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Costs and benefits of fat-free muscle mass in men: Relationship to mating success, dietary requirements, and native immunity
Abstract
On average, men have 61% more muscle mass than women (d=3), a sex difference which is developmentally related to their much higher levels of testosterone. Potential benefits of greater male muscle mass include increased mating opportunities, while potential costs include increased dietary requirements and decreased immune function. Using data on males aged 18–59 years from the third National Health and Nutrition Examination Survey and including other relevant variables, fat-free mass (FFM) and/or limb muscle volume (LMV) are significant predictors of the numbers of total and past-year self-reported sex partners, as well as age at first intercourse. On the cost side, FFM and LMV are strong positive predictors of daily energy intake and strong negative predictors of C-reactive protein and white blood cell count, measures of native immunity.
... Dimorphic traits are either exaggerated or are present in only one sex, and they are typically referred to as masculine in males and feminine in females. Human physical dimorphism is seen in the facial structure (Samal et al., 2007), in body size/shape (Hughes & Gallup Jr, 2003;Plavcan, 2001;Wells, 2007), in physical strength (Lassek & Gaulin, 2009), in the amount of and distribution of muscle and fat mass (Lassek & Gaulin, 2009;Wells, 2007), in voice pitch (Puts et al., 2012), in second to fourth finger length ratios (Manning, 2002), and in the growth of facial and body hair (Dixson et al., 2005). Relative to dimorphism in the body, it is dimorphism in the facial structure that has garnered the most scholarly attention to date. ...
... Dimorphic traits are either exaggerated or are present in only one sex, and they are typically referred to as masculine in males and feminine in females. Human physical dimorphism is seen in the facial structure (Samal et al., 2007), in body size/shape (Hughes & Gallup Jr, 2003;Plavcan, 2001;Wells, 2007), in physical strength (Lassek & Gaulin, 2009), in the amount of and distribution of muscle and fat mass (Lassek & Gaulin, 2009;Wells, 2007), in voice pitch (Puts et al., 2012), in second to fourth finger length ratios (Manning, 2002), and in the growth of facial and body hair (Dixson et al., 2005). Relative to dimorphism in the body, it is dimorphism in the facial structure that has garnered the most scholarly attention to date. ...
... Our species seems to have all the hallmarks of an evolutionary history of males fighting for mates. For example, men have, on average, 60% more muscle mass than women, even 75% more in the upper body, and these differences in musculature translate into significant differences in strength between the sexes [102]. Men, especially young men, have a strong tendency towards physical competition, partially sublimated in sport. ...
Background: This paper explores the evolutionary origins of human mating behavior. By reviewing the behavior of other primates and our ancestors, we try to hypothesize how human mating behavior has evolved into contemporary patterns. Purpose: We observe growing concern about couple relationships and acts of gender-oriented harassment and violence. As psychoanalysts, our patients frequently express anguish and confusion about their sentimental life. We also encounter cases of intra-couple violence and related emotional suffering. Understanding the evolutionary contribution to our behaviors and impulses can help address some of these issues. Methods: We analyze current knowledge on the origins of our species to argue whether human ancestors were high- or low-competition species. We then hypothesize about the evolution of human mating behavior in relation to the introduction of bipedalism and the growth of cranial volume. We interpret contemporary human mating behaviors in light of our phylogenesis. We also present a mathematical approach to mating in an attempt to forge an objective approach to these highly sensitive arguments. Results: We propose that the transition to bipedalism caused humans to evolve rapidly from a medium-competition to a low-competition species due to the immaturity of their newborns. We posit that since this evolution occurred over a relatively short period on an evolutionary scale, it left vestiges of our medium-competition past in our collective subconscious. We conjecture that this understanding may shed some light on the issues we witness in couple relationships, contributing to their interpretation. From the psychoanalytic standpoint, this offers an intriguing perspective on addressing problematic attitudes and the resulting suffering at the personal and social levels.
... Although speculative, self-perceived attractiveness may provide an index of organization effects given that many of the secondary sexual characteristics, on which men's self-perceived attractiveness are based (Lukaszewski et al., 2014;Sneade and Furnham, 2016;Kanavakis et al., 2021), are developmentally driven by androgens (e.g., muscularity and facial masculinity; Lassek and Gaulin, 2009;Whitehouse et al., 2015;Hodges-Simeon et al., 2016). ...
The sexual misperception bias is a cognitive bias in which men tend to overestimate sexual interest from women, potentially shaped by evolutionary mating strategies. Testosterone, often linked to mating behaviors, might play a role in sustaining sexual overperceptions. To explore this possibility, we conducted a placebo-controlled study with 190 heterosexual men, administering either 11 mg of testosterone or a placebo. Participants interacted with an attractive female confederate, while naïve raters assessed the confederate’s affiliative behaviors. Our findings suggest that exogenous testosterone did not broadly impact sexual overperception. However, we found that affiliative behavior from the confederate was positively correlated with perceived sexual interest among testosterone-treated, but not placebo-treated men. In addition, we found that this effect among testosterone-treated men was contingent on their self-perceived attractiveness. Specifically, the confederate’s affiliative behaviors were positively correlated with perceived sexual interest, but only for testosterone-treated men with average or above average self-perceived attractiveness. Furthermore, our data revealed that men’s tendency to project their own short-term and long-term mating interests increases as a function of self-perceived attractiveness, and this coupling is enhanced by testosterone for long-term interest. Taken together, these results suggest that testosterone may potentiate existing biases, particularly when sexual motivation is high, and bias perceptions of friendly behavior when engaging in cross-sex mindreading. This study adds to the understanding of the neuroendocrine bases of social cognition, suggesting that testosterone can affect men’s perceptions of potential mates.
... Previous studies revealed significant differences between male and female scapulae (Maranho et al., 2022;Scholtz et al., 2010;Zdilla & Guzmán-López, 2023), potentially supporting the role of sexual selection in human shoulder evolution (Puts, 2010). Sexual selection on fighting performance in male-male competition is thought to have contributed to why, on average, males have more upper body muscle mass than females (Lassek & Gaulin, 2009;Morris, Link, et al., 2019). This sexual dimorphism in muscle mass may correspond to differences in skeletal shape (Morris, Cunningham, et al., 2019). ...
Scapula shape is highly variable across humans and appears to be sexually dimorphic—differing significantly between biological males and females. However, previous investigations of sexual dimorphism in scapula shape have not considered the effects of allometry (the relationship between size and shape). Disentangling allometry from sexual dimorphism is necessary because apparent sex‐based differences in shape could be due to inherent differences in body size. This study aimed to investigate sexual dimorphism in scapula shape and examine the role of allometry in sex‐based variation. We used three‐dimensional geometric morphometrics with Procrustes ANOVA to quantify scapula shape variation associated with sex and size in 125 scapulae. Scapula shape significantly differed between males and females, and males tended to have larger scapulae than females for the same body height. We found that males and females exhibited distinct allometric relationships, and sexually dimorphic shape changes did not align with male‐ or female‐specific allometry. A secondary test revealed that sexual dimorphism in scapula shape persisted between males and females of similar body heights. Overall, our findings indicate that there are sex‐based differences in scapula shape that cannot be attributed to size‐shape relationships. Our results shed light on the potential role of sexual selection in human shoulder evolution, present new hypotheses for biomechanical differences in shoulder function between sexes, and identify relevant traits for improving sex classification accuracy in forensic analyses.
... 32,33 This decline is less pronounced in males, whose reproductive physiology imposes lower and more stable energetic costs. 34,35 Finally, in older adulthood, the pressure to conserve energy may decrease due to differences in reproductive and survival strategies, 36,37 thereby allowing more energy to be spent in PA at this stage (albeit within age-related functional limitations). For example, evidence from Hadza hunter-gatherers suggests that post-reproductive females engage in approximately 20% more foraging activities than younger mothers, spending additional time on tasks such as food preparation, digging, walking, and carrying. ...
To expand TEMPA, in this paper, we first aimed to clarify 2 fundamental phenomena: (a) the permanent evolutionary drive to conserve energy, which is juxtaposed with (b) seemingly contradictory examples showing that some individuals have a natural urge to move more, especially children. We then highlighted how the strength of these general tendencies could evolve across the lifespan and as a function of biological sex. Finally, we elucidate the key roles of executive function and affective experiences in overcoming the drive to minimize physical effort and promoting engagement in PA, and how these roles may vary across the lifespan and sex.
... Sexual selection on men's intrasexual competitive abilities most likely resulted in sex differences in stature, body mass, and muscular development, akin to differences in apes such as gorillas and chimpanzees. Though mean differences in stature (~8% taller) and body mass (~15-20%) are modest, differences in lean body mass (40%), lean muscle mass (60%), and arm muscle mass (80%), resulting in roughly double the upper-body strength, are substantial (e.g., Lassek & Gaulin, 2009;Puts, 2010). Testosterone, which naturally circulates in men close to 20 times higher than in women (ratio of medians at age 20; Senefeld et al., 2020), affects allocation of energy to muscular development (e.g., Ellison, 2003). ...
... Consistent with the proposal that dominance is a more male-typical route to status, human males are, on average, more dominant than females: they are physically larger and stronger (Lassek & Gaulin, 2009), and more physically aggressive-sex differences among humans in physically aggressive competitions show up as early as nursery school Lee et al., 2007), and among adults there are dramatic sex differences in proneness to aggressive and violent competitiveness, ranging from assault to homicide (Archer, 2019). ...
Why are women underrepresented in positions of leadership? According to the “think manager-think male” model, leaders are stereotyped as male—and, in turn, as dominant—and this stereotype translates into preferences. However, status and leadership can be attained not only by dominance but also by prestige—a less sex-typed pathway. Five studies explored the relationship between leader stereotypes and preferences. University students spontaneously imagined both dominant and prestigious leaders as men (Study 1A, N = 148)—and this generalized across occupational domains (Study 1B, N = 220). However, they preferred women and prestigious leaders over men and dominant leaders. Study 2 (N = 2692) found this preference for female over male leaders using a large nationally representative U.S. sample from the Pew American Trends Panel. Study 3 (N = 461) experimentally replicated the preference for prestigious female over dominant male leader candidates among university students. In Study 4, (N = 952) online MTurk participants judged politicians from face photographs and again showed a preference for women, which may have partially been due to the inference that women are more likely to use prestige- over dominance-based leadership strategies. Collectively, findings suggest that the belief that people prefer “alpha male” leaders, which might discourage women from pursuing leadership roles and others from nominating them, needs to be updated.
