Gender identity is one's personal experience of one's own gender. Gender identity can correlate with assigned sex at birth, or can differ from it. All societies have a set of gender categories that can serve as the basis of the formation of a person's social identity in relation to other members of society. In most societies, there is a basic division between gender attributes assigned to males and females, a gender binary to which most people adhere and which includes expectations of masculinity and femininity in all aspects of sex and gender: biological sex, gender identity, and gender expression. In all societies, some individuals do not identify with some (or all) of the aspects of gender that are assigned to their biological sex; some of those individuals are transgender, genderqueer or non-binary. There are some societies that have third gender categories.
Core gender identity is usually formed by age three. After age three, it is extremely difficult to change, and attempts to reassign it can result in gender dysphoria. Both biological and social factors have been suggested to influence its formation.
Age of formation
There are several theories about how and when gender identity forms, and studying the subject is difficult because children's lack of language requires researchers to make assumptions from indirect evidence. John Money suggested children might have awareness of, and attach some significance to gender, as early as 18 months to two years; Lawrence Kohlberg argues that gender identity does not form until age three. It is widely agreed that core gender identity is firmly formed by age three. At this point, children can make firm statements about their gender and tend to choose activities and toys which are considered appropriate for their gender (such as dolls and painting for girls, and tools and rough-housing for boys), although they do not yet fully understand the implications of gender. After age three, core gender identity is extremely difficult to change, and attempts to reassign it can result in gender dysphoria. Gender identity refinement extends into the fourth to sixth years of age, and continues into young adulthood.
Martin and Ruble conceptualize this process of development as three stages: (1) as toddlers and preschoolers, children learn about defined characteristics, which are socialized aspects of gender; (2) around the ages of 5–7 years, identity is consolidated and becomes rigid; (3) after this "peak of rigidity," fluidity returns and socially defined gender roles relax somewhat. Barbara Newmann breaks it down into four parts: (1) understanding the concept of gender, (2) learning gender role standards and stereotypes, (3) identifying with parents, and (4) forming gender preference.
According to UN agencies, discussions relating to comprehensive sexuality education raise awareness of topics, such as gender and gender identity. 
Factors influencing formation
Nature vs. nurture
Although the formation of gender identity is not completely understood, many factors have been suggested as influencing its development. In particular, the extent to which it is determined by socialization (environmental factors) versus innate (biological) factors is an ongoing debate in psychology, known as "nature versus nurture". Both factors are thought to play a role. Biological factors that influence gender identity include pre- and post-natal hormone levels. While genetic makeup also influences gender identity, it does not inflexibly determine it.
Social factors which may influence gender identity include ideas regarding gender roles conveyed by family, authority figures, mass media, and other influential people in a child's life. When children are raised by individuals who adhere to stringent gender roles, they are more likely to behave in the same way, matching their gender identity with the corresponding stereotypical gender patterns. Language also plays a role: children, while learning a language, learn to separate masculine and feminine characteristics and unconsciously adjust their own behavior to these predetermined roles. The social learning theory posits that children furthermore develop their gender identity through observing and imitating gender-linked behaviors, and then being rewarded or punished for behaving that way, thus being shaped by the people surrounding them through trying to imitate and follow them.
A well-known example in the nature versus nurture debate is the case of David Reimer, otherwise known as "John/Joan". As a baby, Reimer went through a faulty circumcision, losing his male genitalia. Psychologist John Money convinced Reimer’s parents to raise him as a girl. Reimer grew up as a girl, dressing in girl clothes and surrounded by girl toys, but did not feel like a girl. After he tried to commit suicide at age 13, he was told that he had been born with male genitalia, which he underwent surgery to reconstruct. This went against Money’s hypothesis that biology had nothing to do with gender identity or human sexual orientation.
Several prenatal, biological factors, including genes and hormones, may affect gender identity. The biochemical theory of gender identity suggests that people acquire gender identities through such factors rather than socialization.
Hormonal influences are also complex; sex-determining hormones are produced at an early stage of foetal development, and if prenatal hormone levels are altered, phenotype progression may be altered as well, and the natural predisposition of the brain toward one sex may not match the genetic make-up of the fetus or its external sexual organs.
Hormones may affect differences between males' and females' verbal and spatial abilities, memory, and aggression; prenatal hormone exposure affects how the hypothalamus regulates hormone secretion later in life, with "women's sex hormones usually follow[ing] a monthly cycle [while] men’s sex hormones do not follow such a pattern."
A survey of the research literature from 1955–2000 suggests that more than one in every hundred individuals may have some intersex characteristic. An intersex human or other animal is one possessing any of several variations in sex characteristics including chromosomes, gonads, sex hormones, or genitals that, according to the UN Office of the High Commissioner for Human Rights, "do not fit typical binary notions of male or female bodies". An intersex variation may complicate initial sex assignment and that assignment may not be consistent with the child's future gender identity. Reinforcing sex assignments through surgical and hormonal means may violate the individual's rights.
