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Evaluate the evidence for prenatal hormonal influences on the development of sexual orientation in humans.

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Evaluate the evidence for prenatal hormonal influences on the development of sexual orientation in humans. Although the nature-nurture debate is still a topic of popular conversation, in scientific circles it is considered largely irrelevant. As William Byne (1994, p.50) notes: "All psychological phenomenon is ultimately biological". However, of all the aspects of human behaviour that have been scrutinised by psychology, it would seem that objective study of the possible causes of the existence of human homosexuality has been left to last. Consequently, what few explanations exist are badly integrated and what supporting experimental work there is on humans has rarely been replicated. This essay will examine the evidence for one such theory - that of prenatal hormonal influences on the development of sexual orientation - and also attempt to integrate the theory in with other biological theories of homosexuality. Although explanations of biological mechanisms will be confined to a simple level, it is still necessary to include the following: firstly, a short description of sexual dimorphism; secondly, a look at the effect of androgens generally; then more specifically the effect of prenatal hormones on sexual orientation, followed finally by the relevance of heritability of homosexuality. A discussion about the biological origins of homosexuality would not be necessary if it were not for the fact that humans are sexually dimorphic and generally speaking are attracted to the opposite sex. ...read more.


Although Gorski had not in fact made a connection between his rat studies on sexual dimorphism and sexual orientation, as shall be seen next his work has been used to this end and therefore the previous methodological criticisms remain valid. Gorski and Allen (in LeVey & Hamer, 1994) also found that a cell group called INAH3 was sexually dimorphic and that it differed within sex as well as between sex. LeVay (1991 in LeVay & Hamer, 1994) extended this finding to show that specifically there was a difference in size of the INAH3 structure between straight and gay men. As has been noted however (Byne, 1994; Christiansen, 2001; Pinel, 2000), it is very difficult to establish a causal relationship between hormones (especially prenatal action) and behaviour in humans because levels cannot be manipulated and human behaviour is far more complicated than in animals. Indeed it may be that being homosexual actually causes small changed in the size of the INAH3 region, or there may be a third variable. It can be said therefore that there is very weak evidence for implicating sexual dimorphism in sexual orientation. LeVay and Hamer (1994) nevertheless suggest that this may be relevant to a prenatal influence on sexual orientation in the following way. If, as it has been found, the "sexually dimorphic cell group in the medial preoptic area appears plastic in its response to androgens during early brain development but then is largely resistant to change" (p.47), then the size of INAH3 in men may in fact influence sexual orientation. ...read more.


What they suggest however is that a gene may exist that "sway" rather than determine homosexuality. The evidence (through traditional methods of twin and family studies) is relatively strong for some sort of heritability for homosexuality: the concordance rate for male twins is 57% (pooled data, in LeVay & Hamer, 1994). Attempts to find the gene which predisposes people to homosexuality have yielded mixed and unconvincing results. Initially a region was found that correlated with homosexuality but this has not been replicated (Hamer et al, 1993 in LeVay & Hamer, 1994). LeVay and Hamer also point out that it is not know how quantitatively important that region might be in influencing sexual orientation. Looking at genes for androgen receptors and INAH3 has found no significant correlations for the former and mapping has not found any relationship yet for the latter (LeVay & Hamer, 1994). As William Byne (1994, p.50) noted in an introduction to a challenge on biological studies of sexual orientation: "The salient question about biology and sexual orientation is not whether biology is involved but how it is involved." Sexual dimorphism has been well supported by experimental evidence. The mechanisms of androgens have also been well supported by evidence from non-human experiments. The link between prenatal androgenisation and homosexuality has not been proved and although some intuitively appealing hypotheses exist it is possible that they will remain very difficult to confirm simply because hormone levels cannot be manipulated and even if they could it is still not known to what extent social and cultural factors play in sexual orientation. ...read more.

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