Thomas Library

Honors Thesis Archive

Author Beatrice Nichols
Title Sexual Orientation in Adult Females Not Linked to Second to Fourth Digit Length Ratios, Average Whole Brain Area or Average Cortical Area
Department Biology
Advisors Cathy Pederson, Matthew Collier, and Elizabeth George
Year 2014
Honors University Honors
Full Text View Thesis (1423 KB) Note: This is a very large file; it may be easier to download the file to your computer and open it from there.
Abstract Prenatal androgen exposure, which is believed to have significant effects on human behavior and cognition by affecting brain development, has recently been linked to the second to fourth finger length or digit ratios, which develop in utero. There is growing evidence that the second to fourth digit ratio shows correlations with sexual orientation, with recent research focusing on how these may be associated with other sexual dimorphisms, such as brain morphology. The present study examines the second to fourth digit ratios from the left and right hands of right-handed adult female participants (N=36, mean age 27±6 years) of heterosexual (n=21) or homosexual (n=15) orientations, along with analyzing MRIs to assess their average whole brain and cortical areas. No statistically significant differences were found between heterosexual and homosexual groups for the measured variables of second to fourth digit ratios (average, right hand, and left hand), average whole brain area, and average cortical area (p>0.05), excepting for the expected morphological relationship between average whole brain and cortical areas (p=0.038). These results are in contrast with the majority of evidence, which indicate a relationship between prenatal androgen exposure and sexual orientation through second to fourth digit ratios. Additionally, the absence of a connection between average whole brain area with sexual orientation is inconsistent with other preliminary results; however, another scientific analysis that used measurements similar to average cortical area did not find a relationship with second to fourth digit ratios. This lack of correlation based on collected data may have been due to the limitations of this study, such as the small sample size. The conflicting results of this study with current evidence suggest that further research is needed to understand the effects of prenatal androgen exposure on the second to fourth digit length ratios and on average whole brain or cortical areas in females of differing sexual orientations.

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