Biological Influences on Sex, Sex Differences & Preferences | Huberman Lab Podcast #14

Summary

• Andrew Huberman is a professor of Neurobiology and Ophthalmology at Stanford School of Medicine
• This podcast is not affiliated with his teaching or research, but aims to provide zero-cost information about science and science-related tools
• Sponsors of the podcast include Inside Tracker, a personalized nutrition platform that analyzes blood and DNA data, and Helix Sleep, a company that makes mattresses and pillows designed to optimize sleep
• Today's episode will discuss biological influences on sex, sex differences, and preferences
• There is a wide range of variation in how people express their gender and sexual identity
• There are many biological factors that contribute to sex differences and preferences, including genetics, hormones, brain structure and function, and the environment
• It is important to recognize that there is not a single "normal" or "correct" way for people to express their gender or sexuality
• It is also important to recognize that sex and gender are complex and multifaceted, and that no one factor alone determines a person's identity or behavior
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• The goal of the Huberman Lab Podcast is to provide a foundation in topics like neuroplasticity, focus, sleep, and hormones, and to offer tools for these topics
• Episodes will include primers on the basics of a given topic
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• The NSDR protocol is designed to help listeners relax deeply through a combination of breathing and body scanning
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• Hormones play a role in the development of the brain and body, leading to the process of masculinization or feminization
• Chromosomal sex is determined by the number of X and Y chromosomes (XX for female, XY for male, and variations such as XXY and XYY)
• Gonadal sex is determined by the presence of testes or ovaries
• The Y chromosome contains genes that suppress female reproductive organs and promote the development of testes
• The placenta is an endocrine organ that produces hormones during pregnancy, including estrogen and progesterone
• The adrenal glands produce hormones such as cortisol, aldosterone, and androgens
• The hypothalamus and pituitary gland are closely related and release hormones that affect the release of other hormones in the body
• Hormones can have short-term and long-term effects
• Long-term effects of hormones relate to their effects on genes and gene expression
• Masculinization and feminization are not just about changing the body and brain, but also about demasculinizing and defeminizing
• Testosterone and estrogen affect primary and secondary sexual characteristics in the brain and body
• Dihydrotestosterone (DHT) is responsible for the development of the penis in a fetus with an X and Y chromosome
• Estrogen is responsible for the development of the clitoris in a fetus with two X chromosomes
• DHT can demasculinize the brain in some cases, and estrogen can defeminize the brain in some cases
• Secondary sexual characteristics develop during puberty and are influenced by hormones
• Hormone levels can be altered by external factors, such as stress and chemical exposure
• Hormones can have both positive and negative effects on the body and brain.
• Dihydrotestosterone (a type of androgen) is responsible for the primary growth of the penis
• Estrogen, not testosterone, masculinizes the brain in all individuals
• Testosterone can be converted into estrogen by an enzyme called aromatase, which is made by sources including body fat and neurons in the brain
• Estrogen has powerful effects on brain development and behavior in all individuals
• Estrogen levels are higher in males during fetal development, and this may contribute to gender nonconformity in some individuals
• Aromatase inhibitors, which block the conversion of testosterone to estrogen, may be used to treat certain medical conditions but can have negative side effects
• Testosterone therapy may be used to treat gender dysphoria in transgender individuals, but more research is needed on its long-term effects
• Atrazine, a substance present in herbicides, causes severe testicular malformations in frogs
• Human sperm counts are declining
• Evening primrose and testosterone creams may have negative effects on hormone ratios
• Herbicides may reduce sperm counts and impact sexual development in humans
• Exposure to toxins such as PCBs, dioxins, and DDT can cause endocrine disruption and fertility issues in humans
• Vinclozilin, a fungicide, can cause feminization of male fish
• Endocrine disrupting chemicals may have intergenerational effects on fertility and development
• Testosterone levels can impact the appearance of female traits in individuals with complete androgen insensitivity syndrome
• Estrogen establishes masculine brain circuits, while testosterone controls the display of masculine behaviors
• Exposure to THC, alcohol, and potentially cell phone radiation can impact sexual development
• Puberty is a time of increased vulnerability for brain and behavior changes due to hormone exposure
• Hormone levels in adults can be influenced by various factors such as stress, diet, and environment
• DHT is a hormone that plays a role in male physical characteristics and can be predicted based on patterns of DHT receptors and genetic background
• Hair loss drugs aim to prevent the conversion of testosterone to DHT
• Creatine may increase 5-alpha-reductase activity and the conversion of testosterone to DHT, potentially leading to hair loss and beard growth in some individuals
• The rate of physical and cognitive development in puberty is faster than any other point in life and can vary based on hormones such as DHT
• Low testosterone can lead to increased risk of death, but high testosterone levels may not necessarily lead to decreased risk of death
• Testosterone levels naturally decrease with age, but this can be slowed through exercise and other lifestyle factors
• The genitalia of female hyenas are enlarged due to high levels of androstenedione, a pro hormone to testosterone
• Some species of moles can trans differentiate their testes into ovaries in order to balance the ratio of males to females in the population
• Some plants, including marijuana, have estrogenic properties and may increase estrogen levels in animals that consume them
• Pine pollen looks similar to testosterone and some plants have evolved the capacity to produce estrogen-like compounds to manipulate the behavior of animals that consume them
• There are several different types of intersex individuals, including those with hormonal imbalances, chromosomal abnormalities, and physical abnormalities of the reproductive organs
• Intersex traits can be caused by genetics, environmental factors, or a combination of both.
• There is a brain difference in an area called the Interstitial Nucleus of the Anterior Hypothalamus (INAH) in people who self-report as homosexual
• This brain difference is a biological correlate of sexual preference and is tied to androgenization or estrogenization
• The D2 D4 ratio is not predictive of anything, but can be a window into possible androgen exposure early in life
• The probability of a male self-reporting as homosexual increases with the number of older brothers they have
• This may be due to epigenetic effects or the placenta carrying a record of male fetuses and their secretions, increasing the probability of subsequent offspring self-reporting as homosexual
• The effects of hormones on the body and brain can be early, late, acute, or chronic, and can be influenced by environmental factors
• There is evidence for both genetic and environmental factors influencing sexual preference and behavior