Tonight, I am participating in a Zoom-based Secret Science Club lecture featuring Dr Barbara Natterson-Horowitz, of the Department of Human Evolutionary Biology at Harvard University and professor of medicine in the UCLA Division of Cardiology. Dr Natterson-Horowitz is the co-author of the book Wildhood: The Epic Journey from Adolescence to Adulthood in Humans and Other Animals.
Dr Natterson-Horowitz began the lecture with a discussion of the prefrontal cortex, which is not entirely developed in adolescence. Because the prefrontal cortex is not completely developed, adolescents often engage in dangerous behaviors. Many mental illnesses have their start in adolescence as well. Adolescents are also vulnerable to exploitation. This development pattern has its roots in evolutionary biology, and Dr Natterson-Horowitz will discuss the role of evolution in cortical development.
Dr Natterson-Horowitz is a medical doctor, and also studied psychiatry. She became a cardiac consultant to the Los Angeles Zoo, and treated a chimpanzee which had a stroke. She realized that her medical knowledge was anthropocentric, with studies of animals focused on zoonotic infections. She ended up treating animal diseases and studied animal behavior. She realized that she needed to integrate human and veterinary medicine, studying bird cardiology, the parallels between horse and human fainting spells, and self harm in parrots. There is a benefit to having an evolutionary understanding of illnesses. Human exceptionalism is a problem, there is an unexamined assumption about human diseases and vulnerabilities. Vulnerability to disease is an evolutionary trait. She displayed a phylogenetic tree jotted down by Darwin in his notebooks, with an endearing "I think" at the page header:
Adolescents are vulnerable to accidents, they are vulnerable to suicidal ideation, and exploitation, sexual and otherwise. Dr Natterson-Horowitz displayed a video of the evolutionary timescale, and stated that she wanted to begin her discussion of underlying evolutionary roots of disease to the Cambrian explosion. Arteriosclerosis, the underlying issue behind cardiac disease, is common to chordates. Is adolescence unique to humans?
Dr Natterson-Horowitz took us through a whirlwind tour of studies of adolescence from Aristotle to G. Stanley Hall (who spoke of the 'Sturm und Drang' of adolescence), to Sigmund Freud, to Anna Freude, to Margaret Mead, who explored the 'nature vs nurture' issue in a comparative adolescence study. Dr Natterson-Horowitz wanted to expand Dr Mead's model to other species. She defines adolescence a the period between puberty or fledging until sexual maturity. She extolled the beauty of words such as 'elver' for adolescent eels or 'smolts' for adolescent salmon.
Dr Natterson-Horowitz continued with an overview of adolescent ailments, beginning with fainting. Fear-triggered fainting seems to be a paradoxical occurrence, it involves a slowing of the heartrate rather than the expected increasing heart rate. Fainting actually reduces the blood flow to the brain, certain animals use 'tonic immobility' to evade predation. Playing a recording of wolf howls will cause a fawn to freeze, with a lowered heart rate. Adolescents have a greater tendency to faint than older specimens- flight might not be as successful for these individuals than for adults.
Dr Natterson-Horowitz is seeking adaptive answers to similarities rather than a proximate answer. She then went on to discuss adolescents' vulnerability to accidents. Adolescents are more prone to risk taking. Is mortality more common among adolescent animals? Are elvers more vulnerable than adult eels? There are proximate reasons for adolescent vulnerability: inexperience, underestimation of risk, interest in novelty, peer-directed socialization (even among fish species). Adolescents are predator naive, therefore they are easy prey. Dr Natterson-Horowitz displayed a video of a wildebeest migration, directing our attention to the skittishness of the adult animals. There are adaptive learning strategies animals use, such as predator inspection, a dangerous collective behavior in which adolescent animals approach predators in order to study them. Dr Natterson-Horowitz likened this behavior to her own children's experience learning to drive, and the danger that riding with peers holds as risk taking thresholds lower. Is this a 'conserved' evolutionary behavior rooted in predator inspection?
