Are men and women really so different?

Distinct differences in the behaviour and preferences of men and women have conventionally been attributed to Trivers' powerful insights regarding the impact of parental investment on sexual selection and mating systems. This has spawned a huge literature about the evolutionary significance of human sex differences. But are men and women really so different? An elegant new study shows that men and women are strikingly similar in their mate preferences. Have conventional models blinded us to the obvious, and precluded the posing of far more interesting questions?     

Why do men marry and why do they stray?

Humans are quite unusual compared to other great apes in that reproduction typically takes place within long-term, iteroparous pairings--social arrangements that have been culturally reified as the institution of marriage. With respect to male behaviour, explanations of marriage fall into two major schools of thought. One holds that marriage facilitates a sexual division of labour and paternal investment, both important to the rearing of offspring that are born helpless and remain dependent for remarkably long periods (provisioning model). And the other suggests that the main benefits which men receive from entering into marriage derive from monopolizing access to women's fertility (mating effort model). In this paper, we explore extramarital sexual relationships and the conditions under which they occur as a means of testing predictions derived from these two models. Using data on men's extramarital sexual relationships among Tsimane forager-horticulturists in lowland Bolivia, we tested whether infidelity was more common when men had less of an opportunity to invest in their children or when they risked losing less fertility. We found that Tsimane men appear to be biasing the timing of their affairs to when they are younger and have fewer children, supporting the provisioning model.     

Worms and malaria: blind men feeling the elephant?

For thousands of years the deadliest human parasite, Plasmodium falciparum, has been evolving in populations also infected by the most prevalent parasites, worms. This is likely to have shaped the genome of all 3 protagonists--man, worms and malaria. Observational studies in Thailand have shown that although P. falciparum malaria incidence increased two-fold in helminth-infected patients, there was a 64% reduction of cerebral malaria and an 84% reduction of acute renal failure in helminth-infected patients relative to those without helminths. In addition, it was suggested that mixed infections, anaemia and gametocyte carriage were more frequent in helminth-infected patients. On the contrary, fever was lower in helminth-infected patients. The present hypotheses, their implications and the limitations of the results described and of those from studies in Africa are discussed.     

Coronary artery disease: Are men and women created equal?

Background: Ischemic heart disease in women is a difficult issue in cardiovascular medicine, mainly because of our lack of understanding of the early-stage mechanisms and symptoms. A better and earlier understanding of the pathophysiology of coronary artery disease (CAD) in women will enable us to detect ischemic heart disease earlier and prevent adverse clinical outcomes.Objectives: The aims of this article were to describe the phenomenon of ischemic heart disease in women, increase awareness of the difference between men and women in relation to ischemic heart disease, improve our understanding of the mechanisms that cause this difference, and identify new approaches for better and earlier detection and treatment of CAD in women.Methods: We conducted a search of the PubMed database for double-blind studies on the mechanistic pathways of CAD in women published in English within the past 10 years and epidemiologic studies published since 1970. Search terms included women and coronary artery disease and ischemic heart disease in women.Results: The literature search revealed 30 peer-reviewed articles pertaining to this issue. The incidence of CAD was markedly lower in women <60 years of age than in older women. After 60 years of age, the rate of CAD increased and reached the rate seen among men by the 8th decade of life. The gender difference in atherosclerosis in the coronary tree was particularly large in patients <55 years of age and remained large at older ages. The gender difference in the coronary bed was strikingly larger than in other vascular beds. Intensive risk-factor modification had a similar effect on plaque progression in both men and women. Coronary endothelial dysfunction appeared to be related to cardiovascular morbidity and mortality in women as well as in men, and because endothelial dysfunction could be modified, it appeared that the prognosis could be improved by appropriate management. A strong association was found between body mass index (BMI) and metabolic status, but only the metabolic syndrome was associated with CAD. Physical activity was independently associated with fewer risk factors, less CAD, and fewer adverse events in women; however, obesity was not associated with these outcomes.Conclusions: Results of the identified studies suggest that reduction of risk factors is a common approach to fighting heart disease in both sexes. It appears that for women, weight and BMI are not as important as previously thought, but physical exercise and fitness are very important and can change risk factors and clinical outcomes more than any other known intervention. Data suggest that global inflammation may play an important role in women and may predict cardiovascular outcome in women much better than the traditional risk factors that have been used and proved for men.     

