Dr Rick

It doesn't appear to foster child-bearing. If one is going to argue that there is a genetic basis to human sexual preferences, a more straight-forward theoretical case for the existence of a pedophilic gene could be made than one for homosexuality.

RufusAtticus

If there was/is an advantange to have "sub-optimal" males perfer one another, then groups/tribes with homosexuality/bisexuality will do better than other ones. That is how group selection might come into play.

-RvFvS

RufusAtticus

You are right. But, my comments are not about whether homosexuality will eventually "die out." They rather address the question of "why hasn't it died out yet."

-RvFvS

theyeti

But I don't think homosexuality is really comparable to any of these things. Homosexuality doesn't appear to be a "learned" behavior. Homosexuals are very strongly inclined toward their lifestyles, regardless of any social stigma, and it is reasonable to assume that there is an innate tendancy for some people to become that way. This is further evidenced by the fact that homosexuals have measurable differences in brain anatomy. Now it may be that these things are due to early childhood or fetal environmental factors, in which case genetics may not apply, but either way I don't think you can categorize homosexuality as the same thing as a person's tendancy towards mutual-fund purchaces. Doing so completely ignores the strong deterministic factor.

Now it may be that a lot of evolutionary models are speculative. But that's okay, they all start out that way. If polygenic factors are later shown to be responsible for homosexuality, then the kind of model that I outlined will no longer be speculative, it will be well evidenced. If psychology can explain it, then great, but with the "blank slate" model of human behavior that is fashionable within the social sciences, I would say that they're way off the mark.

theyeti

theyeti

Yes, I know what group selection is, but I thought it was largely out of favor with evolutionary biologists. It's too easy for a "selfish" alelle to spread under a group selection scenario. This is espically true in this case since it requires a large sacrifice, in terms of fitness, on the individual that is helping the group. The scenario that you mention is one where the individuals would benefit, so I don't think it would qualify as group selection.

theyeti

RufusAtticus

We discussed group selection in one of my classes last fall. I got no indication that it was losing favor. I don't think that cheaters are much of an issue with group selection. They come into play with altuistic models, though. Group selection does not have to involve cooperation. In the G-S senario, the entire tribe (and its gene pool) benifits. A high proportion of genetic relationship is important to make it work, though. In small tribes, mate competition might be detremental to long term survival.

I'm not necessaryly arguing that G-S is the reason for Homosexuality. This senario, which has been put forth, is a group selection one. I perfer to think of it as a pleiotrophic effect coupled with our unique sexual appitite.

-RvFvS

Dr Rick

So are bondage enthusiasts, fundamentalists, and Pittsburgh Steelers fans. The strength of a human motive has not been shown to be indicative of its origin. Learned behavour is not always choosen behavour. It can be powerfully implanted by environmental influences and beyond our control; most unconscious motivation is. The stigma associated with homosexuality does not allow us to conclude that it has a genetic origin.

A learned behavour can be strongly driven, and it has been well-demonstrated that humans can learn behavour. It is speculative and not well-demonstrated that humans possess evolutionary behavour patterns. Under these circumstances, the only reasonable assumption is that a given human behavour is learned until we have evidence to the contrary.

An observation that begs the questions: What came first? Are these very small differences genetically determined or the result of environmental or intra-uterine influences?

They're both human behavours, both may be the result of environmental influences, and neither one has been shown to have a genetic origin. I'm not ignoring the "strong deterministic factor;" I'm asking you to show that such a thing even exists or influences human behavour.

When it comes to human behavour, they are all speculative.

</strong>

So if one day you have the evidence to support your position then your position will be supported by the evidence that you have. This is a really tough one to argue against; I think I'll just have to let it go.

You may be right, and I cannot disprove your position, but the preponderance of evidence is currently against your speculation.

theyeti

But it's obvious that people learn to be fundies and Pittsburgh Steerlers fans from their parents or local culture (don't know about bondage enthusiasts). This is as disanalogous to homosexuality as mututal-fund purchaces. Furthermore, people often go from being fundies to the complete opposite and vice versa -- how often do homosexuals and heterosexuals do that? The only situation that I'm aware of is in the extreme environment of prison, where the opposite sex is unavaliable, and even then many do so against their will. And perhaps most pertinent, there's nothing about these other behaviors is detrimental to one's ability to survive and reproduce -- there's nothing strange about them. If homosexuality is learned, then how? If it were as easy to explain as these other things, then we wouldn't be having this discussion.

I would say that there is evidence to the contrary. Homosexuality occurs in all cultures all over the world regarless of proximate environment, and it also tends to run in families. I don't think it's speculative that humans possess some evolutionary behavior patterns either -- there is strong evidence that things like incest avoidance are innate and derived from natural selection, as they are in other species. And besides, why should learned behavior be the default explanation? Since the evidence that homosexulaity is learned is exactly zero, we should look for other explanations, even if they're speculative.

Either way, it can be characterized as innate; that is, something which is determined strongly one way or the other instead of being taught by example. Now I never claimed that homosexuality must be genetically determined. I think it probably is to a degree, but if it isn't, then it doesn't require much of a Darwinian explanation. Keep in mind that the ulitmate cause of all behavior is genetic. We have genes, we have an enviornment, and we have their interactions. There is no such thing as behavior that is totally irrespective of genetics.

