Sexual preference is a topic of great debate.  There is valid research in three different areas of sexual preference, trying to decipher the motivation for ones choice in a partner.  The first area of research is, that sexual preference and homosexuality is a personal choice, the second area of research is that psychological factors during childhood decide whether a person is homosexual or heterosexual, and the third that a person is biologically different.  The biological differences are caused by many different experiences and situations.  I believe that sexual orientation is dependent on biological factors, which include:  prenatal hormones, genetics, immunological reactions to the fetus, and the mother’s environment during the pregnancy, sexual dimorphism and latent taxa.  The contradicting theory of psychological influences is relevant and will be discussed, but only to reinforce the underlying theme of biology.  Although I believe that there is possible relevance to the psychological theory; the biological factors has much more significant information to support such theories.  Therefore as the author of this paper, I will be presenting different theories and studies that have been conducted to support my theory that sexual orientation and homosexuality specifically is caused by different biological factors during the prenatal stages of development.
 

There are many influences that a mother has on her child while some of these are controllable others are uncontrollable.  Most of these influences are during the raising of that child, but there are also some, that occur during gestation.  The influences that a mother can most often not control are the hormones that a doctor prescribes her during gestation.  Through research it has been discovered, that behavioural sex differences result in part, from the influences of hormones during the critical periods of early development, specifically during the prenatal and neonatal stages of a child’s life (Collaer & Hines, 1995).   These sex differences, range from sexual orientation, to a persons level of masculinity, or femininity.  The researchers further hypothesized, that exposure to high levels of estrogen, like androgen, leads to masculinization and defeminization.  The researchers studied children of women who were prescribed the hormone estradiol or diethylstilbestrol (DES; a synthetic, nonsteroidal estrogen).  From these studies there have been many different conclusions:  the first being, that DES is a masculinizing hormone, promoting masculine behaviour or defeminizing behaviour.    The researchers studied males and females separately and conclusions were made separately.  DES exposed women were found to be more homosexual or bisexual then those in a control group, including sisters, demographically matched women, and women with similar medical histories, but without DES exposure; whereas men whether they were in the control group or in the DES exposed group, were found to be similar regarding sexual orientation.  The researchers concluded, that altered sexual orientation in DES-exposed women is relevant to suggestions that increased homosexuality or bisexuality relates to altered self-perceptions or other consequences of early hormone exposure.  The results support a masculinizing or defeminizing influence of exogenous estrogens (DES) on relatively restricted behaviours in women but there is no clear conclusion for men.

 The researchers also found two periods in which androgen levels are elevated in men, compared to women.  One is prenatal (about week 8 to 24), and the other is postnatal (from about the 1st month to the 6th month).  During week 8 to 24, the following is developed during gestation:  if it is a male, the external reproductive organs start to form, during about the 9th week, in the following weeks female primitive eggs are created.  These sexual organs and process that are being created and could be affected by different hormonal levels are being created.  From this information, the researchers are now studying hormone levels during early development and relating these levels to childhood, and behaviour in the following years.  Post-natal hormonal levels have not been researched fully and studies are ongoing currently.

 Furthermore, these prenatal hormone levels are being associated with possible brain differences; these brain structure differences are being associated specifically with sexual orientation.  These differences include, female typical brain structure, in men and the causes are being associated with hormones, pre and postnatal.

 I think that this article, has presented valid research on the topic of biological influences on sexual orientation.  The valid points of interest that are further explored during the report:  are brain development and the association between hormonal levels during gestation and sexual orientation.  Brain structure and development, is a topic of vague discovery, because most of the research and study is done post-mortem.  For significant discoveries to be made, studies, have to begin at birth and be carried out through ones full life.
 

Another theory about sexual orientation, that the first article did not support, is the issue, that sexual orientation is dependent on genetic factors and traits transferred through the family.  This article also supports evidence, that a gene on the X chromosome influences male sexual orientation. The study, only contained pairs of Australian twins, and the researchers were studying those that have been raised together, the researchers were addressing four main issues: (a) the comparison of male and female distributions of sexual orientation; (b) the construct validity of sexual orientation self–ratings indicating low but positive levels of homosexual interest; (c) the relative role of genes, shared environment in the development of sexual orientation, and (d) the genetic architecture of their co variation (Bailey, Dunne, & Martin, 2000).  The twins in the study were of all zygosity, and all were individuals who had not had sex.  The study was completed through surveys via the mail, having both twins fill out surveys and comparing the twins’ surveys conclusions could be made about the sexual orientation of the twins.  Bailey et al. also used the Kinsey Scale, to further determine sexual orientation.

