NatureÕs Choice:
What Science Reveals About the Biological Origins of Sexual Orientation.

Cheryl L. Weill, Ph.D., MSW

About the Presentation:

Definition: sexual orientation - the direction of sexual feelings or behavior toward the same sex (homosexual), opposite sex (heterosexual), or some combination of the two (bisexual). Alternatively: affectional orientation.

Homosexuality is not a mental disorder. In 1973 the American Psychiatric Association removed homosexuality from its official Diagnostic and Statistical Manual signifying the end to its official classification as a disease.
Homosexuality is not pedophilia. The sexual desire of pedophiles is directed towards children and can have a heterosexual, homosexual, or bisexual orientation.
There is no evidence that childhood sexual abuse alters sexual orientation.

Neurohormonal-Gestational theory: Put forward in ÒNeurohormonal Functioning and Sexual Orientation: A Theory of Homosexuality-Heterosexuality,Ó Ellis, L. and Ames, M.A. Psychological Bulletin, 101:233-258 (1987). Sexual orientation in all mammals is primarily determined by the degree to which the nervous system is exposed to testosterone and certain other sex hormones during gestation.
Predictions of theory:
a. Homosexuals should have higher frequencies of other sex-typical behaviors normally associated with the opposite sex.
b. Relationships between parents and homosexual offspring often may be strained and/or assume some cross-sex characteristics.
c. Homosexuality should reflect a significant degree of hereditability.
d. Average neurohormonal differences should exist between homosexuals and heterosexuals in both sexes at comparable ages.
e. Attempts to alter sexual orientation after birth should be minimally effective.
f. Homosexuality should be primarily a male phenomenon.

Sexual development occurs both morphologically and neurologically.
Morphological development: In the absence of any hormonal influence, genetically male and female fetuses will develop morphologically as female. Male sexual development requires testosterone and its derivatives dihydrotestosterone and estrogen. Female sexual development can occur in either the presence or absence of estrogen. The sex hormones that operate during development are produced in the fetus, by either the testes or ovaries and the adrenal glands.
Neurological development: Sexual orientation is associated with the establishment of permanent differences in the hypothalamic and limbic areas of the brain. Sex-typical behavior patterns are associated with changes in diverse areas of the brain and extensively involving the cortex.

Animal studies, primarily of rats or primates, demonstrate that neurological development, as assessed behaviorally, can be inverted by altering the availability of testosterone during a critical period. Elimination of circulating testosterone in males during the critical period results in reduced male-typical behavior and display of female-typical behavior. Similarly, increasing the availability of testosterone to developing females results in reduced female-typical behavior and display of male-typical behavior. The same manipulations carried out after the critical period do not affect the normal development and expression of sex-typical behavior in either males or females.
These and additional observations suggest that testosterone masculinizes selected areas of the brain and de-feminizes other areas to provide for male-typical behavior.
Observations of normal animals demonstrate that sex-typical behavior correlates with the circulating levels of testosterone during gestation.
The human conditions, androgen insensitivity, 5-alpha-reductase deficiency, congenital-adrenal-hyperplasia, and TurnerÕs syndrome support the conclusion that sex-typical behavior correlates with the circulating levels of testosterone during gestation.
The area of the brain known to be sexually dimorphic from animal and human studies is the hypothalamus.

New anatomical data:
1. Swaab, D.F. and Hofman, M.A. An enlarged suprachiasmatic nucleus in homosexual men. Brain Res. 537: 141-148 (1990).
2. LeVay S. A difference in hypothalamic structure between heterosexual and homosexual men. Science 253: 1034-1037 (1991).
3. Allen, L.S. and Gorski, R.A. Sexual orientation and the size of the anterior commissure in the human brain. Proc. Natl. Acad. Sci. USA 89: 7199-7202 (1992).

New genetic data:
1. Bailey, J.M. and Pillard, R.C. A genetic study of male sexual orientation. Arch. Gen. Psychiatry 48: 1089-1096 (1991).
2. Bailey, J.M., Pillard, R.C., Neale, M.C., and Agyei, Y. Hertitable factors influence sexual orientation in women. Arch. Gen. Psychiatry 50: 217-223 (1993).
3. Hamer, D.H., Hu., S., Magnuson, V.L., Hu, N., and Pattatucci, A.M.L. A linkage between DNA markers on the X chromosome and male sexual orientation. Science 261: 321-327 (1993).

