Comments on: Genetic effects of gender atypical behavior and sexual orientation: A study of Finnish twins

By: William

William — Wed, 03 Jun 2009 14:52:52 +0000

Identical twins share the same genes while fraternal twins do not.

Sorry if I’m throwing a spanner in the works, but has it not now been established that identical twins don’t, as was previously and more or less universally assumed, have absolutely identical genes?
http://www.sciencedaily.com/releases/2008/02/080215121214.htm

By: Ann

Ann — Fri, 22 May 2009 15:16:37 +0000

B.T. Carolus,
Very funny!

By: Drowssap

Drowssap — Fri, 22 May 2009 13:48:42 +0000

B.T.Carolus
HAHAHA! I love that comic.
You are right and I do understand that studies need to be repeated. But at this point I think everyone gets it. SSA is part genetic and part environment.
This puts it in the same category as virtually every other phenomenon that mankind has discovered.

By: B.T.Carolus

B.T.Carolus — Fri, 22 May 2009 05:11:58 +0000

Drowssap:
Technically, the scientific method demands repetition of the experiment in order to confirm results. Although I do agree with you that sometimes this becomes overkill. And there are pieces of this particular study that I just don’t find convincing (and I don’t just mean the idea that 3,600 Finnish twins can/should be generalized to the world’s population).
At risk of becoming the comic depositor:
http://xkcd.com/242/

By: Drowssap

Drowssap — Thu, 21 May 2009 14:44:41 +0000

This is the part I don't understand. We know from a dozen other studies that SSA is part genetic and part environment. So if we already know the answer why do scientists keep running the same study over and over again? Does it really matter if SSA is 2% heritable or 22% heritable or 42% heritable? Does the difference mean anything? What if a future study finds that SSA is 0% or 100% heritable? Scientists will dismiss that research because it doesn't match the other studies. The entire exercise seems like it's geared to find the same answer over and over again. In any case Ulcers and many other non-genetic phenomenon show "heritability". Here is a study on genetics and peptic ulcers. In case you didn't know peptic ulcers are caused by bacteria and yes human genes also play an important role. Which phenomenon don't have a genetic and environmental component? I can't think of many. It's as if scientists ran a study each morning to determine if the sun was going to come up.

By: carole

carole — Thu, 21 May 2009 04:30:46 +0000

Thanks Warren.

By: Warren

Warren — Thu, 21 May 2009 04:10:25 +0000

In response to several questions above, this passage from the study might help:

Heritability is not a fixed parameter, but may change during life. Further, the heritability estimates obtained from twin studies are population measures (i.e., explain the reasons for variation at a group-level) and cannot be applied to the individual (Plomin et al., 2001). Also, because heritability is population-specific, it is probably not surprising that different studies, based on different populations, have yielded diverse heritability estimates. One limitation of the study is the generalizability of findings. However, as more researchers replicate studies and findings, results become more generalizable.

For some genetics may be quite relevant, for others not so much. This is a global measure of why variation occurs between groups and cannot be applied to individuals. Probably no gay gene, although one cannot tell from this study since no DNA work was done. The authors simply compared the concordances among the various twin types (MZ, DZ) on sexual attractions and GAB.
While this is discussed often in these circles, I believe the nonshared environment can include different experiences in the womb (chorions). Thus hormones and the like are considered environment and not genetics.
Sanders from Chicago will have more on the specific genetic contributions when his team reports, probably not until later this year.

By: carole

carole — Thu, 21 May 2009 02:17:47 +0000

Whoops, that first paragraph above was supposed to be blockquoted–they are Timothy’s words in answer to one of my questions. Sorry.

By: carole

carole — Thu, 21 May 2009 02:16:45 +0000

I’m not speaking to this study specifically, but researchers often compare identical twins to fraternal twins to determine the extent to which something is genetic. Identical twins share the same genes while fraternal twins do not.
Thanks. Yes, I am familiar with the practice of giving concordance figures for a whole assortment of subjects under research , and I understand that it’s very helpful for researchers to compare/contrast the concordance figures using fraternal and identical twins.
However, in reading over the last couple of years about things like panic/anxiety attacks, depression, etc (which tend to run in families and thus have often been termed “genetic, ” which may or may not be true), I note that some researchers have been trying to distinguish what might be “genetic” (in the Mendelian sense) from what they feel might be more accurately termed “biological.” While they agree, of course, that at the base of everything lies our genetics, they disagree on whether something should be termed “genetic” if it requires a non-genetic trigger (biological reaction) to cause it to be expressed.
For example, I know there is some heritability to migraine headaches. However, w/out the trigger (for some it appears to be reaction to a very specific food ingredient while for others the trigger might be the more nebulous trigger of “stress”), the migraine doesn’t occur.

By: Timothy Kincaid

Timothy Kincaid — Thu, 21 May 2009 01:44:10 +0000

carole,
I’m not speaking to this study specifically, but researchers often compare identical twins to fraternal twins to determine the extent to which something is genetic. Identical twins share the same genes while fraternal twins do not.
Thus when you see something with such a huge variance (25% v. 50%) you can pretty much know that genes come into play.
However, because there was not 100% allignment in genetic twins, then genes aren’t 100% of the answer for 100% of the situations.