Well technically no one is born gay or straight. There is no gene for either one.
Firstly, I was responding to that poster’s specific hypothesis about the “gay uncle”. It always comes up in these threads and sounds pretty much like a “just so story”. Not very convincing. But I used sloppy language when I said “easier”, because what I wanted to point out is that people are infertile quite commonly, but we don’t see people needing to postulate about “infertile uncles”. The gay uncle hypothesis looks more like an answer in search of question rather than the other way around. It’s quite possible that whatever gay genes there are, remain in the population for no reason at all related to breeding or not breeding. We just don’t know.
We’ve had the opportunity to observe quite a few primitive societies, and if the gay uncle hypothesis had any merit we’d more than likely see it played out in at least a few. I’m not aware of any, but would gladly be educated on the subject if I’m ignorant.
I also agree that any gay women would almost certainly be paired up with some guy and producing babies whether she was attracted to him or not. Women don’t seem to have a whole lot of choice about the roles they play in primitive societies. Wife and mother is the #1, 2, 3, and 4 choices. Not even sure there is a #5.
Generally what we see in primitive societies is that infant mortality is rather high, and few are beset with an oversupply of children. The idea that there would be some survival advantage to limiting the number of breeding adults doesn’t seem to fit with what we know about those societies. It’s possible things were different 100,000 years ago, but that could be an argument for almost anything. We might postulate that in a tribe with more men than women, it might be advantageous for some men to stay out of the fighting over the few women who are around. (Societies with more women than men seem to adapt by having men take up more than one wife.) But that is pure speculation, too.
Chronos is correct that there is probably no single gene for homosexuality. Rather, multiple genes contribute to our preferences.
To this, I will add that there is probably also no rigorous definition of “being gay.” The phenomenon of sexual arousal and behavior is too complex for there to be a definite “target” of one’s sexual urges, perhaps even if one is having sex with a particular person. Furthermore, people can and do change in their sexual preferences over time. At what point in time do they suddenly stop being straight and become gay, or vice versa?
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I know three sets of gay identical twins. In no set did both come out at the same time. The lag times were 2 years, 4 years, and 12 years. So, if you had surveyed any of those sets during the “lag period,” you would have had what looked like a gay/straight pair, but what you really had was one twin who had not come out yet.
That limited date is based on case histories, most of which happened before American Sign Language was recognized as a full-fledged language, so all the case studies were on hearing children who were severely deprived in many areas: basic human contact, nutrition, play stimulation, sometimes even their movement was limited. Sometimes their lack of contact with people seemed to be self-imposed. It was impossible to separate their other privations from their labguage acquisition.
On the other hand, there have been numerous born-Deaf people who were not exposed to language until what was supposed to be the “critical” period, but they had good nutrition, affection, room and implements to play, and otherwise normal childhoods. A few of them were not exposed to a sign language until they were almost adults, and yet they still learned it.
In the 21st century, you don’t have Deaf children in the 1st world thus deprived, whereas, in happened, with alarming frequency until the 1950s, and still to about 1 in 1,000 Deaf people through maybe 1970. But until PET scans, and fMRIs, no one could prove that when native signers signed, they used the language centers of the brain, and not the motor cortex.
Actually, there is no gene for left-handedness. There is a gene for right-handedness. 80% of the population has it, and if you have it, barring something like being born without a right hand, you will be right-handed. People without the gene have a 50% chance of being right handed, and a 50% chance of being left-handed.
So, maybe there is a straight gene, which some people don’t have. If you have it, you are straight. If you don’t, you are straight, gay, or possibly bi, with equal chances of being one or the other.
The straight gene may have started out as something else, back when we didn’t reproduce sexually. Or it may be that because being straight conferred such an evolutionary advantage, in the cave days, that it was autosomal dominant, so it didn’t entirely penetrate. In fact, it could be discovered that there’s a straight gene, which confers straightness if you have one copy, but may confer some disadvantage if you have two copies, like one copy of the Tay-Sachs gene apparently confers TB resistance, but two causes a devastating disease.
I don’t imagine two copies of the straight gene causes a devastating disease of children, but it could turn out to cause something like a form of dementia that isn’t much of an evolutionary disadvantage, because few people 1,000,000 years ago lived long enough to develop it.
I know it seems counter-intuitive that there is a straight gene which gay people lack, but it’s just as likely as the other way around.
I’m referring to what is published in the scientific literature. If you’ve done studies that refute that, you should publish them.
OK, I could be out of date on that info. Have there actually been peer review publications on this matter? I’d very much like to read them if there are.
Having two straight genes makes you too straight, thus unable to dodge tigers.
For such a complex behavior as sexual orientation, there is like a suite of genes, more akin to eye color. The only thing you can accurately say, based on the data we have, is:
- There is likely some genetic component to sexual orientation
- We don’t know what it is or what purpose it served in our evolution, if it even served any purpose at all.
