I was brought up short in a discussion the other day where I opined that sexual orientation was now thought to be hugely influenced by epi-genetic factors related to hormone levels in the womb at precise fetal growth intervals. I was challenged on this by a person saying that twin studies re this topic have too much variability between the twins to support this conclusion as determinative, and that non-genetic environmental factors were much larger than I believed in how sexual orientation manifested itself.
So… thus chastised I’m asking dopers what the latest science says about the manifestation of sexual orientation in 2016 so I can be up to speed.
The Council for Responsible Genetics as a short summary of the current understanding of genetic and environmental factors in determining sexual orientation, as well as the deficiencies in current methodology. It does not really address the question of the sociological component other than to note that studies look at self-identified homosexuals, and thus will underreport the actual number of people who are somewhere on a spectrum between strict heterosexuality and homosexuality. In truth, we could probably expect more people to identify as gay, bisexual, or some other label that recognizes the fluidity of sexual orientation if there were not such a negative view of homosexual behavior across such a wide segment of the population. However, based upon fraternal twin studies and the absence of a clear genetic cause, it seems that there is at least some reasonable cause to believe that neonatal influences play a part in later sexual development.
I know three sets of identical gay twins. No set came out at the same time. One male set came out at 14 and 22. The 14-year-old got set to a Christian-centered drug rehab to “go straight,” because there weren’t “straightening out” centers at the time. The other one, observing this, kept his feelings to himself, and dated girls. Once he had a college degree (paid for by his parents), he felt safe to peek out just a little.
The second was two women. One came out at 21. The other married at 23, and was totally clueless. She loved her husband. Later, when her children were teens, she “clicked,” and started dating women, when she was almost 40.
The last set I’m not sure about, but I know there was an age difference, so when I hear that one identical twin is gay and one isn’t, I think, “One just hasn’t come out yet,”
There really aren’t any definitive studies of genetic or sociological root cause, at least not in the sense that they definitively exclude or even substantially limit other influences. I’m not even sure how to address the question of epigenetic factors; even looking at fraternal twins (which still share genomes and for males in particular the Y chromosome which likely would have some influence on male sexuality) still has to consider childhood development and common sociological influences. And frankly, sexuality is really kind of a difficult factor to identify; Kinsey, et al put sexuality on a linear spectrum, but taking more than a cursory look into human sexuality and what people find attractive in a sexual partner shows that it really isn’t that simple. I think we have to acknwoledge that at least in the expression of sexuality, there is a large sociological component, but there are also clearly innate biological impulses, whether due to inherited genes, epigenetics during prenatal or neonatal development, or later influences on development from environment, diet, et cetera.
There is some evidence that the more older brothers a male has increases his likelihood of being gay, changes in fetal exposure to hormones like testosterone probably play a role.
It isn’t without contention though and I’m sure its not the only factor and obviously doesn’t explain all cases though.
Unrelated people will not, in general, share any factors. Adoptive siblings will have the same sociological and cultural influences, but different genetics and uterine environment. Half-siblings by the same father may or may not have the same sociological and cultural influences, depending on whether they were raised in the same household or not, and will have some genetic similarity, but will not have the same uterine environment. Full siblings will have more similar genetics and somewhat similar uterine environments, and may or may not have the same sociological and cultural influences depending on whether they were raised together. Fraternal twins will have the same genetic connection as regular siblings, but will have nearly identical uterine environments. Identical twins will have the same very high correlation of uterine environments as fraternal twins, but will also have a near-perfect match of genetics.
For any given one of the three factors you wish to study (genetics, uterine environment, or post-birth nurture), there is at least one pair of groups which differ only in that factor, and which you can compare. For instance, if identical twins have a higher correlation than fraternal twins, then there must be some genetic factor, and if fraternal twins have a higher correlation than non-twin siblings, then there must be some uterine factor. And that’s without even getting into rare cases like identical twins separated at birth, though of course if you do find any of those rare cases, that data helps, too.
Homosexuality is a 19th-century Victorian concept which should be put away ASAP.
Human sexuality OTH is a fascinating topic and one which merits much more study then it has gotten and (I wish) sans the ideological undertones. It probably has some genetic causes, but probably not totally or even mostly.
^These. That’s what the science shows. You can go cherry pick your science and find inconclusive results about your favorite theory, or look at everything and see the conclusion is “We don’t know”.
I suspect there is a good PhD or three is just analysing the range of opinions that are driven by political and religious agendas. This is a really sad problem, as it makes science very hard to do.
Everyone seems to have an agenda. Some seem to keep it better hidden than others.
My anecdote - the only identical twins I know, one is gay, one is not. Guess which one was regional figure skating champion in his early teens, and which one rides a motorcycle, is happily married with 4 children and is a pilot? And the twins had no other siblings.
The only other gay person I know of in my family came out after several decades, he has two sons, neither of whom is gay, both sons and one daughter happily married for almost twenty years (an oddity for our family).
it’s purely anecdote, but I don’t see any evidence of heritability for gay tendencies. If anything, it should be more obvious as the pressure to hide in the closet and fake it with a marriage and kids has been the norm for most societies until now.
That’s a horrible sentence to write on a site dedicated to fighting ignorance. If the topic was a hypothesis for a single dominant gene deciding homosexuality your anecdotes would be weak evidence against, but no one is hypothesizing such. Yes, the sentence is naively true, but it’s also exactly what someone utterly clueless about inheritance would write.
[QUOTE=naita]
That’s a horrible sentence to write on a site dedicated to fighting ignorance. If the topic was a hypothesis for a single dominant gene deciding homosexuality your anecdotes would be weak evidence against, but no one is hypothesizing such. Yes, the sentence is naively true, but it’s also exactly what someone utterly clueless about inheritance would write.
md2000 knows only two gay people. That’s not evidence for heritability of homosexuality, because it’s not evidence for anything about homosexuality. Two is far too small a sample size to make any nontrivial conclusions. And stating that fact isn’t a reflection of an agenda, it’s just simple truth.
And yes, sexuality is not a binary trait, but exists on a full spectrum, probably at least a two-dimensional spectrum, and quite possibly more. That doesn’t mean that we can’t speak of homosexuality, though, any more than the fact that height is a spectrum means that we can’t speak of tallness.
Technically, sexuality is a spectrum, yes, but that glosses over the fact that a large proportion of people say they are exclusively heterosexual. So really, a more accurate description of the data would be that most people are completely heterosexual, but there is a spectrum among the minority with any interest in the same sex.
Sexual orientation isn’t a spectrum in the same sense that intelligence is a spectrum, or height is a spectrum, or political orientation is a spectrum.
Just in case anyone jumps to any conclusions about any agenda I may have in pointing this out, I’m a live-and-let-live kind of guy and absolutely don’t care what anyone’s sexual orientation is.
ETA: I obviously disagree with the conclusion drawn by the author of my cite - and meant only to use the distribution graph to support my point
The problem in studying human sexuality is that this
doesn’t necessarily prove that
For good evidence of that, just look at the cited article: the survey results are very different for different generations. Kind of seems that’s very good evidence that what people say/admit about their sexuality depends a lot on what everyone around them thinks, and so survey responses don’t tell us much about underlying human physiology.
