20. Aggression IV

TL;DR

Prenatal testosterone clearly masculinizes aggressive behavior in rodents and produces strong but weaker patterns in primates, yet in humans the evidence amounts to only faint hints. Studies of androgenized girls are uninterpretable because these children also had ambiguous genitalia and repeated reconstructive surgeries, confounding any hormonal effect on later aggression.

Transcript

[MUSIC PLAYING] Stanford University. OK, let's get started. We pick up with aggression, competition, et cetera. And where have we gotten to? We are now just about to leap to, instead of early environment, early hormonal exposure, parenatal-- hormones both pre, before and after birth. Around that time, what do they have to do with adult behavior in... Read More

Key Insights

• Organizational hormonal effects set up the nervous system early in life to later respond to activational hormones, a framework Sapolsky applies to prenatal androgen exposure and adult aggression in the same way it was used in the sex lectures.
• Prenatally androgenized female rodents show powerful masculinization: as adults they respond to even low bloodstream testosterone with more aggression, more aggressive play, and less maternal behavior toward offspring, forming a clear animal literature.
• Early human studies wrongly classified androgenized girls as more aggressive because they were less interested in dolls and marriage and more interested in careers, mislabeling career ambition as 'assertive dominance' until endocrinologists recognized this as gibberish.
• The claim that androgenized girls have higher IQ is a red herring, because parents show an equivalently higher IQ, pointing to selection of more educated families into these studies rather than any androgenization effect.
• The androgenized-girl literature is uninterpretable because these children were born with hermaphroditic or ambiguous genitals and underwent roughly a dozen reconstructive surgeries in their first decade, so prenatal hormones were not the only difference in their lives.
• Dizygotic twin girls with a male co-twin show slightly more rough-and-tumble play and interest in mechanical things, but the effect is very small and confounded because these girls also grow up alongside a brother.
• The strength of prenatal testosterone's effect on aggression declines across species: clear-cut in rodents, strong but less dramatic in primates, and at most just hints in humans.
• Simon Baron-Cohen's hyper-male hypothesis of autism proposes that autism, far more common in males, is an exaggerated version of male-typical profiles like finger ratio, strong spatial skills, and analytical over empathic social problem solving.

Questions & Answers

Q: What is the difference between organizational and activational hormonal effects?

Organizational hormonal effects occur early in life and set up the nervous system to respond later to some sort of activational hormonal effect. In the context of aggression, prenatal or perinatal androgen exposure organizes the developing brain so that in adulthood the individual responds more strongly to circulating testosterone. Sapolsky notes this is the same concept introduced in the sex lectures, applied here to aggression and competition rather than sexual behavior.

Q: How does prenatal androgen exposure affect aggression in female rodents?

Female rodents exposed to high testosterone levels prenatally or perinatally undergo a powerful organizational masculinization effect. Later in life these females respond to even their low bloodstream testosterone levels with increased aggression and more aggressive play, and they show less maternal behavior when having offspring. Sapolsky describes this as a pretty clear literature demonstrating prenatal masculinization of both aggressive and sexual behavior in rodent species.

Q: Why did early studies wrongly conclude androgenized girls were more aggressive?

By age 10 to 12, researchers declared androgenized girls far more aggressive because they were less interested in playing with dolls, expressed less interest in marriage, and expressed more interest in having a career. Wanting a career was treated as aggression, even relabeled 'assertive dominance.' This appeared in textbooks from the late 1960s into the mid 1980s until endocrinologists recognized that career ambition in a female does not constitute aggression, sending the entire literature back to stage one.

Q: What did the higher IQ finding in androgenized girls turn out to mean?

Androgenized girls were observed to have higher than average IQ, which initially seemed interesting. However, an equivalently higher IQ is found in their parents, so it has nothing to do with androgenization. Instead there is some sort of selection determining who ends up in such a study, perhaps more educated families. Sapolsky concludes the higher IQ was a red herring rather than a genuine effect of prenatal hormone exposure.

Q: Why is the literature on androgenized girls considered uninterpretable?

These girls were not born with prenatal testosterone exposure as their only distinguishing feature. They were born with a hermaphroditic profile of genitals resembling males or sexually ambiguous genitals, and they went through roughly a dozen rounds of reconstructive surgery in their first six to ten years of life. Because these children faced many confounding experiences beyond hormone exposure, any observed differences in adult behavior cannot be attributed to prenatal testosterone, making the whole literature uninterpretable.

Q: What do dizygotic twin studies reveal about prenatal testosterone and behavior?

Dizygotic (non-identical) twin girls who shared the womb with a male sibling secreting testosterone show, on average, more aggressive and rough-and-tumble play in childhood, more interest in cars and mechanical things, and less interest in stuffed animals and dolls. The effect is very small. It is also confounded because such girls not only were exposed to their brother's hormones prenatally but also grew up alongside a brother, which independently increases rough-and-tumble play, making the literature uninterpretable.

Q: How does the effect of prenatal testosterone on aggression differ across species?