Of mice and (Viking?) men: phylogeography of British and Irish house mice

The west European subspecies of house mouse (Mus musculus domesticus) has gained much of its current widespread distribution through commensalism with humans. This means that the phylogeography of M. m. domesticus should reflect patterns of human movements. We studied restriction fragment length polymorphism (RFLP) and DNA sequence variations in mouse mitochondrial (mt) DNA throughout the British Isles (328 mice from 105 localities, including previously published data). There is a major mtDNA lineage revealed by both RFLP and sequence analyses, which is restricted to the northern and western peripheries of the British Isles, and also occurs in Norway. This distribution of the 'Orkney' lineage fits well with the sphere of influence of the Norwegian Vikings and was probably generated through inadvertent transport by them. To form viable populations, house mice would have required large human settlements such as the Norwegian Vikings founded. The other parts of the British Isles (essentially most of mainland Britain) are characterized by house mice with different mtDNA sequences, some of which are also found in Germany, and which probably reflect both Iron Age movements of people and mice and earlier development of large human settlements. MtDNA studies on house mice have the potential to reveal novel aspects of human history.     

Are gonadal steroids linked with orgasm perceptions and sexual assertiveness in women and men?

Past findings suggest links between orgasms and testosterone (T), as well as sexuality and estradiol (E), and we examined hormone–orgasm links in this study via two hypotheses (below). Participants were 86 women and 91 men who provided a saliva sample and completed a demographics questionnaire, the Orgasm Checklist (Mah and Binik, 2002), the Hurlbert (1991) Index of Sexual Assertiveness, and the Sexual Desire Inventory (Spector and Fremeth, 1996). Results supported the first hypothesis of correlations between T and positive orgasm experience in women, specifically with the relaxation, soothing, and peaceful items in both partnered and solitary orgasm contexts. Results also indicated correlations between E and flooding and spreading items in a solitary orgasm context. There were no associations between hormones and men's perceptions of their orgasm experiences. There was no support for the second hypothesis of associations between higher T and more sexual assertiveness. Post hoc analyses showed associations between E and women's sexual desire, and T and men's sexual desire. We discuss implications of these findings including that solitary vs. partnered orgasm experiences may differ, and suggest that T might be associated with perceptions of psychological experiences of orgasms, and E might be associated with perceptions of physical experiences of orgasms.     

Age-Dependent changes of mineral contents in men and women’s calcanei

To elucidate age-related change of mineral contents in human bones, the mineral content and density of human calcanei were determined by inductively coupled plasma atomic emission spectrometry and dual-energy X-ray absorptiometry. Calcanei were removed from 27 subjects (17 men and 10 women) who died in the age range from 40–98 yr old. Both the inductively coupled plasma emission spectrometry and dual-energy X-ray absorptiometry indicated that there were agedependent decreases of the mineral contents and density in the men’s calcaneus in the age range from 40–98 yr, but not in the women’s calcaneus in the age range from 42–87 yr. It was also found that the calcanean masses of the men and women remained constant within the same age range until 98 yr.     

Does adipose tissue influence bioelectric impedance in obese men and women?

Baumgartner, Richard N., Robert Ross, and Steven B. Heymsfield. Does adipose tissue influence bioelectric impedance inobese men and women? J. Appl. Physiol.84(1): 257-262, 1998.Bioelectric-impedance analysisoverestimates fat-free mass in obese people. No clear hypotheses havebeen presented or tested that explain this effect. This study testedthe hypothesis that adipose tissue affects measurements of resistanceby using data for whole body and body segment resistance and by using muscle, adipose tissue, and bone volumesfrom magnetic resonance imaging for 86 overweight and obese men andwomen (body mass index >27kg/m²; age 38.5 ± 10.2 yr). Inmultiple-regression analysis, muscle volumes had strong associationswith resistance, confirming that the electric currents are conductedprimarily in the lean soft tissues. Subcutaneous adipose tissue had aslight but statistically significant effect in women, primarily for theleg, suggesting that adipose tissue can affect measured resistance whenthe volume of adipose tissue is greater than muscle volume, as mayoccur in obese women in particular. This resulted in aslight overestimation of fat-free mass (e.g., +3 kg) when abioelectric- impedance-analysis equation calibrated for nonobese femalesubjects was applied.

