Biological

Introduction

Those who maintain that most gender specific behaviours are prescribed by biology advocate the position that gender identity is irrevocably determined by genetics or by hormonal fluctuations during foetal development.

Whilst there is data to suggest that inherited genetic factors may increase the probability of many borderline personality dynamics, genetic experiments{1} have so far failed to identify any evidence of a genetic explanation for transsexualism{2} and there is no evidence to date that endocrinological factors feature among the causes of gender dysphoria{3}.

Many in the transgendered community go on about a study of the size of a part of the brain called the "Bed nuclei of the Stria Terminalis"{4} and a subsequent study on the same brain samples{5} which produced evidence of the size of the BSTc being concurrent with gender identity{6}. A neurobiological route has yet to be discovered{7}, however, and whilst studies of other psychological disorders have suggested a link between structural changes to the brain and certain kinds of behavior, trauma or early abuse, it is more likely that the above differences are due to hormonally influenced apoptosis occurring later in life.

The possibility of other organic causes have been proposed, such as early encephalitic infections or brain injuries at birth, but no evidence along such lines has as yet been found. A biological cause for transsexuality has been sought for many years but to date no definite data have emerged{8} and there is no conclusive scientific evidence to support the position that transsexualism is anything other than a psychological disorder{9}.

Evolution

Evolutional theory

Evolutionary theory once proposed to the world at large a theoretical perspective of the development of gender identity that provided an explanation for the lack of intellectual pursuits amongst women. Because they have a slightly smaller brain size, they were considered lower on the evolutionary scale than men and thus less intellectual. Also because there was the notion of innateness of behaviour and instincts in early psychology, it was thought that maternal nurturing behaviour, which is shared with other animals indicated that women’s’ higher functions had not evolved as much as men’s’. In the mid 1920’s, however, thinking changed when psychologists started to believe that human behaviour is learned.

Genetic

Genetic influences

There is no evidence for a genetic explanation for transsexualism. Rates of genetic abnormalities occur in the transsexual population with about the same frequency as the general population. (Walters, 1986)

Hormonal

Hormonal influences

Sex hormones are known to affect central nervous system development and neural activity in many species. Gadpaille (1975), amongst others found male babies to be more irritable, active, cry more and to be less timid. (Arndt, 1991) It has been found that androgen causes in animals and to a certain extent humans male-typical sex behaviour, increased activity, increased aggression and reduced maternal behaviour. (Berk, 1991) Money and Ehrhardt (1972) and Ehrhardt and Baker (1974) discovered more masculine characteristics than average in a girl who had been pre-natally androgynized. (Berk, 1991) A similar phenomenon be seen in a study by Reinisch and Karrow in 1972 who investigated the boys of diabetic mothers who were given estrogen and progesterone to prevent pregnancy complications. These boys although being less aggressive, assertive and athletic still had a male gender identity. Contradictions, to these findings have been found, however. Kester in 1984 studied boys whose mothers similarly had taken female hormones while their sons were in utero. It was found in this case that there was little difference in the displays of male-sex typed behaviour. (Arndt, 1991)

Dorner in a study in 1976 found some transsexuals to have raised levels of Lutenizing Hormone and Follicle Stimulating Hormone as well as low Free Plasma Testosterone (Howells (Ed)), 1984 which reflects findings of low plasma testosterone and sperm counts in homosexual men{10}. However the search for abnormal levels of circulating androgens has for the most part, yielded negative{11}. In most investigations there is no evidence of lowered testosterone or higher levels of estrogen as a function of degree of femininity{12}.

Physiological make-up of the brain

Many researchers believe there are structural differences in the brain, resulting from hormone action, which affect males’ and females’ thinking. Experiments have found that male rats are better able to run mazes, a task that requires spatial orientation. Beatty (1979) found that female rats exposed to male hormones at a critical pre-natal period or just after birth, were able to run mazes as well as male rats. (Dworetzsky, 1982) This theory would explain why men tend to be better or more interested in geometric maths or engineering and have superior spatial skills. When evaluating human behaviour, however, social conditioning must be taken into account. The tendency for males to have ‘superior spatial skills’ , for example, is also the result of environmental factors.

Androgens

In the foetus, ‘femaleness’ develops in the absence of a Y chromosome as the ‘default’ mode. For the first few weeks the foetus appears sexless; it has vestigal ducts and a genital tubercle which could develop as either sex. At about six weeks, if there are XY chromosomes the gonads turn into testes which produce androgens; mainly testosterone, and the foetal body is masculinized. Tissue then arranges itself into the male genitalia. At about 4-7 months pre-natal male sex hormones influence the hypothalamic region. Shortly after birth the testes stop secreting androgens but are re-aroused at puberty and initiate the development of secondary sex characteristics, such as lowering of the voice and beard growth. ( Moir and Jessel, 1989)

Gonadotrophin

Neurotransmitters influence the hypothalamus to secrete a Gonadotrophin release hormone which commands the pituitary to secrete Gonadotrophins. Sex hormones exert either a male inhibitory or female stimulatory influence on the secretion and this sex difference is a feature of sex differentiation. Dr. Dorner suggests that there is a Closed Loop Endocrine System otherwise known as the Neuroendocrinal Loop where changes in the external and internal environment effect neurotransmitter metabolism and vice versa. (Howells (Ed), 1984:) Rose, Holady and Berstein in 1976 supported this theory showing animals who showed evidence of environmental stress and social dominance increased their androgen production. (Berk, 1991)

5-ARD

Those who argue that the differences in gender behaviour are physiological in origin suggest their hypothesis is supported by the results of Julienne Imperator-McGinley's 1979 investigation of Dominican Republic children with 5-Alpha- Reductase Deficiency Syndrome{13}. These boys had a deficiency of the enzyme that converts Testosterone into Dihydrotestosterone during the period of foetal differentiation. Dihydrotestosterone governs organ development, prostate growth, facial hair growth and hair recession. Even though the presence of testosterone had created a male internal structure, apparent lack of male genitals lead the boys to be raised as girls. At puberty, however the action of testosterone caused the testicles to drop and the penis to grow as well as voice change, and muscle mass growth. These boys who had been named ‘the penis children' changed genders and took on the male sex role. (Dworetsky, 1982)

It has been suggested that the gender change was due to the action of androgen which over-rode female learning and that physical appearance and the actions of hormones will determine gender identity. Interestingly other studies have shown conflicting results. (Howells, 1994)

In-Utero

In-Utero influences

Some suggest that the cause of Gender Identity Disorder is due to levels of hormones present in-utero which are undetectable in adulthood, and current interest is in the pre-natal influence of H-Y antigen since it is thought that this antigen may somehow affect the sexual centre in the hypothalamus. (Arndt,1991). There are conflicting results in the studies of possible abnormalities in the Hypothalamus-Pituitary Neuroendocrine function. To present there has been no conclusive evidence{14} for the Pre-natal Hormone Hypothesis{15}. There is in fact much more direct evidence which disproves the pre-natal hormone theories of Gender Dysphoria. (Walters, 1986)