A 2012 clinical review paper found that between 8.5% and 20% of people with intersex variations experienced gender dysphoria. Sociological research in Australia, a country with a third 'X' sex classification, shows that 19% of people born with atypical sex characteristics selected an "X" or "other" option, while 52% are women, 23% men, and 6% unsure. At birth, 52% of persons in the study were assigned female, and 41% were assigned male.
A study by Reiner & Gearhart provides some insight into what can happen when genetically male children with cloacal exstrophy are sexually assigned female and raised as girls, according to an 'optimal gender policy' developed by John Money: in a sample of 14 children, follow-up between the ages of 5 to 12 showed that 8 of them identified as boys, and all of the subjects had at least moderately male-typical attitudes and interests, providing support for the argument that genetic variables affect gender identity and behavior independent of socialization.
Biological causes of transgender and transsexuality
Some studies have investigated whether or not there is a link between biological variables and transgender or transsexual identity. Several studies have shown that sexually dimorphic brain structures in transsexuals are shifted away from what is associated with their birth sex and towards what is associated with their preferred sex. In particular, the bed nucleus of a stria terminalis or BSTc (a constituent of the basal ganglia of the brain which is affected by prenatal androgens) of trans women is similar to cisgender women's and unlike men's. Similar brain structure differences have been noted between gay and heterosexual men, and between lesbian and heterosexual women. Another study suggests that transsexuality may have a genetic component.
Research suggests that the same hormones that promote differentiation of sex organs in utero also elicit puberty and influence the development of gender identity. Different amounts of these male or female sex hormones within a person can result in behavior and external genitalia that do not match up with the norm of their sex assigned at birth, and in a person acting and looking like their identified gender.
Social and environmental factors
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In 1955, John Money proposed that gender identity was malleable and determined by whether a child was raised as male or female in early childhood. Money's hypothesis has since been discredited, but scholars have continued to study the effect of social factors on gender identity formation. In the 1960s and 1970s, factors such as the absence of a father, a mother's wish for a daughter, or parental reinforcement patterns were suggested as influences; more recent theories suggesting that parental psychopathology might partly influence gender identity formation have received only minimal empirical evidence, with a 2004 article noting that "solid evidence for the importance of postnatal social factors is lacking." A 2008 study found that the parents of gender-dysphoric children showed no signs of psychopathological issues aside from mild depression in the mothers.
It has been suggested that the attitudes of the child's parents may affect the child's gender identity, although evidence is minimal.
Parental establishment of gender roles
Parents who do not support gender nonconformity are more likely to have children with firmer and stricter views on gender identity and gender roles. Recent literature suggests a trend towards less well-defined gender roles and identities, as studies of parental coding of toys as masculine, feminine, or neutral indicate that parents increasingly code kitchens and in some cases dolls as neutral rather than exclusively feminine. However, Emily Kane found that many parents still showed negative responses to items, activities, or attributes that were considered feminine, such as domestic skills, nurturance, and empathy. Research has indicated that many parents attempt to define gender for their sons in a manner that distances the sons from femininity, with Kane stating that “the parental boundary maintenance work evident for sons represents a crucial obstacle limiting boys options, separating boys from girls, devaluing activities marked as feminine for both boys and girls, and thus bolstering gender inequality and heteronormativity.”
Many parents form gendered expectations for their child before it is even born, after determining the child's sex through technology such as ultrasound. The child thus arrives to a gender-specific name, games, and even ambitions. Once the child's sex is determined, most children are raised in accordance with it to be a man or a woman, fitting a male or female gender role defined partly by the parents.
When considering the parents' social class, lower-class families typically hold traditional gender roles, where the father works and the mother, who may only work out of financial necessity, still takes care of the household. However, middle-class "professional" couples typically negotiate the division of labor and hold an egalitarian ideology. These different views on gender from a child's parents can shape the child's understanding of gender as well as the child's development of gender.
Within a study conducted by Hillary Halpern it was hypothesized, and proven, that parent behaviors, rather than parent beliefs, regarding gender are better predictors for a child’s attitude on gender. It was concluded that a mother’s behavior was especially influential on a child’s assumptions of the child’s own gender. For example, mothers who practiced more traditional behaviors around their children resulted in the son displaying fewer stereotypes of male roles while the daughter displayed more stereotypes of female roles. No correlation was found between a father’s behavior and his children’s knowledge of stereotypes of their own gender. It was concluded, however, that fathers who held the belief of equality between the sexes had children, especially sons, who displayed fewer preconceptions of their opposite gender.
