last updated:

April 10, 2021

[Brain Image]    

PSY 340 Brain and Behavior

Class 26 Variations in Sexual Behaviors [Outline]


A.   Evolutionary Interpretations of Mating Behavior

 Issue  Males Females
Interest in Multiple Mates?
  • M > F: Interest in short-term sexual relationships with multiple partners
  • Limited number of pregnancies -> F have less to gain from multiple mates
What Do Men and Women Seek in Mate?
  •  M = F: healthy, intelligent, honest, physically attractive
  • Younger partner
  • M who are likely to be good providers
  • M who have an acceptable odor
  • M > F are upset over sexual infidelity of mate.
  • F > M are upset over emotional infidelity of mate. 

Caution: Has a behavior evolved or been learned via culture? Survival or reproductive advantage of a behavior and its appearance across cultures is not by itself proof that the behavior is evolved or learned.

B.   Gender Identity & Gender-Differentiated Behaviors


≠ Transgender or Transexual Identity.

Prevalence of transsexualism
The Intersex Society of North America (ISNA) lists these

Not XX and not XY

1 in 1,666 births

Klinefelter (XXY)

1 in 1,000 births

Androgen insensitivity syndrome [Note A]

1 in 13,000 births

Partial androgen insensitivity syndrome [Note A]

1 in 130,000 births

Classical congenital adrenal hyperplasia

1 in 13,000 births

Late onset adrenal hyperplasia

1 in 66 individuals

Vaginal agenesis

1 in 6,000 births


1 in 83,000 births

5 alpha reductase deficiency

no estimate

Mixed gonadal dysgenesis

no estimate

Complete gonadal dysgenesis

1 in 150,000 births

Hypospadias (urethral opening in perineum or along penile shaft)

1 in 2,000 births

Hypospadias (urethral opening between corona and tip of glans penis)

1 in 770 births

Note A: These are higher incidence rates than in my diagram above which uses data from Gottlieb & Trifiro (2017) for the rate of Androgen Insensitivity Syndrome

Rearing & Gender Assignment among Intersex Individuals
[Reimer]David Reimer. Response to tragic experience of a Canadian David Reimer (1965-2004) whose penis was accidentally destroyed during circumcision. After sex reassignment surgery as an infant, he was raised as a girl ("Brenda") under the theory that gender identity is mostly the result of environmental factors. His parents were profoundly influenced to do this by a famous Johns Hopkins' psychologist named John Money. However, David realizes by ages 10-12 he was really a boy and began to live as a male. He eventually married at 25, but  committed suicide when he was 39. (See Colapinto, 2004) [Daily Mail UK 2010 story]

C.    Sexual Orientation in Humans: Possible Biological Aspects 

Bottom Line: No "gay gene," no "gay environment," interaction of genetics x environment early in development, nature probably > social factors

1. Behavioral and Anatomical Differences

2. Genetic Factors

[Concordance Rates for
                Homosexuality in Twins]

3. Evolutionary Perspective

4. Prenatal Influences

5. Brain Anatomy

Simon LeVay and Brain of
              Homosexual Men