... Women's preference for men's masculine upper body is attributed to the association of such body morphs with high quality genes (Sell et al., 2017), immunocompetence, as well as resource acquisition abilities Gallup & Frederick, 2010). A strong body type may reflect disease resistance and genetic quality given the energetic demands (i.e., dietary energy, testosterone) needed in displaying and maintaining muscularity (Lassek & Gaulin, 2009;Sell et al., 2017). Variations in SHR affect both early and late stages of visual processing, impacting posterior brain regions involved in perceiving body form and attractiveness, as well as frontal areas linked to judgment and decision-making (Pazhoohi et al., 2023a). ...
Objectives
Body size and shape are sexually dimorphic in humans, with men being characterized with larger upper bodies, while women typically having broader pelvises. Such sexually dimorphic traits, quantified as shoulder to hip ratio (SHR) in men and waist to hip ratio (WHR) in women, serve as cues of an individual’s genetic fitness, reproductive potential, health, and resource holding power, and, thereby, functioning as attractiveness cues to the opposite sex.
Methods
In the current study, we investigated men’s and women’s preference for the opposite sex body shape (WHR in women and SHR in men) in samples from Iran, Norway, Poland, and Russia. Women rated their preference for men’s SHR (1.20 to 1.50) and men rated their preference for women’s WHR (0.55 − 0.85).
Results and Conclusion
Our results showed that Iranian and Norwegian men preferred less feminine WHRs in women compared to Polish and Russian men. Moreover, Iranian women preferred less masculine SHRs in men than women from other countries. Altogether, the current research showed that there are variations in men’s preferences for women’s WHR and women’s preferences for men’s SHR among these countries.
... Consistent with the proposal that dominance is a more male-typical route to status, human males are, on average, more dominant than females: they are physically larger and stronger (Lassek & Gaulin, 2009), and more physically aggressive-sex differences among humans in physically aggressive competitions show up as early as nursery school Lee et al., 2007), and among adults there are dramatic sex differences in proneness to aggressive and violent competitiveness, ranging from assault to homicide (Archer, 2019). ...
Why are women underrepresented in positions of leadership? According to the “think manager-think male” model, leaders are stereotyped as male—and, in turn, as dominant—and this stereotype translates into preferences. However, status and leadership can be attained not only by dominance but also by prestige—a less sex-typed pathway. Five studies explored the relationship between leader stereotypes and preferences. University students spontaneously imagined both dominant and prestigious leaders as men (Study 1A, N = 148)—and this generalized across occupational domains (Study 1B, N = 220). However, they preferred women and prestigious leaders over men and dominant leaders. Study 2 (N = 2,692) found this preference for female over male leaders using a large nationally representative U.S. sample from the Pew American Trends Panel. Study 3 (N = 461) experimentally replicated the preference for prestigious female over dominant male leader candidates among university students. In Study 4, (N = 952) online MTurk participants judged politicians from face photographs and again showed a preference for women, which may have partially been due to the inference that women are more likely to use prestige- over dominance-based leadership strategies. Collectively, findings suggest that the belief that people prefer “alpha male” leaders, which might discourage women from pursuing leadership roles and others from nominating them, needs to be updated.
... Turning to predictions 1 and 2, the evidence for these is mixed (please note that cited literature here is not exhaustive). Testosterone has variously been found to be positively, negatively, and not at all linked with immunity/health in men (e.g., Booth et al., 1999;Furman et al., 2014;Gettler et al., 2014;Granger et al., 2000;Lassek & Gaulin, 2009;Nowak et al., 2018;Pátková et al., 2022;Rantala et al., 2012;van Anders, 2010)sometimes even showing conflicting associations within the same study. Furthermore, a metaanalysis published in 2021 showed no increased risk of cardiovascular disease or increased mortality in men with high testosterone levels (Marriott et al., 2021). ...
... Thus, there are both weight and lean muscle mass estimates in Fig. 7 for humans. When only considering the latter, the sex difference in modern humans is much larger than might be inferred by differences in weight and as large as the sexual dimorphism found in several of our ancestors (Lassek and Gaulin, 2009). The sex difference in lean muscle mass is especially pronounced in the upper body (Kim et al., 2006), which along with differences in shoulder and arm skeletal structure are consistent with the use of projectile (thrown stones) and blunt-force (clubs) weapons. ...
... Although minimal sex differences in mass (under 20%) might suggest subdued male contest competition throughout human evolution (Fuentes, 2021), the uniquely large fat stores in human females-uncommon among primates-deserve consideration, especially as they likely don't contribute to physical contests as effectively as muscle and lean mass do (Puts et al., 2023). Notably, human males showcase approximately 33% more lean mass and possess 61% and 75% more total and upper-body muscle mass than females (Abe et al., 2003;Lassek & Gaulin, 2009). Such disparities seem to align more with human skeletal dimorphism, which even surpasses that of chimpanzees (Pan troglodytes) -a species known for their aggressive male dominance contests within groups (Plavcan, 2012). ...
Evolutionary changes and interspecific diversity in sexual coercion and autonomy are often linked to indirect selection on mate preferences. Yet, this approach overlooks the small fraction of indirect selection in total selection on mate choice and assumes unnecessarily specific conditions in the recent ‘autonomy-enhancing’ risk-reduction model. This paper proposes a more parsimonious approach based on direct selection and basic signalling theory, incorporating ecological variables to better explain sexual biodiversity. Particularly, the spatial dimensionality of mating environments is emphasized for its role in enhancing sexual freedom through both diminishing monopolization and elevating escape potential from sexual coercion. Empirical evidence, ranging from waterfowl to humans, seems to better align with this ecologically constrained signalling perspective. Furthermore, it suggests that choosers keep coercion risk at ecological baseline by leveraging their escape potential. This repositions intriguing protective elements like bowerbirds' constructions as courtship features that have been bargained to respect sexual autonomy rather than enhancing it through indirect selection. It implies that courtship induced risks, such as reduced mobility, may in principle increase substantially precisely because they are offset by protective measures. Future research could reveal the prevalence of such risk-balancing strategies, advancing our understanding of mating dynamics. This work suggests new theoretical and empirical research avenues within the ecology of mating dynamics.
... With regards the albeit rather limited presence of GMV, we can test the hypothesis that it is exhibited in male sexually selected traits (due to high genetic variance), by investigating whether the traits considered most obviously to contribute to male reproductive success in the available dataset tend to be those (relatively few) that exhibit GMV. Lean muscle mass is a particularly interesting trait to consider in this regard, as greater muscle mass is purported to promote mating opportunities [46]. The traits associated with muscle (total lean mass, leg lean mass, and serum creatinine which positively associates with muscle mass) do not indicate GMV. ...
Many researchers presume greater variability between female participants than between males due to the menstrual cycle. This view has encouraged a sex bias in health and medical research, resulting in considerable knowledge gaps with important clinical implications. Yet in another field-evolutionary biology-the received wisdom is the reverse: that men are more variable, possibly due to male heterogamety. To test these competing hypotheses, we compared variance between the sexes for 50 morphological and physiological traits, analysing data from the NHANES database. Nearly half the traits did not exhibit sexual dimorphism in variation, while 18 exhibited greater female variation (GFV), indicating GFV does not dominate human characteristics. Only eight traits exhibited greater male variation (GMV), indicating GMV also does not dominate, and in turn offering scant support for the heterogamety hypothesis. When our analysis was filtered to include only women with regular menstrual cycles (and men of equivalent age), the number of traits with GFV and GMV were low and not statistically different, suggesting that the menstrual cycle does not typically explain GFV when it occurs. In practical terms, health and medical researchers should no longer simply assume that female participants will induce additional variation in the traits of interest.
... Strength is often closely connected to men's bodily attractiveness (Lidborg, Cross, & Boothroyd, 2022;Sell, Lukazsweski, and Townsley, 2017), as is muscularity (Frederick and Haselton, 2007). Fat-free muscle mass has been linked to having more sex partners (Lassek and Gaulin, 2009). However, when all types of activities aimed at increasing one's beauty were considered here, it was still women who spent more time daily enhancing their appearance compared to men, which confirms the first hypothesis. ...
People across the world and throughout history have gone to great lengths to enhance their physical appearance. Evolutionary psychologists and ethologists have largely attempted to explain this phenomenon via mating preferences and strategies. Here, we test one of the most popular evolutionary hypotheses for beauty-enhancing behaviors, drawn from mating market and parasite stress perspectives, in a large cross-cultural sample. We also test hypotheses drawn from other influential and non-mutually exclusive theoretical frameworks, from biosocial role theory to a cultural media perspective. Survey data from 93,158 human participants across 93 countries provide evidence that behaviors such as applying makeup or using other cosmetics, hair grooming, clothing style, caring for body hygiene, and exercising or following a specific diet for the specific purpose of improving ones physical attractiveness, are universal. Indeed, 99% of participants reported spending >10 min a day performing beauty-enhancing behaviors. The results largely support evolutionary hypotheses: more time was spent enhancing beauty by women (almost 4 h a day, on average) than by men (3.6 h a day), by the youngest participants (and contrary to predictions, also the oldest), by those with a relatively more severe history of infectious diseases, and by participants currently dating compared to those in established relationships. The strongest predictor of attractiveness-enhancing behaviors was social media usage. Other predictors, in order of effect size, included adhering to traditional gender roles, residing in countries with less gender equality, considering oneself as highly attractive or, conversely, highly unattractive, TV watching time, higher socioeconomic status, right-wing political beliefs, a lower level of education, and personal individualistic attitudes. This study provides novel insight into universal beauty-enhancing behaviors by unifying evolutionary theory with several other complementary perspectives.
... Given the relative dearth of evidence linking interindividual aggression rates and testosterone in male primates, behavioural and physiological traits other than aggression plausibly link dominance rank to testosterone. For instance, elevated muscle mass is an especially important somatic investment for adult male primates, a prioritization of mating effort (Bribiescas, 2001) that largely determines success in physical competition (Lassek & Gaulin, 2009;Mitani et al., 1996). Notably, body size and mass have been found to predict male dominance rank in some primates (bearded capuchins, Sapajus libidinosus: Fragaszy et al., 2016;mountain gorillas, Gorilla beringei beringei: Wright et al., 2019;rhesus macaques, Macaca mulatta: Bercovitch & Nürnberg, 1996; southern pig-tailed macaque, Macaca nemestrina: Tokuda & Jensen, 1969) and in many other vertebrates (brown trout, Salmo trutta: Jacob et al., 2007; yellow-bellied marmots, Marmota flaviventris: Huang et al., 2011;Asian elephants, Elephas maximus: Chelliah & Sukumar, 2013). ...
