Freethought & Rationalism Archive

Mecha_Dude · 01-26-2002, 04:20 PM

I've wondered about this topic alot, too...

tronvillain · 01-26-2002, 05:20 PM

Something I posted on one of those threads:

Quote:

Here's a thought (I've mentioned this before elsewhere):
Homosexuality in males correlates well with male birth order - the more males born, the highter the chance of homosexuality. A plausible explanation for this seems to be that the mother's immune system becomes sensitized to H-Y antigens, which are expressed primarily in the male brain. The production of antibodies to those antigens may prevent or at least decrease "masculinization" of the brain by hormones etc.

In a lot of species of birds, the first chick to hatch pushes the other eggs and/or weaker siblings out of the nest. Perhaps male homosexuality in humans (perhaps in other animals as well) is similar. It could have evolved to increase the reproductive success of older siblings, and possibly was favoured even more by the possibility that not all of a female's offspring share the same father. The males born earlier sensitize the mother's immune system against males born later, in order to decrease competition from them (an important things to remember that even a slight decrease in competition for females will be relevant - it need not cause total homosexuality.)

There are various other ideas - social/memetic suppression of homosexuality permitting "deleterious" alles to spread, total accident of biology (environmental influences on hormone levels in the womb, etc.), kin selection (as mentioned by Pantera.) Actually, this theory is almost kin selection seen from a different point of view, and is reasonably compatible with the others.

So Rick, is this one of those "convoluted mechanisms that defy common sense"?

[ January 26, 2002: Message edited by: tronvillain ]</p>

Dr Rick · 01-26-2002, 06:33 PM

You're right to point -out that my post was arrogantly worded; I apologize.

While the evidence for the physical evolution of our bodies is overwhelming and straight-forward, attempts to explain human behavour through evolutionary mechanisms is not.

The birth order thing offered to explain homosexuality is certainly plausible but incomplete. The theory does not explain why some first born males are homosexuals nor why any females are lesbians. First born males are more likely than their younger siblings to be criminals, successful by typical societal standards, and/or mentally-ill. Lots of behavoural traits appear to be correlated with birth-order; it begs the question to try to explain one on the basis of some evolutionary adaption if a similar mechanism does not explain the others.

It seems that one can offer an evolutionary explanation for an individual human behavoural trait, but where evolutionary behavouralists appear to fail is in finding explanations that encompass the amazing variety of human thought and behavour.

Bill · 01-26-2002, 07:11 PM

One of the reasons that human behavior is so difficult to justify in evolutionary terms is that it isn't really a function EXCLUSIVELY of biological evolution, but of some combination of genetic and memetic evolution. There is no real biological justification for what memetic evolution might produce, although you can probably justify meme replicators as a biological advantage if you were pressed to the wall.

Virtually all of the dos and don'ts of human sexual practices are memes. The only thing that counts for biological evolution is the fact that (better than most mammals) humans produce a very diverse set of offspring, particularly in modern times, given our propensity to travel around the world and get laid by local members of the opposite sex. From a biological perspective, I'm sure that homosexuality is counter-productive. But, on the other hand, I'm also certain that its very existence contributes something to human cultural heritage, and thus it would seem to be a meme that will not die. Certainly, it would seem that recorded history has records of homosexual behavior stretching as far back as our records can be reliably trusted (at least 2,500 years ... since homosexual activity is one of the things that made the word "Greek" into a sexual epithet).

== Bill

tronvillain · 01-26-2002, 07:18 PM

robchnermd, do those correlations hold even if sibling are raised independently? If they do, it would seem difficult to avoid some kind of biological explanation.

Actually, the mechanism I mention above could do a lot to cause the correlations with criminal behavior and success. However, I agree with you that it would only be a partial explanation.

[ January 26, 2002: Message edited by: tronvillain ]</p>

MortalWombat · 01-27-2002, 09:00 AM

Here's a hypothetical reason that homosexuality (well, male homosexuality, at least) isn't "weeded out" by evolution: the selective pressure of having males who are really horny outweighs any side effect of male horniness, including a tendency for about 10% of them being horny for other males.

theyeti · 01-27-2002, 11:02 AM

Here's what I posted on one of those other threads.

