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Biological perspective on Sexual Orientation - "nature or nurture" approaches


McGregor10 4 / 20  
Dec 12, 2009   #1
Many perspectives on the nature of sexual orientation exist, each one asserting its point of view as vehemently as the next. Contemporary explanatory models of sexuality have been based more on cultural and religious norms and social stereotypes than on actual objective, scientific facts. Over the last 20 years or so, however, a growing body of research on the biology of sexual orientation has been accumulating. Researchers have explored the relationships between sexual orientation and factors such as hormones, prenatal stress, cerebral asymmetry, neuroanatomy, otoacoustic emissions, anthropometrics, genetics, fraternal birth order, and developmental instability (Mustanski, Chivers, & Bailey, 2002). Although results have been mixed, a number of interesting findings have emerged.

Research has provided evidence that prenatal factors may be involved in sexual orientation. The neurohormonal theory attempts to explain sexual orientation in terms of prenatal testosterone levels which are involved in differentiating physiological, neural, and anatomical structures of both sexes. Swaab and Hofman (1990) found clear differences in the superchiasmatic nucleus (SCN) of the hypothalamus between homosexual and heterosexual men (as cited in Alexander, 2000). Adam et al. (2007) compared neural activation to preferred sexual stimuli and nonpreferred sexual stimuli in heterosexual and homosexual men and discovered that within the amygdala the latter had greater activity for preferred sexual stimuli than the former, suggesting the possibility that male homosexual brains may be characterized by atypical patterns of neural activity. Whether this result was a cause or consequence of the participant's homosexuality, however, is debatable. Other research has postulated that developmental instability in utero may be related to homosexuality. For example, Miller, Hoffmann, and Mustanksi (2008) found that overall index of bodily fluctuating asymmetry (FA) was positively correlated with homosexuality in men. Research by Martin, Puts, & Breedlove (2008), however, failed to confirm the results of the latter. In fact, the researchers reported that FA was lower in homosexual men than heterosexual men.

The most favourable finding to have emerged from the neurohormonal research is the fraternal birth order effect, which was first documented by Blanchard and Bogaert (1996) (as cited in Bogaert, 2006). The researchers found that there was a significant correlation between homosexuality in males and the number of biological older brothers in a Canadian sample. Since then several other studies have confirmed these results in samples from across the world. For example, Blanchard and Lippa (2007) reported that results from an online BBC survey involving 159,779 respondents revealed that older brothers increased the odds of homosexuality in men. Another study (Rahman, Clarke, & Morera, 2009) found evidence of the fraternal birth order effect in a sample of 100 heterosexual and 100 homosexual men. It appears that the fraternal birth order effect has no bearing on female sexuality (Bogaert, 1997). Bogaert (2006) demonstrated that only the number of biological older brothers, and not any other siblings, such as non-biological brothers, significantly predicted homosexuality in men. Moreover, rearing time with older siblings, whether biological or nonbiological, had no effect on sexual orientation, suggesting a prenatal origin to the fraternal birth order effect. Recent studies have indicated that the fraternal birth order effect is evident in right-handed males but not in non-right-handed males (Blanchard & Lippa, 2007; Blanchard, 2008).

The maternal immune system hypothesis was developed to explain these results and posits that the fraternal birth order effect reflects progressive immunization of some mothers to male-antigens with each successive male foetus (Bogaert, 2002). With respect to the interaction of handedness and the fraternal birth order effect, two explanations have been proposed (Blanchard, 2008): It could be that non-right handed foetuses are insensitive to the presence of maternal male-antigens or that mothers of non-right handed foetuses do not produce anti-male antibodies. Although many researchers agree that this explanation, on the surface, seems plausible, it is lacking concrete, empirical support (James, 2004).

Research has also attempted to indentify genetic factors that influence sexual orientation. Concordance rates of homosexuality tend to be higher in monozygotic twins (who share 100% of the same genes) than dizygotic twins (who share 50% of the same genes) (Kendler at al., 2000; Kirk et al., 2000). Ellis et al. (2008) looked at blood type and Rh factor in both heterosexual and homosexual participants and discovered that male and female homosexuals were significantly more likely to be Rh negative than heterosexuals. The researchers also found that female homosexuals exhibited higher incidences of blood A type than male homosexuals, compared to heterosexual male and females who exhibited identical frequencies of the blood type A. Thus, chromosomes 9 and 1, which are responsible for blood type and Rh factor, may be involved in sexual orientation.

