Sexual Behavior, Differences & Attraction – Comprehensive Lecture Notes

Polling data (cited by James Gleick)
- Americans rank sex as #1 in enjoyability—above sports, fishing, bar-hopping, family talk, eating, TV, gardening, bathing, shopping, chores, visiting dentist, car repair, etc.
- Average daily time actually devoted to sex: 4\ \text{min}\ 3\ \text{s}
- Same ballpark as average time Americans spend filling out IRS forms (≈ 4\ \text{min}).
Gleick’s satirical list of activities that indirectly revolve around sex (flirting, gym workouts, beauty parlors, pickup-line rehearsal, showering, post-sex clean-up, repression, sublimation) underscores:
- Sex occupies little clock time but massive psychological, cultural, evolutionary space.
- Downstream stakes: marriage, family, offspring, aggression, competition, art, music, creativity.

Evolutionary fact ≠ moral prescription.
- Steven Pinker ("How the Mind Works"): biology sets possible goals (gene spread), not ethical ones (e.g., birth control, flying, refrigeration).
Dawkins on inevitability:
- Cause (genes vs. environment) ≠ difficulty of change.
- Genetic traits can be easy to remedy (e.g., myopia → glasses); cultural traits can be hard (e.g., beauty ideals about weight).

Sex Cells (gametes), not external genitalia.
- Male: small gamete (sperm) → genes only.
- Female: large gamete (ovum) → genes + nutrients + protective layers.

Parental Investment (PI) = any effort that raises offspring survival at a cost to future reproduction.
Because eggs/gestation are expensive:
- Females: intrinsically higher PI → limited offspring quantity.
- Males: minimal obligatory PI (sometimes just copulation) → potential for many offspring.
Predicted psychological/behavioral consequences:
- Males compete with males; females choose among males.
- Male competition → larger body size & weapons (antlers, tusks, fists) and mating displays (peacock tail, bird song).

Role Reversal (male > female investment) → reversed sex-typical traits.
- Pipefish: males brood eggs in pouch → females larger, fight for males, display bright colors.
- Emperor penguins: near-equal PI → similar body size.
Body-Size Ratio & Mating System Examples
- Elephant seal ♂ ≈ 4× larger → harem polygyny.
- Gibbons: monogamy → size parity.

Mating system: "mildly polygynous" / serial monogamy.
Size dimorphism: ♂ ~ 15\% larger.
Testis size (relative to body): human ♂ between chimp (high sperm competition) and gorilla/gibbon (low).
Summary → ancestral humans: moderate male–male competition & moderate female multiple-mating.

♂ more physically violent across lifespan:
- Prenatal: more kicks in utero.
- Childhood: rough-and-tumble play, violent sports.
- Adulthood: prison demographics, homicide rates.
Testosterone ↑ aggression in humans & primates.

Prostitution: near-universal male clientele; even male sex workers mostly service men.
Pornography: universal production & consumption skewed male (even in rhesus monkey “juice-for-nudes” studies).
Survey results (cross-cultural):
- Desired # partners (men vs. women)
- Next month: ♂ ≈ 2, ♀ < 1.
- Next 2 yrs: ♂ ≈ 8, ♀ ≈ 4–5.
- Lifetime: ♂ ≈ 18, ♀ ≈ 4–5.
- Clark & Hatfield campus study:
- “Go out”: ♀ ≈ 50\%, ♂ ≈ 50\%.
- “Come to my apartment”: ♀ < 10\%, ♂ ≈ 70\%.
- “Have sex tonight”: ♀ 0\%, ♂ 75\% (+ apologies from refusals).
Gay vs. Lesbian behavior: gay men show highest lifetime partner counts; lesbians most monogamous—mirrors underlying ♂ vs. ♀ preferences without compromise of heterosexual pairings.

Universals
- Both sexes value kindness and intelligence highly.
Sex-linked emphases
- Women: resources, status, willingness to invest in offspring.
- Men: youth & fertility cues.

Signals youth: large eyes, full lips, smooth skin.
Signals health: clear eyes/skin, unbroken teeth, absence of deformity.
Averageness: composite faces lack anomalies → perceived attractive even by 2-month-olds.
- Morphing all student photos ⇒ highly attractive composite.
"Improving" average faces:
- Feminizing male face → preferred by ovulating women.
- Masculinizing female face rarely boosts attractiveness.

Babies treated differently when wrapped in pink vs. blue.
Name biases: "John Smith" vs. "Joan Smith" in hiring, publication.
Childhood self-segregation (ages ~4–11): boys with boys, girls with girls → amplifies initial differences (Eleanor Maccoby).

Empathy / Social Cognition (Simon Baron-Cohen)
- ♂ mean lower empathy; murder = "ultimate lack of empathy".
- High testosterone correlates with lower social cognition.
- Autism, Asperger’s, psychopathy ≈ male-biased incidence.
- Slogan: "Male brain = mild autism." (controversial.)
Math & Science Aptitude (Larry Summers controversy)
- Hypothesis: equal means, greater male variance ⇒ more male geniuses & male failures.
- Highly contested; see Pinker vs. Spelke debate on EDGE for pro/con evidence.

Approximate prevalence
- Women: \sim 98\% heterosexual, \sim 2\% exclusive lesbian.
- Men: \sim 96\% heterosexual, \sim 4\% exclusive gay.
Key distinctions
- Orientation = attraction, not behavior.
Non-explanations
- Not conscious “choice.”
- Unlikely post-puberty experience (“seduction”)—early childhood fantasies differ long before puberty.
Genetic evidence
- Twin studies: MZ concordance \approx 50\% > DZ \approx population rate
- Hence partial heritability, but not fully genetic (else concordance =100\%).
Evolutionary mystery: exclusive homosexuality reduces direct reproduction. Theoretical accounts must reconcile with persistence of genes involved.
- Assignment: "Solve this puzzle" respecting empirical facts.
Cross-species note: many animals exhibit homosexual acts, unknown if exclusive orientation common in non-humans.

Gamete size → Parental investment → Competition/choice asymmetries → Body size, weaponry, displays, psychology.
Biological predispositions interact with culture; genetic ≠ destiny, and cultural ≠ easily changed.
Sex differences robust for aggression & short-term mating interest; debated for empathy, cognition.
Beauty preferences largely universal and rooted in honest signals of youth & health.
Sexual orientation partly genetic, partly environmental, and evolutionarily enigmatic.

Average U.S. sex time: 4\text{ min }3\text{ s}/day.
Human size dimorphism: ♂ ≈ 15\% larger than ♀.
Elephant seal dimorphism: ♂ ≈ 4\times ♀.
Desired partner counts (men): 2\rightarrow 8\rightarrow 18 (month→2 yrs→lifetime).
Desired partner counts (women): <1 \rightarrow 4–5 \rightarrow 4–5.
Twin concordance for homosexuality: \sim 50\% (MZ) vs. population <5\%.

Avoid “naturalistic fallacy”: biology doesn’t dictate morality (birth control, non-procreative sex, technological interventions).
Policy/intervention: Genetic inequality can still be addressed (eyeglasses example vs. obesity stigma).
Social equity: Recognize name/gender biases, structural barriers, and self-segregation in education/work.