at marriage.

Rôle du sens de l’effort dans le syndrome d’influence

Centrally generated signals from premotor areas play a key role in voluntary muscle force perception. Indeed, sensations of effort, rather than sensations of intramuscular tension, make it possible to evaluate the intensity of willed muscle forces. We suggest that the sense of effort is involved in agency, the cognitive process by which one is aware of one’s actions. We argue that effort awareness accompanies each action and is the key component of the feeling of will. In delusions of alien control, patients with schizophrenia do not recognize some of their acts as their own and are convinced that they are under the control of someone else. Some experimental data suggest that delusions of control are related to an altered awareness of effort and an exaggerated awareness of afferent neural information, caused by neurological disorders in the frontal and parietal lobes. This impairment could lead to the inability to identify the author of an action. In this pathological condition, the cerebral state coding for “I intend to act” might move toward the state coding for “someone else intends to act”, even in the absence of another agent.     

A Bioeconomic Approach to Marriage and the Sexual Division of Labor

Children may be viewed as public goods whereby both parents receive equal genetic benefits yet one parent often invests more heavily than the other. We introduce a microeconomic framework for understanding household investment decisions to address questions concerning conflicts of interest over types and amount of work effort among married men and women. Although gains and costs of marriage may not be spread equally among marriage partners, marriage is still a favorable, efficient outcome under a wide range of conditions. This bioeconomic framework subsumes both cooperative and conflictive views on the sexual division of labor. We test hypotheses concerning marriage markets, assortative mating, and men’s labor motivations among Tsimane forager-horticulturalists of Bolivia and find that: (1) men and women both value work effort in marital partners, (2) marital labor contributions are complementary, (3) work effort is correlated between spouses, (4) total production is correlated with total reproduction, and (5) better hunters have higher fitness gains within marital unions.     

Divorce in the early years of marriage in England and Wales: results from a prospective study using linked records

A representative sample of over 1000 couples who married during 1979 in England and Wales was followed from the date of marriage until mid-1984 to investigate the characteristics of couples who divorce soon after marriage. Results of this 5 year study show that couples who apparently lived together before marriage had a below average chance of early divorce, whereas couples where the addresses of the partners before marriage were very close had a significantly high rate of early breakdown. The chance of early divorce was significantly above average for spouses marrying in their teens and for both husbands and wives who, at their marriage, belonged to social class 5 (work in unskilled manual occupations). Couples who married with a civil ceremony had an above average (and those marrying with a religious ceremony a below average) risk of early divorce, but such differences were found to be negligible on analyzing the results from a matched case-control study in which each "case" marriage (one which did end in early divorce) was matched with a "control" marriage (one which did not end in early divorce). There is substantial evidence that age at marriage and previous marital status of the marriage partners have a decided influence upon the propensity to divorce. 2 conclusions concerning fertility are more likely than the average married couple to have had a pre-maritally conceived child, and 2) that couples who divorce relatively quickly tend on average to have larger family sizes, even if children who were pre-martitally conceived are exluded.     

Social and family characteristics of marriage in England and Wales: information derived from marriage registration records

Information on social and family aspects of marriage was obtained from a sample of over a thousand marriages solemnised in England and Wales in 1979. The data include the standard demographic variables concerning the couple and their marriage and also: the day of the week the marriage was celebrated; whether the fathers or relatives of similar surname to the spouses acted as witnesses; the patterns of name usage by brides; the numbers of forenames of the marriage partners and their fathers; and the frequency of bridegrooms having one or more forenames in common with their fathers. The factors are analysed in terms of social class differences as well as in relation to the distance over which marriages range and other demographic characteristics of the partners and their marriage.     

