Identical twins and homosexuality?

I honestly don't think orientation is genetic, or at least solely genetic. However, I also don't think you can raise someone to be one or another orientation, so it doesn't really make a difference. Even kids raised by gay parents don't show a higher rate of homosexuality, so the "it's a learned behavior" thing is bs.
I din't think you should distance yourself from your sister. It might become a problem eventually, in which case do what you have to, but until then, there's no reason to make things bad between you two.

 

I'm a twin and he's straight. Don't distance yourself from your sister please. She should be the one that you count on for anything :/.

 

I'm a twin.. However my sister and I are fraternal twins, not identical and she is very much straight.. Married with a 2 and a half year old.

Don't distance yourself from her either.. I know the feeling though cause when my sister began dating her now husband.. I felt jealous he was basically taking her away from me cause we used to go to the movies, football games and stuff together and it all of sudden seemed she didn't have time for me anymore.. I think I finally confided in my mum who them spoke to my sister and she began including me in things and stuff.. So I know feeling.. Been there.. Done that.. Just don't push her away and don't distance yourself from her.

 

I mean, in a way it's true that's it's not strictly speaking all genetics. Epigenetics is what most people are thinking it is, which is about gene expression and how genes are turned on or off depending on certain things. For what it's worth, I have an identical twin who is straight. Certainly a big factor of a spouse would be that he'd have to get along with my twin to an extent. Ultimately, though I know what you mean about wanting to differentiate yourself, that won't be accomplished by distance from your twin necessarily. Just focus on yourself, you know? It can be like having a close sibling but a fair bit closer while looking very similar too. It's ultimately not that big of a deal once people get to know you.

 

Well concerning orientation... would it be possible if both would be bi, relying on circumstances... who you meet etc... one chooses a female partner and one a male partner ?

 

Biology and sexual orientation - Wikipedia, the free encyclopedia

This may be an interesting read for you. I learned in genetics that many traits (that are influenced by multiple variables) have been studied in identical twins (which have the same DNA but not necessarily the same environment, though environment is often similar), and many complex traits (which I believe would include homosexuality.... also things like psychological issues and risks of disease) have a particular percentage that is influenced by genetics (how often both twins have said trait) and the remaining percentage is assumed to be environmental. It's very interesting and identical twin studies give a lot of insight into heredity of complex traits and insight on the nature vs nurture debate.

Skimming the Wikipedia article, it appears that homosexual individuals are not actually "born" that way, but most likely have a slight predisposition that may increase the chances that their environment will turn them gay. Actually, taking another glance, it seems the numbers from different studies vary a lot. Either way, your father is right that it's not likely completely genetic. Regardless, like your genes, you're stuck with the past environment that may have influenced who you are.

And now for a rant about people who claim they "were born this way" and that makes being gay okay. Even if it's not genetic who cares? People should mind their own business.

 

I don't think this disproves that homosexuality is a hard-wired behaviour instead of a learned one.

I think you can compare this to fingerprints. Two twins don't have the same fingerprints and twins don't have to have the same sexuality.

Genes don't control everything a human will be. In the development of a genetic twin, the first difference can be epigenetics (molecules which determine which parts of DNA is active, which are not inherited like DNA). Then there will be environmental factors like hormones and things like that in the womb and when you grow up.

And then there's randomness. This plays a more crucial role than most people would think. Development isn't simply: you have gene A, which says that your arm is going to be 1 meter long. It's messy. You start with cells with different concentrations of signalling molecules on both ends and other genes interact with that to start growing different cells on those ends.

But slight differences in starting position can give massively different results. This is one of the many reasons why cloning can be so extremely difficult, genes alone aren't enough, they're only going to work if the situation of the embryo is right. And the one part of the body where you can easily see this effect are the fingerprints. (Another nice one are twin/cloned calico cats, where the placement of fur colours is totally random).

So even if your DNA is the same, your brains will be different. So this doesn't mean that sexuality is a learned behaviour, it's likely to be hard wired in the brain during development and is different because of those other factors than DNA. If sexuality was actually a learned behaviour, conversion therapy might work, but it simply doesn't.

 

There tends to be a weak correlation between twins, higher than it would be if there were no biological influence on sexuality. Also, I believe twins, even identical ones, can have different epigenetic markers, something that has been suggested may be responsible for sexuality.