Gender variance and non-conformance
Gender identity can lead to security issues among individuals that do not fit on a binary scale. In some cases, a person's gender identity is inconsistent with their biological sex characteristics (genitals and secondary sex characteristics), resulting in individuals dressing and/or behaving in a way which is perceived by others as outside cultural gender norms. These gender expressions may be described as gender variant, transgender, or genderqueer (there is an emerging vocabulary for those who defy traditional gender identity), and people who have such expressions may experience gender dysphoria (traditionally called Gender Identity Disorder or GID). Transgender individuals are greatly affected by language and gender pronouns before, during, and after their transition.
In recent decades it has become possible to reassign sex surgically. Some people who experience gender dysphoria seek such medical intervention to have their physiological sex match their gender identity; others retain the genitalia they were born with (see transsexual for some of the possible reasons) but adopt a gender role that is consistent with their gender identity.
History and definitions
The terms gender identity and core gender identity were first used with their current meaning — one's personal experience of one's own gender — sometime in the 1960s. To this day they are usually used in that sense, though a few scholars additionally use the term to refer to the sexual orientation and sexual identity categories gay, lesbian and bisexual.
Early medical literature
In late-19th-century medical literature, women who chose not to conform to their expected gender roles were called "inverts", and they were portrayed as having an interest in knowledge and learning, and a "dislike and sometimes incapacity for needlework". During the mid 1900s, doctors pushed for corrective therapy on such women and children, which meant that gender behaviors that were not part of the norm would be punished and changed. The aim of this therapy was to push children back to their "correct" gender roles and thereby limit the number of children who became transgender.
Freud and Jung's views
In 1905, Sigmund Freud presented his theory of psychosexual development in Three Essays on the Theory of Sexuality, giving evidence that in the pregenital phase children do not distinguish between sexes, but assume both parents have the same genitalia and reproductive powers. On this basis, he argued that bisexuality was the original sexual orientation and that heterosexuality was resultant of repression during the phallic stage, at which point gender identity became ascertainable. According to Freud, during this stage, children developed an Oedipus complex where they had sexual fantasies for the parent ascribed the opposite gender and hatred for the parent ascribed the same gender, and this hatred transformed into (unconscious) transference and (conscious) identification with the hated parent who both exemplified a model to appease sexual impulses and threatened to castrate the child's power to appease sexual impulses. In 1913, Carl Jung proposed the Electra complex as he both believed that bisexuality did not lie at the origin of psychic life, and that Freud did not give adequate description to the female child (Freud rejected this suggestion).
1950s and 1960s
During the 1950s and '60s, psychologists began studying gender development in young children, partially in an effort to understand the origins of homosexuality (which was viewed as a mental disorder at the time). In 1958, the Gender Identity Research Project was established at the UCLA Medical Center for the study of intersex and transsexual individuals. Psychoanalyst Robert Stoller generalized many of the findings of the project in his book Sex and Gender: On the Development of Masculinity and Femininity (1968). He is also credited with introducing the term gender identity to the International Psychoanalytic Congress in Stockholm, Sweden in 1963. Behavioral psychologist John Money was also instrumental in the development of early theories of gender identity. His work at Johns Hopkins Medical School's Gender Identity Clinic (established in 1965) popularized an interactionist theory of gender identity, suggesting that, up to a certain age, gender identity is relatively fluid and subject to constant negotiation. His book Man and Woman, Boy and Girl (1972) became widely used as a college textbook, although many of Money's ideas have since been challenged.
In the late 1980s, Judith Butler began lecturing regularly on the topic of gender identity, and in 1990, she published Gender Trouble: Feminism and the Subversion of Identity, introducing the concept of gender performativity and arguing that both sex and gender are constructed.
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As of 2014[update], there is some changing of views and new discrepancies about the best way to deal with gender nonconformity. Some members of the medical field, as well as an increasing number of parents, no longer believe in the idea of conversion therapy. On the other hand, there are still a large number of clinicians who believe that there should be interventions for gender nonconforming children. They believe that stereotypical gender-specific toys and games will encourage children to behave in their traditional gender roles.
Transsexual self-identified people sometimes wish to undergo physical surgery to refashion their primary sexual characteristics, secondary characteristics, or both, because they feel they will be more comfortable with different genitalia. This may involve removal of penis, testicles or breasts, or the fashioning of a penis, vagina or breasts. In the past, sex assignment surgery has been performed on infants who are born with ambiguous genitalia. However, current medical opinion is strongly against this procedure, since many adults have regretted that these decisions were made for them at birth. Today, sex reassignment surgery is performed on people who choose to have this change so that their anatomical sex will match their gender identity.
In the United States, it was decided under the Affordable Care Act that health insurance exchanges would have the ability to collect demographic information on gender identity and sexual identity through optional questions, to help policymakers better recognize the needs of the LGBT community.
Gender dysphoria and gender identity disorder
Gender dysphoria (previously called "gender identity disorder" or GID in the DSM) is the formal diagnosis of people who experience significant dysphoria (discontent) with the sex they were assigned at birth and/or the gender roles associated with that sex: "In gender identity disorder, there is discordance between the natal sex of one's external genitalia and the brain coding of one's gender as masculine or feminine." The Diagnostic and Statistical Manual of Mental Disorders (302.85) has five criteria that must be met before a diagnosis of gender identity disorder can be made, and the disorder is further subdivided into specific diagnoses based on age, for example gender identity disorder in children (for children who experience gender dysphoria).
