Evolution and Homosexuality

[pureone]

I knew it was an extra chromosome, I just wasn't sure how to express it.

My question is though, is my point still valid? Could homosexuality be constantly recurring for the same reason that other errors in reproduction constantly occur?

I am more an environment kinda guy (that sexuall orientation is more free will and environment), although if you watch some rodents, they will try to mate with either gender (watch siberian dwarf hamsters). I have never seen any publications that link homosexuality to a gene or protein. I checked PubMed, and I didn't see anything there. If someone can find references to the "gay gene" I would be glad to look at it.
The questions of homosexuality are more in the range of psychology and understanding of humans in general.

 

[lucaspa]

Before writing my question, I want to make it clear that this thread is not the place to argue about the moral implications of homosexuality. There is a place for discussion of that in the S&C forums.

How does evolution explain homosexual orientations. I do not understand because someone born with a homosexual orientation is not a benefit to the species in the sense that the chances of reproduction are so slim. Basically, my point is, if there is a homosexual gene or something of that sort, wouldn't it be recessive, and would it not have been naturally selected against?

Good question. And one, of course, that people have asked. When you have a question like this, your first stop should always be PubMed.

Here's the technical answer. If you don't understand it fully, then be sure to ask:

8: Arch Sex Behav 2000 Feb;29(1):1-34 Homosexuality, birth order, and evolution: toward an equilibrium reproductive economics of homosexuality.Miller EM.Department of Economics and Finance, University of New Orleans, Louisiana 70148,USA. emmef@uno.edu
"The survival of a human predisposition for homosexuality can be explained by sexual orientation being a polygenetic trait that is influenced by a number of genes. During development these shift male brain development in the female direction. Inheritance of several such alleles produces homosexuality. Single alleles make for greater sensitivity, empathy, tender mindedness, and kindness.These traits make heterosexual carriers of the genes better fathers and more attractive mates. There is a balanced polymorphism in which the feminizing effect of these alleles in heterosexuals offsets the adverse effects (onreproductive success) of these alleles' contribution to homosexuality. A similar effect probably occurs for genes that can produce lesbianism in females. The whole system survives because it serves to provide a high degree of variabilityamong the personalities of offspring, providing the genotype with diversification and reducing competition among offspring for the same niches. An allele with a large effect can survive in these circumstances in males, but it is less likely to survive in females. The birth order effect on homosexuality is probably a by-product of a biological mechanism that shifts personalities more in the feminine direction in the later born sons, reducing the probability of these sons engaging in unproductive competition with each other."

Also, one may argue that in past times, when homosexuals were "in the closet" they often married and had children with women to seem socially acceptable. If this cultural reason is the sole reason that homosexuality can be passed on, would you say that now, when homosexuals are in open relationships with each other, the chance of passing along the gene would be lessened, and we could expect to see many homosexuals now, but the more and more they live together and do not procreate, the rarer people will be who are born homosexual?

This is possible. But it doesn't appear to be the sole reason homosexuality has stayed in the population.

Another possibility is called "hitchhiking". This is when a gene is associated closely on the genome with another gene such that when one is passed to the offspring, the second will be also.

It is possible that genes for homosexual orientation are "hitchhiking" to genes that control creativity and artistic expression. As those genes are selected for, the homosexual genes go along for the ride and remain in the population.

 

[lucaspa]

I am more an environment kinda guy (that sexuall orientation is more free will and environment), although if you watch some rodents, they will try to mate with either gender (watch siberian dwarf hamsters). I have never seen any publications that link homosexuality to a gene or protein. I checked PubMed, and I didn't see anything there. If someone can find references to the "gay gene" I would be glad to look at it.
The questions of homosexuality are more in the range of psychology and understanding of humans in general.

