Is there a gay gene?

Ken Natton

I have always had the strongest feeling that the certainty that some people seem to have that homosexuality is genetically programmed and thus has an evolutionary explanation is wrong. It seems to me that you might as well search for an evolutionary explanation for why some people like White Snake and others prefer John Denver. But your dismissal of the possibility of an evolutionary explanation for homosexuality is naïve. The logic that says heterosexuality = reproduction = evolutionarily good, homosexuality = no reproduction = evolutionarily bad is hopelessly simplistic. And your faith in the unwavering nature of your own heterosexuality might also be open to challenge. Plenty of film makers and other artists have done just that, with great skill, to plenty of others who felt just as certain as you are.

There is a clue in your post to just where you are going wrong. You have a common view that heterosexuality or homosexuality is primarily about an urge that you can barely control. We won’t go into all the flaws and potential pitfalls about that view. But the human reality is that, for the most part, expression of sexuality is something that follows the arousing of the emotions, and it is not always so clear cut just who might arouse your emotions.

2AlphaMales?!

Many brain structures develop in later life. The medium strength correlation in similarities between cerebral hemisphere "gay brains" of humans and those of stright people of the opposite sex seeming the most pertinent example:

http://www.wellsphere.com/mental-hea...l-women/413862

There also seems some significant confusion (no pun intended) as to whether the "gay rams" were always in fact bisexual. I've yet to read a study reporting non-human animals as being exclusively homosexual in anything approaching 8% of the population. Perhaps the full text of the study is online somewhere...

Overpopulation as a cause of some homosexuality has also received some support in the past, and sheep often live in artificially dense/engineered communities which could perhaps be causing this possible "neurological predisposition toward homosexuality" to become evident behaviourally.

Given the number of studies involving human brains and sexual orientation I'm not sure looking to sheep for answeres is entirely expedient in any case.

CCWilson

What you are saying is that probably there's no evolutionary explanation for homosexuality, but that I dismiss the possibility is naive. Odd logic. I guess what you're saying is that we shouldn't be too sure of our opinions on this subject, which is true, but there's nothing wrong with drawing tentative conclusions from existing evidence. Without opinions, we wouldn't have anything to talk about.

Of course homosexual men are capable of mating with women. But there's an obvious evolutionary reason that heterosexual men have an intense desire for women - because it promotes sexual congress that will send his genes forward. There can't be many characteristics more important than that in terms of evolutionary success. Evolution works by making more prominent those features which give slight survival or reproductive advantages, and eliminating those features which are even slightly disadvantageous. What trait would be worse in terms of genetic spread than a lack of interest in heterosexual copulation? Granted, it's possible that there's some complicated combination of factors that are at play that we haven't considered, but in terms of basic evolutionary theory, what characteristic would be more disadvantageous than homosexuality? Sometimes we overthink things and overlook the obvious. Again, to me the most likely explanation is that evolution wasn't able to devise a totally reliable scheme for ensuring heterosexuality, and sometimes errors (from an evolutionary standpoint) are made. Nobody's perfect.

Ken Natton

I doubt that homosexulaity is genetically programmed because my observation of real human behaviour does not seem to fit that idea. But dismissing the possibility on the basis that you did so is what I see as naive. When scientists first started to observe the behaviour of hymenoptra, it seemed absolutely impossible to imagine that there could be any evolutionary advantage to sacrificing your own life for the good of others. But then they looked a bit closer and found that there really is such an evolutionary advantage, and that behaviour is indeed, genetically programmed.

CCWilson

With bees and ants, the DNA is so close in all members of a colony that it isn't difficult at all to see how sacrificing oneself can send copies of your own genes forward.

Look, without further evidence we have to make intelligent, informed guesses as to how evolution ended up with the present system of sexual preference determination. But logic tells me that a suicide gene would be weeded out, and a gene for infanticide would be weeded out, and a sexual disinterest gene would be weeded out, and a gay gene would be weeded out. What genetic tendencies would be more important to eliminate than those, from the standpoint of one's ability to send his genes into the next generation? I'll be happy to reevaluate my position if a good argument against it comes along.

Ryan_m_b

You're looking at this too simplistically. Individual genes rarely map directly to physical traits, let alone behavioural ones. But leaving that aside and assuming that there existed a genotype that causes suicide before sexual maturity there are plausible reasons for its existance. Remember evolution favours species, not just indivudual organisms and a genotype that confers a tendancy for suicide may also confer a tendancy in others that causes them to proliferate more. In the case of homosexuality from an evolutionary perspective if we ignore kin selection, assume no homosexual individual reproduces and assume that there is no sociological advantage to having a percentage of the population as homosexual then it could still persist if the mechanism that gives rise to homosexuality some of the time has a greater effect on the rest of the population than without it. What I'm getting at here is that if a species were "programmed" for sexuality then they would have a greater advantage even if a fraction of them are rendered "infertile" by it.

Monique

Indeed, seemingly detrimental traits can have positive influences as well. For example sickle cell anemia in malaria-infested regions.

The idea that natural selection weeds out detrimental traits is flawed as well, just look at all the illnesses that humans suffer from. For a trait to disappear there needs to be a strong negative selection, otherwise it will persist in a population (Hardy-Weinberg equilibrium). Just since how long has it been acceptable to lead a homosexual lifestyle? Before that people with homosexual feelings were in heterosexual relationships and had children. Today people in homosexual relationships can have children as well.