The concept of gender identity appeared in the Diagnostic and Statistical Manual of Mental Disorders in its third edition, DSM-III (1980), in the form of two psychiatric diagnoses of gender dysphoria: gender identity disorder of childhood (GIDC), and transsexualism (for adolescents and adults). The 1987 revision of the manual, the DSM-III-R, added a third diagnosis: gender identity disorder of adolescence and adulthood, nontranssexual type. This latter diagnosis was removed in the subsequent revision, DSM-IV (1994), which also collapsed GIDC and transsexualism into a new diagnosis of gender identity disorder. In 2013, the DSM-5 renamed the diagnosis gender dysphoria and revised its definition.
The authors of a 2005 academic paper questioned the classification of gender identity problems as a mental disorder, speculating that certain DSM revisions may have been made on a tit-for-tat basis when certain groups were pushing for the removal of homosexuality as a disorder. This remains controversial, although the vast majority of today's mental health professionals follow and agree with the current DSM classifications.
International human rights law
The Yogyakarta Principles, a document on the application of international human rights law, provide in the preamble a definition of gender identity as each person's deeply felt internal and individual experience of gender, which may or may not correspond with the sex assigned at birth, including the person's sense of the body (which may involve, if freely chosen, modification of bodily appearance or function by medical, surgical or other means) and other experience of gender, including dress, speech and mannerism. Principle 3 states that "Each person’s self-defined [...] gender identity is integral to their personality and is one of the most basic aspects of self-determination, dignity and freedom. No one shall be forced to undergo medical procedures, including sex reassignment surgery, sterilisation or hormonal therapy, as a requirement for legal recognition of their gender identity." and Principle 18 states that "Notwithstanding any classifications to the contrary, a person's sexual orientation and gender identity are not, in and of themselves, medical conditions and are not to be treated, cured or suppressed." Relating to this principle, the "Jurisprudential Annotations to the Yogyakarta Principles" observed that "Gender identity differing from that assigned at birth, or socially rejected gender expression, have been treated as a form of mental illness. The pathologization of difference has led to gender-transgressive children and adolescents being confined in psychiatric institutions, and subjected to aversion techniques — including electroshock therapy — as a 'cure'." The "Yogyakarta Principles in Action" says "it is important to note that while 'sexual orientation' has been declassified as a mental illness in many countries, 'gender identity' or 'gender identity disorder' often remains in consideration." These Principles influenced the UN declaration on sexual orientation and gender identity In 2015, gender identity was part of a Supreme Court case in the United States called Obergefell v Hodges in which marriage was no longer restricted between man and woman.
Non-binary gender identities
In some Polynesian societies, fa'afafine are considered to be a "third gender" alongside male and female. They are anatomically male, but dress and behave in a manner considered typically female. According to Tamasailau Sua'ali'i (see references), fa'afafine in Samoa at least are often physiologically unable to reproduce. Fa'afafine are accepted as a natural gender, and neither looked down upon nor discriminated against. Fa'afafine also reinforce their femininity with the fact that they are only attracted to and receive sexual attention from straight masculine men. They have been and generally still are initially identified in terms of labour preferences, as they perform typically feminine household tasks. The Samoan Prime Minister is patron of the Samoa Fa'afafine Association. Translated literally, fa'afafine means "in the manner of a woman."
In some cultures of Asia, a hijra is usually considered to be neither a man nor a woman. Most are anatomically male or intersex, but some are anatomically female. The hijra form a third gender role, although they do not enjoy the same acceptance and respect as males and females in their cultures. They can run their own households, and their occupations are singing and dancing, working as cooks or servants, sometimes prostitutes, or long-term sexual partners with men. Hijras can be compared to transvestites or drag queens of contemporary western culture.
The khanith form an accepted third gender in Oman. The khanith are male homosexual prostitutes whose dressing is male, featuring pastel colors (rather than white, worn by men), but their mannerisms female. Khanith can mingle with women, and they often do at weddings or other formal events. Khaniths have their own households, performing all tasks (both male and female). However, similarly to men in their society, khaniths can marry women, proving their masculinity by consummating the marriage. Should a divorce or death take place, these men can revert to their status as khaniths at the next wedding.
Many indigenous North American Nations had more than two gender roles. Those who belong to the additional gender categories, beyond cisgender man and woman, are now often collectively termed "two-spirit" or "two-spirited." There are parts of the community that take "two-spirit" as a category over an identity itself, preferring to identify with culture or Nation-specific gender terms.
- Sexual Orientation and Gender Expression in Social Work Practice, edited by Deana F. Morrow and Lori Messinger (2006, ISBN 0231501862), page 8: "Gender identity refers to an individual's personal sense of identity as masculine or feminine, or some combination thereof."
- Campaign, Human Rights. "Sexual Orientation and Gender Identity Definitions - Human Rights Campaign".
- V. M. Moghadam, Patriarchy and the politics of gender in modernising societies, in International Sociology, 1992: "All societies have gender systems."
- Carlson, Neil R.; Heth, C. Donald (2009), "Sensation", in Carlson, Neil R.; Heth, C. Donald, Psychology: the science of behaviour (4th ed.), Toronto, Canada: Pearson, pp. 140–141, ISBN 9780205645244.
- Jack David Eller, Culture and Diversity in the United States (2015, ISBN 1317575784), page 137: "most Western societies, including the United States, traditionally operate with a binary notion of sex/gender"
- For example, "transvestites [who do not identify with the dress assigned to their sex] existed in almost all societies." (G. O. MacKenzie, Transgender Nation (1994, ISBN 0879725966), page 43.) — "There are records of males and females crossing over throughout history and in virtually every culture. It is simply a naturally occurring part of all societies." (Charles Zastrow, Introduction to Social Work and Social Welfare: Empowering People (2013, ISBN 128554580X), page 234, quoting the North Alabama Gender Center.)
- Pamela J. Kalbfleisch; Michael J. Cody (1995). Gender, power, and communication in human relationships. Psychology Press. pp. 366 pages. ISBN 0805814043. Retrieved June 3, 2011.
- Ann M. Gallagher; James C. Kaufman (2005). Gender differences in mathematics: An integrative psychological approach. Cambridge University Press. ISBN 0-521-82605-5.
- Boles, 2013. Pages 101-102.
- A few authorities say it forms between ages 3-4 rather than precisely at age 3, e.g. George J. Bryjak and Michael P. Soraka, Sociology: Cultural Diversity in a Changing World (ed. Karen Hanson), Allyn & Bacon, 1997; 209-245
- Newmann, Barbara. Development Through Life: A Psychosocial Approach. Cengage Learning. p. 243. ISBN 9781111344665.
- Christopher Bates Doob, Social Inequality and Social Stratification in US Society
- J. A. Kleeman, The establishment of core gender identity in normal girls. I.(a) Introduction;(b) Development of the ego capacity to differentiate, in the Archives of Sexual Behavior, 1971: "Though gender identity formation continues into young adulthood and core gender identity establishment extends into the fourth year and possibly longer, core gender identity is fairly firmly formed by age 3[.]"
- E. Coleman, Developmental stages of the coming out process, in Journal of homosexuality, 1982: "Core gender and sex-role identities are well-formed by the age of 3 (Money & Ehrhardt, 1972). This is believed because attempts to reassign gender identity after age 3 result in further gender dysphoria."
- Stein MT, Zucker KJ, Dixon SD. December, 1997. "Gender Identity", The Nurse Practitioner. Vo. 22, No. 12, P. 104
- Martin, C.; Ruble, D. (2004). "Children's Search for Gender Cues Cognitive Perspectives on Gender Development". Current Directions in Psychological Science. 13 (2): 67–70. doi:10.1111/j.0963-7214.2004.00276.x.
- International technical guidance on sexuality education: An evidence-informed approach (PDF). Paris: UNESCO. 2018. p. 18. ISBN 978-92-3-100259-5.
- Effects of male sex hormones on gender identity, sexual behavior, and cognitive function, Zhong Nan Da Xue Xue Bao, Yi Xue Ban (Journal of Central South University, Medical Sciences), April 2006, 31(2):149-61
- Money, John (1994). "The concept of gender identity disorder in childhood and adolescence after 39 years". Journal of Sex and Marital Therapy. 20 (3): 163–77. doi:10.1080/00926239408403428. PMID 7996589.
- Susan Golombok, Robyn Fivush, Gender Development (1994, ISBN 0521408628), page 44: "When assigned and raised as boys, these genetic girls adopt a male gender identity and role, showing that a Y chromosome is not necessary for gender development to proceed in a male direction."
- Henslin, James M. (2001). Essentials of Sociology. Taylor & Francis. pp. 65–67, 240. ISBN 0-536-94185-8.
- "Factors Influencing Gender Identity".
- Williams, Michael, "Cultural Identity, Language Identity, Gender Identity", "The English Academy of South Africa", 2011
- Myers, David G. (2008). Psychology. New York: Worth.
- Martin, C. L.; Ruble, D. N.; Szkrybalo, J. (2002). "Cognitive theories of early gender development". Psychological Bulletin. 128 (6): 903–906. doi:10.1037/0033-2909.128.6.903. PMID 12405137.
- Nolen-Hoeksema (2014). Abnormal Psychology (6 ed.). McGraw-Hill. p. 368. ISBN 9781308211503.
- Martin, Carol; Diane Ruble; Joel Szkrybalo (2002). "Cognitive Theories of Early Gender Development". Psychological Bulletin. 128 (6): 903–913. doi:10.1037/0033-2909.128.6.903. PMID 12405137.
- Ghosh, Shuvo. "Gender Identity". MedScape. Retrieved October 29, 2012.
- Lynda Birke, In Pursuit Of Difference, scientific studies of women and men, in The Gender and Science Reader, page 310
- Hines, Melissa (2017-02-02). "Prenatal endocrine influences on sexual orientation and on sexually differentiated childhood behavior". Frontiers in Neuroendocrinology. 32 (2): 170–182. doi:10.1016/j.yfrne.2011.02.006. ISSN 0091-3022. PMC . PMID 21333673.
- Lynda Birke suggests that during the early stage of fetal development, specific hormones will enter the brain and “permanently affect how the hypothalamus works. As before, high levels of hormones known as androgens will stop the hypothalamus from ever organizing hormone cycles. If there are low levels, then it will be cyclic.” This early influence on brain determines the different frequency of hormone secretion later in male or female’s life. “Obviously, women’s sex hormones usually follow a monthly cycle,” while “men’s sex hormones do not follow such a pattern.” Birke, Lynda. The Gender and Science Reader. p. 313.
- Blackless, Melanie; Charuvastra, Anthony; Derryck, Amanda; Fausto-Sterling, Anne; Lauzanne, Karl; Lee, Ellen (March 2000). "How sexually dimorphic are we? Review and synthesis". American Journal of Human Biology. 12 (2): 151–166. doi:10.1002/(SICI)1520-6300(200003/04)12:2<151::AID-AJHB1>3.0.CO;2-F. ISSN 1520-6300. PMID 11534012.
- "Free & Equal Campaign Fact Sheet: Intersex" (PDF). United Nations Office of the High Commissioner for Human Rights. 2015. Retrieved 28 March 2016.
- Mieszczak, J; Houk, CP; Lee, PA (Aug 2009). "Assignment of the sex of rearing in the neonate with a disorder of sex development". Curr Opin Pediatr. 21 (4): 541–7. doi:10.1097/mop.0b013e32832c6d2c. PMID 19444113.
- Council of Europe; Commissioner for Human Rights (April 2015), Human rights and intersex people, Issue Paper
- Swiss National Advisory Commission on Biomedical Ethics NEK-CNE (November 2012). On the management of differences of sex development. Ethical issues relating to "intersexuality".Opinion No. 20/2012 (PDF). 2012. Berne.
- World Health Organization (2015). Sexual health, human rights and the law. Geneva: World Health Organization. ISBN 9789241564984.
- Furtado P. S.; et al. (2012). "Gender dysphoria associated with disorders of sex development". Nat. Rev. Urol. 9 (11): 620–627. doi:10.1038/nrurol.2012.182. PMID 23045263.
- "New publication "Intersex: Stories and Statistics from Australia"". Organisation Intersex International Australia. February 3, 2016. Retrieved 2016-08-18.
- Jones, Tiffany; Hart, Bonnie; Carpenter, Morgan; Ansara, Gavi; Leonard, William; Lucke, Jayne (2016). Intersex: Stories and Statistics from Australia (PDF). Cambridge, UK: Open Book Publishers. ISBN 978-1-78374-208-0. Archived from the original (PDF) on 14 September 2016. Retrieved 2 February 2016.
- Rosario, Vernon. "Reiner & Gearhart's NEJM Study on Cloacal Exstrophy – Review by Vernon Rosario, M.D., Ph.D." Intersex Society of North America.
- E. Vilain, Genetics of intersexuality, J. Gay Lesbian Psychother. 10 (2006) 9–26.
- A. Fleming, E. Vilain, The endless quest for sex determination genes, Clin.Genet. 67 (2005) 15–25.
- Savic, I.; Arver, S. (2011). "Sex dimorphism of the brain in male-to-female transsexuals". Cerebral Cortex. 21: 2525–2533. doi:10.1093/cercor/bhr032. Concluded that gynephilic trans women had brains like men's, but in a few areas, trans women's brains were different from both men's and women's brains.
- Gizewski, E. R.; Krause, E.; Schlamann, M.; Happich, F.; Ladd, M. E.; Forsting, M.; Senf, W. (2009). "Specific cerebral activation due to visual erotic stimuli in male-to-female transsexuals compared with male and female controls: An fMRI study". Journal of Sexual Medicine. 6: 440–448. doi:10.1111/j.1743-6109.2008.00981.x. Found that a sample of androphilic trans women was shifted towards the female direction in brain responses.
- Rametti, G.; Carrillo, B.; Gómez-Gil, E.; Junque, C.; Zubiarre-Elorza, L.; Segovia, S.; Gomez, Á; Guillamon, A. (2011). "White matter microstructure in female to male transsexuals before cross-sex hormonal treatment. A diffusion tensor imaging study". Journal of Psychiatric Research. 45: 199–204. doi:10.1016/j.jpsychires.2010.05.006. PMID 20562024. Found that the white matter pattern in gynephilic trans men was shifted in the direction of biological males even before the female-to-male transsexuals started taking male hormones.
- Psychology The Science Of Behaviour, pg 418, Pearson Education, Neil R.Carlson
- Zhou, J.N.; Hofman, M.A.; Gooren, L.J.; Swaab, D.F. (1995). "A sex difference in the human brain and its relation to transsexuality". Nature. 378: 68–70. doi:10.1038/378068a0. PMID 7477289.
- LeVay S (August 1991). "A difference in hypothalamic structure between heterosexual and homosexual men". Science. 253 (5023): 1034–7. doi:10.1126/science.1887219. PMID 1887219.
- Byne W, Tobet S, Mattiace LA, et al. (September 2001). "The interstitial nuclei of the human anterior hypothalamus: an investigation of variation with sex, sexual orientation, and HIV status". Horm Behav. 40 (2): 86–92. doi:10.1006/hbeh.2001.1680. PMID 11534967.
- Male transsexual gene link found BBC News 26 October 2008 (accessed 26 October 2008)
- Oswalt, Angela. "Factors Influencing Gender Identity". Seven Countries Services, Inc. Archived from the original on April 15, 2013. Retrieved October 29, 2012.
- J. Money, J. G. Hampson, and J. L. Hampson, An examination of some basic sexual concepts, 1955
- A. L. C. de Vries, et al., Gender Dysphoria and Disorders of Sex Development (2013, ISBN 1461474418)
- Anne Fausto-Sterling, Sexing the Body: Gender Politics and the Construct
- D. F. Swaab, Sexual differentiation of the human brain: relevance for gender identity, transsexualism and sexual orientation, in Gynecological Endocrinology, 2004: "...direct effects of testosterone on the developing fetal brain are of major importance for the development of male gender identity and male heterosexual orientation. Solid evidence for the importance of postnatal social factors is lacking."
- M. S. C. Wallien, Psychosexual outcome of gender-dysphoric children (2008)
- M Weinraub, LP Clemens, A Sockloff, T Ethridge, The development of sex role stereotypes in the third year: relationships to gender labeling, gender identity, sex-types toy preference, and family characteristics, in Child Development, 1984: "Previous investigators have failed to observe a relationship between parental attitudes and children's early sex role acquisition..."
- Spade, Joan. The Kaleidoscope of Gender. London: SAGE. pp. 177–184. ISBN 978-1-4129-7906-1.
- Halpern, Hillary Paul. "Parents' Gender Ideology and Gendered Behavior as Predictors of Children's Gender-Role Attitudes: A Longitudinal Exploration". Sex Roles. 74. doi:10.1007/s11199-015-0539-0.
- Hoogensen, Gunhild; Rottem, Svein Vigeland (2016-06-29). "Gender Identity and the Subject of Security". Security Dialogue. 35 (2): 155–171. doi:10.1177/0967010604044974.
- Blackless, Melanie; Besser, M.; Carr, S.; Cohen-Kettenis, P.T.; Connolly, P.; De Sutter, P.; Diamond, M.; Di Ceglie, D.; Higashi, Y.; Jones, L.; Kruijver. F.P.M.; Martin, J.; Playdon, Z-J.; Ralph, D.; Reed, T.; Reid, R.; Reiner, W.G.; Swaab, D.; Terry, T.; Wilson, P.; Wylie, K. (2003). "Atypical Gender Development – A Review". International Journal of Transgenderism. 9: 29–44. doi:10.1300/J485v09n01_04. Archived from the original on 2008-10-07. Retrieved 2008-09-28.
- "Toronto couple defend move to keep baby's sex secret". 27 May 2011 – via www.bbc.co.uk.
- "Words Matter: Affirming Gender Identity Through Language". 18 May 2016.
- Boles, 2013. Page 101: "Gender identity is the individual's personal and private experience of his/her gender."
- "The term 'gender identity' was used in a press release, November 21, 1966, to announce the new clinic for transsexuals at The Johns Hopkins Hospital. It was disseminated in the media worldwide, and soon entered the vernacular. ... gender identity is your own sense or conviction of maleness or femaleness." Money, John (1994). "'The concept of gender identity disorder in childhood and adolescence after 39 years'". Journal of Sex and Marital Therapy. 20 (3): 163–77. doi:10.1080/00926239408403428. PMID 7996589.
- Handbook of the Psychology of Women and Gender (2004, ISBN 0471653578), page 102: "Gender identity was introduced into the professional lexicon by Hooker and Stoller almost simultaneously in the early 1960s (see Money, 1985). For example, Stoller (1964) used the slightly different term core gender identity..."