Bad search:

1: New Sci 1994 Mar 5;141(1915):9 Gay gene test 'inaccurate and immoral'Holmes B.Publication Types:NewsPMID: 11656352 [PubMed - indexed for MEDLINE]2: Bioethics 1993 Oct;7(5):iii- From the editors.Kuhse H, Singer P.[T]here had been theories that homosexuality might have a genetic basis. In Junethis year, these theories received a somewhat firmer basis. Researchers at theUnited States National Cancer Institute reported new evidence which suggests that some gay men may have a genetic predisposition to homosexuality. The research team led by molecular biologist Dean Hamer tested 40 pairs ofhomosexual brothers and found that 33 of the pairs shared genetic markers on aparticular area of the X chromosome (called Xq28), indicating a link betweenhomosexuality and a gene in that area. If followed-up research were to confirmthe findings, then, it has been claimed, this would be the first example of abehavioral trait that has been found to have a genetic basis. The study does,however, leave some central questions unanswered. Some revolve around the link between genetics and the nature of sexuality itself. The others concern the ethical and social implications of the Sexual behavior mutants revisited: molecular and cellular basis of Drosophila matingresearch....PMID: 11656253 [PubMed - indexed for MEDLINE]

6: Cell Mol Life Sci 1999 Nov 15;56(7-8):634-46 .Yamamoto D, Nakano Y.ERATO Yamamoto Behavior Genes Project, Mitsubishi Kasei Institute of LifeSciences, Machida, Tokyo, Japan. daichan@mn.waseda.ac.jp The study of Drosophila melanogaster by a combination of forward genetics with specific mutants, and reverse genetics, in which a given gene is expressed in an appropriate brain area to test its effect on behavior, provides a unique opportunity to explore the causal relationship between a particular gene, its function in the cell and the behavioral outcome at the organismic level. Enhanced male-to-male courtship has been shown to occur as a result of mutations in several different genes. For example, the Voila mutant exhibits intense GAL4 reporter expression in the tarsal gustatory sensilla, suggesting the importance of tapping by a male on the female abdomen with his forelegs. Feminization of parts of the antennal lobe and mushroom body by targeted expression of afemale-determining gene transformer+ (tra+) drives the male to court other males. Mutations in the tra target gene fruitless (fru), which is expressed inthe antennal lobe as well as the suboesophageal ganglion (the gustatory inputsare processed here), also induce homosexual courtship in males. These resultssuggest that sensory inputs mediated and/or processed by the tarsal receptors,suboesophageal ganglion, antennal lobe and mushroom body contribute to theregulation of male-female courtship. Mosaic analysis localized the neural centerfor male courtship behavior to the posterior dorsal brain, in which the sensoryinformation processed by the aforementioned neural structures may be integrated.Another mosaic study mapped the neural center for female sexual behavior, asmeasured by her receptiveness to copulation, to the anterior dorsal brain. Theissue as to how the mutations that reduce female sexual receptiveness, e.g.dissatisfaction (dsf), spinster (spin) and chaste (cht), affect the structureand/or function of this neural center deserves to be addressed urgently.Publication Types:ReviewReview, TutorialPMID: 11212311 [PubMed - indexed for MEDLINE]

7: J Neurosci 2001 Jan 15;21(2):513-26 Abnormalities of male-specific FRU protein and serotonin expression in the CNSof fruitless mutants in Drosophila.Lee G, Hall JC.Department of Biology, Brandeis University, Waltham, Massachusetts 02454, USA.The fruitless gene in Drosophila produces male-specific protein (FRU(M)) involved in the control of courtship. FRU(M) spatial and temporal patterns were examined in fru mutants that exhibit aberrant male courtship. Chromosome breakpoints at the locus eliminated FRU(M). Homozygous viable mutants exhibited an intriguing array of defects. In fru(1) males, there were absences ofFRU(M)-expressing neuronal clusters or stained cells within certain clusters,reductions of signal intensities in others, and ectopic FRU(M) expression in novel cells. fru(2) males exhibited an overall decrement of FRU(M) expression inall neurons normally expressing the gene. fru(4) and fru(sat) mutants onlyproduced FRU(M) in small numbers of neurons at extremely low levels, and noFRU(M) signals were detected in fru(3) males. This array of abnormalities was inferred to correlate with the varying behavioral defects exhibited by these mutants. Such abnormalities include courtship among males, which has been hypothesized to involve anomalies of serotonin (5-HT) function in the brain.However, double-labeling uncovered no coexpression of FRU(M) and 5-HT in brainneurons. Yet, a newly identified set of sexually dimorphic FRU(M)/5-HT-positive neurons was identified in the abdominal ganglion of adult males. These sexually dimorphic neurons (s-Abg) project toward regions of the abdomen involved in male reproduction. The s-Abg neurons and the proximal extents of their axons were unstained or absent in wild-type females and exhibited subnormal or no 5-HTimmunoreactivity in certain fru-mutant males, indicating that fruitless controls the formation of these cells or 5-HT production in them.PMID: 11160431 [PubMed - indexed for MEDLINE]

