Status and Reproduction in Humans: New Evidence for the Validity of Evolutionary Explanations on Basis of a University Sample

A strong positive relationship between reproductive success (offspring count) and status (position in the institutional hierarchy) is demonstrated in a contemporary sample of male university employees (n = 2693). Male academics in leading positions have more children than do other male employees. In female university employees (n = 2073), a negative relationship between status and reproductive success was found, but only if childless women were included in the analysis. Although a positive relationship between male status and offspring count has been predicted by evolutionary theory and was found in animal species and ‘traditional’ human societies, in modern societies most of the studies found no or even a negative relationship between status and reproductive success in males. We suggest that status may be a more important dimension for particular subsamples of modern society than for samples representing entire societies, so that associations might actually differ among subsamples. We suggest that analyses on a small and rather uniform level using modern large‐scale hierarchical organizations (such as universities) are candidates for the investigation of appropriate ‘society subsets’. Our results may stress the importance of evolutionary predictions and may be of relevance for theoretical and empirical considerations at the levels of economics and administration.     

The effects of sex and childlessness on the association between status and reproductive output in modern society

Examining the association between socioeconomic status and reproductive output in modern societies has led to conflicting results. In this study, we used a representative sample of contemporary Swedish men and women to analyze possible reasons for the contradictory results. We found that the relationship between socioeconomic status—described here by income and highest educational level attained—and reproductive output is dependent on sex and the inclusion or exclusion of childless individuals. In men, there is a strong positive association between income/education and average offspring count if childless individuals are included in the analysis; this association is absent when such individuals are excluded. We attribute this reversal mainly to the higher proportion of childless individuals among men of lower socioeconomic background. Among other factors, female choice appears to be a major cause of this association because the proportion of men who never married increased with decreasing income category and educational level. In women, however, including and excluding childless individuals both yielded a negative association between income and average offspring count as well as a null or negative relationship between education and average offspring count.     

Resources and reproductive success in women with an example from the Kipsigis of Kenya

Contradictory results regarding the relationship between resources and reproductive success of women have led some social scientists to conclude that evolutionary biological models are inappropriate to the study of human social behavior. This paper suggests instead that the variability across societies in this relationship reflects an inadequate specification of the nature and availability of the resources critical to reproduction as well as a failure to understand the mechanisms whereby resources confer reproductive success in traditional, developing, preindustrial, and modern societies. These methodological and conceptual issues are illustrated through use of data on the association between wealth and reproductive success from the Kipsigis, a polygynous agropastoralist population in southwestern Kenya. In this society, land is owned by men, and women gain access to land through marriage. In 3 of the 5 marriage cohorts studied, women with access to larger land plots had higher lifelong reproductive success than their poorer counterparts both in terms of enhanced fertility and survivorship of offspring. This association was independent of confounding factors such as education, age at menarche, husband's age, or occupation. Moreover, wealthy women were found not to make greater use of modern medical child health services when their children were sick than poor women. The Kipsigis data indicate that wealthy women had more nutritional resources than poor women and were able to introduce more suitable weaning foods, leading to a lower incidence of episodes of illness in offspring. Overall, the findings suggest that wealth-related differences in the nutrition and health of mothers and children are important factors in reproductive differentials in Kipsigis society.     

Implicit motives and gonadal steroid hormones: effects of menstrual cycle phase,oral contraceptive use,and relationship status

Implicit motives for power and affiliation, salivary levels of testosterone, estradiol, and progesterone, and relationship status were measured in 18 normally cycling (NC) women, 18 women using oral contraceptives (OC), and 18 men at three assessments, corresponding to the menstrual, midcycle, and premenstrual phases of women's menstrual cycle. NC and OC women had elevated levels of affiliation motivation and decreased levels of power motivation at midcycle. Power motive changes were particularly pronounced in NC women across cycle phases. OC women and participants not engaged in an intimate relationship had significantly heightened levels of affiliation motivation, averaged across all cycle phases. Testosterone and power motivation, both averaged across all cycle phases, were positively correlated in men and in single women, but not in women engaged in an intimate relationship. Averaged levels of estradiol and power motivation were positively correlated in engaged women, but not in single women or men. Averaged levels of progesterone and affiliation motivation were negatively correlated in men, and there was evidence for a positive association between luteal affiliation motivation and periovulatory and luteal progesterone in NC women. This study therefore provides evidence that implicit motivational states fluctuate across the menstrual cycle, that the power motive is associated with testosterone and, in women, with estradiol, and that the affiliation motive and progesterone are associated in different ways in men and NC women.     