Network Diversity and Affect Dynamics: The Role of Personality Traits

People divide their time unequally among their social contacts due to time constraints and varying strength of relationships. It was found that high diversity of social communication, dividing time more evenly among social contacts, is correlated with economic well-being both at macro and micro levels. Besides economic well-being, it is not clear how the diversity of social communication is also associated with the two components of individuals’ subjective well-being, positive and negative affect. Specifically, positive affect and negative affect are two independent dimensions representing the experience (feeling) of emotions. In this paper, we investigate the relationship between the daily diversity of social communication and dynamic affect states that people experience in their daily lives. We collected two high-resolution datasets that capture affect scores via daily experience sampling surveys and social interaction through wearable sensing technologies: sociometric badges for face-to-face interaction and smart phones for mobile phone calls. We found that communication diversity correlates with desirable affect states–e.g. an increase in the positive affect state or a decrease in the negative affect state–for some personality types, but correlates with undesirable affect states for others. For example, diversity in phone calls is experienced as good by introverts, but bad by extroverts; diversity in face-to-face interaction is experienced as good by people who tend to be positive by nature (trait) but bad for people who tend to be not positive by nature. More broadly, the moderating effect of personality type on the relationship between diversity and affect was detected without any knowledge of the type of social tie or the content of communication. This provides further support for the power of unobtrusive sensing in understanding social dynamics, and in measuring the effect of potential interventions designed to improve well-being.     

Dynamics to Equilibrium in Network Games: Individual Behavior and Global Response

Various social contexts can be depicted as games of strategic interactions on networks, where an individual’s welfare depends on both her and her partners’ actions. Whereas much attention has been devoted to Bayes-Nash equilibria in such games, here we look at strategic interactions from an evolutionary perspective. To this end, we present the results of a numerical simulations program for these games, which allows us to find out whether Nash equilibria are accessible by adaptation of player strategies, and in general to identify the attractors of the evolution. Simulations allow us to go beyond a global characterization of the cooperativeness at equilibrium and probe into individual behavior. We find that when players imitate each other, evolution does not reach Nash equilibria and, worse, leads to very unfavorable states in terms of welfare. On the contrary, when players update their behavior rationally, they self-organize into a rich variety of Nash equilibria, where individual behavior and payoffs are shaped by the nature of the game, the social network’s structure and the players’ position within the network. Our results allow to assess the validity of mean-field approaches we use to describe the dynamics of these games. Interestingly, our dynamically-found equilibria generally do not coincide with (but show qualitatively the same features of) those resulting from theoretical predictions in the context of one-shot games under incomplete information.     

Cyber War Game in Temporal Networks

In a cyber war game where a network is fully distributed and characterized by resource constraints and high dynamics, attackers or defenders often face a situation that may require optimal strategies to win the game with minimum effort. Given the system goal states of attackers and defenders, we study what strategies attackers or defenders can take to reach their respective system goal state (i.e., winning system state) with minimum resource consumption. However, due to the dynamics of a network caused by a node’s mobility, failure or its resource depletion over time or action(s), this optimization problem becomes NP-complete. We propose two heuristic strategies in a greedy manner based on a node’s two characteristics: resource level and influence based on k-hop reachability. We analyze complexity and optimality of each algorithm compared to optimal solutions for a small-scale static network. Further, we conduct a comprehensive experimental study for a large-scale temporal network to investigate best strategies, given a different environmental setting of network temporality and density. We demonstrate the performance of each strategy under various scenarios of attacker/defender strategies in terms of win probability, resource consumption, and system vulnerability.     

A Mathematical Model of Sentimental Dynamics Accounting for Marital Dissolution

Background

Marital dissolution is ubiquitous in western societies. It poses major scientific and sociological problems both in theoretical and therapeutic terms. Scholars and therapists agree on the existence of a sort of second law of thermodynamics for sentimental relationships. Effort is required to sustain them. Love is not enough.

Methodology/Principal Findings

Building on a simple version of the second law we use optimal control theory as a novel approach to model sentimental dynamics. Our analysis is consistent with sociological data. We show that, when both partners have similar emotional attributes, there is an optimal effort policy yielding a durable happy union. This policy is prey to structural destabilization resulting from a combination of two factors: there is an effort gap because the optimal policy always entails discomfort and there is a tendency to lower effort to non-sustaining levels due to the instability of the dynamics.

Conclusions/Significance

These mathematical facts implied by the model unveil an underlying mechanism that may explain couple disruption in real scenarios. Within this framework the apparent paradox that a union consistently planned to last forever will probably break up is explained as a mechanistic consequence of the second law.     

