Thread: Homosexuality in Monozygotic (Identical/Siamese) Twins

I know that cases where identical twins are of different sexualities throws a huge wrench in the nature vs. nurture debate on homosexuality, and so I would like to ask something.

Sometimes people say "people are conditioned to be gay by society," which is quickly debunked because of society tending to discriminate and shun homosexuals. However, is there any evidence to support, or refute, the hypothesis that monozygotic siblings with at least one gay sibling are all gay, and that the straight ones are conditioned by society to be straight?

Logical, science based thoughts and evidence only, please. I'm not asking for peoples' opinion on the morality of homosexuality.

is there any evidence to support, or refute, the hypothesis that monozygotic siblings with at least one gay sibling are all gay, and that the straight ones are conditioned by society to be straight?

Biology is not destiny. So the idea that genetically identical twins must be exactly the same in anything, let alone everything, falls by the wayside. Biology just loads the dice to make some things more likely than others.

However, twin studies show that where one identical twin is gay, the other twin is more than twice as likely to be gay than if they were fraternal twins. (And if you, or any reader is unsure what this means, the reason for a twin study is that it controls for social conditioning.)

There are heaps and heaps of studies in this area. Go to google scholar and you'll find more than you ever needed to know.

Originally Posted by EddyBearr

I know that cases where identical twins are of different sexualities throws a huge wrench in the nature vs. nurture debate on homosexuality, and so I would like to ask something.

Sometimes people say "people are conditioned to be gay by society," which is quickly debunked because of society tending to discriminate and shun homosexuals. However, is there any evidence to support, or refute, the hypothesis that monozygotic siblings with at least one gay sibling are all gay, and that the straight ones are conditioned by society to be straight?

Logical, science based thoughts and evidence only, please. I'm not asking for peoples' opinion on the morality of homosexuality.

I think maybe gay and bi-sexual are being confused in the topic of, whether or not people can be made to turn gay.

From things I have heard scientists say, and my own thoughts. I would say that if you are 100% strait, society can not make you gay. And if you are 100% gay, society can not make you strait.



But perhaps (very lightly) bi-sexual people, could be made gay by society and environment. I heard about this college study, were men that hated gay men, were hooked up to machines that monitored their sexual excitement. The scientists came to the result, that (many/most) of the men who hated gay people, were actually gay or bisexual themselves. One of the scientists said he felt like telling the test subjects "do you know that you are gay."

My point is maybe you can be bisexual, and not even realize it. The above tests say this to me. And perhaps men like those, who were tested that hate gay people. Perhaps being in jail, or society could make them turn bisexual (but they already were, but they just maybe did not know it.)


I did a bit of online research just now, to find out what percentage of people are gay or bi-sexual. And I came to this conclusion, I think many people lie on these scientific survey tests. And also different countries report different results, in what % of their population is gay. But I personally think that in countries, that accept people being gay. In these countries more people will admit to being gay.



One more thing I want to note. I saw this documentary about a group of (gorillas or chimps?). Some event happened that made the group split up. All the females left the group, and only the males remained in that group. Then (most) of the group of male primates, began do sexual acts with each other. The % of male primates in that group that turned gay, was much, much higher than any human % I have ever heard of.

Then (most) of the group of male primates, began do sexual acts with each other

But that's just a bit like what happens in human prisons or other extreme circumstances. These people don't turn gay. They do what they can for sexual gratification if the need is strong enough.

And there's an unspoken aspect to this. There's more to sex than just sex. We're all capable of sexual activities that we would prefer not to engage in if we were free to choose both the partner and the activity. Quite often, our options and our preferences are severely limited. Less often they're ignored or violated.

In chimps and many humans, sex is used as a means of displaying and enforcing dominance hierarchies. Or with bonobos and many humans, sex is used as a means of comfort and maintaining cooperative relationships. Some humans will switch quite readily from one mode to the other depending on circumstance. That might mean accepting or encouraging a same sex partner which we wouldn't normally do.

Sexual orientation has several influences. One is genes. One is epigenetic influences. One is intra-uterine chemical influences. One is societal influences.

Whatever are the influences, the person involved is what he/she is. Anyone who passes judgment on someone because of his/her sexual orientation is judging him/herself. Being straight or gay, either way, is not an indictment. Being so bloody bigoted as to pass sentence on someone due to their sexual orientation is.

Is this a science thread or a morality lesson?

Is this a science thread or a morality lesson?

At the moment it's a bit of both. Depends who says what which way it will go.

To get back to the OP. The fact that not every identical twin will be gay if their twin is gay does not mean that there is no genetic basis for homosexuality. The data shows that they are much more likely to be gay than fraternal twins or other siblings.

Part of what I meant by "conditioned to be straight," is just that: simply conditioned to act that way, while not necessarily being completely straight, or even actually straight, such as the homophobes who turned out to be gay.

I guess a better question is at this point, how likely do you think it is, and what percentage (guesstimate) of, the monozygotic twins of homosexuals are not self-realized in their own sexuality, for whatever reason? I'd assume that a great deal of people who's twin is gay would also be gay (as they obviously have a higher chance,) but I wonder if a large percentage of them aren't gay (or at least, don't realize it,) or aren't very gay, because of our culture.

Originally Posted by EddyBearr

the homophobes who turned out to be gay.

Which homophobes turned out to be gay? (I kind of suspect this is an urban legend.)

Originally Posted by Harold14370

Originally Posted by EddyBearr

the homophobes who turned out to be gay.

Which homophobes turned out to be gay? (I kind of suspect this is an urban legend.)

Worded that poorly. Assuming this "urban legend," and the study Chad posted about, are true, then those kinds of people. I don't know of any specific cases as I've never really looked into it.

Which homophobes turned out to be gay? (I kind of suspect this is an urban legend.)

I think this might be a pop-psychology version of Freud's notion of "latent" homosexuality. Latent homosexuality - Wikipedia, the free encyclopedia

It might have had some, repeat some, validity in Freud's time. Just like most of the rest of Freud, there's no universal or eternal truth here. He was too much a prisoner of his personal and cultural limitations.

Originally Posted by adelady

I think this might be a pop-psychology version of Freud's notion of "latent" homosexuality.

It is also a popular idea with some homosexuals. When I used to hang out with a gay crowd (don't ask) saying you were not homosexual was taken as absolute proof that you were. And, of course, saying you were meant you probably were. About the only way to establish that you might be heterosexual was, "meh, whatever".

its not actually an urban legend. Here is the actual study where the experiment was conducted.
Is homophobia associated with homosexual ar... [J Abnorm Psychol. 1996] - PubMed - NCBI