Quote:

As for the polygenic thing, I thought I'd add this simple example.

Assume that we start out with four gene loci, which we'll call A, B, C, and D. And let's further assume that there are only two alleles for each locus, designated by capital and lower-case letters (eg. A and a). There are therefore three possible genotypes for each gene [two homozygotes (AA, aa) and one heterozygote (Aa)]. With four genes, this gives you 3^4 = 81 possible combinations within the four genes. So you can see that there are a large number of possible genotypes even within such a simplistic example as this.

Now for the good part. Let's say that the most beneficial genotype, the one that maximizes the likelihood of producing the largest number of viable offspring (or other kin) is AABbccDd. But if one has this genotype: AABBccdd, then the result is homosexuality. Here's the kicker: if the first genotype is producing offspring (and presumably plenty), then it is inevitable that the second one will occasionaly arise. It is nothing more than a consequence of independent assortment of the gene alleles. I think that it's quite likely that homosexuality, at least as far as its genetic basis is concerned, is somewhat similar to this.

In theory, the frequency of the alleles will reach an equilibrium such that each has an equal likelihood of producing offspring as the other (this is known as "frequency dependent selection"). For instance, in the above example, 'd' is beneficial only if the frequency of 'D' is high within the population. The higher the frequency of 'd', the less beneficial it becomes. Likewise, 'D' is very beneficial at low frequencies, because those individuals carring it are far more likely to be 'Dd' or have offspring that are. So we would expect equilibrium to be reached at a point where the frequency of 'D' was much higher than 'd', but 'D' would never become fixed. So the outcome is that the 'Dd' genotype will arise with a predictable frequency.

Though I think that something like this is going on with homosexuality, the reality is far more complicated when you add things like the environment in. But this would be a sound example of how something like homosexuality could arise and be maintained through natural selection.

I think that our eventual understanding of the genetic basis of homosexuality (assuming there is one) will include polygenics and dosage effects.

theyeti

RufusAtticus · 01-27-2002, 12:01 PM

When talking about the persistance of homosexulality genes, we should also not forget that being Homosexual does not imply that one does not have children. There are certainly modern instance where homosexuals do have heterosexual relationships for various reasons. Don't forget that in the past, the pressure from your family to get married and have kids was very strong. Both men and women were entered into arranged marriages and had children, despite any desire for the same sex. Homosexuality does not make someone infertile and have a fitness of 0.

This does not even touch on the possibility of group selection or issues with bisexuality.

-RvFvS

theyeti · 01-27-2002, 12:06 PM

Group selection?

Dr Rick · 01-27-2002, 12:22 PM

[QUOTE]Originally posted by theyeti:
<strong>I think that our eventual understanding of the genetic basis of homosexuality (assuming there is one) will include polygenics and dosage effects.</strong>[/QUOTE

Perhaps someday a polygenic and dosage effect will be found to explain foot-fetishisms, terrorism, ice cream flavor preferences, and mutual-fund purchases.

None of these conjectures are currently disprovable, either, but what reason do we have to make them while considering complex human behavours known to be driven by a plethora of conscious, subconscious, and unconscious motives?

The field of psychology has acrued considerable evidence to support the learned aspect of many human behavours; evidence that is sorely lacking in models of human evolutionary behavour. That there are gaps in our understanding of the former does not mean they should just be filled with speculation from the latter.

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01-26-2002, 04:20 PM	#11
Mecha_Dude Veteran Member Join Date: Dec 2001 Location: Everywhere... I'm Watching you... Posts: 1,019	I've wondered about this topic alot, too...

01-26-2002, 06:33 PM	#13
Dr Rick Veteran Member Join Date: Jul 2000 Location: USA Posts: 5,393	You're right to point -out that my post was arrogantly worded; I apologize. While the evidence for the physical evolution of our bodies is overwhelming and straight-forward, attempts to explain human behavour through evolutionary mechanisms is not. The birth order thing offered to explain homosexuality is certainly plausible but incomplete. The theory does not explain why some first born males are homosexuals nor why any females are lesbians. First born males are more likely than their younger siblings to be criminals, successful by typical societal standards, and/or mentally-ill. Lots of behavoural traits appear to be correlated with birth-order; it begs the question to try to explain one on the basis of some evolutionary adaption if a similar mechanism does not explain the others. It seems that one can offer an evolutionary explanation for an individual human behavoural trait, but where evolutionary behavouralists appear to fail is in finding explanations that encompass the amazing variety of human thought and behavour.