The Kinsey Scale has two different questionnaires, one that measures sexual attraction to the sexes, and the other measures sexual fantasy to the sexes, and the scale ranges from 0, exclusively heterosexual, to 6 exclusively homosexual (Kinsey Pomeroy, & Martin, 1948).

According to the Kinsey Scale, women were more likely to have homosexual feelings (5), but men were more likely to be exclusively homosexual (6).  In association with zygosity, women did not differ, whether mono or dizygotic, but men were more likely to be homosexual if they were monozygotic then if they were dizygotic.  Because of these results, the researchers were able to estimate additive genetic and shared environmental effects, with the possibility of genetic dominance.

The higher scores in male homosexuality, indicates sexual orientation is not developed the same between the sexes.  Male sexual orientation development makes extreme departures from heterosexual development, especially likely compared with female sexual orientation development.  It was difficult for the researchers to make distinctions between genetic and shared environmental contributions through family heredity.  The researchers also discovered that male gender nonconformity was significantly hereditary.  This nonconformity is the inherited component of sexual orientation development.

Relating the past article, with this article, could be quite simple, the brain differences cause the nonconformities in the children, and therefore the sexual orientation differences are developed after childhood.  Once there is nonconformity present there is an indicator of childhood differences and developmental differences in a child.  Although there is not specific scientific research presented here, there are assumptions and valid data that are further supported in the following documents.
 

Continued from the last articles, this one further reinforces the idea of changes to the fetus, and brain structure, during gestation.  This study researched factors that affected changes in the brain composition.  Focusing on the differences in the brain affecting sexual orientation, and all of these changes in the brain functionality and development happening during gestation.   Primarily focusing on immunological reactions to the fetus, and how different changes in brain laterality causes sexual orientation to be affected.  The researchers used handedness as the developmental stage in gestation as a determining factor in sexual orientation.  In accordance with brain laterality, Lalumiere, Blanchard, & Zucker, consider left-handedness to be more likely homosexual and right-handedness to be stereotypically heterosexual.  This theory by Lalumiere et al is mediated by immunological phenomena, specifically by the major histocompatibility complex (MHC).  These are significant results suggesting, that autoimmune diseases have associations with handedness.  It was also theorized in this article, that maternal antibodies to Y – linked minor histocompatibility antigens (HY antigens) might pass the placental barrier and divert the sexual differentiation of the fetal brain from the male–typical pattern.  By the male–typical brain, they mean a heterosexual male brain.  Any abnormality that researchers find, they associate with homosexuality, especially, if it is more female typical.

 Significant brain structure differences that are associated with sexual orientation, specifically homosexuality are:  the volume and density of suprachiasmatic nucleus, which is not sexually dimorphic, was greater in homosexual men, the third interstitial nucleus of the anterior hypothalamus, which is smaller in women than in men was smaller in homosexual men.  It has also been found that the midsagittal plan of the anterior commissure, which is larger in women than in men, was larger in homosexual men; and finally it was also found that the isthmus of the corpus callosum, which is larger in women than in men, was also larger in homosexual men.  These results although likely that these differences were present before or during the development of sexual orientation, Lalumiere et al do not completely rule out the possibility that these brain structural differences are the consequences of a person’s sexual orientation.

This study supports the theories about genetics:  the hypothesis of this study also supported the finding that homosexuality in men correlates with an individual’s number of older brothers but not with his number of older sisters.  Therefore it is probable that involvement of HY antigens is the development of sexual orientation and differentiation.  The theories, that a man is more likely, to be homosexual if he has older brothers, then if he has older sisters, and holds no validity considering women.    Lalumiere et al proposed that a maternal immune response to male-specific fetal products could cause a disruption of fetal brain sexual differentiation and prevent the development of a female-typical sexual orientation.  Its association is that the immune system, with each successive pregnancy of a male fetus would increase the likelihood and strength of an immune response.  Although the actual antibodies remain to be identified, a response of the immune system involves the male-specific, Y-linked, minor histocompatibility antigens.

The two theories that were presented here, that coincide, are the brain structure and immunological reactions, reactions to the fetus, cause structural brain differences.  These female typical brains are being found in male homosexuals.  Possible reasons for these differences are immune shut downs.  The female and mother’s body as continuous pregnancies occur the proper hormones and antigens are not being passed on to male fetus’ giving them female typical anomalies.
 

The last study, focused on the anatomy of the brain and possible explanations, for those differences, whereas this study focuses on sexual dimorphism, in the nervous system and in the brain.  Sexual dimorphisms are differences in the human body that are uncharacteristic to heterosexual people, and researchers are now associating these differences with determining sexual orientation.  The article hypothesized that there would be sex differences in the structure of the nervous system and whether people possess a masculine of feminine configuration would depend on whether they were exposed to androgens early in their development (Breedlove, 1994).
The Nervous System

The researcher found, that sexual dimorphism first arising after birth, could represent prenatal hormone malfunction, but the trait could be there from birth but not until social stimulation is it evident of the sexual orientation difference.  It could also be any difference that arises before birth could be the result of different social stimulation to the sexes.

 The spinal cord, in men and women have a different number of spinal motoneurons, men having about 25% more, research supports, that humans undergo a period during which about half the generated motoneurons die (completed by the 26th week of gestation) and this process overlaps the period during which male fetus’ secrete testosterone and the external genitalia become differentiated.

 Therefore, according to Breedlove, this dimorphism, which has been present since birth possibly due to a hormone malfunction, it is possible that until social stimulation, no difference within the sexes or within the single sex will be evident and the child will appear to be heterosexual until influenced or given the chance to be otherwise.
 

As has been stated before brain differences are quite commonly associated with sexual orientation.  This article justifies the previous hypotheses and Breedlove, agrees, that sexual orientation is associated with sexual dimorphism:  supports that the brain structure of homosexual men more closely resembles that of women than that of heterosexual men.  Studies have been conducted using an obvious region of the corpus callosum (CC), because MRI easily studies it.  This has been confirmed and through these tests proves that homosexual men have larger anterior commissure (AC), which is a small tract of axons like the larger CC, and the two cerebral hemispheres, is larger in homosexual men then in heterosexual men.  This may relate to cognitive lateralization, since there have been several reports that homosexual men perform in a female-like behaviour on tests of cognitive function.

According to Breedlove, these dimorphisms are present from birth, but it takes social stimulation for these differences to become evident to the public and to the person themselves.  Sexual orientation is becoming more and more clearly related to biological differences, but the psychological and social factors are now having some influence also on a person’s sexuality.
 

From the previous theories, I have found, this one article, which summarizes and confirms all of the previous research, as well as highlighting, a few other biological possibilities that affect homosexuality and heterosexuality.  The causes of sexual orientation are categorized in this article, as genetic-hormonal, pharmacological, and maternal stress.  The researcher presented a theory of all the possibilities of human sexual orientation is determined (Ellis & Ames, 1987).

There are three genetic hormonal causes for sexual orientation; they are the affects of dihydrotestosterone (DHT), androgen insensitivity syndrome (AIS), and congenital adrenal hyperplasia (CAH).  DHT is required for masculinizing the external genitals, and it has been found, that the absence of DHT causes the genitals to develop feminine or demasculinized appearance, no matter how much testosterone the testes produce.  In almost all of the cases of DHT, the individuals are consistent with their genetic sex, and not with their birth sex, and therefore these individuals would be considered homosexual females.  The second case AIS, or otherwise called the testicular feminization syndrome.  These individuals produce normal male quantities of testosterone, but lack the ability to use the hormone in a normal way.  In most cases these woman are not even aware of the hormonal levels until after puberty and menstruation does not occur.  According to science these women would be considered as heterosexual females. The final example of genetic hormonal causes is CAH, women who normally produce small amounts of adrenalin and cortisol, will produce male – range quantities of testosterone by the fetal adrenal glands instead of cortisol.  This causes female behaviour to be unusually masculine, and women are scientifically classified as homosexuals.

The pharmacological cause of sexual orientation is the administering of other drugs, during gestation.  The leading drug that is known for changing a person’s sexuality is progestins (or progestogens).  Although women’s levels of progesterone rise rapidly during conception, the administering of these drugs, cause masculinizing and feminizing.  Both of these effects take specific timing and dosage, and the possibility of interaction with other substances could be a very important factor in homosexuality.  The masculinizing and feminizing can both be positive and negative, depending on which sex that the result is happening to, most often it’s feminizing to a man, and masculinizing to a woman.  Sexual orientation being caused by pharmacological drugs is not necessarily an answer to the question of a persons motivation to be homosexual or heterosexual, but it is an answer to why a person would be homosexual rather than heterosexual, and that is because it is not a choice at the defeminizing effects or vice versa have genetically changed that person to become attracted to the same sex.
 

 This cause for sexual orientation can so far only be related to men, and there have been two studies to support the hypothesis, that a stressful event during gestation causes a male to be homosexual, rather than heterosexual.  The first study was done after the Second World War, when a large number of homosexual men were born, and this can be related to the stress that the women were under during and right after the war.  The second study was conducted by surveys of mothers who had homosexual bisexual and heterosexual sons.  They were asked if there was an event during gestation, which was significant to them.  The mothers of homosexual sons, nearly two-thirds could remember such an event, of the mothers with bisexual sons almost one third, and not even ten percent of the mothers with heterosexual sons could recall such an event.  This suggests a significant association between a stressful gestation and homosexuality.
 

It has been argued, that homosexuality is related to specific biological factors, that make a person homosexual or heterosexual, according to Kinsey (1948) men exist at every level of the Kinsey Scale, making it hard to label people as strictly heterosexual or strictly homosexual.  Latent taxa are numerical relations between purported indicators of conjectured taxa and the hallmarks of true taxa (Gangestad, Martin, & Bailey, 2000).  In other words, latent taxa are a set of statistics, which psychologists and researchers study and make specific conclusions from these numbers.  The existence of taxa can be supported whether by the demonstration of requisite causal processes or by formal mathematical taxometric methods, which decide whether latent taxa underlie a set of candidate indicators of a conjectured taxon based on numerical relations between them.  In the study, the researchers set out to examine whether latent taxa underlie measures of sexual orientation and two related domains, childhood gender nonconformity (CGN) and continuous gender identity (CGI).  This study, analyzed men and women separately, they studied sexual orientation itself, as assessed by the Kinsey Scale and used the taxometric procedure maximum covariance, making hits maximum (MAXCOV) as well as mean above minus below a cut (MAMBAC).

The results of Gangestad et al, according to the Kinsey Scale, had low homosexuality ratings, approximately 3.6% of the men and 1% of the women had a Kinsey 5, which is primarily homosexual, having a 6 is exclusively homosexual.  From these results that their was a justified number of male and female homosexuals in the study, Gangestad et al discovered the following:  there was an association for men with the Kinsey scores of 6 and their child gender non-conformity, as well as their continuous gender-identity.  This also makes another association, within the article that states the mothers of homosexual men and their androgen levels being significantly higher than heterosexual men’s mothers during gestation.  Women with homosexual tendencies (score of 5) had no association with child gender non-conformity, but their was an interestingly strong association with continuous gender identity, which suggests to me, that these women are still not comfortable with their sexuality and are in constant struggle to understand where they are in their lives.

 Because this article was more or less, studying numbers and making associations with these numbers, it is hard to make clear conclusions from the article but valid points of interest were brought up and in the final argument they will be further supported.
 

This final study that supports the latent taxa, but contradicts the findings of the biological theories supports the idea, that sexual orientation is strictly based on psychological socialization; not the theories, that say it is a personal choice, it is a theory that is dealing with socialization and events from childhood that cause a person to become homosexual or heterosexual.  The article that I find relevant to this topic, is not specific to sexual orientation, but to sex-category constancy.  Sex-category constancy, or gender constancy, which refers to complete understanding of all levels of the construct and emphasizes that this understanding consists of a biologically based categorical distinction between males and females rather than knowledge of gender stereotypes and roles (Szkrybalo & Ruble, 1999).  This article is exploring the ideas of gender constancy and sex categorizing in small children.  Testing their understanding of gender and sex, and their explanations for the differences and similarities of gender and sex.  Szkrybalo & Ruble found from their sample of 195 children between the ages of 3 and 7 that children were able to understand gender easily but questions about sexuality confused them (e.g. a boy dressed up in girls clothes, is he still a boy?).  The children were easily influenced by stereotypes and the older they got the more likely they were to express the stereotypical answers rather than what they really thought.

