Genetically destined to be gay?

Great Debates
1

This is more of a question but I think the topic may spark some debate so I’m placing it here.
Evolution (feel free to correct) postulates that, through random mutations and natural selection, favourable traits are passed down to enough offspring to enable the species to survive and adapt to the environment of that time. A change to the environment will result in a change to the species. No change to environment, no change to species but some optimization takes place. For example, sharks are good at what they do because they first evolved to suit their watery environment, then natural selection ran its course so that the best predators would catch more food, grow healthy, and survive long enough and breed enough to influence future generations of sharks. Extend this process over hundreds of thousands of years and you get a near perfect predator of the deep. If a species came into being that fed on sharks a lot, sharks would then go through another change (over time) that could drastically alter their appearance and activities from what it is today. Am I on the right track? To go further with this, any shark lacking the ability or desire to procreate would have its genetics removed from the gene pool thereby limiting the number of the next generations that would carry this trait.

My question is that, if this is the way things work (albeit an elementary version), shouldn’t the percentage of homosexuals in humanity be all but eliminated? I keep reading that homosexuality is genetic and, as far as I can tell, it doesn’t seem to follow other scientific ideas. And if homosexuality isn’t something that can be naturally selected out of the gene pool, then is it really genetic in the first place?

Now I realize that there would be societal pressures to procreate in past civilizations, but did that exert enough of an influence to account for what appears to be an increase in the number of gays in the populace? Some of the ancient Romans and Greeks viewed homosexuality as normal, keeping lovers of both sexes (no cite but will find one if deemed to be required). Are we, as humanity, still in the process of breeding out these traits after some 2000 years? But, if we go further back to the time when humans were first appearing, shouldn’t the tribes have weeded out the gays at that point so they would not be nearly as prevalant in modern society?

It seems to me that homosexuality is more likely a result of influence throughout a person’s developmental years. The person would not necessarily make a conscious choice to be gay but instead their sexual orientation would be the net influence (positive and negative) exerted on them throughout their developmental years (although there may be exceptions). I have no cite for this but on the surface it appears to have a better chance to fitting the facts than a genetically inherited predisposition to homosexuality.

I am quite aware of how this will read so please don’t bother pointing that out. It is, in my opinion, an honest question that I’ve yet to have answered. Also, I am not interested in the morality of homosexuality so please leave the judgement books at the coatcheck counter. You can have them back when you leave.

2

From the American Psychological Association’s online document Answers to Your Questions About Sexual Orientation and Homosexuality:

From the American Psychiatric Association’s fact sheet on gay, lesbian and bisexual issues:

Just thought I’d give you a quick overview of current scientific thinking on the matter.

3

That’s not neccessarily true. First of all, gay people are able to have heterosexual intercourse, and do reproduce, like you’ve mentioned. But even assuming that no gay man or woman ever reproduces, that wouldn’t mean that homosexuality would neccesarily disappear.

There’s a genetic disease that effects Ashkenazi Jews called Tay-Sachs disease. The person born with Tay-Sachs can’t make an enzyme to metabolize a body chemical. So, that chemical builds up in the brain, and kills people with Tay-Sachs, at no later than the ages of 5 or 6. It’s a really horrible disease, made worse because it affects babies and young children.

In spite of this, and in spite of the fact that no one with Tay-Sachs can ever live long enough to reproduce, babies still come down with it. This is because the gene that causes Tay-Sachs is recessive (so that if a person just has one Tay-Sachs gene, he or she won’t get the disease), and so many people are Tay-Sachs carriers.

If the gene that leads to homosexuality is recessive, or if it’s a combination of genes that all have to be there for the person to be gay, it’s possible for the “gay gene” or genes to survive, even if the manifestation of those genes is detremental to reproductive success.

Of course, this isn’t to say that homosexuality is genetic. It might be environmental, or have environmental components, either in the womb, or after birth. We don’t know enough to say for sure. However, we can’t rule out a genetic component.

4

The main problem here is that genetics, and natural selection, are not nearly as simplistic as you describe.

A few points:

  1. While there is evidence that homosexuality is in part due to genetic, inherited, factors, it is evidently also due in part to developmental, non-inherited, factors. Note that in this latter case sexual preference would still be “innate,” just not genetically determined and heritable.