CCWilson

Actually sickle cell anemia is not a positive for survival; those people die early. It's sickle cell trait - the heterozygous version - that offers some protection against malaria, probably because of alterations of the red cells. There are some American football players with sickle cell trait, which is usually asymptomatic but is associated with a slight risk, especially with prolonged extreme physical activity without time for recovery. Off subject.

Evo

First, you need to provide peer reviewed studies that back you up. Personal opinions don't suffice in the science forums.

CCWilson

Evolution is different from most of the sciences. You can't do experiments to test hypotheses, except maybe to a very limited degree with bacteria and such. Let's be honest. Evolutionary science is mostly a matter of logic. Darwin's theory was based on a lot of observations, not of evolution in action, but of its end results. It was really a brilliant, logical conclusion with no peer reviewed studies to back it up. We know more and more about some of the details of how inheritance works, and how some genes accomplish their tasks, but when it comes to personality traits and how genes affect those changes, we don't know very much. As far as I know, we don't have a clue about how genetics and particular alleles affect the structure of the brains and its chemicals and connections to cause aggressiveness, sexual preference, empathy, selfishness, altruism, and so on. Let's be a little modest in our certainty that peer reviewers have anything useful to tell us about all that.

Bottom line, we don't have the tools yet to investigate the functioning of the brain at the neuronal level. The discovery of mirror neurons was extremely cool but I don't think it's been the major breakthrough we hoped it would be, except as an suggestion of what the mechanism might be for empathy and learning - maybe. Until we get a lot further in our ability to understand how genetics affects the structure and functioning of the brain, we're stuck with using logic, based on what we do know. All this discussion that we're reading now about whether morality and religion are determined by what's in our genes - fascinating subjects - do you think that's come about because of scientific breakthroughs? No, it's the result of people trying to put two and two together based on what we do know.

The best peer reviewers can do when an evolution hypothesis is presented to them is pass judgment on whether it logically fits the facts.

What happened when somebody suggested that maybe homosexuality was selected for, or at least not eliminated, because an extra caregiver might increase survival of kin? Were experiments conducted to demonstrate its truth? If they were, we should have the results in 2000 years or so. No, presumably peer reviewers, if there were any for that idea, would have tried to figure out if that made more sense than other theories, would have tried to fit the possibilities into Hamilton's equation or some such, and they would have published their opinion, which might be right. Or not.

atyy

Here's some discussion in the literature which may be helpful for this thread.

http://www.ncbi.nlm.nih.gov/pubmed/20141266
http://homepage.psy.utexas.edu/homep...gy_AP_2010.pdf
"Exclusive homosexual orientation seems to defy evolutionary logic since it presumably fails to increase an individual’s reproductive success. Although evolutionary hypotheses have been proposed for homosexuality, as discussed earlier, none have received empirical support thus far (e.g., Bobrow & Bailey, 2001)."

http://www.ncbi.nlm.nih.gov/pubmed/19539396
http://www.faculty.ucr.edu/~mzuk/Bai...0behaviour.pdf
"Previous work has emphasized the apparent paradox of selection acting on non-reproductive individuals [1,2],"

"Over the past two decades, Drosophila researchers have examined a multitude of candidate genes implicated in the genetic and neurological control of sexual behavior. These studies have provided insights into sexual behavior in general, and as a byproduct have illustrated different mechanisms that can independently produce same-sex sexual behavior. What are these mechanisms, and what can we learn from them? Mutations in a Drosophila gene called fruitless have been known for nearly half a century to cause males to court other males [4]."

EagleNebula

Speaking from my own knowledge (which is quite limited on this subject) I think so. If we are talking about male sexuality that is, because that's where the most research has been made. For example, let's take a family. There is one father, one mother and four boys. The fifth is on it's way (and he'll be gay in this scenario). Is there any rational explanation to why the chances of getting a gay son would increase? Yes. But wait, so what is happening biologically to the baby boy?

When a mother is pregnant with a boy, the female body sees the male fetus as a foreign object. For protection, the female body sends out antibodies to the boy in the womb. The more antibodies the mother have, the more adapt her body becomes at feminizing the male fetus. Thus, giving birth to gay son.

Of course this not enough to say with 100% confidence that there is something as a gay gene, but I see result like these to be of value. At least we can see that it's not totally a decision for everyone. Maybe I'm talking total rubbish, but that's my opinion right now.

Ryan_m_b

Welcome to the forums. I'm afraid to say that this is mostly total rubbish. Genes are sequences of DNA that are transcribed into RNA, they are not created or altered on the basis of antibodies in the womb. In fact if the mother rejected the embryo in the manner you describe it would not result in a viable pregnancy.

Whilst it has been reported that birth order and sibling sex and number have a statistically significant effect on a child's sexuality the mechanism is likely to be far more subtle and complex than simply a case of genetics.

Antiphon

Not rubbish at all. The probability of a homosexual male offspring increases dramatically with the number of offspring.

It seems to me the evolutionary function is obvious- it prevents any one set of parents from monopolizing the gene pool by creating too many boys.

Suppose a couple decided to have 20 children and they all turned out boys. In a small clan this would greatly reduce the diversity if they all took wives. By ensuring that only the first 3-4 of the males are interested in reproducing the diversity is maintained.

Ryan_m_b

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

Borek

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.

Ryan_m_b

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.