Status competition,inequality, and fertility: implications for the demographic transition

The role that social status plays in small-scale societies suggests that status may be important for understanding the evolution of human fertility decisions, and for understanding how such decisions play out in modern contexts. This paper explores whether modelling competition for status—in the sense of relative rank within a society—can help shed light on fertility decline and the demographic transition. We develop a model of how levels of inequality and status competition affect optimal investment by parents in the embodied capital (health, strength, and skills) and social status of offspring, focusing on feedbacks between individual decisions and socio-ecological conditions. We find that conditions similar to those in demographic transition societies yield increased investment in both embodied capital and social status, generating substantial decreases in fertility, particularly under conditions of high inequality and intense status competition. We suggest that a complete explanation for both fertility variation in small-scale societies and modern fertility decline will take into account the effects of status competition and inequality.     

Ritual fights and male reproductive success in a human population

Ritual fights are widespread across human populations. However, the evolutionary advantage associated with this behaviour is unclear because these fights rarely provide direct benefits such as territory, resources or mates. Here, the reproductive success of men competing in a traditional ritual fight, Sereer wrestling, was investigated for the first time. Involvement in wrestling had a significant positive effect on men’s number of offspring and a marginally significant effect on polygyny, controlling for age, body condition and socio‐economic status. These positive effects suggest that being involved in wrestling competition provides prestige, facilitating access to mates and thereby increasing fecundity. However, when women were interviewed on their preference concerning qualities of potential mates, the quality ‘being involved in wrestling competition’ was poorly ranked. This discrepancy may arise either from deceptive reports or from discordance between parents and daughters in the choice of a husband.     

Childlessness drives the sex difference in the association between income and reproductive success of modern Europeans

The association between reproductive success and income in economically developed societies remains a controversial and understudied topic. The commonly made statement that individuals with a higher income have fewer children defies evolutionary explanation. Here we present results from an analyses of the association between lifetime reproductive success (LRS) and income for modern Europeans from 13 countries. We examine the relationships among income, partner income, sex and LRS, and the role of childlessness in driving the relationships. For women, we find a negative association between LRS and income, while for men, we find a flat or slightly positive one. The sex difference in the association appears to be driven by income's sex-specific association with childlessness; men with a low income have a relatively high risk of childlessness, while women with a low income have a low risk of childlessness. Consequently, once childless people are excluded from the analysis, LRS is negatively associated with income for both sexes. We argue that the observed LRS–income associations may be an outcome of evolved behavioural predispositions operating in modern environments and conclude that, even though humans fail to maximise LRS at all income levels in modern settings, evolutionary theory can still help to explain sex differences in LRS.     

Testosterone levels in women and men who are single, in long-distance relationships, or same-city relationships

Research points to an association between testosterone (T) and partnering in some women and men, and this association has been interpreted as an effect of either relationship status (i.e. differences in relationship status lead to differences in T) or relationship orientation (i.e. T is associated with the likelihood of entering relationships). To address whether physical partner presence was associated with decreased T, we examined T levels in people (72 women; 49 men) who were single, in long-distance relationships, or in same-city relationships. No participants were using exogenous hormones, including hormonal contraceptives. Participants provided a saliva sample and responded to questions about their relationship status. Single men had higher T than long-distance and same-city partnered men, which supports the relationship orientation interpretation. In contrast, same-city partnered women had lower T than single women and women in long-distance relationships, which supports the relationship status interpretation. We conclude that physical partner presence is not necessary to see an association between partnering and hormones in men (since same-city and long-distance partnered men had similar T levels), but may be necessary in women (since same-city partnered women had lower T than long-distance partnered women).     