 

Totally agreed with this, identical twins aren't always 100% identical, epigenetics and hormone exposure also play a known role, homosexuality isn't determined solely on genetics. Look at height, there are genetic factors to height but the environment (nutrition) can play a role in determining it as well. Sexuality also has genetic factors but isn't solely determined by them, hormonal exposure and epigenetics also play a role.

EDIT: here's an interesting article:
http://www.bionews.org.uk/page_160579.asp

 

I am an identical twin and from my experience I think it is unlikely that genes alone play a role in determining sexuality. My twin brother is straight (well, he has a girlfriend so if he wasn't that would be awkward, lol) and I can safely say that I am a little bit less straight... Ok maybe a lot less straight.

 

One major study I saw said 52%. That's not conclusive enough. At 2/3 and upward, I might have taken notice.

 

As others have mentioned, epigenetics is likely to play an important role in this. Just because the genetic starting material is the same it doesn't mean that all the genes are expressed at the same level, if at all. My twin and I are genetically identical, but there are some pretty obvious physical differences between us.

I'm not sure how I feel about the role of hormones in the womb, as it's a shared environment, so that wouldn't explain how one twin ends up straight and the other gay. Also, the environment that we grew up in as kids was the same, so I can't think of any environmental factors that could have caused this.

As far as the whole twin relationship goes, we tend to get on really well. We fought a lot as kids but we always had each others back. We were both pretty independent though and made sure that we were always in separate classes at school whenever possible. We also had completely different friend groups at school, although we hung out together in the same group outside of school.

You don't say how old you are, but I don't think there's anything wrong with distancing yourself from your twin a bit, especially if you're a teenager. The whole point is that you're trying to find your own identity and it can be frustrating when people refer to you as 'one of the twins' etc. It doesn't mean that you can't still have a close relationship with your sister, though.

 

I'm not a twin, but I do know a little about this. To make things short and simple:
The reason one is straight and the other is gay is because one absorbs more hormones than the other. Hormone exposure in the womb is pretty much what makes a baby gay or straight.

 

I think Austin and Aquilo made great points. Twin studies are some of the most useful material we have on this topic and show conclusively that sexual orientation is not purely genetic. Of course, it is possible that twins who have different sexualities diverge because of differential hormone exposure in the womb, and that's that; but it could go beyond that to post-natal experience. AdelOwl suggested that the environment he and his twin shared was identical, but perhaps in human terms no environment is identical for two people, even when they are raised in the same house? There will always be different experiences and different emotions, different encounters at home and at school?

I really feel for you when it comes to the emerging distance between you and your sister. It's tricky - I don't have much to add to the advice above, not having any experience of this sort of thing. The other thing going on is I guess your dad; I understand what it's like to have a parent mouth off about homosexuality, how queasy it can make you feel. Try not to let it get you down too much! (*hug*)

 

a researcher's wet dream

 

I've read about things like this before, and while I forget the exact rates, I'm pretty sure it's something along the lines of "if one identical twin is gay there is a 60% chance that the other one will be as well. A lot of being gay is linked to hormones in the womb and genetics, but it's not the only factor.

 

Well... assuming that the studies can be trusted, it does prove beyond reasonable doubt that sexuality is not decided wholly by pre-birth factors.

Statistics I've read are something along the lines of,

where one sibling is gay:

52% of the time their identical twin will also be
30% of the time their fraternal twin will be
20% of the time their non twin sibling will be
11% of the time their adopted sibling will be (same post-birth environment, completely different genes)

The numbers are around that, but I'm not sure their precise values. What I am sure of is that they are in that order. Again, assuming that the study can be trusted (interviewees being honest, and a large sample of people asked), this shows that both nature and nurture play a part.

 

No, identical twin studies don't prove that sexuality is not wholly determined by pre-birth factors, it proves that genes aren't the only factor. The other known factors (epigenetics, prenatal environment) are in fact pre birth factors. As far as I'm concerned, there's no credible finding of any post birth factors that cause homosexuality, at least not to a significant effect.

Another example that relates to this is the fact that identical twins have different fingerprints and sometimes different weights when born. Both of these characteristic differences occur because of the development in the prenatal environment, so again nature and nurture but the nurture has nothing to do with post natal environment.