Gender

From Wikipedia, the free encyclopedia

Gender symbols intertwined. The red (left) is the female Venus symbol. The blue (right) represents the male Mars symbol.

Gender is the range of characteristics pertaining to, and differentiating between, masculinity and femininity. Depending on the context, these characteristics may include biological sex (i.e., the state of being male, female, or an intersex variation), sex-based social structures (i.e., gender roles), or gender identity. People who do not identify as men or women or with masculine or feminine gender pronouns are often grouped under the umbrella terms non-binary or genderqueer. Some cultures have specific gender roles that are distinct from "man" and "woman," such as the hijras of South Asia. These are often referred to as third genders.

Sexologist John Money introduced the terminological distinction between biological sex and gender as a role in 1955. Before his work, it was uncommon to use the word gender to refer to anything but grammatical categories.^[1][2] However, Money's meaning of the word did not become widespread until the 1970s, when feminist theory embraced the concept of a distinction between biological sex and the social construct of gender. Today the distinction is strictly followed in some contexts, especially the social sciences^[4][5] and documents written by the World Health Organization (WHO).^[3]

In other contexts, including some areas of social sciences, gender includes sex or replaces it.^[1][2] For instance, in non-human animal research, gender is commonly used to refer to the biological sex of the animals.^[2] This change in the meaning of gender can be traced to the 1980s. In 1993, the US Food and Drug Administration (FDA) started to use gender instead of sex.^[6] Later, in 2011, the FDA reversed its position and began using sex as the biological classification and gender as "a person's self representation as male or female, or how that person is responded to by social institutions based on the individual's gender presentation."^[7]

The social sciences have a branch devoted to gender studies. Other sciences, such as sexology and neuroscience, are also interested in the subject. While the social sciences sometimes approach gender as a social construct, and gender studies particularly do, research in the natural sciences investigates whether biological differences in males and females influence the development of gender in humans; both inform debate about how far biological differences influence the formation of gender identity. In the English literature, there is also a trichotomy between biological sex, psychological gender, and social gender role. This framework first appeared in a feminist paper on transsexualism in 1978.^[2][8]

Etymology and usage

The modern English word gender comes from the Middle English gender, gendre, a loanword from Anglo-Norman and Middle French gendre. This, in turn, came from Latin genus. Both words mean "kind", "type", or "sort". They derive ultimately from a widely attested Proto-Indo-European (PIE) root g^en-,^[9][10] which is also the source of kin, kind, king, and many other English words.^[11] It appears in Modern French in the word genre (type, kind, also genre sexuel) and is related to the Greek root gen- (to produce), appearing in gene, genesis, and oxygen. The first edition of the Oxford English Dictionary (OED1, Volume 4, 1900) notes the original meaning of gender as "kind" had already become obsolete.

The word was still widely attested, however, in the specific sense of grammatical gender (the assignment of nouns to categories such as masculine, feminine and neuter). According to Aristotle, this concept was introduced by the Greek philosopher Protagoras.^[12]

In 1926, Henry Watson Fowler stated that the definition of the word pertained to this grammar-related meaning:

"Gender...is a grammatical term only. To talk of persons...of the masculine or feminine g[ender], meaning of the male or female sex, is either a jocularity (permissible or not according to context) or a blunder."^[13]

The modern academic sense of the word, in the context of social roles of men and women, dates at least back to 1945,^[14] and was popularized and developed by the feminist movement from the 1970s onwards (see § Feminism theory and gender studies below). The theory was that human nature is essentially epicene and social distinctions based on sex are arbitrarily constructed. Matters pertaining to this theoretical process of social construction were labelled matters of gender.

The popular use of gender simply as an alternative to sex (as a biological category) is also widespread, although attempts are still made to preserve the distinction. The American Heritage Dictionary (2000) uses the following two sentences to illustrate the difference, noting that the distinction "is useful in principle, but it is by no means widely observed, and considerable variation in usage occurs at all levels."^[15]

The effectiveness of the medication appears to depend on the sex (not gender) of the patient.

In peasant societies, gender (not sex) roles are likely to be more clearly defined.

In the last two decades of the 20th century, the use of gender in academia has increased greatly, outnumbering uses of sex in the social sciences. While the spread of the word in science publications can be attributed to the influence of feminism, its use as a synonym for sex is attributed to the failure to grasp the distinction made in feminist theory, and the distinction has sometimes become blurred with the theory itself; David Haig stated, "Among the reasons that working scientists have given me for choosing gender rather than sex in biological contexts are desires to signal sympathy with feminist goals, to use a more academic term, or to avoid the connotation of copulation."^[2]

In legal cases alleging discrimination, sex is usually preferred as the determining factor rather than gender as it refers to biology rather than socially constructed norms which are more open to interpretation and dispute.^[16] Julie Greenberg writes that although gender and sex are separate concepts, they are interlinked in that gender discrimination often results from stereotypes based on what is expected of members of each sex.^[17] In J.E.B. v. Alabama ex rel. T.B., United States Supreme Court Justice Antonin Scalia wrote:

The word ‘gender’ has acquired the new and useful connotation of cultural or attitudinal characteristics (as opposed to physical characteristics) distinctive to the sexes. That is to say, gender is to sex as feminine is to female and masculine is to male.^[18]

Gender identity and gender roles

Gender depicted as an ambiguous phenomenon, by a young Swedish actor

Gender identity refers to a personal identification with a particular gender and gender role in society. The term woman has historically been used interchangeably with reference to the female body, though more recently this usage has been viewed as controversial by some feminists.^[19]

There are qualitative analyses that explore and present the representations of gender; however, feminists challenge these dominant ideologies concerning gender roles and biological sex. One's biological sex is directly tied to specific social roles and the expectations. Judith Butler considers the concept of being a woman to have more challenges, owing not only to society's viewing women as a social category but also as a felt sense of self, a culturally conditioned or constructed subjective identity.^[20] Social identity refers to the common identification with a collectivity or social category that creates a common culture among participants concerned.^[21] According to social identity theory,^[22] an important component of the self-concept is derived from memberships in social groups and categories; this is demonstrated by group processes and how inter-group relationships impact significantly on individuals' self perception and behaviors. The groups people belong to therefore provide members with the definition of who they are and how they should behave within their social sphere.^[23]
 

A protestor holding a flyer with the words "Gender is like that old jumper from my cousin. It was given to me and it doesn't fit" at a rally for transgender equality in Washington D.C. in 2013

Categorizing males and females into social roles creates a problem, because individuals feel they have to be at one end of a linear spectrum and must identify themselves as man or woman, rather than being allowed to choose a section in between.^[24] Globally, communities interpret biological differences between men and women to create a set of social expectations that define the behaviors that are "appropriate" for men and women and determine women’s and men’s different access to rights, resources, power in society and health behaviors.^[25] Although the specific nature and degree of these differences vary from one society to the next, they still tend to typically favor men, creating an imbalance in power and gender inequalities within most societies.^[26] Many cultures have different systems of norms and beliefs based on gender, but there is no universal standard to a masculine or feminine role across all cultures.^[27] Social roles of men and women in relation to each other is based on the cultural norms of that society, which lead to the creation of gender systems. The gender system is the basis of social patterns in many societies, which include the separation of sexes, and the primacy of masculine norms.^[26]

Philosopher Michel Foucault said that as sexual subjects, humans are the object of power, which is not an institution or structure, rather it is a signifier or name attributed to "complex strategical situation".^[28] Because of this, "power" is what determines individual attributes, behaviors, etc. and people are a part of an ontologically and epistemologically constructed set of names and labels. For example, being female characterizes one as a woman, and being a woman signifies one as weak, emotional, and irrational, and incapable of actions attributed to a "man". Butler said that gender and sex are more like verbs than nouns. She reasoned that her actions are limited because she is female. "I am not permitted to construct my gender and sex willy-nilly," she said.^[20] "[This] is so because gender is politically and therefore socially controlled. Rather than 'woman' being something one is, it is something one does."^[20] More recent criticisms of Judith Butler's theories critique her writing for reinforcing the very conventional dichotomies of gender.^[29]

Social assignment and gender fluidity

According to gender theorist Kate Bornstein, gender can have ambiguity and fluidity.^[30] There are two contrasting ideas regarding the definition of gender, and the intersection of both of them is definable as below:

The World Health Organization defines gender as the result of socially constructed ideas about the behavior, actions, and roles a particular sex performs.^[3] The beliefs, values and attitude taken up and exhibited by them is as per the agreeable norms of the society and the personal opinions of the person is not taken into the primary consideration of assignment of gender and imposition of gender roles as per the assigned gender.^[3] Intersections and crossing of the prescribed boundaries have no place in the arena of the social construct of the term "gender".

The assignment of gender involves taking into account the physiological and biological attributes assigned by nature followed by the imposition of the socially constructed conduct. The social label of being classified into one or the other sex is necessary for the medical stamp on birth certificates. Gender is a term used to exemplify the attributes that a society or culture constitutes as "masculine" or "feminine". Although a person's sex as male or female stands as a biological fact that is identical in any culture, what that specific sex means in reference to a person's gender role as a woman or a man in society varies cross culturally according to what things are considered to be masculine or feminine.^[31] These roles are learned from various, intersecting sources such as parental influences, the socialization a child receives in school, and what is portrayed in the local media. It is also important to note that learning gender roles starts from birth and includes seemingly simple things like what color outfits a baby is clothed in or what toys they are given to play with. The cultural traits typically coupled to a particular sex finalize the assignment of gender and the biological differences which play a role in classifying either sex as interchangeable with the definition of gender within the social context.

In this context, the socially constructed rules are at a cross road with the assignment of a particular gender to a person. Gender ambiguity deals with having the freedom to choose, manipulate and create a personal niche within any defined socially constructed code of conduct while gender fluidity is outlawing all the rules of cultural gender assignment. It does not accept the prevalence of the two rigidly defined genders "man" and "woman" and believes in freedom to choose any kind of gender with no rules, no defined boundaries and no fulfilling of expectations associated with any particular gender.

Both these definitions are facing opposite directions with their own defined set of rules and criteria on which the said systems are based.

Social categories

Mary Frith ("Moll Cutpurse") scandalized 17th century society by wearing male clothing, smoking in public, and otherwise defying gender roles.

Sexologist John Money coined the term gender role in 1955. The term gender role is defined as the actions or responses that may reveal their status as boy, man, girl or woman, respectively.^[32] Elements surrounding gender roles include clothing, speech patterns, movement, occupations, and other factors not limited to biological sex. In contrast to taxonomic approaches, some feminist philosophers have argued that gender "is a vast orchestration of subtle mediations between oneself and others", rather than a "private cause behind manifest behaviours".^[33]

Because social aspects of gender can normally be presumed to be the ones of interest in sociology and closely related disciplines, gender role is often abbreviated to gender in their literature.

Non-binary and third genders

Traditionally, most societies have only recognized two distinct, broad classes of gender roles, masculine and feminine, that correspond with the biological sexes of male and female. When a baby is born, society allocates the child to one gender or the other, on the basis of what their genitals resemble.^[31] However, some societies explicitly incorporate people who adopt the gender role opposite to their biological sex; for example, the two-spirit people of some indigenous American peoples. Other societies include well-developed roles that are explicitly considered more or less distinct from archetypal female and male roles in those societies. In the language of the sociology of gender, they comprise a third gender,^[34] more or less distinct from biological sex (sometimes the basis for the role does include intersexuality or incorporates eunuchs).^[35] One such gender role is that adopted by the hijras of India and Pakistan.^[36][37] Another example may be the muxe (pronounced [ˈmuʃe]), found in the state of Oaxaca, in southern Mexico.^[38] The Bugis people of Sulawesi, Indonesia have a tradition that incorporates all the features above.^[39]

In addition to these traditionally recognized third genders, many cultures now recognize, to differing degrees, various non-binary gender identities. People who are non-binary (or genderqueer) have gender identities that are not exclusively masculine or feminine. They may identify as having an overlap of gender identities, having two or more genders, having no gender, having a fluctuating gender identity, or being third gender or other-gendered. Recognition of non-binary genders is still somewhat new to mainstream Western culture,^[40] and non-binary people may face increased risk of assault, harassment, and discrimination.^[41]

Joan Roughgarden argues that some non-human animal species also have more than two genders, in that there might be multiple templates for behavior available to individual organisms with a given biological sex.^[42]

Measurement of gender identity

Early gender identity research hypothesized a single bipolar dimension of masculinity-femininity, with masculinity and femininity being opposites on one continuum. Assumptions of the unidimensional model were challenged as societal stereotypes changed, which led to the development of a two-dimensional gender identity model. In the model, masculinity and femininity were conceptualized as two separate and orthogonal dimensions, coexisting in varying degrees within an individual. This conceptualization on femininity and masculinity remains the accepted standard today.^[43]

Two instruments incorporating the multidimensional nature of masculinity and femininity have dominated gender identity research: The Bem Sex Role Inventory (BSRI) and the Personal Attributes Questionnaire (PAQ). Both instruments categorize individuals as either being sex typed (males report themselves as identifying primarily with masculine traits, females report themselves as identifying primarily with feminine traits), cross sex-typed (males report themselves as identifying primarily with feminine traits, females report themselves as identifying primarily with masculine traits), androgynous (either males or females who report themselves as high on both masculine and feminine traits) or undifferentiated (either males or females who report themselves as low on both masculine and feminine traits).^[43] Twenge (1997) noted that men are generally more masculine than women and women generally more feminine than men, but the association between biological sex and masculinity/femininity is waning.^[44]

Feminist theory and gender studies

Biologist and feminist academic Anne Fausto-Sterling rejects the discourse of biological versus social determinism and advocates a deeper analysis of how interactions between the biological being and the social environment influence individuals' capacities.^[45] The philosopher and feminist Simone de Beauvoir applied existentialism to women's experience of life: "One is not born a woman, one becomes one."^[46] In context, this is a philosophical statement. However, it may be analyzed in terms of biology—a girl must pass puberty to become a woman—and sociology, as a great deal of mature relating in social contexts is learned rather than instinctive.^[47]

Within feminist theory, terminology for gender issues developed over the 1970s. In the 1974 edition of Masculine/Feminine or Human, the author uses "innate gender" and "learned sex roles",^[48] but in the 1978 edition, the use of sex and gender is reversed.^[49] By 1980, most feminist writings had agreed on using gender only for socioculturally adapted traits.

In gender studies the term gender refers to proposed social and cultural constructions of masculinities and femininities. In this context, gender explicitly excludes reference to biological differences, to focus on cultural differences.^[50] This emerged from a number of different areas: in sociology during the 1950s; from the theories of the psychoanalyst Jacques Lacan; and in the work of French psychoanalysts like Julia Kristeva, Luce Irigaray, and American feminists such as Judith Butler. Those who followed Butler came to regard gender roles as a practice, sometimes referred to as "performative".^[51]

Charles E. Hurst states that some people think sex will, "...automatically determine one's gender demeanor and role (social) as well as one's sexual orientation (sexual attractions and behavior).^[52] Gender sociologists believe that people have cultural origins and habits for dealing with gender. For example, Michael Schwalbe believes that humans must be taught how to act appropriately in their designated gender to fill the role properly, and that the way people behave as masculine or feminine interacts with social expectations. Schwalbe comments that humans "are the results of many people embracing and acting on similar ideas".^[53] People do this through everything from clothing and hairstyle to relationship and employment choices. Schwalbe believes that these distinctions are important, because society wants to identify and categorize people as soon as we see them. They need to place people into distinct categories to know how we should feel about them.

Hurst comments that in a society where we present our genders so distinctly, there can often be severe consequences for breaking these cultural norms. Many of these consequences are rooted in discrimination based on sexual orientation. Gays and lesbians are often discriminated against in our legal system because of societal prejudices.^[54][55][56] Hurst describes how this discrimination works against people for breaking gender norms, no matter what their sexual orientation is. He says that "courts often confuse sex, gender, and sexual orientation, and confuse them in a way that results in denying the rights not only of gays and lesbians, but also of those who do not present themselves or act in a manner traditionally expected of their sex".^[52] This prejudice plays out in our legal system when a person is judged differently because they do not present themselves as the "correct" gender.

Andrea Dworkin stated her "commitment to destroying male dominance and gender itself" while stating her belief in radical feminism.^[57]

Political scientist Mary Hawkesworth addresses gender and feminist theory, stating that since the 1970s the concept of gender has transformed and been used in significantly different ways within feminist scholarship. She notes that a transition occurred when several feminist scholars, such as Sandra Harding and Joan Scott, began to conceive of gender "as an analytic category within which humans think about and organize their social activity". Feminist scholars in Political Science began employing gender as an analytical category, which highlighted "social and political relations neglected by mainstream accounts". However, Hawkesworth states "feminist political science has not become a dominant paradigm within the discipline".^[58]

American political scientist Karen Beckwith addresses the concept of gender within political science arguing that a "common language of gender" exists and that it must be explicitly articulated in order to build upon it within the political science discipline. Beckwith describes two ways in which the political scientist may employ 'gender' when conducting empirical research: "gender as a category and as a process." Employing gender as a category allows for political scientists "to delineate specific contexts where behaviours, actions, attitudes and preferences considered masculine or feminine result in particular" political outcomes. It may also demonstrate how gender differences, not necessarily corresponding precisely with sex, may "constrain or facilitate political" actors. Gender as a process has two central manifestations in political science research, firstly in determining "the differential effects of structures and policies upon men and women," and secondly, the ways in which masculine and feminine political actors "actively work to produce favorable gendered outcomes".^[59]

With regard to gender studies, Jacquetta Newman states that although sex is determined biologically, the ways in which people express gender is not. Gendering is a socially constructed process based on culture, though often cultural expectations around women and men have a direct relationship to their biology. Because of this, Newman argues, many privilege sex as being a cause of oppression and ignore other issues like race, ability, poverty, etc. Current gender studies classes seek to move away from that and examine the intersectionality of these factors in determining people's lives. She also points out that other non-Western cultures do not necessarily have the same views of gender and gender roles.^[60] Newman also debates the meaning of equality, which is often considered the goal of feminism; she believes that equality is a problematic term because it can mean many different things, such as people being treated identically, differently, or fairly based on their gender. Newman believes this is problematic because there is no unified definition as to what equality means or looks like, and that this can be significantly important in areas like public policy.^[61]

Social construction of sex hypotheses

"Rosie the Riveter" was an iconic symbol of the American homefront in WWII and a departure from gender roles due to wartime necessity.

Sociologists generally regard gender as a social construct, and various researchers, including many feminists, consider sex to only be a matter of biology and something that is not about social or cultural construction. For instance, sexologist John Money suggests the distinction between biological sex and gender as a role.^[32] Moreover, Ann Oakley, a professor of sociology and social policy, says "the constancy of sex must be admitted, but so also must the variability of gender."^[62] The World Health Organization states, "'[s]ex' refers to the biological and physiological characteristics that define men and women," and "'gender' refers to the socially constructed roles, behaviours, activities, and attributes that a given society considers appropriate for men and women."^[63] Thus, sex is regarded as a category studied in biology (natural sciences), while gender is studied in humanities and social sciences. Lynda Birke, a feminist biologist, maintains "'biology' is not seen as something which might change."^[64] Therefore, it is stated that sex is something that does not change, while gender can change according to social structure.

However, there are scholars who argue that sex is also socially constructed. For example, gender theorist Judith Butler states that "perhaps this construct called 'sex' is as culturally constructed as gender; indeed, perhaps it was always already gender, with the consequence that the distinction between sex and gender turns out to be no distinction at all."^[65]


She continues:

It would make no sense, then, to define gender as the cultural interpretation of sex, if sex is itself a gender-centered category. Gender should not be conceived merely as the cultural inscription of meaning based on a given sex (a juridical conception); gender must also designate the very apparatus of production whereby the sexes themselves are established. [...] This production of sex as the pre-discursive should be understood as the effect of the apparatus of cultural construction designated by gender.^[66]

Butler argues that "bodies only appear, only endure, only live within the productive constraints of certain highly gendered regulatory schemas,"^[67] and sex is "no longer as a bodily given on which the construct of gender is artificially imposed, but as a cultural norm which governs the materialization of bodies."^[68] Marria Lugones states that, among the Yoruba people, there was no concept of gender and no gender system at all before colonialism. She argues that colonial powers used a gender system as a tool for domination and fundamentally changing social relations among the indigenous.^[69]

With regard to history, Linda Nicholson, a professor of history and women's studies, says that the notion of human bodies being separated into two sexes is not historically consistent. She argues that male and female genitals were considered inherently the same in Western society until the 18th century. At that time, female genitals were regarded as incomplete male genitals, and the difference between the two was conceived as a matter of degree. In other words, there was a gradation of physical forms, or a spectrum. Therefore, the current perspective toward sex, which is to consider women and men and their typical genitalia as the only possible natural options, came into existence through historical, not biological roots.^[70]

In addition, drawing from the empirical research of intersex children, Anne Fausto-Sterling, a professor of biology and gender studies, describes how the doctors address the issues of intersexuality. She starts her argument with an example of the birth of an intersexual individual and maintains "our conceptions of the nature of gender difference shape, even as they reflect, the ways we structure our social system and polity; they also shape and reflect our understanding of our physical bodies."^[71] Then she adds how gender assumptions affects the scientific study of sex by presenting the research of intersexuals by John Money et al., and she concludes that "they never questioned the fundamental assumption that there are only two sexes, because their goal in studying intersexuals was to find out more about 'normal' development."^[72] She also mentions the language the doctors use when they talk with the parents of the intersexuals. After describing how the doctors inform parents about the intersexuality, she asserts that because the doctors believe that the intersexuals are actually male or female, they tell the parents of the intersexuals that it will take a little bit more time for the doctors to determine whether the infant is a boy or a girl. That is to say, the doctors' behavior is formulated by the cultural gender assumption that there are only two sexes. Lastly, she maintains that the differences in the ways in which the medical professionals in different regions treat intersexual people also give us a good example of how sex is socially constructed.^[73] In her Sexing the body: gender politics and the construction of sexuality, she introduces the following example:

A group of physicians from Saudi Arabia recently reported on several cases of XX intersex children with congenital adrenal hyperplasia (CAH), a genetically inherited malfunction of the enzymes that aid in making steroid hormones. [...] In the United States and Europe, such children, because they have the potential to bear children later in life, are usually raised as girls. Saudi doctors trained in this European tradition recommended such a course of action to the Saudi parents of CAH XX children. A number of parents, however, refused to accept the recommendation that their child, initially identified as a son, be raised instead as a daughter. Nor would they accept feminizing surgery for their child. [...] This was essentially an expression of local community attitudes with [...] the preference for male offspring.^[74]

Thus it may be said that determining the sex of children is actually a cultural act, and the sex of children is in fact socially constructed.^[73] Therefore, it is possible that although sex seems fixed and only related to biology, it may be actually deeply related to historical and social factors as well as biology and other natural sciences.

Another work of Ann Fausto-Sterling’s in which she discusses gender is The Five Sexes: Why Male and Female Are Not Enough. In this article, Fausto-Sterling states that Western culture has only two sexes and that even their language restricts the presence of more than two sexes. She argues that instead of having a binomial nomenclature for organizing humans into two distinct sexes (male and female), there are at least five sexes in the broad spectrum of gender. These five sexes include male, female, hermaphrodite, female pseudohermaphrodites (individuals who have ovaries and some male genitalia but lack testes), and male pseudohermaphrodites (individuals who have testes and some female genitalia but lack ovaries). Fausto-Sterling additionally adds that in the category of hermaphrodites, there are additional degrees and levels in which the genitalia are developed; this means that there may be more intersexes that exist in this continuum of gender.

Fausto-Sterling argues that sex has been gradually institutionally disciplined into a binary system through medical advances. She brings up multiple instances where gender in history was not split into strictly male or female, Fausto-Sterling mentioned that by the end of the Middle Age, intersex individuals were forced to pick a side in the binary gender code and to adhere by it. She then adds on that "hermaphrodites have unruly bodies" and they need to fit into society's definition of gender.^[75] Thus, modern-day parents have been urged by medical doctors to decide the sex for their hermaphroditic child immediately after childbirth. She emphasizes that the role of the medical community is that of an institutionalized discipline on society that there can only be two sexes: male and female and only the two listed are considered "normal." Lastly, Fausto-Sterling argues that modern laws require humans to be labelled either as male or female and that "ironically, a more sophisticated knowledge of the complexity of sexual systems has led to the repression of such intricacy."^[75] She mentions this quote to inform the prevailing thought that hermaphrodites, without medical intervention, are assumed to live a life full of psychological pain when in fact, there is no evidence in which that is the case. She finishes up her argument asking what would happen if society started accepting intersex individuals.

The article Adolescent Gender-Role Identity and Mental Health: Gender Intensification Revisited focuses on the work of Heather A. Priess, Sara M. Lindberg, and Janet Shibley Hyde on whether or not girls and boys diverge in their gender identities during adolescent years. The researchers based their work on ideas previously mentioned by Hill and Lynch in their gender intensification hypothesis in that signals and messages from parents determine and affect their children’s gender role identities.

This hypothesis argues that parents affect their children's gender role identities and that different interactions spent with either parents will affect gender intensification. Priess and among other’s study did not support the hypothesis of Hill and Lynch which stated "that as adolescents experience these and other socializing influences, they will become more stereotypical in their gender-role identities and gendered attitudes and behaviors."^[76] However, the researchers did state that perhaps the hypothesis Hill and Lynch proposed was true in the past but is not true now due to changes in the population of teens in respect to their gender-role identities.

Authors of Unpacking the Gender System: A Theoretical Perspective on Gender Belief’s and Social Relations, Cecilia Ridgeway and Shelley Correll, argue that gender is more than an identity or role but is something that is institutionalized through "social relational contexts." Ridgeway and Correll define "social relational contexts" as "any situation in which individuals define themselves in relation to others in order to act."^[77] They also point out that in addition to social relational contexts, cultural beliefs plays a role in the gender system. The coauthors argue that daily people are forced to acknowledge and interact with others in ways that are related to gender. Every day, individuals are interacting with each other and comply with society's set standard of hegemonic beliefs, which includes gender roles. They state that society's hegemonic cultural beliefs sets the rules which in turn create the setting for which social relational contexts are to take place. Ridgeway and Correll then shift their topic towards sex categorization. The authors define sex categorization as "the sociocognitive process by which we label another as male or female."^[77]

Biological factors and views

In most cases, men and women and boys and girls are similar in behavior, with little gender difference, but some gendered behavior is influenced by prenatal and early life androgen exposure. This includes, for example, gender normative play, self-identification with a gender, and tendency to engage in aggressive behavior.^[78] Males of most mammals, including humans, exhibit more rough and tumble play behavior, which is influenced by maternal testosterone levels. These levels may also influence sexuality, with non-heterosexual persons exhibiting sex atypical behavior in childhood.^[79]

The biology of gender became the subject of an expanding number of studies over the course of the late 20th century. One of the earliest areas of interest was what became known as "gender identity disorder" (GID) and which is now also described as gender dysphoria. Studies in this, and related areas, inform the following summary of the subject by John Money. He stated:

The term "gender role" appeared in print first in 1955. 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. The definitions of gender and gender identity vary on a doctrinal basis. In popularized and scientifically debased usage, sex is what you are biologically; gender is what you become socially; gender identity is your own sense or conviction of maleness or femaleness; and gender role is the cultural stereotype of what is masculine and feminine. Causality with respect to gender identity disorder is sub-divisible into genetic, prenatal hormonal, postnatal social, and post-pubertal hormonal determinants, but there is, as yet, no comprehensive and detailed theory of causality. Gender coding in the brain is bipolar. 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.^[80]

Money refers to attempts to distinguish a difference between biological sex and social gender as "scientifically debased", because of our increased knowledge of a continuum of dimorphic features (Money's word is "dipolar") that link biological and behavioral differences. These extend from the exclusively biological "genetic" and "prenatal hormonal" differences between men and women, to "postnatal" features, some of which are social, but others have been shown to result from "post-pubertal hormonal" effects.

Although causation from the biological—genetic and hormonal—to the behavioral has been broadly demonstrated and accepted, Money is careful to also note that understanding of the causal chains from biology to behavior in sex and gender issues is very far from complete. For example, the existence of a "gay gene" has not been proven, but such a gene remains an acknowledged possibility.^[81]

There are studies concerning women who have a condition called congenital adrenal hyperplasia, which leads to the overproduction of the masculine sex hormone, androgen. These women usually have ordinary female appearances (though nearly all girls with congenital adrenal hyperplasia (CAH) have corrective surgery performed on their genitals). However, despite taking hormone-balancing medication given to them at birth, these females are statistically more likely to be interested in activities traditionally linked to males than female activities. Psychology professor and CAH researcher Dr. Sheri Berenbaum attributes these differences to an exposure of higher levels of male sex hormones in utero.^[82]

Sexual reproduction

Sexual differentiation demands the fusion of gametes that are morphologically different.

— Cyril Dean Darlington, Recent Advances in Cytology, 1937.

Hoverflies mating

Sexual reproduction is a common method of producing a new individual within various species. In sexually reproducing species, individuals produce special kinds of cells (called gametes) whose function is specifically to fuse with one unlike gamete and thereby to form a new individual. This fusion of two unlike gametes is called fertilization. By convention, where one type of gamete cell is physically larger than the other, it is associated with female sex. Thus an individual that produces exclusively large gametes (ova in humans) is called female, and one that produces exclusively small gametes (spermatozoa in humans) is called male.

An individual that produces both types of gametes is called hermaphrodite (a name applicable also to people with one testis and one ovary). In some species hermaphrodites can self-fertilize (see Selfing), in others they can achieve fertilization with females, males or both. Some species, like the Japanese Ash, Fraxinus lanuginosa, only have males and hermaphrodites, a rare reproductive system called androdioecy. Gynodioecy is also found in several species. Human hermaphrodites are typically, but not always, infertile.

What is considered defining of sexual reproduction is the difference between the gametes and the binary nature of fertilization. Multiplicity of gamete types within a species would still be considered a form of sexual reproduction. However, of more than 1.5 million living species,^[83] recorded up to about the year 2000, "no third sex cell—and so no third sex—has appeared in multi-cellular animals." Why sexual reproduction has an exclusively binary gamete system is not yet known. A few rare species that push the boundaries of the definitions are the subject of active research for light they may shed on the mechanisms of the evolution of sex. For example, the most toxic insect,^[87] the harvester ant Pogonomyrmex, has two kinds of female and two kinds of male. One hypothesis is that the species is a hybrid, evolved from two closely related preceding species.

Fossil records indicate that sexual reproduction has been occurring for at least one billion years.^[88] However, the reason for the initial evolution of sex, and the reason it has survived to the present are still matters of debate, there are many plausible theories. It appears that the ability to reproduce sexually has evolved independently in various species on many occasions. There are cases where it has also been lost, notably among the Fungi Imperfecti.^[89] The blacktip shark (Carcharhinus limbatus), flatworm (Dugesia tigrina) and some other species can reproduce either sexually or asexually depending on various conditions.^[90]

Gender taxonomy

The following systematic list gender taxonomy illustrates the kinds of diversity that have been studied and reported in medical literature. It is placed in roughly chronological order of biological and social development in the human life cycle. The earlier stages are more purely biological and the latter are more dominantly social. Causation is known to operate from chromosome to gonads, and from gonads to hormones. It is also significant from brain structure to gender identity (see Money quote above). Brain structure and processing (biological) that may explain erotic preference (social), however, is an area of ongoing research. Terminology in some areas changes quite rapidly as knowledge grows.

• chromosomes:

46,XX (genetic female); 46,XY (genetic male) ;45,X (Turner's syndrome); 47,XXY (Klinefelter syndrome); 47,XYY (XYY syndrome); 47,XXX (XXX syndrome); 48,XXYY (XXYY syndrome); 46,XX/XY mosaic; other mosaic;

• gonads:

testicles; ovaries; ovarian and testicular tissues, not in same gonad (true hermaphroditism), ovotestes, or other gonadal dysgenesis;

• hormones:

androgens (including testosterone, dihydrotestosterone, etc.), estrogens (including estradiol, estriol, etc.), antiandrogens, progestogens, and others;

• primary sexual characteristics:

genitals (genital development);

• secondary sexual characteristics

dimorphic physical characteristics, other than primary characteristics (such as body hair, development of breasts); certain changes in brain structure due to organizing effects of sex hormones (Is it useful to view the brain as a secondary sexual characteristic?);

• gender identity:

one’s sense of oneself as a man, woman, or gender non-conforming;

• gender role:

social conformity with expectations for males or females;

Sexual dimorphism

Sexual differentiation in peafowl

Although sexual reproduction is defined at the cellular level, key features of sexual reproduction operate within the structures of the gamete cells themselves. Notably, gametes carry very long molecules called DNA that the biological processes of reproduction can "read" like a book of instructions. In fact, there are typically many of these "books", called chromosomes. Human gametes usually have 23 chromosomes, 22 of which are common to both sexes. The final chromosomes in the two human gametes are called sex chromosomes because of their role in sex determination. Ova always have the same sex chromosome, labelled X. About half of spermatozoa also have this same X chromosome, the rest have a Y-chromosome. At fertilization the gametes fuse to form a cell, usually with 46 chromosomes, and either XX female or XY male, depending on whether the sperm carried an X or a Y chromosome. Some of the other possibilities are listed above.

Genes which are specific to the X or Y chromosome are called sex-linked genes. For example, the genes which create red and green retinal photoreceptors are located on the X chromosome, which men only have one of. Thus red-green color blindness is an X-linked recessive trait and is much more common in men. However, sex-limited genes on any chromosome can be expressed and "say", for example, "if you are in a male body do X, otherwise do not."

The human XY system is not the only sex determination system. Birds typically have a reverse, ZW system—males are ZZ and females ZW.^[91] Whether male or female birds influence the sex of offspring is not known for all species. Several species of butterfly are known to have female parent sex determination.^[92]

The platypus has a complex hybrid system, the male has ten sex chromosomes, half X and half Y.^[93]

Human brain

Human brain

"It is well established that men have a larger cerebrum than women by about 8–10% (Filipek et al., 1994; Nopoulos et al., 2000; Passe et al., 1997a,b; Rabinowicz et al., 1999; Witelson et al., 1995)."^[94][95] However, what is functionally relevant are differences in composition and "wiring". Richard J. Haier and colleagues at the universities of New Mexico and California (Irvine) found, using brain mapping, that men have more grey matter related to general intelligence than women, and women have more white matter related to intelligence than men – the ratio between grey and white matter is 4% higher for men than women.^[94]

Grey matter is used for information processing, while white matter consists of the connections between processing centers. Other differences are measurable but less pronounced.^[96] Most of these differences are produced by hormonal activity, ultimately derived from the Y chromosome and sexual differentiation. However, differences that arise directly from gene activity have also been observed.

A sexual dimorphism in levels of expression in brain tissue was observed by quantitative real-time PCR, with females presenting an up to 2-fold excess in the abundance of PCDH11X transcripts. We relate these findings to sexually dimorphic traits in the human brain. Interestingly, PCDH11X/Y gene pair is unique to Homo sapiens, since the X-linked gene was transposed to the Y chromosome after the human–chimpanzee lineages split.

— ^[97]

Language areas of the brain: 

  Angular gyrus

  Supramarginal gyrus

  Broca's area

  Wernicke's area

  Primary auditory cortex

It has also been demonstrated that brain processing responds to the external environment. Learning, both of ideas and behaviors, appears to be coded in brain processes. It also appears that in several simplified cases this coding operates differently, but in some ways equivalently, in the brains of men and women.^[98] For example, both men and women learn and use language; however, bio-chemically, they appear to process it differently. Differences in female and male use of language are likely reflections both of biological preferences and aptitudes, and of learned patterns.

Gender studies

Gender studies is a field of interdisciplinary study and academic field devoted to gender, gender identity and gendered representation as central categories of analysis. This field includes Women's studies (concerning women, feminity, their gender roles and politics, and feminism), Men's studies (concerning men, masculinity, their gender roles, and politics), and LGBT studies.^[99] Sometimes Gender studies is offered together with Study of Sexuality. These disciplines study gender and sexuality in the fields of literature and language, history, political science, sociology, anthropology, cinema and media studies, human development, law, and medicine.^[100] It also analyses race, ethnicity, location, nationality, and disability.^[101][102]

Psychology and sociology

Many of the more complicated human behaviors are influenced by both innate factors and by environmental ones, which include everything from genes, gene expression, and body chemistry, through diet and social pressures. A large area of research in behavioral psychology collates evidence in an effort to discover correlations between behavior and various possible antecedents such as genetics, gene regulation, access to food and vitamins, culture, gender, hormones, physical and social development, and physical and social environments.

A core research area within sociology is the way human behavior operates on itself, in other words, how the behavior of one group or individual influences the behavior of other groups or individuals. Starting in the late 20th century, the feminist movement has contributed extensive study of gender and theories about it, notably within sociology but not restricted to it.

Spain's desperate situation when invaded by Napoleon enabled Agustina de Aragón to break into a closely guarded male preserve and become the only female professional officer in the Spanish Army of her time (and long afterwards).

Social theorists have sought to determine the specific nature of gender in relation to biological sex and sexuality,^{[citation needed]} with the result being that culturally established gender and sex have become interchangeable identifications that signify the allocation of a specific 'biological' sex within a categorical gender.^{[citation needed]} The second wave feminist view that gender is socially constructed and hegemonic in all societies, remains current in some literary theoretical circles, Kira Hall and Mary Bucholtz publishing new perspectives as recently as 2008.^[103]

Contemporary socialisation theory proposes the notion that when a child is first born it has a biological sex but no social gender.^{[citation needed]} As the child grows, "...society provides a string of prescriptions, templates, or models of behaviors appropriate to the one sex or the other,"^[104] which socialises the child into belonging to a culturally specific gender.^{[citation needed]} There is huge incentive for a child to concede to their socialisation with gender shaping the individual’s opportunities for education, work, family, sexuality, reproduction, authority,^[105] and to make an impact on the production of culture and knowledge.^[106] Adults who do not perform these ascribed roles are perceived from this perspective as deviant and improperly socialized.^[107]

Some believe society is constructed in a way that splits gender into a dichotomy via social organisations that constantly invent and reproduce cultural images of gender. Joan Acker believes gendering occurs in at least five different interacting social processes:^[108]

• The construction of divisions along the lines of gender, such as those produced by labor, power, family, the state, even allowed behaviors and locations in physical space
• The construction of symbols and images such as language, ideology, dress and the media, that explain, express and reinforce, or sometimes oppose, those divisions
• Interactions between men and women, women and women and men and men that involve any form of dominance and submission. Conversational theorists, for example, have studied the way that interruptions, turn taking and the setting of topics re-create gender inequality in the flow of ordinary talk
• The way that the preceding three processes help to produce gendered components of individual identity, i.e., the way they create and maintain an image of a gendered self
• Gender is implicated in the fundamental, ongoing processes of creating and conceptualising social structures.

Looking at gender through a Foucauldian lens, gender is transfigured into a vehicle for the social division of power. Gender difference is merely a construct of society used to enforce the distinctions made between what is assumed to be female and male, and allow for the domination of masculinity over femininity through the attribution of specific gender-related characteristics.^[109] "The idea that men and women are more different from one another than either is from anything else, must come from something other than nature… far from being an expression of natural differences, exclusive gender identity is the suppression of natural similarities."^[110]

Gender conventions play a large role in attributing masculine and feminine characteristics to a fundamental biological sex.^[111] Socio-cultural codes and conventions, the rules by which society functions, and which are both a creation of society as well as a constituting element of it, determine the allocation of these specific traits to the sexes. These traits provide the foundations for the creation of hegemonic gender difference. It follows then, that gender can be assumed as the acquisition and internalisation of social norms. Individuals are therefore socialized through their receipt of society’s expectations of 'acceptable' gender attributes that are flaunted within institutions such as the family, the state and the media. Such a notion of 'gender' then becomes naturalized into a person’s sense of self or identity, effectively imposing a gendered social category upon a sexed body.^[110]

The conception that people are gendered rather than sexed also coincides with Judith Butler’s theories of gender performativity. Butler argues that gender is not an expression of what one is, but rather something that one does.^[112] It follows then, that if gender is acted out in a repetitive manner it is in fact re-creating and effectively embedding itself within the social consciousness. Contemporary sociological reference to male and female gender roles typically uses masculinities and femininities in the plural rather than singular, suggesting diversity both within cultures as well as across them.

The difference between the sociological and popular definitions of gender involve a different dichotomy and focus. For example, the sociological approach to "gender" (social roles: female versus male) focuses on the difference in (economic/power) position between a male CEO (disregarding the fact that he is heterosexual or homosexual) to female workers in his employ (disregarding whether they are straight or gay). However the popular sexual self-conception approach (self-conception: gay versus straight) focuses on the different self-conceptions and social conceptions of those who are gay/straight, in comparison with those who are straight (disregarding what might be vastly differing economic and power positions between female and male groups in each category). There is then, in relation to definition of and approaches to "gender", a tension between historic feminist sociology and contemporary homosexual sociology.^[113]

Legal status

A person's sex as male or female has legal significance—sex is indicated on government documents, and laws provide differently for men and women. Many pension systems have different retirement ages for men or women. Marriage is usually only available to opposite-sex couples; in some countries and jurisdictions there are same-sex marriage laws.

The question then arises as to what legally determines whether someone is female or male. In most cases this can appear obvious, but the matter is complicated for intersex or transgender people. Different jurisdictions have adopted different answers to this question. Almost all countries permit changes of legal gender status in cases of intersexualism, when the gender assignment made at birth is determined upon further investigation to be biologically inaccurate—technically, however, this is not a change of status per se. Rather, it is recognition of a status deemed to exist but unknown from birth. Increasingly, jurisdictions also provide a procedure for changes of legal gender for transgender people.

Gender assignment, when there are indications that genital sex might not be decisive in a particular case, is normally not defined by a single definition, but by a combination of conditions, including chromosomes and gonads. Thus, for example, in many jurisdictions a person with XY chromosomes but female gonads could be recognized as female at birth.

The ability to change legal gender for transgender people in particular has given rise to the phenomena in some jurisdictions of the same person having different genders for the purposes of different areas of the law. For example, in Australia prior to the Re Kevin decisions, transsexual people could be recognized as having the genders they identified with under many areas of the law, including social security law, but not for the law of marriage. Thus, for a period, it was possible for the same person to have two different genders under Australian law.

It is also possible in federal systems for the same person to have one gender under state law and a different gender under federal law.

Intersex people

For intersex people, who according to the UN Office of the High Commissioner for Human Rights, "do not fit typical binary notions of male or female bodies",^[114] access to any form of identification document with a gender marker may be an issue.^[115] For other intersex people, there may be issues in securing the same rights as other individuals assigned male or female; other intersex people may seek non-binary gender recognition.^[116]

Non-binary and third genders

Some countries now legally recognize non-binary or third genders, including Canada, Germany, Australia, and India. In the United States, Oregon, California, and the District of Columbia legally recognize non-binary gender.

Gender and society

Languages

Natural languages often make gender distinctions. These may be of various kinds, more or less loosely associated by analogy with various actual or perceived differences between men and women. Some grammatical gender systems go beyond, or ignore, the masculine-feminine distinction. ^[117]

• Many languages include terms that are used asymmetrically in reference to men and women. Concern that current language may be biased in favor of men has led some authors in recent times to argue for the use of a more gender-neutral vocabulary in English and other languages.
• Several languages attest the use of different vocabulary by men and women, to differing degrees. See, for instance, Gender differences in spoken Japanese. The oldest documented language, Sumerian, records a distinctive sub-language only used by female speakers. Conversely, many Indigenous Australian languages have distinctive registers with a limited lexicon used by men in the presence of their mothers-in-law (see Avoidance speech). As well, quite a few sign languages have a gendered distinction due to boarding schools segregated by gender, such as Irish Sign Language.
• Several languages such as Persian or Hungarian are gender-neutral. In Persian the same word is used in reference to men and women. Verbs, adjectives and nouns are not gendered. (See Gender-neutrality in genderless languages)
• Grammatical gender is a property of some languages in which every noun is assigned a gender, often with no direct relation to its meaning. For example, the word for "girl" is muchacha (grammatically feminine) in Spanish, Mädchen (grammatically neuter) in German, and cailín (grammatically masculine) in Irish.
• The term "grammatical gender" is often applied to more complex noun class systems. This is especially true when a noun class system includes masculine and feminine as well as some other non-gender features like animate, edible, manufactured, and so forth. An example of the latter is found in the Dyirbal language. Other gender systems exist with no distinction between masculine and feminine; examples include a distinction between animate and inanimate things, which is common to, amongst others, Ojibwe, Basque and Hittite; and systems distinguishing between people (whether human or divine) and everything else, which are found in the Dravidian languages and Sumerian.
• Several languages employ different ways to refer to people where there are three or more genders, such as Navajo or Ojibwe.

Science

Historically, science has been portrayed as a masculine pursuit in which women have faced significant barriers to participate.^[118] Even after universities began admitting women in the 19th century, women were still largely relegated to certain scientific fields, such as home science, nursing, and child psychology.^[119] Women were also typically given tedious, low-paying jobs and denied opportunities for career advancement.^[119] This was often justified by the stereotype that women were naturally more suited to jobs that required concentration, patience, and dexterity, rather than creativity, leadership, or intellect.^[119] Although these stereotypes have been dispelled in modern times, women are still underrepresented in prestigious "hard science" fields such as physics, and are less likely to hold high-ranking positions.^[120]

Religion

This topic includes internal and external religious issues such as gender of God and deities creation myths about human gender, roles and rights (for instance, leadership roles especially ordination of women, sex segregation, gender equality, marriage, abortion, homosexuality)
According to Kati Niemelä of the Church Research Institute, women are universally more religious than men. They believe that the difference in religiousity between genders is due to biological differences, for instance usually people seeking security in life are more religious, and as men are considered to be greater risk takers than women, they are less religious. Although religious fanaticism is more often seen in men than women.^[121]

yin and yang

In Taoism, yin and yang are considered feminine and masculine, respectively. The Taijitu and concept of the Zhou period reach into family and gender relations. Yin is female and yang is male. They fit together as two parts of a whole. The male principle was equated with the sun: active, bright, and shining; the female principle corresponds to the moon: passive, shaded, and reflective. Male toughness was balanced by female gentleness, male action and initiative by female endurance and need for completion, and male leadership by female supportiveness.

In Judaism, God is traditionally described in the masculine, but in the mystical tradition of the Kabbalah, the Shekhinah represents the feminine aspect of God's essence. However, Judaism traditionally holds that God is completely non-corporeal, and thus neither male nor female. Conceptions of the gender of God notwithstanding, traditional Judaism places a strong emphasis on individuals following Judaism's traditional gender roles, though many modern denominations of Judaism strive for greater egalitarianism. As well, traditional Jewish culture dictates that there are six genders.

In Christianity, God is traditionally described in masculine terms and the Church has historically been described in feminine terms. On the other hand, Christian theology in many churches distinguishes between the masculine images used of God (Father, King, God the Son) and the reality they signify, which transcends gender, embodies all the virtues of both men and women perfectly, which may be seen through the doctrine of Imago Dei. In the New Testament, Jesus at several times mentions with the masculine pronoun i.e. John 15:26 among other verses. Hence, the Father, the Son and the Holy Spirit (i.e. Trinity) are all mentioned with the masculine pronoun; though the exact meaning of the masculinity of the Christian triune God is contended.

In Hinduism

One of the several forms of the Hindu God Shiva, is Ardhanarishwar (literally half-female God). Here Shiva manifests himself so that the left half is Female and the right half is Male. The left represents Shakti (energy, power) in the form of Goddess Parvati (otherwise his consort) and the right half Shiva. Whereas Parvati is the cause of arousal of Kama (desires), Shiva is the killer. Shiva is pervaded by the power of Parvati and Parvati is pervaded by the power of Shiva.

While the stone images may seem to represent a half-male and half-female God, the true symbolic representation is of a being the whole of which is Shiva and the whole of which is Shakti at the same time. It is a 3-D representation of only shakti from one angle and only Shiva from the other. Shiva and Shakti are hence the same being representing a collective of Jnana (knowledge) and Kriya (activity).

Adi Shankaracharya, the founder of non-dualistic philosophy (Advaita–"not two") in Hindu thought says in his "Saundaryalahari"—Shivah Shaktayaa yukto yadi bhavati shaktah prabhavitum na che devum devona khalu kushalah spanditam api " i.e., It is only when Shiva is united with Shakti that He acquires the capability of becoming the Lord of the Universe. In the absence of Shakti, He is not even able to stir. In fact, the term "Shiva" originated from "Shva," which implies a dead body. It is only through his inherent shakti that Shiva realizes his true nature.

This mythology projects the inherent view in ancient Hinduism, that each human carries within himself both female and male components, which are forces rather than sexes, and it is the harmony between the creative and the annihilative, the strong and the soft, the proactive and the passive, that makes a true person. Such thought, leave alone entail gender equality, in fact obliterates any material distinction between the male and female altogether. This may explain why in ancient India we find evidence of homosexuality, bisexuality, androgyny, multiple sex partners and open representation of sexual pleasures in artworks like the Khajuraho temples, being accepted within prevalent social frameworks.

— ^[122]

In a number of North American Indigenous cultures, non-man/-woman individuals sometimes carried specific roles within that nation's religious structures. These could be the Lakota wíŋkte, Navajo Nádleehi, Anishinaabe niizh manidoowag and hundreds more. Recently, North American Native Americans and First Nations have adopted the term Two-Spirit to refer to the mosaic of different genders cross-culturally.

Poverty

Gender inequality is most common in women dealing with poverty. Many women must shoulder all the responsibility of the household because they must take care of the family. Oftentimes this may include tasks such as tilling land, grinding grain, carrying water and cooking.^[123] Also, women are more likely to earn low incomes because of gender discrimination, as men are more likely to receive higher pay, have more opportunities, and have overall more political and social capital then women.^[124] Approximately 75% of world's women are unable to obtain bank loans because they have unstable jobs.^[123] It shows that there are many women in the world's population but only a few represent world's wealth. In many countries, the financial sector largely neglects women even though they play an important role in the economy, as Nena Stoiljkovic pointed out in D+C Development and Cooperation.^[125] In 1978 Diana M. Pearce coined the term feminization of poverty to describe the problem of women having higher rates of poverty.^[126] Women are more vulnerable to chronic poverty because of gender inequalities in the distribution of income, property ownership, credit, and control over earned income.^[127] Resource allocation is typically gender-biased within households, and continue on a higher level regarding state institutions.^[127]

A bar graph comparing poverty differences based on age and gender in 2012.

Gender and Development (GAD) is a holistic approach to give aid to countries where gender inequality has a great effect of not improving the social and economic development. It is a program focused on the gender development of women to empower them and decrease the level of inequality between men and women.^[128]

The largest discrimination study of the transgender community, conducted in 2013, found that the transgender community is four times more likely to live in extreme poverty (income of less than $10,000 a year) than people who are cisgender (not transgender).^[129][130]

General strain theory

According to general strain theory, studies suggest that gender differences between individuals can lead to externalized anger that may result in violent outbursts.^[131] These violent actions related to gender inequality can be measured by comparing violent neighborhoods to non-violent neighborhoods.^[131] By noticing the independent variables (neighborhood violence) and the dependent variable (individual violence), it's possible to analyze gender roles.^[132] The strain in the general strain theory is the removal of a positive stimulus and or the introduction of a negative stimulus, which would create a negative effect (strain) within individual, which is either inner-directed (depression/guilt) or outer-directed (anger/frustration), which depends on whether the individual blames themselves or their environment.^[133] Studies reveal that even though males and females are equally likely to react to a strain with anger, the origin of the anger and their means of coping with it can vary drastically.^[133] Males are likely to put the blame on others for adversity and therefore externalize feelings of anger.^[131] Females typically internalize their angers and tend to blame themselves instead.^[131] Female internalized anger is accompanied by feelings of guilt, fear, anxiety and depression.^[132] Women view anger as a sign that they've somehow lost control, and thus worry that this anger may lead them to harm others and/or damage relationships. On the other end of the spectrum, men are less concerned with damaging relationships and more focused on using anger as a means of affirming their masculinity.^[132] According to the general strain theory, men would more likely engage in aggressive behavior directed towards others due to externalized anger whereas women would direct their anger towards themselves rather than others.^[133]

Economic development

Gender, and particularly the role of women is widely recognized as vitally important to international development issues.^[134] This often means a focus on gender-equality, ensuring participation, but includes an understanding of the different roles and expectation of the genders within the community.^[135]

In modern times, the study of gender and development has become a broad field that involves politicians, economists, and human rights activists. Gender and Development, unlike previous theories concerning women in development, includes a broader view of the effects of development on gender including economic, political, and social issues. The theory takes a holistic approach to development and its effects on women and recognizes the negative effects gender blind development policies have had on women. Prior to 1970, it was believed that development affected men and women in the same way and no gendered perspective existed for development studies. However, the 1970s saw a transformation in development theory that sought to incorporate women into existing development paradigms.

When Ester Boserup published her book, Woman’s Role in Economic Development, there was a realization that development affected men and women differently and there began to be more of a focus on women and development. Boserup argued that women were marginalized in the modernization process and practices of growth, development, and development policy threatened to actually make women worse off. Boserup’s work translated into the beginning of a larger discourse termed Women in Development (WID) coined by the Women’s Committee of the Washington DC Chapter of the Society for International Development, a network of female development professionals. The primary goal of WID was to include women into existing development initiatives, since it was argued that women were marginalized and excluded from the benefits of development. In so doing, the WID approach pointed out that the major problem to women’s unequal representation and participation were male biased and patriarchal development policies. In short, the WID approach blamed patriarchy, which did not consider women’s productive and reproductive work. In fact, women were tied to domestic work hence were almost invisible in development programs. The WID approach, however, began to gain criticism as ignoring how women’s economic marginalization was linked to the development model itself.

Some feminists^[who?] argued that the key concept for women and development should be subordination in the context of new capitalist forms of insecure and hierarchical job structures, rather than marginalization as WID approaches emphasized. The rise of criticism against the WID approach led to the emergence of a new theory, that of Women and Development (WAD).^{[citation needed]}

However, just as WID had its critics, so did WAD. Critics^[who?] of WAD argued that it failed to sufficiently address the differential power relations between women and men, and tended to overemphasize women’s productive as opposed to reproductive roles. Also, rising criticism of the exclusion of men in WID and WAD led to a new theory termed Gender and Development (GAD). Drawing from insights developed in psychology, sociology, and gender studies, GAD theorists shifted from understanding women’s problems as based on their sex (i.e. their biological differences from men) to understanding them as based on gender – the social relations between women and men, their social construction, and how women have been systematically subordinated in this relationship.

At their most fundamental, GAD perspectives link the social relations of production with the social relations of reproduction – exploring why and how women and men are assigned to different roles and responsibilities in society, how these dynamics are reflected in social, economic, and political theories and institutions, and how these relationships affect development policy effectiveness. According to proponents of GAD, women are cast not as passive recipients of development aid, but rather as active agents of change whose empowerment should be a central goal of development policy. In contemporary times, most literature and institutions that are concerned with women's role in development incorporate a GAD perspective, with the United Nations taking the lead of mainstreaming the GAD approach through its system and development policies.^{[citation needed]}

Researchers at the Overseas Development Institute have highlighted that policy dialogue on the Millennium Development Goals needs to recognize that the gender dynamics of power, poverty, vulnerability and care link all the goals.^[136] The various United Nations international women’s conferences in Beijing, Mexico City, Copenhagen, and Nairobi, as well as the development of the Millennium Development Goals in 2000 have taken a GAD approach and holistic view of development. The United Nations Millennium Declaration signed at the United Nations Millennium Summit in 2000 including eight goals that were to be reached by 2015, and although it would be a difficult task to reach them, all of them could be monitored. The eight goals are:

1. Halve the proportion of people living in extreme poverty at the 1990 level by 2015.
2. Achieve universal primary education
3. Promote gender equality and empower women
4. Reduce child mortality rates
5. Improve maternal health
6. Combat HIV/AIDS, Malaria and other diseases
7. Ensure environmental sustainability
8. Global partnership

The MDGs have three goals specifically focused on women: Goal 3, 4 and 5 but women’s issues also cut across all of the goals. These goals overall comprise all aspects of women’s lives including economic, health, and political participation.

Gender equality is also strongly linked to education. The Dakar Framework for Action (2000) set out ambitious goals: to eliminate gender disparities in primary and secondary education by 2005, and to achieve gender equality in education by 2015. The focus was on ensuring girls’ full and equal access to and achievement in good quality basic education. The gender objective of the Dakar Framework for Action is somewhat different from the MDG Goal 3 (Target 1): "Eliminate gender disparity in primary and secondary education, preferably by 2005, and in all levels of education no later than 2015". MDG Goal 3 does not comprise a reference to learner achievement and good quality basic education, but goes beyond the school level. Studies demonstrate the positive impact of girls’ education on child and maternal health, fertility rates, poverty reduction and economic growth. Educated mothers are more likely to send their children to school.^[137]

Some organizations working in developing countries and in the development field have incorporated advocacy and empowerment for women into their work. The Food and Agriculture Organization of the United Nations (FAO) adopted a 10-year strategic framework in November 2009 that includes the strategic objective of gender equity in access to resources, goods, services and decision-making in rural areas, and mainstreams gender equity in all FAO's programs for agriculture and rural development.^[138] The Association for Progressive Communications (APC) has developed a Gender Evaluation Methodology for planning and evaluating development projects to ensure they benefit all sectors of society including women.^[139]

The Gender-related Development Index (GDI), developed by the United Nations, aims to show the inequalities between men and women in the following areas: long and healthy life, knowledge, and a decent standard of living. The United Nations Development Programme (UNDP) has introduced indicators designed to add a gendered dimension to the Human Development Index (HDI). Additionally, in 1995, the Gender-related Development Index (GDI) and the Gender Empowerment Measure (GEM) were introduced. More recently, in 2010, UNDP introduced a new indicator, the Gender Inequality Index (GII), which was designed to be a better measurement of gender inequality and to improve the shortcomings of GDI and GEM.

Climate change

Gender is a topic of increasing concern within climate change policy and science.^[140] Generally, gender approaches to climate change address gender- differentiated consequences of climate change, as well as unequal adaptation capacities and gendered contribution to climate change. Furthermore, the intersection of climate change and gender raises questions regarding the complex and intersecting power relations arising from it. These differences, however, are mostly not due to biological or physical differences, but are formed by the social, institutional and legal context. Subsequently, vulnerability is less an intrinsic feature of women and girls but rather a product of their marginalization.^[141] Roehr^[142] notes that, while the United Nations officially committed to gender mainstreaming, in practice gender equality is not reached in the context of climate change policies. This is reflected in the fact that discourses of and negotiations over climate change are mostly dominated by men.^{[143][144][145]} Some feminist scholars hold that the debate on climate change is not only dominated by men but also primarily shaped in ‘masculine’ principles, which limits discussions about climate change to a perspective that focuses on technical solutions.^[144] This perception of climate change hides subjectivity and power relations that actually condition climate-change policy and science, leading to a phenomenon that Tuana^[144] terms ‘epistemic injustice’. Similarly, MacGregor^[143] attests that by framing climate change as an issue of ‘hard’ natural scientific conduct and natural security, it is kept within the traditional domains of hegemonic masculinity.^[143][145]

Social media

Gender roles and stereotypes have slowly started to change in society within the past few decades. These changes occur mostly in communication, but more specifically during social interactions.^[146] The ways people communicate and socialize have also started to change alongside advancement in technology.^[147] One of the biggest reasons for this change is due to social media.

Over the past few years, the use of social media globally has started to rise.^[148] This rise can be contributed to the abundance of technology available for use among youth. Recent studies suggest that men and women value and use technology differently.^{[147][148][149]} Forbes published an article in 2010 that reported 57% of Facebook users are women, which attributed to the fact that women are more active on social media, because on average women have 8% more friends and account for 62% of posts that are shared via Facebook.^[150] Another study in 2010 found that in most Western cultures, women spend more time sending text messages compared to men as well as spend more time on social networking sites as a way to communicate with friends and family.^[151] Hayat, Lesser and Samuel-Azran (2017) have further shown that while men write more posts in social networking sites, women commented on other people's posts more often. They further showed that women's posts enjoyed higher popularity than men's posts.

Social media is more than just the communication of words. With social media increasing in popularity, pictures have become a large role in how many people communicate. Research conducted in 2013 found that over 57% of pictures posted on social networking sites were sexual and were created to gain attention.^[152] More shockingly, 58% of women and 45% of men don't look into the camera, which is creating an illusion of withdrawal.^[152] Other factors to be considered are the poses in pictures such as women laying down in subordinate positions or even touching themselves in child like ways.^[152] In conclusion, research has found that images shared online through social networking sites help establish personal self-reflections that individuals want to share with the world.^[152]

According to recent research, gender plays a strong role in structuring our social lives, especially since society assigns and creates "male" and "female" categories.^[153] Individuals in society might be able to learn the similarities between gender rather than the differences. Until then, gender will never truly be equal, which is a problem.^[154] Social media helps create more equality, because every individual is able to express him or herself however they like. Every individual also has the right to express their opinion, even though some might disagree, but it still gives each gender an equal amount of power to be heard.^[155]

Young adults in the U.S. frequently use social networking sites as a way to connect and communicate with one another, as well as to satisfy their curiosity.^[156] Adolescent girls generally use social networking sites as a tool to communicate with peers and reinforce existing relationships; boys on the other hand tend to use social networking sites as a tool to meet new friends and acquaintances.^[157] More importantly, social networking sites have allowed individuals to truly express themselves, as they are able to create an identity and socialize with other individuals that can relate.^[158] Social networking sites have also given individuals access to create a space where they feel more comfortable about their sexuality.^[158] Recent research has indicated that social media is becoming a stronger part of younger individuals media culture, as more intimate stories are being told via social media and are being intertwined with gender, sexuality, and relationships.^[158]

Teens are avid internet and social media users in the United States. Research has found that almost all U.S. teens (95%) aged 12 through 17 are online, compared to only 78% of adults. Of these teens, 80% have profiles on social media sites, as compared to only 64% of the online population aged 30 and older. According to a study conducted by the Kaiser Family Foundation, 11-to-18 year olds spend – on average – over one and a half hours a day using a computer and 27 minutes per day visiting social network sites, which accounts for more than one fourth of their daily computer use.^[159]

Teen girls and boys differ in what they post in their online profiles. Studies have shown that female users tend to post more "cute" pictures, while male participants were more likely to post pictures of them doing action activities. Women in the U.S. also tend to post more pictures of friends, while boys tend to post more about sports and humorous links. The study also found that males would post more alcohol and sexual references.^[159] The roles were reversed however, when looking at a teenage dating site. Women referred to sexual references significantly more than males.

Boys share more personal information, like their hometown and phone number. While girls are more conservative about the personal information they allow to go public on these social networking sites. Boys, meanwhile, are more likely to orient towards technology, sports, and humor in the information they post to their profile.^[160]

Social media goes beyond the role of helping individuals express themselves, as it has grown to help individuals create relationships, particularly romantic relationships. A large amount of social media users have found it easier to create relationships in a less direct approach, compared to the traditional approach of awkwardly asking for someone's number.^[161]

Social media plays a big role when it comes to communication between genders. Therefore, it's important to understand how gender stereotypes develop during online interactions. Research in the 1990s suggested that different genders display certain traits such as being active, attractive, dependent, dominant, independent, sentimental, sexy, and submissive when it comes to online interaction.^[162] Even though these traits continue to be displayed through gender stereotypes, recent studies show that this isn't necessarily the case anymore.

Automating molecule design to speed up drug development

Machine-learning model could help chemists make molecules with higher potencies, much more quickly.

 
Rob Matheson | MIT News Office | July 6, 2018

Original link:  http://news.mit.edu/2018/automating-molecule-design-speed-drug-development-0706?utm_source=&utm_medium=&utm_campaign=

Designing new molecules for pharmaceuticals is primarily a manual, time-consuming process that’s prone to error. But MIT researchers have now taken a step toward fully automating the design process, which could drastically speed things up — and produce better results.

Drug discovery relies on lead optimization. In this process, chemists select a target (“lead”) molecule with known potential to interact with a specific biological target, then tweak its chemical properties for higher potency and other factors.

Chemists use expert knowledge and conduct manual tweaking of the structure of molecules, adding and subtracting functional groups — groups of atoms and bonds with specific properties. Even when they use systems that predict optimal desired properties, chemists still need to do each modification step themselves. This can take a significant amount of time at each step and still not produce molecules with desired properties.

Researchers from MIT’s Computer Science and Artificial Intelligence Laboratory (CSAIL) and Department of Electrical Engineering and Computer Science (EECS) have developed a model that better selects lead molecule candidates based on desired properties. It also modifies the molecular structure needed to achieve a higher potency, while ensuring the molecule is still chemically valid.

The model basically takes as input molecular structure data and directly creates molecular graphs — detailed representations of a molecular structure, with nodes representing atoms and edges representing bonds. It breaks those graphs down into smaller clusters of valid functional groups that it uses as “building blocks” that help it more accurately reconstruct and better modify molecules.

“The motivation behind this was to replace the inefficient human modification process of designing molecules with automated iteration and assure the validity of the molecules we generate,” says Wengong Jin, a PhD student in CSAIL and lead author of a paper describing the model that’s being presented at the 2018 International Conference on Machine Learning in July.

Joining Jin on the paper are Regina Barzilay, the Delta Electronics Professor at CSAIL and EECS and Tommi S. Jaakkola, the Thomas Siebel Professor of Electrical Engineering and Computer Science in CSAIL, EECS, and at the Institute for Data, Systems, and Society.

The research was conducted as part of the Machine Learning for Pharmaceutical Discovery and Synthesis Consortium between MIT and eight pharmaceutical companies, announced in May. The consortium identified lead optimization as one key challenge in drug discovery.

“Today, it’s really a craft, which requires a lot of skilled chemists to succeed, and that’s what we want to improve,” Barzilay says. “The next step is to take this technology from academia to use on real pharmaceutical design cases, and demonstrate that it can assist human chemists in doing their work, which can be challenging.”

“Automating the process also presents new machine-learning challenges,” Jaakkola says. “Learning to relate, modify, and generate molecular graphs drives new technical ideas and methods.”

Generating molecular graphs

Systems that attempt to automate molecule design have cropped up in recent years, but their problem is validity. Those systems, Jin says, often generate molecules that are invalid under chemical rules, and they fails to produce molecules with optimal properties. This essentially makes full automation of molecule design infeasible.

These systems run on linear notations of molecules, called “simplified molecular-input line-entry systems,” or SMILES, where long strings of letters, numbers, and symbols represent individual atoms or bonds that can be interpreted by computer software. As the system modifies a lead molecule, it expands its string representation symbol by symbol — atom by atom, and bond by bond — until it generates a final SMILES string with higher potency of a desired property. In the end, the system may produce a final SMILES string that seems valid under SMILES grammar, but is actually invalid.

The researchers solve this issue by building a model that runs directly on molecular graphs, instead of SMILES strings, which can be modified more efficiently and accurately.

Powering the model is a custom variational autoencoder — a neural network that “encodes” an input molecule into a vector, which is basically a storage space for the molecule’s structural data, and then “decodes” that vector to a graph that matches the input molecule.

At encoding phase, the model breaks down each molecular graph into clusters, or “subgraphs,” each of which represents a specific building block. Such clusters are automatically constructed by a common machine-learning concept, called tree decomposition, where a complex graph is mapped into a tree structure of clusters — “which gives a scaffold of the original graph,” Jin says.

Both scaffold tree structure and molecular graph structure are encoded into their own vectors, where molecules are group together by similarity. This makes finding and modifying molecules an easier task.

At decoding phase, the model reconstructs the molecular graph in a “coarse-to-fine” manner — gradually increasing resolution of a low-resolution image to create a more refined version. It first generates the tree-structured scaffold, and then assembles the associated clusters (nodes in the tree) together into a coherent molecular graph. This ensures the reconstructed molecular graph is an exact replication of the original structure.

For lead optimization, the model can then modify lead molecules based on a desired property. It does so with aid of a prediction algorithm that scores each molecule with a potency value of that property. In the paper, for instance, the researchers sought molecules with a combination of two properties — high solubility and synthetic accessibility.

Given a desired property, the model optimizes a lead molecule by using the prediction algorithm to modify its vector — and, therefore, structure — by editing the molecule’s functional groups to achieve a higher potency score. It repeats this step for multiple iterations, until it finds the highest predicted potency score. Then, the model finally decodes a new molecule from the updated vector, with modified structure, by compiling all the corresponding clusters.

Valid and more potent

The researchers trained their model on 250,000 molecular graphs from the ZINC database, a collection of 3-D molecular structures available for public use. They tested the model on tasks to generate valid molecules, find the best lead molecules, and design novel molecules with increase potencies.

In the first test, the researchers’ model generated 100 percent chemically valid molecules from a sample distribution, compared to SMILES models that generated 43 percent valid molecules from the same distribution.

The second test involved two tasks. First, the model searched the entire collection of molecules to find the best lead molecule for the desired properties — solubility and synthetic accessibility. In that task, the model found a lead molecule with a 30 percent higher potency than traditional systems. The second task involved modifying 800 molecules for higher potency, but are structurally similar to the lead molecule. In doing so, the model created new molecules, closely resembling the lead’s structure, averaging a more than 80 percent improvement in potency.

The researchers next aim to test the model on more properties, beyond solubility, which are more therapeutically relevant. That, however, requires more data. “Pharmaceutical companies are more interested in properties that fight against biological targets, but they have less data on those. A challenge is developing a model that can work with a limited amount of training data,” Jin says.

“The algorithms described in the paper are an important step toward the goal of beginning to mimic the lead optimization molecular design work a medicinal chemist currently performs,” says Angel Guzman-Perez, director of medicinal chemistry at the pharmaceutical company Amgen, who was not involved in the research. “Since this computational method optimizes the properties in vector space, it has the potential to generate completely different and novel chemical structures than a medicinal chemist would propose by thinking in chemical structure space. Hence, algorithms such as this one have the potential to complement and enhance the work done by medicinal chemists.”

The work was supported by the Defense Advanced Research Projects Agency “Make-It” program.

Sex

From Wikipedia, the free encyclopedia

Organisms of many species are specialized into male and female varieties, each known as a sex.  Sexual reproduction involves the combining and mixing of genetic traits: specialized cells known as gametes combine to form offspring that inherit traits from each parent. The gametes produced by an organism define its sex: males produce small gametes (e.g. spermatozoa, or sperm, in animals; pollen in seed plants) while females produce large gametes (ova, or egg cells). Individual organisms which produce both male and female gametes are termed hermaphroditic. Gametes can be identical in form and function (known as isogamy), but, in many cases, an asymmetry has evolved such that two different types of gametes (heterogametes) exist (known as anisogamy).

Physical differences are often associated with the different sexes of an organism; these sexual dimorphisms can reflect the different reproductive pressures the sexes experience. For instance, mate choice and sexual selection can accelerate the evolution of physical differences between the sexes.

Among humans and other mammals, males typically carry XY chromosomes, whereas females typically carry XX chromosomes, which are a part of the XY sex-determination system. Other animals have different sex-determination systems, such as the ZW system in birds, the X0 system in insects, and various environmental systems, for example in crustaceans. Fungi may also have more complex allelic mating systems, with sexes not accurately described as male, female, or hermaphroditic.^[3]

Overview

The male gamete (sperm) fertilizing the female gamete (ovum)

One of the basic properties of life is reproduction, the capacity to generate new individuals, and sex is an aspect of this process. Life has evolved from simple stages to more complex ones, and so have the reproduction mechanisms. Initially the reproduction was a replicating process that consists in producing new individuals that contain the same genetic information as the original or parent individual. This mode of reproduction is called asexual, and it is still used by many species, particularly unicellular, but it is also very common in multicellular organisms, including many of those with sexual reproduction.^[4] In sexual reproduction, the genetic material of the offspring comes from two different individuals. As sexual reproduction developed by way of a long process of evolution, intermediates exist. Bacteria, for instance, reproduce asexually, but undergo a process by which a part of the genetic material of an individual donor is transferred to another recipient.^[5]

Disregarding intermediates, the basic distinction between asexual and sexual reproduction is the way in which the genetic material is processed. Typically, prior to an asexual division, a cell duplicates its genetic information content, and then divides. This process of cell division is called mitosis. In sexual reproduction, there are special kinds of cells that divide without prior duplication of its genetic material, in a process named meiosis. The resulting cells are called gametes, and contain only half the genetic material of the parent cells. These gametes are the cells that are prepared for the sexual reproduction of the organism.^[6] Sex comprises the arrangements that enable sexual reproduction, and has evolved alongside the reproduction system, starting with similar gametes (isogamy) and progressing to systems that have different gamete types, such as those involving a large female gamete (ovum) and a small male gamete (sperm).^[7]

In complex organisms, the sex organs are the parts that are involved in the production and exchange of gametes in sexual reproduction. Many species, both plants and animals, have sexual specialization, and their populations are divided into male and female individuals. Conversely, there are also species in which there is no sexual specialization, and the same individuals both contain masculine and feminine reproductive organs, and they are called hermaphrodites. This is very frequent in plants.^[8]

Evolution

Different forms of anisogamy:
A) anisogamy of motile cells, B) oogamy (egg cell and sperm cell), C) anisogamy of non-motile cells (egg cell and spermatia).

Different forms of isogamy:
A) isogamy of motile cells, B) isogamy of non-motile cells, C) conjugation.

Sexual reproduction first probably evolved about a billion years ago within ancestral single-celled eukaryotes.^[9] The reason for the evolution of sex, and the reason(s) it has survived to the present, are still matters of debate. Some of the many plausible theories include: that sex creates variation among offspring, sex helps in the spread of advantageous traits, that sex helps in the removal of disadvantageous traits, and that sex facilitates repair of germ-line DNA.

Sexual reproduction is a process specific to eukaryotes, organisms whose cells contain a nucleus and mitochondria. In addition to animals, plants, and fungi, other eukaryotes (e.g. the malaria parasite) also engage in sexual reproduction. Some bacteria use conjugation to transfer genetic material between cells; while not the same as sexual reproduction, this also results in the mixture of genetic traits.

The defining characteristic of sexual reproduction in eukaryotes is the difference between the gametes and the binary nature of fertilization. Multiplicity of gamete types within a species would still be considered a form of sexual reproduction. However, no third gamete type is known in multicellular plants or animals.^[10][11][12]

While the evolution of sex dates to the prokaryote or early eukaryote stage,^[13] the origin of chromosomal sex determination may have been fairly early in eukaryotes (see evolution of anisogamy). The ZW sex-determination system is shared by birds, some fish and some crustaceans. XY sex determination is used by most mammals,^[14] but also some insects,^[15] and plants (Silene latifolia).^[16] The X0 sex-determination is found in most arachnids, insects such as silverfish (Apterygota), dragonflies (Paleoptera) and grasshoppers (Exopterygota), and some nematodes, crustaceans, and gastropods.^[17][18]

No genes are shared between the avian ZW and mammal XY chromosomes,^[19] and from a comparison between chicken and human, the Z chromosome appeared similar to the autosomal chromosome 9 in human, rather than X or Y, suggesting that the ZW and XY sex-determination systems do not share an origin, but that the sex chromosomes are derived from autosomal chromosomes of the common ancestor of birds and mammals. A paper from 2004 compared the chicken Z chromosome with platypus X chromosomes and suggested that the two systems are related.^[20]

Sexual reproduction

The life cycle of sexually reproducing organisms cycles through haploid and diploid stages

Sexual reproduction in eukaryotes is a process whereby organisms form offspring that combine genetic traits from both parents. Chromosomes are passed on from one generation to the next in this process. Each cell in the offspring has half the chromosomes of the mother and half of the father.^[21] Genetic traits are contained within the deoxyribonucleic acid (DNA) of chromosomes—by combining one of each type of chromosomes from each parent, an organism is formed containing a doubled set of chromosomes. This double-chromosome stage is called "diploid", while the single-chromosome stage is "haploid". Diploid organisms can, in turn, form haploid cells (gametes) that randomly contain one of each of the chromosome pairs, via meiosis.^[22] Meiosis also involves a stage of chromosomal crossover, in which regions of DNA are exchanged between matched types of chromosomes, to form a new pair of mixed chromosomes. Crossing over and fertilization (the recombining of single sets of chromosomes to make a new diploid) result in the new organism containing a different set of genetic traits from either parent.

In many organisms, the haploid stage has been reduced to just gametes specialized to recombine and form a new diploid organism; in others, such as cryptogamic plants the gametes are capable of undergoing cell division to produce multicellular haploid organisms. In either case, gametes may be externally similar, particularly in size (isogamy), or may have evolved an asymmetry such that the gametes are different in size and other aspects (anisogamy).^[23] By convention, the larger gamete (called an ovum, or egg cell) is considered female, while the smaller gamete (called a spermatozoon, or sperm cell) is considered male. An individual that produces exclusively large gametes is female, and one that produces exclusively small gametes is male.^[24] An individual that produces both types of gametes is a hermaphrodite; in some cases hermaphrodites are able to self-fertilize and produce offspring on their own, without a second organism.^[25]

Animals

Hoverflies mating

Most sexually reproducing animals spend their lives as diploid, with the haploid stage reduced to single-cell gametes.^[26] The gametes of animals have male and female forms—spermatozoa and egg cells. These gametes combine to form embryos which develop into a new organism.

The male gamete, a spermatozoon (produced in vertebrates within the testes), is a small cell containing a single long flagellum which propels it.^[27] Spermatozoa are extremely reduced cells, lacking many cellular components that would be necessary for embryonic development. They are specialized for motility, seeking out an egg cell and fusing with it in a process called fertilization.

Female gametes are egg cells (produced in vertebrates within the ovaries), large immobile cells that contain the nutrients and cellular components necessary for a developing embryo.^[28] Egg cells are often associated with other cells which support the development of the embryo, forming an egg. In mammals, the fertilized embryo instead develops within the female, receiving nutrition directly from its mother.

Animals are usually mobile and seek out a partner of the opposite sex for mating. Animals which live in the water can mate using external fertilization, where the eggs and sperm are released into and combine within the surrounding water.^[29] Most animals that live outside of water, however, use internal fertilization, transferring sperm directly from to female to prevent the gametes from drying up.

In most birds, both excretion and reproduction is done through a single posterior opening, called the cloaca—male and female birds touch cloaca to transfer sperm, a process called "cloacal kissing".^[30] In many other terrestrial animals, males use specialized sex organs to assist the transport of sperm—these male sex organs are called intromittent organs. In humans and other mammals this male organ is the penis, which enters the female reproductive tract (called the vagina) to achieve insemination—a process called sexual intercourse. The penis contains a tube through which semen (a fluid containing sperm) travels. In female mammals the vagina connects with the uterus, an organ which directly supports the development of a fertilized embryo within (a process called gestation).

Because of their motility, animal sexual behavior can involve coercive sex. Traumatic insemination, for example, is used by some insect species to inseminate females through a wound in the abdominal cavity—a process detrimental to the female's health.

Plants

Flowers are the sexual organs of flowering plants, usually containing both male and female parts.

Like animals, plants have developed specialized male and female gametes.^[31] Within seed plants, male gametes are contained within hard coats, forming pollen. The female gametes of seed plants are contained within ovules; once fertilized by pollen these form seeds which, like eggs, contain the nutrients necessary for the development of the embryonic plant.

Female (left) and male (right) cones are the sex organs of pines and other conifers.

Many plants have flowers and these are the sexual organs of those plants. Flowers are usually hermaphroditic, producing both male and female gametes. The female parts, in the center of a flower, are the pistils, each unit consisting of a carpel, a style and a stigma. One or more of these reproductive units may be merged to form a single compound pistil. Within the carpels are ovules which develop into seeds after fertilization. The male parts of the flower are the stamens: these consist of long filaments arranged between the pistil and the petals that produce pollen in anthers at their tips. When a pollen grain lands upon the stigma on top of a carpel's style, it germinates to produce a pollen tube that grows down through the tissues of the style into the carpel, where it delivers male gamete nuclei to fertilize an ovule that eventually develops into a seed.

In pines and other conifers the sex organs are conifer cones and have male and female forms. The more familiar female cones are typically more durable, containing ovules within them. Male cones are smaller and produce pollen which is transported by wind to land in female cones. As with flowers, seeds form within the female cone after pollination.

Because plants are immobile, they depend upon passive methods for transporting pollen grains to other plants. Many plants, including conifers and grasses, produce lightweight pollen which is carried by wind to neighboring plants. Other plants have heavier, sticky pollen that is specialized for transportation by insects. The plants attract these insects or larger animals such as humming birds and bats with nectar-containing flowers. These animals transport the pollen as they move to other flowers, which also contain female reproductive organs, resulting in pollination.

Fungi

Mushrooms are produced as part of fungal sexual reproduction

Most fungi reproduce sexually, having both a haploid and diploid stage in their life cycles. These fungi are typically isogamous, lacking male and female specialization: haploid fungi grow into contact with each other and then fuse their cells. In some of these cases, the fusion is asymmetric, and the cell which donates only a nucleus (and not accompanying cellular material) could arguably be considered "male".^[32] Fungi may also have more complex allelic mating systems, with other sexes not accurately described as male, female, or hermaphroditic.^[3]

Some fungi, including baker's yeast, have mating types that create a duality similar to male and female roles. Yeast with the same mating type will not fuse with each other to form diploid cells, only with yeast carrying the other mating type.^[33]

Many species of higher fungi produce mushrooms as part of their sexual reproduction. Within the mushroom diploid cells are formed, later dividing into haploid spores. The height of the mushroom aids the dispersal of these sexually produced offspring.^{[citation needed]}

Sex determination

Sex helps the spread of advantageous traits through recombination. The diagrams compare evolution of allele frequency in a sexual population (top) and an asexual population (bottom). The vertical axis shows frequency and the horizontal axis shows time. The alleles a/A and b/B occur at random. The advantageous alleles A and B, arising independently, can be rapidly combined by sexual reproduction into the most advantageous combination AB. Asexual reproduction takes longer to achieve this combination, because it can only produce AB if A arises in an individual which already has B, or vice versa.

The most basic sexual system is one in which all organisms are hermaphrodites, producing both male and female gametes—^{[citation needed]} this is true of some animals (e.g. snails) and the majority of flowering plants.^[34] In many cases, however, specialization of sex has evolved such that some organisms produce only male or only female gametes. The biological cause for an organism developing into one sex or the other is called sex determination.

In the majority of species with sex specialization, organisms are either male (producing only male gametes) or female (producing only female gametes). Exceptions are common—for example, the roundworm C. elegans has an hermaphrodite and a male sex (a system called androdioecy).

Sometimes an organism's development is intermediate between male and female, a condition called intersex. Sometimes intersex individuals are called "hermaphrodite"; but, unlike biological hermaphrodites, intersex individuals are unusual cases and are not typically fertile in both male and female aspects.

Genetic

Like humans and other mammals, the common fruit fly has an XY sex-determination system.

In genetic sex-determination systems, an organism's sex is determined by the genome it inherits. Genetic sex-determination usually depends on asymmetrically inherited sex chromosomes which carry genetic features that influence development; sex may be determined either by the presence of a sex chromosome or by how many the organism has. Genetic sex-determination, because it is determined by chromosome assortment, usually results in a 1:1 ratio of male and female offspring.

Humans and other mammals have an XY sex-determination system: the Y chromosome carries factors responsible for triggering male development. The "default sex," in the absence of a Y chromosome, is female-like. Thus, XX mammals are female and XY are male. In humans, biological sex is determined by five factors present at birth: the presence or absence of a Y chromosome (which alone determines the individual's genetic sex), the type of gonads, the sex hormones, the internal reproductive anatomy (such as the uterus in females), and the external genitalia.^[35]

XY sex determination is found in other organisms, including the common fruit fly and some plants.^[34] In some cases, including in the fruit fly, it is the number of X chromosomes that determines sex rather than the presence of a Y chromosome (see below).

In birds, which have a ZW sex-determination system, the opposite is true: the W chromosome carries factors responsible for female development, and default development is male.^[36] In this case ZZ individuals are male and ZW are female. The majority of butterflies and moths also have a ZW sex-determination system. In both XY and ZW sex determination systems, the sex chromosome carrying the critical factors is often significantly smaller, carrying little more than the genes necessary for triggering the development of a given sex.^[37]

Many insects use a sex determination system based on the number of sex chromosomes. This is called X0 sex-determination—the 0 indicates the absence of the sex chromosome. All other chromosomes in these organisms are diploid, but organisms may inherit one or two X chromosomes. In field crickets, for example, insects with a single X chromosome develop as male, while those with two develop as female.^[38] In the nematode C. elegans most worms are self-fertilizing XX hermaphrodites, but occasionally abnormalities in chromosome inheritance regularly give rise to individuals with only one X chromosome—these X0 individuals are fertile males (and half their offspring are male).^[39]

Other insects, including honey bees and ants, use a haplodiploid sex-determination system.^[40] In this case, diploid individuals are generally female, and haploid individuals (which develop from unfertilized eggs) are male. This sex-determination system results in highly biased sex ratios, as the sex of offspring is determined by fertilization rather than the assortment of chromosomes during meiosis.

Nongenetic

Clownfishes are initially male; the largest fish in a group becomes female

For many species, sex is not determined by inherited traits, but instead by environmental factors experienced during development or later in life. Many reptiles have temperature-dependent sex determination: the temperature embryos experience during their development determines the sex of the organism. In some turtles, for example, males are produced at lower incubation temperatures than females; this difference in critical temperatures can be as little as 1–2 °C.

Many fish change sex over the course of their lifespan, a phenomenon called sequential hermaphroditism. In clownfish, smaller fish are male, and the dominant and largest fish in a group becomes female. In many wrasses the opposite is true—most fish are initially female and become male when they reach a certain size. Sequential hermaphrodites may produce both types of gametes over the course of their lifetime, but at any given point they are either female or male.

In some ferns the default sex is hermaphrodite, but ferns which grow in soil that has previously supported hermaphrodites are influenced by residual hormones to instead develop as male.^[41]

Sexual dimorphism

Common pheasants are sexually dimorphic in both size and appearance.

Many animals and some plants have differences between the male and female sexes in size and appearance, a phenomenon called sexual dimorphism. Sex differences in humans include, generally, a larger size and more body hair in men; women have breasts, wider hips, and a higher body fat percentage. In other species, the differences may be more extreme, such as differences in coloration or bodyweight.

Sexual dimorphisms in animals are often associated with sexual selection – the competition between individuals of one sex to mate with the opposite sex.^[42] Antlers in male deer, for example, are used in combat between males to win reproductive access to female deer. In many cases the male of a species is larger than the female. Mammal species with extreme sexual size dimorphism tend to have highly polygynous mating systems—presumably due to selection for success in competition with other males—such as the elephant seals. Other examples demonstrate that it is the preference of females that drive sexual dimorphism, such as in the case of the stalk-eyed fly.^[43]

Other animals, including most insects and many fish, have larger females. This may be associated with the cost of producing egg cells, which requires more nutrition than producing sperm—larger females are able to produce more eggs.^[44] For example, female southern black widow spiders are typically twice as long as the males.^[45] Occasionally this dimorphism is extreme, with males reduced to living as parasites dependent on the female, such as in the anglerfish. Some plant species also exhibit dimorphism in which the females are significantly larger than the males, such as in the moss Dicranum^[46] and the liverwort Sphaerocarpos.^[47] There is some evidence that, in these genera, the dimorphism may be tied to a sex chromosome,^[47][48] or to chemical signalling from females.^[49]

In birds, males often have a more colourful appearance and may have features (like the long tail of male peacocks) that would seem to put the organism at a disadvantage (e.g. bright colors would seem to make a bird more visible to predators). One proposed explanation for this is the handicap principle.^[50] This hypothesis says that, by demonstrating he can survive with such handicaps, the male is advertising his genetic fitness to females—traits that will benefit daughters as well, who will not be encumbered with such handicaps.