Is Being Gay Genetic? Unbiased Answers & Studies | PhysicsForums

[Ryan_m_b]

From The Red Queen: Sex and the Evolution of Human Nature by Matt Ridley:

¹Earlier he wrote that there is some kind of evidence that the gay gene is inherited from the mother and not from the father.

Perhaps there is more not stated here but this seems to ignore the wealth of sexual diversity seen in human societies as well as ignore female sexuality.

IMO discussions around sexuality from a biological standpoint only are insufficient. If we are to determine what it is about biology that leads to sexuality we need to look at the social sciences (and especially queer studies) to parameterize the discussion. For starters we'd do well to get rid of the notion of discrete sexuality i.e homo/bi/hetero in favour of something more representative of human experience.

 

[Borek]

This is just one paragraph from the whole chapter. And I have posted it to show possible explanations do exist. Whether they are correct and/or final is another question.

 

[CCWilson]

It's not impossible that a gene by chance had two effects - one for homosexuality which was negative with regard to reproductive success and one with some other positive effect on survival or reproductive success. But it seems unlikely that a random mutation which caused both a tendency toward homosexuality and some survival advantage would be of benefit in terms of Darwinian success. Also I doubt that there's any parallel to insect inheritance, since insects operate almost exclusively by instinct and humans don't. And the idea that an increasing rate of homosexuality in women who've had sons before is evidence of a gay gene is almost surely incorrect; that finding is much more compatible with the effects of changing hormones in the mother.

Here's what I've said before. Think of how sexual attraction works. We all have the plumbing to engage in heterosexual or homosexual activity. We all find members of both sexes attractive or unattractive in a non-sexual way. What determines sexual orientation is which body parts and general appearance characteristics are sexually stimulating. That has to do with connections of neurons in the brain somehow, and how that's wired to accomplish sexual preference we really don't have a clue. And we know that the hormones produced by both mother and embryo affect the development of our sex parts. If the hormones go wrong, there may be errors in the formation of penis, uterus, and so on - regardless of whether there are one or two X chromosomes. So if physical sexual characteristics are dramatically affected by hormones, it's pretty likely that sexual preference, the setting of which in the brain is much more subtle, I suspect, is likewise affect by hormones and maybe some other conditions in the womb.

So my conclusion, which is strongly supported by the increased rate of homosexuality in later sons, is that homosexuality is a developmental error (in Darwinian terms) caused by hormonal or other influences and not by one or more specific genes. It goes without saying that homosexuality is an error only in evolutionary terms and has nothing to do with the worth of those individuals; some errors are beneficial.

 

[Antiphon]

Aside from the mention that number of siblings has an effect on sexuality I don't see how you can say this.

I can say it because its a well-established phenomenon.

http://en.m.wikipedia.org/wiki/Fraternal_birth_order_and_male_sexual_orientation

http://userwww.service.emory.edu/~afranc5/Family%20and%20Sexual%20Orientation.pdf

 

[CCWilson]

Antiphon, you're not thinking clearly on this. Assuming the same father, the first born and the last born have the same chances of having certain genes. To say that the difference in frequency of homosexuality due to birth order is genetically related is not logical. Let's say, for the sake of argument, that a woman has four boys, each of which has the same genes, at least with respect to sexual orientation. If it were entirely genetic, all four would either be homosexual or heterosexual. Since boy #4 has a greater chance of being gay, according to those studies, it's likely that factors in the womb, not the DNA, are the reason for that. We know that the woman's ability to produce hormones changes with time and pregnancies, so the obvious conclusion is that bathing the fetus in slightly different hormones results in different outcomes.

 

[Antiphon]

It's not the genes inherited that predispose the offspring to homosexuality. It's the hormonal cocktail in the womb.

This argues against a gay inherited gene but still militates in favor of a genetic motivation for the presence of homosexuality. It's enforced by the mother's biochemistry as programmed by *her* genes.

Again, the conferred advantage is twofold; no one couple will dominate the male transmission to the next generation, but the excess males, as uncles, can still aid in survival of the original line.

Edit: it follows from this that homosexuality is not an error at all- it's a genetic diversity strategy that works for medium sized clans which is how the species grew up. Does this help in a city of 8 million? No, but neither does the tonsil anymore.

 

[marty1]

No. There is not.

 

[Antiphon]

No. There is not.

Apparently there is, but it's not carried exclusively by or expressed in gays; it's carried (presumably) by all women and perhaps men, but expressed exclusively in childbearing women and progressively with each pregnancy.

