Can homosexuality or transsexualism be biologically determined ?

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   This chapter will demonstrate that there are numerous indications of biological determinants of homosexuality and transsexualism.     In humans, genetic differences, brain differences,  endocrinological differences,  and neuropsychological differences have been documented between these two groups and «straight» comparison groups.   All of these will be reviewed in detail in pages that follow.    One problem in concluding from such evidence that homosexuality or transsexualism can be biologically determined is that  you can never argue that biological factors would be sufficient cause  for such upheavals of sexual orientation or identity.   However,  if one were to observe,  say,  a full fledged preferential and durable homosexual relationship in intact animals,  then given that culture as we know it does not exist for them,  we would have an existence proof of biological determination as sufficient  cause.    Such an existence proof has indeed been provided in the scientific research literature for homosexuality.  In a 1976 issue of the juornal Archives of Sexual Behavior Erwin and Maple described a relationship in Rhesus monkeys in which the two males prefered each other for sexual contact over a sexually receptive unfamiliar female.

Sexual genotypic and phenotypic configurations.   The way I see it,  there are two fundamental aspects of human sexuality,  sexual orientation (the object of one's sexual desire) and sexual identity (whether a person subjectively feels like a man or like a woman). Nature delivers us,  the vast majority of times,  encased in a clearly male-looking or female-looking body.   The various forms of apparent hermaphroditism are the exception.   Our sexual appearance, feelings, desires and behavior are phenotypical,  they are the manifestations of things largely determined by our genes (genotype).  Of course, not all inflections of inner life and behavior are direct emanations of our genes.   However, as I shall explain,  the big picture (our basic sexual orientation and sexual identity)  certainly is determined,  to a very large extent, by details of brain anatomy and brain physiology.  Most of this brain anatomy and physiology is directly determined by our genes, and most of the balance is greatly determined by congenital factors (not necessarily hereditary, but nevertheless biological and present at birth:  trisomy-21 or Down’s syndrome is a congenital non-hereditary condition consisting of an accident of meiosis occurring before birth).  Of course,  extremely disfavorable environmental conditions (maternal alcoholism or malnutrition) can play a part in congenital defects.  However,  curiously,  even though there is a much greater heterogeneity of psychosexual configurations in genotypic males,  the details of phenotypic expression are under tighter genetic and/or congenital control in males than in females of the human species.  In other words, atypical sexual orientation or identity  in genotypic females is relatively more influenced by life experience, i.e., by culture, and relatively less by nature.  The typical sexual configuration is that the XY individual is, by definition, a genotypic male,  feels like a male, and is sexually attracted to females.  Likewise,  the typical XX individual is by definition a genotypic female,  feels like a female, and is attracted to males.  You knew that !  Let’s review the neuropsychology of variations of this basic normal configuration.