Walking fast-ranking high: A sociobiological perspective on pace

Sexual selection theory says that because females are the limiting factor in reproduction, males have to compete for them. Females in turn choose among males. In humans, socioeconomic status is a much more important mate choice criterion of women than of men. Thus, striving for status and signaling status is more important for men. We chose walking to test this sex difference because upright posture and walking probably were under sexual selection pressure for a long time. The latter is illustrated by upright threat displaying, quite common in male primates; for example, men may walk stiff and erect and accelerate to vigorous striding, both to impress women and to threaten rivals (in which case they may also raise their arms). Moreover, gathering and hunting, the condition of all modern humans until about 15,000 years ago, implies a division of labor, with men playing the more mobile hunter part. In view of the outstanding importance of food for female reproduction, women probably highly valued men's hunting capabilities, among which are locomotory speed and perseverance. Long-standing quantitative data on walking speed also suggest a sex-specific association between pace and status. We hypothesized that habitual fast walking might be a means to acquire and/or to display status, and predicted a positive correlation between walking speed and socioeconomic status in men, not in women. We found that men walked faster, the higher their status, whereas the pace of women was independent of their status. This result held when proximate factors like age, body height, next destination, and number of dates were controlled for.     

Socioeconomic status, marital status and childlessness in men and women: an analysis of census data from six countries

This study compares the effects of two distinct forms of human capital - income and education - on marital status and childlessness separately by sex in six different countries. Nearly 10 million individual records on individuals aged 16 to 50 were used from censuses from Brazil, Mexico, Panama, South Africa, USA and Venezuela dating from 2000 or later, to analyse the relationship between education, income and marital status and childlessness in men and women. Regarding income, the findings for both outcome variables are strongly consistent across all six countries. Highest-income males and lower-income females have the highest proportion of ever-married and the lowest proportion of childlessness (using a proxy for childlessness: own children in the household or not). There is no corresponding consistency of findings as regards education either between the sexes or among the countries. To conclude, a lower percentage of low-income men are selected by females, because for women male status and resources provided by men are important criteria in mate selection. Therefore a higher proportion of low-income men remain unmarried and childless. Thus selection seems to play a role in modern societies.     

Sexual dimorphism in stature and women's work: a phylogenetic cross-cultural analysis.

The following cultural variables were tested for their association with sexual dimorphism: sexual division of labor, type of subsistence (hunting and agriculture), and polygyny. The transmission of these traits among populations was investigated. All the traits were found to be associated with phylogeny, indicating that they are inherited from mother to daughter populations. A cross-cultural comparative method was used which controls for the statistical effects of similarity due to common ancestry (Galton's problem). Cross-cultural variation in sexual dimorphism in stature is negatively associated with women's contribution to subsistence. Women are taller, relative to men, in societies where women contribute more to food production. This may be because female nutritional status is better in these societies. No relationship was found between sexual dimorphism and other aspects of subsistence or polygyny. These results are discussed in relation to other studies of sexual dimorphism in modern and archaeological populations, and in relation to cross-cultural variation in sex-biased parental investment.     

God,sex, and money among the ultra-Orthodox in Israel: An integrated sociocultural and evolutionary perspective

The origin of the tendency for men to value wealth more than women can be explained by both social role theory and evolutionary theory. We integrate these two perspectives to provide insight into a unique cultural context, the Jewish ultra-Orthodox community in Israel, where social roles are reversed, such that women are the primary breadwinners in the family. Studies 1a and 1b provide support for social role theory's claim that men and women will internalize attitudes toward wealth that are consistent with their gender role in society. These findings are then integrated with an evolutionary perspective suggesting that men strive to elevate their personal status as a means of attracting mates. In most modern societies this equates to the accumulation of wealth, but in the ultra-Orthodox community it is religious devotion and piety that determine the status of men. An examination of mating preferences in the ultra-Orthodox community confirms many predictions from an evolutionary perspective and departs only in that women do not show a preference for mates with good financial prospects, but rather, owing to the unique sociocultural definition of status, women display a preference for men of strong religious devotion (Study 2). This contrasts with the secular Jewish community where women show the typical preference for wealthy men (Study 3). These findings are consistent with the idea that men may have evolved preferences for achieving status given the mating advantages it confers with women, but how status is achieved may be culturally specific.     