 

[CCWilson]

Antiphon, I thought you were arguing in favor of a gay gene in the conventional sense. But apparently you believe, as I do, that it's most likely the change in hormones in the uterus from first born to last born that results in higher rates of homosexuality. I agree that it's possible that this is something that evolution has found to be useful in every mother's genetics, but that's far from a settled question. Evolution doesn't do everything perfectly; it makes plenty of design mistakes; and it seems more likely to me that this is one of them than it is a group selection effect.

 

[Pythagorean]

When I hear about a "this" gene or a "that" gene, I tend to think of it as meaning 'genes associated with a disposition towards this or that'; not as a deterministic, life damning, molecule of human puppeteering, but as a shorter path to some behaviors or diseases (stress-diathesis).

 

[Antiphon]

Antiphon, I thought you were arguing in favor of a gay gene in the conventional sense. But apparently you believe, as I do, that it's most likely the change in hormones in the uterus from first born to last born that results in higher rates of homosexuality. I agree that it's possible that this is something that evolution has found to be useful in every mother's genetics, but that's far from a settled question. Evolution doesn't do everything perfectly; it makes plenty of design mistakes; and it seems more likely to me that this is one of them than it is a group selection effect.

Yes, many mistakes and dead ends get tried out. But they should get rejected when there's no advantage and a heavy cost. If homosexuality had no evolutionary advantage then I'd think the reasoning about it getting weeded out would apply. It would be tried and rejected, or at least not be expressed so much. It's an expensive thing to have a sizable portion if your population not participate in genetic propagation. It would be as if 2-5% of the population were born sterile. It's too expensive to do unless there's a survival advantage that offsets the cost.

 

[CCWilson]

Whether the survival advantages of adding non-reproductive participators outweigh the cost - that's what I question. Less food for everybody else in exchange for additional warriors and caregivers - I'm not sure how that equation works out.

Just as we peak in our athletic abilities in our early twenties, even though it would be better for personal and group survival to maintain our athleticism, it may be that a woman's reproductive capabilities naturally decline as well, just from wear and tear.

 

[Ken Natton]

These forums discourage mere assertion of opinion and prefer reference to evidence based conclusions. As has been discussed further up this thread, the reality is that the answer to this question remains unknown to science and it is not particularly certain if or when science will know more. But, as seems to be usual with this topic, there are some strikingly obvious false assumptions running through the posts made on this thread since its revival, centrally that homosexuality has anything whatever to do with non-reproduction. Lots of homosexuals have children. The desire to have children and all of the emotions associated with children are actually quite separate from the sexual urge. Again, the overwhelming majority of human sexual behaviour has nothing whatever to do with reproduction.

 

[CCWilson]

Ken, homosexuality would, I'm pretty sure, reduce the number of offspring. I suspect that statistics would bear that out today, as would logic. I'm sure that nobody here believes that homosexuals don't have kids, just fewer. It may not have expressed exactly that way, but we aren't stupid.

Darwin didn't observe evolution occurring. He saw the results after the fact. He didn't do experiments. His theory was a triumph of logic, based on available evidence. The time scale required for evolution of human behavior makes it impossible to observe or to conduct experiments. The best we can do is apply our powers of logic - what were the survival or reproductive advantages that would promote a "gay gene"? What does the available evidence suggest? Evolutionary science is different from other disciplines. If you read the literature, you'll find that most new proposals are speculative and are judged on how well they fit whatever evidence there is.

 

[Pythagorean]

So... why don't you provide the evidence, rather than attaching the word "logic" to it and "stupid" to the opposing view. I don't find that to be very sound reasoning.

 

[Ryan_m_b]

Ken, homosexuality would, I'm pretty sure, reduce the number of offspring. I suspect that statistics would bear that out today, as would logic. I'm sure that nobody here believes that homosexuals don't have kids, just fewer. It may not have expressed exactly that way, but we aren't stupid.

Rather than assume it would be best to look for some evidence bearing in mind the cultural attitudes towards homosexuality throughout human history.

Darwin didn't observe evolution occurring. He saw the results after the fact. He didn't do experiments. His theory was a triumph of logic, based on available evidence. The time scale required for evolution of human behavior makes it impossible to observe or to conduct experiments. The best we can do is apply our powers of logic - what were the survival or reproductive advantages that would promote a "gay gene"? What does the available evidence suggest? Evolutionary science is different from other disciplines. If you read the literature, you'll find that most new proposals are speculative and are judged on how well they fit whatever evidence there is.

