Brief Summary
This episode of Father Offspring Interviews explores the evolutionary and biological aspects of human sexuality. It addresses questions about penis size variation, the origins of clothing as sexual modesty, the neuroscience of BDSM, and the prevalence of the missionary position. The discussion covers topics such as natural and sexual selection, sperm competition, body dysmorphia, and the role of the amygdala in sexual motivation and aggression.
- Penis size variation is influenced by both natural and sexual selection, with sperm competition playing a role.
- The use of clothing for sexual modesty is a unique human behavior with uncertain origins, possibly linked to the evolution of clothing-adapted lice.
- BDSM may involve an intermixing of circuitry in the amygdala, confusing sexual arousal with aggressive arousal.
- The prevalence of face-to-face sex in humans may be related to anatomical adaptations in the female reproductive system.
Question 1 (P*nis Sizes)
The discussion begins by addressing the question of why there is such dramatic variance in penis sizes among humans and whether sexual selection explains larger penises. It clarifies that evolution is about leaving copies of one's genes, not just survival. Natural selection favors traits that aid survival and reproduction, while sexual selection favors traits that make an individual attractive to the opposite sex. These two forms of selection can often conflict. The conversation then shifts to testes size, which correlates with sperm count and competition. Humans fall in between pair-bonding and tournament species in terms of testes size. Natural selection plays a role in penis size only concerning sperm competition, where a longer penis can deposit sperm closer to the egg. Sexual selection, however, is the primary driver, with studies using digital avatars to gauge female preferences. These studies indicate an optimal penis size, not too big or too small, and that size is more important for hookups than long-term relationships. Many women feel men are too preoccupied with penis size, aligning with body dysmorphic syndromes. Research is often biased towards heterosexual, WEIRD (Western, Educated, Industrialized, Rich, and Democratic) individuals, and cross-cultural studies reveal varying preferences throughout history. There are no consistent differences in penis size based on race or correlation with hand or foot size, except for a Japanese study linking nose size to penile length in cadavers. Over the past three decades, there has been a secular trend of increasing average penis size worldwide. Initial research was skewed by self-reporting, which tended to inflate size.
Question 2 (Clothing as sexual modesty)
The conversation addresses the question of when and why humans started using clothing as a means of sexual modesty. It notes that humans are unique in having private sex, a culturally universal trait. The origins of clothing for modesty are unclear, as the oldest clothing is only about 5,000 years old, but clothing existed long before that. The appearance of clothing-adapted lice around 70,000 years ago suggests when clothing became widespread, though the reasons for sexual modesty remain unknown.
Question 3 (BDSM)
The discussion addresses questions about the biology of non-consensual sexual sadism and the neuroscience behind consensual BDSM tendencies. It distinguishes between non-consensual sexual violence and consensual BDSM. Studies on sexual sadists reveal a history of childhood abuse, instability, parental infidelity, substance abuse, and suicide attempts. Neuroimaging studies show neurological abnormalities, particularly in the temporal parietal junction (TPJ), which is involved in theory of mind and empathy. Consensual BDSM is more prevalent than expected, with 20-30% of people experimenting with it. The amygdala, known for mediating aggression, also plays a role in male sexual motivation. This suggests that BDSM may involve an intermixing of circuitry in the amygdala, confusing sexual arousal with aggressive arousal. This explanation is complicated by the fact that female sexual motivation is not based in the amygdala, yet women also participate in BDSM. The two-factor theory of emotion and misattribution of arousal are discussed, highlighting how physiological states of fear, aggression, and sexual arousal can be confused.
Question 4 (Missionary Position)
The discussion explores the evolutionary reasons behind the prevalence of face-to-face intercourse in humans compared to other mammals. While not unique to humans (bonobos, gorillas, orangutans, gibbons, and even heirds also engage in it), it is far more common. The term "missionary position" is examined, debunking the myth that missionaries imposed it. The term originated from anthropologist Bronoslov Melanowski's observations in the Trobriand Islands. The theory that face-to-face sex stabilizes pair bonds is dismissed due to humans not being a pair-bonding species. The more plausible explanation is anatomical: human vaginas are larger in cross-section and have a unique angle due to bipedalism and upright birthing. Face-to-face sex may facilitate fertilization by accommodating this unique angle.