Parental age difference, educationally assortative mating and offspring count: evidence from a contemporary population in Taiwan

Using contemporary population data from Taiwan, we examine the relationships between parental age difference, educationally assortative mating, income and offspring count. Controlling for women's reproductive value (measured by age at first birth), we find that an older husband is associated with fewer offspring, whereas a husband with similar or higher education is associated with more offspring. Concerning resources, we find that women's income is negatively associated with fertility and husband's income is positively associated with fertility among highly educated women. These results are consistent with the view that women compensate for trade-offs between education, income generation and childbearing by seeking mates with a higher status.     

Optimizing Modern Family Size

Modern industrialized populations lack the strong positive correlations between wealth and reproductive success that characterize most traditional societies. While modernization has brought about substantial increases in personal wealth, fertility in many developed countries has plummeted to the lowest levels in recorded human history. These phenomena contradict evolutionary and economic models of the family that assume increasing wealth reduces resource competition between offspring, favoring high fertility norms. Here, we review the hypothesis that cultural modernization may in fact establish unusually intense reproductive trade-offs in wealthy relative to impoverished strata, favoring low fertility. We test this premise with British longitudinal data (the Avon Longitudinal Study of Parents and Children), exploring maternal self-perceptions of economic hardship in relation to increasing family size and actual socioeconomic status. Low-income and low-education-level mothers perceived the greatest economic costs associated with raising two versus one offspring. However, for all further increases to family size, reproduction appears most expensive for relatively wealthy and well-educated mothers. We discuss our results and review current literature on the long-term consequences of resource dilution in modern families.     

Educational homogamy lowers the odds of reproductive failure

Assortative mating based on education is a common phenomenon. We investigated whether it affected parameters of reproductive performance such as childlessness, offspring number and age at first marriage. On the basis of the US census from 1980 (n = 670,631 married US couples), we find that the proportion of childless individuals is usually minimal in women married to a husband of the same educational level. This holds particularly true in the highest and the lowest educated women. Educational homogamy is also associated with a lower average age at first marriage. No obvious effect of educational homogamy on a woman''s average offspring number is found, where mean offspring number generally increases both with decreasing woman''s and decreasing husband''s educational attainment. We conclude that educational homogamy reduces the likelihood of reproductive failure.     

Cooperation and conflict: The behavioral ecology of the sexual division of labor

When it comes to subsistence, men and women in almost all societies do it differently. One long-standing explanation for this sexual division of labor is that men and women pair up to provision offspring and specialize in subsistence activities in order to maximize household productivity. This model of cooperative parental provisioning has generally been supported by the proposal that both male and female reproductive success is maximized by provisioning current offspring rather than deserting them in order to seek new mating opportunities. But recent analyses of bird behavior have often failed to support this premise. We now know that among many species conflicting reproductive strategies between males and females often result in less than optimal compromises with regard to mating and parenting. This new focus on the role of sexual selection in creating compromise and conflict between the sexes has the potential to illuminate many puzzling aspects of human partnerships between men and women. To demonstrate its potential, I compare the explanatory power of a cooperative provisioning model of sex difference in human foraging and food sharing with a model incorporating conflicting reproductive goals.     

