I have found that nature AND nurture are at work in Homosexuality and, for that matter, heterosexuality, and also all of the sexualities in between in the males and females and the neithers...
SO, Read on, My friends...
(excerpts from the book Genome by Matt Ridley)
I will try not to take too much out of this so that it is easy to follow rapidly. It is, however, heavily pruned, and should be read verbatim for full comprehension. However, the main thoughts are, I think, included.
Quotes from the book follow
Chromosomes X and Y
Conflict
P 108
The X and Y chromosomes are known as the sex chromosomes for the obvious reason that they determine, with almost perfect predestination, the sex of the body. Everybody gets an X chromosome from his or her mother. But if you inherited a Y chromosome from your father, you are a man; if you inherited an X chromosome from your father, you are a woman.
There are rare exceptions
But there are things about the X and Y chromosomes most people do not know, disturbing, strange things that have unsettled the very foundations of biology.
P 109 - 110
On the Y chromosome, genes accumulate that benefit males but are often bad for females; on the X accumulate genes that are good for females and deleterious in males. For instance, there is a new gene called DAX, found on the X chromosome. A few people are born with one X and one Y chromosome, but with two copies of the DAX gene on the X chromosome. The result is, that although such people are genetically males, they develop into normal females.
P115
Rice and Holland come to the disturbing conclusion that that the more social and communicative a species is, the more likely it is to suffer from sexually antagonistic genes, because communication between the sexes provides the medium in which sexually antagonistic genes thrive. The moist social and communicative species on the planet is humankind. Suddenly it begins to make sense why relations between the human sexes are such a minefield, and why men have such vastly different interpretations of what constitutes sexual harassment from women. Sexual relations are not driven by what is good, in evolutionary terms, for men and women, but for their chromosomes.
P 116
Probably one of the most sensational, controversial and hotly disputed genetic discoveries was the announcement by Dean Hamer in 1993 that he had found a gene on the X chromosome that had a powerful influence on sexual orientation, or, as the meia quickly called it, a gay gene. Hamers study was one of several published about the same time all pointing towards the conclusion that homosexuality was biological as opposed to being the consequence of cultural pressure or conscious choice.
P116-117
But however much some of the researchers may have desired a particular outcome, the studies are objective and sound. There is no room for doubt that homosexuality is highly heritable. In one study, for example, among fifty-four gay men who were fraternal twins, there were twelve whose twin was also gay; and among fifty-six gay men who were identical twins, there were twenty-nine whose twin was also gay. Since twins share the same environment, whether they are fraternal or identical, such a result implies that a gene or genes account for about half of the tendency for a man to be gay. A dozen other studies came to the same conclusion.
Intrigued, Dean Hamer decided to seek the genes that were involved. HE and his colleagues interviewed 110 families with gay male members and noticed something unusual. Homosexuality seemed to run in the female line. If a man was gay, the most likely other member of the previous generation to be gay was not his father but his mothers brother.
That immediately suggested to Hamer that the gene might be on the X chromosome, the only set of nuclear genes a man inherits exclusively from his mother. By comparing a set of genetic markers between the gay men and the straight men in his sample, he quickly found a candidate region in Xq28, the tip of the long arm of the chromosome. Gay men shared the same version of the marker seventy-five percent of the time; straight men shared a different version of the marker seventy-five percent of the time. Statistically, that ruled out coincidence with ninety-nine percent confidence. Subsequent results reinforced the effect, and ruled out any connection between the same region and lesbian orientation.
P 118
It is becoming increasingly clear that sexual orientation correlates with birth order. A man with one or more elder brothers is more likely to be gay than a man with no siblings, only younger siblings, or with one or more elder sisters.
P119
The answer probably lies, once more, in the realm of sexual antagonism.
(By this it is meant that the X and the Y gene are in conflict.)