8: Arch Sex Behav 2000 Feb;29(1):1-34 Homosexuality, birth order, and evolution: toward an equilibrium reproductive economics of homosexuality.Miller EM.Department of Economics and Finance, University of New Orleans, Louisiana 70148,USA. emmef@uno.edu The survival of a human predisposition for homosexuality can be explained by sexual orientation being a polygenetic trait that is influenced by a number of genes. During development these shift male brain development in the female direction. Inheritance of several such alleles produces homosexuality. Single alleles make for greater sensitivity, empathy, tender mindedness, and kindness.These traits make heterosexual carriers of the genes better fathers and more attractive mates. There is a balanced polymorphism in which the feminizing effect of these alleles in heterosexuals offsets the adverse effects (onreproductive success) of these alleles' contribution to homosexuality. A similar effect probably occurs for genes that can produce lesbianism in females. The whole system survives because it serves to provide a high degree of variabilityamong the personalities of offspring, providing the genotype with diversification and reducing competition among offspring for the same niches. An allele with a large effect can survive in these circumstances in males, but it is less likely to survive in females. The birth order effect on homosexuality is probably a by-product of a biological mechanism that shifts personalities more in the feminine direction in the later born sons, reducing the probability of these sons engaging in unproductive competition with each other.Publication Types:ReviewReview, TutorialPMID: 10763427 [PubMed - indexed for MEDLINE]

9: Behav Genet 1999 Mar;29(2):79-86 A family history study of male sexual orientation using three independentsamples.Bailey JM, Pillard RC, Dawood K, Miller MB, Farrer LA, Trivedi S, Murphy RL.Department of Psychology, Northwestern University, Evanston, Illinois60208-2710, USA. jm-bailey@nwu.edu Available evidence suggests that male homosexuality is both familial and somewhat heritable and that some cases may be caused by an X-linked gene.However, most studies have recruited subjects in a relatively unsystematic manner, typically via advertisements, and hence suffer from the potential methodological flaw of ascertainment bias due to volunteer self-selection. In the present study we assessed the familiality of male homosexuality using two carefully ascertained samples and attempted to replicate findings consistent with X-linkage in three samples. The percentage of siblings of the probandsrated as either homosexual or bisexual, with a high degree of certainty, ranged from 7 to 10% for brothers and 3 to 4% for sisters. These estimates are higher than recent comparable population-based estimates of homosexuality, supporting the importance of familial factors for male homosexuality. Estimates of lambda s for male homosexuality ranged from 3.0 to 4.0. None of the samples showed a significantly greater proportion of maternal than paternal homosexual uncles or homosexual male maternal first cousins. Although our results differed significantly with those of some prior studies, they do not exclude the possibility of moderate X-linkage for male sexual orientation.PMID: 10405456 [PubMed - indexed for MEDLINE]