Dr Natterson-Horowitz then shifted the focus to mental illness. Anthropocentrism is seen more in studies of mental illness than in studies of other diseases. The study of mental states in other animals has been stunted by human exceptionalism, which even has implications when discussing the stigma against mentally ill persons. Adolescence is when mental illnesses such as schizophrenia and social anxiety emerge.
Most animals exhibit social hierarchies. Serotonergic pathways are involved in dominance behavior in zebrafish. There is a connection between social status shifts in other chordates and human moods, with serotonin playing a role. There are no level playing fields in nature. Dr Natterson-Horowitz initially thought of privilege as an exclusively human characteristic, but 'privileged' animals inherit the status of their parents- territory, 'royal' status, parental intervention in contests. She even broke listed the various animals that benefit from inherited privilege. Studying this can help to understand human inequity without bogging discussion down in culture war baggage.
Dr Natterson-Horowitz then shifted the discussion to the study of vulnerability to sexual abuse. Humans are reaching puberty earlier than used to be normal, and early onset menarche can lead to increased sexual abuse, depression, and scholastic failure. In a study of captive ringtail lemurs on St Catherine's Island, the lemurs are better fed than their wild peers. Wild ringtail lemurs have female dominance structures. The better fed captive lemurs reach puberty earlier than their wild counterparts, and the females reach sexual maturity before achieving social dominance, so they can become targets of sexual coercion. Among the fossa of Madagascar, female adolescents exhibit a transient masculinization- adult males have spiny penes, adolescent females temporarily develop spiky clitorises, perhaps as a protective adaptation. Phenotypes change to help protect animals which haven't developed behaviors which protect them.
The lecture was followed by a Q&A session. The first question was from a transgender individual who discussed 'going through puberty' again at the age of twenty-eight. Sexuality in animals is not monolithic, with clownfish having both testes and ovaries, and fossa going through transient masculinization. Evolutionary biology has been seen through a heternormative lens, and an adultocentrist lens. There is dynamic diversity in sexual expression among animals. A medical student called about further resources for medical students, Dr Natterson-Horowitz discussed dog breeds which have to be delivered by C-section, and noted that there needs to be better collaboration between doctors and veterinarians. Another caller asked about the tendency of male humans to engage in riskier behavior than female humans, and whether other animals exhibited this... the data is insufficient to determine if the pattern holds. Another question involved arrested adolescence in humans. Adulthood in animals- you have to keep yourself safe, you have to know status, you have to be able to successfully communicate sexually, and you have to be self-reliant. Humans with arrested development have a mismatch between the inherited neurobiology and the modern world. There is a possibility that the adolescent males which engage in risky behavior tend to be more successful in terms of sexual selection.
Dr Natterson-Horowitz likened human exceptionalism in medical research as a 'blindfold' which should be discarded, the onset of diseases such as cancer and mental disease should not be overlooked as a source of insight into human health.
Another question regarded predator inspection among humans. Dr Natterson-Horowitz noted that adolescents are attracted to risk. Adolescents tend to like horror movies and amusement park rides. There is an innate attraction to scary stuff. When her kids were adolescents, she hadn't heard of predator inspection, but she recounted a time when one of her kids wanted to drive during a dangerous storm. Fish kept from their peers have a hard time dealing with predators and don't learn how to school. Isolated birds have a hard time learning their songs, and developing proper breeding behaviors. Peer experience is necessary for safety and proper mating. An organism suffering from the 'oddity effect' is at risk, conformity is adaptive in large groups subject to predation.
Can treatment of animal trauma result in better non-verbal treatment of humans suffering from trauma. The accumulation of adverse childhood experiences can result in adult trauma. Puppies raised in puppy mills are separated from their mothers at a premature age, and the adverse puppy experience can result in psychopathologies such as aggression and aberrant behavior. There are breed differences in psychopathologies, and the study of the genetics of resilience might help in the study of human pyschopathologies.
Risk-taking in adolescence, particularly the desire for novelty, often has a connection to the dispersal of adolescents. Some organisms disperse and individuals, some (such as king penguins) in large groups. Adolescents need to be innovators. Among carnivores, such as hyenas, adolescents presented with puzzle boxes tend to be more persistent in trying to extract the reward within.