Biology of gender

The biology of gender is scientific analysis of the physical basis for behavioural differences between men and women. It is more specific than sexual dimorphism, which covers physical and behavioural differences between males and females of any sexually reproducing species, or sexual differentiation, where physical and behavioural differences between men and women are described.

Biological research of gender has explored such areas as: intersex physicalities, gender identity, gender roles and sexual preference. Late twentieth century study focused on hormonal aspects of the biology of gender. With the successful mapping of the human genome, early twenty-first century research started making progress in understanding the effects of gene regulation on the human brain.

Research in this area is generally motivated by the search for causes of diseases in human beings, and ways of treating or preventing those diseases; it is thought that men and women might require different kinds of treatment for certain diseases. The results are relevant to gender issues, but that is not their direct concern.

History

It has long been known that there are correlations between the biological sex of animals and their behaviour. [Charles Darwin, "On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life", (London: John Murray, 1859).] [Charles Darwin, "The Descent of Man, and Selection in Relation to Sex", 2 volumes, (London: John Murray, 1871).] [Helena Cronin, "The Ant and the Peacock: Altruism and Sexual Selection from Darwin to Today", (Cambridge: Cambridge University Press, 1991).]

The late twentieth century saw an explosion in technology capable of aiding sex research. John Money and Milton Diamond made great progress towards understanding the formation of gender identity in humans. Extensive advances were also made in understanding sexual dimorphism in other animals. For example, there were studies on the effects of sex hormones on rats. The early twenty first century started producing even more amazing results concerning genetically programmed sexual dimorphism in rat brains, prior even to the influence of hormones on development. "Genes on the sex chromosomes can directly influence sexual dimorphism in cognition and behaviour, independent of the action of sex steroids." [cite journal|last=Skuse|first=David H|title=Sexual dimorphism in cognition and behaviour: the role ofX-linked genes|journal=European Journal of Endocrinology|volume=155|pages=99–106|date=2006|doi=10.1530/eje.1.02263]

Differences

Brain

The brains of many animals, including humans, are significantly different for males and females of the species. [ [https://mitpress.mit.edu/catalog/item/default.asp?ttype=2&tid=10042&mode=toc Robert W Goy and Bruce S McEwen. "Sexual Differentiation of the Brain: Based on a Work Session of the Neurosciences Research Program". MIT Press Classics. Boston: MIT Press, 1980.] ] Both genes and hormones affect the formation of many animal brains before "birth" (or hatching), and also behaviour of adult individuals. Hormones significantly affect human brain formation, and also brain development at puberty. Both kinds of brain difference affect male and female behaviour.

In 2006, Alexandra M. Lopes and others published that:

It is commonly accepted that there are many sex-related differences in behavior in the human species. These differences and their neurobiological bases have been sought. Gur "et al." suggested that women have a higher percentage of grey matter (GM) in comparison to men, and that men have a higher percentage of white matter (WM) and of cerebrospinal fluid (CSF). In Gur's study, in men the percentage of GM was higher in the left hemisphere, the percentage of WM was symmetric, and the percentage of CSF was higher in the right hemisphere. In women, no asymmetry was shown. Gur "et al." stated that the higher percentage of GM in women could compensate for less space in the cranium, since GM is used for computation more than transfer of information across distant regions. They state that the sex-based differences in percentage and asymmetry of GM and WM in the brain may account for the differences in cognitive functioning of the two sexes. They also stated:cite journal
last = Gur
first = Ruben C.
authorlink =
coauthors = Bruce I. Turetsky, Mie Matsui, Michelle Yan, Warren Bilker, Paul Hughett, Raquel E. Gur
title = Sex Differences in Brain Gray and White Matter in Healthy Young Adults: Correlations with Cognitive Performance
journal = The Journal of Neuroscience
volume = 19
issue = 10
pages = 4065–4072
publisher =
location =
date = 1999-05-15
url = http://www.jneurosci.org/cgi/content/full/19/10/4065
doi =
id =
accessdate = 2008-05-24]

Haier and colleagues used voxel-based morphometry (VBM) to identify brain areas where clusters GM and WM volumes are located in correlation to the FSIQ test. In 2004, Haier et al. claimed that: cquote|These findings support the view that individual differences in grey and white matter volumes, in a relatively small number of areas distributed throughout the brain, account for considerable variance in individual differences in general intelligence. [Haier, R., et al. 2004. Structural brain variation and general intelligence. Neuroimage 23: 425-433.] However, both neuronal cell bodies (grey matter) and axons (white matter) are essential to the function of the nervous system, so the functional implication of having more of one or the other is not clear.

See the sex and intelligence article for more information and research findings on this subject.