This is misleading, of course evolutionary hypothesis can be tested experimentally. That's why we have model organisms.

 

[CCWilson]

Geez, guys. I said that WE weren't stupid, not that anybody else was. And remind me again how we can test human behavioral genetics experimentally. We can do evolutionary experiments on organisms that reproduce thousands of times as fast as we do, but not on humans, especially regarding things as subtle as personality traits and sexual preference. And any conclusions I draw are based on logic, trying to find the best explanation based on the evidence we have - in this case, the increased rate of homosexuality as the number of children increases - with absolutely no value judgments considered or implied.

 

[Pythagorean]

"Logic" or intuition? Our intuition in science is to not trust our intuition without evidence.

To answer your question about measuring behavioral genetics: twin studies

 

[CCWilson]

Darwin's theory was based strictly on logic - and intuition. He came up with an explanation that best suited the evidence. He didn't observe evolution in action. He didn't "prove" anything. Should we throw out his theory?

How do you propose that we prove why certain people are homosexual and others are heterosexual and how genetics are involved?

I think there's a fundamental misunderstanding of how advances in evolutionary theory come about. It all starts with speculation. A premise is proposed, and people examine it to see if it fits the existing evidence. If it makes more sense than previous theories, it becomes accepted. For example, there's a controversy about whether group selection (also called multi-level selection) occurs in evolution - whether certain traits are selected for because they benefit the group rather than the individual. Most experts say no, E.O. Wilson says yes. There are heated discussions about which side best fits the evidence. It's all based on logic, because there's damn little hard evidence.

Should we tell them to all shut up, because nobody can prove it definitively one way or the other? After all, they're just using - horrors - logic?

Oh, and twin studies are part of the evidence, as is the increased rate of homosexuality with additional sons. Still nothing is proved. Should we therefore stop thinking and discussing this issue?

 

[Pythagorean]

That's all well and good to practice in your own institution when writing grants and publishing papers, but at physicsforums, we try to stick to mainstream, accepted, theory.

Anyone can sit around and speculate hundreds of different "logical" explanations, but can you do the initial research and provide evidence? Any number of experts are likely already working on some manifestation of the answer to the question and may have already cleared the logical pitfalls that you might be falling into.

So maybe you provide the right answer, maybe you don't. Who knows? You're just speculating, not providing the actual evidence. It's not about "proving" in the rigid, mathematical sense, it's about providing evidence (time and time again) that supports your assertions. That is where evolution is now, that is why we accept it; not just because it sounded logical to Darwin, but because we've been able to reject a century of null hypotheses through quantitative analysis of the evidence.

 

[CCWilson]

So you wouldn't want no Darwin coming in here with an unproved theory, cluttering up this otherwise pristine scientific bastion.

You seem to be saying that opinions are not to be tolerated here - even evidence- and logic-based opinions; only hard facts will be allowed. That kind of rule would eliminate about 95% of the posts on this forum.

 

[Ryan_m_b]

Darwin's theory was based strictly on logic - and intuition. He came up with an explanation that best suited the evidence. He didn't observe evolution in action. He didn't "prove" anything. Should we throw out his theory?

Please stop referring to evolution as "Darwin's theory". We've had over 150 years of research that has massively expanded on his initial, limited theory.

I think there's a fundamental misunderstanding of how advances in evolutionary theory come about. It all starts with speculation. A premise is proposed, and people examine it to see if it fits the existing evidence. If it makes more sense than previous theories, it becomes accepted. For example, there's a controversy about whether group selection (also called multi-level selection) occurs in evolution - whether certain traits are selected for because they benefit the group rather than the individual. Most experts say no, E.O. Wilson says yes. There are heated discussions about which side best fits the evidence. It's all based on logic, because there's damn little hard evidence.

This borders on misinformation. You seem to be implying that hypothesis can't be tested in evolutionary science, that's just not the case.

So you wouldn't want no Darwin coming in here with an unproved theory, cluttering up this otherwise pristine scientific bastion.

You seem to be saying that opinions are not to be tolerated here - even evidence- and logic-based opinions; only hard facts will be allowed. That kind of rule would eliminate about 95% of the posts on this forum.

No the rules are very clear: no personal theories, unpublished research or crackpottery. The reasons have been explained multiple times in the feedback forums.