Dimorphisme sexuel chez Homo sapiens

  1. Différences physiques entre hommes et femmes aujourd’hui
  2. Performances sportives
  3. Autres aspects médicaux et biologiques

Voir aussi :
Sexe, genre et évolution : dimorphisme sexuel
Sexe, genre et évolution : division du travail

 


Différences physiques entre hommes et femmes aujourd’hui

Sexual dimorphism in human arm power and force: implications for sexual selection on fighting ability
Morris et al.
Journal of experimental biology, 2020
https://jeb.biologists.org/content/223/2/jeb212365.abstract

our results indicate the presence of pronounced male-biased sexual dimorphism in muscle performance for protracting the arm to propel the fist forward. We also compared overhead pulling force between males and females, to test the alternative hypothesis that sexual dimorphism in the upper body of humans is a result of selection on male overhead throwing ability. We found weaker support for this hypothesis, with less pronounced sexual dimorphism in overhead arm pulling force. The results of this study add to a set of recently identified characters indicating that sexual selection on male aggressive performance has played a role in the evolution of the human musculoskeletal system and the evolution of sexual dimorphism in hominins.

Three‐dimensional analysis of sexual dimorphism in ribcage kinematics of modern humans
Garcia-Martinez et al.
American journal of physical anthropology, 2019
https://onlinelibrary.wiley.com/doi/full/10.1002/ajpa.23829?casa_token=g-JbHy9EgssAAAAA%3ACp_CLw_FkzI-DVOZUdz1BKwoffXhCpHsEgRRNUeNCk64uxURUTl_RNKDP5igYPoMa_zVwFiVB5uD0nSU

Our results show significant size differences between males and females both in inspiration and expiration (p < .01) as well as significant shape differences, with males deforming more than females during inspiration, especially in the mediolateral dimension of the lower ribcage. Finally, dummy regressions of shape on kinematic status showed a small but statistically significant difference in vectors of breathing kinematics between males and females (14.78°; p < .01).

Discussion

We support that sex‐related differences in skeletal ribcage kinematics are discernible, even when soft tissues are not analyzed. We hypothesize that this differential breathing pattern is primarily a result of more pronounced diaphragmatic breathing in males, which might relate to differences in body composition, metabolism, and ultimately greater oxygen demand in males compared to females. Future research should further explore the links between ribcage morphological variation and basal metabolic rate.

Cochlear shape reveals that the human organ of hearing is sex-typed from birth
Braga et al.
Nature scientific reports, 2019
https://www.nature.com/articles/s41598-019-47433-9

Sex differences in behavioral and neural characteristics can be caused by cultural influences but also by sex-based differences in neurophysiological and sensorimotor features. Since signal-response systems influence decision-making, cooperative and collaborative behaviors, the anatomical or physiological bases for any sex-based difference in sensory mechanisms are important to explore.
[…] We conclude that the human cochlea is sex-typed from an early post-natal age.
[…] Our observed sex-typed cochlear shape from birth is likely associated with complex evolutionary processes in modern humans for reasons not yet fully understood.

On The Evolution of The Sex Differences in Throwing: Throwing is a Male Adaptation in Humans
Lombardo & Deaner
The quarterly review of biology, 2018
https://www.journals.uchicago.edu/doi/abs/10.1086/698225

The development of the ability to throw projectiles for distance, speed, and accuracy was a watershed event in human evolution. We hypothesize that throwing first arose in threat displays and during fighting and later was incorporated into hunting by members of the Homo lineage because nonhuman primates often throw projectiles during agonistic interactions and only rarely in attempts to subdue prey. Males, who threw more often than females in both combat and hunting, would have been under stronger selection than females to become proficient at the ability to throw, intercept, and dodge projectiles as throwing skills became critical to success in combat and hunting. Therefore, we predict that males, more than females, should display innate anatomical and behavioral traits associated with throwing. We use data from a variety of disciplines to discuss: the sex differences in throwing speed, distance, and accuracy; sex differences in the development of the throwing motion; inability of training or cultural influences to erase the sex differences in throwing; sex differences in the use of throwing in sports, combat, and hunting; and sex differences in anatomical traits associated with throwing that are partly responsible for male throwing superiority. These data contradict the view held by many commentators that socialization rather than innate sex differences in ability are primarily responsible for male throwing superiority. We suggest that throwing is a male adaptation.

Gorillas in Our Midst? Human Sexual Dimorphism and Contest Competition in Men
Hill et al.
On human nature, 2017
https://www.sciencedirect.com/science/article/pii/B9780124201903000156

The literature on human sexual selection has historically focused on the role of female mate choice, but cumulating experimental, correlational, and cross-cultural evidence suggests that male contest competition may have been more influential in shaping men’s phenotypes. Cross-species comparison has shown similarities between humans and our closest extant phylogenetic relatives, the Great Apes, in male–male aggression, and archeological evidence also indicates a great antiquity for male–male violence. Compared to women, men possess substantially greater muscle mass, strength, cranial robusticity, physical aggression, pain tolerance, risk-taking, weapons use, and participation in coalitional aggression. Men also exhibit displays of physical prowess and acuity to the formidability of male conspecifics, as well as possessing a suite of traits, such as facial hair and low vocal pitch, that increase perceptions of dominance. These traits are consistent with having been shaped by contest competition over mates: they are sexually dimorphic, appear at sexual maturity, and predict success in male contests as well as success in mating and reproduction. While alternative explanations for some of these sexually dimorphic traits are possible, contest competition among males throughout human evolutionary history is the most parsimonious.

The importance of physical strength for males
Sell et al.
Human nature, 2012
https://www.researchgate.net/publication/223959003_The_Importance_of_Physical_Strength_to_Human_Males

Fighting ability, although recognized as fundamental to intrasexual competition in many nonhuman species, has received little attention as an explanatory variable in the social sciences. Multiple lines of evidence from archaeology, criminology, anthropology, physiology, and psychology suggest that fighting ability was a crucial aspect of intrasexual competition for ancestral human males, and this has contributed to the evolution of numerous physical and psychological sex differences. Because fighting ability was relevant to many domains of interaction, male psychology should have evolved such that a man’s attitudes and behavioral responses are calibrated according to his formidability. Data are reviewed showing that better fighters feel entitled to better outcomes, set lower thresholds for anger/aggression, have self-favoring political attitudes, and believe more in the utility of warfare. New data are presented showing that among Hollywood actors, those selected for their physical strength (i.e., action stars) are more likely to believe in the utility of warfare.

Men physical strenght

Le dimorphisme sexuel au XXIe siècle
Junien et al.
INSERM, 2012
https://www.medecinesciences.org/fr/articles/medsci/pdf/2012/02/medsci2012282p185.pdf

En ce début du XXIe siècle, une redéfinition du dimorphisme sexuel s’impose. Elle se doit d’incorporer conjointement non seulement les hormones sexuelles et le formatage socio culturel spécifique du genre, mais aussi l’importance des gènes localisés sur les chromosomes sexuels. Ces différentes composantes ont des effets indé-pendants et parallèles et qui interagissent dès la conception et tout au long de la vie. Des mécanismes épigénétiques assurent la mise en place de marques spécifiques du sexe qui modulent l’expression des gènes sans changer leur séquence. Ces marques représentent une sorte de mémoire pour se « souvenir » de son sexe, mais aussi pour « archiver » les impacts de l’environnement, selon l’expérience. Dans tous les tissus, ces marques et d’autres à venir, façonnées en fonction du sexe et du genre au gré de l’environnement, établissent des réseaux de gènes différents chez le mâle et la femelle, tant au niveau basal que pour les réponses immédiates et futures.

Costs and benefits of fat-free muscle mass in men: relationship to mating success, dietary requirements, and native immunity
Lassek & Gaulin
Evolution and human behavior, 2009
https://www.sciencedirect.com/science/article/pii/S1090513809000397?casa_token=SKWanCcb0Y8AAAAA:9kF3T7xE7_fiwS8p5zNEntPPV8TqYgXU4waLqykjOefr6B6JUxURwuPVjgZa-mesTqNPwyPLUps

Despite claims of reduced levels of sexual dimorphism in the genus Homo (e.g., compared to Australopithecus) (McHenry, 1994, Plavcan, 2001), muscle mass and resulting muscular strength are very sexually dimorphic traits in contemporary humans. On average, men have approximately 61% more total muscle mass than women (Illner et al., 2000, Kim et al., 2004, Phillips, 1995, Shen et al., 2004, Wetter & Economos, 2004). Relatively more of this muscle mass is allocated to the upper body, with men having about 75% more arm muscle mass than women (Abe et al., 2003, Fuller et al., 1992, Gallagher et al., 1997, Nindl et al., 2002). Not surprisingly, this latter difference translates into approximately 90% greater upper body strength in men

Hand-grip strength of young men, women and highly trained female athletes
Leyk et al.
European journal of applied physiology, 2007
https://link.springer.com/article/10.1007/s00421-006-0351-1

Mean maximal hand-grip strength showed the expected clear difference between men (541 N) and women (329 N). Less expected was the gender related distribution of hand-grip strength: 90% of females produced less force than 95% of males. Though female athletes were significantly stronger (444 N) than their untrained female counterparts, this value corresponded to only the 25th percentile of the male subjects. Hand-grip strength was linearly correlated with LBM. Furthermore, both relative hand-grip strength parameters (F max/body weight and F max/LBM) did not show any correlation to hand dimensions. The present findings show that the differences in hand-grip strength of men and women are larger than previously reported. An appreciable difference still remains when using lean body mass as reference. The results of female national elite athletes even indicate that the strength level attainable by extremely high training will rarely surpass the 50th percentile of untrained or not specifically trained men.


Performances sportives, spatiales, etc.

Nature Versus Nurture: Have Performance Gaps Between Men and Women Reached an Asymptote ?
Millard-Stafford et al.
Human kinetics journal, 2017
https://journals.humankinetics.com/view/journals/ijspp/13/4/article-p530.xml

Men outperform women in sports requiring muscular strength and/or endurance, but the relative influence of “nurture” versus “nature” remains difficult to quantify. Performance gaps between elite men and women are well documented using world records in second, centimeter, or kilogram sports. However, this approach is biased by global disparity in reward structures and opportunities for women. Despite policies enhancing female participation (Title IX legislation), US women only closed performance gaps by 2% and 5% in Olympic Trial swimming and running, respectively, from 1972 to 1980 (with no change thereafter through 2016). Performance gaps of 13% in elite middistance running and 8% in swimming (∼4-min duration) remain, the 5% differential between sports indicative of load carriage disadvantages of higher female body fatness in running. Conversely, sprint swimming exhibits a greater sex difference than sprint running, suggesting anthropometric/power advantages unique to swim-block starts. The ∼40-y plateau in the performance gap suggests a persistent dominance of biological influences (eg, longer limb levers, greater muscle mass, greater aerobic capacity, and lower fat mass) on performance. Current evidence suggests that women will not swim or run as fast as men in Olympic events, which speaks against eliminating sex segregation in these individual sports.

The Performance Gap in Sport Can Help Determine Which Movements Were Most Essential to Human Evolution
Colin Carroll
Frontiers in physiology, 2019
https://www.frontiersin.org/articles/10.3389/fphys.2019.01412/full

This difference suggests that general sexual dimorphism does not explain why female performance is relatively closer to male performance at some track and field events than others. We hypothesize that this trend can be explained by the presence of sex-blind musculoskeletal adaptations (SBMA’s), which accumulate over generations to reduce the size of the PG in certain movements. We conclude that the selection trend favoring in humans should be explored further to determine whether the PG in sport can indeed be used to determine movements to which the human body is adapted.

Robust Sex Differences in Jigsaw Puzzle Solving—Are Boys Really Better in Most Visuospatial Tasks?
Kocijan et al.
Frontiers in behavioral neurosciences, 2017
https://www.frontiersin.org/articles/10.3389/fnbeh.2017.00194/full?utm_source=F-AAE&utm_medium=EMLF&utm_campaign=MRK_436006_55_Neuros_20171026_arts_A

Sex differences are consistently reported in different visuospatial tasks with men usually performing better in mental rotation tests while women are better on tests for memory of object locations. In the present study, we investigated sex differences in solving jigsaw puzzles in children. In total 22 boys and 24 girls were tested using custom build tablet application representing a jigsaw puzzle consisting of 25 pieces and featuring three different pictures. Girls outperformed boys in solving jigsaw puzzles regardless of the picture. Girls were faster than boys in solving the puzzle, made less incorrect moves with the pieces of the puzzle, and spent less time moving the pieces around the tablet. It appears that the strategy of solving the jigsaw puzzle was the main factor affecting differences in success, as girls tend to solve the puzzle more systematically while boys performed more trial and error attempts, thus having more incorrect moves with the puzzle pieces. Results of this study suggest a very robust sex difference in solving the jigsaw puzzle with girls outperforming boys by a large margin.

Morphological and functional implications of sexual dimorphism in the human skeletal thorax
Garcia-Martinez et al.
American journal of physical anthropology, 2016
https://onlinelibrary.wiley.com/doi/full/10.1002/ajpa.23051?casa_token=Hy72RfRgNKoAAAAA%3AVNPJiZvoDip4AKq6rZwcLZq1QNO2PgKkmIouhFfSoFRzwGdpUrjfXFK3B7vmMz7WQWrAhmDpaBIPDomB

Males showed significantly larger thorax size (p < .01) and functional size (p < .05) than females. In addition, the 3D‐shape differed significantly between sexes (p < .01). Male rib cages were wider (particularly caudally) and shorter, with more horizontally oriented ribs when compared to females. While thorax widening and rib orientation were unrelated to allometry, thorax shortening showed a slight allometric signal.

Conclusions

Our findings are in line with previous research on sexual dimorphism of the respiratory system. However, we add that thorax shortening observed previously in males is the only feature caused by allometry. The more horizontally oriented ribs and the wider thorax of males may indicate a greater diaphragmatic contribution to rib cage kinematics than in females, and differences in functional size fit with the need for greater oxygen intake in males.

 


Autres aspects médicaux et biologiques

Expanding the evolutionary explanations for sex differences in the human skeleton
Holly M. Dunsworth
Evolutionnary anthropology, 2020
https://onlinelibrary.wiley.com/doi/full/10.1002/evan.21834?casa_token=uzRAzFseRFEAAAAA%3AsuTxxQBUFmtduYqqNvyFh3kvxhfYKxKWewQqsdtt1XlTtF1BvhL3s7z5kVkSdNhORD2NMV7IF1iUW90j

While the anatomy and physiology of human reproduction differ between the sexes, the effects of hormones on skeletal growth do not. Human bone growth depends on estrogen. Greater estrogen produced by ovaries causes bones in female bodies to fuse before males’ resulting in sex differences in adult height and mass. Female pelves expand more than males’ due to estrogen and relaxin produced and employed by the tissues of the pelvic region and potentially also due to greater internal space occupied by female gonads and genitals.

False dichotomies and human sexual size dimorphism: A comment of Dunsworth (2020)
Font & Carazo
Evolution and human behavior, 2020
https://www.sciencedirect.com/science/article/abs/pii/S1090513820300970

Opposite molecular signatures of depression in men and women
Seney et al.
Biological psychiatry, 2018
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6014892/

Of the 706 genes differentially expressed in men with MDD and 882 genes differentially expressed in women with MDD, only 21 were changed in the same direction in both sexes. Notably, 52 genes displayed expression changes in opposite directions between men and women with MDD. Similar results were obtained using a threshold-free approach, where the overall transcriptional profile of MDD was opposite in men and women. Gene ontology indicated that men with MDD had decreases in synapse-related genes, whereas women with MDD exhibited transcriptional increases in this pathway. Cell type-specific analysis indicated that men with MDD exhibited increases in oligodendrocyte- and microglia-related genes, while women with MDD had decreases in markers of these cell types.

Conclusions

The brain transcriptional profile of MDD differs greatly by sex, with multiple transcriptional changes in opposite directions between men and women with MDD.

The biology of human gender
Manning et al.
Encyclopedia Evolutionary Psychological Science, 2017
https://www.researchgate.net/publication/321017244_The_Biology_of_Human_Gender

The development of human gender identity may be inuenced by organizational effects of prenatal hormones. This includes physical and neural development. Digit ratio (or 2D:4D) is a proxy of fetal hormones that correlates negatively with prenatal testosterone and positively with prenatal estrogen. Studies investigating associations
between 2D:4D and sex-dependent traits suggest that in addition to genetics, prenatal hormonescontribute to the determination of gender.

The landscape of sex-differential transcriptome and its consequent selection in human adults
Gershoni & Pietrokovski
BMC biology, 2017
https://bmcbiol.biomedcentral.com/articles/10.1186/s12915-017-0352-z

Sex-differential expression (SDE) was tested in each of the 45 common tissues by comparing the individual expression values of 18,670 out of 19,644 informative protein-coding genes in men versus women.
[…] there are over 6500 protein-coding genes with significant SDE in at least one tissue. Most of these genes have SDE in just one tissue, but about 650 have SDE in two or more tissues, 31 have SDE in more than five tissues, and 22 have SDE in nine or more tissues

Sex-related variation in human behavior and the brain
Melissa Hines
Trends in cognitive science, 2010
https://www.researchgate.net/publication/45720564_Sex-related_variation_in_human_behavior_and_the_brain

Male and female fetuses differ in testosterone concentrations beginning as early as week 8 of gestation. This early hormone difference exerts permanent influences on brain development and behavior. Contemporary research shows that hormones are particularly important for the development of sex-typical childhood behavior, including toy choices, which until recently were thought to result solely from sociocultural influences. Prenatal testosterone exposure also appears to influence sexual orientation and gender identity, as well as some, but not all, sex-related cognitive, motor and personality characteristics. Neural mechanisms responsible for these hormone-induced behavioral outcomes are beginning to be identified, and current evidence suggests involvement of the hypothalamus and amygdala, as well as interhemispheric connectivity, and cortical areas involved in visual processing.