ETA: Oops, I said more than those two things in that post. 
Miller wrote: “This is significant to this conversation, because a possible “gay gene” is not going to have any impact on an individual’s survivability, but is going to have an obvious impact on their ability to pass on their genetics.”
To clarify my earlier comment, “survival value” is not at the level of the individual but at the level of the gene itself. A “gay uncle” caring for orphaned kids need only shepherd them through to reproductive age for there to be a genetic payoff.
We also don’t have a ton of people going around saying that infertile people are unnatural. an abomination before God, unfit to be around children, and unworthy of the rights everyone else gets as a matter of course. If we did, there’d probably be more public discourse on the nature of infertility and how it fits into the history of human evolution.
And it is very much an answer that was developed in response to a question. Specifically, “How can homosexuality be natural if it prevents people from reproducing?” It may not be the right answer to that question, but it very much post-dates it.
Again, we’re talking about an evolutionary process in which very small advantages are magnified across hundreds of thousands of generations. Anthropology is something that we invented less than two hundred years ago. So I’m not entirely sure how you think we’d see this “play out” by now. If the hypothesis is completely, 100% true, this is what we’ve observed:
A) there are people in every society who are primarily or exclusively attracted to their own gender.
B) people will help out their extended family in times of need.
C) having more people involved in the care of a child increases the odds of that child surviving to adulthood.
D) people who are primarily or exclusively attracted to their own gender will have fewer children than people who are primarily or exclusively attracted to the opposite gender.
So far as I’m aware, all of these observations are true. The only area of debate is whether, taken together, they amount to a sufficient reproductive advantage to prevent homosexuality from being selected against. That last part isn’t provable, but it’s also not disprovable simply by studying existing hunter/gatherer societies. At least, not for any time interval less than, say, a hundred thousand years or so.
This is a pretty standard evolutionary trade-off. Species tend to either have lots and lots and lots of children, which are ignored by their parents, or they have fewer children, which require intense care to raise. Humans are pretty far over to one end of this spectrum: multiple births are very rare among humans, and our offspring are incredibly helpless for a long time. We can also observe, among other social mammals, a number of reproductive strategies that limit the number of breeding adults in the group. If there’s an evolutionary advantage to only the alpha wolf in a pack being allowed to mate, it’s not out of the realm of possibility that homosexuality evolved in humans for roughly the same purpose.
Can said Gay Uncle breast feed?
If not, i don’t think that is it.
Mother Nature knows nothing of even-flo bottles and gerber formula, she knows boob milk and thats it, so it would stand to reason she would only be making lesbians?
I just don’t think group selection works for this. Genes are the units of selection, not groups or individuals. Individuals in a group who do not possess “the gay gene” will still get any benefit from being in a group where there are “gay uncles” without bearing the evolutionary cost of being non-reproductive themselves. Their genes will therefore come to dominate the gene pool, overwhelming any group benefit.
I really don’t believe that there is an evolutionary survival value to being exclusively gay. It seems much more likely that there would be a survival cost associated with perfectly ensuring that all humans were always attracted to the opposite sex. It is easier for evolution to accept some percentage of individuals who are less likely to reproduce, than to overhaul the whole system. Nobody has ever explained to me, any plausible conditions under which gay individuals are not, at least somewhat less likely to reproduce. It’s not enough to talk about possible early humans’ societal structures. Exclusive homosexuality is observed throughout the animal kingdom.
From our perspective, homosexuality is about love, and so is one form of the most valuable aspect of human existence. Evolution doesn’t share our values though. It’s a cruel and wasteful process of endless suffering and death. As far as I can see, from evolution’s “point of view”, homosexuality is a bad thing.
I can’t stress enough, that this doesn’t make it a bad thing to us. We defy evolution when we use contraception or adopt a child, and I consider those pretty great things.
There isn’t really any reason to assume there must be some survival benefit for the “gay gene” in there first place, given how many things we know persist even though they inhibit reproduction. Humans love to explain things, but in science we should be more evidence based.
There is another genetic mechanism which can account for survival of an inherently disadvantageous genetic trait - Linkage.
There is no need for the gay uncle providing a survival benefit to relatives. If that gene (or genes) which confer homosexuality are physically located on the chromosome in close physical proximity to a totally unrelated trait which confers a reproductive advantage greater than the disadvantage of the homosexuality trait then both traits get passed on at a higher level. This is known in genetics as Linkage.
This may not be the actual real life case with regards to homosexuality, but I mention it because this is a well understood mechanism by which one trait can ride the coattails of a more advantageous trait.
Is that debate settled? I didn’t think it was. Unit of selection - Wikipedia
I think there’s a point at which the signal is buried under noise. If there larger, more probable, and more numerous selection pressures, the smaller, less probable, less numerous ones are still present, but don’t make much difference, at least, not one that wins out against all the other changes and random factors at play.