Repayment Flexibility Can Reduce Financial Stress: A Randomized Control Trial with Microfinance Clients in India

Financial stress is widely believed to cause health problems. However, policies seeking to relieve financial stress by limiting debt levels of poor households may directly worsen their economic well-being. We evaluate an alternative policy – increasing the repayment flexibility of debt contracts. A field experiment randomly assigned microfinance clients to a monthly or a traditional weekly installment schedule (N = 200). We used cell phones to gather survey data on income, expenditure, and financial stress every 48 hours over seven weeks. Clients repaying monthly were 51 percent less likely to report feeling “worried, tense, or anxious” about repaying, were 54 percent more likely to report feeling confident about repaying, and reported spending less time thinking about their loan compared to weekly clients. Monthly clients also reported higher business investment and income, suggesting that the flexibility encouraged them to invest their loans more profitably, which ultimately reduced financial stress.     

Male age mediates reproductive investment and response to paternity assurance

Theory predicts that male response to reduced paternity will depend on male state and interactions between the sexes. If there is little chance of reproducing again, then males should invest heavily in current offspring, regardless of their share in paternity. We tested this by manipulating male age and paternity assurance in the burying beetle Nicrophorus vespilloides. We found older males invested more in both mating effort and parental effort than younger males. Furthermore, male age, a component of male state, mediated male response to perceived paternity. Older males provided more prenatal care, whereas younger males provided less prenatal care, when perceived paternity was low. Adjustments in male care, however, did not influence selection acting indirectly on parents, through offspring performance. This is because females adjusted their care in response to the age of their partner, providing less care when paired with older males than younger males. As a result offspring, performance did not differ between treatments. Our study shows, for the first time, that a male state variable is an important modifier of paternity–parental care trade-offs and highlights the importance of social interactions between males and females during care in determining male response to perceived paternity.     

Dynamic influence of maternal and pup traits on maternal care during lactation in an income breeder, the antarctic fur seal

Life-history theory predicts that selection will favor optimal levels of parental effort that balance benefits of current reproduction with costs to survival and future reproduction. The optimal level of effort depends on parental traits, offspring traits, and provisioning strategy. Additionally, how these factors influence effort may differ depending on the stage of reproduction. The relative importance of maternal and offspring traits on energy allocation to offspring was investigated in known-age Antarctic fur seals Arctocephalus gazella across four stages of reproduction, using birth mass and milk-consumption measurements. Maternal traits were important during three of the four stages investigated, with larger females giving birth to larger pups and investing more in pups during perinatal and molt stages. Pup mass influenced maternal effort during the premolt stage, and provisioning strategy influenced postnatal maternal effort at all stages. Energy provided to the offspring during an attendance visit was positively related to the duration of the foraging-trip/visit cycle; however, when investment was controlled for trip/visit cycle duration, the overall rate of energy transfer was similar across trip durations. In addition to strong effects of maternal mass, pup traits affected energy allocation, suggesting that pup demand is important in determining maternal care. These findings emphasize the importance of considering state variables in life-history studies and suggest that timing of measurements of effort in species with long provisioning periods may influence conclusions and our ability to make comparisons of reproductive effort among species.     

Legalization of consensual unions in Mexico

Abstract

There is ample evidence that there are important behavioral differences in Latin America between couples living in consensual unions and those who are legally married. In this paper, we examine the frequency of and variations in legalization of consensual unions in Mexico, using data from the 1976–77 Encuesta Mexicana de Fecundidad. Our results indicate that the frequency of legalization of consensual unions appears to have risen among recent cohorts. Women in first unions, those who start a union at older ages, and those who are more highly educated are also more likely to marry their partners. Our results also indicate that pregnancy does not appear to be a major factor precipitating legalization, and that whether a couple lived together before marriage has no effect on the stability of the marriage.     