 I chose this article rather than one, which specifically relates to a psychological argument, because articles that have been presented earlier to you support the psychological argument influencing the already present biological factors and effects on sexual orientation.  This article presents an argument about the perception children have about themselves and others, and human sexuality.
 

 Sexual Orientation and the popularity of it as a topic for reasonable and plausible solutions, has seen many possible solutions.  Through this paper, I have developed a reasonable thesis, that sexual orientation is related to specific biological factors and the only psychological influences related to sexual orientation, are those that influence the development of ones own sexual orientation.  Psychological social factors can help a person stay true to ones self and be themselves, whether it means being heterosexual or homosexual.  The biological factors that control homosexuality, specifically are, hormones, genetics, and brain structure.  The hormone levels of a mother can affect a child during gestation, causing structural differences in the brain.  Genetically, as a mother continues to have children, the amount of hormones that she will pass off to her children, lowers, causing male children to present reasons for his homosexuality.  The brain structure, is probably most needing explanation, because along with how it affects the spinal cord, this is where most of the differences are found between men and women who are homosexual, rather than heterosexual.  From female typical brain structure, to unexplained anomalies this is where the researchers are investing there time, trying to understand the brain and why these structural differences occur and how significant they are in association with homosexuality.

 Sexual Orientation, has always been of discussion, in the Western world, heterosexuality was attributable to what God had ordained as natural and good, and all deviations from it were seen as the work of the devil or a sinful person’s freely choosing to be evil (Ellis & Ames, 1987).  I chose this statement, because it still explains the view of a lot of the general public:  in my opinion, people just want explanations as to why some people are homosexual and others are not heterosexual.  We live in a world, where an explanation, must be found for everything, homosexuality, is part of this imaginary list.  I think that from the research that has been presented, there are valid points and enough research so far, to conclude that biological factors, during gestation, are the cause for homosexuality or heterosexuality.  There is no reason to believe, in my opinion, from the research that is available, to think that homosexuality, or heterosexuality is a personal choice.  Psychology could have some influence on human sexuality, but only influencing the already present biological difference.

 The future of homosexuality is now, and researchers are currently trying to explain further the differences of human make up, in homosexuals to heterosexuals.  More research in the near future will show a more specific connection to the points of interest in this article and hopefully more specific definitions on sexual orientation and genetic make up; research on the gestation period, with hormones and pharmacological drugs is being conducted and being compared to past research to distinguish between assumptions and reality.

 Homosexuality is not a lifestyle and it is not a personal choice, I think that it is obvious, that the previous biological factors have complete control over human’s feelings, toward the opposite and the same sex.
 
 

Bailey, J.M., Dunne, M.P., & Marin, N.G. (2000).  Genetic and environmental influences on sexual orientation and its correlates in an Australian twin sample.  Journal of Personality and Social Psychology, 78, (3), 524-536.

Bohan, J.S. (1996) Psychology and Sexual Orientation.  New York.

Breedlove, M.S.  (1994).  Sexual differentiation of the human nervous system.  Annual Reviow of Psychology, 45, 389-418.

Collaer, M.L., Hines, M.  (1995).  Human behavioural sex differences:  a role for gonadal hormones during early development.    Psychological Bulletin, 118, (1), 55-107.

Ellis, L. Ames, A.M. (1987).  Neurohormonal functioning and sexual orientation:  a theory of homosexuality-heterosexuality.  Psychological Bulletin, 101 (2), 233-258.

Gangestad, S.W., Bailey, M.J., & Martin, N.G. (2000).  Taxometric analyses of sexual orientation and gender identity.  Journal of Personality and Social Psychology, 78 (6) 1109-1121.

Kinsey, A.C., Pomeroy, W.B., & Martin, C.E. (1948).  Seuxal Behavior –in the human male.  Philadelphia:  W B Saunders.
Lalumiere, M.L., Blanchard, R. & Zucker, K.J. (2000).  Sexual orientation and handedness in men and women: a meta-analysis.  Psychological Bulletin, 126, (4), 575-592.

Szkrybalo, J., & Ruble, D.N. (1999).  “God made me a girl”:  sex-category constancy judgments and explanations revisitied.  Developmental Psychology, 35, (2), 392-402.

Veniegas, R.C., Conley, T.D. (2000).  Biological research on women’s sexual orientations:  evaluating the scientific evidence.  Journal of Social Issues, 56, (2), 267-282.