The strength of prenatal testosterone's effect on aggressive behavior weakens as you move up in species. In rodents there is very clear-cut androgenization of aggressive behavior from prenatal testosterone. In primates there are some pretty strong patterns but nowhere near as dramatic as in rodents. By the time you examine humans, there is maybe just some hints of an effect at the most, reflecting how much less deterministic prenatal hormones become in more complex species.

Q: What is Simon Baron-Cohen's hyper-male hypothesis of autism?

Simon Baron-Cohen, an Oxford autism expert, proposes that autism represents an exaggerated male-typical profile driven perhaps by prenatal androgenization. Autism is far more frequent in males than females. Baron-Cohen studied sex differences including finger ratio, neural anatomy, spatial versus language skills, and analytical versus empathic problem solving, where males tend toward analytical approaches. Individuals with autism, regardless of sex, show even more exaggerated versions of these male-typical traits, suggesting normal male behavior sits near the edge of dysfunctional socialization.

Summary

In this video, the lecturer discusses aggression, competition, and their relationship to early hormonal exposure and genes. He explores the effects of prenatal hormonal exposure on aggression in animals and humans and examines the role of genes in aggressive behavior. The lecturer also discusses cultural and ecological factors that contribute to aggression and violence in different societies. He concludes by discussing the profile of individuals involved in terrorism and the challenges in understanding their motivations.

Questions & Answers

Q: What is the difference between organizational and activational hormonal effects?

Organizational hormonal effects occur early in life and set up the nervous system to respond to activational hormonal effects later on. Organizational effects can lead to long-lasting changes in behavior, while activational effects are transient and dependent on the presence of specific hormones.

Q: What are the effects of prenatal hormonal exposure on aggression in females?

In animal studies, females that were exposed to high levels of testosterone prenatally exhibited masculinized behavior, with increased levels of aggression. They displayed more aggressive play, less maternal behavior, and responded to low levels of testosterone with increased aggression. However, the effects of prenatal hormone exposure on aggression in humans are less clear.

Q: What is the relationship between prenatal hormonal exposure and aggression in humans?

Studies on individuals with congenital adrenal hyperplasia and exposure to diethylstilbestrol have shown mixed results in terms of aggression. While some studies initially suggested a link between prenatal hormone exposure and increased aggression in females, subsequent research has questioned these findings and highlighted confounding variables such as surgical intervention or societal perceptions of assertiveness as aggression.

Q: Are there genetic factors associated with aggression?

Yes, genes have been implicated in aggression. Research has identified genes related to neurotransmitters such as serotonin and dopamine, as well as genes associated with impulsivity and pain sensitivity. However, the relationship between genes and aggression is complex, and gene-environment interactions play a significant role in determining behavior.

Q: How do ecosystems and cultural factors influence aggression?

Nomadic pastoralist cultures, which tend to live in deserts, have higher rates of violence compared to other societies. These cultures often have warrior classes and engage in raiding and warfare. Additionally, cultures with strong ideologies and myths of victimization coupled with a focus on retribution are more prone to aggression. Levels of trust, social capital, and cultural norms also influence aggression within societies.

Q: What are some characteristics of individuals involved in terrorism?

The profile of terrorists has evolved over time, with recent Middle Eastern fundamentalist terrorists having different characteristics compared to past profiles. Contemporary terrorists tend to be educated, middle-class individuals in their thirties and forties, with no direct experience of the persecution they are fighting against. This profile challenges traditional interpretations of terrorism, and the motivations behind these individuals' actions are not well understood.

Takeaways

Understanding the relationship between hormones, genes, culture, and ecology is essential in comprehending aggressive behavior. While prenatal hormonal exposure can influence aggressive behavior in animals, its effects in humans are more complex and influenced by social factors. Genes play a role in aggression, but their impact is mediated by the environment. Cultural factors such as past victimization, ideology, and social capital also contribute to aggression. The profile of individuals involved in terrorism is changing, and new factors, such as education and lack of direct experience of persecution, need to be considered in understanding their motivations.

Summary & Key Takeaways

• Sapolsky shifts from early environment to prenatal and perinatal hormone exposure, invoking the organizational-versus-activational framework. In rodents, prenatally androgenized females become clearly masculinized adults who respond to low testosterone with heightened aggression, more aggressive play, and reduced maternal behavior, forming an unambiguous animal literature on prenatal masculinization of aggressive behavior.

• Human studies used congenital adrenal hyperplasia and DES cases. Early researchers labeled androgenized girls aggressive for preferring careers over dolls and marriage, coining 'assertive dominance.' That literature collapsed once this was recognized as bias. Reanalysis found higher IQ was a parental-selection red herring, and aggression findings remained ambiguous with little going on.

• Androgenized-girl studies are uninterpretable because these children had ambiguous genitalia and many reconstructive surgeries, so hormones were not the only difference. Dizygotic-twin studies show small effects also confounded by growing up with a brother. Baron-Cohen's hyper-male hypothesis frames autism, skewed toward males, as an exaggerated male-typical profile.