Born this way? An evolutionary view of 'gay genes'

by Jenny Graves
Credit: darcyandkat/Flickr, CC BY-NC-SA

The claim that homosexual men share a "gay gene" created a furore in the 1990s. But new research two decades on supports this claim – and adds another candidate gene.

To an evolutionary geneticist, the idea that a person's genetic makeup affects their mating preference is unsurprising. We see it in the animal world all the time. There are probably many that affect human sexual orientation.

But rather than thinking of them as " genes", perhaps we should consider them "male-loving genes". They may be common because these variant genes, in a female, predispose her to mate earlier and more often, and to have more children.

Likewise, it would be surprising if there were not "female-loving genes" in lesbian women that, in a male, predispose him to mate earlier and have more children.

Evidence for 'gay genes'

We can detect genetic variants that produce differences between people by tracking traits in families that display differences.

Patterns of inheritance reveal variants of genes (called "alleles") that affect normal differences such as hair colour, or disease states such as sickle cell anaemia.

Quantitative traits, such as height, are affected by many different genes, as well as environmental factors.

It's hard to use these techniques to detect genetic variants associated with male homosexuality, because many prefer not to be open about their sexuality. It is even harder because twin studies show that shared genes are only part of the story; hormones, birth order and environment play roles too.

In 1993, American geneticist Dean Hamer found families with several gay males on the mother's side, suggesting a gene on the X chromosome. He showed that pairs of brothers who were openly gay shared a small region at the tip of the X, and proposed that it contained a gene that predisposes a male to homosexuality.

Hamer's conclusions were extremely controversial. He was challenged at every turn by people unwilling to accept that homosexuality is at least partly genetic, rather than a "lifestyle choice".

Gay men were divided: it vindicated the oft-repeated claims that "I was born this way" but also opened frightening new possibilities for detection and discrimination.

Similar studies gave contradictory results. A later search found associations with genes on three other chromosomes.

This year, a larger study of gay brothers, using the many genetic markers now available through the Human Genome Project, confirmed the original finding, and also detected another "gay gene" on chromosome 8. This has unleashed a new flurry of comment.

But why such a furore when we know of gay gene variants in species from flies to mammals? Homosexuality is quite common throughout the animal kingdom. For instance, there are variants that influence mating preference in mice and a mutation in the fruit fly makes males court other males instead of females.

Is the 'gay gene' really a 'male-loving allele'?

The puzzle is not whether "gay genes" exist in humans, but why they are so common (estimates from 5-15%). We know that gay men have fewer children on average, so shouldn't these gene variants disappear?

There are several theories that account for the high frequency of homosexuality. A decade ago I wondered if gay gene variants have another effect that boosts the chances of leaving offspring ("evolutionary fitness"), and passing the gay allele on.

This is a well-known situation (called "balanced polymorphism") in which an allele is advantageous in one situation and not in another. The classic case is the blood disease , which leads to disease and death if you have two alleles, but to malaria resistance if you have only one, making it common in malarial regions.

A special category is "sexually antagonistic genes" that increase genetic fitness in one sex, but not in the other; some are even lethal. We have many examples across many species. Maybe the gay allele is just another of these.

Perhaps "male-loving" alleles in a female predispose her to mate earlier and have more children. If their sisters, mother and aunts have more kids who share some of their genes, it would make up for the fewer children of gay males.

And they do. Lots more children. An Italian group showed that the female relatives of gay men have 1.3 times as many children as the female relatives of straight men. This is a huge selective advantage that a male-loving allele confers on women, and offsets the selective disadvantage that it confers on men.

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I am surprised that this work is not better known, and its explanatory power is neglected in the whole debate about the "normality" of homosexual behaviour.

How 'normal' are gay alleles?

We have no idea whether these genetic studies identified "gay alleles" of the same or different genes.

It is interesting that Hamer detected the original "gay gene" on the X, because this chromosome has more than its fair share of genes that affect reproduction, but I would expect that there are genes all over the genome that contribute to mate choice in humans (female-loving as well as male-loving).

If there are male-loving and female-loving of tens or hundreds of genes battling it out in the population, everyone will inherit a mixture of different variants. Combined with environmental influences, it will be hard to detect individual genes.

It's a bit like height, which is influenced by variants in thousands of genes, as well as the environment, and produces a "continuous distribution" of people of different heights. At the two extremes are the very tall and the very short.

In the same way, at each end of a continuous distribution of human mating preference, we would expect the "very male-loving" and the "very female-loving" in both sexes.