The new genetic data do not at this time unequivocally support the idea that there is a gay gene. These data need to be replicated on a 10-fold larger population. It is still unlikely that there is a single gene that codes for a complex behavior like sexual orientation or sex-typical behavior. It seems more likely, that unlike eye color, which is associated with a single gene, sexual orientation results from a subset of traits, associated with a number of genes and gestational environmental factors, that together give rise to a complex behavior.

Conclusion: Homosexuality is naturally determined through normal developmental processes and represents one end of a continuous spectrum of accessible sexual behaviors.

Further reading:
1. Brain Sex, Anne Moir & David Jessel, Dell Publishing, New York, NY, 1991.
2. Discover (magazine) Vol. 3, Number 6, June 1992.
3. The Sexual Brain, Simon LeVay, MIT Press, Cambridge, MA, 1993.
4. The Science of Desire, Dean Hamer & Peter Copeland, Simon and Schuster, NY, 1994.
5. Sex on the Brain, Deborah Blum, Penguin Putnam, Inc., NY, 1997.

Contact: [email protected]; 303-442-8242.
5/02

About the Presenter:

CHERYL LYNN WEILL

Curriculum Vitae

CURRENT:

I retired from Louisiana State University Medical Center in January of 2000 and have completed the masters program in the Graduate School of Social Work at the University of Denver. I received a MSW degree in June 2001. I am a Licensed Social Worker and am working as a psychotherapist. I also write, and lecture on the biological origins of human sexual orientation My long-term goal is to be a Licensed Clinical Social Worker providing psychotherapy primarily to adult survivors of childhood incest, abuse, and trauma.

EDUCATION AND RESEARCH EXPERIENCE:

1. Undergraduate research under the direction of Dr. Henry Rapoport, Department of Chemistry, University of California, Berkeley, CA. Summer 1969.
2. B.S., Chemistry, University of California, Berkeley, CA. June 1969.
3. Cold Spring Harbor course in Neurobiology, June 1973.
4. Ph.D., Organic Chemistry, University of California, Santa Barbara, CA. June 1974. Doctoral research under the direction of Dr. Daniel V. Santi.
5. Woods Hole Marine Biology Laboratory course in Neurobiology, summer, 1976.
6. Molecular Endocrinology and Techniques for Hormone Action Workshop, Department of Cell Biology, Baylor College of Medicine, February 1986.
7. Sabbatical leave, supported by an NSF fellowship, in the laboratory of Dr. Noboru Sueoka, Department of MCD Biology, University of Colorado, Boulder. Cloning of a mammalian homolog of the C. elegans programmed cell death gene, ced 4.
8. MSW, University of Denver, Denver, CO. June 2001.

HONORS:

1. National Science Foundation undergraduate summer research grant, 1969.
2. Muscular Dystrophy Association research fellowship, 7/77-7/79.
3. National Science Foundation Visiting Professorship for Women, 7/89-6/90.
4. National Research Service Award, National Institutes of Health, NS08731, 7/89, declined.

POSITIONS:

1. Research Assistant, Department of Chemistry, University of California, Santa Barbara, CA, 9/69-2/74.
2. Staff Assistant, Department of Neurology, Columbia University, College of Physicians and Surgeons, New York, NY, 2/74-6/76.
3. Research Fellow, Department of Pharmacology, Harvard Medical School, Boston, MA, 7/76-7/79.
4. Assistant Professor, Department of Neurology, Louisiana State University Medical Center, New Orleans, LA, 8/79-7/86.
5. Assistant Professor, Joint Appointment, Department of Anatomy, Louisiana State University Medical Center, New Orleans, LA, 6/81-7/86.
6. Associate Professor, Departments of Neurology and Anatomy, Louisiana State University Medical Center, New Orleans, LA, 7/86 to 2/00.
7. Visiting Associate Professor, Department of MCD Biology, University of Colorado, Boulder, CO, 7/89-4/91.
8. Retired from Louisiana State University Medical Center February 1, 2000.