     

Why do men seek status? Fitness payoffs to dominance and prestige

In many human societies, high male social status associates with higher fertility, but the means by which status increases lifetime fitness have not been systematically investigated. We analyse the pathways by which male status begets reproductive success in a small-scale, Amerindian society. Men who are more likely to win a dyadic physical confrontation, i.e. dominant men, have higher intra-marital fertility for their age, and men with more community-wide influence, i.e. prestigious men, exhibit both higher intra-marital fertility and lower offspring mortality. Both forms of status elicit support from allies and deference from competitors, but high status men are not provisioned more than their peers. Prestigious but not dominant men marry wives who first give birth at earlier ages, which multivariate analysis suggests is the strongest pathway between status and fitness in this population. Furthermore, men are motivated to pursue status because of fitness gains both within and outside of marital unions: dominant and prestigious men have more in-pair surviving offspring as well as more extra-marital affairs.     

Mate choice trade-offs and women’s preference for physically attractive men

Researchers studying human sexuality have repeatedly concluded that men place more emphasis on the physical attractiveness of potential mates than women do, particularly in long-term sexual relationships. Evolutionary theorists have suggested that this is the case because male mate value (the total value of the characteristics that an individual possesses in terms of the potential contribution to his or her mate’s reproductive success) is better predicted by social status and economic resources, whereas women’s mate value hinges on signals conveyed by their physical appearance. This pattern may imply that women trade off attractiveness for resources in mate choice. Here I test whether a trade-off between resources and attractiveness seems to be occurring in the mate choice decisions of women in the United States. In addition, the possibility that the risk of mate desertion drives women to choose less attractive men as long-term mates is tested. The results were that women rated physically attractive men as more likely to cheat or desert a long-term relationship, whereas men did not consider attractive women to be more likely to cheat. However, women showed no aversion to the idea of forming long-term relationships with attractive men. Evidence for a trade-off between resources and attractiveness was found for women, who traded off attractiveness, but not other traits, for resources. The potential meaning of these findings, as well as how they relate to broader issues in the study of sex differences in the evolution of human mate choice for physical traits, is discussed.     

Facial attractiveness signals different aspects of “quality” in women and men

We explored the relationships between facial attractiveness and several variables thought to be related to genotypic and phenotypic quality in humans (namely fluctuating asymmetry (FA), body mass index (BMI), health, age). To help resolve some controversy around previous studies, we used consistent measurement and statistical methods and relatively large samples of both female (n=94) and male (n=95) subjects (to be evaluated and measured), and female (n=226) and male (n=153) viewers (to rate attractiveness). We measured the asymmetry of 22 traits from three trait families (eight facial, nine body and five fingerprint traits) and constructed composite asymmetry indices of traits showing significant repeatability. Facial attractiveness was negatively related to an overall asymmetry index in both females and males, with almost identical slopes. Female facial attractiveness was best predicted by BMI and past health problems, whereas male facial attractiveness was best predicted by the socioeconomic status (SES) of their rearing environment. Composite FA indices accounted for a small (<4%) but usually significant percentage of the variation in facial attractiveness in both sexes, when factors related to asymmetry were controlled statistically. We conclude that, although facial attractiveness is negatively related to developmental instability (as measured by asymmetry), attractiveness also signals different aspects of “quality” in the two sexes, independent of FA.     