13: Science 1993 Dec 24;262(5142):2063-5 Comment on:Science. 1993 Jul 16;261(5119):321-7Male sexual orientation and genetic evidence.Risch N, Squires-Wheeler E, Keats BJ.Publication Types:CommentLetterPMID: 8266107 [PubMed - indexed for MEDLINE]14: Nat Genet 1995 Nov;11(3):248-56 Linkage between sexual orientation and chromosome Xq28 in males but not in females.Hu S, Pattatucci AM, Patterson C, Li L, Fulker DW, Cherny SS, Kruglyak L, HamerDH.Laboratory of Biochemistry, National Cancer Institute, National Institutes ofHealth, Bethesda, Maryland 20892, USA.We have extended our analysis of the role of the long arm of the X chromosome(Xq28) in sexual orientation by DNA linkage analyses of two newly ascertainedseries of families that contained either two gay brothers or two lesbian sistersas well as heterosexual siblings. Linkage between the Xq28 markers and sexualorientation was detected for the gay male families but not for the lesbianfamilies or for families that failed to meet defined inclusion criteria for thestudy of sex-linked sexual orientation. Our results corroborate the previously reported linkage between Xq28 and male homosexuality in selected kinships andsuggest that this region contains a locus that influences individual variationsin sexual orientation in men but not in women.PMID: 7581447 [PubMed - indexed for MEDLINE]15: Sci Am 1994 May;270(5):44-9 Evidence for a biological influence in male homosexuality.LeVay S, Hamer DH.Publication Types:ReviewReview, TutorialPMID: 8197444 [PubMed - indexed for MEDLINE]16: Science 1993 Jul 16;261(5119):321-7 Comment in:Science. 1993 Jul 16;261(5119):291-2.Science. 1993 Sep 3;261(5126):1257; discussion 1259.Science. 1993 Sep 3;261(5126):1258-9.A linkage between DNA markers on the X chromosome and male sexual orientation.Hamer DH, Hu S, Magnuson VL, Hu N, Pattatucci AM.Laboratory of Biochemistry, National Cancer Institute, National Institutes ofHealth, Bethesda, MD 20892.The role of genetics in male sexual orientation was investigated by pedigree andlinkage analyses on 114 families of homosexual men. Increased rates of same-sexorientation were found in the maternal uncles and male cousins of thesesubjects, but not in their fathers or paternal relatives, suggesting thepossibility of sex-linked transmission in a portion of the population. DNAlinkage analysis of a selected group of 40 families in which there were two gaybrothers and no indication of nonmaternal transmission revealed a correlationbetween homosexual orientation and the inheritance of polymorphic markers on theX chromosome in approximately 64 percent of the sib-pairs tested. The linkage tomarkers on Xq28, the subtelomeric region of the long arm of the sex chromosome,had a multipoint lod score of 4.0 (P = 10(-5), indicating a statisticalconfidence level of more than 99 percent that at least one subtype of malesexual orientation is genetically influenced.PMID: 8332896 [PubMed - indexed for MEDLINE]

17: J Pers Soc Psychol 2000 Mar;78(3):524-36 Genetic and environmental influences on sexual orientation and its correlates inan Australian twin sample.Bailey JM, Dunne MP, Martin NG.Department of Psychology, Northwestern University, Evanston, Illinois60208-2710, USA. jm-bailey@nwu.eduWe recruited twins systematically from the Australian Twin Registry and assessedtheir sexual orientation and 2 related traits: childhood gender nonconformityand continuous gender identity. Men and women differed in their distributions of sexual orientation, with women more likely to have slight-to-moderate degrees of homosexual attraction, and men more likely to have high degrees of homosexual attraction. Twin concordances for nonheterosexual orientation were lower than in prior studies. Univariate analyses showed that familial factors were important for all traits, but were less successful in distinguishing genetic from shared environmental influences. Only childhood gender nonconformity was significantly heritable for both men and women. Multivariate analyses suggested that the causal architecture differed between men and women, and, for women, provided significant evidence for the importance of genetic factors to the traits'covariation.Publication Types:Twin StudyPMID: 10743878 [PubMed - indexed for MEDLINE]

18: Arch Sex Behav 2000 Apr;29(2):155-63 Familial aspects of male homosexuality.Dawood K, Pillard RC, Horvath C, Revelle W, Bailey JM.Department of Psychology, Northwestern University, Evanston, Illinois60208-2710, USA.Research has generally supported the existence of familial-genetic factors for male sexual orientation, but has not shed much light on the specific nature of those influences. Gay men with gay brothers provide the opportunity to examine several hypotheses. Sixty-six men, representing 37 gay male sibling pairs,completed questionnaires assessing behavior on various measures includingchildhood and adult gender nonconformity, timing of awareness of homosexualfeelings, self-acceptance, and the quality of family relationships. Consistentwith prior findings using twins, gay brothers were similar in their degree ofchildhood gender non-conformity, suggesting that this variable may distinguish etiologically (e.g., genetically) heterogeneous subtypes. The large majority of gay men with brothers knew about their own homosexual feelings before they learned about their brothers' homosexual feelings, suggesting that discovery of brothers' homosexuality is not an important cause of male homosexuality.PMID: 10842723 [PubMed - indexed for MEDLINE]

 

[pureone]

Lucaspa, do they list the specific genes? No, I just looked it up and cannot get the full text.
I was unaware of this work, BTW, but there are many things I am unaware of.
yeah, sometimes I don't know what to put in the window and come up with unrelated things...

