Monday, December 15, 2014

ANS -- Twins With Different Sexual Orientations: How Could it Happen?

Here's a short article responding to an anti-gay billboard purporting to say that gayness can't be genetic because TWINS!!!!!  Note that the "twins" in the billboard picture are really two pictures of the same guy.  Besides, the rate of two twins being both gay is much higher than two non-twin siblings.  What the article doesn't explicitly say, though it does say that twins may not be exactly genetically identical, is that not being exactly identical may be what makes twins instead of one fetus. 
I think the right wing sees gayness as an issue slipping away from them -- and this is evidence of increasing desperation in trying to hold on to it.  Plus, they lie so easily, it's appalling. 
Find it here:  

Twins With Different Sexual Orientations: How Could it Happen?

Twins With Different Sexual Orientations: How Could it Happen?  

An ex-gay group is making headlines across the United States after erecting a billboard in Richmond, Virginia, proclaiming that twin studies prove no one is "born gay."

The billboard, paid for by the group Parents and Friends of Ex-Gays and Gays (PFOX), features (what we're meant to assume are) identical twins, one labeled gay and the other labeled straight.

As the PFOX website aping its press coverage tells us, the billboard is based on the notion that (emphasis theirs):

Identical twins have the same genes or DNA. They are nurtured in equal prenatal conditions. If homosexuality is caused by genetics or prenatal conditions and one twin is gay, the co-twin should also be gay … because identical twins are always genetically identical, homosexuality cannot be genetically dictated. No-one is born gay.

To understand why this isn't convincing, we have to ask the question: how can twins have different sexual orientations, or in fact any other differences?

Well it's important to know right from the outset that recent scientific studies have shown that identical twins may not actually have exactly the same genetic code due to what are known as copy number variants. This is where in certain parts of the genome the usual two-copy rule is thrown out and a person may have anywhere between zero to in excess of 14 copies of a gene. This process isn't faithful and may differ between twins despite splitting from the same egg.

I raise this not to suggest this is the reason twins may have different sexualities, as there's no specific evidence to suggest this, but rather as an example of how identical twins can have significant differences at the genetic level despite being classed as "identical"–and why PFOX's line of argument falls flat from the very start.

Next, PFOX makes a massive leap of logic: it asserts that twins are exposed to exactly the same conditions in the womb. That's not necessarily true.

For instance, we have reasonably consistent research to suggest that the more older brothers a man has, the more likely that he is to be gay. Researchers believe this is the result of the youngest sibling being exposed to a slightly different hormone profile. We're not exactly sure what that might be, but one theory is that after carrying a number of male children, the mother begins to produce antibodies to certain "male" proteins. These antibodies would then be delivered to the fetus through the placenta and may result in different genes being switched on or off during the pregnancy, and thereby giving different sexual characteristics.

While obviously that doesn't neatly translate for identical twins, they can still be born with significant differences too. For instance, and to take a very obvious example, one twin may be born heavier than the other, and that difference may only grow over time as that heavier twin becomes a stockier adult than his or her sibling. How does that happen? Well, it can be the result of one twin getting a better connection to the mother's placenta than their sibling. In turn, this could even lead to different hormone exposures which again could affect how one sibling develops in a different way to the other.

This is due to what are known as potential epigenetic factors, that is to say environmental factors both inside the womb and during infancy that can affect what characteristics we inherit and what are active in us.

Don't misunderstand this use of "environmental," though. To those unfamiliar with this topic, "environmental" might be thought to refer to just things like how we are taught as we grow up, for instance. This, certainly, is the way that PFOX wants us to think about the "nurture" portion of the " nature v. nurture" argument, but it isn't usually what scientists mean in this context.

Researchers have long believed that something as complex as sexuality isn't just the result of our DNA, but rather that it is a mix of different factors like different genes being switched on or off at various stages of early development coupled with things like the womb environment, our formative diets, our early exposure to stress/pleasant conditions, and more.

There are many more environmental factors but these are the kinds of things that we are often talking about when we discuss the formation of sexuality, ones that are completely out of our control because they happen so subtly and so early on in life that we couldn't possibly make any kind of choice.

As you can see, PFOX's insistence that identical twins with different sexualities disproves the idea that people are born gay simply isn't true, and it misunderstands what is a very complex issue.

The reason that PFOX took out this billboard though is a direct response to a Northwestern University Study released in 1991 that found 52 percent of identical twin brothers of gay men also were gay. This sharply contrasts to just a 22 percent rate among fraternal twins, and an 11 percent rate between genetically unrelated brothers (i.e. siblings who are not the product of one egg splitting or sharing a womb). This suggested a strong genetic relationship for homosexuality that excited research in the field.

That PFOX would bother to return to that study after all this time represents how desperate they are to attack what they believe are the underpinnings of modern-day research into homosexuality. This just isn't true, though. While that study was crucial at the time, we have much more recent findings that have added depth and nuance, including a study released in the past few months that tracked homosexuality in men to two chromosome regions, which together with other evidence suggests our genes really may provide the basis for same gender attraction in men which may in turn combine with other contributing factors to "switch on" homosexuality.

PFOX has created a logical fallacy where it has supposed something must be false simply because it doesn't appear to be aware of (or is willing to ignore) the wider research on this topic. Unfortunately, because general knowledge of the research behind sexuality isn't particularly high, their line of argument might sound convincing to some ­ but we shouldn't be fooled.

It's also worth mentioning, however, that there is a significant gap in our understanding of the environmental factors that shape us and there are a number of ongoing studies on twins that are attempting to track how different environments during our formative years changes us, and indeed may shape our sexuality.

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