Steroid sulfatase activities in normal and cirrhotic livers and plasma levels of estrone sulfate,estrone and estradiol-17β in men

Estrone and dehydroepiandrosterone (DHEA) sulfatases were studied in livers of normal and cirrhotic men. Their Km were 3.2μM and 1.2μM respectively. The musomal sulfatases were solubilized by Miranol H2M and ultrasound. After gel filtration, the soluble material gave a single peak of activity for both substrates with a molecular weight of approximately 330,000. In terms of pmol of product.min^?1 per mg of fresh tissue, the mean (±SD) values of estrone and DHEA sulfatase activities were lower in cirrhotic livers [(n=7) (4.09±2.90 and 0.38±0.20)] than in normal livers [(n=13)(8.29±4.00 and 0.69±0.20)]. The differences were statistically significant: p<0.03 for estrone sulfatase and p<0.01 for DHEA sulfatase. In cirrhotic men, the mean level of plasma estrone is increased whereas that of estrone sulfate is decreased. The variations may be related to the decrease of serum albumin in cirrhotic subjects.     

Of lice and men: The return of the ’comparative parasitology‘ debate

The question of whether or not parasite phylogeny provides information about host relationships (‘comparative parasitology’) reached a peak in 1957 in a vigorous debate between Gunther Timmermann and Ernst Mayr. Timmermann argued that parasites were associated with their hosts by descent and that this produced congruent host and parasite phylogenies. In contrast, Mayr argued that parasites were often associated by colonization and that this led to incongruence between host and parasite phylogenies. To test these differing views. Adrian Paterson, Russell Gray and Graham Wallis derived a procellaniform phylogeny. This tree is here compared with Timmermann's tree based on the relationships of feather lice. Timmermann's tree is more similar to the seabird phylogeny than would be expected by chance. Thus, support is found for the ‘comparative parasitology’ approach.     

Improved survival in both men and women with diabetes between 1980 and 2004 – a cohort study in Sweden

Background

In Sweden, diabetes prevalence is increasing in spite of unchanged incidence, indicating improved survival. In recent US studies mortality in diabetic subjects has decreased over three decades, but only in men. Our aim was to study mortality over time in diabetic subjects.

Methods

The annual Swedish Living Conditions Survey from 1980 to 2004 has been record-linked to the Cause of Death Register in order to study trends in mortality risk for those reporting diabetes as a chronic illness. Survival and the relative mortality risk within 5 years of follow-up have been calculated for a random sample of men and women aged 40–84 years with (n = 3,589) and without diabetes (n = 85,685) for the period 1980 to 2004. Poisson regression models were used.

Results

The age-adjusted mortality risk relative to non-diabetics within 5 years of follow-up for men was doubled during all periods. The relative risk for women was initially about 2.5, with a substantial drop in mortality in 1995–1999 to 1.45 although it increased to 1.90 in the last period. Using models that took into consideration the presence of heart disease, hypertension, daily smoking, and socio-economic status at the initial interview did not change the relative mortality risk. The age-adjusted 10-year observed survival rate for men with diabetes increased from 41.4% 1980–1984 to 51.5% in 1995–1999. The observed survival for women increased from 43.7% to 61.0%.

Conclusion

Survival rates have improved in subjects with diabetes since the early 1980s, more so in women than in men, thereby decreasing the gap to non-diabetic women.

     

Relative digit lengths predict men’s behavior and attractiveness during social interactions with women

Recent evidence suggests that the ratio of the lengths of the second and fourth fingers (2D:4D) may reflect degree of prenatal androgen exposure in humans. In the present study, we tested the hypotheses that 2D:4D would be associated with ratings of men’s attractiveness and with levels of behavioral displays during social interactions with potential mates. Our results confirm that male 2D:4D was significantly negatively correlated with women’s ratings of men’s physical attractiveness and levels of courtship-like behavior during a brief conversation. These findings provide novel evidence for the organizational effects of hormones on human male attractiveness and social behavior. This work was supported by a Hind’s Fund Research Grant from the Committee on Evolutionary Biology at the University of Chicago to J.R.R. and by NIH grants R01-MH62577 and K02-MH63097 to D.M. James Roney, Ph.D., is now an assistant professor of psychology at the University of California, Santa Barbara. His research interests are in human evolutionary psychology and behavioral endocrinology. Dario Maestripieri, Ph.D., is an associate professor of Human Development at the University of Chicago. He has broad research interests in behavior, development, and evolution.