 

[fragmentsofdreams]

I don't really know why homosexuality would appear. Bisexuality has obvious perks in that something doesn't need to rely solely on the opposite sex for sexual gratification.

If have heard it suggested that it might be a genetic response to overpopulation. Though I wouldn't have the foggiest how that would work since overpopulation is a concept humans came up with and not really something genes alone could recognize.

If bisexuality was advatageous, it is likely that the genes for bisexuality might cause homosexuality if one person had all of them.

The response to overpopulation is very unlikely. It is only very recently that population pressures have become a real problem. There simply has not been enought time for them to have a significant effect. It also cannot explain homosexuals in the ancient world.

 

[lucaspa]

Lucaspa, do they list the specific genes? No, I just looked it up and cannot get the full text.
I was unaware of this work, BTW, but there are many things I am unaware of.
yeah, sometimes I don't know what to put in the window and come up with unrelated things...

In humans, no. They simply have a linkage to a chromosome. In the fruit flies, they do have a specific gene: the Fru gene. That abstract is in my list.

Try "homosexual, gene" for your search. Be sure to use the "Related Links" button for those papers that look like they cover what you want.

 

[fragmentsofdreams]

It would only be bred out if it was a large disadvantage, but since the human (and other animal species) populations are not seriously hampered by a few homosexuals there is no pressure to remove it.

It is my understanding that homosexuality is too common for a gene to survive without a benefit. A population with five percent of its people not reproducing would be at a disadvantage to a population with everyone reproducing unless that five percent made up for their lack of reproduction in other ways.

 

[fragmentsofdreams]

I knew it was an extra chromosome, I just wasn't sure how to express it.

My question is though, is my point still valid? Could homosexuality be constantly recurring for the same reason that other errors in reproduction constantly occur?

The frequency of homosexuality is too high for it to be entirely the result of random mutation.

 

[revolutio]

If bisexuality was advatageous, it is likely that the genes for bisexuality might cause homosexuality if one person had all of them.

Just to clarify I was referring to advantageous in a purely hedonistic sense not in terms of survival nor reproduction.

 

[Arnold_Philips]

Just to clarify I was referring to advantageous in a purely hedonistic sense not in terms of survival nor reproduction.

What are the advantages to hedonism?

 

[Volos]

Originally posted by : PS 139

Evolution and Homosexuality

How does evolution explain homosexual orientations. I do not understand because someone born with a homosexual orientation is not a benefit to the species in the sense that the chances of reproduction are so slim. Basically, my point is, if there is a homosexual gene or something of that sort, wouldn't it be recessive, and would it not have been naturally selected against?

First it might be good to clarify that sexual orientation is more than a mating or reproducing instinct. Sexual orientation is about more than sex it involves romantic inclination as well as social interactions.



I believe that sexual orientation (and this includes heterosexual, bisexual and homosexual) are complex systems of behavior that while genetically linked are not simply the result of one single gene. Further I believe that homosexuality has a root spiritual cause. Anthropological studies of shamanism in non-technological tribes show that tribes where the spiritual leader (shaman) of the tribe is a position passed on from parent to child ( almost exclusively father to son) these tribes use psychedelics or other mind altering drugs to obtain ecstatic states. However in tribes where Shamans are not passed on in families or are taught these tribes do not use psychedelics or mind altering drugs to obtain similar ecstatic states. In the tribes selecting and training their shamans those selected and able to achieve ecstatic states are homosexuals. It may be the benefit you are not seeing in being gay has to do with the spiritual benefits.



An interesting side note on this topic: The phrase out of the closet refers of course to being public with ones sexual orientation. The word closet has only recently come to mean a tiny room used for the storage of clothes and similar objects. Historically a closet was a room set aside in a household for prayer and meditation.

Also, one may argue that in past times, when homosexuals were "in the closet" they often married and had children with women to seem socially acceptable. If this cultural reason is the sole reason that homosexuality can be passed on, would you say that now, when homosexuals are in open relationships with each other, the chance of passing along the gene would be lessened, and we could expect to see many homosexuals now, but the more and more they live together and do not procreate, the rarer people will be who are born homosexual?

