Stay or stray? Evidence for alternative mating strategy phenotypes in both men and women

No Association between 2D:4D Ratio and Hunting Success among Hadza Hunters

The ratio of index- and ring-finger lengths (2D:4D ratio) is thought to be related to prenatal androgen exposure, and in many, though not all, populations, men have a lower average digit ratio than do women. In many studies an inverse relationship has been observed, among both men and women, between 2D:4D ratio and measures of athletic ability. It has been further suggested that, in hunter-gatherer populations, 2D:4D ratio might also be negatively correlated with hunting ability, itself assumed to be contingent on athleticism. This hypothesis has been tested using endurance running performance among runners from a Western, educated, and industrialized population as a proximate measure of hunting ability. However, it has not previously been tested among actual hunter-gatherers using more ecologically valid measures of hunting ability and success. The current study addresses this question among Tanzanian Hadza hunter-gatherers. I employ a novel method of assessing hunting reputation that, unlike previous methods, allows granular distinctions to be made between hunters at all levels of perceived ability. I find no statistically significant relationship between digit ratio and either hunting reputation or two important hunting skills. I confirm that Hadza men have higher mean 2D:4D ratios than men in many Western populations. I discuss the notion that 2D:4D ratio may be the consequence of an allometric scaling relationship between relative and absolute finger lengths. Although it is difficult to draw clear conclusions from these results, the current study provides no support for the theorized relationship between 2D:4D ratio and hunting skill.

Genetic Influences on Social Relationships: Sex Differences in the Mediating Role of Personality and Social Cognition

Objectives

In humans (and primates more generally), evolutionary fitness arises by two separate routes: conventional reproduction build around dyadic relationships and, reflecting the processes of group augmentation selection, how well individuals are embedded in their community. These processes are facilitated by a suite of genetically inherited neuroendocrines and neurotransmitters. It is not, however, known whether these effects are directly due to genetic factors or are mediated by aspects of personality, or whether there are sex differences in the way this is organised.

Methods

We examine whether dispositional factors related to the processing of social information, such as personality (Big 5 and Impulsivity), attachment style (Anxious and Avoidant dimensions) and sociocognitive capacity (emotion recognition) mediate associations between variation in receptor genes for oxytocin, vasopressin, beta-endorphin, dopamine, serotonin, testosterone and two core social relationship indices (the Sociosexual Orientation Index [SOI] and Support Network size).

Results

In men, variation in dopamine genes indirectly influences SOI through its effect on Impulsivity. In contrast, in women, variation in endorphin and vasopressin genes independently affect Openness to Experience, which mediates indirect effects of these genes on SOI. Moreover, endorphin gene variation also impacts on Network Size in women (but not men), via Extraversion.

Conclusions

These findings reveal that dispositional aspects of personality mediate some genetic effects on behaviour, thereby extending our understanding of how genetic and dispositional variation interact to determine individual differences in human sexual and social cognition and behaviour. The differences between the sexes seem to reflect differences in the two sexes’ social strategies.

Associations between neurochemical receptor genes, 2D:4D, impulsivity and relationship quality

The ratio between the second and fourth digits (2D:4D) has been widely used as a proxy for fetal exposure to androgens and has been linked to a number of sociosexual traits in humans. However, the role of genes in this equation remains unknown. Here (N = 474), we test, firstly, for associations between 2D:4D and single-nucleotide polymorphisms (SNPs) in nine neurochemical receptor genes (AR, OXTR, AVPR1A, OPRM1, DRD1/2, ANKK1, 5HTR1A/2A), and secondly, whether digit ratios mediate the relationship between genetic variation and sociosexuality. We demonstrate significant associations between AR, OPRM1 and AVPR1A and 2D:4D. Moreover, mediation analysis indicates that, in women, AR and OPRM1 variation drives digit ratios, which are related positively to impulsivity and, for OPRM1, negatively to romantic relationship quality. Although these findings are subject to multiple testing issues, this study provides preliminary evidence that in women genetic factors may affect both impulsivity and perceived relationship quality through influencing factors indexed by digit ratios.