By way of analogy, you could move a grain of rice across a table by nudging it a hair’s breadth each day, but an overnight hurricane turns your small, orderly change into a big random one.
People will no doubt disagree, but I think it’s been pretty well settled. Animals (apart from asexual ones) don’t make copies of themselves, groups don’t make copies of themselves. Genes do.
That may be true, but I’m not quite sure I understand how it relates to the point you quoted me on. I think my main point there was that the variation might not exist, or there may be no smooth, continuous improvements leading to it. We could ask why humans don’t have skeletons made of titanium. Perhaps it’s that bone is just better, or perhaps there is no way for nature to have produced metal bones. Even if something seems like it would be beneficial, the selection pressures and the variation have to be present at every stage to produce it. I think, something like this, is likely the reason why we don’t have a mechanism to ensure all female animals have a preference for males and vice versa. Evolution gets it to the stage where it’s true for a high percentage of bodies, and then it either can’t make further improvements, or the cost of doing so becomes greater than the benefit.
Instead of asking why nature produces some non-reproductive individuals, I think it’s potentially more useful to look at how consistently it produces reproductive ones. Since we don’t know how precisely this happens, it seems strange to assume that it could be doing it more reliably.
Linkage, as Iggy described, is also a possibility.
This is not correct. Genes are units of heritability but are not units of selection. Natural selection acts upon organisms, or more pointedly, on the phenotype expressed by the organism (including, if you believe in the notion, the “extended phenotype” that can be jointly expressed between organisms, or an organism and its environment). A gene may code to express a specific phenotype but most phenotypes are the result of combinations of genes, or even a particular epigenetic expression of one or more genes, which may be predicated on external (environmental, nutritional, et cetera) factors.
On the topic of behavior we know that many behaviors have genetic or epigenetic controlling factors but behavior in organisms with significant levels of sentience is so complex that making any definitive statement about what fraction is dominated by genetics versus environment is very difficult except in very narrow (pathological) cases. We can say, for instance, that crying is genetically coded into human physiology in a number of ways (both anatomy and the universality of behavior in infants), but what causes people to be more or less prone to crying is an almost impossible question to even frame clearly much less answer with any definition. In the case of social behaviors (which sex, by definition, falls into) there is such a ridiculously complex interplay between inborn instinct and social expectations that it is again difficult to make clear distinctions. There is clearly an innate attraction to a certain “type” (be it predicated on gender, height, attitude, et cetera) but given the radically different standards of what different societies hold as physical and emotional beauty it is clear that social expectations often frame what is found to be attractive by the individual.
Group selection in general is such an abstraction that it is difficult to drive any conclusions about genetic factors, and in fact I’d go so far as to say that while group selection has some merit in terms of framing apparently altrustic behavior it doesn’t actually exist independent of specific selective responses at the individual level. The apparent altruism of some behavoirs can be addressed by benefit to the carrier of the genes involved in assuring that the genes are perpetuated. However, not all behavior in creatures with higher cognition and deep social interplay can be attributed to selective fitness; as humans we often do things that are decidedly in opposition to effectively propagating our genes.
Stranger
Good points. And the idea that there is one gene controlling sexual orientation is not at all on obvious assumption to make. Same goes for the notion that there is one reason why homosexuality persists in human societies. There could be 5 different reasons or no reason at all.
I think maybe we’re using “unit of selection” slightly differently. I don’t deny that selection acts primarily on bodies. Phenotypes are the means by which the selection occurs, but it is the genes which are actually selected. Organisms are not true replicators. There is only ever one of an organism and it always dies (at least in sexually reproductive animals). Genes are the only part of the organism which can potentially survive indefinitely and can vary in frequency.
I don’t think of the notion of the extended phenotype as a hypothesis to be believed or disbelieved. I see it as an illuminating alternate perspective which makes sense of some otherwise puzzling aspects of evolution.
Your language, and therefore the concepts you are defining using it, is backward. Phenotypes are not “the means by which selection occurs”; they are an expression of genes in a particular form, and may be expressed differently depending on the action of other genes also invovled in the pertinent phenotype. Selective pressures act at the organism level; a gene that contributes to a phenotype that makes the organism more successful in an evolutionary context (i.e. improves chances for survival and reproduction) will be statistically propagated, and are the carriers of information, but by themselves are not selected.
Note that the same gene can be found in different organisms, or repeated in different areas of an organism’s genome, and will only be successfully propogated over time if they are expressed in a phenotype which improves the selective fitness of the organism or can ride along with other genes that are expressed in a way that improves selective fitness. Genes outside the context of an organism do nothing and if not expressed (as many are not) they are just ‘free riders’ that neither contribute or detract from selective fitness. Genes are units of inheritance, but are not units of selection.
Stranger