Testosterone promotes mating effort, which involves intraspecific aggression for males of many species. Therefore, males with higher testosterone levels are often thought to be more aggressive. For mammals living in multimale groups, aggression is hypothesized to link male social status (i.e. dominance rank) and testosterone levels, given that high status predicts mating success and is acquired partly through
aggressive intragroup competition. In male chimpanzees, Pan troglodytes, dominance rank has been repeatedly linked to interindividual variation in testosterone levels, but evidence directly linking interindividual variation in testosterone and aggression is lacking. In the present study, we test both aggression levels and lean muscle mass, as measured by urinary creatinine, as links between dominance rank and testosterone levels in a large sample of wild male chimpanzees. Multivariate analyses indicated that dominance rank was positively associated with total rates of intragroup aggression, average urinary
testosterone levels and average urinary creatinine levels. Testosterone was positively associated with creatinine levels but negatively associated with total aggression rates. Furthermore, mediation analyses showed that testosterone levels facilitated an association between dominance rank and creatinine levels.
Our results indicate that (1) adult male chimpanzees with higher average testosterone levels are often higher ranking but not more aggressive than males with lower testosterone and (2) lean muscle mass links dominance rank and testosterone levels in Ngogo males. We assert that aggression rates are
insufficient to explain links between dominance rank and testosterone levels in male chimpanzees and that other social variables (e.g. male-male relationship quality) may regulate testosterone's links to aggression.
... Studies show that human males are 15 -20% heavier and 7-8% taller than females (Isen et al., 2014) but are 90% stronger in upper body. This difference can be explained by the fact that men have 61% more total muscle mass and 75% more arm muscle mass (see Lassek and Gaulin, 2009). ...
Handgrip strength is a quick way to assess overall muscle strength. Low handgrip strength is an indicator of poor health. While handgrip strength is related with mortality and morbidity, for some parameters, handgrip strength is even a stronger predictor of health than chronological age alone. Handgrip strength is highly sexually dimorphic and has a high heritability. It is thought that this is an outcome of sexual selection and intrasexual competition in our evolutionary history. Some anthropological studies confirm this view, and it is claimed that there are relationships between grip strength and aggression, athletic performance and attractiveness, especially in men. The aim of this study is to review the relationship of diseases with handgrip strength in anthropological perspective and examine the idea that handgrip strength being a marker of biological fitness.
The growing presence of women in the Norwegian state and military heralds an epoch-making, worldwide transformation. A key challenge is to explain why institutions which excluded women for more than a millennium no longer promote all-male membership. This tectonic shift is investigated with a data-based synthetical methodology. Multidisciplinary evidence going back five thousand years is combined with a graphical analysis of two centuries of time series data. The guiding theory is that historical pathways for cultural information flow have coevolutionary spatial and energetic sociodynamics. Accordingly, women’s exclusion from warfare and politics in agrarian-era Norway coevolved with three interconnected constraints: oral communication, dependence on musculoskeletal energy, and the spatial limitations of person-to-person contact. The contemporary relaxation of such constraints is investigated using two centuries of data culled from Norway’s statistical yearbooks. These data show that women’s entry into Norway’s national legislature, pushed by women’s organizations, roughly coevolved with literacy-based communication and education, industrial-era extrasomatic energy, and distance-closing motorization. Multidisciplinary evidence also indicates that women’s military and political careers were spatiotemporally handicapped by inflexible work hours and worksites far from childrearing locations. The Norwegian military prioritized physical endurance rather than the competencies that women would later bring to a 21st-century rapid reaction force. Today, with new information pathways forming, the digitalized knowledge economy is reversing the human-capital advantage of men compared to women. Instantaneous information exchange and high-tech energetics are reducing spatiotemporal barriers via remote work. Cross-disciplinary and time-series evidence suggest that these digital-age dynamics contribute to a more gender-neutral state and military.
Despite well-documented disparities disadvantaging women (e.g. discrepancies between men and women in salaries and leadership roles), we argue that there are contexts in which disparities disadvantage men. We review the literature suggesting harm to women is perceived as more severe and unacceptable than identical harm to men, a bias potentially rooted in evolutionary, base rate, stereotype-based and cultural shift explanations. We explore how these biases manifest in protective responses toward women and harsher judgements toward men, particularly in contexts of victimization and perpetration. Our review aims to complement the existing literature on gender biases by presenting a balanced view that acknowledges men and women face unique challenges. By understanding these biases, we hope to foster a more equitable discourse on gender and harm, encouraging empathy and validation of suffering irrespective of gender. This holistic approach aims to de-escalate gender-based conflicts and promote effective interventions for both men and women.
Most of the 7.1 million current global COVID deaths could likely have been prevented if the initial behavioral response in Wuhan, China had been different. Since the virus has spread globally, national death rates have varied from less than 1 to 660 deaths per 100,000. If all countries had responded like neighboring countries in Asia, half of global deaths could have been prevented. The United States with 1.2 million COVID deaths, 17% of the global total, has one of the highest COVID death rates, more than five times higher than expected from age, income, and temperature and more than six times the rate in Japan, which has more elderly. Five-year age-adjusted COVID death rates in US states vary from 66 to 410 per 100,000 in Non-Hispanic Whites, a six-fold difference. The state’s percentage of Trump votes in 2020 explains 51% of these differences, with death rates 69% higher in high vs low percentage states overall and 225% higher in 2021, the year with the most deaths. Residents of states with more Trump votes have been half as likely to be vaccinated and to practice social distancing. If the US had responded to COVID like Japan, almost a million American lives would have been saved. If all states had responded like the best Blue State, Hawaii, more than 900,000 lives would have been spared. In addition, using death certificate data, we estimate that the prevalence of Long COVID is 2.7 times higher in states with more vs less Trump votes (10.5±2.3% vs 3.8±1.2%). We discuss how three mental traits evolved through natural and sexual selection may help to explain such dysfunctional behavioral responses to life threatening danger: the tendency to form dominance hierarchies, rampant ingroup favoritism, and the often lethal combination of risk taking and overconfidence, especially in males.
Objective
Human sexual dimorphism in physical strength manifests itself in men having a greater muscle mass than women, reflecting ancestral roles in competition, protection, and provisioning. Prenatal testosterone exposure, approximated via the second‐to‐fourth digit ratio (2D:4D), is linked to increased muscular strength in both sexes, indicating a developmental influence. Previous research has shown that both physical strength and 2D:4D have facial shape correlates, especially in men, but most studies have focused on Western populations and one trait. We therefore hypothesized a broader relationship between facial shape and both physical strength and 2D:4D.
Materials and Methods
In this study, we quantified the association between facial shape, handgrip strength (HGS), and 2D:4D in a non‐Western Turkish sample (72 men, 55 women; Md = 22 y, SIR = 1.8 y) using two dimensional geometric morphometrics. Thirty‐eight somatometric and 32 semi‐landmarks were digitized on facial photographs taken in frontal view. Physical strength was assessed via handgrip strength (HGS), and the second digit length was divided by the fourth digit length to calculate 2D:4D.
Results
Both HGS and 2D:4D were significantly associated with shape in both sexes, but only in men did they explain a significant amount of facial variation. Thin‐plates spline deformation grids and geometric morphometric morphs visualized the facial shape changes related to variations in handgrip strength, 2D:4D, and sexual dimorphism, enabling trait comparisons.
Conclusion
This study contributes a comparative sample from the Middle East, which is indispensable to discern universalities from Western peculiarities. It provides evidence to better understand the biological basis of facial traits, which can potentially serve as increasingly relevant social cues in today's online and digital environments.
This book reevaluates Carl Jung’s ideas in the context of contemporary research in the evolutionary sciences.
Recent work in developmental biology, as well as experimental and psychedelic neuroscience, have provided empirical evidence that supports some of Jung’s central claims about the nature and evolution of consciousness. Beginning with a historical contextualisation of the genesis of Jung’s evolutionary thought and its roots in the work of the 19th century Naturphilosophen, the book then outlines a model of analytical psychology grounded in modern theories of brain development and life history theory. The book also explores research on evolved sex based differences and their relevance to Jung’s concept of the anima and animus.
Seeking to build bridges between analytical psychology and contemporary evolutionary studies and associated fields, this book will appeal to scholars of analytical and depth psychology, as well as researchers in the evolutionary and brain sciences.
Free preview chapter and full book for purchase at Routledge: https://www.routledge.com/Carl-Jung-and-the-Evolutionary-Sciences-A-New-Vision-for-Analytical-Psychology/Clark/p/book/9781032624518
Also available for purchase on Amazon.
Evolutionary changes and interspecific diversity in sexual coercion and autonomy are often linked to indirect selection on mate preferences. Yet, this approach overlooks the small fraction of indirect selection in total selection on mate choice and assumes unnecessarily specific conditions in the recent ‘autonomy-enhancing’ risk-reduction model. This paper proposes a more parsimonious approach based on direct selection and basic signalling theory, incorporating ecological variables to better explain sexual biodiversity. Particularly, the spatial dimensionality of mating environments is emphasized for its role in enhancing sexual freedom through both diminishing monopolization and elevating escape potential from sexual coercion. Empirical evidence, ranging from waterfowl to humans, seems to better align with this ecologically constrained signalling perspective. Furthermore, it suggests that choosers keep coercion risk at ecological baseline by leveraging their escape potential. This repositions intriguing protective elements like bowerbirds' constructions as courtship features that have been bargained to respect sexual autonomy rather than enhancing it through indirect selection. It implies that courtship induced risks, such as reduced mobility, may in principle increase substantially precisely because they are offset by protective measures. Future research could reveal the prevalence of such risk-balancing strategies, advancing our understanding of mating dynamics. This work suggests new theoretical and empirical research avenues within the ecology of mating dynamics.
The chapter explains how the concepts of physical and sexual attraction differ from each other. The materials of the chapter describe the ideas and research on beauty and physical attractiveness.