MEMBERSHIPS:

1. National Science Foundation Advisory Panel for Cellular Neuroscience 4/91 to 11/92.

PROFESSIONAL AFFILIATIONS:

Current: Colorado Association of Clinical Social Workers 5/00.

PUBLICATIONS: Twenty-nine peer-reviewed research-papers and book chapters published.

ABSTRACTS: Twenty-two research-abstracts published.

FUNDING: Twelve research-grants funded for a total of $787,834.

SEMINARS: Twenty research-seminars given.

TEACHING: Sixteen research-based graduate courses taught.

THESES AND DISSERTATIONS: Directed one masters thesis and was a dissertation committee member for five Ph.D. students.

PRESENTATIONS:

ÒNatureÕs Choice: What Science Reveals About the Origins of Sexual OrientationÓ

PFLAG chapter meeting, New Orleans, LA 8/93.
PFLAG National Convention, New Orleans, LA 9/93.
Tulane University Medical School, Introduction to Clinical Medicine, New Orleans, LA 10/93.
ÒHealing the Hurt: Conference on Homophobia,Ó Houston, TX 3/94.
University of Houston, Gay and Lesbian Students Association, Houston, TX 3/94.
ÒCelebration,Ó Louisiana Gay and Lesbian Association, New Orleans, LA 6/94.
Tulane University Medical School, Introduction to Clinical Medicine, New Orleans, LA 10/94.
Gay and Lesbian Taskforce/PFLAG, Little Rock AR, 2/95.
Grand Rounds, Dept. of Psychiatry, University of Arkansas Medical School, Little Rock, AR 2/95.
Louisiana State University Medical School, Social Issues in Medicine, New Orleans, LA 3/95.
ÒHealing the Hurt: Conference on Homophobia,Ó Houston, TX 3/95.
Rice University, Gay and Lesbian Student Association, Houston, TX 3/95.
The Louisiana Council on Child Abuse, 9th Annual Conference, Baton Rouge, LA 4/95.
Tulane University Medical School, Introduction to Clinical Medicine, New Orleans, LA 10/95.
Louisiana State University Medical School, Social Issues in Medicine, New Orleans, LA 3/96.
Tulane University, Graduate School of Social Work, New Orleans, LA 5/96.
Gay Pride, Santa Fe, NM, 6/96.
PFLAG chapter meeting, Santa Fe, NM, 6/96.
PFLAG chapter meeting, Taos, NM, 6/96.
Tulane University School of Medicine, Introduction to Clinical Medicine, New Orleans, LA 3/97.
Continuing Medical Education for Family Practice Physicians, Louisiana State University Medical School, New Orleans, LA 5/97.
PFLAG chapter meeting, Houston, TX 6/98.
PFLAG chapter meeting, New Orleans, LA 6/99.
College of Santa Fe, Adult education, Santa Fe, NM 10/99.
PFLAG chapter meeting, Houston, TX 4/00.
University of Denver, Graduate School of Social Work, Denver, CO 5/00.
Community College of Santa Fe, Santa Fe, NM 2/01.
College of Santa Fe, adult education, Santa Fe, NM 2/01.
29. PFLAG chapter meeting, Dillon/Summit Counties, CO 5/01
30. PFLAG chapter meeting, Boulder, CO 8/01
31. PFLAG chapter meeting, Houston, TX 9/01.
32. PFLAG Mountain West Regional Conference, Denver, CO 10/01.
33. PFLAG chapter meeting, Evergreen, CO 2/02.
34. PFLAG chapter meeting, Denver, CO 3/02.
35. PFLAG chapter meeting, Salt Lake City, UT 3/02.
36. GLBT Chamber of Commerce, Houston, TX 4/02.
37. Boulder Valley School District, Boulder, CO 4/02.
38. WomenÕs Outdoor Club, Arvada, CO 5/02.
39. National PFLAG Conference, Columbus, OH 9/02.
40. United Church of Christ, Denver, CO 10/02.

INTERVIEWS:

Radio:
1. KPFT, Houston, TX 4/02.

Television:
1. PBS, KUHT Houston, TX 4/02. Thirty-minute interview; broadcast 6/02.

Additional Resources: