Gender is generally conceived as a set of characteristics or traits that are associated with a certain biological sex (male or female). In non-western countries, gender is not always conceived as binary, or strictly linked to biological sex. As a result, in some cultures there are third, fourth, fifth or "some" genders. The characteristics that generally define gender are referred to as masculine or feminine. The formation of gender is controversial in many scientific fields, including psychology. Specifically, researchers and theorists take different perspectives on how much of gender is due to biological, neurochemical, and evolutionary factors (nature), or is the result of culture and socialization (nurture). This is known as the nature versus nurture debate. The subfields of psychology note specific differences in the traits of each gender, based on their perspective of the issue on the nature versus nurture debate.
The study of gender took off in the 1970s. During this time period, academic works were published reflecting the changing views of researchers towards gender studies. Some of these works included textbooks, as they were an important way that information was compiled and made sense of the new field. In 1978 Women and sex roles: A social psychological perspective was published, one of the first textbooks on the psychology behind women and sex roles. Another textbook to be published, Gender and Communication, was the first textbook to discuss the topic of its subject.
Other influential academic works focused on the development of gender. In 1966, The Development of Sex Differences was published. This book went into what factors influence a child’s gender development, with contributors proposing the effects of hormones, social learning, and cognitive development in respective chapters. Man and Woman, Boy and Girl, by John Money was published in 1972, reporting findings of research done with intersex subjects. The book proposed that the social environment a child grows up in is more important in determining gender than the genetic factors he or she inherits. In recent years, the majority of Dr. Money's theories regarding the importance of socialization in the determination of gender have come under intense criticism, especially in connection with the false reporting of success in the 'John/Joan' experiment (see David Reimer).
In 1974, The Psychology of Sex Differences was published. It said that men and women behave more similarly than had been previously supposed. They also proposed that children have much power over what gender role they grow into, whether by choosing which parent to imitate, or doing activities such as playing with action figures or dolls. These works added new knowledge to the field of gender psychology.
Biological differentiation is a fundamental part of human reproduction. Males have two different sex chromosomes, an X and a Y. Females have two X chromosomes. The Y chromosome is what determines sexual differentiation. If the Y chromosome is present, growth is along male lines; it results in the production of testes, which in turn produce testosterone. In addition to physical effects, this prenatal testosterone increases the likeliness of certain "male" patterns of behavior after birth, though the exact impact and mechanism are not well understood. Parts of the SRY and specific parts of the Y chromosome may also possibly influence different gender behaviors, but if so, these impacts have not yet been identified.
The biological approach states that the distinction between men and women are due to inherent and hormonal differences. Some critique this approach because it leaves little room for sexual expression and gender because it claims both are dependent on biological makeup. Biological explanations of gender and sexual differences have been correlated to the work done by Charles Darwin regarding evolution. He suggested that just as wild animals and plants had physiological differences between sexes, humans did as well. Biological perspectives on psychological differentiation often place parallels to the physical nature of sexual differentiation. These parallels include genetic and hormonal factors that create different individuals, with the main difference being the reproductive function. The brain controls behavior by individuals, but it is influenced by genes, hormones and evolution. Evidence has shown that the ways boys and girls become men and women is different, and that there are variations between the individuals of each sex. There have been studies conducted to try and associate hormones with the gender identity of males and females. Okayama University in Japan did a study investigating the biological nature of gender identity disorder. The researchers looked at five different sex related hormones and whether or not they increased the chances of an individual being a transsexual. They examined male to female (MTF) and female to male (FTM) transsexuals, using control males and females for comparison. Their research did not find a significant difference in the distribution of the examined genes. The results currently can not provide evidence that the different genetic variants of sex hormone genes influence an individual to MTF or FTM transsexualism.
Sex-related differences of cognitive functioning is questioned in research done on the areas of perception, attention, reasoning, thinking, problem solving, memory, learning, language and emotion. Cognitive testing on the sexes involves written tests that typically have a time limit, the most common form being a standardized test such as the SAT or ACT. These test basic individual abilities rather than complex combination of abilities needed to solve real life problems. Analysis of the research has found a lack of credibility when relying on published studies about cognition because most contain findings of cognitive differences between the males and females, but they overlook those that do not show any differences, creating a pool of biased information. Those differences found are attributed to both social and biological factors. The introduction of cultural factors are in congruence to necessary biological elements. An article published in the Review of Educational Research summarizes the history of the controversy around sex differences in variability of intelligence. Through modern research, the main idea has held that males have a much wider range in test performance in IQ tests. The study also analyzes data concerning differences in central tendencies through environmental and biological theories. Males were found to have much wider variation than females in areas of quantitative reasoning, spatial visualization, spelling, and general knowledge than females. In the studies conclusion, to form an accurate summary, both the variability in sex differences and in the central tendencies must be examined to generalize the cognitive variances of males and females. Doreen Kimura, a psychobiologist, has published books and articles specifically on the subject of sex and cognition. Since studying gender differences in cognition, Kimura has further proved generalizations made from research data collected in the field of cognitive psychology. Males are found to be better at the motor skill of aiming, while females excel at the coordination of fine motor skills. Male chimpanzees, for example, are much more likely to throw stones or clumps of earth than their corresponding gender. In spatial tasks, males found it easier to visualize geometrically and rotationally while females used references to objects when guiding through a route. Females test higher on object location memory and verbal memory, approximately over a half of a standard deviation. These tests have not been comprehensively studied over an adequate amount of time to make a full and accurate conclusion. Standardized spatial tests, like the Vandenberg mental rotations test, have consistently shown sex differences in this area over the last thirty years. The differences for such tests average to a full standard deviation. These scientific findings have not been generalized cross culturally. Females have shown to have a higher ability in reading facial and body cues than their male counterparts. Though studies have found females to have more advanced verbal skills, men and women in adulthood do not have varied vocabularies. Women tend to have better spelling capabilities and verbal memory. Kimura refers to an example of a study done in east Africa, which correlated children, mostly males, who travelled the farthest from their tribe with excelled performance in spatial tasks. She offers three possible explanations for the correlation. First, those with the more trained spatial ability tend to take part in experiences that require those skills. The unconscious positive reinforcement a person receives from doing something well, and the praise that follows, may make certain activities more attractive and more likely to occur. This phenomenon, where people end up taking part in activities or occupations in a self-directed way, is called self-selection. Second, the experience trained the person to develop spatial abilities. The type of experience determines which traits are developed. Third, an outside factor, such as early exposure to androgens, could influence both the biological and environmental components.
Although there is a large collection of information about how men and women differ in cognitive functioning and the physical differences of each gender's brain, both sets of information have not been definitely related to each other in research. The biggest difference between the genders are the sizes of the brains. Men's brains are larger and heavier than women's by 10-15%, though the ratio of brain to body size in both males and females varies based on body size. Researchers propose the extra brain weight in males is the reason for the large sex difference in spatial ability. Women appear to have larger areas of connective fibers between the two hemispheres, called hemispheric asymmetry. It is suggested that there are more clearly defined roles of the hemispheres in males than there are in females because of this asymmetry. A report by Simon LeVay in 1991, disclosed information about the sex related difference of the interstitial nuclei of the anterior hypothalamus, or INAH. Females were found to have smaller areas of the INAH in postmortem analysis by Dutch and American researchers. The same differences were found between homosexual and heterosexual men. An inference has been made that the size of this region is somehow related to the preference of an individual's sex partner. LeVay notes that these findings are correlational.
In most cultures, humans are subject from infancy to gender socialization. For example, infant girls typically wear pink and infant boys typically wear blue. Gender schemas, or gendered cultural ideals which determine a person’s preferences, are also installed into our behaviors beginning at infancy. Studies show that toddler children are more likely to interact with children of the same sex than they are to interact with children of the opposite sex or even a mixed group.
As people get older, gender stereotypes become more applied. The social role theory primarily deals with such stereotypes, more specifically the division of labor and a gender hierarchy. When this theory is applied in social settings, such as the workplace, it can often lead to sexism. This theory also applies to certain personality trails, such as men are more typically more assertive and women more passive. According to this theory, ideally, in most cultures, the woman is to stay and tend to the house and home while the man works to both better the house itself and increase finances.
In the midst of so many idealistic concepts on the roles of a specific gender in society, there are also individuals who choose to not to conform to the ideas of their culture. Throughout history, gender roles have been altered and are much more flexible than they were in recent centuries. Such alterations include equal political rights as well as employment and education opportunities solely available to females. Homosexual people are also subject to go against gender conformities. The term congenital gender invert is used to define homosexuals who possess a trait of the opposite sex. Such individuals tend to have the most social difficulty in regards to cultural norms.