Prenatal Determination

Dr. Cynthia Chappell discusses prenatal hormones, hypothalamic activation, and dimorphic characteristics positing that sexual orientation is determined during the 8th through the 16th week of pregnancy.

  • Brain Development
  • Hypothalamus Development
  • Gene Regulation and Signaling Pathways

Dimorphic Characteristics

Dimorphic characteristics that are gender dimorphic, characteristics that differ by gender, have been studied. It was found that characteristics exist where gay males and straight females respond in the same way, while straight males and gay females respond similarly. Hormonal factors during gestation produce variations.

  • Brain Structure
  • Hypothalamus
  • Functional Asymmetries

Role of Prenatal Hormones

Hormone studies have been done that point to the role of prenatal hormones in the determination of sexual orientation.

  • Androgen Insensitivity
  • Congenital Adrenal Hyperplasia

Brain Asymmetry

When looking structural asymmetry of the brain and comparing volumes of left and right hemispheres, men have a slightly larger right hemisphere as compared to their left hemisphere. In women, the hemispheres are the same. The results when looking at gay men and gay females differ from the findings in straight men and women. Gay men have hemispheres that are the same while gay females have a slightly larger right hemisphere. Gay women have the same brain structural asymmetry as straight men. Gay men have the same brain structural asymmetry as straight women.

Functional Connectivity

The functional connectivity in the amygdala of the female and male brains has a different pattern. The gay females mimic that of the males and the gay males mimic that of the females.


The hypothalamus is an area of the brain that has a connection to sexual behavior.  The INAH3 part of the hypothalamus is gender dimorphic.  Studies done in this area have not included gay females but the findings have found that the INAH3 in gay males is like that of straight females.

Dimorphic Study

A particular dimorphic study, P. E. T., was conducted and findings have been consistent in demonstrating how results of homosexual men mimic heterosexual females.  A variety of characteristics were examined and reported.

  • Background and Design
  • P. E. T. Findings
  • Other Functional Asymmetries

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