What Determines Homosexual Orientation

1
What Determines Homosexual Orientation?

• Huw Goodwin and Louise Vesely

2
Introduction

• News article reporting on new research in
  homosexuality
• Indication of structural differences in
  homosexual rams
• Are these biological differences also present in
  humans?

• Is it genetic or are there social determinants of
  sexual orientation?
• Is sexual orientation the same as sexuality?

Gay Pride
3
The Mind of Gay Sheep

• Roselli et al (2004) The Volume of a Sexually
  Dimorphic Nucleus in the Ovine Medial Preoptic
  Area/Anterior Hypothalamus Varies with Sexual
  Partner Preference
• Ovine Sexually Dimorphic Nucleus (oSDN) 2x as
  large in heterosexual rams as homosexual
• Larger in rams than ewes
• Contains aromatase responsible for converting
  testosterone into estradiol

4
Other Gay Minds?

• Hypothalamus in various animals and humans has
  been implicated
• Sheep oSDN
• Rats SDN-POA (e.g. Bakker Slob, 1997)
• Humans SDN? SCN AC (LeVay, 1991 Swaab
  Hoffman, 1990 Allen Gorski, 1992)
• Cognitive abilities indicative of structural
  differences.

5
The Brain
6
Other Gay Minds?

• Hypothalamus in various animals and humans has
  been implicated
• Sheep oSDN
• Rats SDN-POA (e.g. Bakker Slob, 1997)
• Humans SDN? SCN AC (LeVay, 1991 Swaab
  Hoffman, 1990 Allen Gorski, 1992)
• Cognitive abilities indicative of structural
  differences.

7
The Paradox

• How can homosexuality be maintained if it reduces
  the reproductive fitness of the individual?

8
The Adaptive Problem

• Intra-sex aggression in the Environments of
  Evolutionary Adaptedness (Rahman Wilson, 2003)
• Alliance formation (Trivers, 1985 Muscarella,
  1999, 2000 Kirkpatrick, 2000 Rahman Wilson,
  2003)

9
Other Determinants

• EBE Theory (Bem, 1996)
• Williams et al (2000) bisexual at birth, and
  culture/social factors determining our sexuality
• Sexuality is flexible
• Buchwald (1999) purpose of sex

10
Critique

• Is evolution always for the good of the species?
  (Cosmides Tooby, 1997)
• Lack of definitions
• Identity formation
• Difference between erotic and romantic attraction

11
Conclusions and Thoughts.

• Homosexual orientation is complex
• This complexity lies in the lack of definition in
  such terms as sexual orientation,
  homosexuality, and sexual behaviour
• Multitude of determinants

• Evolution can explain the occurrence of
  homosexual behaviour but can it explain
  homosexuality?
• Is there any utility in the evolutionary
  story-telling?

12
References

• Allen, L.S., Gorski, R.A. (1992). Sexual
  orientation and the size of the anterior
  commissure in the human brain. Proceedings of
  the National Academy of Sciences, 89, 7199-7202.
  
• Bakker Slob, 1997
• Bem, D.J. (1996). Exotic becomes erotic A
  developmental theory of sexual orientation.
  Psychological Review, 103 (2), 320-335.
• Buchwald, A. (1999). Nature, evolution, and
  homosexuality. Retrieved from the web April 10,
  2004. http//www.mirapuri-enterprises.com/Anan
  d/NatHomoE.htm
• Cosmides, L., Tooby, J. (1997). Evolutionary
  psychology A primer. Retrieved from the web
  April 5, 2004. http//www.psych.ucsb.edu/resea
  rch/cep/primer.html

13
References

• Harris, J.R. (1995). Where is the childs
  environment? A group socialisation theory of
  development. Psychological Review, 102, 458-489.
• Kirkpatrick, R.C. (2000). The evolution of human
  homosexual behaviour. Current Anthropology, 41
  (3), 385-413.
• LeVay, S. (1991). A difference in hypothalamic
  structure between heterosexual and homosexual
  men. Science, 253, 1034-1037.
• Miller, E.M. (2000). Homosexuality, birth order
  and evolution Toward an equilibrium
  reproductive economics of homosexuality.
  Archives of Sexual Behaviour, 29 1-34.
• Muscarella, F. (1999). The homoerotic behaviour
  that never evolved. Journal of Homosexuality,
  37, 1-18.

14
References

• Rahman, Q. Wilson, G.D. (2003). Born gay? The
  psychobiology of human sexual orientation.
  Personality and Individual Differences, 34
  1337-1382.
• Roselli, C.E., Larkin, K., Reski, J.A.,
  Stellflug, J.N., Stormshak, F. (2004). The
  volume of a sexually dimorphic nucleus in the
  ovine medial preoptic area/anterior hypothalamus
  varies with sexual partner preference.
  Endocrinology, 145 (2), 478-483.
• Schacter, S., Singer, J.E. (1962). Cognitive,
  social, and physiological determinants of
  emotional state. Psychological Review, 69,
  379-399.
• Swaab, D.F., Hoffman, M.A. (1990). An enlarged
  suprachiasmatic nucleus in homosexual men. Brain
  Research, 537, 141-148.
• Trivers, R.L. (1974). Parent-offspring conflict.
  American Zooligist, 14 249-264.