The chapter demonstrates how attractive physical appearance influences overall interpersonal attraction. Evolutionary, ecological, social, cultural, and psychological perspectives show that the values and notions of physical attractiveness depend on many of these contextual factors. The studies reviewed in the chapter have demonstrated variability in preferences for physical appearances across cultures.
The chapter presents research findings that reveal the effects of familiarity, imprinting, and exposure on the impressions of how physically attractive a person looks. The features of physical attractiveness are sexually polymorphic and differ between genders. The sections of this chapter provide an overview of the qualities of physical appearance that make a person attractive, as well as multisensory qualities of attractive appearance, including visual, auditory, tactile-kinesthetic, olfactory, and gustatory modalities of sensation and perception.
The chapter describes in detail how people experience and express physical and sexual attraction. The last section of the chapter presents varieties of sexual attraction in love that depend on sexual identities, sexual orientations, and factors influencing diversity in sexual attraction.
Introduction
In being an important lifestyle factor, the physical activity influences people's health status, including life expectancy. Specific forms of physical activity are exercises related to hand-to-hand combat in the broadest sense, often overlapping and containing similar elements associated with combat sports (for Western culture) and martial arts (for Far Eastern culture). There are many types of forms of practising hand-to-hand combat exercises, which can be seen as opposing or in some ways complementary, e.g.: “traditional”—e.g., karate or kung fu, practised for hundreds or even thousands of years, usually adhering to moral codes of conduct, and drawing ideas from philosophy, religion vs. “modern”—e.g., American pro wrestling or mixed martial arts—MMA, suggesting a combination of various traditional forms of martial arts. In terms of shaping a healthy lifestyle with mental health elements based on the implementation of hand-to-hand combat exercises, an analysis of these fundamental insights into physical activity is warranted. This study aims to investigate the development direction of the hand-to-hand exercises in Western culture, opposing the “traditional” and “modern” forms.
Discussion
In this study, INNOAGON theory responds to the overuse of the term “science of martial arts”. It is currently being used to promote extreme aggression and violence as an acceptable means of achieving success, and this model is expressively permeating other spheres of social interaction. In INNOAGON's understanding, hand-to-hand combat should be associated with the ancient thought of “doing good” (ancient Greece) or “wisdom” (Far Eastern cultures) including aesthetic and philosophical aspects. This links to numerous psychosocial benefits, self-esteem, discipline, body-mind coordination including breath control and relaxation, respect for others. The modern form of hand-to-hand combat, framed in these discussions as MMA or American pro wrestling, historically refers to the gladiatorial fights held during the Roman Games. The holding of fights in so-called “cages” refers to the arena in which Roman slave fights were held, and the athletes performing there are often referred to as modern-day “gladiators”.
Conclusion
Proper education, including education in the area of physical culture, leading to the development of a society turned towards values broader than just fun or self-satisfaction should be the basis for the development of the next generations. It actually remains to decide which path of social change we will choose: in the case of INNOAGON a positive one, and in the case of modern gladiator a destructive one. Only a proper education combined with a broad programme of social role modelling, social facilitation—the foundations of which are laid by INNOAGON—including promotion on the Internet and social media can provide the right counterbalance to the pathology increasingly penetrating our lives, leading to the promotion of aggression and threats to physical and mental health.
Scapular morphology is highly variable across the human population and appears to be sexually dimorphic - differing significantly between males and females. However, previous investigations of sexual dimorphism in scapula shape have not considered the effects of allometry (the relationship between size and shape). Disentangling allometry from sexual dimorphism is necessary because apparent sex-based differences in morphology could be due to inherent differences in body size. This study aimed to investigate sexual dimorphism in scapula shape and examine the role of allometry in sex-based variation. We used three-dimensional geometric morphometrics with Procrustes ANOVA to quantify scapula shape variation associated with sex and size in 125 scapulae. Scapular morphology significantly differed between males and females, and males tended to have larger scapulae than females for the same body height. We found that males and females exhibited distinct allometric relationships, and sexually dimorphic shape changes did not align with male- or female-specific allometry. A secondary test revealed that sexual dimorphism in scapula shape persisted between males and females of similar body heights. Overall, our findings indicate that sex-based differences in scapular shape are independent of size-shape relationships. Our results shed light on the potential role of sexual selection in human shoulder evolution, present new hypotheses for biomechanical differences in shoulder function between sexes, and identify relevant traits for improving sex classification accuracy in forensic analyses.
Background
Understanding differential strength capability between sexes is critical in ergonomics and task design. Variations in study designs and outcome measures generates challenges in establishing workplace guidelines for strength requirements to minimize upper extremity risk for workers. The purpose of this systematic review was to collate and summarize sex differences in strength at the shoulder across movement directions and contraction types.
Methods
A total of 3,294 articles were screened from four databases (Embase, Medline, SCOPUS, and Web of Science). Eligibility criteria included observational studies, direct measurement of muscular joint, and healthy adult participants (18–65 years old). Strength outcome measures were normalized to percentages of male outputs to allow comparisons across articles.
Results
A total of 63 studies were included within the final review. Majority of articles observed increased strength in males; the gap between male–female strength was greater in flexion and internal/external rotation, with females generating ~30% of male strength; scaption strength ratios were most consistent of the movement groups, with females generating 55–62% of male strength.
Conclusion
Sex strength differences should be considered as an important factor for workplace task design as women are more at risk for occupational-related injuries than men in equivalent strength requirements. Differences in strength were not synonymous across motions; females demonstrated increased disparity relative to male strength in horizontal flexion/extension, forward flexion and internal/external rotation. Some movements had an extremely limited pool of available studies for examination which identified critical research gaps within the literature. Collating and quantifying strength differences is critical for effective workstation design with a range of users to mitigate potential overexertion risk and musculoskeletal injury.
Women participate in hunting in some foraging societies but not in others. To examine the socioecological factors that are conducive to women’s hunting, we conducted an ethnographic survey using the Human Relations Area Files and other selected sources authored in the past 200 years. Based on life history theory and behavioural ecology, we predicted that women should engage in hunting when: i) it poses few conflicts with childcare, ii) it is associated with few cultural restrictions around the use of hunting technology, iii) it involves low-risk game within range of camp, with the aid of dogs, and/or in groups, and, iv) women fulfil key logistical or informational roles. We systematically reviewed ethnographic documents across 64 societies and coded 242 paragraphs for the above variables. The data largely support theoretical expectations. When women hunted, they did so in a fundamentally different manner than men, focusing on smaller game and hunting in larger groups near camp, often with the aid of dogs. There was little evidence to suggest that women only participated in hunting during non-reproductive years; instead, allocate networks were a prominent strategy for mitigating trade-offs between hunting and childcare responsibilities. Women commonly fulfilled crucial informational, logistical and ritualistic roles. Cultural restrictions limited women’s participation in hunting, but not to the extent commonly assumed. These data offer a cross-cultural framework for making inferences about whether and how women’s hunting occurred in the past.
Objectives:
The aim of our study was to compare morphometric patterns of facial sexual dimorphism with strength-face relationship in members of two distinct populations of European and Central Asian origin: Russians and Tuvans.
Methods:
Handgrip strength (HGS) measures and facial photographs were collected from Russian (n = 233) and Tuvan (n = 187) men and women. We digitized 70 landmarks and semilandmarks on full-face and 54 landmarks and semilandmarks on profile photos. This was done to capture variation in facial morphology. After that, we performed the shape regressions of landmarks' coordinates upon sex and HGS. Results were visualized in forms of thin-plate deformation grids and geometric morphometric morphs.
Results:
In both populations, HGS was associated significantly with male facial shape only. In Russian men, strength-related changes of facial shape were almost completely in direction of increase in male-typicality. This was especially evident for the relative lower facial width, which was higher in men compared to women, as well as in stronger men compared to weaker ones. On the contrary, in Tuvans the lower face was relatively narrower in men than in women. However, the facial shape of strong Tuvan men was also associated with relatively wider lower face. Our results indicate that the effect of strength on facial shape is relatively independent of facial sexual dimorphism.
Conclusions:
Our findings clearly demonstrate that physical strength is associated with the shape of the lower part of male faces even in populations with a mismatched direction of lower face sexual dimorphism.
In most social species, position in the male social hierarchy and reproductive success are positively correlated; in humans, however, this relationship is less clear, with studies of traditional societies yielding mixed results. In the most economically advanced human populations, the adaptiveness of status vanishes altogether; social status and fertility are uncorrelated. These findings have been interpreted to suggest that evolutionary principles may not be appropriate for the explanation of human behavior, especially in modern environments. The present study tests the adaptiveness of social status with actual mating and reproductive data in a representative sample of males from an industrial society. Reproductive success, even when assessed by a more reliable measure of actual male fertility than the one commonly used, fails to correlate with social status. In striking contrast, however, status is found to be highly correlated with potential fertility, as estimated from copulation frequency. Status thus accounts for as much as 62% of the variance in this proximate component of fitness. This pattern is remarkably similar to what is found in many traditional societies and would result in a substantial positive relationship between cultural and reproductive success in industrial populations were it not for the novel conditions imposed by contraception and monogamy. Various underlying mechanisms are suggested for these findings, illustrating the value of current behavioral and reproductive data in the study of adaptation. It is concluded that evolutionary explanations of human behavior remain entirely relevant in modern societies.
Human physical attractiveness appears to be an important signal of mate value that is utilized in mate choice We argue that performance-related physical fitness (PF) was an important facet of ancestral male mate value and, therefore, that a positive relationship exists between PF and physical attractiveness as well as mating success. We investigated these relationships in a sample of 80 young men. In line with our predictions, we found that (i) a composite measure of PF correlated substantially with body attractiveness (r=.43, after controlling for confounds) but not with facial attractiveness; (ii) PF was positively related to various measures of self-reported mating success (rS ≈ .22); (iii) the relationship between PF and self-reported mating success was partly mediated by body attractiveness. We conclude it is a key function of men's body attractiveness to signal their PF and that men's faces and bodies signal different facets of mate value.