01-26-2002, 07:11 PM	#14
Bill Veteran Member Join Date: Dec 2002 Location: Gatorville, Florida Posts: 4,334	One of the reasons that human behavior is so difficult to justify in evolutionary terms is that it isn't really a function *EXCLUSIVELY* of biological evolution, but of some combination of *genetic* and *memetic* evolution. There is no real biological justification for what memetic evolution might produce, although you can probably justify meme replicators as a biological advantage if you were pressed to the wall. Virtually all of the dos and don'ts of human sexual practices are memes. The only thing that counts for biological evolution is the fact that (better than most mammals) humans produce a very diverse set of offspring, particularly in modern times, given our propensity to travel around the world and get laid by local members of the opposite sex. From a biological perspective, I'm sure that homosexuality is counter-productive. But, on the other hand, I'm also certain that its very existence contributes something to human cultural heritage, and thus it would seem to be a meme that will not die. Certainly, it would seem that recorded history has records of homosexual behavior stretching as far back as our records can be reliably trusted (at least 2,500 years ... since homosexual activity is one of the things that made the word "Greek" into a sexual epithet). == Bill

01-26-2002, 07:18 PM	#15
tronvillain Veteran Member Join Date: Oct 2000 Location: Alberta, Canada Posts: 5,658	robchnermd, do those correlations hold even if sibling are raised independently? If they do, it would seem difficult to avoid some kind of biological explanation. Actually, the mechanism I mention above could do a lot to cause the correlations with criminal behavior and success. However, I agree with you that it would only be a partial explanation. [ January 26, 2002: Message edited by: tronvillain ]</p>

01-27-2002, 09:00 AM	#16
MortalWombat Veteran Member Join Date: Apr 2001 Location: St Louis area Posts: 3,458	Here's a hypothetical reason that homosexuality (well, male homosexuality, at least) isn't "weeded out" by evolution: the selective pressure of having males who are really horny outweighs any side effect of male horniness, including a tendency for about 10% of them being horny for other males.

01-27-2002, 12:01 PM	#18
RufusAtticus Veteran Member Join Date: Nov 2001 Location: NCSU Posts: 5,853	When talking about the persistance of homosexulality genes, we should also not forget that being Homosexual does not imply that one does not have children. There are certainly modern instance where homosexuals do have heterosexual relationships for various reasons. Don't forget that in the past, the pressure from your family to get married and have kids was very strong. Both men and women were entered into arranged marriages and had children, despite any desire for the same sex. Homosexuality does not make someone infertile and have a fitness of 0. This does not even touch on the possibility of group selection or issues with bisexuality. -RvFvS

01-27-2002, 12:06 PM	#19
theyeti Veteran Member Join Date: Jun 2001 Location: Denver, CO, USA Posts: 9,747	Group selection?

01-27-2002, 12:22 PM	#20
Dr Rick Veteran Member Join Date: Jul 2000 Location: USA Posts: 5,393	[QUOTE]Originally posted by theyeti: <strong>I think that our eventual understanding of the genetic basis of homosexuality (assuming there is one) will include polygenics and dosage effects.</strong>[/QUOTE Perhaps someday a polygenic and dosage effect will be found to explain foot-fetishisms, terrorism, ice cream flavor preferences, and mutual-fund purchases. None of these conjectures are currently disprovable, either, but what reason do we have to make them while considering complex human behavours known to be driven by a plethora of conscious, subconscious, and unconscious motives? The field of psychology has acrued considerable evidence to support the learned aspect of many human behavours; evidence that is sorely lacking in models of human evolutionary behavour. That there are gaps in our understanding of the former does not mean they should just be filled with speculation from the latter.

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