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The study of sexual development and orientation has attracted much attention in the field of psychology due to the emergence of aberrant sexual orientations like gay, lesbian, asexual, and bisexual predilections. Psychological study on the forces underlying sexual development and orientations has led to the formulation of diverse theories ranging from biological to the environmental.
According to Hammack (2005), “…sexual orientation continues to be intellectually fragmented along disciplinary lines, primarily due to the divergent epistemological, methodological, and meta-theoretical perspectives” (p.267).
The divergent perspectives together with the transformation of society significantly change the sexual orientations of gays, lesbians, and bisexuals because the current society recognizes their rights more than in the past.
Many psychological theories regarding sexual development hold that human nature and nurture are the two main factors that determine sexuality in an individual. Therefore, what are the biological and environmental factors that determine sexual development and orientation in human?
Sexual development involves organizational and activational stages of differentiation that occur during pregnancy and adolescence respectively. At birth, primary sexual characteristics differentiate gender due to difference in external and internal sex organs. “All these structural differences result from a system of ducts, which release hormones, which in turn affect internal structures, which are stimulated to differentiate into characteristically male or female organs” (Hall, 1998, p. 1).
When a baby is born, the gonads are undifferentiated but after about four months, sexual differentiation begins to occur in the gonads. In males, gonads differentiate into testes while in females gonads differentiate into ovaries. This differentiation completes the development of primary sexual characteristics.
The testes and ovaries are the sex organs that are responsible for the productions of hormones that determine the secondary sexual characteristics in adolescence. The differentiation of gonads during early childhood forms the basis of development of the secondary sexual characteristics during adolescence.
During early childhood, the sexual process of sexual development is latent due to lack of hormonal expressions essential for the development of secondary sexual characteristics. The sexual development characteristics become evident at the ages between 11-13 for girls and 12-14 for boys.
This is an activational stage in sexual development since activation of hormones occurs. Hall argues that, “…at adolescence, a series of events takes place referred to as the activational effects of hormones, which result in secondary sex characteristics and process begins in the hypothalamus, which affects the pituitary gland, testes and ovaries” (1998, p.3).
Activation of hormones occurs in a cascading manner where stimulation of the hypothalamus leads to the secretion of gonadtropic releasing hormone, which in turn stimulates pituitary gland to release gonadtropic hormone.
Gonadotropic hormone then acts on the ovaries and testes simulating them to release estrogen and testosterone respectively. The two hormones, estrogen, and testosterone are responsible for the maturation of the secondary sexual characteristics during adolescence.
Hormones and Sexuality
Hormonal effects during adolescence are responsible for development of sexual orientations such as homosexuals, heterosexuals, asexual and bisexuals. Normal secondary sexual characteristics in male are deepening of voice, broadening of shoulders and experiences of wet dreams.
On the other hand, female secondary sexual characteristics involve widening of hips, experiences of menstruation and enlargement of breasts. The different orientations of the secondary sexual characteristics are due differing hormonal levels.
The two primary hormones that determine the orientation of secondary sexual characteristics are estrogens and testosterones, which are female and male hormones respectively. “Sex hormones have direct influence on the physiology and morphology that is why male and female bodies are differently shaped and work somewhat differently at a biological level” (Rogers, 2000, p.25).
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This explains the secondary sexual characteristics that occur differentially at puberty. In addition to estrogen, females have extra hormones like progesterone, follicle stimulating hormone, and luteinizing hormone that are involved in the regulation of the menstrual cycle until menopause.
The physiology of the brain seems to have sexual orientation due to the differing hormonal effects. Even though there are other morphological and biological differences between the male brain and the female brain, the hormonal interaction with the brain gives a physiological difference.
The ability of the testosterone, which is a male sexual hormone, to enter into the brain and the inability of the estrogen not to enter into the brain provides physiological difference of the brains.
Rogers (2000) explains that, “although estrogen is produced by the females’ ovaries in the development, it never gets into the brain, because it binds with the alpha-fetoprotein and as a result cannot pass into the brain” (p.26).
Unlike estrogen in females, testosterone in males cannot bind to the alpha-fetoprotein and it readily enters into the brain and undergoes aromatization process, which converts it into estrogen thus activating the medial preoptic area in the brain. The activation of the medial preoptic area of the brain in males and inactivation in females makes difference in physiological and morphological aspects of the brain.
Environmental and Sexual Orientation
Evolutionary psychologists supports that environmental factors play a role in sexual development and sexual orientations. Hammack argues that, “sexual lifestyles are the culturally specific erotic ideas and emotions that constitute the life-course development within a particular sexual culture, which control sexual behavior and conduct” (2005, p. 275).
Therefore, cultural environments have the potential to influence sexual development and orientations, depending on cultural sexual lifestyles embraced by the society.
For example, recognition of homosexuals’ rights in the United States of America has tremendously increased the number of homosexuals, proving that sexual lifestyles in the cultural environment have significant effect on the sexual orientation of the individual members in the society.
In the family level, research studies has shown that children who experience tough parenting times such as divorced parents, separated parents or missed parental love are more likely to become homosexuals in future. Numerous research studies have found out that, “there is substantive evidence to supporting that the nature of parenting, early childhood experiences, sexual abuse, or other adverse life play significant role in the formation of a person’s fundamental heterosexual or homosexual orientation” (Hammack, 2005, p. 277).
There is a strong correlation between intact or stable families with the heterosexual marriages of the kids. Hence, family is a microenvironment that imposes primary influence on the sexual orientation of the kids.
Sexual development and orientation has puzzled many psychologists and biologists in the light of emerging aberrant sexual orientations such as lesbianism, gay, bisexual, or asexual. Despite the fact that biological studies clearly stipulate sexual orientations, the understanding of the deviant sexual orientations demands psychological studies in order to shed more light concerning psychological aspect of these ‘abnormalities.’
Many research studies have attributed anomalies of sexual orientations to genetic, hormonal, cultural, and social factors, which act together in determination of sexual orientations.
Hall, R. (1998). Sexual Development. Developmental Psychology Journal, 1-10.
Hammack, P. (2005). The Life Course Development of Human Sexual Orientation: An Integrated Paradigm. The Human Development, 48. 267-290
Rogers, W. (2000). The Psychology of Gender and Sexuality. Buckingham: Open University Press.