Models of sexual selection typically assume a cost to the production and maintenance of sexually selected traits. However, within a population, individuals of high phenotypic quality may not only show greater expression of the trait but may also have higher survival rates. In such a case, the true cost of the trait may be difficult to detect. Comparative studies can circumvent some of the difficulties inherent in intraspecific studies. In this study, I used a comparative approach to examine the relation between sexual size dimorphism and adult mortality in natural populations of mammals. After controlling for the effects of phylogeny, I found that the degree of male-bias in adult mortality was positively correlated with the degree of sexual size dimorphism across taxa. This is the first comparative evidence for a cost of sexually selected traits in natural populations of mammals. In contrast to the general rule that mortality in mammals is male-biased, I also found that it is frequently female-biased in monogamous taxa of mammals. I suggest that in monogamous species the cost of reproduction to females will be similar to that of polygynous species. However, males of monogamous species will be spared the costs of male-male competition and dimorphic growth. This decrease in male costs relative to females may then lead to a female-bias in mortality.
According to current evolutionary theory, advertising traits that honestly indicate an organism's genetic quality might be costly to produce or maintain, though the kind of costs involved in this process are controversial. Recently the immunocompetence hypothesis has proposed that testosterone (T) stimulates the expression of male sexually selected traits while decreasing im- munocompetence. Even though some recent studies have shown an effect of T on ectoparasite load, the dual effect of the hormone has not been addressed in free-living populations. Here we report results of an experiment in a free-living population of the lizard Psammodromus algirus during the mating season. Males implanted with T had larger patches of breeding color and behaved more aggressively than control males. In T-implanted males, the increase in number of ticks during the mating season was significantly higher than in control males and this negatively affected several hematological parameters. T-males suffered significantly higher mortality than control males during the experiment The results from the manipulation of T are consistent with the dual effect of this hormone. Key words: parasites, Psammodromus algirus, secondary sexual characters, tes- tosterone. (BehavEcol 7:145-150 (1996))
We examined the hypothesis that increased aggression results in decreased survivorship. We tested this hypothesis by increasing aggression of free-living male lizards Sceloporus jarrovi with testosterone implants and evaluating the effects on survivorship. A previous study showed that testosterone-implanted males were more aggressive than controls, suggesting a greater degree of success in male-male competition. Results of the present study show that the same testosterone-implanted lizards experienced greater mortality. Testosterone-treated males were also seen more frequently and more conspicuous ones were less likely to survive. Testosterone-treated males lost more weight over the summer. In controls, survivorship was negatively correlated with the body weight index. These data suggest that conspicuousness and energetic demands interact in their influence on survivorship. Thus, the natural plasma level of testosterone may be at an optimal level balancing any potential selection pressures for a higher level of testosterone through sexual selection with selection pressures for a lower level through a decrease in survivorship.
It has been argued that females should be able to choose parasite-resistant mates on the basis of the quality of male secondary sexual characters and that such signals must be costly handicaps in order to evolve. To a large extent, handicap hypotheses have relied on energetic explanations for these costs. Here, we have presented a phenomenological model, operating on an intraspecific level, which views the cost of secondary sexual development from an endocrinological perspective. The primary androgenic hormone, testosterone, has a dualistic effect; it stimulates development of characteristics used in sexual selection while reducing immunocompetence. This "double-edged sword" creates a physiological trade-off that influences and is influenced by parasite burden. We propose a negative-feedback loop between signal intensity and parasite burden by suggesting that testosterone-dependent signal intensity is a plastic response. This response is modified in accordance with the competing demands of the potential costs of parasite infection versus that of increased reproductive success afforded by exaggerated signals. We clarify how this trade-off is intimately involved in the evolution of secondary sexual characteristics and how it may explain some of the equivocal empirical results that have surfaced in attempts to quantify parasite's effect on sexual selection.
Energy expenditure varies among people, independent of body size and composition, and persons with a "low" metabolic rate seem to be at higher risk of gaining weight. To assess the importance of skeletal muscle metabolism as a determinant of metabolic rate, 24-h energy expenditure, basal metabolic rate (BMR), and sleeping metabolic rate (SMR) were measured by indirect calorimetry in 14 subjects (7 males, 7 females; 30 +/- 6 yr [mean +/- SD]; 79.1 +/- 17.3 kg; 22 +/- 7% body fat), and compared to forearm oxygen uptake. Values of energy expenditure were adjusted for individual differences in fat-free mass, fat mass, age, and sex. Adjusted BMR and SMR, expressed as deviations from predicted values, correlated with forearm resting oxygen uptake (ml O2/liter forearm) (r = 0.72, P less than 0.005 and r = 0.53, P = 0.05, respectively). These findings suggest that differences in resting muscle metabolism account for part of the variance in metabolic rate among individuals and may play a role in the pathogenesis of obesity.
Sumario: The purposes of the present study were: (1) to determine the magnitude of the sex difference in upper and lower-body strenght in groups of men and women with similar physical activity backgrounds and (2) to determine the extent to which the sex difference in strenght is explained by differences in FFW and FFCSA. By deduction, the portion of the sex difference in strength not acounted for by FFW and FFCSA could be attributed to neuromuscular and/or other factors
This study examined possible gender differences for relative upper (elbow) to lower (knee) body strength and endurance, as well as relative flexion to extension strength and endurance. Seven women and nine men who were matched for both upper and lower body aerobic power were tested on an isokinetic strength instrument. Absolute isokinetic strength was lower (P<0-01) for the women than the men for all measurements. When strength was expressed per lean body weight, the women were weaker (P<005) only for elbow flexion strength. The women had a lower (P<005) upper to lower body strength ratio for flexion, but not for extension. There were also no differences (P>005) in isokinetic endurance fatigue decrements, or upper to lower body endurance ratios between genders. These data indicated that there were differences in absolute strength between the genders, but strength per lean body weight, as well as upper to lower body ratios for strength and endurance were similar for both genders. It was recommended that aerobic fitness and level of training be taken into account when strength and endurance were compared between the genders.
To date, there have been very few studies on the age dependence of maximal isometric muscle strength (MIMS) in healthy subjects aged 20-80 years, based upon measurements of a large number of functional muscle groups (FMGs). Using a hand-held pull gauge it is possible to measure MIMS of nearly every FMG. The objectives of this study were to obtain normative values for MIMS, to evaluate differences in MIMS in relation to gender and body side and to compare the age dependence of muscle strength between women and men. In a convenience sample of 290 healthy women (aged 20-82 years) and 253 men (aged 21-79 years), MIMS of 51 FMGs was measured. For each FMG the age dependence of MIMS was depicted, side and gender specific, as percentile curves and was analysed using linear quantile regression analysis. MIMS was found to be significantly higher in men than in women and higher on the right than on the left side. A biphasic model with linear equations for strength medians was derived for each gender. The age at transition from phase 1 to phase 2 was 55 years (SD 8) for women and 49 years (SD 13) for men. During phase 1, MIMS did not decrease significantly. During phase 2, MIMS decreased in all FMGs in both genders with a steeper slope in women (-0.92) than in men (-0.63). The age dependence of MIMS differed significantly between women and men. The present study gives gender-specific equations which enable one to calculate normative values for MIMS, as measured with a pull gauge, based upon age. These normative values will allow an objective assessment of patients with diminished muscle strength as, for example, in myositis, rheumatoid arthritis and nerve root compression syndromes or in the elderly.
Sexually selected traits provide a mating advantage to the bearer but they should also exact a cost through natural selection. Whereas the mating benefits from such traits have been well documented, the costs have been difficult to demonstrate. In this analysis of mortality patterns across 28 North American passerine bird species, we show that sex-biased mortality (log1o male mortality - log1o female mortality) is positively correlated with both sexual size dimorphism and male plumage brightness. Male (but not female) mortality is positively correlated with sexual size dimorphism, suggesting a cost to male-male competition. Female (but not male) mortality is negatively correlated with male brightness, and we argue from this that the evolution of male brightness has been constrained by mortality costs. Thus sexual dimorphism in body size and plumage colour within bird species appears to be influenced by the opposing forces of sexual selection, acting to increase dimorphism, and adult mortality rates, which constrain the evolution of these traits. Differences in the expression of ornamental traits across species may be explained not only by variation in the mating benefits that accrue from ornaments, as is so often assumed, but also by variation in the costs of these traits.
Recent advances in human life history theory have provided new insights into the potential selection pressures that were instrumental in the evolution of human and non-human primate males. However, gaps remain in our understanding of how primate males regulate and allocate energetic resources between survivorship and reproductive effort. Defense against parasitic infection is an important force shaping life history evolution. Proper performance of immunological responses against infection is influenced by many physiological systems, including metabolic, reproductive, and stress hormones. Because androgens influence and modulate immune, reproduc-tive, and somatic metabolic functions, assessing changes in testosterone and immune factors during infection may yield insight into male physiological ecology. In this review, we examine male life history trade-offs between immune and reproductive endocrine functions as well as provide a comprehensive review of testosterone–immunocompetence relationships. Emphasis is placed on testosterone because it is a primary hormone shown to be crucial to energy-allocation processes in vertebrates. Non-primate species have been used more extensively in this research than humans or non-human primates, and therefore this extensive literature is organized and reviewed in order to better understand potential parallel relationships in primates, especially humans. Furthermore, we attempt to reconcile the many inconsistent results obtained from field studies on immune–endo-crine interactions as well as detail various methodologies that may be used to forward this research in evolutionary anthropology. Am.
Recent advances in human life history theory have provided new insights into the potential selection pressures that were instrumental in the evolution of human and non-human primate males. However, gaps remain in our understanding of how primate males regulate and allocate energetic resources between survivorship and reproductive effort. Defense against parasitic infection is an important force shaping life history evolution. Proper performance of immunological responses against infection is influenced by many physiological systems, including metabolic, reproductive, and stress hormones. Because androgens influence and modulate immune, reproduc-tive, and somatic metabolic functions, assessing changes in testosterone and immune factors during infection may yield insight into male physiological ecology. In this review, we examine male life history trade-offs between immune and reproductive endocrine functions as well as provide a comprehensive review of testosterone–immunocompetence relationships. Emphasis is placed on testosterone because it is a primary hormone shown to be crucial to energy-allocation processes in vertebrates. Non-primate species have been used more extensively in this research than humans or non-human primates, and therefore this extensive literature is organized and reviewed in order to better understand potential parallel relationships in primates, especially humans. Furthermore, we attempt to reconcile the many inconsistent results obtained from field studies on immune–endo-crine interactions as well as detail various methodologies that may be used to forward this research in evolutionary anthropology. Am.