Gay men and lesbian women may simply be the two ends of the same distribution.

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Returners
1 / 5 (4) Jun 02, 2014
To an evolutionary geneticist, the idea that a person's genetic makeup affects their mating preference is unsurprising. We see it in the animal world all the time. There are probably many genes that affect human sexual orientation.


Okay, you've already contradicted yourself, because homosexuality is not a "mating behavior".

While I am sure all sorts of things in our behavior (social anxiety for example) are caused by genes, that doesn't justify the negative behavior.

As a person with social anxiety and primary depression, I don't want this behavior, and I (now) take medicine to help remove that anxiety, for the past 3 years or so.

Primary depression is believed to be genetic, so from that perspective you could view it as a disease, which since we are treating it as an "illness" then it is a "disease" in that sense.

Thus you can see if homosexuality is a genetic problem, it is a defect, and is therefore a disease which ought to be treated with medicine and discouraged.
Returners
1 / 5 (4) Jun 02, 2014
And look, I'm a bit of a hypocrite, okay, because almost every straight guy has fantasies of a threesome with a couple of bisexual girls, and some follow through and get that.

As a guy, if I wasn't dating anyone, and I knew nobody would get hurt out of it, and the opportunity was there, then sure, I'd probably go for the threesome. That's because I'm straight, not because I "approve" of homosexuality. If I was gonna be polygamous, I guess I'd ideally prefer two 100% straight girls, for example, but then that wouldn't be fair to them I guess.

Doesn't mean I hate anybody, regarding the gay gene thing, I just get upset that people on the one hand want to claim it's a genetic disorder(medically), but on the other hand they want it to be treated as a "social norm" which is also hypocritical.

If it's a genetic disorder, then let's medically treat it as a genetic disorder, and stop promoting it to the youth on every network television sit-com or drama.
meeow74
5 / 5 (2) Jun 02, 2014
Your logic is flawed. Do we look at someone with blue eyes or being 6' 4" as having a genetic disorder? All the research is saying is that it a genetic variation not that it is a genetic flaw. I think equating anxiety and depressive disorders, which have already been proven to more than just genetic, to a potentially genetic predisposition to homosexuality is ridiculous.
katesisco
1 / 5 (2) Jun 02, 2014
Seems confusing. Cystic Fibrosis should have disappeared long ago yet it is still with us. Again the dual role is proposed; that there is some conferred advantage over the very obvious disadvantage.
Perhaps the role of our sun, a fading magnetar, in its almost-gone monopole cycle is responsible. Perhaps our sun was a monopole first, and in losing energy, became a dipole and with each subsequent 'magnetic reversal' became more dipole and less monopole. Perhaps the origin of multicellular life 640 mya was a monopole energy form, the enigmatic comb jellies with muscles the first form of multi cellular life. Science was astounded to discover sponges a later form or even a second start to life. A more degraded start. Perhaps the life began under a monopole sun was replaced with life under a dipole sun. I suggest this happened and it conforms to the Second Law of Thermodynamics.
Returners
1 / 5 (2) Jun 02, 2014
you gotta be kidding. An evolutionary advantage to homosexuality?

Seriously, what possible advantage does that promote, since it decreases the liklihood of a person's genes being passed on?

A gene that decreases the likelihood of it's own passing, particularly a sex related gene, should fade out of a population relatively fast. Though it could re-appear through mutation if the mutation is simple enough to happen often.

We do not find habitual, repeated homosexual encounters of animals in nature. 2 critters trapped in a cell in a zoo doesn't count.

If there was a "gay gene" it should appear in the animal kingdom at large, and clearly it does not, because there is no documented behavior.

Again, a single incidence of two male animals "making a pass" at one another is not the same thing as a human gay habitual life style choice.
Vietvet
5 / 5 (2) Jun 02, 2014
@Returners

Your response shows a complete lack of reading comprehension.
RobertKarlStonjek
2 / 5 (2) Jun 03, 2014
1] This is another piece of complete and utter rubbish and quite unscientific. There are many paths to sexual orientation and there is likely to be some genetic predisposition in all of them. The fact that they did not identify which form of homosexual behaviour shows the lie.

Sex is only one component pair of bonding. Having offspring is only one predisposition. Being in close company (companionship) of same-different sex is only one predisposition. There is opportunistic mating (sex only) and pair bonding (raising kids) which are entirely different thought they can occur within a single relationship or separately or one side not at all.

There are no genes for sexual orientation, only genes for various components of sexual orientation that raise the probability of a particular sexual orientation *in a given cultural environment*.
RobertKarlStonjek
1 / 5 (2) Jun 03, 2014
2] Once we consider complainant preference, sexual preference, sexual identification (only some percentage and not all cross dressers are homosexual), attitude to parenthood, status of marriage and so on.

Thus we may have heterosexual cross dresser, a heterosexual who spends all his time with male buddies who he will die for, a homosexual who has a wife and family and so on.

These combinations and many more are possible sexuality in humans is a multidimensional thing.

That bisexuality, asexuality, paedophilia and other sexual variations and deviation are not mentioned indicates the extremely shallow depth of this theory.
RobertKarlStonjek
1 / 5 (2) Jun 03, 2014
3] The evolutionary utility of homosexuality includes much higher incidence of homosexuality when population is under stress due to over population for a given environment. For instance religious texts appear at times when the population is under threat and more children are needed, hence a cultural attitude against homosexuality. Without family commitment, individuals are more able to experiment with technological and artistic advancement.
Returners
1 / 5 (3) Jun 03, 2014
@Returners

Your response shows a complete lack of reading comprehension.


No, blue eyes are not a negative trait, as they don't negatively effect reproduction or inclusive fitness.

Homosexuality reduces the probability of reproduction, therefore it is a negative trait in the strictest biological terms, because IF it is caused by a defective gene, then the Gene is not inclusively fit, and should fade away.

However, I will admit the hypocritical male polygamist gene may offset this if the Lesbians are actually Bisexual instead, cause he may be inclined to have sex with both of them, thereby off-setting some of the negative influence.

But on the whole, if 5% of a population is gay, then on average the reproductive fitness of the population is 5% lower than it would be if they were all straight.

Therefore it should be a negative trait on the whole, and that means it should be treated like cancer or a Dystrophy disease.
JVK
1 / 5 (4) Jun 03, 2014
News article excerpt: "...a mutation in the fruit fly makes males court other males instead of females."

My comment: Non-heterosexuals may object to anything that links their sexual preferences to mutations.

No one objected to use of the same model for development of sexual preferences that I detailed in an award-winning journal publication and concurrently published book chapter. The Mind's Eyes: Human pheromones, neuroscience, and male sexual preferences http://www.sexarc...kohl.htm

Instead, the model was virtually ignored -- even though Simon LeVay said this about it (p 210 Gay, Straight, and the Reason Why):

"This model is attractive in that it solves the "binding problem" of sexual attraction. By that I mean the problem of why all the different features of men or women (visual appearance and feel of face, body, and genitals; voice quality, smell; personality and behavior, etc.) attract people as a more or less coherent package..."

Evolutionists ignore that fact!
JVK
1 / 5 (4) Jun 03, 2014
That bisexuality, asexuality, paedophilia and other sexual variations and deviation are not mentioned indicates the extremely shallow depth of this theory.


Actually, it indicates what happened due to attempts by evolutionary theorists to convince everyone that mutation-initiated natural selection explains differences in individuals and species. That pseudoscientific nonsense cannot be taught to students for decades without confusing everyone, since some of those students become teachers and science journalists who think there was experimental evidence to support the theory.

It was invented and defined in the 1920's when virtually nothing was known about molecular epigenetics. Thus, neo-Darwinism was framed in the context of population genetics (i.e., pseudoscientific nonsense that does not include the biophysical constraints of physics, chemistry, and molecular biology).

http://www.huffin...211.html
Captain Stumpy
5 / 5 (3) Jun 04, 2014
My comment: Non-heterosexuals may object to anything that links their sexual preferences to mutations
@jk
so they can object to your model as well then!
mutation-initiated natural selection explains differences in individuals and species. That pseudoscientific nonsense cannot be taught to students for decades without confusing everyone, since some of those students become teachers and science journalists who think there was experimental evidence to support the theory
well..
since YOUR model causes mutations
and evolution also includes mutations and your model
then you are saying here that YOUR MODEL is PSEUDOSCIENCE and confuses everyone!
YOUR WORDS jk, not mine!

and you are mensa?

Captain Stumpy
5 / 5 (3) Jun 04, 2014
The Mind's Eyes: Human pheromones, neuroscience, and male sexual preferences http://www.sexarc...kohl.htm
(i.e., pseudoscientific nonsense that does not include the biophysical constraints of physics, chemistry, and molecular biology).
@jk
there! I fixed it for you...
given your argument above, and given
Non-heterosexuals may object to anything that links their sexual preferences to mutations
and given our conversations where I asked
DOES your model make any changes to the nucleotide sequence of the genome of an organism, virus, or extrachromosomal genetic element?
This is a yes or no answer
(this is the DEFINITION of Mutation) to which you answered
YES!
--Thanks for asking
so we KNOW that your model creates mutations, and you are here arguing that your "model" is the answer, but you also argue against mutations, which means that either you are severely mentally incapacitated or being blatantly stupid

Osiris1
1 / 5 (2) Jun 07, 2014
So it, gayness, is a biological inheritance capable probably of appearing in any and all of us to varying degrees. In a new empty world that we may find and want to settle, this could easily be declared 'non grata' for candidates for settlers of such where new human life would be strongly desired to sustain small populations' genetic pool and to create a self sustainable population. However our world is full, so self sequestration of such biological dead enders may not be desirable. Maybe if millions of gays were openly allowed even in muslim countries, then that nation's population would start to fall. As it fell, however, a point would be reached where other nations would seek to take it over to settle their 'excess population' like Indonesia and China are looking with hungry eyes at 'relatively empty' Australia whose many decades of restrictive immigration have left it weak and full of stuffy dilettantes and hypocrites.
travisr
1 / 5 (2) Jun 08, 2014
Most of the people commenting here don't even have a basic understanding of partial differential equations. It would take such an advanced knowledge of PDEs and genetics (such that it doesn't exist today) employed on a super computer that certainly doesn't exist to simulate and define the role of the genome on a topic like this conclusively. Yet, all these people come out with their opinions on the direct answer without clearly having even the capability to understand what their position means.

Ahh, now we come to the crux of why a mankind that defines truth by popularity is absolutely doomed.

Likewise, this same idea can be applied to AGW, evolution in general, etc.
Bookbinder
5 / 5 (2) Jun 08, 2014
Thank you for a very informative, logical and incisive article which manages to communicate complex material in an easy to understand form. Unfortunately, some here aren't even up to the easy to understand form and I apologize to you for them.
JVK
1 / 5 (3) Jun 08, 2014
Population geneticists popularized pseudoscientific nonsense before anyone intelligent realized they had invented everything about it. The ridiculous theory was taught in many parts of the world with the most notable exception of Israel, which is where most of the accurate information has been coming from on the biological basis of cause and effect. It links the epigenetic landscape to the physical landscape of DNA in the organized genomes of species from microbes to man via conserved molecular mechanisms that also link ecological variation to ecological adaptations. That's why the Israelis are now going to teach evolution -- so that their students learn about ecology and are less likely to to accept ridiculous theories about mutations, natural selection, and the evolution of biodiversity that makes mutants out of those with atypical cell type differentiation.
http://www.educat...olution/
JVK
1 / 5 (3) Jun 08, 2014
Each time you see information like this reported: http://medicalxpr...ion.html "Levels of a small molecule found only in humans and in other primates are lower in the brains of depressed individuals...' "...antidepressants change the levels of this microRNA." -- ask yourself why evolutionary theorists have been unable to grasp the fact that conserved molecular mechanisms are involved in cell type differentiation, which means the nutrient-dependnet microRNA/messenger RNA must be involved and that mutations are not involved in increasing organismal complexity and biodiversity. It's a simple concept. All organisms must eat, none must mutate. Let's make it simpler: Food is good for all organisms; mutations are bad. Evolutionary theorists aren't very bright, are they? Who is teaching your children and grand-children?
Captain Stumpy
5 / 5 (1) Jun 09, 2014
mutations are not involved in increasing organismal complexity and biodiversity
@jk
so what you are saying then is that your model for diversity is completely out the window, because you say
mutations are bad.
but at the same time promote mutations with this
Nutrient-dependent/pheromone-controlled adaptive evolution: a model
no wonder you are considered a pseudoscience crackpot. remember when we talked about mutations?I asked
DOES your model make any changes to the nucleotide sequence of the genome of an organism, virus, or extrachromosomal genetic element?
This is a yes or no answer
to which you answered
YES!
--Thanks for asking
so, drawing from your own words AGAIN...
IF mutations are BAD AND you say yourself that your model causes mutations
YES!
--Thanks for asking
THEN one can only conclude, per your own words and conclusions, that YOU are an IDIOT!
it also means that, in your own words, you don't know whats going on!

this is your own logic and in your own words, jk.

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