  2. The genetic component of homosexuality is in all probability not due to a single allele of a single gene, but multiple alleles of multiple genes. If these alleles provide strong selective advantage in other combinations, they can be selected for overall even if they happen to cause behavioral sterility in the combination in which they cause homosexuality.

  3. Some have postulated that homosexuality might be maintained in the population through kin selection, for example, if non-breeding adults provide additional resources to the offspring of their siblings. I personally think this one is pretty unlikely.

This said, as a biologist it seems to me that homosexuality occurs at a higher frequency in human populations than I would expect given the fact that it often causes behavioral sterility. But we are so far from understanding its actual causes and origin that it is difficult to speculate on what the actual selective forces might be.

I would also point out, however, that a significant percentage of the heterosexual population is also behaviorally sterile. You might make the same argument about why nerdiness, geekiness, or for that matter religious celibacy are not selected out of the population. :wink:

5

Also, I’d like to point out genetics is a complex field, and understanding the mechanics of it is a vocation unto itself. Consider, if you will, sickle cell anemia. You’d think that a genetic disease that kills its victims early in life woul die out quickly, right? Except that it’s a recessive trait; the disease only manifests if both the father and the mother of a child have it. And the carriers of this genetic mutation have an increased resistance to malaria. So it persists.

This topic (as you can probably tell by my practiced diatribe on the subject) has been discussed extensively on these boards. Eventually, if this thread keeps going, someone who’s less of a layman than I am will be along to explain in more detail. Meanwhile, I’d suggest you do some reading on the subject. Here are a couple of good links:

http://en.wikipedia.org/wiki/Genetic_basis_for_homosexuality

http://www.gaysouthafrica.org.za/homosexuality/studies.asp

http://www.talkorigins.org/indexcc/CB/CB403.html

6

[QUOTE=Greenback]
This is more of a question but I think the topic may spark some debate so I’m placing it here.
Evolution (feel free to correct) postulates that, through random mutations and natural selection, favourable traits are passed down to enough offspring to enable the species to survive and adapt to the environment of that time. A change to the environment will result in a change to the species. No change to environment, no change to species but some optimization takes place.

[QUOTE]

This definition contains a number of errors. Rather than try now to address them all individually, I’ll first just give you a good definition of “evolution”: The process by which species change over time, through genetic mutation and recombination, and natural selection of traits.

No more, no less. Learn to avoid using value-laden terms like “favorable” and “optimize”, even when the experts use them. They’re not technically “wrong” per se, and it’s very difficult to express oneself without them, but the effort spent in doing so helps change the way you think about natural selection. There is no “good” and “bad”. Just selective pressure, or the lack thereof. Also, it’s a subtle point, but species don’t “adapt”. I know, I know, everybody says they do, they use words like “adaptation” and so on, but it’s really not a good way to put it. Any trait that one or more individuals within a species has that allows it to survive selective pressure is, by definition, extant. It was not “adapted”, because it was already there. That trait comes to predominate because other members of the species who lacked the trait couldn’t reproduce at the same rate, or perhaps couldn’t even survive to reproduce. Repeat this many, many times over many, many generations, and a sub-set of the species may become genetically isolated from its relatives. Hence, a new species is defined.

Mr Visible gave you a nice summary of the current understanding of the nature of homosexuality. The facts are, what causes people to be “gay” or “straight” or “bi” aren’t at all well understood, and pretty much all we have to go on at this point is statistics. What precise genetic and environmental factors determine sexual orientation isn’t known at all. After decades of searching, we’re not much better off than we’ve ever been as far as basic knowledge goes. All one can say is it can’t be purely genetic, because some identical twins have differnt orientations, and it can’t be purely environmental, because many more identical twins do have the same orientation than your average sibling. Really, someone could have told you this 1000 years ago, if they chose to study it rigorously.

I see a lot of people arguing that homosexuality is “detrimental” or “beneficial” to the species. I think these people probably are influenced by their politics, or have an agenda. The fact is, we don’t really know, and no hypothesis on the subject produced so far is at all bullet-proof (lets not confuse “theory”, the way people commonly refer to something that should be called “hypothesis” and “THEORY”, a well-supported and tested scientific priniciple). Nothing about natural selection precludes homosexuality from existing, so long as it doesn’t predominate. Its effect on the species overall could be completely neutral. The effect on the individual may not matter because nothing stops homosexuals from procreating (lots of them do).

Suffice to say homosexuality exists, it’s natural, and it’s worth trying to figure out because human nature and its diversity is a fascinating subject.

7

Thanks for the links MrVisible. It appears I’m rather dated on what I’ve been told :o

That is the reason I posted the question. You phrased it much better though.

Not true. There’s always someone for nerds. I know lots of nerds who get some tail. Well, I knew one. Okay, I heard a rumour that one time a nerd scored but it turned out he just touched her hair. But it shows that there’s hope :slight_smile:

LoopyDude, I am aware that I used some subjective adjectives in my summary of evolution. However, favourable traits I would define as any trait that allows the species a greater chance of survival. Optimization, in the context I used, would be defined as a species adaptation in any stable environment. I will be more explicit in future posts.

8

You’re very welcome. It’s enormously encouraging to me that, when presented with data that contradicts your theory, you re-evaluated your theory. Thank you for being open to new information.

You’d be amazed at how seldom that happens.

9

In a related vein, I remember seeing a television program several years ago (over a decade) that was looking at possible causes of homosexuality.

They had an experiment where a colony of white mice were living inside a plexiglass “apartment.” All of the mice’s needs were tended to, and they were allowed to do whatever they want. The number of homosexual mice in the colony (defined by males who attempted copulation with other males) was almost non-existent.

After a while, overpopulation set in, and the apartment got more and more crowded. As things became more dense, the percentage of homosexual mice increased. Eventually, the population maintained itself into a steady state, with more homosexual mice appearing whenever the population increased.

Now, I’m not claiming that this is the answer for how/why homosexuality occurs, but it does show that you can have evolution and homosexuality without any apparent contradiction, such as the theory that crowded conditions cause mice embryos to have a greater chance of preferring the same gender.

Anyway, just wanted to share.

10

I seem to remeber a New Scientist article on a simlair issue a few weeks ago in which they sated that homosexuality had a too high frequency for it to be genetic.

11

It may or may not be relevant to note that transexuality is believed to do with the development of the brain in the womb. Male brains have several places that are more developed (and by more developed, I simply mean ‘larger’) than in female brains, transexuality is believed (though I don’t know how orthodox this view is, but it is one that comes from a post-mortem study on the brains of transexuals) to be caused by some of these ‘male places’ failing to develop in the womb meaning they are essentially ‘female places’.

12

We’ve had a couple of threads on this topic before. Here’s one. I learned a lot from annaplurabelle’s explanation of what the best working theories are. I think that’s on page 2.

13

Whaaa . . . ?

I’m gay. I have put a great deal of energy into the lives of my sister’s kids. Do the math.

And here’s some more math. I have three sisters. We share one set of parents, therefore we share many genes in common. My “gay gene” is therefore almost certainly passed down through my sisters’ kids.

I’m not making this up; see Dawkins re: Altruism is the new Selfishness.

14

Ironically enough, Dawkins thought Trivers’ kin selection hypothesis was going too far, and he co-wrote an article with Mark Ridley around about 1980 which parodied that theory, entitled the “Sneaky Male” hypothesis. While I haven’t read it, one can easily draw a rough idea from it’s title: gay guys tend to be closer to women, so they use this closeness as a strategy for procreation. While this is quite absurd, it’s no more absurd than Trivers’ theory. Neither has any data for or against, so to borrow from Gould both are “just-so stories”.

Also, in addition to MC’s comments about pre-natal conditions affecting sexuality, I’ve heard that there is a statistically significant effect whereby second sons are more likely to be homosexual. These second-born homosexual sons generally have a lower weight at birth than heterosexual babies (about 200g less IIRC). It’s not a huge correlation or anything, but it’s significant.

15

Something that happens with a high frequency and has multiple causal factors - most people confuse “homosexuality is genetic” with “there’s gay gene” - is not easy to breed out of the gene pool. Probably impossible, and that still works from the assumption that there is no evolutionary advantage to having gays around. This seems to be untrue since it’s very prevalent in the animal world as well.

How is that possible? All people have two legs (for practical purposes), and that’s genetic…