The extant research on sexual orientation has not gone without its fair share of criticism. Because the prevalence of homosexuals is relatively low within a given population, random sampling is not a viable option in experiments. Instead, researchers often have to place ads in homosexual magazines, recruit participants from recognized gay areas, or rely on word of mouth, all of which increase the chances of sampling biases. Another problem is researchers tendency to define sexuality in "either or" terms; that is, participants are classified as either gay or straight. Sexual orientation, like gender, is not a fixated entity for which criteria can easily be defined. For example, it is not uncommon for male prisoners to have sex with other males yet still consider themselves "straight". Also, although some individuals do not engage in sexual relations with the same sex, they do frequently fantasize about it. Thus, it is more fruitful for researchers to place sexual orientation along a continuum, with homosexuality and heterosexuality at the extreme ends and bisexuality in the middle. Furthermore, Alexander (2000) comments that research on human sexuality should employ the "double confirmation method", whereby sexual dimorphism is established before sexual orientation differences. In other words, a firm understanding of the biological differences between the sexes is necessary before researchers can even consider the possible prenatal factors involved in sexual orientation. It's also been noted that studies exploring the etiology of female homosexuality are lacking (Mustanski, Chivers, & Bailey, 2002). The most profound limitation of the literature on sexual orientation is its predominant usage of correlational studies, which make casual attributions next to impossible.

Despite the considerable amount of research that has been generated over the last two decades on the biology of sexual orientation, psychology's understanding of the topic is far from complete. This is not surprising, though, when one takes into consideration the complexity of the issue at hand and the fact that in the not so distant past homosexuality was classified in the DSM-III as a mental disorder. Researchers studying human sexuality are faced with two daunting tasks. Not only do they have to find consistent, biological differences between people of different sexual orientations, but they have to clearly demonstrate that these biological differences (i.e., number of biological older brothers, blood type), and not other confounding variables (i.e., social upbringing, sexual experiences), account for sexual orientation. For example, neurological differences between homosexuals and heterosexuals could be caused by prenatal factors, but it's also just as likely that postnatal sexual experiences may have caused the differences in brain structures (Alexander, 2000).

Although it's not likely that future research will be able to identify the exact etiological pathway from which sexual preferences in human beings develops, the articles summarized above should make it clear that biology influences a person's sexual orientation to some extent. Future research should take a scientific interactionist approach to studying sexual orientation, which acknowledges the importance of both biology and the environment. Such an approach is likely to produce more cogent findings than the current "nature or nurture" approaches.
Jeannie 10 / 214  
Dec 13, 2009   #2
Hi, Justin!

This paper is really interesting; I had no idea these kinds of studies had advanced this far. Good stuff.
Your paragraphs flow smoothly, and the vast majority of your sentences were very clear. All in all, a good read! I am not fluent in the topic, but I did find a couple of things that I wanted to bring to your attention:

Adam et al. (2007) compared neural activation to preferred sexual stimuli and non- preferred sexual stimuli in heterosexual and homosexual men and discovered that within the amygdala the latter had greater activity for preferred sexual stimuli than the former, suggesting the possibility that male homosexual brains may be characterized by atypical patterns of neural activity.

This sentence is so long, I lost track of what's going on! :) Also, this confused me, "...latter had greater activity for preferred sexual stimuli than the former,..."

an online BBC survey involving 159,779 respondents revealed that older brothers increased the odds of homosexuality in men.

Revealed that having older brothers...

It appears that the fraternal birth order effect has no bearing on female sexuality (Bogaert, 1997). Bogaert (2006) demonstrated that only the number of biological older brothers, and not any other siblings, such as non-biological brothers, significantly predicted homosexuality in men. Moreover, rearing time with older siblings, whether biological or non- biological, had no effect on sexual orientation, suggesting a prenatal origin to the fraternal birth order effect.

This is fascinating!

non-right-handed males

...Left-handed males?

foetus

Is this a typo, or is it just how y'all spell fetus? It seems I have seen it spelled that way...Oh, ok, you used it several more times, so it must be the acceptable spelling. Why is it spelled different here, I wonder? anyway...

Sexual orientation, like gender, is not a fixatedfixed entity for which criteria can easily be defined.

