I was asked by Plook to give some input on the genetic behaviour determination issue. This a very muddy terrain, since most genetic research is done by manipulation, say as controlling mating patterns or knocking down genes on a test subject and that's obviously out of limits with human beings. In the case of humans we must rely on other techniques such as Twin studies (when identical twins are raised separately, because each twin pair member has exactly the same "genetic content" as the other)...
That is not to say there ain't reasoning over the broader issue of genetic determination with the famous Nature-Nurture debate. I have touched on this subject elsewhere, but it is never enough to outline the theory underpinnings:
Phenotype = The manifestation of any given trait: colour of the eye's iris or any anatomical feature, your stature, weight, any specific biochemical characteristic, health predispositions, constitution or a behavioural trait (say pedophile sexual behaviour), psychiatric, emotional capacity and cognition. All the living being's characteristics...
Genotype = The genetic content of each individual. That is to say, the single unique combination of genes that only you posses (when compared at the individual genomic scale - genome means the whole set of genes of an organism), but also what could be understood as genetic states that some of us among the human population can can share in common, differing from other individuals (genetic variation) in one single gene. Example, Some of us are Type O blood, so regarding that genetic locus (=gene) all people who have in common being Type O blood would have the same genotype (at least with simplistic assumptions) at that locus. Genotypes can be modernly accessed through molecular markers such as variations in DNA sequence that we can determine in lab tests.
Environment=The place, specific conditions, constraints, stimulation, stochastic fluctuations and set of events that take place during one's development and life history. For example you could have raised on a very starving nation with poor diet and energy intake throughout childhood, have been committed by a serious parasite that made you ill, you could have been educated in music since you were three, you you could have broken your leg causing one to be shorter that the other and etc... In this case a clear example of environment would be, say, the sexual offender having been exposed to sexual abuse himself during his childhood...
So any phenotype (characteristic) can be understood under the simple conceptual model:
P = G + E + GEWhere, P stands for Phenotype, E stands for Environment and GE stands for the Phenotype x Environment interaction.
What factor, G or E or GE will be determinant, or if they will all have equal shares of influence over one's characteristic often depends and varies widely with the trait under scrutiny. Example: no matter what environment you were raised in, you will always retain your blood type phenotype. I will always be type O no matter if I was raised in the tundra or Managua... Other conditions will be highly sensitive to the environment: if you eat too much you will gain weight eventually, no matter at what rate... Other undergo complex interaction: you might have a genetic predisposition to accumulate fat at a faster rate that the average. Then you eat too much and get fat. This leads to a mild depression that is counteracted with more eating of caloric and endorphin related treats such as chocolate, which eventually leads to more fat, and more depression on a feedback basis.
The geneticist's goal is to unravel the causations of each phenotype trait, which can be complex because many traits of interest can be influenced by many different genes and many different environmental sources of influence.
One important question to be considered is whether any genetic variation can account for the phenotype variation, which means you have to control for the environmental sources of variation. Such systems are yet poorly understood in human beings.
Ultraorthodox Genetic Determinism is part of the agenda of trans-humanism (former eugenicists) and has been under fire lately, because of other layers of complexity, such as gene interaction and epigenetic control of gene expression/function. For instance, genetic test for the allele for the predisposition to breast cancer has been under criticism, because it was often associated with the radical measure of recommending mastectomy (to remove the breast before any tumour can manifest there) and it seems to be later shown that not necessarily having the genotype in question would mean 100% chance of developing disease. The problem is that living being are genetic mosaics of fractal layer complexity and if you screens and select someone for for a particular genetic variation, you are not taking into account all the rest of its genetic composition.
In the case of sexual behaviour both certainly play important determinant roles on shaping one's phenotype (sexual hormones, certain uncover genetic variation, environment conditions, media, accepted/taboos, community, laws, family, history) and so do complex interaction with those G and E variables...
More reading:
http://en.wikipedia.org/wiki/Behavioural_geneticshttp://en.wikipedia.org/wiki/Nature_versus_nurture
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plook wrote:
