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I decided to post this here rather than in the Gay People thread because it's more directly relevant here. This is supposed to be between Svarog and Asmodean, and I understand that. However, there seem to be some misconceptions about what defines "genetic in origin." Since I work in the field, I suppose part of my job is to spread knowledge and whatnot, so here it goes:

First of all, Dominant/Recessive is barely the tip of the iceberg for genetics. Or rather, it represents the level of sophistication that existed before molecular biology. The study of genetically inherited traits preceeded even the knowledge that DNA was the primary heritable material and far preceeded a mechanistic understanding of how a given sequence of DNA can lead to a phenotypic difference. In addition to dominance and recessivity there are numerous other more complex scenarios. There is partial dominance where having a single copy will lead to an intermediate phenotype between having no copies and having two copies -- for instance, many flower pigmentation genes -- +/+ would be red, +/- would be pink and -/- would be white or the sickle cell trait where being homozygous for the mutant allele has a considerably more severe phenotype than being heterozygous.

There are also genes that don't automatically generate a phenotype but do increase the risk or chance of developing a certain trait -- the BRCA (breast cancer allele) genes are good examples of this. If one has a BRCA mutation, then one has a dramatically increased chance of developing breast cancer, but not everyone with a BRCA mutation develops breast cancer. Conversely, not everyone who develops breast cancer has a BRCA mutation, but that doesn't mean that there are not genetic factors to breast cancer. (if you would like to help fight breast cancer, http://www.bcrfcure.org/sup_howyoucan.html).

The phenomenon of a genotype not always leading to a phenotype is measured by a genes "penetrance." In other words, the percentage of the individuals with a given genotype having the phenotype associated with it. An example of a gene with a variable penetrance is the gene in which mutations lead to Huntington's disease. In this case, the exact form of the mutation is a duplication of a repetitive sequence in the gene. Depending on the individual, there can be different numbers of duplications. The more duplications, the more likely one is to develop and the more severe the Huntington's disease will be. An analogy would be to look at the gene as a tool -- for instance a hammer. And the mutation as an increase in the length of the handle. Eventually, the handle becomes so long that the hammer becomes useless in a practical sense.

There are other, more complicated scenarios, but I'll skip them here, the main points are that 1. there are more subleties and gradations in genetics than dominant/recessive and 2. there are genes that don't automatically result in a phenotype but increase the likelihood of developing a phenotype.


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If it was a ‘learned’ behaviour, then one would expect these results to be skewed, with some societies showing a higher prevalence than others, but the 10% seems to be a universal figure.

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Constant prevelance of a trait across the human race is not evidence of a genetic basis. It also isn't evidence of it not being genetic. I'm also not aware of any study showing the 10% number to be a universal figure. My recollection is that the 10% number came from a survey that was anything but universal. It should be noted that normally one uses a certain trait being clustered in a certain ethnic group or family as evidence that the trait IS of genetic origin -- look at Tay Sachs disease or Sickle Cell Amemia.



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Well not necessarily, if it was paired of like: H-h, where H = straight and h = gay.

Say that you parents both had this genetic make up. Then by drawing that little genetics square you would find out that there’s a 25% chance of H-H, a 50% chance of H-h and a 25% chance of h-h embryos.

So potentially 25% of all people in the world would be gay. However, the offspring of H-H parents will never transmit the gay gene (they don’t have it), which brings this number down…..perhaps even down to….10%?!!

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All this is is a potential scenario where the trait "homosexuality" could be genetically inherited. You provide no evidence that this is how it actually happens. The world of biological research is full of ways things could be, but the only thing that ultimately matters is what really does happen.


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However, the trait examined here has a “suicidal tendency”. Meaning, in genetics some traits exhibit a “fitness cost” which is the likeliness of the gene being transmitted to the next generation, i.e. reduces the person’s chance of procreating. Healthy and normal genes have a fitness cost of 0%, while a fitness cost of 1% would mean that the gene would die out in hundred generations; a cost of 50% within 2 generations and so on. The supposed “gay gene” also posses this fitness cost. (Studies show that today fitness cost for gay genes is as high as 80%!) Now, if homosexuality was genetical (and therefore present since the earliest times), it would have to disappear many times by now. As far as I know, it’s increasing rather than disappearing.

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You should reference that 80% fitness cost number, it seems unlikely. I would argue that if there is a gay gene or multiple gay genes, the fitness cost is probably not as high as you assume here. First, there is the issue of penetrance (no pun intended) the gene may increase the chance of homosexual tendencies but not automatically lead to them. This would allow the gene to survive. Second, there is a huge difference between homosexual tendencies and homosexual behavior. There is such a large societal pressure against homosexual behavior that quite a large number of homosexuals closet themselves, get married and miserably produce children. This, too allows the gene to survive. Third, homosexual behavior only carries a fitness cost if it is practiced to the exclusion of heterosexual behavior. How many homosexuals have never had heterosexual sex? My impression, from the homosexual people I know is not many. (Caveat, the next couple sentences are mere speculation, and is just meant to present a scenario where homosexual tendecies would not lead to a fitness cost). In fact, many of the traits one associates with homosexuality in men seem to be ones that many women look for in a mate. I even know one woman who refers to herself as a "fruit fly" because she's always falling for gay guys. Maybe a straight guy gets it on with a chick 100% of the time he has the chance and a gay guy gets it on with a chick only 50% of the time, but has twice as many opportunities. On the other side of the coin, come on guys, how many of you wouldn't jump at the opportunity to get with a couple of lesbians? (out of speculation mode) The point is, one can't automatically assume that there is a huge fitness cost to homosexual tendencies or even to homosexual behavior.

This particular debate has the problem of arguing about an issue of fact when the fact itself is not at this time known. There either are genetic factors that lead to homosexual tendencies or there are not. Unfortunately, it is extremely difficult to study these traits in humans (I will say that if you get fruit flies drunk, they males will start trying to mate with each other. I'm not kidding.) When doing human studies, the first problem is that you always are working with small sample sizes. This makes figuring out the statistical relevance of the study very difficult. Additionally, the human genome is very large and complicated. If there are multiple genes that all lead to the same trait or that are all required for a trait it can make sorting through the data extraordinarily difficult. If any or all of the genes also have varying degrees of penetrance, it makes the study even more difficult. For a trait as complex as homosexuality, even defining who is and isn't homosexual is difficult. You basically have to take the subjects word for who he or she is attracted to. They could be lying or in denial. This further confounds the study.

To the best of my knowledge, there is not definitive study one way or the other on the subject. There are some studies which have found weak genetic correlations, but they are controversial and cause and effect certainly has not yet been established.

I think one of the problems is that my feeling from reading this debate is that there is a confusion between "genetic cause" and "determined during development." There are things that are not genetic but are nevertheless hardwired while in the womb for one reason or another or during early development. I get the sense, and I may be wrong, that Asmodean's argument is closer to "determined during development, possibly by genetics" than actually genetically determined. I don't normally read the development or psychology journals, but my understanding is that there is much more evidence that homosexuality is determined by factors like those (which, mind you is very distinct from "learned" behavior. Learned behavior can be unlearned, there is no credible evidence that homosexuality can be "unlearned.") than by strictly genetic factors. It's also quite possible that some people are homosexual by birth and some by choice.

Sorry if I posted this in the wrong place. Feel free to move it where you want, but I think it's most relevant to be posted here.

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borty, what the hell happened? That post was way too long for even an interested party to get through.

If homosexuallity was ever a genetic trait it would have been lost thousands of years ago. Life seeks to propogate itself. Gayness is anti-propogation so it would have been lost through the evolutionary process.

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