Sex differences in humans
Sex differences in humans have been studied in a variety of fields.
Sex differences in medicine include sex-specific diseases, which are diseases that occur only in people of one sex; and sex-related diseases, which are diseases that are more common to one sex, or which manifest differently in each sex. For example, certain autoimmune diseases may occur predominantly in one sex, for unknown reasons. 90% of primary biliary cirrhosis cases are women, whereas primary sclerosing cholangitis is more common in men. Gender-based medicine, also called "gender medicine", is the field of medicine that studies the biological and physiological differences between the human sexes and how that affects differences in disease. Traditionally, medical research has mostly been conducted using the male body as the basis for clinical studies. The findings of these studies have often been applied across the sexes and healthcare providers have assumed a uniform approach in treating both male and female patients. More recently, medical research has started to understand the importance of taking the sex into account as the symptoms and responses to medical treatment may be very different between sexes.
Neither concept should be confused with sexually transmitted diseases, which are diseases that have a significant probability of transmission through sexual contact.
Sex-related illnesses have various causes:
- Sex-linked genetic illnesses
- Parts of the reproductive system that are specific to one sex
- Social causes that relate to the gender role expected of that sex in a particular society.
- Different levels of prevention, reporting, diagnosis or treatment in each gender.
Sex differences in human physiology are distinctions of physiological characteristics associated with either male or female humans. These can be of several types, including direct and indirect. Direct being the direct result of differences prescribed by the Y-chromosome, and indirect being a characteristic influenced indirectly (e.g. hormonally) by the Y-chromosome. Sexual dimorphism is a term for the phenotypic difference between males and females of the same species. Sex differences are also increased or decreased according to societal situations.
Direct sex differences follow a bimodal distribution. Through the process of meiosis and fertilization (with rare exceptions), each individual is created with zero or one Y-chromosome. The complementary result for the X-chromosome follows, either a double or a single X. Therefore, direct sex differences are usually binary in expression (although the deviations in complex biological processes produce a menagerie of exceptions). These include, most conspicuously, male (vs female) gonads.
Indirect sex differences are general differences as quantified by empirical data and statistical analysis. Most differing characteristics will conform to a bell-curve (i.e. normal) distribution which can be broadly described by the mean (peak distribution) and standard deviation (indicator of size of range). Often only the mean or mean difference between sexes is given. This may or may not preclude overlap in distributions. For example, most males are taller and stronger than females, but an individual female could be taller and/or stronger than an individual male. These differences and their extent vary across societies.
The most obvious differences between males and females include all the features related to reproductive role, notably the endocrine (hormonal) systems and their physiological and behavioural effects, including gonadal differentiation, internal and external genital and breast differentiation, and differentiation of muscle mass, height, and hair distribution.
Research on biological sex differences in human psychology investigates cognitive and behavioral differences between men and women. This research employs experimental tests of cognition, which take a variety of forms. Tests focus on possible differences in areas such as IQ, spatial reasoning, aggression, emotion, and brain structure and function.
Most IQ tests are constructed so that there are no overall score differences between females and males. Areas where differences have been found include verbal and mathematical ability.
Because social and environmental factors affect brain activity and behavior, where differences are found, it can be difficult for researchers to assess whether or not the differences are innate. Studies on this topic explore the possibility of social influences on how both sexes perform in cognitive and behavioral tests. Stereotypes about differences between men and women have been shown to affect a person's behavior (this is called stereotype threat).
Differences in male and female jealousy can also be observed. While female jealousy is more likely to be inspired by emotional infidelity, male jealousy is most likely to be brought on by sexual infidelity. A clear majority of approximately 62% to 86% of women reported that they would be more bothered by emotional infidelity and a clear majority of 47% to 60% of men reported that they would be more bothered by sexual infidelity.
Sex differences in crime are differences between men and women as the perpetrators and/or victims of crime. Such studies may belong to fields such as criminology or sociobiology (which attempts to demonstrate a causal relationship between biological factors, in this case sex, and human behaviors), etc. Despite the difficulty to interpret them, crime statistics may provide a way to investigate such a relationship, whose possible existence would be interesting from a gender differences perspective. An observable difference in crime rates between men and women might be due to social and cultural factors, crimes going unreported, or to biological factors (as sociobiological theories claim). Furthermore, the nature of the crime itself must be considered.
Crime can be measured by such data as arrest records, imprisonment rates, and surveys. However, not all crimes are reported or investigated. Moreover, some studies show that men can have an overwhelming bias against reporting themselves to be the victims of a crime (particularly when victimized by a woman), and some studies have argued that men reporting intimate partner violence find disadvantageous biases in law enforcement.
Sometimes and at some places, there are sex differences in educational achievement. This may be caused by sex discrimination in the law, in the culture, or may reflect natural differences in the interests of the sexes.
At all levels women are achieving higher representation and success. At the post-secondary level women are earning most of the degrees awarded.
Research has been undertaken to examine whether or not there are sex differences in leadership. Until recently, leadership positions have predominantly been held by men and men were therefore stereotyped to be more effective leaders. Women were rarely seen in senior leadership positions leading to a lack of data on how they behave in such positions. However, due to current research and women becoming more prevalent in the workforce over the past two decades, especially in management and leadership positions, these stereotypes are changing and various conclusions about gender effects on leadership are being made. The two main lines of research contradict one another, the first being that there are significant sex differences in leadership and the second being that gender does not have an effect on leadership.
Sex differences in religion can be classified as either "internal" or "external". Internal religious issues are studied from the perspective of a given religion, and might include religious beliefs and practices about the roles and rights of men and women in government, education and worship; beliefs about the sex or gender of deities and religious figures; and beliefs about the origin and meaning of human gender. External religious issues can be broadly defined as an examination of a given religion from an outsider's perspective, including possible clashes between religious leaders and laity; and the influence of, and differences between, religious perspectives on social issues. For example, various religious perspectives have either endorsed or condemned alternative family structures, homosexual relationships, and abortion. External religious issues can also be examined from the "lens of gender" perspective embraced by some in feminism and/or critical theory and its offshoots.
Social capital 
Sex differences in social capital are differences between men and women in their ability to co-ordinate actions and achieve their aims through trust, norms and networks. Social capital is often seen as the missing link in development; as social networks facilitate access to resources and protect the commons, whilst co-operation makes markets work more efficiently. Social capital has been thought of as women's capital as whereas there are gendered barriers to accessing economic capital, women's role in family, and community ensures that they have strong networks. There is potential that the concept can help to bring women's unpaid 'community and household labour', vital to survival and development, to the attention of economists. However, research analysing social capital from a gendered perspective is rare, and the notable exceptions are very critical.
Sex differences in suicide have been shown to be significant; there are highly asymmetric rates of attempted and completed suicide between males and females. The gap, also called the gender paradox of suicidal behavior, can vary significantly between different countries. Statistics indicate that males die much more often by means of suicide than do females, however reported suicide attempts are 3 times more common among females than males.
- Cuozzo, Karen; Bratman, Steven (reviewer) (2005, September (last reviewed)). "Women, Men, and Medicine: We're Not Equal". EBSCO Publishing.
- Birke, Lydia. The Gender and Science Reader ed. Muriel Lederman and Ingrid Bartsch. New York, Routledge, 2001. 306-322
- Gustafsson A & Lindenfors P (2004). "Human size evolution: no allometric relationship between male and female stature". Journal of Human Evolution 47 (4): 253–266. doi:10.1016/j.jhevol.2004.07.004. PMID 15454336.
- Neisser, U.; Boodoo, G.; Bouchard, T. J. , J.; Boykin, A. W.; Brody, N.; Ceci, S. J.; Halpern, D. F.; Loehlin, J. C. et al. (1996). "Intelligence: Knowns and unknowns". American Psychologist 51 (2): 77. doi:10.1037/0003-066X.51.2.77.
- Fine, Cordelia (2010). Delusions of Gender: How Our Minds, Society, and Neurosexism Create Difference. W. W. Norton. ISBN 0-393-06838-2.
- Ann M. Gallagher, James C. Kaufman, Gender differences in mathematics: an integrative psychological approach, Cambridge University Press, 2005, ISBN 0-521-82605-5, ISBN 978-0-521-82605-1
- Pietrzak, Laird, Stevens, Thompson, Robert, James, David, Nicholas (March 2002). "Sex differences in human jealousy: A coordinated study of forced-choice, continuous rating-scale, and physiological responses on the same subjects". Evolution and Human Behavior: 83–94. Retrieved 21 March 2013.
- "[M]en who are involved in disputes with their partners, whether as alleged victims or as alleged offenders or both, are disadvantaged and treated less favorably than women by the law-enforcement system at almost every step." Brown, G. (2004). Gender as a factor in the response of the law-enforcement system to violence against partners. Sexuality and Culture, 8, (3-4), 3-139.
- Felson, R. B., & Pare, P. (2005). The reporting of domestic violence and sexual assault by nonstrangers to the police. Journal of Marriage and Family, 67, 597-610
- Felson, R. B. (2008). The legal consequences of intimate partner violence for men and women. Children and Youth Services Review, 30, 639-646.
- Pearson, Jennifer. "Gender, Education and." Blackwell Encyclopedia of Sociology. Ritzer, George (ed). Blackwell Publishing, 2007. Blackwell Reference Online. 31 March 2008 <http://www.blackwellreference.com.libproxy.lib.unc.edu/subscriber/tocnode?id=g9781405124331_chunk_g978140512433113_ss1-16>
- as cited in Andersen, J. A. & Hansson, P. H. (2011). "At the end of the road? On differences between women and men in leadership behavior." Leadership and Organization Development Journal, 32 (5), 428-441.
- Juschka, Darlene. "Gender." In ed. J. Hinnels. The Routledge Companion to the Study of Religion. 2nd ed. New York: Routledge, 2010:245-258.
- 'Unborn Child Protection Bill', State Parliament of New South Wales, 2006.
- Laurie, Nina; Andolina, Robert; and Radcliffe, Sarah (2005) 'Ethnodevelopment: Social Movements, Creating Experts and Professionalising Indigenous Knowledge in Ecuador' Antipode 37(3): 470-496
- Putnam, Robert. (1993) Making Democracy Work. Civic Traditions in Modern Italy. Princeton University Press.
- Moser, Caroline (1993) Gender Planning and Development: Theory, Practice and Training London and New York: Routledge
- Molyneux, Maxine (2002) Gender and the Silences of Social Capital: Lessons from Latin America Development and Change 33 (2):167-188
- Maclean, Kate (2010) 'Capitalising on Women's Social Capital? Women-targeted Microfinance in Bolivia' Development and Change 41 (3) pp 495-515
- Rankin, K (2002) Social Capital, Microfinance and the Politics of development Feminist Economics 8 (1) pp 1-24
- Udry, J. Richard (November 1994). "The Nature of Gender". Demography 31 (4): 561–573. doi:10.2307/2061790. JSTOR 2061790. PMID 7890091.
- Canetto, Silvia. "The Gender Paradox in Suicide". Suicide and Life Threatening Behavior 28 (1): 5.
- "Suicide Statistics at Suicide.org". Suicide prevention, awareness, and support. Suicide.org. 2005.