Research Article

Sexually Antagonistic Selection in Human Male Homosexuality

  • Andrea Camperio Ciani mail,

    Affiliation: Dipartimento di Psicologia Generale, Università di Padova, Padova, Italy

  • Paolo Cermelli,

    Affiliation: Dipartimento di Matematica, Università di Torino, Torino, Italy

  • Giovanni Zanzotto

    Affiliation: Dipartimento di Metodi e Modelli Matematici per le Scienze Applicate, Università di Padova, Padova, Italy

  • Published: June 18, 2008
  • DOI: 10.1371/journal.pone.0002282

Reader Comments (4)

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Have you considered the possibility of multiple causes for male homosexuality?

Posted by avatar on 16 Aug 2008 at 18:09 GMT

First of all, I must congratulate you by the approach that you gave to the model and, previously, to the empirical study (2004).

Almost all the studies realised on this subject using interviews and questionnaires to separate the participants in two categories (" homo" and " hetero") suffer from a fundamental failure: the bias towards the "hetero" group due to homofobia more or less explicit that still exists in many societies.

The fact to choose a group of recognized homosexuals and to compare it with a representative sample of the general population gives a greater quality to the conclusions of the work.

Recently (June, 2008), a Swedish study has been published that shows a correlation between the structure of the brain and certain basic characteristics of behavior, among others, sexual orientation (1).

If we consider other previous studies of cerebral morphology, realised on human beings and animals (Simon LeVay (2) and Kay Larkin (3)), which point at significant differences in the hypothalamus between homosexual and heterosexual individuals, it seems that the hypothesis of a biological cause for homosexuality takes increasing force.

Still more, it seems that one of the places of the brain in which, in some way, sexual orientation resides, is the hypothalamus.

Nevertheless, the origin of these differences in the brain could be tracked back to several factors, not all strictly genetic, just as not all headaches have the same cause.

I will mention a few:

- Several parts of the brain are developed during the gestation and are, in some way, influenced by the hormonal "atmosphere" within the maternal uterus. Are these hormonal levels defined by the maternal genetics? In this case, the genetics of the son could not give any clue of what has happened really.

- Several syndroms related to the form in which the organism methabolizes androgens are known (4). Some homosexual men are effeminate, while others are not. Has homosexuality in both cases the same origin?

- Nowadays, it is well known that all the fetuses of mammals are, during the first weeks of gestation, female. Their hormonal system is the maternal one. Only from the fourth month (in the human species), the masculine fetus starts a complex process of "differentiation" , composed of several stages, that finally transforms him into an individual of masculine sex. It is obvious that, during that process, many things can leave unexpected results and give rise to the known different inter-sexual stages, of which masculine homosexuality is perhaps one (a very "soft" case of inter-sexuality).

- Finally, I would like to mention a phenomenon that is being proposed as an explanation for some cases of masculine homosexuality (Sven Bocklandt, (6)). In words of the article that I mention

"Normally in each cell of a female body one of the two X chromosomes has been deactivated by the placement of methyl groups (a carbon and 3 hydrogens) along the backbone of the DNA double helix. That deactivation is random. "

"Suppose there are two X chromosomes in a woman called A and B where the A chromosome came from her mother and the B chromosome came from her father. In approximately half of the cells the A's will be deactivated and in the other half of the cells the B's will be deactivated. "

"Well, in women who have gay sons the deactivation of the X chromosomes is skewed with one of the X's more often deactivated than the other."

"But when Sven Bocklandt of the University of California, Los Angeles, compared blood and saliva samples from 97 mothers of gay men with samples from 103 mothers without gay children he found this process was extremely skewed in the mothers with gay sons, with one X chromosome being far more likely to be inactivated than the other."

"Only 4% of the mothers without gay sons showed this skewing, compared with 14% of mothers with at least one gay son. Among mothers with two or more gay sons, the figure was 23%."

"This result suggests that eventually any woman will be able to have a genetic test done what will predict the odds that one of her sons will be born homosexual."

Has this "overactive" "X" chromosome any role in male homosexuality ?

Is there a kind of "compeition" among some genes in the "X" chromosome ?

Have you thought about putting in correlation masculine or feminine homosexuality and other physical or psychological characteristic of the opposite gender?

As you can see, the proposed models are still far from picking up all the possibilities.

(1) http://www.sciencedaily.c...





(6) http://www.futurepundit.c...

RE: Have you considered the possibility of multiple causes for male homosexuality?

k24anson replied to avatar on 21 Aug 2008 at 13:03 GMT

The overall tone of this and most every article of the "origin of homosexuality" is thoughts determine what behaviour will occur.

— "This result suggests that eventually any woman will be able to have a genetic test done what will predict the odds that one of her sons will be born homosexual."

Born homosexual? The bias to this conclusion causes me to become critical of the author's conclusions for any of the facts presented.

I can't argue with the jarble of facts, so I'll try this train of thought to bring my point across:

In an environment where the subject, a mother's effeminate son who meets all the criteria of being "born homosexual," said person is observed by Alexander the Great as they travel through Kashmir, twenty centuries ago any male, any mother's son would probably succumb to the advances of the Great Alexander, for the status and the quality of life this would bring said subject while toyed with by Alexander as they travel from one campaign to the next. Simply for the better quality of life this person succumbs and engages in homosexual behavior.

Consider this same type of mother's effiminate son who meets all the criteria of being "born homosexual" inside today's world, and Dad is concerned about the effiminate manner of his fifteen year old. A heart-to-heart, father-son discussion occurs along the following lines:

"Son, little girls grow into psychologically, sexually healthy women because of things called androgens. These androgens are mild hallucinogens that make girls like the idea of having some foreign thing inserted into their bodies. All biologcial brains of all animals will naturally be repulsed and attempt to resist penetration of their bodies, and these androgens inside females make their brains accept the behavior of others who will then penetrate their bodies. Well son, guys act like girls sexually because they have an inordinate amount of these girly androgen molecules trickling in their bloodstream. Some of these men like to "play" with these mildly hallucinogenic molecules. Girly type of thoughts are generated inside the minds of these guys because a few of these hallucinogenic molecules happen to be trickling through the bloodstream at the moment. And instead of empathy for the female, guys instead will adopt these thoughts as part of their own identity. They'll begin to act like girls sexually."

"Son, stay focused and be strong. Chart a course for a brave new world, a better world and life for yourself and others. Not many have travelled this road. And it is kind of fun to feel like a female feels every so often. Don't worry about it so much whem it happens. You can always and at anytime go safely insane inside your mind. No one really gets hurt there."

"Dad, have you ever gone safely insane inside your mind?"

Dad lets out a hearty chuckle. "Oh, you bet. Many, many times. It's no big deal. It's fun, in fact ... sometimes. Not at first though. Kind of scary when, as a teenager it first started happening. After five, ten years I found a way to laugh at it all though."

"Son, think your Moms is pretty?"

Son looks up and nods his head. "She must've been really pretty when you first met her, Dad."

"She's a treasure. Quality, your mother has good genes. A feast for my eyes, every single day. I'm proud to have her. ... and there's a reason why I couldn't settle for just anyone to have around with me for the rest of my life. The word is quality, and the definition of that word is something you have to find for yourself. My mere words don't have the umphf ..., but your Moms is mine, all mine. Not yours or anyone elses. And she's quite happy this way."