Handgrip strength (HGS) is a noninvasive measure of physical health that is negatively correlated with disability, morbidity, and mortality rates in adults. Highly heritable, HGS is indicative of blood testosterone levels and levels of fat-free body mass. In this study, we investigated whether HGS was related to measures of body morphology [shoulder-to-hip ratio (SHR), waist-to-hip ratio, and second-digit-to-fourth-digit ratio (2D:4D)], aggressive behavior, and sexual history in 82 male and 61 female college students. Results showed that HGS was correlated with SHRs, aggressive behavior, age at first sexual intercourse, and promiscuity in males but not in females. HGS appears to be an honest signal for genetic quality in males.
Upper-body fat has negative effects and lower-body fat has positive effects on the supply of long-chain polyunsaturated fatty acids that are essential for neurodevelopment. Thus, waist-hip ratio (WHR), a useful proxy for the ratio of upper-body fat to lower-body fat, should predict cognitive ability in women and their offspring. Moreover, because teenage mothers and their children compete for these resources, their cognitive development should be compromised, but less so for mothers with lower WHRs. These predictions are supported by data from the Third National Health and Nutrition Examination Survey. Controlling for other correlates of cognitive ability, women with lower WHRs and their children have significantly higher cognitive test scores, and teenage mothers with lower WHRs and their children are protected from cognitive decrements associated with teen births. These findings support the idea that WHR reflects the availability of neurodevelopmental resources and thus offer a new explanation for men's preference for low WHR.
BACKGROUND
Prostate cancer and benign prostatic hyperplasia are important age-related prostatic diseases that are under the influence of testicular hormones. However, the disparity between male and female life expectancy within the human population cannot be explained solely by the prevalence of prostatic disease-related mortality. The purpose of this paper is to explore the possibility that the testis exerts a detrimental effect on life span.METHODS
First, we review previously published and unpublished data on the influence of the testis on the life span of dogs and men. Aging in pet dogs and men is then discussed in terms of evolutionary theory, emphasizing the significance of a prolonged postreproductive life span and possible consequences of late-acting deleterious genes in these two species. Finally, we present preliminary data that orchiectomy can reduce DNA damage within the brain of elderly male dogs.RESULTS AND CONCLUSIONS
Taken together, these observations raise the intriguing possibility that interventions to antagonize the testis might have much broader therapeutic applications that will extend well beyond the treatment of prostate cancer. Prostate 43:272–277, 2000. © 2000 Wiley-Liss, Inc.
Males generally exhibit reduced immune responses as well as increased intensity and prevalence of infections compared to female conspecifics. Physiologically, these sex differences may reflect the immunosuppressive effects of androgens. In addition to suppressing immune function, androgens maintain several characteristics important for reproductive success. Thus, a dynamic relationship is assumed to exist among hormones, secondary sex traits, and the immune system. Ultimately, the extent to which this relationship exists may be related to the mating system. Because polygynous males generally have higher circulating testosterone concentrations and rely more heavily on testosterone-dependent traits for reproductive success than monogamous males, sex differences in immune function are hypothesised to be more pronounced among polygynous as compared to monogamous species. Additionally, if secondary sex traits are used to advertise infection status, then females should be able to use the condition of male secondary sex traits to discern the immune/infection status of males during mate selection. The purpose of this review is to survey current studies that examine both the proximate mechanisms and ultimate function of variation in immune function and susceptibility to infection and determine whether immunological variation influences mate preference and possibly reproductive success.
Opinions vary but one interpretation of the vastly expanded hominid postcranial sample from 4 to 1·3 M.Y. hominids leads to the following working hypotheses: (1) The average female of the earliest known species of Hominidae, Australopithecus afarensis, weighed about 29 kg and the male, 45 kg. (2) Average female body weight remains between 29 and 34 kg in all species of hominids before the appearance of Homo erectus at 1·7 M.Y. (3) Average male body weight ranged between 40 and 52 kg in these pre-erectus species. (4) The origin of H. erectus marked a dramatic increase in body size especially in the female. (5) The brain size increase from A. afarensis to A. africanus to the "robust" australopithecines does not appear to be an artifact of body size increase but reflects progressive encephalization. (6) The expansion of absolute brain size with the appearance of Homo is beyond what would be expected from body size increase alone. These working hypotheses have implications for how members of early hominid species behaved to enhance their chances of survival and reproduction within the constraints and requirements of their environments. For example, the relatively high level of body size sexual dimorphism in the earliest species implies a polygynous mating system and a ranging pattern in which females foraged in smaller territories than the males. Although one might expect from analogy with Pan to have social groups consisting of closely related males and less closely related females, the high level of sexual dimorphism is not expected. Perhaps the substantial body size increase and reduction in sexual dimorphism apparent in Homo by 1·7 M.Y. is related to a significant expansion in ranging area. The energetic requirement of the expanded brain may imply altered feeding strategies in both the "robust" australopithecine and Homo lineages.
Physical competition is widespread in human societies. Because performance in competitive sports can signal phenotypic quality and fighting ability, high level performance, especially on the part of men, is likely to be attractive to the opposite sex. We investigated the relationship between involvement in competitive sport and self-reported numbers of sexual partners. Both male and female students who compete in sports reported significantly higher numbers of partners than other students, and within the athletes, higher levels of performance predicted more partners. Among men, body mass index (BMI) and educational level also had significant effects. We discuss possible implications for the evolution of competitive sport, ritual fighting behavior, and the persistence of left-handedness.
The immunocompetence handicap hypothesis was formulated 12 years ago in an attempt to offer a proximate mechanism by which female choice of males could be explained by endocrine control of honest signalling. The hypothesis suggested that testosterone has a dual effect in males of controlling the development of sexual signals while causing immunosuppression. Our purpose in this review is to examine the empirical evidence to date that has attempted to test the hypothesis, and to conduct a meta-analysis on two of the assumptions of the hypothesis, that testosterone reduces immunocompetence and increases parasitism, to ascertain any statistical trend in the data. There is some evidence to suggest that testosterone is responsible for the magnitude of trait expression or development of sexual traits, but this is by no means conclusive. The results of many studies attempting to find evidence for the supposed immunosuppressive qualities of testosterone are difficult to interpret since they are observational rather than experimental. Of the experimental studies, the data obtained are ambiguous, and this is reflected in the result of the meta-analysis. Overall, the meta-analysis found a significant suppressive effect of testosterone on immunity, in support of the hypothesis, but this effect disappeared when we controlled for multiple studies on the same species. There was no effect of testosterone on direct measures of immunity, but it did increase ectoparasite abundance in several studies, in particular in reptiles. A funnel analysis indicated that the results were robust to a publication bias. Alternative substances that interact with testosterone, such as glucocorticoids, may be important. Ultimately, a greater understanding is required of the complex relationships that exist both within and between the endocrine and immune systems and their consequences for mate choice decision making.
The efficacy of a 10-week program of circuit weight training to elicit specific physiological alterations was evaluated in a group of men (n = 16) and a group of women (n = 12), with an additional group of men (n = 10) and a group of women (n = 11) serving as controls. The circuit consisted of 10 stations performed on a Universal Gym, 3 circuits per day (approximately 22.5 min/day), 3 days/week. The subjects exercised at 40-55% of 1-RM, executing as many repetitions as possible in 30 sec on each of the lifts, followed by a 15 sec rest as the subject moved to the next station. Following the training program, the experimental groups demonstrated significant increases in lean body weight, flexed biceps girth, treadmill endurance time, VEmax (women only), Vo2max in ml/kg-min (women only), flexibility and strength. Significant decreases were found in selected skinfold measurements, and in resting heart rate (control group showed similar decreases). No change was found in body weight or in relative or absolute body fat. Generally, the women exhibited equal or greater changes when compared to the men for all variables assessed, which could be a function of their lower initial starting levels, or a more intense training program. It was concluded that circuit weight training is a good general conditioning activity, i.e., attends to more than one component of fitness.
Summary Dual-energy X-ray absorptiometry (DEXA) has been used to assess and compare the composition of whole body and major body regions in 12 female (weight, 56.9 ± 6–2 kg; BMI, 17.25 kg m-2) and 16 male (weight, 73.1 ± 9–6 kg; BMI, 20.28 kg m-2) healthy subjects. Standard deviations (and % coefficients of variation) of the differences between repeated measurements of fat ranged from 0.11 kg (9.0%) for arms to 0.42 kg (30%) for whole body; for arm bone mineral, 0.01 kg (2.0%), and for fat-free soft tissue of the whole body, 0.42 kg (0.8%). Limb muscle mass was estimated using a new theoretical model of body composition, and the corresponding precision ranged from 015 kg (3.8%) to 0.27 kg (1.5%) for arms and total limb muscle mass, respectively.
Proportions of each region consisting of fat were greater in females than in males (range, 20.31% vs. 16.18%), respectively, but the ratio of trunk to leg fat was lower (34:49% vs. 46:38%, respectively). Regional proportions of bone were similar between the sexes (all in the range 2.9–5.6%, for both females and males).
Mean total limb muscle masses were 14.2 kg (arms, 2.8 kg; legs, 11.4 kg) for females and 22.2 kg (arms, 4.8 kg; legs, 17.4 kg) for males, which were 33.6% and 36.0% of fat-free mass, respectively. The correlation coefficients between limb muscle (DEXA) and other indices of muscle mass were: for DEXA vs. total body potassium, 0.90 (SEE 1.1kg muscle mass) to 0.94 (1.6 kg); and for DEXA vs. anthropometry, 0.43 (1.2 kg) to 0.85 (1.3 kg). Those for limb volume (DEXA) vs. anthropometric volume, 0.91 (0.78 1) to 0.94 (1.91 1).
It is concluded that DEXA enables the valid and reproducible estimation of fat, fat-free soft tissue, bone, and limb muscle mass.