The K-complex and slow oscillation in terms of a mean-field cortical model

We use a mean-field macrocolumn model of the cerebral cortex to offer an interpretation of the K-complex of the electroencephalogram to complement those of more detailed neuron-by-neuron models. We interpret the K-complex as a momentary excursion of the cortex from a stable low-firing state to an unstable high-firing state, and hypothesize that the related slow oscillation can be considered as the periodic oscillation between two meta-stable solutions of the mean-field model. By incorporating a Hebbian-style learning rule that links the growth in synapse strength to fluctuations in soma potential, we demonstrate a self-organization behaviour that draws the modelled cortex close to the edge of stability of the low-firing state. Furthermore, a very slow oscillation can occur in the excitability of the cortex that has similarities with the infra-slow oscillation of sleep. Action Editor: Nicolas Brunel     

Population and prehistory III: Food-dependent demography in variable environments

The population dynamics of preindustrial societies depend intimately on their surroundings, and food is a primary means through which environment influences population size and individual well-being. Food production requires labor; thus, dependence of survival and fertility on food involves dependence of a population’s future on its current state. We use a perturbation approach to analyze the effects of random environmental variation on this nonlinear, age-structured system. We show that in expanding populations, direct environmental effects dominate induced population fluctuations, so environmental variability has little effect on mean hunger levels, although it does decrease population growth. The growth rate determines the time until population is limited by space. This limitation introduces a tradeoff between population density and well-being, so population effects become more important than the direct effects of the environment: environmental fluctuation increases mortality, releasing density dependence and raising average well-being for survivors. We discuss the social implications of these findings for the long-term fate of populations as they transition from expansion into limitation, given that conditions leading to high well-being during growth depress well-being during limitation.     

Multiple-year optimization of conservation effort and monitoring effort for a fluctuating population

We consider optimal conservation strategies for an endangered population. We assume that juvenile survival is affected by unpredictable environmental fluctuation and can be improved by costly conservation effort. The initial population size is not accurately known at the time that the conservation effort level is chosen, but the uncertainty of its estimate can be reduced by a costly monitoring effort. In a previous paper, we analysed the optimal management strategy that minimizes a weighted sum of extinction probability and economic costs when only a single year is considered. Here we examine the case in which the conservation period lasts for several years by dynamic programming with incompletely observed process states. We study the optimal levels of the conservation and the monitoring efforts, and their dependence on the length of the conservation period and other parameters. The main conclusions are: (1) The optimal conservation effort in the first year depends on the accuracy of the information on the population size in the first year, but is almost independent of the accuracy of the information in later years. (2) When the risk of population extinction is small, the optimal conservation effort increases with the uncertainty of the population size. In contrast when the population is endangered, the optimal conservation effort decreases with the uncertainty of the population size. (3) The optimal conservation and monitoring efforts both increase with the length of the conservation period, provided that the population is relatively safe. However, if the population is endangered, both types of effort become smaller when the conservation period increases.     

Simple models for complex systems: exploiting the relationship between local and global densities

Simple temporal models that ignore the spatial nature of interactions and track only changes in mean quantities, such as global densities, are typically used under the unrealistic assumption that individuals are well mixed. These so-called mean-field models are often considered overly simplified, given the ample evidence for distributed interactions and spatial heterogeneity over broad ranges of scales. Here, we present one reason why such simple population models may work even when mass-action assumptions do not hold: spatial structure is present but it relates to global densities in a special way. With an individual-based predator–prey model that is spatial and stochastic, and whose mean-field counterpart is the classic Lotka–Volterra model, we show that the global densities and densities of pairs (or spatial covariances) establish a bi-power law at the stationary state and also in their transient approach to this state. This relationship implies that the dynamics of global densities can be written simply as a function of those densities alone without invoking pairs (or higher order moments). The exponents of the bi-power law for the predation rate exhibit a remarkable robustness to changes in model parameters. Evidence is presented for a connection of our findings to the existence of a critical phase transition in the dynamics of the spatial system. We discuss the application of similar modified mean-field equations to other ecological systems for which similar transitions have been described, both in models and empirical data.     

The Affective Creativity of a Couple in Dementia Care

The capacity to feel and express themselves in response to worldly surroundings is a defining feature of who a person living with dementia is, and can have profound effects on the ways in which they think, act and express creativity. Drawing on a year of intensive collaborative work with residents living with dementia in an Orthodox Jewish care home in London, I extend our perceptions and understandings of how a couple experiences their day-to-day lives, with particular attention paid to their affective practice in creativity. I demonstrate how the affective creativity of the couple emerges, circulates, and transforms as a spouse’s dementia develops, whilst feeling bodies continuously (re)make relations and familiarize themselves with the immediate surroundings through the making of artworks.