Aptitude

A 2001 report by Richard J. Coley of the ETS stated, "A review of the elementary and secondary education achievement data included in this report from NAEP found that females in all racial/ethnic groups scored higher, on average, than males in reading, writing, and civics. There was an advantage found in science for Hispanic and White males. In mathematics, essentially no differences between males and females were found." [cite web
last =
first =
authorlink =
coauthors =
title = Differences in the Gender G

work =
publisher = Educational Testing Service; Research Division: Policy Information Center
date =
url = http://www.ets.org/research/researcher/PIC-GENDER.html
format =
doi =
accessdate = 2008 [http://www.ets.org/Media/Research/pdf/PICGENDER.pdf] .]

Kiefer and Sekaquaptewa proposed that a source of some women's underperformance and lowered perseverance in mathematical fields is these women's underlying "implicit" sex-based stereotypes regarding mathematical ability and association, as well as their identification with their gender. [ [http://www.sciencedaily.com/releases/2007/01/070124104155.htm "Implicit Stereotypes and Gender Identification May Affect Female Math Performance."] Science Daily (Jan 24, 2007).]

A number of studies have looked for sex differences in the brain that might relate to sex differences in intelligence or performance on different tasks. These studies have included measures of total brain size, relative amounts of grey and white matter, and a wide variety of measures of brain activity patterns (Sex and Intelligence). However, findings of sex differences in the brain do not answer the Nature versus Nurture controversy raised again by Summers' comments, because studies of neuroplasticity show that the brain can be altered by experience.

In mathematical reasoning, Benbow et al. stated of a 1983 study: cquote|When graphed (Benbow, 1988), the male and female SAT-V [verbal] distributions were found to be essentially equivalent, but the male SAT-M [math] distributions manifested a higher mean and larger variance than was observed for the females. Consequently, an exponential intensification of the male:female ratio occurred in the upper tail of the combined distribution. The ratio was 2:1 for adolescents with SAT-M scores of at least 500, 4:1 for those with scores of at least 600, and 13:1 for those with scores of at least 700. [cite journal
last = Benbow
first = Camilla Persson
authorlink =
coauthors = David Lubinski, Daniel L. Shea, Hossain Eftekhari-Sanjani
title = Sex Differences in Mathethematical Reasoning Ability at Age 13: Their Status 20 Years Later
journal = Psychological Science
volume = 11
issue = 6
pages = 474–480
publisher =
location =
date = 2000-11
url = http://www.vanderbilt.edu/Peabody/SMPY/SexDiffs.pdf
doi =
id =
accessdate = 2008-05-25] In 1983, Benbow stated of the study, "The results obtained by both procedures establish that by age 13 a large sex difference in mathematical reasoning ability exists and that it is especially pronounced at the high end of the distribution [...] ." [Camilla Persson Benbow and Julian C Stanley, [http://www.sciencemag.org/cgi/content/abstract/222/4627/1029 'Sex Differences in Mathematical Reasoning Ability: More Facts'] , "Science" 222 (1983): 1029-1031. ]

Baron-Cohen states that the male:female ratio of autism is 4:1, and examines autism beginning from a theory of the "male brain type," a hypothetical construct defined as "an individual whose folk physics skills are in advance of his or her social folk psychology skills. That is, they show a folk physics>folk psychology discrepancy. This is regardless of one’s chromosomal sex." [cite web
last = Baron-Cohen
first = Simon
url = http://www.autismresearchcentre.com/docs/papers/1999_BC_extrememalebrain.pdf
title = The Extreme-Male-Brain Theory of Autism]