The fact that such genes controlling homosexuality are recessive is pretty obvious. When homosexuals reproduce biologically there children have no more or less chance of being homosexual.

 

[lucaspa]

It is my understanding that homosexuality is too common for a gene to survive without a benefit. A population with five percent of its people not reproducing would be at a disadvantage to a population with everyone reproducing unless that five percent made up for their lack of reproduction in other ways.

Lewis is mistaken. Even alleles that are slightly disadvantageous will be removed by natural selection. Of course, in a large population this takes time if the selection coefficient is small (not very disadvantageous). Therefore we may still be in the period where the alleles are being removed.

However, Fragments, you are correct. Which is why the paper dealt with ways that a supposed deleterious gene would be kept in the population.

 

[lucaspa]

However in tribes where Shamans are not passed on in families or are taught these tribes do not use psychedelics or mind altering drugs to obtain similar ecstatic states. In the tribes selecting and training their shamans those selected and able to achieve ecstatic states are homosexuals. It may be the benefit you are not seeing in being gay has to do with the spiritual benefits.

This is another way to say that the alleles responsible for homosexuality are linked to traits that are beneficial. As you select for the beneficial traits -- the ability to have precognitive visions -- you also inadvertently select for the homosexual alleles.

The fact that such genes controlling homosexuality are recessive is pretty obvious. When homosexuals reproduce biologically there children have no more or less chance of being homosexual.

That turns out not to be true, as the familial studies in homosexuality show. See the list of papers/abstracts I posted.

 

[ReUsAbLePhEoNiX]

What are the advantages to hedonism?

The advantages of Hedonism are well documented in the Bonobo Ape Culture.

Non violent
non agressive
peaceful
female dominated
they even share food with each other!


And boy are they ever hedonistic! There is even a grassroots world peace organization that advocates social change towards the "bonobo Way"! I cannot post link cause it would breaK rules, but here is a info on Bonobo Apes
http://songweaver.com/info/bonobos.html

 

[revolutio]

Well that explains to term wild monkey sex.

I have read this before that frequent sexual release (also castration) severely decreases aggression in males. Also it decreases the chances of testicular cancer. (castration removes the chance obviously) Judging by the female dominance I would say that it also makes the males more submissive.

Really interesting I was surprised out how varied the apes were in their relationships. I knew a few of them having studied great apes a good bit but the part about Gibbons was particularly interesting. Animals usually go either solo or in large groups, the concept of a pair on their own was new to me.

 

[BigBlueHouse]

Here is food for thougtht:

The occurance of homosexuality in the human population could be a meaure in slowing the growth of the species. True, the aim of evolution is to make a species survive, reproduce, and spread, but when the population grows too large and threatens the survival of other species, something must be done. Basically, homosexuals are a form of population control, as are diseases, predetors, etc.

 

[Just]

That doesn't explain why they are still in the population...
The mutations would have to be continually occuring - since they are random this is highly unlikely.
Remember: mutation then change. Not change therefore mutation.

Possibly there are more environmental factors than genetic.

 

[Arnold_Philips]

The advantages of Hedonism are well documented in the Bonobo Ape Culture.

Non violent
non agressive
peaceful
female dominated
they even share food with each other!


And boy are they ever hedonistic! There is even a grassroots world peace organization that advocates social change towards the "bonobo Way"! I cannot post link cause it would breaK rules, but here is a info on Bonobo Apes
http://songweaver.com/info/bonobos.html

Thanks. Just wondering.

 

[Osiris]

Do you guys think that it has anything to do with birth?
I mean, at one point we were all females, but while inside the womb, we are subjected to chemicals which determine what we later become, if we stay females or become males.
Maybe unbalances of these chemicals could result in homosexuality.

Too little, but enough to create a male
or too much, but enough to stay as a female

Do you think these could be one of the many reasons which causes homosexuality?

 

[Data]

Do you guys think that it has anything to do with birth?
I mean, at one point we were all females, but while inside the womb, we are subjected to chemicals which determine what we later become, if we stay females or become males.
Maybe unbalances of these chemicals could result in homosexuality.

Male/Female isn't controlled by chemicals in the womb, but by the chromosomes that you have.

We weren't all female, btw. If you're male, you've always had a Y chromosome, making you male.