| HappySqurriel said: No, the research (twin studies) demonstrates quite clearly that it is not (predominantly) a genetic trait ... What I was trying to demonstrate is that the proportion of people who identify as being "homosexual" or "bisexual" varies quite a bit across different cultures. I initially went looking for a study I saw earlier this year that demonstrated vast differences between the percentage of gay men in different ethnic groups across the United States but I couldn't find it; and, from what I remember, on a percentage basis the study demonstrated that homosexuality was more common among black males than white males even though the black community was far less supportive of homosexuality. |
First of all, I didn't quote your first post in this thread but that's fine, let's give it a go:
You are understanding of the whole thing is wrong, you can't say genes don't play a role even if more than 50% of the MZ twins aren't both gay. There are diseases (or traits) that are classified as single gene diseases (or traits) and there are others that are classified as multifactorial diseases (or traits).
To explain further, the inheritance of a Single abnormal gene alone guarantees the appearance of the disease in single genetic diseases. An Example of this is sickle cell disease. A wrong example of this would be homosexuality, because it clearly it isn't a single gene trait.
Multifactorial diseases, however, require the abnormal gene + environmental factor + lifestyle and a plethora of other precipitating factors = then you may get the disease. Examples of these are asthma, multiple sclerosis, vitiligo, depression, hypertension and other autoimmune diseases like rheumatoid arthritis etc. An example of a multifactorial trait is height or how tall someone is.
So when it the studies say that 20% of homosexuality is due to environmental and 60% due to "unique" environmental, it actually DOESN'T exclude the genetic role for any of them. It only excludes the possibility of homosexuality being due to ONLY and ONLY a genetic cause. Clearly it isn't. So these studies support what's already accepted by scientists and physicians that homosexuality is multifactorial.
Let's take asthma for an example, MZ twins concordance rate is around 40% (not sure what's the exact number but it's in the 40s), does that mean the 60% don't have the asthma gene? NO IT DOESN'T, since MZ twins share 100% of the genes. So it only means that the asthma gene alone doesn't guarantee the occurrence of the diseases, why? Because precipitating factors may not be strong enough to cause asthma, but what happens when the patient does get asthma? Do we switch the blame entirely to the environmental (or precipitating) factors and exclude the gene that predisposed the wholes mess in the first place? No, we don't, we simply say asthma is multifactorial. Same principles can be applied for homosexuality.
Now with that introduction in mind let's go back to the studies you linked, these types of studies were criticized a lot, SOME of the valid criticism was mentioned in the wikipedia page you linked, but I'll try to add some of the points that I remember and aren't mentioned in wikipedia:
First of all, if we assumed that homosexuality is multifactorial then we have to know the other factors besides gene that may cause someone to be homosexual, for example in asthma patients, the precipitating factors are identified, from fumes to dusts and pollens, in diabetic patients, it's diets with high carbohydrates and lack of physical activities (other stuff weird stuff like skin conditions!!!) so those precipitating factors were mentored throughout the studies.
But what about the precipitating factors of homosexuality? What are they? Orange juice? Nudity? Music? We can’t tell and we can’t assume that both siblings had the same precipitating factors even if they are twins. For example, if hormonal levels during puberty turned out to be a precipitating factor then the retrospective twin studies would be rendered moot, since hormonal levels weren’t mentored.
Second of all, HOMOSEXUALITY ISN'T BLACK AND WHITE. These studies DON'T use kinsey scale or any similar scale in identifying how homosexual a person is and how heterosexual the other sibling is. Therefore, the results are not always applicable.
Third point I want to mention and this one is specific to the studies you posted, some of the studies has environmental and unique environmental factors , and under “unique environmental” factors they included a collection of factors that included almost all factors from non-biologic to biologic prenatal factors under one big umbrella… which is… awkward. Because usually it's environmental vs biological (genetic is a biological factor) or environmental vs genetic. "Unique" environmental in this case included all the biological factors vs genetics and that skwed the %
Finally, there are recent studies out there that clearly states that calcium intake before the age of 30 doesn't prevent osteoporosis but physicians still advise women to drink milk and whatnot. Why? It’s because these studies aren't large enough and they weren't carried out on a "large enough" scale. Same goes for most the studies out there, scientists and physicians will continue to believe that homosexuality is multifactorial as long as there are no available studies with much less bias. The ones you mentioned by the way support the multifactorial theory more than anything really (as explained above). The size of the Published studies doesn’t reflect their importance.
Now for the other stats you posted later, I already pointed out how inaccurate they are, but I wouldn't be surprised in the future if race and ethnicity turn out to be precipitating factors for homosexuality. DM for example has "race" under the list of precipitating factors.
Purely environmental or not, that’s the pointless question. So far it's obvious that homosexuality is multifactorial, I don't see that changing, but who knows, maybe at some point it turns out to be purely environmental. The important point is that I still think the amount of resources we are wasting on something like this is stupid, let's move on from these pointless discussions and try to think of ways to help homosexuals in oppressed countries to get their basic rights and keep the focus of our medical resources on important stuff, like actual diseases that actually affect people's life quality.