Aggression

Campbell argues that "female competition is more likely to take the form of indirect aggression or low-level direct combat than among males." Campbell goes on to state that "cultural interpretations have 'enhanced' evolutionarily based sex differences by a process of imposition which stigmatises the expression of aggression by females and causes women to offer exculpatory (rather than justificatory) accounts of their own aggression." [cite journal
last = Campbell
first = A.
title = Staying alive: evolution, culture, and women's intrasexual aggression.
journal = Behav Brain Sci.
volume = 27
issue = 2
pages = 203–214
publisher =
location =
date = 2004-04
url = http://www.ncbi.nlm.nih.gov/pubmed/11301523
doi =
id =
accessdate = 2008-05-25] Research has shown that stimulation of the amygdala induces a delayed and prolonged increase of aggressiveness in male Syrian golden hamsters, [Decoster, M, M Herbert, J L. Meyerhoff, and M Potegal. "Brief, High-Frequency Stimulation o the Corticomedial Amygdala Induces a Delayed and Prolonged Increase of Aggressiveness in Male Syrian Golden Hamsters." Behavioral Neuroscience 110 (1996): 401-412. 7 Dec. 2006 . ] and in the hypothalamus of male rats. [Hermans, J, M R. Kruk, A H. Lohman, W Meelis, J Mos, P G. Mostert, and A M. Van Der Poel. "Discriminant Analysis of the Localization of Aggression-Inducing Electrode Placements in the Hypothalamus of Male Rats." Brain Research 260 (1983): 61-79.. ] . Many studies have examined the correlation between aggression and certain hormones and neurotransmitters, specifically testosterone. However, the link between testosterone and aggression in humans remains unclear [Albert, D.J., M L. Walsh, and R H. Jonik. "Aggression in Humans: What is Its Biological Foundation?" Neuroscience and Biobehavioral Reviews 4 (1993): 405-425..] [Beresford, B., E F. Coccaro, T. Geracioti, J. Kaskow, and P. Minar. "CSF Testosterone: Relationship to Aggression, Impulsivity, and Venturesomeness in Adult Males with Personality Disorder." Journal of Psychiatric Research (2006).. ] [Chandler, D W., J N. Constantino, F J. Earls, D Grosz, R Nandi, and P Saenger. "Testosterone and Aggression in Children." Journal of the American Academy of Child and Adolescent Psychology 32 (1993): 1217-1222..] . A more established negative correlation has been discovered between serotonin and aggression, meaning that higher levels of serotonin are correlated with lower levels of aggression and vice versa [Cherek, D. R., D. Collins, C. M. Davis, D M. Dougherty, F G. Moeller, and A C. Swann. "Tryptophan Depletion and Aggressive Responding in Healthy Males." Psychopharmacology 126 (1996): 97-103.. ] .

ee also

*Brain Sex, a book by Anne Moir (geneticist) and David Jessel (journalist)
*Platypus (complex sex chromosomes)
*Prenatal hormones and sexual orientation

References

External links

* [http://www.ibangs.org International Behavioural and Neural Genetics Society]
* Kritz, Francesca Lunzer. [http://www.washingtonpost.com/wp-dyn/content/article/2006/12/15/AR2006121501879.html 'Not Feeling Each Other's Pain:] Men and Women Hurt Differently – and Some of The Difference May Really Be in Their Heads'. "The Washington Post", 19 December 2006. Page HE01.
* Stanton, Laura, and Maloney, Brenna. [http://www.washingtonpost.com/wp-dyn/content/graphic/2006/12/18/GR2006121800372.html 'The Perception of Pain', "Washington Post" (19 December 2006).]
* Marks, Jonathan. [http://personal.uncc.edu/jmarks/pubs/Un-Textbook/MarksUnTextbook08.pdf 'Essay 8: Primate Behavior'.] In "The Un-Textbook of Biological Anthropology". Unpublished, 2007.
* Pinker vs. Spelke. [http://www.edge.org/3rd_culture/debate05/debate05_index.html 'The Science of Gender and Science'.] "Edge" (The Third Culture) 16 May, 2005. (multimedia record of public debate)
* Rabinowicz T, and others. [http://www.ncbi.nlm.nih.gov/sites/entrez?cmd=Retrieve&db=PubMed&list_uids=10073431&dopt=Abstract 'Gender differences in the human cerebral cortex:] more neurons in males; more processes in females'. "Journal of Child Neurology" 14 (1999): 98-107.
* Runyan, Andrea. [http://www.possibility.com/epowiki/Wiki.jsp?page=SexIsMoreThanSocialization 'Sex Is More Than Socialization'.] "epowiki", August 18, 2005.
* Shaywitz, BA, and others. [http://www.ncbi.nlm.nih.gov/sites/entrez?cmd=Retrieve&db=PubMed&list_uids=7854416&dopt=Abstract 'Sex differences in the functional organisation of the brain for language'.] "Nature" 373 (1995): 607-609.

Literature

* Baron-Cohen, Simon. "The Essential Difference: The Truth about the Male and Female Brain". New York: Perseus Books Group, 2003.
* Brizendine, Louann. "The Female Brain". New York: Morgan Road Books, 2006.
* Brown, Donald E. "Human Universals". New York: McGraw Hill, 1991.
* Kimura, Doreen. "Sex and Cognition". MIT Press, 1999.
* Moir, Anne and David Jessel. "Brain Sex: The Real Difference Between Men and Women".
* Pinker, Steven. "The Blank Slate: A Modern Denial of Human Nature". London: Penguin Books, 2002.

Journals

* [http://www.blackwellpublishing.com/journal.asp?ref=1601-1848 "Genes, Brains and Behavior"]