Testosterone,cortisol, and human competition

Testosterone and cortisol figure prominently in the research literature having to do with human competition. In this review, we track the history of this literature, concentrating particularly on major theoretical and empirical contributions, and provide commentary on what we see as important unresolved issues. In men and women, athletic competition is typically associated with an increase in testosterone (T) and cortisol (C). Hormone changes in response to non-athletic competition are less predictable. Person (e.g., power motivation, mood, aggressiveness, social anxiety, sex, and baseline levels of T and C) and context (e.g., whether a competition is won or lost, the closeness of the competition, whether the outcome is perceived as being influenced by ability vs. chance, provocations) factors can influence hormone responses to competition. From early on, studies pointed to a positive relationship between T and dominance motivation/status striving. Recent research, however, suggests that this relationship only holds for individuals with low levels of C – this is the core idea of the dual-hormone hypothesis, and it is certain that the broadest applications of the hypothesis have not yet been realized. Individuals differ with respect to the extent to which they embrace competition, but the hormonal correlates of competitiveness remain largely unexplored. Although rapid increases in both T and C associated with competition are likely adaptive, we still know very little about the psychological benefits of these hormonal changes. Administration studies have and will continue to contribute to this inquiry. We close with a discussion of what, we think, are important methodological and mechanistic issues for future research.     

Sex,status, and reproductive success in the contemporary United States

This paper reexamines the relationship between status and reproductive success (at the ultimate and proximate levels) using data on sex frequency and number of biological children from representative samples of the U.S. population. An ordered probit analysis of data from the 1989–2000 General Social Survey (GSS) shows that high-income men report greater frequency of sex than all others do. An OLS regression of data from the 1994 GSS shows that high-income men have more biological children than do low-income men and high-income women. Furthermore, more educated men have more biological children than do more educated women. Results also show that intelligence decreases the number of offspring and frequency of sex for both men and women.     

Human Lactation, Pair-bonds, and Alloparents

The evolutionary origin of human pair-bonds is uncertain. One hypothesis, supported by data from forgers, suggests that pair-bonds function to provision mothers and dependent offspring during lactation. Similarly, public health data from large-scale industrial societies indicate that single mothers tend to wean their children earlier than do women living with a mate. Here we examine relations between pair-bond stability, alloparenting, and cross-cultural trends in breastfeeding using data from 58 “traditional” societies in the Standard Cross-Cultural Sample (SCCS). Analyses show that stable conjugal relationships were associated with significantly later weaning among the societies in the SCCS. The relationship between pair-bond stability and age at weaning was not mediated by women’s ability to provision themselves or women’s kin support. Availability of alloparental care was also inversely related to age at weaning, and the association was not significantly reduced after controlling for frequency of divorce. This study indicates that among a woman’s kin relationships, a pair-bond with a child’s father is especially supportive of breastfeeding. These cross-cultural findings are further evidence that human pair-bonds may have evolved to support lactation.     

Over, under, or about right: misperceptions of body weight among food stamp participants

The purpose of this research was to investigate the associations between misperception of body weight and sociodemographic factors such as food stamp participation status, income, education, and race/ethnicity. National Health and Nutrition Examination Survey (NHANES) data from 1999-2004 and multivariate logistic regression are used to estimate how sociodemographic factors are associated with (i) the probability that overweight adults misperceive themselves as healthy weight; (ii) the probability that healthy-weight adults misperceive themselves as underweight; and (iii) the probability that healthy-weight adults misperceive themselves as overweight. NHANES data are representative of the US civilian noninstitutionalized population. The analysis included 4,362 men and 4,057 women. BMI derived from measured weight and height was used to classify individuals as healthy weight or overweight. These classifications were compared with self-reported categorical weight status. We find that differences across sociodemographic characteristics in the propensity to underestimate or overestimate weight status were more pronounced for women than for men. Overweight female food stamp participants were more likely to underestimate weight status than income-eligible nonparticipants. Among healthy-weight and overweight women, non-Hispanic black and Mexican-American women, and women with less education were more likely to underestimate actual weight status. We found few differences across sociodemographic characteristics for men. Misperceptions of weight are common among both overweight and healthy-weight individuals and vary across socioeconomic and demographic groups. The nutrition education component of the Food Stamp Program could increase awareness of healthy body weight among participants.