Monogamy and Nonmonogamy: Evolutionary Considerations and Treatment Challenges

INTRODUCTION

Few topics generate such controversy and emotional reactivity as the nature of human mating behavior. Unfortunately, and potentially to the detriment of good patient care, sexual medicine practitioners have largely avoided this matter. An understanding of the scientific literature can empower practitioners to more effectively confront the inevitable monogamy and nonmonogamy challenges present in research and clinical practice.

AIM

To review and summarize relevant scientific literature as a context to evaluate the more common myths and misunderstanding relating to the practice of monogamy and nonmonogamy in humans. This review also is intended to promote a discussion of the ways human mating strategies may impact sexual function and dysfunction for the individual and couple.

METHODS

A review of English written peer-reviewed evolutionary, anthropological, neuropsychiatric, zoological research, and other scholarly texts was conducted. Work published between 2000 and 2016 concentrating on evolutionary theory, long- and short-term mating strategies in primates and most specifically in humans, and consensual nonmonogamy was highlighted.

MAIN OUTCOME MEASURES

Main outcomes included a brief explanation of evolutionary theory and a review of relevant literature regarding long- and short-term mating behaviors and consensual nonmonogamy.

RESULTS

Serial sexual and social monogamy is the norm for humans. Across time and cultures, humans have adapted both long- and short-term mating strategies that are used flexibly, and sometimes simultaneously, based on unique personal, social, and environmental circumstances.

CONCLUSION

Human mating behavior is individualistic, the result of numerous biopsychosocial influences. The clinician cannot assume that an individual presenting as a patient maintains a monogamy-valued view of his or her intimate relationship. Patients may experience conflict between the cultural monogamous ideal and their actual sexual behaviors. This conflict may be critical in understanding a patient's sexual concerns and in treatment planning. Awareness of these issues will aid the practitioner in sexual medicine.

Three hundred years of low non-paternity in a human population

When cuckoldry is frequent we can expect fathers to withhold investment in offspring that may not be theirs. Human paternal investment can be substantial and is in line with observations from tens of thousands of conceptions that suggest that cuckoldry is rare in humans. The generality of this claim seems to be in question as the rate of cuckoldry varies across populations and studies have mostly been on Western populations. Two additional factors complicate our conclusions, (1) current estimates of the rate of cuckoldry in humans may not reflect our past behaviour as adultery can be concealed by the use of contraceptives; and (2) it is difficult to obtain samples that are random with respect to their paternity certainty. Studies that combine genealogies with Y-chromosome haplotyping are able to circumvent some of these problems by probing into humans' historical behaviour. Here we use this approach to investigate 1273 conceptions over a period of 330 years in 23 families of the Afrikaner population in South Africa. We use haplotype frequency and diversity and coalescent simulations to show that the male population did not undergo a severe bottleneck and that paternity exclusion rates are high for this population. The rate of cuckoldry in this Western population was 0.9% (95% confidence interval 0.4-1.5%), and we argue that given the current data on historical populations we have to conclude that, at least for Western human populations, cuckoldry rate is probably in the range of 1%.

ARE WITHIN-SEX MATING STRATEGY PHENOTYPES AN EVOLUTIONARY STABLE STRATEGY?

Humans have been found to display considerable variety in their pursuit of mating strategies, varying in their preference for short-term mating encounters versus established long-term relationships. While we know that differences in mating strategy exist between the two sexes (as predicted by parental investment theory), it has recently been shown that each sex may further exhibit two mating phenotypes. Here we explore the possibility that the presence of two phenotypes may be frequency dependent, thus comprising an Evolutionary Stable Strategy (ESS). We suggest that the presence of these phenotypes reflects a compromise between male preference for promiscuity and a female preference in favour of long-term mating by males.