- Brym, Roberts, Lie, Rytina. "Sociology". Nelson Education Ltd., 2013.
- Padawer, Ruth. "What's So Bad About a Boy Who Wants to Wear a Dress?". The New York Times. Retrieved October 29, 2012.
- Freud, Sigmund (1931). "Female Sexuality". The Standard Edition of the Complete Psychological Works of Sigmund Freud. 21: 229.
- Haraway, Donna (1991). Simians, Cyborgs, and Women: The Reinvention of Nature. London: Free Association Books. p. 133. ISBN 0-415-90386-6.
- Fixing Sex: Intersex, Medical Authority, and Lived Experience by Katrina Karkazis, Duke University Press, November 2008
- Butler, Judith (1990). Gender Trouble: Feminism and the Subversion of Identity. London: Routledge Classic. pp. front/backmatter. ISBN 0415389550.
- Singal, Jesse (February 7, 2016). "How the Fight Over Transgender Kids Got a Leading Sex Researcher Fired". New York. Retrieved April 25, 2017.
- Diamond, Milton (2002). "Sex and Gender are Different: Sexual Identity and Gender Identity are Different". Clinical Child Psychology & Psychiatry. 7 (3).
- Baker, Kellan. "FAQ: Collecting Sexual Orientation and Gender Identity Data". Center for American Progress. Retrieved October 29, 2012.
- "Gender Identity Disorder | Psychology Today." Psychology Today: Health, Help, Happiness Find a Therapist. Psychology Today, 24 Oct. 2005. Web. 17 Dec. 2010. http://www.psychologytoday.com/conditions/gender-identity-disorder.
- Gender Dysphoria Organization Research and Education - About Gender Dysphoria
- Zucker, KJ; Spitzer, RL (Jan–Feb 2005). "Was the gender identity disorder of childhood diagnosis introduced into DSM-III as a backdoor maneuver to replace homosexuality? A historical note". Journal of Sex and Marital Therapy. 31 (1): 31–42. doi:10.1080/00926230590475251. PMID 15841704.
- Parry, Wynne (June 4, 2013). "DSM-5 Reflects Shift In Perspective On Gender Identity". The Huffington Post. Retrieved 2015-10-23.
- The Yogyakarta Principles, Principle 3. The Right to recognition before the law
- The Yogyakarta Principles, Principle 18. Protection from medical abuse
- Jurisprudential Annotations to the Yogyakarta Principles, page 43 Archived November 22, 2010, at the Wayback Machine.
- "Activist's Guide to the Yogyakarta Principles, p. 100" (PDF).
- Sua'ali'i, Tamasailau, "Samoans and Gender: Some Reflections on Male, Female and Fa'afafine Gender Identities", in: Tangata O Te Moana Nui: The Evolving Identities of Pacific Peoples in Aotearoa/New Zealand, Palmerston North (NZ): Dunmore Press, 2001, ISBN 0-86469-369-9
- Schmidt, Johanna (May 2003). "Paradise Lost? Social Change and Fa'afafine in Samoa". Current Sociology. 51 (3): 417–432. doi:10.1177/0011392103051003014.
- Field, Michael (5 July 2011). "Transsexuals hailed by Samoan PM". Stuff.co.nz. Retrieved 1 October 2011.
- Pual L. Vasey, Nancy H. Bartlett, "What Can the Samoan "Fa'afafine" Teach Us About the Western Concept of Gender Identity Disorder in Childhood?", Biology and Medicine, 50.4 (2007) 481-490
- Lorber, Judith. Paradoxes of Gender. Yale University Press:Yale, 1994. pp. 92–93.
- Lorber, Judith. Paradoxes of Gender. Yale University Press:Yale, 1994. pp. 94–95.
- Hunt, Sarah (2016). "An Introduction to the Health of Two-Spirit People: Historical, contemporary and emergent issues" (PDF). National Collaborative Centre Aboriginal Health. Archived from the original (PDF) on 2017-02-02.
- Boles, Jacqueline, and Tatro, Charlotte, Androgyny (subsection Gender-identity formation), in Men in Transition: Theory and Therapy, 2013, edited by Kenneth Solomon
- "Gender identity." Encyclopædia Britannica Online
- Dr. Money And The Boy With No Penis
- International Foundation for Gender Education
- National Center for Transgender Equality
- National Transgender Advocacy Coalition
- Gender PAC
- Gender Spectrum
- Transgender Law Center
- Gender Issues - Human Rights
- Human Rights Campaign Foundation, Transgender Resources for the Workplace
- World Professional Association for Transgender Health
- Genderology Directory Project, International listing of service providers for those affected by GID
- Gender Identity Research and Education Society (GIRES), British Charity encouraging and reporting on research into gender variance
- Gender Anarchy Project
- TransFemmeButch A forum and discussion board for transmen, femmes, and butches
- Born Free and Equal - Sexual orientation and gender identity in international human rights law (OHCHR)