oxytocin & testosterone underlie male disposability

Sex-differentiated physiological responses to stress favor male disposability.  Oxytocin, a neuroactive hormone linked to maternal behavior and enhanced by estrogen, facilitates approach behavior and more generally, social affiliation. Oxytocin has been found to increase trust in mammals.[1]  Oxytocin is more up-regulated in women’s stress response than in men’s.  In response to stress, women tend-and-befriend in-group members and rally social antagonism toward out-group individuals.  Men’s response to stress tends toward decreasing trust, indiscriminate avoidance, and isolation.  Men’s behavioral response to stress is associated with down-regulation of oxytocin.[2]

Compared to women, men have on average about a ten times higher level of serum testosterone.  Increases in testosterone suppress immune system functioning and are correlated with competing for dominance.[3]  The large difference in males’ and females’ basal testosterone levels is also correlated with greater male risk of predation, greater male susceptibility to infectious diseases, much higher male suicide rates, and increased male-female mortality protrusion under conditions of chronic stress.

Gender protrusion in male mortality is common across animals and is linked to stress.  Among 26 mammalian species for which data are available, the median male/female predation death ratio is about 1.7.[4]  Death from parasites (infectious disease) is also male-biased.[5]  In the U.S., the male/female suicide mortality ratio is 3.9, the highest sex ratio among enumerated causes of death.  Under conditions of chronic stress, male testosterone levels typically fall while female testosterone levels rise.  Russia from 1990 to 2000 provides a historical example of significant, sex-differentiated effects of chronic stress.  Across those years, the gender protrusion in mortality grew from 10 years shorter expected lifespan for males to 13 years shorter expected lifespan for males.[6]

A man’s physiological response to stress tends to separate him from others and increase his mortality risk.  A woman’s physiological response to stress tends to integrate her with others and socialize concern about risk to her.  Social effects of those biological mechanisms of male disposability are starkly evident in the sex-differentiated social response to interpersonal violent injury and to rape.

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Notes:

[1] Anacker & Beery (2013), Curley & Keverne (2005), Lieberwirth & Wang (2014).  As Lieberwirth & Wang (2014) p. 8 observes, sex differences in hormonal response have been relatively under-studied.

[2] Taylor et al. (2000), Tamres, Janicki & Helgeson (2002), De Dreu et al. (2011), Palgi, Klein & Shamay-Tsoory (2014).  Estrogen strongly increases oxytocin’s effects.  Taylor (2006) p. 276.

[3] Grant (2005) p. 2.  In males, testosterone is secreted primarily from the testes.  In females, testosterone originates in peripheral tissues.  On behavioral effects of sex differences in testosterone, Klein (2000), Grant (2005) pp. 3-11, Lamason et al. (2006), and Edwards (2006).  Grant convincingly argues that dominance, understood as “acting overtly to change the views or actions of another” is not the same as aggression.  She also documents that dominance is more closely correlated with testosterone differences than is aggression.  The hormone arginine vasopressin (AVP) also has sex-differentiated activity:

In men, AVP stimulates agonistic facial motor patterns in response to the faces of unfamiliar men and decreases the perceptions of the friendliness of those faces. In contrast, in women, AVP stimulates affiliative facial motor patterns in response to the faces of unfamiliar women and increases perceptions of the friendliness of those faces.

Thompson et al. (2006) p. 7889.  In males, AVP is associated with the formation of bonds with female mates, as well as territorial marking and aggression. Curley & Keverne (2005) p. 562.

[4] Christe, Keller & Roulin (2006).

[5] Lamason et al. (2006).

[6] See workbook Male-Female Gender Protrusion in Mortality in Russia (Excel version).  That data come from World DataBank Gender Statistics.  The WorldBank’s summary page for the Russian Federation reflects now-dominant anti-men gender bigotry.  Shkolnikov & Meslé (1996) Table 4.1 provides a century-long perspective.

References:

Anacker, Allison M. J., and Annaliese K. Beery. 2013. “Life in groups: the roles of oxytocin in mammalian sociality.” Frontiers in Behavioral Neuroscience. 7.

Christe, P., L. Keller and A. Roulin. 2006. “The predation cost of being a male: implications for sex-specific rates of ageing.” Oikos 114(2): 381-384.

Curley, James P. and Eric B. Keverne (2005). “Genes, brains and mammalian social bonds.” Trends in Ecology and Evolution 20(10): 561-567.

De Dreu Carsten K.W., Lindred L. Greer, Gerben A. Van Kleef, Shaul Shalvi, and Michel J.J. Handgraaf. 2011. “Oxytocin promotes human ethnocentrism.” Proceedings of the National Academy of Sciences of the United States of America. 108 (4): 1262-6.

Edwards, David. 2006. “Competition and testosterone.” Hormones and Behavior 50: 681-3.

Grant, Valerie J. 2005. “Dominance, Testosterone and Psychological Sex Differences.” Pp. 1-28 in Janice W. Lee, ed. Psychology of Gender Identity. New York, Nova Science Publishers: 1-28.

Klein, Sabra L. 2000. “Hormones and mating system affect sex and species differences in immune function among vertebrates.” Behavioural Processes 51(1-3): 149-166.

Lamason, Rebecca, Po Zhao, Rashmi Rawat, Adrian Davis, John C. Hall, Jae Jin Chae, Rajeev Agarwal, Phillip Cohen, Antony Rosen, Eric P. Hoffman and Kanneboyina Nagaraju. 2006. “Sexual dimorphism in immune response genes as a function of puberty.” BMC Immunology 7(2): 1-14.

Lieberwirth, Claudia, and Zuoxin Wang. 2014. “Social bonding: regulation by neuropeptides.” Frontiers in Neuroscience. 8 (4).

Palgi, Sharon, Ehud Klein, and Simone G. Shamay-Tsoory. 2014. “Intranasal administration of oxytocin increases compassion toward women.” Social Cognitive and Affective Neuroscience. (5).

Shkolnikov, Vladimir M. and France Meslé. 1996. “The Russian Epidemiological Crisis as Mirrored by Mortality Trends.” In Julie DaVanzo and Gwen Farnsworth, eds. Russia’s Demographic “Crisis”. RAND Conference Proceedings CF-124-CRES.

Tamres, Lisa K., Denise Janicki, and Vicki S. Helgeson. 2002. “Sex Differences in Coping Behavior: A Meta-Analytic Review and an Examination of Relative Coping.” Personality and Social Psychology Review. 6 (1): 2-30.

Taylor, Shelley E., Laura Cousino Klein, Brian P. Lewis, Tara L. Gruenewald, Regan A.R. Gurung and John A. Updegraff. 2000. “Biobehavioral Responses to Stress in Females: Tend-and-Befriend, not Fight-or-Flight.” Psychological Review 107(3): 411-429.

Taylor, Shelley E. 2006. “Tend and Befriend: Biobehavioral Bases of Affiliation Under Stress.” Current Directions in Psychological Science. 15 (6): 273-277.

Thompson, R. R., K. George, J. C. Walton, S. P. Orr and J. Benson. 2006. “Sex-specific influences of vasopressin on human social communication.” Proceedings of the National Academy of Science 103(20): 7889-7894.

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