Furthermore, Alexander (2000) comments that research on human sexuality should employ the "double confirmation method", whereby sexual dimorphism is established before sexual orientation differences. In other words, a firm understanding of the biological differences between the sexes is necessary before researchers can even consider the possible prenatal factors involved in sexual orientation.

True! I always wondered how they could even begin to understand or study the vagaries of homosexuality vs. bisexuality (and everything in between...) when we don't really have a significant understanding of human sexuality to begin with. Interesting.

Future research should take a scientific interactionist approach to studying sexual orientation, which acknowledges the importance of both biology and the environment. Such an approach is likely to produce more cogent findings than the current "nature or nurture" approaches.

This is a great final statement.

If you change nothing, it is still very well written!
OP McGregor10 4 / 20  
Dec 13, 2009   #3
Once again, thankyou very much for your constructive feeback. I have another essay I am currently working on with which I am having a little trouble. I will try and post it ASAP as it is due soon. I also have some other essays on bullying and violent video games which I'm sure could benefit from your feedback :) Perhaps I'll post them later.

Thanks again!
Jeannie 10 / 214  
Dec 13, 2009   #4
I look forward to reading it! I will keep my eyes peeled.

Jeannie
EF_Kevin 8 / 13,321 129  
Dec 14, 2009   #5
Although results have been mixed, a number of interesting findings have emerged.

Right here, you sort of leave the reader hanging. You should list those interesting findings, maybe even in the form of a bulleted list. Give some good, solid support for the rest of the essay by reinforcing this intro.

That's what I think...

:-)
OP McGregor10 4 / 20  
Dec 14, 2009   #6
I see what you mean, but I follow that statement by exploring the findings in detail
Jeannie 10 / 214  
Dec 14, 2009   #7
Right here, you sort of leave the reader hanging.

The whole rest of the paper is spent telling about the research findings; it is an excellent segue in my opinion...P.S. No bullets allowed in APA. :)

Oops, I just read ahead to your post, Justin, and I see that you already responded...well, at least we are a united front! teehee!
OP McGregor10 4 / 20  
Dec 15, 2009   #8
Great minds think alike :P
EF_Kevin 8 / 13,321 129  
Dec 16, 2009   #9
Yes, that sure is true. The rest of the essay does expound the new advances. What I am trying to say something about is the impression the reader has at the end of the 1st para. Oftentimes, the thesis statement is given at the end of the first para, and if that were the case here, the thesis for this essay would be: Although results have been mixed, a number of interesting findings have emerged. That is a little too general, but in this kind of essay it would be excellent to use a bulleted list to prepare the reader for what is to come. That bulleted list can serve as part of the thesis statement. However, it is just th thought that came to mind for me. Like Jeanie said, this essay is already looking very good!
Jeannie 10 / 214  
Dec 16, 2009   #10
That is a little too general, but in this kind of essay it would be excellent to use a bulleted list

Ah Ha! I understand what Kevin is saying now! You could expand the last sentence with a listing of general areas of study that support your main idea (no bullets, please, don't make me get out the ruler...)

Kevin, are you saying to write something like (making it up again...):

...interesting findings have emerged through the study of prenatal hormonal influences, chocolate pudding intake, birth order, and even hand-dominance.

Hmm, that would be better!
OP McGregor10 4 / 20  
Dec 16, 2009   #11
Thanks for the input guys! I think I will expand the last sentence in the introductory paragraph.
EF_Kevin 8 / 13,321 129  
Dec 19, 2009   #12
Well... like I said, it is great already. It made me think, though, of the different types of thesis sentences. Sometimes the thesis takes the form of a question. Sometimes it consists of a single, succinct sentence (my favorite kind, because it identifies the soul of the essay; sometimes it consists of a few sentences that list the points to be covered in the essay, and that is what I had in mind here.

However, don't let all this discussion create the illusion that it is necessary to expand the thesis to list all points covered. It is just what came to mind for me. I had to give SOME kind of suggestion, ha ha.

So, yes Jeannie, what you wrote is what I meant. But what do you have against bulleted lists? Bulleted lists are people too!
Jeannie 10 / 214  
Dec 19, 2009   #13
Bulleted lists are people too!

:D

I dunno...It looks like they're hollering at me...:)

Blue skies!
EF_Kevin 8 / 13,321 129  
Dec 21, 2009   #14
Well...

*they are not actual bullets
*they cannot holler, ha ha, and
*they are harmless in every way.

But then again, some eloquence is sacrificed for clarity when using such a list. So... I guess you are right.


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