We have examined the effect of testosterone enanthate injections (3 mg/kg.week, im) on the basal metabolic rate (BMR) estimated by indirect calorimetry and on lean body mass (LBM) estimated by 40K counting in four normal men and nine men with muscular dystrophy. Testosterone treatment increased plasma testosterone levels in all subjects (3-fold mean elevation). BMR increased significantly after 3 months of testosterone treatment (mean, 10%; P less than 0.01; 13% mean increase in the men with muscular dystrophy and 7% mean increase in the normal subjects). BMR remained elevated (mean increase, 9%) after 12 months of testosterone treatment in four men with muscular dystrophy. LBM also was significantly higher after 3 months of treatment (mean, 10%; P less than 0.01) and remained elevated at 12 months. The percent increase in LBM was similar in men with muscular dystrophy (+10%) and normal men (+11%). When BMR was adjusted for the increase in LBM by linear regression, the men with muscular dystrophy had an increase in adjusted BMR after 3 months of testosterone treatment (mean increase, 7%), but not after 12 months. The normal men did not have an increase in adjusted BMR. Testosterone treatment for 12 months slightly reduced body fat, whereas there was an increase in body fat in subjects with muscular dystrophy who were treated with placebo for 12 months. We conclude that there is a significant increase in BMR associated with pharmacological testosterone treatment, which for the most part is explained by the increase in LBM. However, in men with muscular dystrophy, there is a small hypermetabolic effect of testosterone beyond that explained by increased LBM.
To assess whether alterations in the normal pattern of testosterone (T) secretion might be beneficial or detrimental, we studied a breeding population of dark-eyed juncos in which we elevated T experimentally and measured its effect on potential correlates of fitness. We treated both free-living and captive males with implants that were either empty (C-males, controls) or packed with T (T-males, experimentals). Timing of implant varied and was designed to mimic natural peak breeding levels except that peaks were either prolonged or premature. We bled the birds at recapture and analyzed their plasma, and that of their female mates, for T and corticosterone (B). We also measured body mass and fat score in free-living T- and C-males. In the field, T-implants elevated T and kept it elevated for at least a month. Experimental males also had higher B than controls. In captives, the effect of the implants on plasma T was detectable within 24 hr. B in captive T-males was again higher than in captive C-males. In females, neither T nor B differed between mates of T- and C-males. T-males implanted in early spring lost more mass between implant and recapture in late spring than did controls and also had lower fat scores when recaptured. When implants were inserted in summer, treatment did not influence mass. Elevated T in early spring apparently hastened the transition from the winter to the breeding mode of fat storage. We suggest that prolonged elevation of testosterone might be selected against because of the association between T and B. Premature elevation of T might be costly because of the resultant loss of mass and fat reserves, which could lead to mortality when spring snowstorms prevent access to food.
We have studied the effect of a pharmacological dose of testosterone enanthate (3 mg.kg-1.wk-1 for 12 wk) on muscle mass and total-body potassium and on whole-body and muscle protein synthesis in normal male subjects. Muscle mass estimated by creatinine excretion increased in all nine subjects (20% mean increase, P less than 0.02); total body potassium mass estimated by 40K counting increased in all subjects (12% mean increase, P less than 0.0001). In four subjects, a primed continuous infusion protocol with L-[1-13C]leucine was used to determine whole-body leucine flux and oxidation. Whole-body protein synthesis was estimated from nonoxidative flux. Muscle protein synthesis rate was determined by measuring [13C]leucine incorporation into muscle samples obtained by needle biopsy. Testosterone increased muscle protein synthesis in all subjects (27% mean increase, P less than 0.05). Leucine oxidation decreased slightly (17% mean decrease, P less than 0.01), but whole-body protein synthesis did not change significantly. Muscle morphometry showed no significant increase in muscle fiber diameter. These studies suggest that testosterone increases muscle mass by increasing muscle protein synthesis.
Sex hormones have been implicated in the pathogenesis of many autoimmune disorders, presumably through regulatory influences on the immune system. However, the mechanisms of sex steroid action on humoral and cellular immune responses are not precisely understood. In this study, the in vitro effects of physiologic concentrations of 17 beta-estradiol and testosterone on the Ag non-specific differentiation of human PBMC were examined using optimal and sub-optimal doses, respectively, of PWM. In cultures of PBMC from 14 normal donors (7 men and 7 women, aged 25 to 45 yr), 17 beta-estradiol (0.5 to 30 ng/ml) enhanced PWM-induced generation of PFC by 46% (p less than 0.01), whereas testosterone (10 to 300 ng/ml) inhibited PFC generation by a mean of 36% (p less than 0.001). The enhancing and suppressing effects of the sex steroids on PBMC occurred early inasmuch as estradiol and testosterone had to be added to the cultures at their initiation (6 and 24 h, respectively) in order to observe their influence. Moreover, deletion of the hormones from the cultures after as short a period as 12 h did not obviate their effects. There was no alteration of the kinetics of the response to PWM or an effect on the number of spontaneous PFC generated in vitro in the absence of PWM. In addition, there was no difference among men and women in response to either sex steroid, and within the female group, no variation was observed on different days of the menstrual cycle. These studies demonstrate direct immunoregulatory effects of specific sex steroids on human PBMC and support the idea that these hormones may have a role in the pathogenesis and treatment of some autoimmune disorders.
The immune system is regulated by the gonadal steroids estrogen, androgen, and progesterone, but the circulating levels of
these steroids can also be affected by immune system function. Such interactions appear to be mediated through the hypothalamic-pituitary-gonadal-thymic
axis and depend on pituitary luteinizing hormone released by thymic factors under the control of the gonadal steroids.
Immune reactivity is greater in females than in males. In both experimental animals and in man there is a greater preponderance of autoimmune diseases in females, compared with males. Studies in many experimental models have established that the underlying basis for this sex-related susceptibility is the marked effects of sex hormones. Sex hormones influence the onset and severity of immune-mediated pathologic conditions by modulating lymphocytes at all stages of life, prenatal, prepubertal, and postpubertal. However, despite extensive studies, the mechanisms of sex hormone action are not precisely understood. Earlier evidence suggested that the sex hormones acted via the thymus gland. In recent years it has become apparent that sex hormones can also influence the immune system by acting on several nonclassic target sites such as the immune system itself (nonthymic lymphoid organs), the central nervous system, the macrophage-macrocyte system, and the skeletal system. Immunoregulatory T cells appear to be most sensitive to sex hormone action among lymphoid cells. Several mechanisms of action of sex hormones are discussed in this review. The possibility of using sex hormone modulation of immune responses for the treatment of autoimmune disorders is a promising area for future investigation.
Normal age- and sex-related standards for shoulder range of motion (ROM) and muscle strength are unavailable in the literature. Active range of shoulder motion and maximum isometric strength (torque) of several shoulder muscle groups were measured in normal healthy men and women between 25 and 36 and between 55 and 66 years of age. Values for joint motion were similar for the two age and sex groups. The strength of the women was 45% to 66% of that in men, and strength of the older subjects was 66% to 93% of that in younger subjects. Strength of the second attempt at contraction was greater than that of the first attempt. Arm dominance did not significantly affect strength values.
Eleven groups of fifty rats each were kept under uniform conditions of management and their life-spans under different treatments were compared. Females lived longer than males, while ovariectomy tended to shorten the life-span of females and castration to lengthen that of males. Implantation of gonadectomized rats with oestradiol benzoate did not prolong the life-span of the females but it did tend to prolong that of males. Implantation of gonadectomized rats with testosterone propionate tended to shorten the average life-span of both sexes. Unbred females outlived bred ones, on the average, but the difference was not significant at the 5% level. Late initial breeding appeared to be more harmful than breeding for the first time at the usual age for laboratory rats. Light breeding had little or no effect upon the average longevity of males. These conclusions are tentative. The results are consistent but they mostly lack acceptable statistical significance. The most significant result statistically was that rats exposed to their own or implanted oestrogens had a longer average life-span than did those exposed to their own or to implanted testosterone.
Based on measurements of triceps skinfold thickness and upper arm circumference of a cross-sectional sample of 19,097 white subjects aged 1 to 74 yr, derived from the United States Health and Nutritional Examination Survey of 1971 to 1974, the arm muscle circumference, arm muscle area, and arm fat area were calculated. Thereafter, age- and sex-specific percentiles for all three estimates of upper arm tissues were obtained. Based on empirical and theoretical evidence, it is recommended that assessments of nutritional status be made on the basis of areas of fat and areas of muscle rather than direct skinfold thickness and arm circumference. It is also recommended that these new norms should replace those currently in use.
Recent studies show reduced fetal growth is associated with insulin resistance and a raised prevalence of glucose intolerance in adult life. Because early growth retardation in animal models leads to permanent changes in body composition and a reduction in the mass of muscle, a major insulin sensitive tissue, reduced adult muscle mass could explain the link between impaired fetal growth and glucose intolerance. To investigate this hypothesis, muscle mass has been determined in a group of men and women aged around 50 who were born in Preston, Lancashire and compared with their birthweight or body size at birth and their current insulin resistance and glucose tolerance. Subjects who had lower birthweights were shorter and lighter but their weight adjusted for height (BMI) was similar to that of other subjects. Much of the difference in weight was accounted for by a reduction in muscle mass. Muscle mass as estimated by the urinary creatinine excretion rose from 18.8% of body weight in women who had birthweights of 2.5 kg or less to 24.7% of bodyweight in those with birthweights of 3.4 kg or more. Trends in men were similar. Regression analysis showed that adult muscle mass was predicted by low birthweight (p = 0.004), low placental weight (p = 0.02), and small head circumference (p = 0.02) but not, however, by thinness at birth, the birth measurement most predictive of insulin resistance. In addition there were no significant relationships between muscle mass and insulin resistance or glucose tolerance in either men or women.(ABSTRACT TRUNCATED AT 250 WORDS)
Previous studies have suggested that healthy subjects of African ancestry have lower total white cell counts, neutrophil counts and platelet counts than Caucasian subjects and that, at least among Caucasians, women have higher neutrophil and platelet counts than men. The primary aim of this study was to confirm and quantify the ethnic differences, confirm the sex difference in Caucasians and determine whether there was a similar sex difference in non-Caucasians. A secondary aim was to establish reference ranges for white cell and platelet counts for the different ethnic and sex groups.
The study population comprised 417 healthy volunteers (201 women and 216 men), of whom 200 were Caucasian, 102 were Afrocaribbean and 115 were African. Full blood counts, including a differential white cell count, were measured using a H.2 automated differential counter. White cell and platelet counts were compared between the three different ethnic groups and between men and women. Reference ranges were determined for each ethnic and sex group.
Africans and Afrocaribbeans had lower total white cell, neutrophil and platelet counts than Caucasians and counts were lower in Africans than in Afrocaribbeans. Women had higher neutrophil and platelet counts than men in all ethnic groups.
Sex and ethnic origin should be taken into consideration when assessing white cell and platelet counts.