Like I said, brain anatomy, the fact that homosexuals are strongly inclined toward their lifestyles, and the fact that they often have correlated behavioral differences. This and the fact that trying to "cure" people from homosexuality often causes severe phychological problems. People don't just say, "hey, I think I'll be gay this week." People realize they're gay, often in their teen years, and often when they desperately wish they weren't. They have no more control over their desire for the same sex as heteros do over their desire for the opposite. How is this at all similar to mutual-funds?

Okay, I admit that was worded stupidly. The point being that a polygenetic basis for homosexuality is perfectly plausible, as it is with many complex behaviors. Polygenetic inheritance is not an easy thing to pin down. Things like asthma are known to run in families, as does homosexuality, and yet no one has been able to pin down any correlated genes. That doesn't mean that they're not there, just that classical genetic methods are not sufficient. When better molecular methods are available, then the hypothesis can be mroe easily tested.

As a matter of fact, there have been genetic studies that show loci correlated to homosexulality, in particular Xq28 on the X chromosome (see Genetics and Male Sexual Orientation, Science 1999 August 6; 285: 803 {I had to remove the link 'cause it was screwin' up da page}). This is probably only one of many genes, and it is probably affected by other loci as per pleiotropy, as one would expect. The authors of that study further claim that "the heritability of sexual orientation is supported by substantial evidence independent of the X-chromosome linkage data." Other studies say the same.

I don't agree at all. There is no evidence to suggest that the human mind is a "blank slate" and there never was; it was just politically correct for social scientists to think that way. There is more and more evidence of a strong genetic influence on human behavior accumulating every day.

theyeti

{edited to remove url}

[ January 27, 2002: Message edited by: theyeti ]</p>

Dr Rick

So it seems that at least some human behavours can be learned...

... and those that are learned have something in common. Homosexuality is "disanalogous" from belief systems, loyalty, other sexual preferences, and every other learned human behavour if it offers a heritable reproductive advantage and the others do not. If it does not, then it has something in common with all of these otherwise disparate behavours.

There is a similarity amongst all of these behavours if they are not evolutionarily derived. Homosexuality is analogous to every other learned behavour if it is learned; it is analogous to every other evolutionarily determined behavour if it confers a selective reproductive advantage over alternative traits. It is not obvious that homosexuality does so, but it is obvious that most human behavour is learned.

If homosexuality has an evolutionary basis, do other sexual behavours and tendencies as well? Where does the "strong deterministic factor" stop and learning begin? Does necrophilia offer a selective reproductive advantage? Is there an evolutionary explanation for coprophilia? How about "golden showers?" Voyeurism?

The strength of a tendency or behavour does not dictate its origin. Since when does the persistence of a behavoural pattern allow us to call it genetic? Foot fetishism is suppressable but rarely reversible; does it therefore provide a reproductive advantage?

I don't know: I suppose I could act like an evolutionary behavouralist and speculate...

So does religion.

Of course, no species comes even close to demonstrating the variety of behavours, sexual or otherwise, observed in humans, and our behavours can be very different from those of other animals: some non-human species will predictably eat their mates, and others will greet eachother by sniffing and licking eachothers genitals. Humans don't usually do this stuff, so what allows us to draw any other comparison between our behavours and theirs?

It's well-established that humans can learn behavour; it's uncertain that we can inherit any.
This thread began by asking for the evolutionary explanation of homosexuality; if there is one, it is purely speculative. On the other hand, one can cite endless examples of human learning.

If other human behavours are learned, it makes sense to look for a learned origin for this behavour as well.

<strong> Learning is not always taught by example; foot fetishism is a strong drive not usually taught by example but learned, just the same.

In the same way that all behavour is ultimately derived from the Big Bang. There is no behavour that is totally irrespective of the universe. These statements are all self-evident but not particularly useful.

None of this says anything about causality. Temporal lobe activity has been associated with religiosity, many transvestities are strongly inclined toward their predilections, pedophiles have statistically correlateable behavours, one can really mess with the mind of a fundie, masochists don't choose their variant desires, and exhibitionists have difficulty with behavoural control. As with stock purchases, there is no convincing evidence that these behavours are genetically pre-determined.

...and purely speculative.

Since when is asthma comparable to homosexuality?

In the meantime, evolutionary behavouralism remains speculative while evidence that humans learn their behavours is plentiful.

Hemophilias run in families but have not been shown to confer a reproductive advantage. Cystic fibrosis has an established chomosomal focus, but an evolutionary explantion for its persistence goes wanting. Genetic linkage does not confer an evolutionary explanation.

[ January 27, 2002: Message edited by: rbochnermd ]</p>

Dr Rick

One more comment that occured to me after I went to bed last night:

QUOTE]Originally posted by theyeti:
<strong> If this was true, then identical twins would demonstrate identical complex behavours, but they don't. Furthermore, identical twins of homosexuals are usually not homosexuals. If homosexuality was genetic or polygenetically based, they would be.