An important clue lies in the fact that that is no such birth-order effect for lesbians, who are randomly distributed within their families. In addition, the number of elder sisters is also irrelevant in predicting male homosexuality. There is something specific to occupying a womb that has already held other males which increases the probability of homosexuality.
Chromosome 11
P161
To seek out the genes that influence personality, it is time to move from the hormones of the body to the chemicals of the mind though the distinction is by no means a hard and fast one. On the short arm of chromosome 11, there lies a gene called D4DR.
P 162
It is the recipe for a protein called a dopamine receptor.
Dopamine is a neurotransmitter.
That is the way the brain works: electrical signals that cause chemical signals that cause electrical signals.
It is misleading to think of the brain as a computer for many reasons, but one of the most obvious reasons is that an electrical switch in a computer is just an electrical switch. A synapse in a brain is an electrical switch embedded in a chemical reactor of great sensitivity.
P164
People with long D4DR genes have low responsiveness to dopamine, so they need to take a more adventurous approach to life to get the same dopamine buzz that short gened people get from simple things. In search of these buzzes they develop novelty seeking personalities.
Among heterosexual men, those with the long D4DR gene are six times more likely to have slept with another man than those with the short genes. Among homosexual men, those with the long genes are five times more likely to have slept with a woman than those with the short genes. In both groups, the long gened people had more sexual partners than the short gened people.
P 165
Hamer claims to explain no more than 4 percent of novelty seeking by reference to this one gene. He estimates that novelty seeking is about forty percent heritable, and that here are about ten equally important genes whose variation matches the variation in personality. That is just one element in personality, but that there are many others, perhaps a dozen. Making the wild assumption that they all involve similar numbers of genes leads to conclusion that there may be 500 genes that vary in tune with human personalities.
Meanwhile, the discovery that personality has a strong genetic component can be used in some very non-genetic therapy. When naturally shy monkeys are fostered to confident monkey mothers, they quickly outgrow their shyness. It is almost certainly the same with people the right kind of parenting can alter an innate personality. Curiously, understanding that it is innate seems to help to cure it.
P 166
One trio of therapists, reading about the new results emerging from genetics, switched from trying to treat their clients shyness to trying to make them content with whatever their innate predispositions were. They found that it worked. The clients felt relieved to be told that their personality was a real, innate part of them and not just a bad habit they had got into.
The parents of a homosexual are generally more accepting when they believe that homosexuality is an immutable part of nature rather than a result of some aspect of their parenting. Far from being a sentence, the realization of innate personality is often a release.
P 167
Dopamine and norepinephrine are so-called monoamines.
Their close cousin, another monoamine, found in the brain is serotonin, which is also a manifestation of personality.
It is remarkably hard to pin down its characteristics.
P 168
serotonin is the chemical that abets, rather than alleviates, anxiety and depression.
Yet all sorts of evidence points in the other direction: that you feel better with more serotonin, not less.
P 169
Are you still with me? You eat cookies on winter evenings to cheer yourself up by raising your brain serotonin.
It is a curious fact that nearly all studies of cholesterol-lowering drugs and diets in ordinary people show an increase in violent death compared with control samples that usually matches the decrease in deaths from heart disease. In all studies put together, cholesterol treatment cut heart attacks by fourteen percent, but raised violent deaths by an even more significant seventy-eight percent. Because violent deaths are rarer than heart attacks, the numerical effect roughly cancels out, but violent deaths can sometimes involve innocent bystanders.
P 170
The link between low cholesterol and violence almost certainly involves serotonin.
Indeed, low serotonin is an accurate predictor of aggressiveness in monkeys, just as it is an accurate predictor of impulsive murder, suicide fighting or arson in humans.
The higher our self-esteem and rank relative to those around you, the higher your serotonin level is.
P 171
Your chances of becoming a criminal are effected by your brain chemistry. But that does not mean, as it usually is assumed to mean, that your behavior is socially immutable. Quite the reverse: your brain chemistry is determined by the social signals to which you are exposed. Biology determines behavior yet is determined by society.
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