We studied the in vitro effect of testosterone on spontaneous immunoglobulin production by human peripheral blood mononuclear cells (PBMC). Testosterone inhibited IgG and IgM production by PBMC both from males and females. The inhibitory effect of testosterone was revealed at doses more than 1 nM, increased dose-dependently, and reached a plateau at 100 nM. At doses < 1000 nM, testosterone did not reduce cell viability. Testosterone treatment reduced IgG production by 59.0% and that of IgM by 61.3% compared with control. Immunoglobulin production by B cells was also suppressed by testosterone, though the magnitude of the suppressive effect on B cells was lower than that on whole PBMC; testosterone-induced decrease of IgG production compared with control was 26.9% and that of IgM was 24.9%. Exogenous IL-6 partially restored the impaired immunoglobulin production of testosterone-treated PBMC; IgG production in testosterone culture was increased by IL-6 from 35.6% to 66.5% of control and that of IgM was also increased from 38.9% to 71.2%, respectively. Testosterone treatment reduced IL-6 production of monocytes by 78.4% compared with control, but neither affected that of T cells or B cells. These results suggest that testosterone may suppress immunoglobulin production of human PBMC directly by inhibiting B cell activity and indirectly by reducing IL-6 production of monocytes. It is thus indicated that this hormone may have protective and therapeutic effects on human autoimmune diseases.
Sex differences in parasite infection rates, intensities, or population patterns are common in a wide range of taxa. These differences are usually attributed to 1 of 2 causes: (1) ecological (sociological in humans); and (2) physiological, usually hormonal in origin. Examples of the first cause include differential exposure to pathogens because of sex-specific behavior or morphology. The second cause may stem from the well-documented association between testosterone and the immune system; sexually mature male vertebrates are often more susceptible to infection and carry higher parasite burdens in the field. Although many researchers favor one explanation over the other, the requisite controlled experiments to rule out confounding variables are often neglected. We suggest that sex differences in disease have evolved just as sex differences in morphology and behavior, and are the result of selection acting differently on males and females. Research has often focused on proximate mechanistic explanations for the sex difference in infection rates, but it is equally important to understand the generality of the patterns in an evolutionary context. Because males potentially gain more than females by taking risks and engaging in competition, sexual selection pressure has shaped male behavior and appearance to maximize competitive ability and attractiveness. Many of the classic male attributes such as antlers on deer are testosterone-dependent, putting males in what appears to be a cruel bind: become vulnerable to disease by developing an attractive secondary sexual ornament, or risk lowered mating success by reducing it. A variety of hypotheses have been put forward to explain why males have not circumvented this dilemma. The mating system of the host species will influence the likelihood of sex differences in parasite infection, because males in monogamous species are subject to weaker sexual selection than males in polygynous species. Whether these evolutionary generalizations apply to invertebrates, which lack testosterone, remains to be seen.
Only a few studies have provided reference values for muscle strength obtained by hand-held dynamometry. Such values are essential for establishing the degree to which an individual's strength is impaired. This descriptive study was conducted to provide reference values for the strength of 10 extremity muscle actions. SUBJECTS AND INSTRUMENTATION: A convenience sample of 106 men and 125 women volunteers was tested twice with an Ametek digital hand-held dynamometer.
The measurements were found to be reliable. Predictive equations are provided for the measurements. Reference values generated are expressed in Newtons and as a percentage of body weight and are organized by gender, decade of age, and side.
The values can be employed in a clinical setting to document whether an individual is impaired relative to healthy subjects of the same gender and age.
This study tested the hypothesis that skeletal muscle mass is reduced in elderly women and men after adjustment first for stature and body weight. The hypothesis was evaluated by estimating appendicular skeletal muscle mass with dual-energy X-ray absorptiometry in a healthy adult cohort. A second purpose was to test the hypothesis that whole body 40K counting-derived total body potassium (TBK) is a reliable indirect measure of skeletal muscle mass. The independent effects on both appendicular skeletal muscle and TBK of gender (n = 148 women and 136 men) and ethnicity (n = 152 African-Americans and 132 Caucasians) were also explored. Main findings were 1) for both appendicular skeletal muscle mass (total, leg, and arm) and TBK, age was an independent determinant after adjustment first by stepwise multiple regression for stature and weight (multiple regression model r2 = approximately 0.60); absolute decrease with greater age in men was almost double that in women; significantly larger absolute amounts were observed in men and African-Americans after adjustment first for stature, weight, and age; and >80% of within-gender or -ethnic group between-individual component variation was explained by stature, weight, age, gender, and ethnicity differences; and 2) most of between-individual TBK variation could be explained by total appendicular skeletal muscle (r2 = 0.865), whereas age, gender, and ethnicity were small but significant additional covariates (total r2 = 0.903). Our study supports the hypotheses that skeletal muscle is reduced in the elderly and that TBK provides a reasonable indirect assessment of skeletal muscle mass. These findings provide a foundation for investigating skeletal muscle mass in a wide range of health-related conditions.
Administration of either 1 microgram kg-1 BW oestradiol 17 beta (E2), 0.1 mg kg-1 BW testosterone (T) or 0.2 mg kg-1 BW dihydrotestosterone (DHT) in feed to broiler chicks for 50 days caused increased serum concentration of the hormones compared to the control birds that were given no drugs. E2 and T but not DHT resulted in a significant decrease of the total number of leukocytes, lymphocytes and the weight of bursa of Fabricious. The hormones significantly reduced the macrophage phagocytic activity compared to controls. It is suggested that prolonged administration of low doses of E2 and T but not DHT to chicken may induce immunosuppressant effect.
To explore the hypothesis that lower body muscle mass correlates with orthostatic tolerance, 18 healthy volunteers (age 18-48 yr; 10 men, 8 women) underwent a graded lower body negative pressure (LBNP) protocol consisting of six, 5-min stages of suction up to 60 mmHg in 10-mmHg increments. Forearm blood flow, heart rate, and blood pressure were measured, and forearm vascular resistance was calculated. Leg muscle mass was assessed by dual-energy X-ray absorptiometry. All subjects received standard intravenous hydration for at least 8 h before the study. Six men and four women completed all stages of LBNP. Four men and four women developed presyncopal symptoms, including marked bradycardia and/or hypotension, at LBNP levels of 30 mmHg (n = 2;1 man, 1 woman), 40 mmHg (n = 2;1 man, 1 woman), and 50 mmHg (n = 4;2 men, 2 women). The presyncopal subjects had leg muscle masses ranging from 19.5 to 25.2 kg in men and from 11.7 to 16.6 kg in women. In subjects who completed all stages of LBNP, leg muscle mass ranged from 17.5 to 24.1 kg in men and from 10.4 to 18.0 kg in women. Leg muscle mass did not differ between presyncopal subjects and those who completed the protocol. Furthermore, there were no differences in the hemodynamic responses to LBNP between subjects with low vs. high leg mass. These data suggest that leg muscle mass is not a critical determinant of LBNP tolerance in otherwise healthy men and women.
Resting energy expenditure (REE) and components of fat-free mass (FFM) were assessed in 26 healthy nonobese adults (13 males, 13 females). Detailed body composition analyses were performed by the combined use of dual-energy X-ray absorptiometry (DEXA), magnetic resonance imaging (MRI), bioelectrical impedance analysis (BIA), and anthropometrics. We found close correlations between REE and FFM(BIA) (r = 0.92), muscle mass(DEXA) (r = 0.89), and sum of internal organs(MRI) (r = 0.90). In a multiple stepwise regression analysis, FFM(BIA) alone explained 85% of the variance in REE (standard error of the estimate 423 kJ/day). Including the sum of internal organs(MRI) into the model increased the r(2) to 0.89 with a standard error of 381 kJ/day. With respect to individual organs, only skeletal muscle(DEXA) and liver mass(MRI) significantly contributed to REE. Prediction of REE based on 1) individual organ masses and 2) a constant metabolic rate per kilogram organ mass was very close to the measured REE, with a mean prediction error of 96 kJ/day. The very close agreement between measured and predicted REE argues against significant variations in specific REEs of individual organs. In conclusion, the mass of internal organs contributes significantly to the variance in REE.
Background:
Prostate cancer and benign prostatic hyperplasia are important age-related prostatic diseases that are under the influence of testicular hormones. However, the disparity between male and female life expectancy within the human population cannot be explained solely by the prevalence of prostatic disease-related mortality. The purpose of this paper is to explore the possibility that the testis exerts a detrimental effect on life span.
Methods:
First, we review previously published and unpublished data on the influence of the testis on the life span of dogs and men. Aging in pet dogs and men is then discussed in terms of evolutionary theory, emphasizing the significance of a prolonged postreproductive life span and possible consequences of late-acting deleterious genes in these two species. Finally, we present preliminary data that orchiectomy can reduce DNA damage within the brain of elderly male dogs. RESULTS AND CONCLUSIONS Taken together, these observations raise the intriguing possibility that interventions to antagonize the testis might have much broader therapeutic applications that will extend well beyond the treatment of prostate cancer.
Body proportions and tissue composition (e.g., relative contributions of muscle, skin, bone, and adipose to total body mass) were determined through dissection of four adult captive lowland gorillas. The relative contribution of bone varies little among the four animals (10.2-13.4%) despite considerable range in body weights (99.5-211 kg). In tissue composition, three animals have on average 37.3% muscle relative to body mass. Maximum estimates of body fat range between 19.4-44%. Differences in age, sex, and life history events partially explain the observed variation in body proportions and tissue composition among the four animals. Although gorillas are considered extremely sexually dimorphic in body weight and canine size, differences in tissue are not as dramatic as body mass differences suggest. This study found sex differences mostly in the upper body; males have relatively heavier forelimbs, including heavier deltoid, trunk-binding, and deep back muscles compared to the younger female. The old, obese female had one half the muscle tissue of the other three animals (16% vs. 37.3%), and twice the body fat (44%); forelimbs and upper body musculature were relatively well-developed to compensate for the restricted hip-joint movement due to arthritis. Data on the variation in tissue composition and body proportions in gorillas provide a basis for comparison with other hominoids, including humans. For example, compared to highly dimorphic orangutans, gorillas have more muscle, less adipose tissue, lighter forelimbs and heavier hindlimbs. Such analyses complement studies of the skeleton and contribute to our understanding of human evolution and adaptation.